-*11~
Model
Manual of Operation
E-2
and Maintenance
TENNELEC/NUCLEUS
601 Oak Ridge
Oak Ridge,
tC
Turnpike
Tennessee
(615) 483-8405
37831-2560
MODEL
E-2 NUCLEAR
Manual of Instructions
SCALER
and Experiments
CONTENTS
Introduction
and General Description
6
II. Specifications
III.
..5
7
Operation
8
IV.NuclearScience
a.
b.
c.
d.
e.
f.
g.h.
Preface
Detection
UnitsofRadiation
Basic
Background
Radioactivity
Radiation
RadiationSafety
Terms.
Instruments.
from
Radiation.
Nuclei.
8
8
8
9
10
10
11
12
15
V.Experiments a.
c.
d.
b.
e.
f.
Plateau
Tracer
Absorption
Beta
ShelfRatios
Half-Life
Determination.
Decay Studies.
..
15
16
17
18
19
20
Studies.
Energy.
VI. Maintenance and Trouble Shooting
VII.
v III.
Circuit Description and Diagram
Warranty
-I
nside
front
cover
22
25
INTRODUCTION
The
Nucleus
replacement
rates
the
for
latest
ruggedness,
for
the
nuclear
Features
one
tube,
minute
provides
tion
and
in electronics
preset
Adjustable
plateau
measurements.
provide
Model
end
detecting
timer,
and
to
its predecessor.
the
a built-in
of
E.2
new total
Scaler,
the
solid
and
state
incorpo.
same simplicity,
Exclusively
Scaler
controlled
is
voltage
designed
practically
Packaged
rocker
without
0 to
a
for
total
1200
precise
geiger-
radiation.
A
integrated
circuits,
sol id state
construc-
a time
in a distinctive
switches
quenched
and gamma
advanced
timi ng, and
from
halogen
beta,
by
operation
high
window
alpha,
conven ient
instantaneous
has simplified
of
is the
E Student
station.
include
capable
Scaler
Model
economy
laboratory,
period.
E-2
Nuclear
popular
training
accurate
means
E.2
very
advances
safety
teaching
complete
muller
Model
the
volts
wasting
allows
warm-up
geiger
steel cabinet,
cut-off,
count
the
tube
Model
and
reset
action.
Its
Nucleus
quality,
low
price,
tradition
of
providing
instrumentation,
exceptional
and
three
year
students
and
performance,
5
warranty
educators
and proven
continue
with
service.
The
reliable
II. SPECIFICATIONS
CIRCUITRY
COUNT
-Solid
State
CAPACITY
VO L TAG E -0
PA ESET
TI MEA
frequency.
-99,999
to
1200
-1
in 5 seven segment
volts,
continuously
minute
accuracy
and
LED decades
variable
continuous;
derived
from
power
line
to 0.03%
POWER REQUIREMENT-
105-125 volts, 60 Hz (optional
230 volt, 50
Hz)
BUILT.IN
DETECTOR -Halogen
quenched end window Geiger.Muller
tube; 0.6" ( 1.5 cm) x 2.0" (5.1 cm) with 2-3 mg!cm2 window,
2%/100 volt plateau slope, 100 microsecond resolving time, 400 volt
operating potential.
SAMPLE
POSITIONER
OPERATIONAL
-6
CONTROLS-
COUNT.
HIGH VOLTAGE
SHIPPING
DIMENSIONS
precision
WEIGHT
-5"
positions
3 rocker
with
switches;
two
slide
trays
POWER,
RESET,
control
-10
pounds
(13 cm)
high
(4.5 kg)
x 11~"
deep
6
(29 cm)
wide
x 6~"
(16 cm)
III.
OPERATION
1. Rotate the HIGH VOLTAGE
control counterclockwise
to the zero
position. Depress the POWER switch to OFF, and the COUNT switch
to STOP.
2. Connect the power line cord to a standard AC, 110 volts and 60 Hz,
outlet.
3. Place a radioactive source on a shelf in the sample holder directly
under the end window of the G/M detector tube.
4. Depress the POWER switch to on (POWER), and set the COUNT
switch to CONTINUOUS.
Now,.slowly
rotate the HIGH VOLTAGE
control clockwise,
increasing the high voltage until counting just
begins as observed on the LED readout. This is the threshold voltage,
and normally occurs between 280 and 300 volts. Note the threshold
voltage and move the HIGH VOL TAGE control 75 volts higher for
best operation. To stop counting, depress the COUNT switch to
STOP.
