Integrated Radiation Protection Training Programme
Module 3. Unsealed Sources or Radioactivity
3.0 Introduction
Having completed the College Management of Radiation Protection training
module, you will already be familiar with the principles of ionising radiation
protection.
This training module provides the training required for personnel who will be
carrying out work with unsealed sources of radioactivity within designated
Controlled or Supervised areas.
This module will also be useful for those appointed as Radiation Protection
Supervisors, for areas where unsealed sources are used.
The training will describe the types of unsealed sources that you may encounter
at the College and the nature of the hazards that they present. The procedures and
protection methods adopted at the College to ensure control of both internal and
external radiation hazards will be described in detail.
At the end of the module, there will be a short on-line test and successful
completion of the test, as well as completion of local area induction and
registration as a radiation worker, will be required before you can start work.
We hope you find this training helpful and interesting. There are many
information resources that can be linked to from this training module, but if you
have any technical questions during or following the training, you may contact a
member of the College radiation protection team.
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3.1 Types of Unsealed Sources in Use at ICL
Unlike a sealed (or encapsulated) radioactive source, which will only present an
external radiation hazard, unsealed sources can, if uncontrolled, lead to workplace
contamination and a potential internal radiation hazard, as well.
We, therefore, need to consider safeguards to reduce the likelihood of spilling or
dispersing unsealed sources, so intakes of radioactive material or uncontrolled
releases to the environment can be avoided.
At Imperial College, unsealed sources are commonly used in tracer studies,
whereby the radioactive material may be used to track a physical, chemical or
biological process. Radioactive tracers are most commonly used in solution, but
they may also be present as solids (such as radiochemical powders) or in gaseous
form.
Phosphorus-32 is commonly used for analysing metabolic pathways in Pulse
Chase experiments. Here, a culture of cells is treated for a short time with a
Phosphorus-32 containing substrate. The sequence of chemical changes affecting
the substrate can then be traced by detecting which molecules have incorporated
the Phosphorus-32, at multiple time points following the initial treatment.
All steps within this procedure are carefully controlled to ensure the Phosphorus32 is contained, the contamination of equipment is minimised and the
contamination of personnel is avoided.
Other unsealed sources in use at Imperial College include tritium (H-3), Carbon14, Suphur-35 and Iodine-125. Fluorine-18 is used extensively in nuclear
medicine, where its properties are widely exploited in Positron Emission
Tomography (PET).
In all cases, work with unsealed sources is carefully controlled to ensure the
material is contained, so all exposures, both internal and external, are kept As Low
As Reasonably Practicable.
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3.2 Radioactivity and Radiation Units
Radioactivity is an, often natural, property, displayed by unstable atoms. At the
core of this instability are unbalanced attractive and repulsive forces, within the
nucleus of the atom.
The disintegration of unstable atoms may result in the emission of particles or
energy from the nucleus, as it moves towards a more stable nuclear configuration.
Radioactivity is measured in Becquerels - a Bq being defined as one disintegration
per second. In practice, we define quantities of radioactive material in terms of
kBq, MBq, GBq and so on.
Some materials may be quantified in non-SI units, such as μCi or mCi, but
conversion is straight forward.
One microCurie is equal to 37 kilo Becquerels, while one milliCurie is equal to 37
MegaBecquerels.
1. Half-Life
The more unstable an atom is, the shorter its lifetime will be, and the speed of
radioactive decay is described by a material’s half-life.
The half-life of a radioisotope is the time for half the radioactive nuclei in any
sample to undergo radioactive decay. After two half-lives, there will be one-fourth
the original sample remaining, after three half-lives, one-eighth the original
sample, and so on.
Half-lives vary from fractions of seconds to billions of years. For ease of
management, many radioisotopes in use at Imperial College have relatively short
half-lives.
Phosphorous-32, commonly used in biochemistry, has a half-life of about 14 days,
while Fluorine-18, popular in Positron Emission Tomography, has a half-life of
only 110 minutes.
The disintegration process is known as radioactive decay, and the matter or
energy released during decay, is what we call radiation. Because these radiations
have enough energy to cause ionisation in matter, they are known as ionising
radiations.
The main types of ionising radiations are alpha, beta and gamma radiation.
2. Alpha Radiation
α-radiation is commonly emitted by heavy elements, such as the radioisotopes of
Lead or Uranium. To move the nuclei towards stability, α-particles are ejected
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form the nucleus - these are high energy particles, composed of 2 protons and 2
neutrons – a very stable collection of nucleons, having the same composition as a
Helium nucleus.
Because α-particles have both mass and charge, they are strongly ionising, but
have limited penetrating power. In fact, an alpha particle will give up all its energy
in just a few centimetres in air and will be stopped completely by a thin sheet of
paper. The body’s dead skin layer will stop an α-particle and that’s why alpha
emitters only present an internal radiation hazard, where they may deposit their
energy directly into live tissue.
3. Beta Radiation
β-radiation is commonly emitted by lighter elements, such as the radioisotopes of
carbon or phosphorous.
