University of Newcastle upon Tyne
Basic Radiation Training Guide
V12
September 2004
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28/09/2004
CONTENTS
1
INTRODUCTION
2
ATOMIC STRUCTURE & NUCLEAR DECAY
2.1 The Atom
2.2 Beta Decay
2.3 Alpha Decay
2.4 Activity
2.5 Radioactive Decay
2.6 Half Life
2.7 Energy
3
PROPERTIES OF RADIATION
3.1 Ionisation
3.2 Alpha Particles
3.3 Beta Particles
3.4 Bremsstrahlung
3.5 Positrons
3.6 Gamma Rays and X-rays
3.7 Absorption of Gamma Rays and X- rays
3.8 Neutrons
4
RADIATION UNITS
4.1 Absorbed Dose
4.2 Weighting Factors
4.3 Equivalent Dose
4.4 Effective Dose
4.5 Dose Rate
4.6 Inverse Square Law
5
HEALTH EFFECTS OF RADIATION
5.1 Deterministic Effects
5.2 Stochastic Effects
5.3 Dose Limitation
6
PRACTICAL RADIATION PROTECTION
6.1 Internal Exposure
6.2 External Exposure
6.3 General Procedure for the Use of Unsealed Sources
7
CONTAMINATION CONTROL
7.1 Contamination Monitoring
7.2 Methods of Contamination Monitoring
7.3 Contamination Monitor Response
7.4 Contamination Limits & Emergency Action Levels
7.5 Emergency Action
7.6 Emergency Procedure
7.7 Area Decontamination
7.8 Personal Contamination
8
THE LAW
9
STOCK CONTROL & RADIOACTIVE WASTE DISPOSAL
9.1 Stock Control
9.2 Radioactive Waste Disposal
10 RADIOISOTOPE DATA
APPENDIX 1: SI Units and Prefixes
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3
4
7
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14
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26
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1
INTRODUCTION
This Training Guide is provided as a supplement to the Radiation Safety Training course,
which all potential radiation workers are required to attend. Anyone who obtains a
reasonable understanding of the concepts and issues addressed within should be able to
pass the Radiation Competency Test.
It is beyond the scope of this Guide to cover all the procedures that must be followed by
radiation workers. Different administrative arrangements on different sites require that
different sets of Local Rules apply. In addition, certain Schools and individual laboratories
are covered by specific local rules for those areas. Knowledge of this Guide alone will not
therefore be sufficient to enable all the legislative requirements placed upon them. All
radiation workers must also know, understand and abide by the University Safety
Policy on the Use of Ionising Radiation (& specific local rules) that apply in the
area(s) that they will be working with ionising radiation within.
V12
University of Newcastle upon Tyne
September 2004
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2
ATOMIC STRUCTURE & NUCLEAR DECAY
2.1 The Atom
An atom consists of a central core (the nucleus), surrounded by a cloud of electrons
moving in defined orbits. The outermost shell contains the valency electrons which take
part in chemical combination. Each orbit represents a definite energy level. Movement of
electrons from one orbit to another involves energy changes, and X-rays, with wavelengths
characteristic of the element concerned, may be produced from movements between the
innermost shells.
The nucleus contains virtually all the mass of the atom, and is composed of protons and
neutrons. The atom itself is electrically neutral as the positive charge on the nucleus, due
to the protons, is balanced by the negative charge on the equal number of electrons
around the nucleus. The mass of an electron is only 1/1837 of that of a proton. The
neutron has a mass very similar to that of the proton, but is uncharged.
An element is defined by the number of protons in the nucleus (known as the atomic
number, Z), which determines the number and arrangement of electrons in the uncharged
atom and hence the chemical properties.
Isotopes of a given element vary in the number of neutrons within the nucleus. The mass
number, A, of an atom is the sum of the number of protons and neutrons in the nucleus.
Isotopes are written as
A
Z
< SYMBOL >
e.g.
32
15
P
is an isotope of phosphorous
with an atomic number of 15 and a mass number of 32. It contains 15 protons and 17 (3215) neutrons, and is surrounded by 15 electrons. It is often written simply as 32P, as all
isotopes of phosphorous (P) have Z=15.
The relative numbers of protons and neutrons within the nucleus determines whether the
nucleus is stable or unstable. Isotopes which are unstable undergo nuclear transformation
(decay) with the liberation of energy as various forms of ionising radiation and are termed
radioisotopes (“radioactive isotopes”)
2.2 Beta decay
If there is an excess of neutrons in the nucleus, a β- particle (fast electron) will be emitted,
and the nucleus will then have an extra positive charge, i.e. a neutron has been changed
to a proton and a β-particle.
14
e.g.
14
6
C decay
C →
14
7
N + β
−
The total number of protons and neutrons has remained unchanged (14), but the protons
have increased from 6 to 7 and the neutrons decreased from 8 to 7. This nuclide is initially
formed as an ion having a charge of +7 in the nucleus but only -6 from the orbital
electrons. If the new nucleus is in an excited state it will emit the excess energy as
electromagnetic radiation, (gamma radiation).
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If there is instability in the nucleus due to a neutron deficiency, then either a positive
particle needs to be emitted or an electron captured to achieve stability.
In the first case a proton within the nucleus changes to a neutron and a positron is emitted.
A positron (β+) has the same mass as an electron but is positively charged.
Positron emission
1
1
p
→
1
0
n
+
β
+
Positrons do not survive long in matter. A positron will react with an atomic electron
resulting in the annihilation of both particles and the release of two gamma rays of 0.51
MeV each (corresponding to the energy equivalent of the electron masses.)
In the second case the nucleus achieves stability by capturing an electron from an inner
orbital, the vacant position being filled by an electron from an outer orbit, the excess
energy being emitted as an X-ray.
2.3 Alpha decay
Many heavy, unstable nuclides lose energy by emission of alpha particles. These consist
of two protons and two neutrons and are in fact helium nuclei ejected at high velocity.
Alpha emission is usually followed by emission of a gamma ray.
α decay of Radium-226
226
88
Ra →
222
86
Rn +
4
2
α
The original radioactive isotope is called the parent isotope and the new one formed is
called the "daughter". In some cases the daughter is also unstable and further radioactive
decay occurs until a stable daughter product is formed.
2.4 Activity
Activity is the term used to indicate the number of atoms in a sample of radioactive
material which are disintegrating per unit time. The SI unit of activity is the becquerel (Bq).
One becquerel equals one disintegration per second. It replaces the old unit of the curie
(Ci) which was equal to 3.7 x 1010 disintegrations per second. (see Appendix 1.for details
of SI units and prefixes)
Table 1: Conversions between Becquerels and Curies
Bq to Ci
1
Bq
1
kBq
1
MBq
1
GBq
=
=
=
=
Ci to Bq
27 pCi
27 nCi
27 mCi
27 mCi
1
1
1
1
nCi
µCi
mCi
CI
=
=
=
=
37
37
37
37
Bq
kBq
MBq
GBq
Disintegration is a random event. The probability that a particular radioactive atom will
decay in a given time is unaffected by neighbouring atoms, their chemical state or the
physical conditions. Each unstable nucleus of a particular radionuclide has the same
probability of disintegrating in unit time. This probability is called the decay constant, l. If
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there are N radioactive atoms at time t, and after a further time dt, dN of these have
disintegrated, then
dN = -lNdt
or
dN/dt = - lN
(1)
where dN/dt is the disintegration rate, or the "activity" (A).