5. Depress the RESET switch to zero the five decade LED's. NOTE: The
COUNT switch must be in the STOP position before the RESET switch
will zero the LED's.
6. To make a one minute count, depress the COUNT switch to the 1
MINUTE COUNT position. When making a one minute count, the
transition time from STOP through CONTINUOUS to the 1 MINUTE
COUNT position does not affect the duration of the preset time. For
example, if the count switch is left in the CONTI NUOUS position
for 45 seconds, and then switched to the 1 MINUTE
COUNT
position, the scaler will operate 15 seconds longer and stop.
7. To measure background radiation, check all around the scaler to see
that no radioac:tive samples are close. Then make a one minute
count. Record this count reading as the background
count per
minute.
7
IV.
NUCLEAR
SCIENCE
A. PREFACE
Nuclear
cal tests,
and
science
industrial
physics
inception
research.
by
widespread
the
very
made
in power
design
existence
in the
and
need
is utilized
engineering
field
of
of
it
be
included
nuclear
chemistry
interdisciplinary
that
production,
and biology,
nature
in the
science
and
of
had
physics.
nuclear
science
medi-
chem istry ,
its
This
science
curriculum
of
schools.
The
application
studying
students.
been
slow
high
cost
solid
biological
5cience
state
program
of
nuclear
science
and physical
curricula
with
in development.
of
reasonably
system,
it
B.
The
studies
utilization
established
today's
technology
processing,
equipment,
circuitry
A major
scalers
used
by
technology
as
cause for
this
or ratemeters.
"The
Nucleus
situation
Recent
Inc."
of
for
has
has been the
developments
has
made
priced
scalers and ratemeters.
Using the Model
now is feasible
for any school
to develop
an
in nuclear
a means
processes
is a unique
experience
nuclear
science
experimentation
in
possible
E-2 Scaler
educational
science.
RADIOACTIVIY
In the 1890'5, Henri Becquerel accidentally
discovered radioactivity when he found that photographic
plates in light-tight
boxes
were fogged by unseen rays from uranium salts placed over them. This
simple observation led to later research which showed that the isotopes
of certain elements were unstable and emitted unseen radiations. This
phenomenon is called radioactivity and such isotopes are called radioisotopes.
All elements of atomic number greater than 82 (and some with
less) possess naturally radioactive isotopes. Man has created artificiallyradioactive isotopes by bombardment with neutrons and other nucleons.
To date over 2000 different radioisotopes have been identified.
C.
BASIC
TERMS
A nuclide
number
of
is any
protons
atom
and
which
neutrons
differs
in
8
the
from
the
nucleus.
many
A
others
nucleon
in the
is any
particle
found
following
in the
nucleus.
Nuclides
are further
identified
by the
symbolism:
AX
where
= X =
Chemical
n
mined
~
~ =
symbol
of
the
nuclide,
as deter-
by ~
atomic
number,
or
number
of
protons
in
of neutrons
in
the nucleus
n =
neutron
number,
or number
the nucleus
A =.
mass number,
as found
by A = ~ + N
An isotope is one nuclide of a set with the same atomic number
but different neutron number, and consequently different mass number .
Since the chemical symbol also indicates the atomic number, and the
mass number also indirectly
indicates the neutron number, sometimes
only the symbol and mass number are written, as 32p and 137 Cs' or
P-32 and Cs-137.
D. RADIATIONS
The
three
alpha
origin.
An
light,
given
consist
of two
by
radioisotopes
protons
a particles
being
a
has a +2
particle
has great
exhibits
paper.
radiations
were
found
to be of
types:
particles
with
and
unseen
major
Alpha
FROM NUCLEI
ionizing
poor
Alpha
identical
power
charge,
during
penetrating
particles
( 2 p) and two
to a helium
travels
its short
power-
emitted
being
from
a single
and
positrons
neutrons
ion except
about
range
0.1
the
(about
stopped
nuclear
speed
of
5 cm in air)
by
radioisotope
(2 n),
for
a sheet
of
generally
are
monoenergetic.
Beta
particles
particles
having
electron
to 0.9
(negatrons
except
the
(about
speed
300
cm
power-
traveling
emitted
from
maximum
identification
only
for
(3-
~
the
nuclear
origin.
light,
exhibit
of
depending
up
a
energy
to
source
of
mass
in
a beta
a
a proton,
(3 particles
upon
a few
of
(3+)
ionizing
power
its
energy)
and
millimeter
spectrum
purposes.
