ASTM E1855-15

5.1 The neutron test spectrum must be known in order to use a measured device response to predict the device performance in an operational environment (E1854). Typically, neutron spectra are determined by use of a set of sensors with response functions sensitive over the neutron energy region to which the device under test (DUT) responds (E721). For silicon bipolar devices exposed in reactor neutron spectra, this effective energy range is between 0.01 and 10 MeV. A typical set of activation reactions that lack fission reactions from nuclides such as  ²³⁵U,  ²³⁷Np, or  ²³⁹Pu, will have very poor sensitivity to the spectrum between 0.01 and 2 MeV. For a pool-type reactor spectrum, 70 % of the DUT electronic damage response may lie in this range.

5.2 When dosimeters with a significant response in the 10 keV to 2 MeV energy region, such as fission foils, are unavailable, silicon transistors may provide a dosimeter with the needed response to define the spectrum in this critical energy range. When fission foils are part of the sensor set, the silicon sensor provides confirmation of the spectral shape in this energy region.

5.3 Silicon bipolar transistors, such as type 2N2222A, are inexpensive, smaller than fission foils contained in a boron ball, and sensitive to a part of the neutron spectrum important to the damage of modern silicon electronics. They also can be used directly in arrays to map 1 Mev(Si) equivalent displacement damage fluence. The proper set of steps to take in reading the transistor-gain degradation is described in this test method.

5.4 The energy-dependence of the displacement damage function for silicon is found in E722. The major portion of the response for the silicon transistors will generally be above 100 keV.

1.1 This test method covers the use of 2N2222A silicon bipolar transistors as dosimetry sensors in the determination of neutron energy spectra and as 1 Mev(Si) equivalent displacement damage fluence monitors.

1.2 The neutron displacement in silicon can serve as a neutron spectrum sensor in the range 0.1 to 2.0 MeV when fission foils are not available. It has been applied in the fluence range between 2 × 10¹² n/cm ² to 1 × 10¹⁴ n/cm² and should be useful up to 1 × 10¹⁵ n/cm². This test method details the acquisition and use of 1 Mev(Si) equivalent fluence information for the partial determination of the neutron spectra by using 2N2222A transistors.

1.3 This sensor yields a direct measurement of the silicon 1 Mev equivalent fluence by the transfer technique.

1.4 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.

1.5 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory requirements prior to use.