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RCRS provides:
• Pick-up and delivery of
meters
• Required 9-month calibration
• Preventive maintenance and
repairs
• Shipping for extensive repairs
RCRS Contact:
John Parker
Nuclear Science Center
392-7359
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Direct
measurements
o Portable survey instruments
Indirect
measurements
o Swipes and use of counters (Liquid
Scintillation and Gamma)
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 Read the instrument’s operating manual
 Check the batteries before each use
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 Use a check source to determine operability
of detector
 Determine efficiency of detector
 Determine the instruments response time
 Determine the operating background
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 GM are tubes filled with a mixture
of Q-gas
 Used for radioactive contamination
monitoring
 Detects high energy beta radiation
 GM measures each individual
interaction inside the detector
 Do NOT identify the radioisotope or
specific energy
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 Probe has a NaI crystal and a
photomultiplier tube
 Detection is based on emission
of photons
 Used for radioactive
contamination monitoring
 Detects low energy x-rays
 Does NOT identify the
radioisotope
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 Ion Chambers are filled with air
 Used for measuring radiation field
intensity (exposure rate)
 Detect x-rays and gamma radiation
 Measure average current produced
over many interactions
 Do NOT identify the radioisotope or
specific energy
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A.K.A. - Dose Rate Meter
Roentgen (R): a unit of exposure to x-rays or
gamma rays. One roentgen is the amount of
gamma or x-rays needed to produce ions
carrying 1 electrostatic unit of electrical
charge in 1 cubic centimeter of dry air under
standard conditions.
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 Detection is based on emission of
visible or near visible light (photon)
 Sample vial must contain scintillation
cocktail
 Interaction between radiation and
cocktail causes photons to be emitted
 Photomultiplier tubes are used to
detect and amplify the photons
 It can identify the activity and energy of
a beta emitter in a sample vial
 It is much more efficient than a
portable survey meter
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 Beta particles are emitted, which
cause solvent molecules to become
excited.
 The energy of the solvent molecule is
transferred to the fluor molecule,
which in turn emits light.
Radioactive
molecule
Solvent
molecule
Fluor
molecule
Photomultiplier
tube
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 Detection is based on emission of
visible or near visible light (photons)
 Uses solid scintillation (no scintillation
cocktail required)
 Interaction between radiation and a
solid scintillator causes photons to be
emitted
 Photomultiplier tubes detect and
amplify photons
 Used to determine the activity of a x-ray
or gamma emitter in a sample vial
 Gamma counters can identify activity
and energy of gamma emitters
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 Radiation Field / Dose Rate (mR/hr)
Ion chamber
 Activity / Contamination amounts
Beta emitters
Low and Mid energy
LSC only
High energy
GM Detector
LSC (for documentation purposes)
Gamma emitters
Sodium Iodide
Gamma counter (for documentation
purposes)
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 1 µCi = 2.22 x 106 dpm
Hmm…a
conversion
might help
here!
 net cpm = gross cpm –
background
 efficiency = (net cpm) / (dpm)
 dpm = (net cpm) / (efficiency)
 cpm = (dpm) x (efficiency)
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GM
Tube
Ion
Chamber
NaI Probe
GC
LSC
P-32
x-ray
I-125
Tritium
Cr-51
Radiation
Field
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You have a swipe that was counted for 5
minutes that yields 5800 counts.
If the background is 125 cpm and the
counter efficiency is 80%, what is the dpm
of the swipe?
Hint:
5800 counts /
5 minutes =
1160 gross
cpm
Big Hint:
Hint:
1160 gcpm –
125
background
cpm = 1035
net cpm
1035 net cpm /
0.80 efficiency
= 1294 dpm
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You have a standard that has an activity of
105,000 dpm.
After 2 minutes of counting in a gamma counter
you get 120,000 counts.
If the background is 350 cpm, what is the
efficiency of the gamma counter?
Hint:
120,000 counts /
2 minutes =
60,000 gross cpm
Big Hint:
Hint:
60,000 gcpm –
350 background
cpm = 59,650 net
cpm
59,650 ncpm /
105,000 dpm =
57% efficiency
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You are using P-32 as a tracer and determine
that 20% of fed material ends up in your final
sample.
If you need a count rate of 2,000 cpm in a
sample, determine how many microcuries you
must use given the fact that your LSC has an
efficiency of 50% for P-32.
Big Hint:
Hint:
2,000 cpm /
0.20 = 10,000
cpm
Hint:
10,000 cpm /
0.50 efficiency
= 20,000 dpm
20,000 dpm /
2.22 x 106
dpm/µCi =
0.009 µCi
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Life is not measured by
the number of breaths
we take, but by the
moments that take our
breath away…
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