2.5 Radioactive Decay
Integration of the previous equation, with N = N0 at the time t = 0 gives:
As seen previously, activity (A) = dN/dt and is proportional to N
i.e. The activity of a radionuclide decays exponentially.
N = N0e-lt (2)
A = A0e-lt (3)
2.6 Half Life
The half-life, (t½), of a radionuclide is the time taken for the activity to reach half its initial
value. Half-lives range from a fraction of a second to millions of years but the half-life is a
constant for each individual radionuclide.
i.e. when A = A0/2, e-lt = 1/2, → t½= ln(2)/l = O.693/l
(4)
Activity (%)
After two half-lives the activity equals A0/4, after n half-lives the activity equals A0/2n ,
∴after 10 half-lives the activity will be A0 /1024.
100
90
80
70
60
50
40
30
20
10
0
0
1
2
3
4
5
6
7
Half-lives
2.7 Energy
The energy carried by various forms of ionising radiation ranges from several kiloelectron
volts (keV = 1,000eV) to several megaelectron volts (MeV = 1,000,000eV). One electron
volt = 1.6 x 10-19 J. These energies are enormous when compared to the energies
involved in chemical and biological processes – for example, the mean energy required to
ionise a molecule of water is 75eV.
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3
PROPERTIES OF RADIATION
3.1 Ionisation
If a charged particle passes close enough to an atom, electrostatic forces may operate
between it and the orbital electrons and cause one of the electrons to acquire sufficient
energy to escape. The process is called ionisation. The remaining positively charged
atom is known as a positive ion. This and the negatively charged electron are together
described as an ion pair. Gamma rays and neutrons, being uncharged, do not cause
direct ionisation. Their detection depends on secondary effects.
3.2 Alpha particles
Alpha particles (α) are doubly charged helium nuclei with energies of the order of several
MeV. They produce high specific ionisation (rate of energy loss per unit length of path), but
they are not very penetrating. They acquire electrons from the medium through which they
are travelling and become stable atoms of helium. Alpha particles have a range of a few
centimetres in air, but can be stopped by a sheet of paper, or the dead outer layer of skin,
and therefore they are not a significant external radiation hazard. If taken into the body
however, by inhalation or ingestion, or as a result of a wound becoming contaminated,
they become a serious internal hazard.
3.3 Beta particles
Beta (β-) particles are electrons, with kinetic energy ranging up to 3MeV or more, which
are ejected from the nucleus during radioactive decay. Such electrons have a continuous
energy distribution from zero to a maximum, Emax, characteristic of the source. The mean
energy is about one-third of the maximum.
The penetration, or range, depends on the maximum energy, and is greater than that of
alpha particles. A 0.5MeV β will travel about 1 metre in air, and a 3MeV β will travel about
10 metres. Beta particles can normally be shielded by moderate thickness of low atomic
weight material such as aluminium, perspex or other plastic material, or glass. Perspex
4mm thick will absorb all β particles up 1MeV. Low energy β emitters such as 14C, 35S will
be completely shielded by normal laboratory glassware. Tritium emits a particularly low
energy β (0.018MeV) which is stopped by a few mm of air whereas 32P, which has the
highest energy of the commonly used β emitters (1.7MeV), requires about 7mm perspex or
4mm glass for complete shielding.
Beta particles, depending on their energy, may penetrate up to a centimetre or so of
tissue, and can therefore cause superficial damage. They can also be a hazard to internal
organs if they become incorporated in them.
3.4 Bremsstrahlung
If materials with a high atomic number are used to shield β emitters an electromagnetic
radiation called bremsstrahlung (slowing-down) radiation is produced, which is far more
penetrating than the particles which produce it. The dose rate due to bremsstrahlung is
directly proportional to the atomic number (Z) of the shielding material. Therefore, this type
of shielding (particularly heavy metals) must be avoided. The fraction of β-ray energy
which appears as bremsstrahlung is approximately
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fbremms ≈ 13 ZE max × 10 −3
(5)
where Z = atomic number of the shielding material, and Emax is in MeV
3.5 Positrons
Positrons or β+ particles have the same mass and charge as electrons but their charge is
of the opposite sign. Positron emission is always accompanied by x-ray emission.
3.6 Gamma Rays and X-rays
Gamma (χ) and X-rays are both photons of electromagnetic radiation similar to light and
radio waves, but carry much greater energy. The only difference between the two is in
their method of production and both are very penetrating compared with both alpha and
beta particles.
When a nucleus is left in an excited state, i.e. with an excess of energy, after a nuclear
transformation, the excess energy is promptly emitted in the form of a gamma ray.
X-rays are produced whenever inner orbital electrons move between different energy
levels.
There are three main ways in which gamma rays (and X-rays) interact with matter. These
are the photoelectric effect, Compton scattering and pair production. In the photoelectric
effect, all the energy is transferred to an atomic electron, which is ejected from its parent
atom. In Compton scattering part of the energy of the gamma photon is transferred to an
atomic electron. The gamma photon is therefore scattered with a reduced energy. In pairproduction, an energetic photon in the intense electric field close to a charged particle,
usually a nucleus, may be converted into an electron pair (β- + β+). The absorption of
photons by the photoelectric effect is most probable for low energy g radiation (<200 keV)
and high atomic number (Z>50) absorbers. Compton scattering is most probable for
intermediate energy photons (500-1000 keV), and is the only significant interaction for
materials of low atomic number. Pair production is most probable for high energy photons
(>1.02MeV) and high atomic number absorbers.
3.7 Absorption of gamma rays and X-rays
When a narrow beam of gamma or X-rays falls on an absorber, the intensity of the beam
emerging decreases exponentially with the thickness of the absorber.
I = I0e-mx where
I0
x
m
is the initial intensity
is the absorber thickness
is the total absorption coefficient
(6)
The half-thickness is the amount of absorber required to reduce the beam to half of its
original intensity. When a broad beam of gamma rays passes through thick layers of
material there is considerable multiple scatter, some along the direct beam (build-up), and
attenuation is no longer exponential.
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3.8 Neutrons
Neutrons are unstable, uncharged particles and cause ionisation indirectly. They are
normally produced either in a nuclear reactor or by bombardment of beryllium with alpha
particles, (e.g.Am-241/Be). As with gamma radiation they ultimately transfer their energy
to charged particles. "Fast" neutrons have energies of several MeV. "Slow" or "Thermal"
neutrons may have energies as low as fractions of an eV. They are most efficiently
slowed down by materials of low-atomic number, e.g. water, hydrocarbons, graphite etc.
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4
RADIATION UNITS
4.1 Absorbed dose
Absorbed dose (D) is a measure of the energy absorbed per unit mass in any medium by
any type of ionising radiation. It is dependent on the energy of the radiation and the nature
of the medium. The unit of 1 joule per kilogram is called the Gray (Gy).
The organ absorbed dose (DT) is the mean absorbed dose in any given tissue (T).
