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Spectral Info
Ordering Info


FWT’s 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 I micron to 10 microns in diameter.

Spectral Measurements
Connection of the detector to a preamplifier, such as used with Ge(Li) detectors, 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 the aid of computer techniques or by hand if less resolution is satisfactory.

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.


Tissue Equivalent Plastic Sphere: Wall thickness 0.125 in, (0.318 cm), 2.24 in. (5.69 cm) inside diameter, Shonka type A-150 plastic
Gas Filling Requirements: Tissue equivalent proportional counting gas; 1.26 cm Hg of T.E. gas of density 1.062 g/ l 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 O-QC4-D-400
Signal Output: Suitable for use directly into a low noise preamplifier (removing input coupling capacitors will result in substantial noise reduction) or can be applied directly into a electrometer for absorbed dose measurements and yields approx. 1 x 10E-14 A per microrad per hour at 1700V and 20 cm Hg TE gas pressure
Signal Connector: MHVt
High Voltage Requirements: Negative polarity. -500 V at 2 cm Hg, -1300 V at 10 cm Hg, -1700 V at 20 cm Hg
High Voltage Connector: MHV
Optional Internal Source: Cm244, approx. 0.3 microcuries; average alpha energy - 5.8 MeV; gravity operated shutter
Exterior Can: Vacuum tight, aluminum, wall thickness 0.060 in. (0-152 cm); grounded to serve as electrostatic shield; 3.625 in. (9 cm) in diameter, 6.125 in. (15.5 cm) high, including connector for gas filling

Weight: 560 grams

Ordering Information
LET-SW2: Tissue equivalent proportional counter with storage box
-Cm244 Curium 244 source in counter option

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Specifications subject to change without notice.
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