Speaker
Description
In high-energy accelerator facilities, severe radiation exposure may occur in accidental scenarios, such as personnel being inadvertently left inside an accelerator tunnel during beam operation or unexpected beam delivery. Personal dosimeters may provide essential information for estimating the received dose after such events. However, the reliability of dose assessment using personal neutron dosimeters under extremely high-dose and high-energy mixed radiation fields has not yet been fully established.
Monte Carlo simulations have been widely used to evaluate complex high-energy radiation fields in accelerator facilities. Nakao et al. measured high-energy neutron streaming through an access maze at the CERN High-energy AcceleRator Mixed-field (CHARM) facility using activation detectors and showed that Monte Carlo simulations can reasonably reproduce the measured radiation field [1]. In the present study, PHITS simulations were used to calculate neutron dose values for comparison with CR-39 measurements.
An irradiation experiment with CR-39 personal neutron dosimeters was conducted in the access maze of the CERN/CHARM. The neutron doses evaluated from the CR-39 dosimeters were compared with the calculated neutron dose values. In the typical neutron response energy range of CR-39, from 25 keV to 15 MeV, the measured and calculated doses agreed within a factor of 1.9. When the comparison was extended to a wider neutron energy range from 0.025 eV to 1 GeV, the agreement remained within a factor of 2.5.
In addition to the dose comparison, microscope images of the chemically etched CR-39 detectors were further analyzed to investigate track features possibly related to high-energy neutron interactions. Pit candidates were extracted using a simplified image analysis method based on size and shape features. Multi-charged-particle candidates relevant to observable etched pits were selected from PHITS T-Product dump data by combining particle type, energy, emission direction, and generation position with SRIM-based LET and stopping range in CR-39. The PHITS results indicated that such candidates were mainly associated with neutrons above approximately 10 MeV.
Some observed multi-pit clusters showed spatial patterns similar to the multi-charged-particle topologies predicted by PHITS. These results suggest that topology-based information from CR-39 microscope images may complement conventional track-count-based dose evaluation and help interpret observed track features in relation to high-energy neutron-induced charged-particle production predicted by Monte Carlo simulations.
[1] Measurements and Monte Carlo simulations of high-energy neutron streaming through the access maze using activation detectors at 24 GeV/c proton beam facility of CERN/CHARM, N. Noriaki, et al., J Nucl Sci Technol. 2021;58(8):899–907.
| Topics | T4. Shielding and dosimetry |
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