4.2 Weighting Factors
The biological effects due to a particular absorbed dose of radiation are dependent on both
the type of radiation absorbed and the particular tissue or organ irradiated. Therefore, in
order to obtain quantities for use in radiation protection which provide better indices of the
detriment caused by a particular radiation dose, two weighting factors have been defined
by the ICRP: the radiation weighting factor (wR); and the tissue weighting factor (wT). The
values of these weighting factors (as defined in ICRP Publication 60, 1991) are given in
tables 2 & 3 below.
Table 2: Radiation Weighting Factors(WR)
Table 3: Tissue Weighting
Factors(WT)
Type of radiation and energy range
WR
Tissue or Organ
WT
1
Gonads
0.20
X rays and γ rays, all energies
1
Bone marrow (red)
0.12
Electrons (β-) and positrons (β+)
Neutrons, E<10keV
5
Colon
0.12
Neutrons, E 10keV - 100keV
10
Lung
0.12
Neutrons, E >100keV - 2MeV
20
Stomach
0.12
Neutrons, E >2MeV - 20MeV
10
Bladder
0.05
Neutrons, E >20MeV
5
Breast
0.05
Protons >2MeV
5
Liver
0.05
20
Oesophagus
0.05
α particles, fission fragments, heavy nuclei
Thyroid
0.05
Skin
0.01
Bone surface
0.01
Remainder
0.05
(ΣWT = 1.00)
4.3 Equivalent Dose
Equivalent dose (HT,R) is the absorbed dose in an organ or tissue multiplied by the relevant
radiation weighting factor (wR), which is a measure of the radiation’s relative ability to
produce biological damage.
(7)
HT,R = w R . D T,R
where DT,R is the absorbed dose over the tissue or organ, T, due to radiation R.
When the radiation field consists of mixed radiations, the total equivalent dose (HT) is
given by the sum of the equivalent doses from each type of radiation, i.e.
(8)
H T = ∑ w R .D T,R
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4.4 Effective Dose
The relationship between the probability of stochastic effects and equivalent dose also
depends on the organ or tissue irradiated. The effective dose (E) is a measure of the
combined effect on the body of the doses to several individual organs or tissues within the
body. It is calculated from the summation of the equivalent dose in each tissue or organ
multiplied by the weighting factor for that tissue or organ, i.e.
(9)
E = ∑ w T .H T
An important related quantity is the effective dose equivalent (HE) which is the weighted
average of the dose equivalents (HT) received over the course of a year.
4.5 Dose Rate
•
The rate of absorption of energy in a given volume of air or tissue is the dose rate, D . It is
related to the rate of emission of energy from a radioactive substance. For a flux of N
particles per cm2 per second at a point, each giving up an energy of ε <units> per cm of
path:
•
(10)
D = N× ε
<units>.cm-3.s-1
4.6 Inverse Square Law
The dose-rate associated with any point source of gamma or x-radiation in a nonabsorbing, non-scattering medium is inversely proportional to the square of the distance
from the source.
D∝
where
D = dose rate
e.g. if r1 = 2 cm and r2
D 1 (4) 2
=
D 2 (2) 2
(13)
D 1 r2 2
1
or
=
D 2 r12
r2
&
r = distance from source.
= 4 cm.
→
D 1 = 4D 2
∴ doubling the distance from the source reduces dose rate by a factor of 4.
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5.
Health Effects of Radiation
Biological effects in the body, due to either external radiation, or to internal contamination
following ingestion or inhalation of radioactive substances, include both damage to the
body directly, and hereditary (genetic) effects in future generations due to damage to the
germ cells in the reproductive organs.
Radiation causes ionisation of water (the main cell constituent) and other molecules
producing free radicals such as H• and OH•, which are chemically highly reactive, and
hydrogen peroxide, H2O2 (a strong oxidising agent).
These may then attack molecules of DNA, causing a variety of lesions including: single- or
double-strand breaks in the duplex molecule; chemical alteration of the bases or sugar
moieties; and cross-linking to DNA related matrix proteins or nucleotides in the DNA
molecule itself. Most of these lesions can be repaired by the excision repair process with
phenomenal accuracy (less than 1 error in 10 million). However the rarer double strand
breaks are much more difficult to repair - some research indicates an accuracy of ~75%.
Failure to repair, or mis-repair, of DNA can cause early death of the cell, prevent or delay
cell division, or pass on a permanent modification to the daughter cells.
5.1 Deterministic Effects
High acute doses of radiation to the whole body cause a number of effects due to the
death of large numbers of cells within particular bodily systems: haematological syndrome
(>1 Gy), gastrointestinal syndrome (>10 Gy) and neurological syndrome (>20 Gy). These
effects are said to be deterministic or nonstochastic (“non-random”) in that they have a
definite threshold (of dose) below which they do not occur, and the severity of the effect
depends on the dose. For example: a dose of 2 Gy will cause sickness but not death; at
~4 Gy about half the exposed population would die if untreated; and at 10 Gy everybody
dies whether they receive medical treatment or not. These doses are extremely unlikely to
occur in the laboratory - an acute dose of ~1Gy could only occur if you ingested 400MBq
of 32P or carried 10GBq (10,000MBq) of 22Na in your back pocket for 24 hours!
Cataract formation is a deterministic effect which can occur after repeated exposure to
radiation. The threshold dose is ~15 Gy, and therefore the statutory dose limit for the eye
is set so that this value will not be exceeded over a whole working lifetime
Erythema (reddening of the skin) is the one deterministic effect (threshold ~ 1Gy) which
may possibly occur in the laboratory - 1MBq of 32P contamination on the skin could
produce this magnitude of dose in under an hour, as could repeated direct handling of
MBq quantities of 32P in thin walled eppendorfs!
Large doses of β and low energy γ-ray exposure will produce reddening of the skin
(erythema), and larger doses (>3 Gy) may lead to changes in skin pigmentation, blistering
and ulceration.
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5.2 Stochastic Effects
The stochastic (“random”) effects of radiation damage are characterised by the fact that
they have no threshold dose and that the probability of the effect is proportional to the
dose. The main stochastic effects are cancer and transmissible genetic damage.
Radiation induced damage to DNA can inactivate the gene in which the damage occurs. If
the effected gene is involved in the regulation of the cell’s proliferation carcinogenesis may
result. Therefore, despite the fact that carcinogenesis is a multistage process, a single
radiation induced lesion could potentially cause a pre-cancerous cell to develop into a fatal
cancer. This is why no excess dose of radiation can be considered to be completely safe.
Similarly, inactivation of a gene within a germ cell may result in damage to or death of a
foetus.
The foetus is also particular sensitive to radiation damage, due to the small number of
cells, lack of redundancy and the rapid rate of cell division (which limits the time in which
repair mechanisms can function). For this reason doses to the female abdomen and the
developing foetus are subject to additional dose limits.
5.3 Dose Limitation
The most important legal requirement with regard to radiation protection is that all doses
(to all persons) resulting from work with ionising radiation are kept as low as reasonably
achievable (the ALARA principle). This requirement is applicable to both employers and
employees and is explicitly stated in regulations 8 & 34 of the Ionising Radiation
Regulations 1999 (IRR99). This requirement is justified by the fact that there is no
minimum dose that may be considered safe (due to the possibility of stochastic effects).