In β-decay, a β-particle is emitted, following the conversion of neutron into a
proton within the nucleus. The β-particle is just a fast moving, free electron and
(as such) it’s more penetrating than an α-particle, but less strongly ionising. A βparticle will pass through a sheet of paper, but will be stopped by a thin sheet of
aluminium or plastic. High-energy β-particles are capable of penetrating the
body’s dead skin layer and will deposit their energy in live tissue, which at high
levels of exposure can result in beta-radiation burns.
A positron (an electron’s anti-particle) may be emitted by some radioactive
species, such as Fluorine-18, following the conversion of a proton into a neutron.
4. Gamma Radiation
γ-radiation may be released along with α-alpha or β-radiation and (unlike these
radiations) γ-radiation is pure electromagnetic radiation.
γ-radiation is located at the high frequency end of the electromagnetic spectrum
and is highly penetrating. γ-radiation will penetrate paper and aluminium and
will only be attenuated by high atomic number materials such as lead.
5. Radiation Dose
Radiation is energy. When a person is exposed to ionising radiation, the health
impact is determined by how much energy is absorbed by that person.
This is known as the “Absorbed Dose”.
Absorbed dose is measured in Grays (Gy), the units of which are Joules per Kg
The Absorbed Dose is a useful quantity if we are interested in the harm that may
be caused by large, acute radiation exposures.
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But, at the exposure levels we are likely to encounter occupationally, it’s the
potential long-term health effects that we are interested in. To measure radiation
dose in this context, the quantities we are interested in are the Equivalent Dose
and the Effective Dose, both of which are measured in Sieverts (Sv).
These quantities reflect the level of radiation harm, in terms of the likelihood of
developing cancer, some time after the exposure. Statutory limits on radiation
exposure are expressed in terms of Equivalent and Effective Dose.
The Equivalent Dose recognises the differing ionising powers of different
radiation types, and describes this in terms of dose within individual organs.
Because of their high ionising power, α-particles are 20 times more damaging than
photons or β-particles, and this is factored into the Equivalent Dose calculation.
The Effective Dose is a measure of overall (or whole body) radiation harm.
The Effective Dose is the sum of all the individual Equivalent Doses to individual
organs multiplied by a Tissue Weighting Factor.
The weighting factor reflects individual tissue sensitivities, so the Effective Dose
product represents an averaged whole body dose, which is weighted for both
radiation type and tissue sensitivity.
If you wear a whole body personal dosemeter, this will give an estimate of your
Effective Dose.
6. Committed Dose
Of particular interest to users of unsealed radiation sources, is the concept of
Committed Dose. The Committed Dose indicates the level of harm resulting from
the inhalation, ingestion or absorption of radioactive material into the body.
As radioactive material taken into the body will irradiate the body for as long as it
remains. So, a radiation dose will continue to accumulate until the material decays
or has been excreted.
Some radionuclides, such as tritium are excreted rapidly, and so deposit very little
dose per unit intake. Other radionuclides, however, such as Iodine-125, which is
bound strongly within the thyroid gland, deposits significantly more dose per unit
intake.
For workers, the dose delivered over a period of 50 years following intake, is
considered in calculating what in known as the Committed Effective Dose.
6. Summary
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An understanding of radioactivity, radiation types and how we quantify radiation
dose will be helpful in understanding the protection methods that can be applied
to ensure you work safely with unsealed sources of radioactivity.
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3.3 Contamination and the Internal Radiation Hazard
1. Radioactive Contamination
As we have seen, radioactivity can give rise to the emission of potentially harmful
ionising radiations.
Under normal circumstances, protection from these radiations can be achieved by
applying the principles of time, distance and shielding.
However, if we are unaware of the presence of radioactive material in the
workplace, for example because it has been spilled or splashed on equipment,
restricting our exposure becomes more difficult. This is what’s meant by
radioactive contamination.
Put simply, radioactive contamination is radioactive material, somewhere it
shouldn’t be. This could be anything from spot of radioactivity on a glove or
laboratory coat to a plume of radioactivity rising from a damaged nuclear reactor.
Most commonly, radioactive contamination arises in the workplace following
accidents or breaches of procedure.
Surface Contamination can be considered to be either “fixed” or “removable”. As
the name implies, “removable” contamination can be readily removed from a
surface, and as such, its presence in a work area could easily lead to personal
contamination or an intake of radioactive material. Examples include spills of
liquids or powders.
“Fixed” contamination, on the other hand, may be more firmly attached to a
surface or incorporated in a material. While less of an immediate radiological
hazard, low-level fixed contamination may well affect the disposal or clearance or
contaminated items or areas.
2. The Internal Radiation Hazard.
As we have seen, radioactive materials can present both “internal” and “external”
radiation hazards. Workplace contamination may well result in an internal
radiation hazard. If you are unaware of its presence, poor practice, such as eating,
drinking or hand to mouth contact, will provide an easy route for radioactive
materials to enter the body.
Following an intake of radioactive material, radiation exposure will continue as
long as it remains inside the body and is removed only through radioactive decay
or excretion.
3. Internal hazards of alpha, beta and gamma emitters
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Small quantities of radioactive material, harmless outside the body, may present
a significant hazard, if taken inside the body.
