The Measurement of Neutron Energy Spectra in Different Licensed Facilities Using the Nested Neutron Spectrometer
Abstract of the technical paper/presentation presented at:
Meeting of the Task Force on Shielding Aspects of Accelerators, Targets and Irradiation Facilities
October 10, 2016
Canadian Nuclear Safety Commission
The Canadian Nuclear Safety Commission (CNSC) regulates many different types of accelerator facilities across Canada. To fulfill its mandate, the CNSC evaluates the shielding design of proposed facilities prior to issuing a licence to construct each facility. For complex facilities, Monte Carlo simulations are used to validate the applicant’s shielding design. Once facilities become operational, inspections are performed to verify compliance with applicable CNSC regulatory safety requirements. These inspections include verification of both photon and neutron dose rates in the facility.
The neutron spectrum has a major impact on the shielding design and resulting dose rates, but often this information is not available in any of the literature for a particular type of accelerator, so onsite measurements of the spectrum may be required. Traditionally, Bonner sphere systems (BSS) with activated foils and TLDs are used for this type of measurement.
The nested neutron spectrometer (NNS) is a recent invention by a Canadian company (DETEC, Gatineau, Quebec). Because of the design of the NNS, it is much less cumbersome to manipulate than a typical BSS. In addition, the NNS can operate in current-mode, which solves the problem of pulse pile-up in pulsed detectors, since the current is measured in a manner analogous to that used in an ionization chamber. The NNS detector was tested in five different types of accelerator facilities, including: a PET cyclotron facility, a medical linear accelerator radiotherapy facility, a proton therapy facility, a neutron generator facility and a neutron calibration facility. Neutron spectra obtained with the NNS were compared to Monte Carlo simulations for similar setups, and demonstrated reasonable agreement. In terms of dose measurement, neutron equivalent doses obtained with the NNS agreed very well with measurements made with bubble detectors. This presentation reviews some of the results of the neutron spectra measurements performed at these facilities.
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To read the paper, please see page 250 in Shielding Aspects of Accelerator, Target and Irradiation Facilities (SATIF) (PDF)
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