Automated MCNP photon source generation for arbitrary configurations of radioactive materials and first-principles calculations of photon detector responses

Abstract

A patch to the Los Alamos Monte Carlo code MCNP has been developed that automates the generation of source descriptions for photons from arbitrary mixtures and configurations of radioactive isotopes. Photon branching ratios for decay processes are obtained from national and international data bases and accessed directly from computer files. Code user input is generally confined to readily available information such as density, isotopic weight fractions, atomic numbers, etc. of isotopes and material compositions. The availability of this capability in conjunction with the "generalized source" capability of MCNP Version 3A makes possible the rapid and accurate description of photon sources from complex mixtures and configurations of radioactive materials, resulting in improved radiation transport predictive capabilities. This capability is combined with a first-principles calculation of photon spectrometer response-functions for Nal, BGO, and HPGe for £ 7 < 1 MeV,

Absolute calibration in vivo measurement systems

“…Monte Carlo techniques have previously been used to compute absolute measurement efficiencies for in vivo measurement systems. [6][7][8] However, these previous computations used theoretical phantoms that were physiologically inadequate (e.g., both lungs were of equal size). Biomedical imaging will provide an exact replica tion of the individual physiology.…”

Recent MCNP developments

“…• Next-event estimators such as point detectors and the • The source model will include intrinsic radiation DXTRA.N variance reduction scheme can now be used sources [12] to model radioactive decay. with S(c_, ft) thermal scattering.…”

A simple ionizing radiation spectrometer/dosimeter based on radiation sensing field effect transistors (RadFETs)

“…The model-based RadFET array design consists of four elements with two metal filters for blocking low energy photons below two energy levels, a thin foil for amplifying the low energy photons through dose enhancement effects, and a bare (epoxy coated) device for measuring photons from the entire energy spectrum. composition of some arrangement of special nuclear materia1 (SNM), the MCNP code computes the distribution of photons emitted due the decay of the radioactive materials [4]. The code keeps track of the energy, spatial, and angular distribution of the emitted photons and accounts for.…”