9
and
have a -1
low
wide
are
in
spectrum
(Emax)
skin.
of
relatively
identical
charge,
Beta
an
up
range
penetrating
particles
energies,
usually
to
travel
over a great
possess
light
with
determined
are
the
for
Gamma
radiation
radiation.
origin
and
gamma
radiation.)
power
during
radiation
one gamma
OF
The
variable
energy
truly
no charge
or rest
but
very
feet
of
radiate
from
for
the nuclear
greater
energy
mass, very
great
low
or
power ,
a foot
radiations,
of
ionizing
penetrating
concrete
as monenergetic
electromagnetic
except
of
though
lead.
more
the same isotope.
RADIOACTIVITY
upon
The
is
consequently
a few
may
of
radiations
its particular
a, {3-, and {3+ radiations,
thereof
that
to X-rays
(and
range,
by
is emitted
emission
depending
have
stopped
type
are similar
wavelength
a
Gamma
UNITS
radiation
'"I rays
being
E.
a
photons'"1
shorter
typically
than
is
Gamma
proper
unit
can be indicated
interaction
the
initial
to indicate
with
atom
in a variety
matter.
actually
radioactivity
of ways
In the emission
of
disintegrates.
is the curie
and multiples
.
one curie (Ci) = 3.7 x 1010 disintegrations
one millicurie
(mCi) = 3.7 x 107 dps
one microcurie (.uCi) = 3.7 x 104 dps
per second (dps)
Most often the absolute decay rate is not needed, but a relative
indication of radioactivity
will suffice. The relative count rate may be
expressed as counts per minute, roentgens per hour, etc., or any other
indication given by a detection device.
F.
RADIATION
DETECTION
Every
elementsused
radiation
detection
a sensor
through
the
and
film,
and
probably
device
an indicator.
years
photographic
others,
INSTRUMENTS
for
the
electroscopes,
the
of
chambers,
popular
consists
many
detection
cloud
most
essentially
Although
devices
of
two
have been
radioactivity,
such
scintillation
counters,
instrument
is
the
as
"Geiger
Counter".
The
sensor
Nucleus
in this
above
the sample
ind icator
-the
The
taining
(anode)
the
tube
Model
unit
Scaler
System
is a Geiger-Mueller
tube
shelves.
The
remainder
is a Geiger
affixed
Counter.
inside
of the cabinet
the
The
cabinet
is devoted
to the
scaler .
Geiger-Mueller
two
E-2
electrodes
is a thin
acts
metal
as the
tube
and
consists
a special
of
wire
in the center
negative
electrode
10
a small
gas filling.
metal
The
of the tube,
(cathode).
cylinder
positive
while
The
con-
electrode
the wall
of
gas is a special
mixture
that
"window"
recombines
exists,
radiations
I n operation,
to
pairs
when
by
ionized.
At
one end of the tube,
piece
of
fragile
a thin
mica,
a
allowing
to penetrate.
electrodes.
inside
easily
covered
450
Radiation
ionize
drifting
volts
difference
passes
in an avalanche
to
the
in potential
through
the
effect,
electrodes
of
is applied
window
resulting
opposite
and
in a million
charge
across the
causes
the
gas
ion-electron
in a time
of
perhaps
100 microseconds.
The
number
electricity
to
The
gas mixture
are
more
Charged
readily
with
would
end
of
particles
of the
wall
particles.
scaler
is really
which
entering
counted.
Thus
1-5% of the
the
most
nothing
of
ground
is always
count
photons
({3)
more
usually
are detected
the
as
near the
betas at the
low end
window
in a unit
by
a sophisticated
records
and
the
rapid
electronic
accumulation
of time.
a source
subtended
emitted
our
even
background
contamination,
than
and
G-M tube
arc
in all directions,
by
the
Geiger
tubes
by a source
below.
lives,
universe.
soils,
determinations
scaler
particles
particles
such as alphas
penetrate
of
readout.
tube
will
only
above
only
it
that
will
detect
be
about
RADIATION
day
in the
and
beta
the
which
weak
to
a pulse
for
to be repeated.