The IRR99 also specify Dose Limits which set an absolute maximum on the doses that
may be received by different categories of persons. These are summarised below:
Annual Limits
Classified
Workers
20 mSv
Radiation Workers
Whole body
6 mSv
Any 1cm2 skin
Hands, wrists, feet
500 mSv
150 mSv
& ankles
Lens of eye
150 mSv
50 mSv
Additional restrictions
Female abdomen: 13 mSv in any three month period
Foetus:
1 mSv from notification of pregnancy*
Others
1 mSv
50 mSv
15 mSv
*Female radiation workers are obliged to inform their employer if they believe that
they may be pregnant so that potential risks may be assessed.
These limits create the need for a number of secondary limits, the most relevant of which
is the Annual Limit on Intake (ALI). The ALI for a given radioisotope is the activity which, if
inhaled or ingested, would result in a dose of 20mSv in the year after ingestion.
All limits are for doses resulting from work involving radiation, and do not include doses
received from background radiation (~1-2 mSv per year in the UK).
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6
Practical Radiation Protection
Radioactive materials are uniquely hazardous due to the fact that unlike chemical and
biological materials, they do not need to enter the body to cause harm. It is therefore
necessary when dealing with radioisotopes to take action to minimise the dose received
from both internal and external exposures.
6.1 Internal Exposure
Internal exposures occur when the radioactive materials enter the body. In addition to
following the procedures set out in the Local Rules, there is a need to consider the
potential pathways for internal exposure when planning the experiment, so that
appropriate action can be taken. The four main pathways for internal exposure in the
laboratory environment are ingestion, inhalation, absorption and (more rarely) injection.
6.1.1 Ingestion
In addition to following the general procedures for the use of unsealed sources, effective
means of contamination control are required.
The use of radioisotopes should be confined to demarcated areas and both these areas
and the worker themselves must be monitored after each use of radioactive materials. In
multi-user areas, prior monitoring of the working area is also necessary. In addition
routine monitoring of the whole laboratory in addition to the radiation areas should be
undertaken on a weekly or monthly basis, depending on the amount of work undertaken.
6.1.2 Inhalation
The possible production of aerosols during the handling of liquid form radioisotopes needs
to be considered. Activities likely to cause aerosol production should be avoided or, if this
is not possible, must be undertaken within a fume cupboard.
The possible production of volatile reaction products also needs consideration - particularly
with 125I-, 14C-, 35S- and 3H-labelled radiochemicals. All 125I-labelled radiochemicals
contain small quantities of volatile iodine and should be handled within a fume cupboard
(with the exception of very low activity RIA kits). Other radiochemicals (notably sodium
14
C-bicarbonate!) will liberate radioactive gases when involved in some chemical reactions.
In addition, even when stored under ideal conditions, radiochemicals are subject to
chemical, biological and radiolytic decomposition over time. Aged stocks are likely to
contain significant impurities, including volatiles, and should be only be opened in a fume
cupboard. For this reason, unused stocks should not be allowed to accumulate, but
should be disposed of promptly when no longer required. For information on the effective
shelf life of a radiochemical stock the manufacturer’s safety data sheet should be
consulted.
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6.1.3 Absorption
Although latex gloves give good protection against aqueous solutions, organic solvents
(ethanol, toluene, etc.) will pass through both latex and skin (carrying their radioactive
solute with them) in a matter of minutes. Potential users of organic solutions of
radiochemicals should seek advice from the DRPS/URPO/RPA as to the appropriate
gloves to be used.
6.1.4 Injection
The use of hypodermic needles in the manipulation of unsealed sources should be
avoided wherever possible. Where there use is required the URPO should be consulted
and an appropriate system of work established prior to the work being undertaken.
6.2 External exposure
Protection against external exposure is also of concern when planning an experiment and
again four factors need to be considered - activity, time, distance and shielding.
6.2.1 Activity
The minimum quantity of radioisotope that is required for the experiment should be used in
order to keep any dose received as low as reasonably achievable. It is also cost effective.
6.2.2 Time
Minimising the amount of time spent in proximity to radioactive materials is not achieved
by doing the procedure as fast as possible - it is achieved by pre-planning. Practice the
experimental procedure beforehand, ensure that stocks (especially of gamma emitters) are
returned to store promptly, and check that you have all required equipment available
before commencing each experiment.
6.2.3 Distance
The inverse square law implies that for a doubling of distance there is a four-fold reduction
in the dose received. For medium energy beta emitters such as 14C, 35S and 33P, where
there is significant air absorption of the beta energy, the effective of increasing distance is
even greater.
However, the converse also applies - if you halve the distance, the dose quadruples and
for this reason it is important to avoid direct handling (particularly 32P) - forceps or shielded
blocks should be used where possible.
6.2.4 Shielding
Where necessary the appropriate shielding must be used. In particular: 1cm thick
perspex shields for 32P, lead impregnated glass or PVC for 125I, and lead blocks for high
energy gamma emitters.
When higher energy gamma or X-ray emitters are used, it is not possible to shield against
all emitted radiation. In these cases, the activity used needs to be considered in the risk
assessment to determine the appropriate thickness of shielding required. The half value
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thickness (HVT) of a given shielding material is the thickness required to stop 50% of the
gamma energy. Values for lead are given below for a range of energies.
Radionuclide
125
I
123
I
51
Cr
60
Co
E (γ/X)
35 keV
170 keV
320 keV
1.3 MeV
HVT (lead)
0.02 mm
0.5 mm
3 mm
9 mm
6.3
General Procedure for the Use of Unsealed Sources
1
All users must be registered as radiation workers; inexperienced workers should not
work alone. Whenever possible a preliminary experiment with inactive materials should
be carried out before a new procedure is attempted, to identify possible handling
difficulties.
2
Eating, drinking, smoking, or the application of cosmetics etc. are not permitted in areas
where radioactive materials are handled. No food, drink, crockery or cutlery should be
brought into such areas.
3
No mouth operated equipment (e.g. pipettes) may be used. Self-adhesive, not gummed,
labels should be used.
4
A laboratory coat or overall must be worn for all work with unsealed radioactive
materials. In certain circumstances the RPS may, after consultation with the URPO,
prescribe more stringent safety measures such as special safety clothing and changing
facilities.
5
Disposable surgical gloves, or equivalent, must be worn when there is a possibility of
hands becoming contaminated. Tissues should be used to prevent spread of
contamination when handling switches, taps, monitoring instruments etc.
6
Any cut or break in the skin of the hands or other vulnerable area liable to contamination
must be covered with a waterproof adhesive dressing before entering the isotope
laboratory. Any injury received during work with radioactive materials must be reported
to the RPS who will arrange suitable first-aid. If significant intake of radioactivity or
excessive skin contamination is suspected the RPS should be informed immediately
and appropriate remedial action commenced.
7
A high standard of cleanliness must be maintained to avoid spread of contamination.
Working areas should be kept free of articles not required for the work. Each worker
must be responsible for tidying up after him/herself at the end of each working session.
8
Paper tissues must be used instead of handkerchiefs. They should be disposed of as
solid waste.
9
Personal dosimeters (body badges and/or extremity dosimeters) must be worn if issued
by the URPO.
10
Each consignment of radioactive material must be checked for leakage of radioactivity
during transit, by monitoring packing materials.