So why is this? Unlike the dead skin later on the outside of the body, there is
nothing inside the body to protect cells and tissues from the potentially damaging
effects of alpha and beta radiations. Alpha particles are particularly hazardous,
because their short range means their energy is deposited within a small volume
of tissue, increasing the likelihood of biological damage.
Once inside the body, much of the radiation energy will be absorbed by cells,
tissues, and organs. The actual radiation dose delivered depends on quantity of
intake, the type of radiation emitted, where it goes in the body and how long it
stays there.
Following an intake, some radioactive materials will be concentrated within
specific organs, while others may be dispersed uniformly throughout the body.
Materials for which the body has no biological demand, will be excreted rapidly
and will deposit comparatively little radiation dose.
For instance, the element phosphorous will be concentrated in the bones, so an
intake of Phosphorus-32 will deposit radiation dose selectively in this region.
Tritium, on the other hand, readily exchanged with stable hydrogen in water,
disperses uniformly throughout the body and is excreted relatively quickly. This,
together with the higher Phosphorus-32 β-particle energy, means that the dose
per unit intake for Phosphorus-32 is a hundred times greater than that of tritium.
Understanding the nature of any contamination and the potential exposure
pathways are key to establishing effective safeguards to ensure internal radiation
dose remains As Low As Reasonably Practicable.
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3.4 Control of the Internal Hazard
So, what do we mean by “internal hazard”?
An internal radiation hazard exists where radioactive material has the potential
to enter the body.
In the workplace, this may be due the presence of Contamination, in the form of
solids, liquids or gases.
1. Routes of entry
There are three principal pathways by which radioactive contaminants can enter
the body. These are:
1) Inhalation of airborne contamination.
2) Ingestion (or entry via the mouth).
3) Entry through the skin (absorption or entry through a contaminated
wound)
2. The Internal Hazard
Special precautions are required if an internal radiation hazard is present. This is
because, once inside the body, there are few interventions available to stop the
radiation exposure occurring. So, exposure could continue for many years.
Work, therefore, needs to be carefully controlled to prevent the contamination of
equipment, work areas and personnel. This may be achieved by following some
simple rules.
3. Control of Contamination
As with the external radiation hazard, the primary objective in the control of the
internal hazard is to ensure that doses are as low as reasonably practicable
(ALARP).
This achieved by the careful planning and execution of your work.
As was discussed in Module 1, consideration of the Hierarchy of Control Measures
will be a central to safe management of your work.
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As such, you should consider:
1)
2)
3)
4)
Eliminating radioactive material, if possible.
Minimising the amount of activity being handled.
Containing the radioactive material.
Following the correct administrative and management procedures (such
as Local Rules and Risk Assessment).
5) And finally, ensuring the use of appropriate personal protective
equipment.
If incidents or accidents do result in spills or releases of radioactive material,
these should be attended to immediately employing pre-planned procedures
and equipment.
3.1 Containment
Once it has been established that the use of radioactive materials is essential and
the amounts used have been minimised, containment of the material is essential
to safe working. Multiple levels of containment should be used where possible (it
is recommended to use at least two).
Containment may be achieved by:
1.
2.
3.
4.
Using suitable bottles and receptacles to hold the radioactive material.
Working on a spill tray.
Working in a fume cupboard.
Using suitably positioned shields and splashguards.
3.2 Area Classification
Area Classification is a helpful tool for managing potentially contaminated work
areas.
The actual classification for an area will be determined through the risk
assessment process. And may be either:
Uncontrolled, where there is no potential for radioactive contamination.
Supervised, where the potential for contamination is low, but needs to keep
under review.
or Controlled, where there is high potential for contamination and where detailed
precautions and protective measures are needed to restrict exposure.
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3.3 Protective Clothing
Protective clothing requirements will depend on the nature and amount of
contamination that could be present.
In Supervised areas, where there is low potential for contamination, an ordinary
laboratory coat, gloves and safety spectacles will normally be sufficient.
In Controlled areas, the standard of protective clothing may be different and
additional items, such as overshoes or respiratory protection may also be
required.
All PPE must be properly maintained and stored when not in use (for example in
a dry, clean cupboard). If it is reusable, it must be cleaned and kept in good
condition.
Regardless of the personal protective clothing used, where contamination may be
present, the following facilities should also be available:
1) Hand washing facilities.
2) Contamination monitoring instruments.
3) Suitable storage for PPE and suitable containers for the disposal of
contaminated PPE.
4) Plenty of readily available, clean PPE.
3.4 Good Laboratory Practice (GLP).
Good laboratory practice is essential for the effective management of the internal
radiation hazard. As such, general “house rules” for radiation work areas must
include:
1) No eating/drinking.
2) No mouth operations (such as pipetting).
3) Any wounds must be covered with a waterproof dressing before entering
the active area (open wounds will provide a direct route of entry into the
blood stream for radioactive materials).
4) The transfer of radioactive samples should be minimised (so as to help
avoid contamination spread).
5) Any items being removed from the active area should be subject to
clearance monitoring prior to transfer.
6) Regular contamination monitoring of the area must be carried out.
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3.5 Clearance and Decontamination of Areas and Equipment.
Where work with unsealed sources is discontinued, or when an area is to be
refurbished or transferred to a new owner, the area needs to be decontaminated
and certified before reuse.
