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DEVELOPMENT OF A UNIVERSAL PERSONAL DOSIMETER USING SEMI- CONDUCTOR SENSORS FOR MIXED RADIATION FIELDS

Objective


Supports and other were built hardware for exposing solid state detectors in the calibration facilities with the best possible accuracy and reproducibility. The amplifier system was built from conventional nuclear instrumentation module (NIM) electronics with a low noise preamplifier placed next to the detector in the irradiation room and with the main amplifier, bias supply and analyser etc, in an adjacent control room. Read out was in most cases done with an integral discriminator and a scaler time system. Each detector was exposed in collimated beams of americium-241 (60 keV), caesium-137 (662 keV) and cobalt-60 (1.25 meV) and at 2 different settings of an X-ray machine. The photon response of the detectors is 10 times higher with americium (60 keV) than caesium (662 keV). Detectors 55 to 59 had different resistivity and measurements with X-rays and gamma rays showed that the sensitivity increased almost linearly with resistivity. Photon sensitivity is independent of detector thickness from 200 um to 1000 um. A correlation was found between window size and photon sensitivity for both low and high energies. The results show that a measuring channel with a silicon detector might be useful for measuring the gamma component in a mixed field when a multichannel analyzer (MCA) is available. It might also be used for building a spectrometer for X-rays up to about 100 keV.

Fast neutrons were detected by the n, p scattering process (proton recoil) by mounting a polythene radiator in front of the detector window. Measuring efficiency as a function of polythene radiator thickness, it was found that approximately 1 mm polythene was sufficient to give maximum concentrate and it increased the initial reading by a factor of 2. A single detector was used for measuring the response as a function of bias voltage when it was exposed to plutonium beryllium neutrons. The result was no sign of a plateau up to the highest permissible voltage (250 V). The efficiences for californium and plutonium beryllium differ by more than a factor of 2 which means there is no simple proportionality between the sum of counts in channels 21 to 256 and the dose equivalent.

A new type of thermal neutron detector, based on gadolineum oxide foil, was tested for measuring of the dose equivalent from lower energy neutrons. An acceptable response has not been produced.

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Coordinator

CERN Organisation Europeenne pour la Recherche Nucleaire
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Address

1211 GENEVE
Switzerland

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