Gamma
electrons
more
end-window
BACKGROUND
water
mixture.
be able
is emitted
the
radiation
Every
(a) and
of radiation,
scales down
radiation
radiation
sources
not
process
because
range and the very
may
of pulses sent to it by the
G.
gas
types
the
tube
dislodge
Weak
for
causes
the pulses
be counted.
machine
Since
the
counts
particles
a G-M
to
produced
which
as alpha
by
of
tube
spectrum,
not
The
adding
such
ionization
pairs
scaler,
and is ready
monoenergetic
beta
thus will
the
detected
the
be beta
the
ion-electron
to
recombines
easily
cause
react
of
be sent
The
count
used
(radium
are subject
rays,
radioactive
count.
of
we
Cosmic
dial
is reasonably
atoms
to
yield
same
constant.
must
the
location,
watches
to
radiation
uranium
in our
background
rate
in the
radium,
bodies
and
natural
in
all contribute
to
be subtracted
corrected
or spilled
from
and potassium
count
from
rate.
if care is taken
radioisotopes))
all
If the
to avoid
the back-
H. RADIATION
SAFETY
Radioactive
materials
can provide
exciting
laboratory
experiments
students
at all levels. But, just as with corrosive
acids and flammable
for
chemicals
proper
we
use routinely
handling
observed
in the
All
student
amount
of
by
persons
who
educational
licensing
exempt"
topes
are
form
Solid
be
packaged
sealed
year
are, of
after
sources
are
be
year.
used
Commission
or
quantities
of
small
that
or
"Iicense-
student
small
inside
case, the
radioiso-
much
using
with
solid
certain
material
supplied
epoxy.
in
container
the
2.
solution
for
radioisotope,
the
the
material."
easier
one
educational
a durable
immediate
"radioactive
for
radioactive
with
identifying
radioisotopes
for
the
glass bottles,
a label
when
prepared
in which
Additionally,
required
contain
and
"Iicense-free"
however,
sealed
course,
contain
and decontamination
Liquid
and
bear
Nucleus
handled,
Energy
sources
and the warning
usually
must
care and respect.
sources
in
The
these
as
mean,
I n either
will
sources
they
reused
spills
powder.
Atomic
to
radioactive
disc,
of activity,
Because
not
with
in a plastic
material
quantity
does
1. Solid
or as a dry
radioactive
by
Consequently,
types:
sources
are also
which
be procured,
U.S.
referred
speaking,
two
there
precautions
supplied
may
from
be handled
Generally
Unsealed
This
not
is deposited
exempt
sometime
sources.
should
use are of
sources
which
requirements.
radioisotopes
laboratories,
safety
laboratory.
radioactivity
are
chemistry
and
radioisotope
an
state
in our
techniques
to use and account
for .
long
can
is not
half-1 ives, they
faced
with
possible
sealed sources.
experiments.
Thin
rubber
or
disposable
gloves should
always be worn when handling
liquid
sources,
and it is also a good practice
to work over a tray lined with absorbent
paper when using these solutions.
A word of caution:
Never wear the
same
rubber
gloves
while
on
food
are ever
permitted
acquire
is never
or drink
good
habit
part
of
to
the
the
operating
contamination
body,
glove
or
will
another
your
counting
be transferred
instrument,
to
the
in a radioisotope
allowing
the
individual,
laboratory.
hands
while
as any
instrument.
to
touch
working
No
Another
any
other
with
liquid
Material."
They
sources.
Educational
sources
are "not
for human
drugs,
or
medicals,
distribution
(from
USAEC
bear
the
words
use -introduction
or into
products
is prohibited
-exempt
"Radioactive
into foods, beverages, cosmetics,
manufactured
for
commercial
quantities
regulations).
12
should
not
be combined."
STORAGE
OF RADIOACTIVE
Because
storing
sealed
of
the
low
MATERIALS:
levels
of
activity
these radioactive
materials
sources can be safely stored
which
are
received.
thickness
by
the
room
metal,
Quantity
storage
be
kept
cabinet,
material
is also a good
on hand,
brick
warning
The
very
fact
and
it
be disposed
results
from
and
prevent
usually
as empty
magenta
of solid
sources
time,
can be a
with
burial
are two
paper,
the
use of
routine
that
the
from
any
and
even
All
leaves of
other
empty
at the
"caution
isotoptJ
on
part
end
in
-be-can
of
each
-radioactive
bottles
the
used
material
radioisotopes
trash
containirg
labora-
disposable
plants
waste
quantity
laboratory
apprehension
in the
bottles,
of this
exempt
labels
the
accumulates
radioisotope
experiments.
of with
be removed
to
decay
Dilution
which
such
absorbent
is suggested
material"
container
and
inventory
or
.
isotope
yellow
materials
disposal.
or uptake
safely
simply
lead
the
WASTE:
waste
syringes,
cause
It
or
upon
lead sheet,
methods.
materials
autoradiographs
day.
with
shielding
approved
A frequent
radioactive
of
radioactive
includes
gloves
that
method
disposal
Solid
tory
made of wood,
habit.
effective
convenient
the
labels.
