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FWT’s
5 inch single wire counter is a spherical tissue equivalent proportional
counter for measuring the spectra of absorbed dose in LET (actually
P(Y) spectra).
The detector is furnished in a vacuum-tight aluminum can designed
to be filled by the user with tissue equivalent gas at a low pressure,
typically 2 to 20 cm Hg. These low pressures enable the spherical
counter volume to simulate small tissue volumes from less than 1
micron to 10 microns in diameter.
Spectral Measurements
Connection of the detector to a preamplifier and a linear amplifier
will enable a P(Y) spectrum to be accumulated on a pulse height
analyzer when the detector is exposed to a radiation source. Proper
choice of amplifier gain settings will enable data to be obtained
for Y values from 0.2 keV per micron to 1000 keV per micron. These
data may be converted to a spectrum of absorbed dose in LET with
a specific program.
The optional internal CM244 alpha source makes calibration of the
Y axis in keV per micron particularly simple. The source allows
collimated alpha particles to cross the detector on a diameter,
producing a peak in the pulse height analyzer display. The peak
channel is characteristic of the average keV per micron expended
by the alpha particles in traversing the sphere. The alpha source
has a gravity-operated shutter mechanism that allows operation free
of unwanted alpha counts when desired.
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Specifications
 Tissue Equivalent
Plastic Sphere: Wall thickness. 084 in.(.213 cm),4.94 in.(l 2.55
cm) inside diameter, Shonka type A-1 50 plastic
Gas Filling
Requirements: Tissue equivalent proportional counting gas: 0.56
cm Hg of T.E. gas of density l.062 g/liter corresponds to a cavity
of 1 micron diameter, gas must be made up of high purity components
and be moisture free.
Gas Filling:
Bellows seal valve, connector mates with Swagelok B-QC4-D-400
Signal Output:
Suitable for use directly into a low noise preamplifier for spectral
data (removal of input coupling capacitors will result in substantial
noise reduction), can be applied directly into a electrometer for
absorbed dose measurements and yields- 1 X 1 0E-14 A per microrad
per hour at 1 700 V and 20 cm Hg TE gas pressure
Signal Connector:
MHV
High Voltage
Requirements: Negative polarity, -700 V at .56 cm Hg. -800 V at
1.14 cm Hg
High Voltage
Connector: MHV
Optional
Interior Source: CM244, ~0.3 microcuries; average alpha energy-
5.8 MeV; gravity operated shutter
Exterior
Can: Vacuum tight, aluminum, wall thickness 0.050 in). @0.1 27 cm);
grounded to serve as electrostatic shield; 6.0 in. in diameter,
6.75 in, (1 7.1 cm) high including connector for gas filling
Weight: 1370
grams
Ordering
Information
LET-SW5:
Tissue equivalent proportional counter with storage box
-Cm244 Curium
244 source in counter option
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