1-MeV(Si)-equivalent-neutron

This 1-MeV(Si)-equivalent response function corresponds to the
ASTM E722-14 recommended displacement damage function used to
assess damage effects in silicon electronics, e.g. Frenkel pair 
production and changes in the minority carrier recombination 
lifetime and, hence, the gain of bipolar silicon devices. The 
response function is useful as an exposure parameter and has been 
validated to correspond to gain degradation for cases where the
predominant source of displacement damage is from neutrons of 
energy between 10 keV and 20 MeV. The correlation with measured 
damage in many neutron fields has been confirmed with 
uncertainties no larger than 10%. This response function has 
not been validated for thermal neutron sources.

Because use of this functional form is required within the 
standard, ASTM E722-14 does not report an energy-dependent 
uncertainty for this response function. However, an uncertainty
characterization in the form of an energy-dependent covariance 
matrix is available. This covariance matrix takes into account
uncertainty due to: a) the underlying neutron cross sections; 
b) the displacement threshold energy; c) the silicon interaction
potentials and the resulting change in the recoil atom electronic
stopping power; d) the damage partition function; e) model defect 
in some aspects of the calculational methodology, e.g. in the 
NJOY-2016 kerma modeling; f) and the normalization to a reference 
1-MeV value. The covariance matrix can be found in IEEE TNS 
Vol. 66, No. 1, pp. 327-336, doi: 10.1109/TNS2018.2876058

This response function has units of MeV-mb. Each factor can be
multiplied by 3.435E-13 to convert to units of rad(Si)*cm^2 or by
3.435E-19 to convert to J*m^2/kg or Gy(Si)*m^2. The tabulation 
uses a histogram representation and is presented in the SAND-II 
640-group energy structure. 

The 1-MeV(Si)-equivalent neutron fluence is obtained by folding 
this response function with the neutron spectrum and dividing 
this by the reference value of 95 MeV-mb. See ASTM E722-14 for
details. 

This response function corresponds to the microscopic 
displacement kerma factor derived using the ENDF/B-VII.1 cross
sections, the Robinson damage partition function, a displacement
threshold energy of 20.5 eV, and the Norgett-Robinson-Torrens 
(NRT) treatment in the displacement threshold region. It applies 
to natural silicon, i.e. it represents a composite of the 
isotopic (Si-8, Si-29, and Si-30) microscopic displacement kerma
factors properly weighted by the natural abundances.