Unexpected bias in NIST 4πγ ionization chamber measurements.

  title={Unexpected bias in NIST 4πγ ionization chamber measurements.},
  author={Michael P Unterweger and Ray Fitzgerald},
  journal={Applied radiation and isotopes : including data, instrumentation and methods for use in agriculture, industry and medicine},
  volume={70 9},
In January of 2010, it was discovered that the source holder used for calibrations in the NIST 4πγ ionization chamber (IC) has not been stable. The positioning ring that determines the height of the sample in the reentrant tube of the IC has slowly shifted during 35 years of use. This has led to a slow change in the calibration factors for the various… CONTINUE READING