DISPOSAL OF RADIOACTIVE
most
cabinet,
and depending
additional
drawer,
with
that
all radioactive
in the instructor's
can be lined
for
locked
labeled
This
be fabricated
building
properly
radioactive
cabinet.
can easily
by ordinary
Any
is recommended
place, preferably
in a locked
radioisotopes
surrounded
should
and
or plastic
of
box
shielding.
safe storage
of radioisotopes.
It
materials
be kept
in one specific
preparation
plastic
sources,
matter.
Solid
containers
in
Liquid
sources are normally
received in glass bottles surrounded
absorbent
packing
material.
These containers,
too, are sufficient
for
sheet
of the
student
in
cases, sufficient
The
in
simple
plastic
provides,
most
they
used
is a relatively
in the original
before
of
discard,
the
janitoral
personnel.
It
liquid
waste."
time
waste
is a normal
waste
This
into
liquid
as possible
material
practice
a single
waste
in order
can then
in
radioisotope
wide-mouth
should
to
be held
allow
be safely
bottle
for
by
the
normal
discharged
13
laboratories,
labeled
into
to
pour
"radioactive
teacher
decay.
a public
for
all
liquid
as long
In general,
sewer
a
this
system,
diluted with large volumes of water. For additional information
on the
use, storage, and disposal of radioactive materials, we suggest the
following references:
1. "How
to Handle Radioisotopes
Safely :' available from National
Science Teachers Association, 1201 Sixteenth Street, N.W., Washington, D.C. 20036. 12 pages, $1.00 per copy.
2. "Teacher's Guide to Experiments in Nuclear Science," Second Edition,
by Chase, Rituper, Sulcoski. Available from The N"ucleus, Box R, Oak
Ridge, Tenn. 37830. 90 pages, $4.00 per copy. (Student Experiment
Manual to above; 200 pages, $6.95 per copy) .
GENERAL LABORATORY
1. Eating,
drinking,
and
the
use of
REGULATIONS
cosmetics
in the
laboratory
are not
permitted.
2. Pipetting
by
pipette
3. Gloves
liquid
4.
and
Before
laboratory
leaving
for
permitted.
coats
the
possible
radioactive
container,
and
6.
is never
Use suction
device
such
as a
should
be worn
when
working
with
all
radioisotopes.
check
5. All
mouth
filler .
laboratory,
liquid
never
wash
contamination
wastes
into
contaminated
with
are to
a laboratory
materials
"contaminated
waste."
Report
spills,
or other
wounds,
All
into
solid
be placed
emergencies
thoroughly,
and
then
instrument.
be poured
sink.
should
marked
hands
survey
in the
the
liquid
radioactive
trash
to the instructor
waste
waste
receptable
immedi-
ately.
7. Maintain
8. Store
not
good
housekeeping
radioactive
remove
sources
materials
from
at all times
only
the
in the
laboratory.
14
in the
laboratory.
designated
storage
area.
Do
v. EXPERIMENTS
A. PlOTTING
A GEIGER
PlATEAU
Purpose
To determine
the
plateau
and operating
voltage
of a G-M tube.
Commentary
All
because
G-M
this
experiment,
also
examine
minute
tubes
of differences
against
you
the
tube
do
not
operate
satisfactorily
in the construction
will
plateau
find
region
the
by
proper
operating
constructing
voltage.
15
at the
and gas filling
same
voltage
of the tubes.
voltage.
a graph
You
of counts
In
will
per
Apparatlls
& Materials
Model
E-2 Scaler,
beta source
such as Sr-90
or TI-204
Procedure
1. Place the prepared beta sample into position
shelf from the top of the sample holder .
on the fourth
2. With the High Voltage adjusted at it's lowest setting which will
produce a count, take a one minute count. Observe and record
the number of counts per unit time at various voltages by
increasing the high voltage control in 50 volt steps.