The owner of the area is responsible for the completion of decontamination and
issue of a valid certificate.
Similarly, to prevent the spread of contamination to areas outside the work area,
equipment transferred from the area should be decontaminated and certified.
This process is aided by ensuring that all equipment used within designated areas,
is clearly marked to indicate that it’s potentially contaminated.
The administration of the system for the decontamination and certification of
equipment and areas is described on the College’s Safety Department website.
4. Summary
Successful management of the internal radiation hazard is achieved through
careful planning of work and by the adoption of practices, by everyone within the
work area, which will minimise the creation and spread of radioactive
contamination.
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3.5 Control of the External Hazard
A wide range of unsealed radioactive sources are in use at the College. And as
well as being hazardous if taken internally, many radionuclides will also present
an external radiation hazard.
As you will recall, protection against the external hazard is based on the principles
of limiting Source Strength, minimising exposure Time, maximising Distance and
making use of Shielding, where practicable.
The type of radiation emitted by the radionuclide in use will determine nature of
the hazard and the most effective methods of protection.
Because the β-particle range in air for a high energy beta particle emitter, such a
Phosphorus-32, can be up to eight metres, significant skin dose can be received,
even remotely, and even more so, if skin is actually contaminated.
While a low energy β-particle emitter, such as Sulphur-35, because of its low βparticle range, will only present an external radiation hazard in the event of skin
contamination.
1. Shielding as a Protection Measure
As you may recall, a β-particle source will be easily shielded employing material
such as Perspex or aluminum. 1 cm of Perspex will be sufficient to shield against
the β-radiation from most β-emitters in use at the College. This will often be
incorporated in equipment such as waste bins, splash guards or Ependorf tube
holders.
However, a secondary photon hazard may be associated with β-particle emitters,
known as bremsstrahlung (or braking) radiation. Bremsstrahlung radiation is
created when β-particles are slowed down in material with a high atomic number,
such as steel or lead. This is identical to the process which produces X-rays in an
X-ray tube. And it’s for this reason that we avoid using steel or lead when shielding
against β-radiation and instead make use of Perspex or other plastics
Photos may also be emitted directly by radionuclides such as Iodine-125, which is
commonly used nuclear medicine and as a radiotracer in biochemistry research.
Iodine-125 decays with the emission of γ-radiation, which is most effectively
shielded using high atomic number materials, such as lead or steel.
Photons will also be produced following the decay of Fluorine-18, used widely as
a tracer in Positron Emission Tomography. Positrons emitted by Fluorine-18
combine with electrons and annihilate with the creation of two high energy
photons. And again, shielding of these photons is best achieved with materials
such as lead or steel.
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But just how much shielding will be required for photons? This depends upon the
photon energy and the shielding material used and is best described by a graph.
The effectiveness of shielding against photons may be quantified in terms of halfvalue or tenth-value thickness. The half value thickness is the shield thickness
required to reduce the radiation intensity to half its original value, while tenth
value thickness will reduce the radiation intensity to a 10th of its original value.
As already indicated, the photon energy also needs to be considered – the higher
the energy, the thicker the shielding requirement. For example, the Lead HVL for
high energy Fluorine-18 photons is 6mm, while the HVL for low energy Iodine125 photons is only 0.02mm.
For this reason, facilities for the handling of Fluorine-18 or other high energy γemitters may be heavily engineered, and care needs to be taken due the weight of
shielding and ancillary equipment.
Shielding will be incorporated, wherever practicable, to reduce the radiation
exposure of personnel. Lead shielding may be included in walls and doors,
permanent and mobile screens and in equipment such as syringes and waste bins.
Checks should be carried out periodically to ensure that all the necessary shielding
is in place and has not been moved or disrupted.
2. Distance as a Protection Measure
Distance will also provide an effective means of limiting external radiation
exposure from unsealed sources.
By maximizing your distance from an unsealed source, you will reduce the overall
radiation exposure according to the inverse square law.
Plan your experimental work to make sure you can maximize distance. The use of
tongs or forceps may be an option in some instances, providing they don’t add
significantly to the task time.
Whenever possible, remote manipulation must be carried out when handling
Phosphorus-32 at the College.
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3. Summary
When using unsealed radioactive sources, we must remember that both internal
and external radiation hazards may be present.
Employing the principles of limiting Source Strength, minimising exposure Time,
maximising Distance and making use of appropriate shielding, will ensure that
external radiation risks are kept As Low As Reasonably Practicable.
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3.6 Controlled & Supervised Areas
The safe management of work with unsealed radioactive sources will be assisted
by the appropriate classification of work areas.
The designation of a Controlled or Supervised Areas acknowledges the need for
special procedures to ensure radiation hazards are carefully managed and
radiation exposure is kept As Low as Reasonably Practicable.
The need for a designated area will be established following the completion of a
Prior Risk Assessment (or PRA) and consultation with the College’s Radiation
Protection Adviser (RPA).
Depending of the level of hazard, areas will be designated Controlled or
Supervised, or may be Non-Designated.
1. Controlled Areas
A Controlled Area will be designated where special procedures are required to
ensure the adequate restriction of exposure. This may be due to the quantity of
radioactive material in use, the potential for creating or spreading contamination,
or where a person is likely to receive an annual effective dose in excess of 6mSv.