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11
Radioactive solutions should always be handled over a suitable tray lined with absorbent
paper or a disposable liner. Benches should also be covered with absorbent paper with
a non-porous backing.
12
Shielding and handling equipment (e.g. forceps etc.) should be used as appropriate. For
accurately transferring small volumes of liquid a disposable-tip, automatic pipette is
recommended. Whenever reasonably practicable, dose rates should be kept below 2.5
mSv h-1.
13
Radioactive solutions should always be manipulated behind a splash barrier. All
procedures which are considered likely to produce vapour, spray, dust or radioactive
gas should be carried out in an approved fume cupboard, glove box or safety cabinet.
14
If a hypodermic needle is to be used to dispense from a multidose vial, care should be
taken to avoid aerosols/splashing due to pressure build up. Cooling the vial before
puncturing the rubber septum should ensure that the pressure inside is less than
atmospheric.
15
All radioactively contaminated waste must be segregated and disposed of in accordance
with the EA authorisation.
16
Disposal sinks must be clearly labelled and not used for handwashing. Due to the risk of
contamination from splashing etc. the space below such sinks must be kept clear at all
times and not used for storage.
17
All radioactive samples must be clearly labelled, in appropriate containers, and securely
stored in a locked room, cupboard, freezer or refrigerator when unattended. Each store
should have an accurate up-to-date stock list.
18
Accurate records must be kept of all receipts, current stock and waste disposals. It is an
offence under the Radioactive Substances Act 1993 not to have records up-to-date at all
times.
19
Monitoring of the work area should be carried out at the end of each work session. No
item may be removed from the radioisotope area until it has been monitored and found
to be free of contamination.
20
On completion of work disposable gloves must be washed and monitored before
removal. Hands and clothing must also be monitored and washed where necessary. All
protective clothing must be removed before leaving the laboratory.
21
A full area monitoring survey should be undertaken at regular intervals and records kept
of all results, even if no contamination is found.
22
Potential radiation hazards should be assessed and, if necessary, contingency plans
drawn up for use in an emergency. In the event of any such incident the RPS / URPO
must be informed immediately.
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7
Contamination Control
7.1
Contamination Monitoring
Monitoring is used to indicate whether levels of radiation and contamination are satisfactory
for work with ionising radiation to continue. It helps to establish the adequacy of current
working methods, to detect breakdowns in controls or systems and to detect any other
unforeseen changes in levels of radiation.
7.1.1 Active Area Monitoring
All areas where unsealed sources of radioactive materials are used ("active areas") must
be monitored both before and after each session. The term "area", in this instance, also
includes any equipment that could have been contaminated (e.g. gilsons, centrifuges,
hybridisation ovens, and heating blocks. In addition,
If an area is discovered to be contaminated prior to undertaking work, the RPS must be
informed and the incident investigated. Minor spills or splashes which occur during the
course of an experiment should be cleaned up by the user in accordance with the
University Policy. Where it is impossible to remove contamination to below the working
limit for the radioisotope in question, the RPS should be contacted for advice.
Contamination in all areas should be kept as low as reasonably achievable. Monitoring
should aim to detect all contamination, not merely that which exceeds the limits. If
contamination is detected by monitoring, the area (and/or skin) must be decontaminated
without delay. If surface contamination above the working limits persists, and cannot be
removed by standard methods, the RPS must be informed
All measurements of contamination must be recorded in a Contamination Monitoring
Record (CMR) in such a manner that it can be directly compared with the working limit.
Generally this is achieved by converting the measured count into Bq/cm2.
7.1.2 Laboratory Monitoring
Once per month (weekly in Controlled areas), the entire laboratory (including inactive
areas) should be surveyed for contamination. A schematic diagram of the lab should be
used to demarcate all the areas to be surveyed and the results recorded in the CMR. Any
levels of contamination above the working limit should be reported to the RPS. If it is
unclear which radioisotope is the contaminant, the most restrictive working limit (based on
counts per second) should be used.
7.1.3 Personal Monitoring
Hands and protective and personal clothing (including shoes) must always be monitored
before leaving a controlled or supervised area. If there is any reason to suspect that the face
or any other skin areas may have been contaminated, these areas should also be monitored.
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7.2
Methods of Contamination Monitoring
Two main methods of contamination monitoring exists:
(which gives an instant reading); or by wipe testing.
using a hand-held instrument
Tritium contamination cannot be detected with any hand-held instrument- wipe tests must
be used.
Geiger-Muller probes (e.g. Mini Instruments types EL and EP15) must be used for other
beta emitters. Mini Instruments type E probes are relatively insensitive and are only
recommended for use with 32P.
X-ray and gamma emitters require the heavier scintillation probes (such as the Mini type
44A).
The responses of such instruments vary with the energy emitted, and users should check
that the instrument that they intend to use is suitable for the purpose. For details of the
instrument (see s7.3)
7.2.1 Procedure for using a Hand Held Monitor
1
Select an appropriate instrument.
2
Switch on the instrument; allow 30s for warm-up, then take a background reading
well away from the active area(s)
3
Move the face of the detector slowly across the area at a distance of approximately
1cm from the surface. Note the maximum reading obtained.
4
Subtract the background from the reading to obtain the counts per second (CPS) due
to contamination [treat negatives as zero].
5
Use the tables in the appropriate CMR to establish the level of contamination in
Bq/cm2
6
Record the result.
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7.2.2 Procedure for conducting a wipe test
1.
Moisten a suitable wipe, such as a glass-fibre disc small enough to fit into a liquid
scintillation vial, with water or other solvent in which the contamination is soluble.
2.
Wipe a known area of surface, normally 100 or 1000 cm2.
3.
Place the wipe into a scintillation vial with 10 cm3 of liquid scintillant.
4.
Count the activity in a liquid scintillation counter programmed to detect the isotope(s)
required.
5.
In the absence of any more accurate information assume that 10% of the activity on
the wiped surface has been transferred to the wipe.
6.
Calculate the contamination level using the formula:
C 100 100
×
contamination level (Bq cm-2) = ×
T
A Eff
C
=
count-rate in cps, corrected for background
where
A
=
area wiped in cm2
Eff =
percentage counting efficiency for isotope
T
=
percentage of contamination picked up (normally 10%)
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7.3
Contamination Monitor Response
Responses are quoted as counts per second per Bq.cm-2 (above background) for large-area
sources at a distance of 1 cm.
Beta emitters
14
C/35S
Instrument
33
P/45Ca
Gamma/X-ray emitters
32
Instrument
P
57
Cr
Co
125
I
not
suitable
not
suitable
0.6
Mini 44A
0.06
2.1
3.8
Mini 44B
0.5
3.2
3.8
Mini 900E
0.6
1.0
1.7
Mini 42
Mini 900EL
1.3
2.0
4.8
Mini EP15
1.3
1.7
4.0
7.4
51
Contamination Limits & Emergency Action Levels
Table A4: Working Limits & Emergency Action Levels for selected radionuclides
Column 1
Nuclide
Column 2
*Working Limit
(Bq cm-2)
Column 3
**Emergency Action Level
(MBq)
H-3
300
3000
C
30
120
Na
3
21
32
3
24
33
3
240
35
S
30
210
Ca
3
60
51
Cr
300
1200
57
Co
30
180
60
3
9
86
3
24
I
30
3
Cs
3
3
14
22
P
P
45
Co
Rb
125
137
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7.5 Emergency Action
Spills of radioactivity at the levels used within the University will not generally warrant any
drastic emergency action. Simple remedial action by local staff, as part of their routine
procedures, will normally be adequate to control the spread of contamination.
