Radiation Detection

1
Radiation Detection Multi Channel Analyzer and a
Phototube The study of a flat panel
scintillator Janet Sanford , Chris George Advisor
Dr. Thomas Dooling
How well do these detectors work? The following
two tables show data from the multi channel
analyzer for two different modes. Table 1 shows
the energy curves for each of the four sources
using the multi channel analog mode. This mode
Records energy data observed for a specific
channel. Each of these runs are compared to a
Monte Carlo Simulation. Table 2 shows each
source using the multi channel scalar mode, which
records data for each channel observed within a
set time frame. Each graph is a comparison scale
of each source at different positions above the
paddle along with a background run. These are
also compared with a Monte Carlo Simulation. A
graph of the log of the average count versus
distance is plotted to show the increase of
sensitivity as the source nears the paddle
Abstract This experiment investigated the
effectiveness and sensitivity of an inexpensive,
handheld, flat paddle scintillator at detecting
weak radioactive sources. The sources implored
during this study were Strontium-90, Cesium-137,
Thallium-204, and Cobalt-60 with activities per
second of 0.1 µ Ci, 5.0 µ Ci, 1.0 µ Ci, and 1.0 µ
Ci, respectively. The multi channel analyzer,
along with a phototube were used in conjunction
with the scintillator paddle for the source
detection. The sources were placed at different
distances away from the paddle and compared to a
background run. Each of the detection runs were
compared to a Monte Carlo Fortran Simulation run.
These data runs are used to determine specific
settings needed to make the Monte Carlo
simulations more accurate.
What purpose do these inexpensive radiation
detection devices serve? These small devices
provide preliminary detection of potentially
harmful substances used in making dirty bombs or
other explosives. These detectors are set up by
hand and easy to use. They can provide post
offices and other government agencies the
opportunity to detect harmful radiation before
the package reaches the public. If something is
detected by these handheld detectors, that
substance can be subjected to more extensive and
accurate analysis. For example, the cost of
detecting every package that comes through a post
office everyday with a state-of-the-art radiation
detector, is not efficient and very costly. By
using the smaller, yet still sensitive detectors,
the efficiency of detection will increase, while
the price decreases.
Multi Channel Analog at position (0,0,0) Monte Carlo Simulation Multi Channel Analog at Position (0,0,0)




Multi Channel Scalar Monte Carlo MCS Comparison of Distance versus the log (average count)




Results The Monte Carlo program needs to be ran
with higher statistical simulations. The higher
statistical simulation will show the separation
between distances more clearly. The Multi
Channel scalar mode graphs, clearly show how
effective the scintillator paddle detects sources
with respect to distance above background noise.
The positions (0,0,35) and (0,0,45) are
noticeable above background in all sources, but
only slightly in the Thallium 204. The position
(0,0,15) and closer are the most noticeably
detectable above all background noise. These
handheld devices have proven to be effective in
detecting everyday weak radiation sources, and
therefore it can be assumed they will be able to
detect sources of stronger energy.
Table 1
Table 2
Each multi channel scalar graph shows the four
sources at positions (0,0,0) (0,0,3)
(0,0,6) (0,0,9) (0,0,12) (0,0,15) (0,0,30)
(0,0,45)
The energy curves provide a way to calculate an
equation for the Monte Carlo simulation. These
curves also provide comparison for the fine
detailing of the Fortran program. The idea
behind the Monte Carlo program is to be able to
predict what the sensitivity of a detector might
be with given parameters of height, width, and
length. The Monte Carlo program is providing the
user with the basic shape that is seen from the
raw data. One possible solution would be to run
the Monte Carlo under much higher statistics.
Another solution is to reconfigure the Monte
Carlos calculations to provide more accurate
data for comparison.
Equipment Used
Multi Channel Analyzer Company Spectrum Techniques Multiple Settings Upper Level Discriminate up to 105 Lower Level Discriminate as low as 0 Coarse Gain 2,4,8,16,32,64 Fine Gain 1.00 2.00 Total Gain Fine Gain Coarse Gain Conversion Gain 256,512,1024,2048 Live Time The time data is available to take Real Time Actual time the MCA takes data (Real time may be higher than live time) PRICE 1000 Hamamatsu Phototube Radiation Sources Scintillator Paddle Company Bicron (Saint-Gobain Crystals) Blue-Emitting Plastic Scintillator Sheet 305 x 305 x 5mm PRICE 150.00
Company Hamamatsu Series H5783/H6780 Dimensions
Length 22.0 mm Width 22.0 mm Height 50.0 mm
This phototube has an optimum Wavelength
spectrum from 420 nm to 630 nm which falls in the
visible light spectrum corresponding respectively
to violet and orange light. PRICE
Company Spectrum Techniques Cobalt 60 Gamma Ray
producer Activity per second
1.0 µ Ci. Cesium 137 Beta Particle Gamma Ray
producer Activity per
second 5.0 µ Ci Strontium 90 Beta Particle
producer Activity per
second 0.1 µ Ci Thallium 204 Beta Particle
producer Activity per
second 1.0 µ Ci. PRICE 250