Under these circumstances, special work procedures are required and access is
only permitted to trained and adequately supervised personnel.
Designation may be permanent, where work is continuous, or temporary, if work
is more infrequent.
Controlled areas within the College include Iodination laboratories -where
proteins are labelled with Iodine-125, then tracked in-vitro through metabolic
processes.
Controlled areas are also designated where large activities of Fluorine-18 are in
use, such as in hot labs where radiopharmaceuticals are manufactured, or in
clinical areas where these compounds are administered to patients undergoing
PET scanning.
2. Supervised Areas
Within a Supervised Area, a lower level of radiation hazard is normally present.
In these areas, conditions need to be kept under review, for example to ensure that
contamination does not spread beyond the designated area.
Written work procedures are still required, but the overall potential for significant
radiation exposure is low.
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Supervised Areas within the College include laboratories where small quantities
of H-3, Sulphur-35 or Carbon-14 are used. The Supervised area is often limited to
a small area within a laboratory where other, non-radiological, work may be
taking place.
3. Non-designated (Registered) Areas
Where very small quantities of radioactive materials are in use and the potential
for radiation exposure is minimal, work within a non-designated area is often
permitted. This includes the use of low concentration solutions of Naturally
Occurring Radioactive Material (NORM) or where liquid scintillation equipment,
or samples, are in use.
4. Local Rules
As we have said, within designated areas, special procedures are required to
ensure the restriction of exposure. These procedures are described in an area’s
Local Rules.
Local Rules describe the conditions for entry to the area, including training and
PPE requirements. They describe the nature of the work being carried out, and its
boundaries, and the radiological safety procedures to be followed. Importantly,
Local Rules identify the actions to be taken in the event of foreseeable incidents,
such spills or personal contamination.
All personnel permitted to work within designated areas need to have a detailed
understanding of the Local Rules, to ensure their own safety and the safety of
others working in the area.
5. Radiation Protection Supervisors (RPS).
A Radiation Protection Supervisor (or RPS) is appointed for each Designated Area.
The main purpose of the RPS is to ensure that Local Rules are adhered to within
the area.
Before starting work within Designated Area, the RPS will provide pre-work
induction training and the laboratory’s Local Rules will be central to this
induction.
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3.7 Contingency Plans
By law, the College needs to have arrangements in place for dealing with accidents,
that could result in radiation exposure. This includes events such as personal
contamination or spills of radioactive material within the work area.
Everyone involved needs to know the actions that they may need to take to
prevent or limit radiation exposure, in such an event.
The need for a specific contingency plan may be identified in the Prior Risk
Assessment, completed for a proposed programme of work. And the
arrangements will be included in the Area’s Local Rules.
1. An effective contingency plan will include the following elements:
•
The immediate actions that need to be taken (and by whom) to minimise
the effects of the incident. For example, the withdrawal of personnel from
the affected area, the containment of a spill with bunding or absorbent
material, or the monitoring and decontamination of personnel.
•
The plan will identify any specialist equipment, such as Personal Protective
Equipment (PPE), monitoring equipment or decontamination materials
that may be required, and where they can be found.
•
Points of contact for personnel who must be informed of the incident, such
as the RPS, RPO or RPA will be included.
For example, when using unsealed Phosphorus-32 at the College, it is considered
to be reasonably foreseeable that a spill of material could occur, leading to
personal contamination and contamination of the work area. For this reason, a
spill kit should be available within the lab for use in this eventuality.
The spill kit will include.
•
•
•
•
PPE, including rubber and latex gloves, safety glasses, a plastic apron and
overshoes.
(Because Phosphorus-32 is a high energy beta-emitter) tongs should be
included for handling contaminated items.
Materials to absorb spilled liquids, such as vermiculite and tissues.
To assist with the task of personal decontamination, liquid soap should be
included and eye irrigation, if it’s not already available in the lab.
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2. Decontamination Procedure
If an event leads to you becoming personally contaminated with radioactive
material:
•
•
•
•
•
•
•
Stay calm and let a colleague or, if available, the RPS, know of the situation.
Step away from the contaminated area, taking care not to further spread
the contamination.
With assistance, remove any contaminated PPE and place it in a plastic bag,
clearly marked as radioactive.
You should be carefully monitored to identify any personal contamination,
bearing in mind the impact of background radiation on the measured
radiation levels. This is best carried out with assistance.
Any residual contamination should be removed with soap and water, using
minimal abrasion.
Following decontamination, monitoring should be repeated.
Any further decontamination should be carried out following consultation
with RPS, RPO or the College RPA.
The Phosphorus-32 spill in the work area will need to be dealt with, also.
•
•
•
•
•
To clear up a minor spill, the liquid should be absorbed onto absorbent
tissues. Mindful of the high energy beta-emitter, tongs should always be
used.
Waste material should be placed in a local, shielded bin.
Monitoring of the area should be carried out.
And further decontamination may be required with a decontamination
agent.
The monitoring should be recorded on a survey sheet and, if not already
done so, the matter should be reported to the RPS.