An emergency kit containing protective clothing, decontamination materials, plastic bags,
handling tools, warning signs, tissues etc. should be available in each department.
An incident must be treated as an emergency if it involves the dispersal of activities in excess
of the Emergency Action Levels given in s7.4 above, or if there is a high dose rate due to
mechanical failure.
If fire or serious injury are involved, these must be given priority. The radiation hazard is
likely to be negligible compared to the risk of fire.
Suspected loss/theft must be reported to the RPS without delay, and, where practicable,
recovery attempted. Loss/theft also has to be reported to the EA; no minimum values are
specified.
Where necessary the public emergency services should be called by dialling 6666 from
a University telephone with internal access only, or 9-999 from a phone with external
access.
The University Safety and Radiation Protection Officers can be contacted out of hours, in an
emergency, via Estates Services ext. 6817.
7.6
Emergency Procedure
If the assistance of public services is not required, the following procedure should be
observed:c
Personnel in the immediate vicinity should be warned and, if appropriate, the area
evacuated. Anyone with suspected contamination should remain nearby to await
monitoring and, if necessary, decontamination.
d
The RPS should be contacted for advice and assistance.
e
First aid treatment, or any other assistance, should be given as appropriate.
f
Anyone entering the area to carry out emergency procedures should wear
protective clothing.
g
Apparatus and other services should be switched off, and doors closed to prevent
access.
h
In the case of radioactive solids and liquids steps should be taken to contain the
dispersal and prevent further spread of contamination. Radioactive gases or
vapours should be dispersed as quickly as possible by leaving mechanical
ventilation on and/or opening windows.
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i
To minimise the spread of contamination, contaminated clothing and shoes should
be removed and left in or near the affected area.
j
Only when the emergency situation is under control, and all aspects involving
personnel have been attended to, should decontamination of the working area
commence using the appropriate procedure(s) described in s7.7 below.
7.7
Area Decontamination
To prevent the spread of contamination, spillages of radioactive materials should be cleaned
up without delay using either physical or chemical methods as appropriate. If parts of the floor
have become contaminated access should be restricted until the decontamination procedure
has been completed. If the spillage is greater than 5MBq the RPS should be contacted for
advice, otherwise the following procedures should be observed:7.7.1
Liquid spills in a tray.
Appropriate protective clothing and disposable gloves should be put on before
decontamination is commenced.
All objects should be removed from the tray, monitored, and decontaminated as necessary,
either by rinsing over a designated sink or, if more appropriate, by wiping with paper tissues.
Contaminated tissues should be placed in a plastic bag. Each item should be monitored again
to confirm decontamination before being placed outside the affected area. Extensive
decontamination of equipment should not be attempted if the risks and cost of
decontamination outweigh its value. If equipment has persistent contamination from a shortlived nuclide it may be appropriate to store it in a safe place, with adequate shielding, until the
activity has decayed to an acceptable level.
Glassware should be cleaned with an appropriate detergent. If necessary ammonium citrate,
chelating agents or proprietary solutions (e.g. Decon) should be used.
Plastics may be cleaned with detergent or, in some cases, dilute nitric acid, but care should
be taken to avoid using ketonic solvents or chlorinated hydrocarbons which will dissolve some
plastics.
Metals may be cleaned with heavy-duty detergent. Other cleaning agents should be chosen
carefully taking into account both the metal concerned and the nature of the contaminant.
Unsuitable decontamination methods may cause corrosion making the removal of future
contamination more difficult.
The above procedures should be repeated as necessary, and then the tray itself should be
cleaned over the designated sink. If excessive persistent contamination remains, the RPS
should be contacted for advice.
Any solid waste produced should be disposed of by an authorised route as radioactive solid
waste, and in conformity with authorised disposal limits. The activity disposed of by each
route, both solid and liquid, must be included in the waste disposal returns.
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7.7.2
Liquid spills on the bench or floor.
Protective clothing, including overshoes if appropriate, and disposable gloves should be put
on before decontamination is commenced.
Paper tissues should be dropped onto the spillage to absorb the liquid, and then the spill
mopped up, if necessary using a remote handling tool to hold the tissues. Contaminated
materials should be placed in a plastic bag.
The affected area should be washed and dried, working from the outside towards the centre
to prevent further spread of contamination. Paintwork and flooring should, in the first
instance, be cleaned with soap and water, if necessary followed by an abrasive cleanser
and/or complexing agent.
The area should be monitored to confirm decontamination and the procedure repeated if
necessary.
If persistent contamination by a long-lived nuclide remains, it may be necessary to use more
aggressive treatments as appropriate, such as paint stripper.
If persistent contamination remains from a short-lived nuclide the surface may be covered
with an impermeable material, and shielded as appropriate (e.g. with 1cm perspex for 32P)
until the activity has decayed to an acceptable level.
Any solid waste produced should be disposed of by an authorised route (see Section 11), and
in conformity with authorised disposal limits. The activity disposed of by each route, both solid
and liquid, should be included in the waste disposal returns.
If excessive contamination persists the RPS should be contacted for advice and assistance.
7.7.3
Solid spillages.
To prevent airborne dispersal of powdery materials, and therefore an inhalation hazard,
brushing must be avoided. Moist paper tissues should be used and then the procedure above
should be followed. Insoluble particulate materials may be picked up using adhesive tape, blutack etc.
7.7.4
Spillages on clothing.
Clothing which is contaminated in excess of the Working Limits for surface contamination
detailed in Appendix 3 should not be sent to a public laundry but should be rinsed in hot
water until the level of contamination is acceptable. Clothing contaminated with short lived
nuclides should be stored in impermeable bags until the activity has decayed below the limit.
Items which cannot be decontaminated satisfactorily, or held for storage, should be treated as
radioactive waste.
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7.8
Personal Contamination
If personal contamination is accompanied by injury requiring urgent medical assistance the
procedures in s7.5 should be followed. In all other cases any contaminated clothing should be
carefully removed, placed in a plastic bag, and then the appropriate following procedure
observed:The affected part of the body should be washed with soap and water taking care not to
spread the contamination nor to allow contaminated liquid to enter the eyes, mouth, ears or
nostrils. Showering is not recommended for this reason. Vigorous scrubbing which could
damage the skin should be avoided, as it could allow contamination to enter the blood stream.
For the same reason organic solvents or strong detergents should not be used. Particular
attention should be paid to the fingernails as contamination can get trapped underneath. It
may be necessary to clip the nails to remove persistent contamination. Successful
decontamination should be confirmed by monitoring. If necessary the above procedure should
be repeated.
Wounds or broken skin should be washed under running water taking care, as before, not to
wash the contamination into the wound or contaminate other areas of the body. Within
reason, bleeding should be encouraged to assist in flushing the contamination from the
wound.
If the eyes have been contaminated they should be irrigated immediately with water or saline
solution.
