Intercalibration of Radiation Effects Testing Facilities, and Radiation Damage Measurements: Implied D(E) Accuracy

The effectiveness of the neutron displacement cross section DSi(En) in characterizing the radiation damage in silicon was investigated by simultaneous measurements of diverse neutron spectra and of the damage coefficient K resulting from each spectrum. The simultaneous measurements for diverse neutron spectra offer a unique approach to testing DSi(En) with good accuracy because the three essential ingredients are available for the identically same neutron fields: widely varying spectra above the 0.2 MeV radiation-damage threshold in Si, accurate measurements of the neutron spectra ϕ(E), and accurate measurements of radiation damage D = Kϕ. Threshold foil neutron spectrometry measurements were carried out with a standardized technique(12) that combines both activation-foil measurements and neutron transport calculations. The resultant spectra were folded in with Dsi(En) to obtain ϕeq, the equivalent number of near-l MeV neutrons. The values of D = Kϕ, measured for batches of 2N2222A transistors, were divided by ϕeq to obtain the damage coefficients K for all the neutron fields. The values of K were constant, within 4-5% (one standard deviation) for five basically different neutron fields: TRIGA reactor, FBR-reactor glory hole, and three FBR leakage spectra; free field, polyethylene filtered, and iron filtered. When normalized at the 0.2 MeV Si-damage "threshold", differences of as much as an order of magnitude were observed at higher energies for the last two neutron fields. These differences, extending to energies above 10 MeV, provide essential data with regard to characterizing radiation damage effectiveness via DSi(En) and ϕeq for diverse neutron fields.