As well as notifying the RPS of the incident, the College Radiation Protection
Officer or Radiation Protection Adviser should be notified, as well as Security,
if the incident occurs outside normal working hours. In addition, the incident
should be reported on the College incident reporting system (or SALUS).
3. Summary
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Incidents of this type, can be dealt with effectively by remaining calm and
following the predetermined course of actions. All personnel working within
the area should have knowledge and experience of the relevant contingency
plans, and frequent rehearsals will ensure their effective execution in the real
event.
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3.8
Radiation & Contamination Monitoring
The monitoring of work areas and personnel for the presence of contamination is
a routine activity, essential for the effective management of the internal radiation
hazard.
Monitoring is often achieved using a portable contamination monitor. However,
as a wide range of monitors are available, which may look quite similar, care needs
to be taken to ensure that the monitor used is appropriate for the radiation type
and energy in use.
1. Low Energy β-emitting radionuclides
1. For low energy β-emitting radionuclides such as C-14, S-35 and P-33, a MiniMonitor 900 with an EP15 or EL probe (or similar instrument) may be used for
contamination monitoring.
These instruments incorporate a GM tube with a thin Mica end-window, which
allows low energy β-particles to pass into the detector.
It has an analogue scale, which reads up to 2000 counts per second, depending on
the variant of the instrument.
2. High energy β-emitting radionuclides
For higher energy β-emitting radionuclides, such as P-32, a Mini-Monitor 900 with
a Type E probe is suitable. This has a smaller end window GM Tube and an
analogue scale which reads up to 2000 counts per second. For monitoring βemitting surface contamination, the protective end-cap must be removed, to allow
the β-radiation to pass into the detector.
3. Photon-emitting radionuclides
For photon-emitting radionuclides such as I-125 or In-111, a Mini-Monitor 900
with a type 44A Scintillation Detector should be used. The instrument employs a
Sodium Iodide crystal detector with an Aluminium window. This window means
that photons below 20keV will be screened, however, a 44B variant is available
with a Beryllium window, which extends the range down to 6 keV. This allows use
of the 44B probe for monitoring very low energy photons.
These instruments have an analogue scale, which read up to 5000 counts per
second
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4. Monitor Scaling
Contamination instruments are normally scaled in units of counts per second - this
gives an indication of how much radiation the monitor is detecting. The actual
amount of contamination present, in terms of Becquerels/cm2, however, depends
on the radiation energy and the instrument’s efficiency, and this may be quantified
by reference to instrument’s calibration data.
5. External Radiation
Where an external radiation hazard exists, the hazard will normally be assessed
using an instrument which measures the radiation dose rate. So, for radionuclides
such as F-18 or I-125, an instrument such as Mini 900 Type D will be suitable. This
instrument is scaled in micro-Sieverts per hour and will measure dose rates up to
1mSv/h.
6. Monitoring Procedure.
Effective radiation and contamination monitoring will be achieved by following a
number of simple, but important, steps.
Pre-use checks are essential:
•
•
•
•
•
Firstly, check that the monitor has been calibrated within the last 12
months – this will be shown on the calibration label.
Now check the battery and audio signal.
Check the cable and connectors for damage by gently pulling these and
watching out for signal spikes.
Away from the work area check the instrument’s background radiation
reading - and record this.
And finally, check the instrument’s response to radiation. You may have
access to a check source, but if not, a functional test may be carried out on
any available radiation source - such as stock pot or radioactive materials
store.
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Having completed your pre-use checks, you can now carry out monitoring.
•
•
•
•
Ensure you have selected an instrument that is suitable for radiations that
may be present.
Move the probe slowly over the suspect area – a probe to surface distance
of about 3mm is ideal.
Avoid touching the surface, as this could contaminate the probe.
Record the instrument’s readings and their location.
A record of monitoring is legally required. This will include monitor details, the
levels detected and their precise location.
7. Indirect Monitoring
An indirect method of monitoring is required for low energy β-emitting
radionuclides, such as Tritium (H-3) and Carbon-14.
•
•
•
This is achieved by swabbing the area with a moistened cotton bud or filter
paper.
The sample is then counted in a liquid scintillation counter (LSC), which is
specifically calibrated for the radionuclide under examination.
Just as for the direct survey, the findings of indirect monitoring should be
recorded together with the monitoring locations and counter details.
8. Summary
Effective workplace and personal monitoring are essential to the effective
management of the internal radiation hazard. The monitoring task is routine, but
its value and importance must not be underestimated.
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3.9 Personal Dosimetry
Where there is potential for significant exposure to ionising radiations, it may be
necessary to monitor an individual’s personal radiation dose.
Monitoring will normally confirm the assessment of personal dose made during
the Prior Risk Assessment and will demonstrate that adequate safeguards are in
place to keep dose ALARP. Monitoring may be carried out for legal compliance
purposes, for example, if an individual is a designated Classified Person.
The need for the assessment of personal dose will be determined as part of the
work registration and risk assessment process and will normally only be required
for work with specific unsealed sources.
This includes use of:
•
•
•
High energy beta emitters (e.g. P-32).
Some gamma emitters (e.g. Cr-51).
Positron emitters (e.g. F-18).
1. Dosemeters are of two types.
When radiation exposure is uniform, whole body dosimeters are worn on the
trunk to give an indication of the whole body, or Effective Dose.