Conclusions
Plot
and voltage
The
of the
B.
a Geiger
on the
resulting
G-M tube
SHELF
Plateau
graph
with
counts
per minute
on the y -axis
X-axis.
curve
will
in your
ill ustrate
Model
the operating
voltage
and plateau
E-2 Scaler.
RATIOS
Purpose
To determine
the
shelf
ratios
of the sample
holder.
Commentary
Since all types of radiation, whether particulate or' not, obey the
inverse square law quite closely, the count rate from a certain source
will vary when different
shelves are used to hold the source. Sources
which display a high count rate .may sometimes jam the register of a
scaler, so in such a case the source is moved down to a lower shelf .
Apparatus
& Materials
Model E2 scaler,
Procedure
1. Determine
2.
Determine
Sr-90,
the
the
TI-204
background
count
or Co-60
count
rate
source,
and record.
of the
sample
on the
first
shelf
and
record.
3.
Determine
shelves
the
count
rate
and record.
16
of
the
sample
on
the
succeeding
observed
shelf
cpm corrected
for background
count
background
cpm
shelt
ratio
#1
#2
,#3
#4
#5
#6
1.00
Conclusions
Normally shelf #2 is the shelf most often used, so this is assigned
a shelf ratio of 1.00 as the standard shelf. Compute the shelf ratios of
the other shelves from this relationship:
Once
the
the
shelf
activity
result
if the
source
Remember
point source and
1. 6 inch diameter
end
c.
ratio
window
on
were
that
the
for
one
placed
each
shelf
shelf.
on another
inverse
it is possible
with
square
the
activity
of the
G-M tube.
Then
to
compare
which
would
shelf .
law is strictly
correct
point detector.
This can be approximated
hole in a sheet of lead. and placing the
ABSORPTION
Purpose
To
is known
determined
use a beta
source
only
for
a
by drilling
a
lead over the
(TI-204
or Sr-90).
STUDIES
investigate
the absorption
of alpha,
beta,
and gamma
radiations
in matter.
Commentary
The absorption
of
emitted
experiment,
radiation
radiationyou
will
of
radiation
its
mass,
investigate
by matter
its
the
is dependent
charge,
absorption
and
its
upon
energy.
of three
the type
In
this
representative
types.
Apparatus & Materials
Model E-2 Scaler; calibrated absorber
Sr-90 beta source; Co-60 gamma source.
17
set; Po-210 alpha source;
Procedure
1. Determine
the background
count and record.
2. Place the Po-210 alpha source in the second shelf of the
sample holder, determine its count rate, and record.
3. Cut a thin piece of index card to fit the sample holder,
place the index card in the first shelf (between tube
source).
4. With the card in place, again determine
alpha source and record.
and
and
the count rate of the
5. Remove both the card and the alpha source.
6. Place the Sr-90 beta source in the third shelf of the sample
holder, and place the empty absorber slide in the second shelf.
7. Determine
the count rate of the beta source and record.
8. Put the thinnest absorber in the absorber slide, determine
count rate, and record.
9. Repeat step 8 with absorbers of increasing density
determine each count rate, and record.
the
thickness,
10. Repeat steps 6-9 with the Co-60 gamma source in place.
Conclusions
How does the penetration of alpha particles
with beta particles and gamma radiation?
in matter
compare
Plot the data from the beta and gamma absorption with the
corrected count rate on the y-axis against the absorber thickness on the
x-axis. The graph will yield curves which show both beta and gamma
radiation
D.
absorption.
HALF-LIFE
Purpose
To
determine
Commentary
The rate
nuclear
pressure,
tope
change,
or
the
at
which
cannot
catalysis
has its own
half-life
decay
of
a radioisotope.
a radioisotope
be
influenced
as in ordinary
rate.
18
emits
by
chemical
its
radiations,
variations
reactions.
in
being
temperature,
Each
radioiso-
a
I n most
Instead,
as the
half
cases it
a concept
time
the
necessary
initial
graphically
value.
from
is not
known
for
the
In this
the
necessary
as half-:ife
data
to know
the
is utilized.
radioactivity
experiment,
secured
from
of
absolute
The
a sample
you
will
the
decay
decay
half-life
to decay
determine
of
rate.
is defined
the
a short
to one
half-life
half-life
radioisotope.
