David K. Miko

A method for correcting NaI spectra for attenuation losses in hand-held instrument applications

In this paper we present the gross-count material basis set (GC-MBS) method for estimating transmission losses in measurements of radionuclides using low-resolution gamma-ray detectors such as NaI or CdZnTe. The application to continuum-subtracted peaks measured with high-purity Ge detectors is also discussed. To illustrate the method, we apply it to the correction of spectra from enriched uranium that have been distorted by various intervening absorbers. We also examine the application to simultaneous determination of the uranium enrichment through an unknown absorber using an NaI detector.

An innovative method for extracting isotopic information from low-resolution gamma spectra

Abstract A method is described for the extraction of isotopic information from attenuated gamma-ray spectra using the gross-count material basis set (GC-MBS) model. This method solves for the isotopic composition of an unknown mixture of isotopes attenuated through an absorber of unknown material. For binary isotopic combinations the problem is nonlinear in only one variable and is easily solved using standard line optimization techniques. Results are presented for NaI spectrum analyses of various binary combinations of enriched uranium, depleted uranium, low burnup Pu, 137 Cs, and 133 Ba attenuated through a suite of absorbers ranging in Z from polyethylene through lead. The GC-MBS method results are compared to those computed using ordinary response function fitting and with a simple net peak area method. The GC-MBS method was found to be significantly more accurate than the other methods over the range of absorbers and isotopic blends studied.

Estimation of obliquely scattered gamma-ray response functions in the gross-count tomographic gamma scanner (GC-TGS) method

It was recently shown that a logarithmic response-function technique based on the material basis set (MBS) formalism used in the tomographic gamma scanner (TGS) method allows gross spectra from NaI detectors to be used in both measuring MBS transmission corrections using external transmission sources and in applying the corrections to emission spectra to arrive at radionuclide mass estimates. In this work we have attempted to show that addition of the oblique scatter component can increase the accuracy of the GC-TGS measurements with both NaI and high-purity germanium detectors. This paper describes the formalism behind the GC-TGS method and the improvement achieved in the analysis by including the scatter component.