If the radiation exposure is non-uniform, for example if the fingers are very close
to the radiation source, extremity Dosemeters, in this case, finger dosemeters,
may be required.
Depending on the nature of the work, it may be necessary to use one or both types
of dosemeter.
When issued, it’s essential that dosemeters are worn when working and worn
correctly.
2. Whole Body Dosemeters
Whole Body Dosemeters are worn on the trunk. Because of the construction of
the dosemeter, it’s essential that dosemeters are worn in the correct orientation.
The back of the dosemeter is usually marked “back” to ensure it’s worn correctly.
3. Extremity (or finger) Dosemeters
As the name suggests, finger dosemeters must always be worn on the fingers. Two
finger rings are normally issued, one for the left and one for the right hand.
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When wearing these, it is important that radiation sensitive element faces the
radiation source. It is also important that the dosemeter is positioned as close as
possible to the radiation source.
Typically, the rings will be worn on the middle segment of the 2nd finger with the
detector facing inwards, as shown.
Dosemeters should be worn next to the skin and, to avoid dosemeter
contamination, under any PPE, such as disposable gloves.
4. Dosemeter Issue
Dosemeters are issued with instructions for their use and care. This includes, for
example not passing dosemeters through security X-ray scanners, avoiding
extremes of heat and light and ensuring dosemeters are not laundered.
Dosemeters will normally be issued by the Radiation Protection Supervisor (RPS)
for an agreed wear period, either monthly or quarterly, depending on the nature
of the work.
At the end of each wear period, dosemeters should be exchanged. Again, this will
be co-ordinated by the RPS.
Used dosemeters are returned to the supplier (or Approved Dosimetry Service)
for reading and assessments will normally be reported with one month.
5. Unusual or Unexpected Dose
If a dosemeter records an unusual or unexpected dose, you will be contacted by
the College RPO. The RPO (together with the RPS) will investigate matter and may
review working arrangements to ensure that ongoing exposures are ALARP.
Dose Investigation Levels are predetermined for each designated radiation area
and are documented in the area Local Rules.
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3.10 Accountancy of Radioactive Materials
1. Legal Requirement for Source Accountancy and Security
As we saw in Module 1, the principal regulations relevant to work involving
ionising radiations are the Ionising Radiation Regulations (IRR) and the
Environmental Permitting Regulations (EPR).
These regulations require radioactive materials, to be stored suitably and
securely, as well as being accounted for, throughout their life-cycle.
2. Suitable storage
Radioactive materials should be kept in a fireproof store, segregated from other
materials, so that cross contamination is minimised in the event of incidents such
as leakage or a spill.
To safeguard sources or containers, radioactive materials should never be stored
alongside corrosive, hazardous or flammable materials.
3. Secure Storage
The College is required to take appropriate measures to ensure the security its
radioactive holdings.
To this end, proportionate physical and administrative measures are
implemented throughout the College, the principles of which are described in a
College Code of Practice.
3. Sealed (closed) sources:
For sealed sources, steps must be taken to prevent access to the sources by
unauthorised persons, ideally by continuous surveillance. Where this is not
possible, the sources must be kept in a suitable container, within in a store which:
1) prevents theft or unauthorised access
2) is clearly and legibly marked with the word ‘Radioactive’
3) is marked with a radiation hazard symbol.
Loss or theft of radioactive material should be reported immediately to the RPS
and College RPO, who will co-ordinate all legal investigation and reporting actions.
4. Accountancy
Owners of radioactive sources are required to keep records of all holdings, which
will include the date of receipt, the radionuclide, its activity and its location (at all
times).
5. Un-sealed (open) sources:
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All unsealed sources must be secure at all times, from arrival at the College until
their ultimate disposal or transfer. Stocks must be kept in locked fridges, freezers
or cupboards, as appropriate. Signage comprising a radiation trefoil, details of the
radionuclide and the nature of the hazard must be displayed.
Users must ensure that radioactive materials are accounted for at all stages of
their life cycle. That is upon receipt, during use and upon their ultimate disposal.
Processes are in place to ensure suitable accountancy takes place. These will be
described later and are included on the Safety Department’s website.
Many of the processes relating to radioactive materials accountancy and security
will be carried out by the appointed RPS. This will include a monthly report to the
College RPO of all radioactive materials holdings, usage and disposals.
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3.11 Acquisition and Disposal of Radioactive Materials
The key legislation relating to the regulation of Radioactive Substances in the UK
is the Environmental Permitting Regulations. These regulations allow for the
issue of Environmental Permits to operators, which describe, in precise terms, the
quantities and types of radioactive material that may be kept or disposed of from
their premises.
Each College campus is permitted separately and Permits may be held for
unsealed (or open) sources, sealed (or closed) sources and for the disposal of
radioactive waste. The limits, specified within Permits, apply to the campus as a
whole.
For example, at South Kensington, the Permit allows 2000MBq of Phosphorus-32
to be kept and used at any one time.
As several laboratories across the South Kensington campus keep and use
Phosphorus-32, to ensure site holdings limits are not exceeded, a central
accountancy system tracks the quantities present in each laboratory, at all times.