Apparatus and Material
Model E-2 Scaler, semilog graph paper, short half-life source
as P-32 or 1-131. (The MINI-GENERATOR
SYSTEMS supplied by
Nucleus are ideal for this experiment providing isotopes with half
of 2.6 minutes for 137Cs/137BaM,
100 minutes for 113Snf131nM
64 hours for 90Sr/90y.)
Procedure
1. Determine
the background
such
The
lives
and
count and record.
2. Determine the count rate of the sample at intervals convenient
to obtain good, quantitative
data on the half-life of the
radioisotope being used. For example, count 1-131 every other
day. Record the time and count rate data.
Conclusions
On semilog graph paper, plot the corrected count rate (count rate
minus background) on the Y-axis against the elapsed time on the X-axis.
(If semilog paper is not available, plot the logarithm of the corrected
count rate on the X-axis on regular graph paper, or make your own
semilog graph paper using the C scale of a slide rule as a guide.) Draw
the best line to connect the points on the graph. Find the point on the
X-axis which corresponds to one-half the initial activity, then draw a
line from this point to the X-axis to find the half-life. Compare your
value with that obtained from a handbook.
E. BETA
DECAY
ENERGY
Purpose
T o determine
Commentary
Beta
energies.
penetration
the
particles
The
energy
are emitted
greater
through
decay
the
matter.
can be u~ed as a means
of
from
energy
of
a beta
particle.
a nucleus
a beta
in a wide
particle,
Thus
the
range of beta
of finding
the
maximum
19
the
particles
beta energy.
spectrum
of
greater
its
in absorbers
Apparatus
& Materials
Model
E-2 Scaler;
set; semilog
graph
TI-204
and/or
Sr-90
source;
calibrated
absorber
count
in this
experiment.
paper .
Procedure
1. Do not
2. Place
3.
the
background
absorber
slide
in the
and the TI-204
source
in the
Determine
count
rate
place
4.
determine
the
second
third
of
shelf
of
the
tube
stand
shelf .
the
source
with
no
absorber
in
and record.
Determine
the
absorber
in
count
place
rate
and
of
the
record.
source
Repeat
with
with
the
thinnest
succeeding
thick-
nesses of absorbers.
Conclusions
Plot on graph paper the logarithm of the activity on the y-axis
against absorber thickness on the x-axis. This curve of beta absorption
will show a straight line except in the
region of lowest activity.
Extrapolate
this absorption curve to background as
I
shown in the sample graph. This extrapolated
value is the maximum
beta
particle
into
Am
range
the
+ 0.212
energy
Am.
empirical
where
expressed
Substitute
this
formula
Em
in
is the
MeV
value
Em = 1.84
:f I
'U
..
maximum
and
Am
go
-
I
is
mg/cm2.
absorber thickness
This
energy
of
theoretical
F.
experimental
TRACER
a beta
value
method
particle
found
is a gross approximation
thus
the
result
should
for
be
mg/cm2
finding
compared
the
with
in a handbook.
STUDIES
Purpose
To
in
determine
absorption
and
distribution
of
a radioactive
solution
plants.
Commentary
The root system of a plant serves as the anchor that holds the
plant in the soil and absorbs water and dissolved minerals for distribution throughout
the plant. The other parts of the plant such as the
20
stem,
leaves
insure
grovvth,
and
flowers
food
A radioactive
same
will
manner
young
supply
is absorbed
and
dissolved
absorption
and
of water
etc.,
and nutrient
to
of the species.
and distributed
minerals.
In
distribution
of
this
in plants,
in the
experiment
you
a radioisotope
in
a
plant.
Apparatus
and Materials
Model
broad
the
on this
reproduction,
solution
as water
determine
depend
storage,
leafed
E-2 Scaler;
plant};
small
plant
3'. to 4"
P-32 solution;
10-ML
tall
(tomato.
bean,
or other
test tube.
Procedure
1. Gently wash plant roots in running tap water.
2. Pour the P-32 solution
plant int.o the solution
3. Remove the plant
running tap water
stems and leaves.
into the test tube, place the roots of the
and let stand for 24 hours.
from the P-32 solution, rinse the roots in
and divide the plant into samples of roots,
4. With each sample on the second shelf of the sample holder ,
count and record activity readings for various plant parts.
