Environment scattering in GADRAS.

Abstract

Radiation transport calculations were performed to compute the angular tallies for scattered gamma-rays as a function of distance, height, and environment. Green's Functions were then used to encapsulate the results a reusable transformation function. The calculations represent the transport of photons throughout scattering surfaces that surround sources and detectors, such as the ground and walls. Utilization of these calculations in GADRAS (Gamma Detector Response and Analysis Software) enables accurate computation of environmental scattering for a variety of environments and source configurations. This capability, which agrees well with numerous experimental benchmark measurements, is now deployed with GADRAS Version 18.2 as the basis for the computation of scattered radiation.

GADRAS Detector Response Function.

“…Green's functions are used to interpolate MCNP calculations to estimate the profile of scatter radiation as a function of source-detector distance, detector height, and environment clutter [8].…”

“…The resolution at 661 keV is the same according to Eqs. (6) through (8), so transitions vary smoothly with energy.…”

“…GADRAS applies Eqs. (6) through (8) to compute the resolution for all types of detectors, but parameters that are displayed on the detector response function parameter page (see Figure 8) display values according to common conventions. Accordingly, the resolution parameter is represented in units of keV at 1332 keV for HPGe detectors; the resolution is specified as a percent of FWHM at 661 keV for other types of detectors.…”

GADRAS-DRF 18.5 User's Manual.

“…Neutron detector response is computed by interpolating on a pre-computed database of thermal ( 3 He) detector responses [5] [6]. For both gamma-ray and neutron detectors, the response to radiation that scatters into the detector from the surrounding environment is determined by a combination of first-principals calculations and empirical modeling [7]. For new detectors, known detector parameters such as size and resolution are all that is necessary to compute an initial response function.…”

“…This option allows users to select and view gamma-ray peak energies and yields for selected isotopes in the library. Figure 53 shows the Isotope DB form populated with information for 7 Be. The drop-down list at the topleft corner of the window allows users to select an isotope.…”