Determining soil contamination profiles from intensities of capture-gamma rays using above-surface neutron sources.

Four methods are presented to estimate contaminant concentration profiles in soil from the intensities of neutron-induced capture-gamma photon intensities measured at the soil surface. In particular, the method of linear regularization with and without an iterative positivity constraint, the Backus-Gilbert method, and the maximum entropy method are applied to the soil contamination problem. Example results obtained with the four methods are given for photon intensities calculated for idealized test contaminant profiles in soil irradiated by neutron sources above the surface.

Determining soil contamination profiles from intensities of capture-gamma rays using above-surface neutron sources.

Four methods are presented to estimate contaminant concentration profiles in soil from the intensities of neutron-induced capture-gamma photon intensities measured at the soil surface. In particular, the method of linear regularization with and without an iterative positivity constraint, the Backus-Gilbert method, and the maximum entropy method are applied to the soil contamination problem. Example results obtained with the four methods are given for photon intensities calculated for idealized test contaminant profiles in soil irradiated by neutron sources above the surface.

Absorbed doses to skin from radionuclide sources on the body surface.

Beta-particle and electron doses are reported for radionuclides on the skin surface. Upper and lower bounds on doses are based on Monte Carlo calculations that include or exclude electron scattering in air, respectively. Upper bounds agree well with results of point-kernel calculations performed by others.

Dosimetry calculations for concentric cylindrical source and target regions with application to blood vessels.

Geometry factors are derived for source and target regions consisting of concentric circular cylinders and cylindrical shells. Line-source kernels are derived from point kernels for monoenergetic electrons and photons. The geometry factors and line-source kernels are then combined to yield electron and photon absorbed fractions that, in turn, are used to calculate conversion factors for dose rates in blood vessel walls from radionuclides in the blood. Example calculations are presented for selected radionuclides and for blood vessels of three representative sizes.

Simulation of angular and energy distributions of the PTB beta secondary standard.

Calculations and measurements have been performed to assess radiation doses delivered by the PTB Secondary Standard that employs 147Pm, 204Tl, and 90Sr:90Y sources in prescribed geometries, and features "beam-flattening" filters to assure uniformity of delivered doses within a 5-cm radius of the axis from source to detector plane. Three-dimensional, coupled, electron-photon Monte Carlo calculations, accounting for transmission through the source encapsulation and backscattering from the source mounting, led to energy spectra and angular distributions of electrons penetrating the source encapsulation that were used in the representation of pseudo sources of electrons for subsequent transport through the atmosphere, filters, and detectors. Calculations were supplemented by measurements made using bare LiF TLD chips on a thick polymethyl methacrylate phantom. Measurements using the 204Tl and 90Sr:90Y sources revealed that, even in the absence of the beam-flattening filters, delivered dose rates were very uniform radially. Dosimeter response functions (TLD:skin dose ratios) were calculated and confirmed experimentally for all three beta-particle sources and for bare LiF TLDs ranging in mass thickness from 10 to 235 mg cm-2.