5. Determine
below.
the mass (grams) of each sample and record results
6. Dispose of P-32 solution
(GRAMS)
ACTIVITY
(CPM)
plant
show
MASS
SAMPLE
Conclusions
Did all
and plants as directed by instructor.
parts
CPM CORRECTED
FOR BACKGROUND
evidence
parts showed the greatest corrected
Which
showed
the least corrected
activity
activity
21
of
CORRECTED
ACTIVITY
(CPM/GRAM)
radioactivity?
mass (CPM/gram)
mass (CPM/gram).
Which
.and
and
plant
why?
why?
VI.
MAINTENANCE
General
The
opera-tion
Model
E-2
with
Scaler
minimum
tronics
may occasionally
that
most
often
when
electronic
service
fatal
component
quickly
voltages
employed
by
is at fault,
inside
trouble
designed
experience
a failure
simply
exist
when
is
maintenance.
the
maximum
the
trouble-free
very
best
elec-
failure.
It has been our experience
does occur,
some relatively
minor
and the
replacing
the
cabinet,
shooting
for
However,
with
instruments
faulty
and
the cover
can be returned
component.
extreme
to
Potentially
caution
must
be
removed.
Preventive Maintenance
1. Since the Model E-2 requires no warm-up period, it is not
necessary to leave the instrument power on during periods of
inactivity.
2. The most vulnerable component in your Model E-2
the G/M tube. Care must be exercised when working
thin end window of the tube that nothing is allowed
this window.
A broken or punctured
G/M tube
replaced with a new one.
Scaler is
near the
to touch
must be
3. As with all electronic instruments, good "housekeeping"
habits
are most important.
Do not allow containers with liquids, such
as a beaker or a planchet, to be placed on top of the
instrument. Acid spills will deteriorate the paint and electronic
components
Trouble
very quickly.
Shooting
Symptom
1. LED'S fail to light
Possible Cause
Blown fuse, 1 amp. Fuse
No power; check line cord
Transformer
Power Switch
5 volt regulator
2. No counting when high voltage
is increased to at least 450
volts.
Faulty G/M tube
Loose connection to G/M tube
Input transistor faulty (01 )
No high voltage
22
3. Faulty readout
counts O.K.
on
LED's
but
LED failure
Integrated Circuit decoder (7447)
fau Ity
Broken wire from Printed Circuit
board to LED board.
4. Scaler will
not count
with
count switch in CONTINUOUS
or 1 MINUTE
COUNT position.
Wire broken on count switch or
faulty switch
Faulty timing I.C:s
Check G/M tube, high voltage and
01
5. Scaler will not stop at end of 1
MINUTE COUNT.
Wire broken on count
faulty switch
Faulty timing I.C.'s
6. LED's will not reset
Wire broken on RESET switch or
faulty switch
7.
Check
Erratic
counting
switch
or
first for normal statistical
variation
Failing G/M tube; check plateau
High voltage regulator
23
VII.
A.
Low
CIRCUIT
Voltage
The
low
voltage
output
voltage regulator]
.This
readouts, and the input
B.
High
The
high
by
voltage
voltage.
voltage
circuit.
volts
high
is +5 volts.
It is regulated
supplies voltage
circuitry
.
for
the timing
by VR 1 [ (7805)
circuitry,
the LED
thru
a voltage
Voltage
multiplier
0-1200
DESCRIPTION
The
AC
is
a 1 meg ohm
filter
CAUTION:
on
Fatal
rectified
resulting
the
DC
and
potentiometer
DC
voltages
boosted
is continuously
output
controlled
on the high
further
are present
stabilizes
inside
from
voltage
AC.
the
A
output
the cabinet.
C. Detector
A
heart
2%
miniaturized
of the detector
in
100
operates
at
halogen
section.
volts
plateau
about
400
alpha, beta and gamma
tube to conduct
slightly
second).
transmitted
This
slope,
volts.
pulse shaper
100
This
radiation.
for a very
pulse of current
to the
quenched
It is 0.6"
end
x 2",
window
microsecond
end
geiger
tube
has a 2-3 mg/cm2
window
resolving
G/M
tube
time,
can
An ionizing
event causes the
short time (about
100 millionths
produces
circuit
a negative
through
voltage
is the
window,
and
detect
geiger
of a
pulse which
is
an RC network.
D. Pulse Shaper and Readout
The pulse shaper circuit accepts the fast rise, negative signal pulses of
0.3 volts or greater from the GM tube. This signal is inverted and amplified
by 01 and sent to the scaling circuits when switched to the count mode.
The scaling circuitry
contains five seven-segment LED's
driven by integrated circuits in a multiplexed configuration.
24
that
are