Contamination of the mouth should be treated by rinsing several times with water or hydrogen
peroxide solution (1 tablespoon of 10 volume solution to a tumbler of water).
If internal contamination is suspected, as a result of ingestion, inhalation, a wound, or
penetration of the skin, the RPS must be notified immediately. It may be possible, after
consultation with the URPO/RPA to enhance the rate of elimination from the body. e.g. the
uptake of radioactive iodine by the thyroid may be reduced by taking stable potassium iodide
or iodate. Treatment should never be commenced without medical advice.
Whenever high level contamination of parts of the body, other than the hands, is
suspected, or if excessive contamination persists after any of the above procedures,
the RPS should be contacted at once for further assistance.
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8
The Law
The use of ionising radiation is subject to strict regulation within the United Kingdom. The
main pieces of legislation relevant to work within a University environment are:
The Radioactive Substance Act 1993 requires that all organisations using radioactive
materials or disposing of radioactive waste are licensed to undertake such work.
Authorisations and Registrations under this Act specify the types and quantities of
radioactive materials that may be used or disposed of. The Act is enforced by the
Environment Agency (EA), whose inspectors have the power to suspend or prohibit work
with ionising radiation, revoke site licences, or prosecute institutions which have failed to
comply with the terms of their licences.
The Ionising Radiation Regulations 1999 are concerned with the protection of all
persons from exposure to ionising radiations used in working practices.
These
Regulations require the appointment of Radiation Protection Advisers* and Radiation
Protection Supervisors, the formulation of Local Rules and the provision of training for all
radiation workers. They place specific requirements on both employers and employees (a
term which includes research students!) and are enforced by the Health and Safety
Executive (HSE). Failure to comply with the IRR99 may lead to prosecution of the
institution or the individuals responsible for the alleged offence.
The University Policy for the Use of Ionising Radiation has been designed to ensure that
any person following it will be complying with the requirements of the RSA93 and IRR99.
In Controlled Radiation areas and in some larger laboratories, further Specific Local Rules
apply.
The Radioactive Material (Road Transport) (Great Britain) Regulations 1996 govern
the transport of radioactive materials. Any person who wishes to transfer radioactive
materials either into or out of the University, must do so via the University Radiation
Protection Officer - this is particularly important for radioactive samples being transferred
between research institutions!
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9
Stock Control & Radioactive Waste Disposal
The RSA93 requires that all radioactive substances kept, used or disposed of must be
properly accounted for. As any discrepancy in such records which could indicate that any
quantity of radioactive material has been lost (however small), records relating to
dispensations from stock and waste disposal must balance.
9.1 Stock Control
The URPO must be informed of all potential acquisitions of radioactive substances before
they are brought into the University – this applies not only to those radiochemicals ordered
from commercial suppliers, but also to radioactive materials transferred from other
institutions.
Once a pot of radioisotope is received by a radiation user (whether from an external
organisation or by transfer from another laboratory / School), a stock record must be
generated so that dispensations may be recorded. These records should include: date of
receipt; the radionuclide present; activity at time of receipt; where the material is to be stored;
the person/group responsible for the material; and an ID number (also to be marked on the
pot itself) so that the material can be identified.
Each user then has a responsibility to maintain accurate records relating to the radioisotopes
they use. Any suspected loss of radioactive material must be reported immediately to the
URPO. Users must record all radioactive waste disposed of and of any radioactive products
that are being kept for further use (“retained samples”). Retained samples must be
appropriately labelled and marked with the radiation hazard trefoil.
At the end of each month information relating to the activity held and radioactive waste
disposals are passed to the RPS together with details of any stock transfers to or from other
departments. The RPS then reports back to the URPO.
9.2 Radioactive Waste Disposal
It is vitally important that all users of radioactive materials understand what constitutes
radioactive waste and know the appropriate disposal route for each type of waste
generated. Disposal of radioactive waste by an unauthorised route, or failure to keep
adequate records relating to waste disposals, will result in prosecution and is likely to
interfere with (or terminate) research activities involving radioisotope use.
Procedures for the disposal of radioactive waste are specific to each of the University sites
and the exact requirements are set out in each site's Local Rules. The available routes
are described in the following sections. It should be noted that none of the sites are
authorised to dispose of any alpha emitting radionuclides and these materials must not be
brought onto University premises.
Aqueous Waste
The normal disposal route for aqueous liquid wastes which are radioactive but otherwise
innocuous is via one of the designated disposal sinks in the radioisotope laboratories.
Wherever possible, contaminated solid articles should be rinsed within designated sinks to
reduce the activity going into the solid waste stream. Departments may have daily or monthly
Page 27
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limits on the activities that may be disposed of and limits must not be exceeded unless prior
permission is obtained from the URPO. All disposals via this route should be accompanied by
a plentiful supply of running water, to ensure adequate dilution.
Biodegradable liquid scintillant fluids may also be disposed of via the designated sinks or (in
the Medical School) via the granulator.
Very Low Level Waste
The term Very Low Level Waste applies only to solid waste placed in black bags (i.e. the
“domestic” waste stream) and transferred to landfill. The law allows items of radioactive
waste containing less than 40kBq (400kBq for 3H & 14C) to be disposed of via this route as
long as the total activity in any one bag does not exceed 400kBq (4 MBq for 3H & 14C).
However, all items of waste generated within the laboratory either constitute (radioactive)
clinical waste or are similar in appearance to clinical waste. Their appearance on a landfill
site therefore invites unwanted attention and possible prosecution (in the event that true
clinical waste - whether radioactive or not - accidentally ends up being disposed of via this
route). Use of this route should therefore be avoided and, if possible, black bags should
be kept out of laboratories completely. If there is a perceived need to use this route, the
URPO must be consulted for advice prior to any disposal. This route is solely intended
for large objects such as sinks and work surfaces from laboratories being
refurbished.
Radioactive Clinical Waste
This is the preferred route for all solid radioactive waste. A record of the isotopes and
activities placed in any radioactive clinical waste container should be kept beside each
container and updated immediately after each disposal. The containers themselves must
be marked with the radiation hazard trefoil so that they may be distinguished from nonradioactive clinical waste. Under no circumstances should items which may be
contaminated with radioactive materials be placed in the non-radioactive clinical
waste stream.
The University is currently charged £8/MBq for disposal via this route. Where possible
items of radioactive waste should be decontaminated in order to reduce costs. From 1st
January 2003, all sites will have access to radioactive decay storage for short-lived
radioisotopes. Waste can not be stored in laboratories.
Organic Solvents contaminated with radioactive materials
Organic solvents (including non-biodegradable liquid scintillation fluids) may not be
disposed of to drain. Radioactive organic solvents (such as those generated by HPLC
work) require specialist and expensive disposal. The advice of the URPO should be
sought prior to commencing work likely to generate such waste.
