Patrick J. Griffin

Neutron dosimetry with planar silicon p-i-n diodes

New nonionizing energy losses (NIEL) sensors based on silicon planar p-i-n diodes of different geometry have been investigated and their response to fast neutron field compared with bulk diodes. The possibility of obtaining a wide range of sensitivities in these NIEL sensors simultaneously with measurements of IEL has been demonstrated.

Neutron damage equivalence in GaAs

A 1-MeV neutron damage equivalence methodology and damage function have been developed for GaAs based on a recoil-energy dependent damage efficiency and the displacement kerma. This method, developed using lifetime degradationIn GaAs LEDs in a variety of neutron spectra, is also shown to be applicable to carrier removal. A validated methodology, such as this, is required to ensure and evaluate simulation fidelity in the neutron testing of GaAs semiconductors. >

The role of thermal and fission neutrons in reactor neutron-induced upsets in commercial SRAMs

Reactor neutron environments can be used to test/screen the sensitivity of unhardened commercial SRAMs to low-LET neutron-induced upset. Tests indicate both thermal/epithermal (<1 keV) and fast neutrons can cause upsets in unhardened parts. Measured upset rates in reactor environments can be used to estimate the upset rates from thermal and fast portions of arbitrary neutron spectra.

Benchmarking the Sandia Pulsed Reactor III cavity neutron spectrum for electronic parts calibration and testing

The SPR (Sandia Pulsed Reactor) III bare cavity spectrum and integral parameters have been determined with 24 measured spectrum sensor responses and an independent, detailed, transport calculation. This environment qualifies as a benchmark field for electronic parts testing. The measured SPR III cavity spectrum is characterized by a very smooth curve that predicts the measured activities with a standard deviation of 3.5% for the 24 sensors. Within the limitations of the computational model, the spectrum is also very close to that provided by MCNP (Monte Carlo Neutron Photon) calculations. >

Use of silicon bipolar transistors as sensors for neutron energy spectra determinations

Recent reevaluation of the neutron displacement damage function for silicon qualifies it as a sensor for spectra determinations. This development is especially useful in the critical energy region from 0.2 to 2.0 MeV where, in the absence of fission foils, there is a shortage of response functions needed to define spectra satisfactorily. How silicon bipolar devices can be used to improve neutron spectra determinations and therefore to better predict the displacement damage induced in devices is described. >

A rigorous treatment of self-shielding and covers in neutron spectra determinations

Most neutron spectrum determination methodologies ignore self-shielding effects in dosimetry foils and treat covers with an exponential attenuation model. This work provides a quantitative analysis of the approximations in this approach. It also provides a methodology for improving the fidelity of the treatment of the dosimetry sensor response to a level consistent with the users spectrum characterization approach. A library of correction functions for the energy-dependent sensor response has been compiled that addresses dosimetry foils/configurations in use at the Sandia National Laboratories Radiation Metrology Laboratory.

Neutron contribution to CaF/sub 2/:Mn thermoluminescent dosimeter response in mixed (n//spl gamma/) field environments

Thermoluminescent dosimeters (TLDs), particularly CaF/sub 2/:Mn, are often used as photon dosimeters in mixed (n//spl gamma/) field environments. In these mixed field environments, it is desirable to separate the photon response of a dosimeter from the neutron response. For passive dosimeters that measure an integral response, such as TLDs, the separation of the two components must be performed by postexperiment analysis because the TLD reading system cannot distinguish between photon- and neutron-produced response. Using a model of an aluminum-equilibrated TLD-400 (CaF/sub 2/:Mn) chip, a systematic effort has been made to analytically determine the various components that contribute to the neutron response of a TLD reading. The calculations were performed for five measured reactor neutron spectra and one theoretical thermal neutron spectrum. The five measured reactor spectra all have experimental values for aluminum-equilibrated TLD-400 chips. Calculations were used to determine the percentage of the total TLD response produced by neutron interactions in the TLD and aluminum equilibrator. These calculations will aid the Sandia National Laboratories-Radiation Metrology Laboratory (SNL-RML) in the interpretation of the uncertainty for TLD dosimetry measurements in the mixed field environments produced by SNL reactor facilities.

Effect of new cross section evaluations on neutron spectrum determination

Several neutron cross section libraries, such as ENDF/B-VI and IRDF-90, have been made available to the dosimetry community. Recommendations are made for the source selection of reaction cross sections that vary significantly among the libraries. In general, integral parameters from spectra obtained from unfold/adjustment codes using the cross sections will not significantly change. A 61-reaction compendium of dosimetry cross sections drawn from existing evaluations has been compiled for use at the Sandia National Laboratories Radiation Metrology Laboratory. This dosimetry library (SNLRML) is recommended for use in spectrum determination with unfold/adjustment methods. >

Estimation of 1-MeV equivalent neutron fluence from dosimetry responses without spectrum unfolding

The paper demonstrates the estimation of 1-MeV equivalent (Si) neutron fluence from radiometric monitor data without prior spectrum knowledge and without estimation of the neutron fluence spectrum. >

Simultaneous Evaluation of Neutron Spectra and 1-MeV-Equivalent (Si) Fluences at SPR-III and ACRR

Simultaneous least-squares adjustment of calculated neutron spectra in the central cavity of SPR-III and in the Pb-B4C bucket at ACRR is described, and the resulting 1-MeV-equivalent fluences are compared with damage measurements in 2N2222A transistors.