For this reason, prior notification must always be given to the College RPO, before
radioactive materials are acquired.
1. Acquisition Process
The process starts when a user identifies the need for radioactive materials - this
could be for new work or to replace depleted stock.
The user e-mails a fully completed “Order Notification” to the College RPO, before
any order is placed with a supplier.
Once the form has been received and checked by the RPO, the details of the
proposed acquisition are entered onto the central College database and the
radioactive material is assigned a unique identification number know as a TAD (or
Tracking, Acquisition and Disposal) number.
The TAD number, along with an accounting (TAD) form are sent to the user and
RPS.
The user prints off the TAD form and enters the TAD number on the form – this
process may be completed electronically. The user is required to keep the TAD
form up-to-date, by entering details, whenever radioactive material is used or
disposed of.
To aid identification and stock control, the TAD number must also be written on
the pot of radioactive material, upon receipt.
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2. Radioactive Waste
There are three main types of radioactive waste produced by researchers at
Imperial College. These are:
1) Solid waste
2) Aqueous waste
3) Organic waste
The general arrangements for the management of these waste streams are as
follows:
Solid waste
Solid waste is placed in dedicated bins for on-site storage and (where appropriate)
decay, pending disposal to an approved contractor.
Aqueous waste
Aqueous waste is the preferred waste stream for radioactive waste disposal and
is normally disposed of to drains via dedicated disposal sinks located in work
areas.
Organic waste
Organic waste is liquid waste, which is not miscible with water. Organic liquids
must be collected in dedicated bins for on-campus storage pending disposal.
3. Limits
All of these waste streams are subject to limitation in terms of accumulation times
and disposal quantities, as specified in the College’s Environmental Permits.
Laboratory accumulation times must be minimised and waste must not be stored
locally for longer than is absolutely necessary.
4. Records
Maintaining accurate records of radioactive waste holdings, accumulation times
and disposal quantities is a legal duty, which is under constant scrutiny by the
Environment Agency.
Each bin of solid radioactive waste must display the following:
1) A record detailing its contents, containing the date, radionuclide and
estimated activity (in MBq) of each disposal made to it.
and…
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2) A tag issued by the Safety Department, which allows tracking of the waste
accumulation time.
5. Solid Waste Disposal
The retention of waste in laboratories for excessive time periods should be
avoided.
Prior to transfer from the lab, solid radioactive waste bins are irreversibly sealed,
then transferred to a central site store.
Here, waste is securely stored, in line with the site’s Environmental Permit
conditions, pending disposal to an approved waste management contractor.
The College operates the “polluter pays” principle and, as such, the cost of the final
disposal of radioactive waste is recharged to the waste producer.
6. Best Available Technique (BAT)
The principle of the Best Available Technique (or BAT) is central to the College’s
radioactive waste policy and practice. As such, waste management processes have
been optimised to ensure that public radiation exposure resulting from College
radioactive waste disposals is ALARP. A full description is provided on the Safety
Department’s radioactive waste management webpage.
BAT means that the College applies the best techniques of waste management
throughout its processes, including the design, operation, maintenance and
decommissioning of its facilities.
Central to BAT is the principle of the Waste Hierarchy.
1. The preferred option is to avoid the use of radioactive materials whenever
possible and therefore eliminate the possibility of waste. As you are aware,
the use of radioactive substances in research needs to be justified during
the work registration and risk assessment process, and if practical
alternatives exist, radioactive materials should not be used.
2. Secondly, the use of minimal quantities of radioactive material, and the
disciplined practice of contamination control will minimise the activity and
volume of waste produced. Properly equipped laboratories, with surfaces
that may be readily decontaminated and the selection of low radiotoxicity
materials or short half-life radionuclides (which may be allowed to decay
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in secure storage), will further minimise the environmental and
radiological impact of any disposal.
3. The segregation of equipment for use in radiological applications such as
pipettes, cell counters or centrifuges and their reuse, will limit the number
of contaminated instruments and, again, will reduce the volume of waste
produced.
4. Having applied all of these waste management principles, the disposal of
radioactive waste may be carried out secure in the knowledge that the
disposal has been optimised in economic terms, makes best use of
resources and has minimal public and environmental impact.
7. Summary
The control of radioactive materials within the College, from acquisition to
disposal, involves all users of radioactive materials. Compliance with the College’s
arrangements is mandatory and following these procedures will ensure legal
compliance, protect the environment and ensure the safety of College personnel
and the general public.
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3.12 Further Information
Well done - you have now completed the Unsealed Sources Module of the College’s
Integrated Radiation Protection Training Programme. We hope you found it
interesting and helpful.
To demonstrate your knowledge of safe working with Open Sources of
Radioactivity, you now need to complete a short test.
Following this, if you haven’t already done so, you will need to complete a Personal
Registration form - this can be downloaded from the “before you start” page on
the Safety Department’s website.
Your RPS or Laboratory Manager will then provide you with a Local Area
Induction and you should familiarise yourself with the Local Rules for your area
of work.
You will then be ready to start work with Open Sources of Radioactivity.
Further information including guidance and codes of practice for safe working
with radiation are available via College’s Ionising Radiation Safety webpage, or by
contacting a member of the Radiation Protection Team.
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