Energy dependence of neutron damage in silicon bipolar transistors

2N2222A transistors were exposed in neutron fields ranging in energy from thermal to 14 MeV. Spectrum characterization data are reported for the three fast reactors used in hardness testing. The neutron energy dependence of transistor damage response was measured and compared with predictions based on ASTM standards and recent compilations of the silicon kerma factors calculated using NJOY. For all the environments considered, the hardness parameters calculated using the NJOY displacement kerma factors are significantly smaller than those calculated using the ASTM standard values, using the same value of 95 MeV-mbarn for the kerma factor at 1 MeV. The NJOY calculations actually show that this value is too high, so that if the standard is revised the 1-MeV value should also change. The spectrum evaluations for the fast reactors improve the agreement between the observed and predict hardness ratios, provided consistent methods are used for the unfolding. The thermal reactors and the moderated californium source show consistent results only when thermal and epithermal neutrons are removed by boron filters. The ASTM standards should be revised to include this precaution as well