In Situ Gamma Spectrometry Measurements and Monte Carlo Computations for the Detection of Radioactive Sources in Scrap Metal

Abstract

A very limited number of field experiments have been performed to assess the relative radiation detection sensitivities of commercially available equipment used to detect radioactive sources in recycled metal scrap. Such experiments require the cooperation and commitment of considerable resources on the part of vendors of the radiation detection systems and the cooperation of a steel mill or scrap processing facility. The results will unavoidably be specific to the equipment tested at the time, the characteristics of the scrap metal involved in the tests, and to the specific configurations of the scrap containers. Given these limitations, the use of computer simulation for this purpose would be a desirable alternative. With this in mind, this study sought to determine whether Monte Carlo simulation of photon flux energy distributions resulting from a radiation source in metal scrap would be realistic. In the present work, experimental and simulated photon flux energy distributions in the outer part of a truck due to the presence of embedded radioactive sources in the scrap metal load are compared. The experimental photon fluxes are deduced by in situ gamma spectrometry measurements with portable Ge detector and the calculated ones by Monte Carlo simulations with the MCNP code. The good agreement between simulated and measured photon flux energy distributions indicate that the results obtained by the Monte Carlo simulations are realistic.

Passive neutron detection for interdiction of nuclear material at borders

“…A number of detector materials, such as 6 LiI or 3 He, have large low-energy neutron cross-sections that vary inversely with the neutron velocity. The high sensitivity of detectors based on these materials to slow neutrons can be advantageous since the lower energy neutrons may more likely be encountered in the search for illicit sources due to moderation from cargo.…”

“…Radiation portal monitor (RPM) systems have been deployed to detect illicit trafficking in radioactive materials at international border crossings over the last several years [1]. Such systems have also long been used for safeguards applications [2] and for screening of scrap metal [3]. These large, passive detection systems are currently based upon panels of polyvinyl toluene plastic scintillator for gammaray detection and pressurized 3 He-based neutron detector tubes.…”

“…Such systems have also long been used for safeguards applications [2] and for screening of scrap metal [3]. These large, passive detection systems are currently based upon panels of polyvinyl toluene plastic scintillator for gammaray detection and pressurized 3 He-based neutron detector tubes. Radiation alarm algorithms used in such systems are typically based upon the net-counts above background observed in the gamma-ray or neutron detectors.…”

Fogging in polyvinyl toluene scintillators used in outdoor environments

“…Such detectors have also long been used for safeguards applications and for screening of scrap metal [3]. It has been observed that large polyvinyl toluene (PVT)-based gamma ray detectors can suffer internal "fogging" when subject to years of outdoor exposure, resulting in changes to performance.…”

Monte Carlo simulation of portal detectors of a steel factory. Comparison of measured and simulated response

“…The determination of the minimum detection limits (MDL) of homogeneously contaminated scrap metal or of shielded sources embedded in scrap metal loads is currently an important topic of research and investigation [1]. Furthermore, the estimation of the radiological risk for both workers and public in the case that a non-detectable radioactive source enters the manufacturing process is of great interest.…”