Evaluation of the instrument correction factors needed in beta dosimetry
Generally, the same survey instruments used for the measurement of gamma dose rates are used for monitoring beta fields by making measurements with and without a shield over the detector to separate the penetrating and nonpenetrating components of the radiation field. Survey meters are calibrated using fields that uniformly irradiate the detector volume with the center of the volume used as a reference point. However, under field survey conditions, sources are frequently encountered that have irregular shape and large or small dimensions compared with the detector volume. When the distance from the source to the detector volume (reference point) is small such sources produce non-uniform radiation fields in the detector. Similarly, low energy beta sources cause non-uniform irradiation of the volume due to attenuation of the radiation. In addition, when survey meters are used close to the source, the surveyor is generally interested in dose rates at contact or within a few centimeters of the source. In these cases the reference point is the center front surface of the detector. The resulting readings from such fields are based on an average of the uneven distribution of energy deposition occurring within the detector. In general, this reading would be significantly less than the actual dose existing at the surface of the meter entrance window. To compensate for this discrepancy, correction factors are applied to the readings to give the actual dose. These factors can be in excess of a factor of 100. This paper summarizes observations on energy, angular and source geometry response of survey instruments.
- Research Organization:
- Pacific Northwest Lab., Richland, WA (USA)
- DOE Contract Number:
- AC06-76RL01830
- OSTI ID:
- 5247871
- Report Number(s):
- PNL-SA-14735; CONF-880404-17; ON: DE88008188
- Resource Relation:
- Conference: 7. international congress of the International Radiation Protection Association, Sydney, Australia, 10 Apr 1988
- Country of Publication:
- United States
- Language:
- English
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