Gaseous Waste
The University Main Campus (BT7698) is authorised to discharge very small quantities of
carbon-14 gaseous waste to atmosphere. Restrictive daily and annual limits apply and
anyone intending to undertake work which may give rise to gaseous emissions must
obtain the approval of the URPO or URPA
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10
Radioisotope Data
10.1 Tritium (3H)
Half-life:
12.3 years
Emissions
β, Emax = 0.019 MeV (100%)
Max range (air)
6 mm
Max range (water)
0.006 mm
Shielding
Non Required
Monitoring
Wipe test only
Working Limit (Contamination)
300 Bq.cm-2
Annual Limit on Intake (ALI): Ingestion 1 GBq
Annual Limit on Intake (ALI):
1 GBq
Inhalation
External dose from 1 MBq at 30 cm
0 mSv.h-1:
External dose from 1 kBq on skin
0 mSv.h-1
Special Considerations
Tritium contamination cannot be measured directly and special care is needed
to keep the work area free from contamination. Regular monitoring by means
of wipe tests must be conducted in and around areas where this nuclide is
used. Tritium can be absorbed through the skin. DNA precursors (e.g. tritiated
thymidine) are regarded as more radioactive than tritiated water since activity
can be concentrated within the cell nuclei. Decomposition of labelled
compounds during storage/use may produce tritiated water (potentially
inhalable - evaporation/sublimation).
10.2 Carbon-14 (14C)
Half-life:
Emissions
Max range (air)
Max range (water)
Shielding
Monitoring
5730 years
β, Emax = 0.157 MeV (100%)
24 cm
0.28 mm
Total absorption by 3 mm perspex
Thin end window G-M detector
(Mini EL, Mini EP15)
Working Limit (Contamination)
30 Bq.cm-2
Annual Limit on Intake (ALI): Ingestion 40 MBq
Annual Limit on Intake (ALI):
40 MBq (organic compounds
Inhalation
External dose from 1 MBq at 30 cm
0 mSv.h-1:
External dose from 1 kBq on skin
0.32 mSv.h-1
Special Considerations
Some organic compounds may penetrate gloves. Potential for production of
inhalable 14CO2 during use/or storage.
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10.3 Phosphorous-32 (32P)
Half-life:
Emissions
Max range (air)
Max range (water)
Shielding
Monitoring
14.3 days
β, Emax = 1.710 MeV (100%)
790 cm
8 mm
Total absorption by 10 mm perspex
G-M detector
(Mini E, Mini EL, Mini EP15)
2 Bq.cm-2
8 MBq
5 MBq
Working Limit (Contamination)
Annual Limit on Intake (ALI): Ingestion
Annual Limit on Intake (ALI):
Inhalation
External dose from 1 MBq at 30 cm
0.12 mSv.h-1:
External dose from 1 kBq on skin
1.9 mSv.h-1
Special Considerations
1cm perspex shielding must be used during all work with this high energy beta
emitter. Procedures (exposure time/distance/shielding) should minimise
exposure to fingertips even where very small quantities are being handled.
10.4 Phosphorous-33 (33P)
Half-life:
Emissions
Max range (air)
Max range (water)
Shielding
Monitoring
25.6 days
β, Emax = 0.249 MeV (100%)
50 cm
0.5 mm
Total absorption by 1mm perspex
Thin end window G-M detector
(Mini EL, Mini EP15)
3 Bq.cm-2
70 MBq
30 MBq
Working Limit (Contamination)
Annual Limit on Intake (ALI): Ingestion
Annual Limit on Intake (ALI):
Inhalation
External dose from 1 MBq at 30 cm
0 mSv.h-1:
External dose from 1 kBq on skin
0.86 mSv.h-1
Special Considerations
Safer but more expensive alternative to 32P.
Page 30
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10.5 Sulphur-35 (35S)
Half-life:
Emissions
Max range (air)
Max range (water)
Shielding
Monitoring
87.4 days
β, Emax = 0.168 MeV (100%)
26 cm
0.32 mm
<1 mm Perspex (if required)
Thin end window G-M detector
(Mini EL, Mini EP15)
30 Bq.cm-2
100 MBq
30 MBq
Working Limit (Contamination)
Annual Limit on Intake (ALI): Ingestion
Annual Limit on Intake (ALI):
Inhalation
External dose from 1 MBq at 30 cm
0 mSv.h-1:
External dose from 1 kBq on skin
0.35 mSv.h-1
Special Considerations
Decomposition of 35S labelled compounds is known to give rise to small
amounts of volatile impurities during storage. Although less than 0.1% of the
total activity is likely to have become volatile, even after several weeks of
storage, vials should be opened within fume cupboards where practicable.
10.6 Chromium-51 (51Cr)
Half-life:
Emissions
Shielding: Tenth Value Layer
Monitoring
Working Limit (Contamination)
Annual Limit on Intake (ALI): Ingestion
Annual Limit on Intake (ALI):
Inhalation
External dose from 1 MBq at 30 cm
External dose from 1 kBq on skin
Special Considerations
27.7 days
β, Emax = 0.004 MeV (67%)
γ, E = 0.320 MeV (10%)
X, E = 0.005 MeV (20%)
7 mm lead
Scintillation detector
(Mini 44A)
300 Bq.cm-2
500 MBq
200 MBq
6.0 x 10-5 mSv.h-1:
0.015 mSv.h-1
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10.7 Iodine-125 (125I)
Half-life:
Emissions
60.1 days
X, E = 0.027 MeV (114%)
γ, E = 0.031 MeV (26%)
γ, E = 0.036 MeV (7%)
β, Emax = 0.004 MeV (79%)
β, Emax = 0.023 MeV (20%)
β, Emax = 0.031 MeV (11%)
<1 mm lead
Scintillation detector
(Mini 44A, Mini 42)
30 Bq.cm-2
2 MBq
1 MBq
Shielding: Tenth Value Thickness
Monitoring
Working Limit (Contamination)
Annual Limit on Intake (ALI): Ingestion
Annual Limit on Intake (ALI):
Inhalation
External dose from 1 MBq at 30 cm
3.9 x 10-4 mSv.h-1:
External dose from 1 kBq on skin
0.021 mSv.h-1
Special Considerations
All 125I labelled compounds will contain extremely volatile free iodide- any
procedure/dispensation from stock solutions containing more then 400 kBq
must be conducted in a fume cupboard. Iodinated compounds may rapidly
penetrate rubber gloves (and skin). Any spillages should be stabilised by
treating the area with sodium thiosulphate solution prior to decontamination.
APPENDIX 1: SI Units and Prefixes
Although the International System of Units (SI) has been in general use for Radiation
Protection, the older units may still be encountered on sealed sources, monitoring
equipment, or when purchasing radioisotopes. Conversions between the more common
units are given below:
Table A1: Comparison of units
Quantity
SI Unit
Old Unit
Activity
becquerel (Bq) = 1
curie (Ci) = 3.7 x 1010
1
1
Exposure*
No special unit
roentgen (R) = 2.58 x 10-4
1
Absorbed
gray (Gy) = 1 J.kg-1
rad = 0.01 Gy
Equivalent
sievert (Sv)
rem = 0.01 Sv
*Some (very old) monitoring instruments measure exposure. For the purposes
of radiation protection an exposure of 1R can be regarded as being equivalent
to an absorbed dose of 0.01 Gy.
Common prefixes used with both systems of units are:
Prefix
Name
Value
Table A2: Prefixes
T
G
M
k
m
n
p
µ
tera giga mega kilo
milli micro nano pico
12
9
6
3
10
10 10 10
1 10-3 10-6 10-9 10-12
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