Monte Carlo Based Method for Conversion of In-Situ Gamma Ray Spectra Obtained with a Portable Ge Detector to an Incident Photon Flux Energy Distribution

Abstract

A Monte Carlo based method for the conversion of an in-situ gamma-ray spectrum obtained with a portable Ge detector to photon flux energy distribution is proposed. The spectrum is first stripped of the partial absorption and cosmic-ray events leaving only the events corresponding to the full absorption of a gamma ray. Applying to the resulting spectrum the full absorption efficiency curve of the detector determined by calibrated point sources and Monte Carlo simulations, the photon flux energy distribution is deduced. The events corresponding to partial absorption in the detector are determined by Monte Carlo simulations for different incident photon energies and angles using the CERN's GEANT library. Using the detector's characteristics given by the manufacturer as input it is impossible to reproduce experimental spectra obtained with point sources. A transition zone of increasing charge collection efficiency has to be introduced in the simulation geometry, after the inactive Ge layer, in order to obtain good agreement between the simulated and experimental spectra. The functional form of the charge collection efficiency is deduced from a diffusion model.

Decommissioning a phosphoric acid production plant: a radiological protection case study

“…Based on the above and in particular for phosphogypsum usage as soil conditioner, GAEC has established a concentration limit for 226 Ra equal to 400 Bq/kg (GAEC's Decision 414/875/2001, 2001. For the scrap metals, the criteria used for their recycling, with no further restrictions, were based on the EC recommended radiological protection criteria for the recycling of metals from the dismantling of nuclear installations (EC Publications RP 89, 1998).…”

“…To be in compliance with the legislative provisions mentioned before, the dose criterion for metals recycling was converted to specific activity through dosimetric models (GAEC Sub/01/325929/2004, GAEC, 2004Clouvas et al, 1998). The scenarios took into account the entire sequence of scrap processing, starting with transport and handling of the scrap metal up to exposure from consumer goods made of recycled metal.…”

“…Members of the public might be exposed to external radiation from gamma emitting radioisotopes retained in the final product. The above scenario resulted to the assumption that if the specific activity of 226 Ra was less than 300 Bq/kg, the object could be used for recycling (GAEC Sub/01/325929/2004, GAEC, 2004Clouvas et al, 1998).…”

“…3. Use the phosphogypsum as a soil conditioner (GAEC's Decision 414/875/2001, 2001, provided that the activity concentrations are within the allowed limits. 4.…”

Characteristics of signals originating near the lithium-diffused N+ contact of high purity germanium p-type point contact detectors

“…In 1989, Clouvas et al [19] noted that the efficiency measurements for their detector yielded a dead layer thickness of 2.5 mm that did not agree with the value of 0.5 mm provided by the manufacturer. They additionally found that in order to model the energy spectrum from their p-type coaxial detector at low energies, they needed to include a transition layer where partial charge collection occurred.…”