Speaker
Description
NanoTerasu is a 3-GeV synchrotron radiation facility in Japan that has been routinely operated at the design beam current of 400 mA since November 2025. In electron storage rings, gas bremsstrahlung produced by interactions between stored electrons and residual gas molecules is unavoidable, and thus shielding against both high-energy photons and photoneutrons is essential. The shielding design of NanoTerasu was evaluated using analytical calculations based on residual gas composition and PHITS Monte Carlo simulations. To validate these calculations and benchmark PHITS simulations, we performed the first direct measurements of gas bremsstrahlung at NanoTerasu.
We installed a $3\times3$ array of CsI(Tl) scintillation detectors ($5\times5\times30$ cm$^3$ each) to capture the lateral development of electromagnetic showers induced by gas bremsstrahlung downstream of a long straight section of the storage ring. Plastic scintillators were additionally used for charged-particle discrimination, and a lead absorber with selectable thicknesses was placed in front of the detector array to suppress low-energy photons. Charge signals from the CsI detectors were recorded using a mesytec MDPP-16-QDC digitizer during routine beam operation periods.
Reliable energy calibration from the MeV to GeV region was achieved using $^{60}$Co and $^{137}$Cs $ \gamma$-ray sources, environmental radiation peaks, and energy-deposition peaks of cosmic-ray muons [1]. Energy-calibrated gas-bremsstrahlung spectra were compared with PHITS calculations of energy deposits in the CsI detectors. The presentation will discuss the measurement and calibration procedures, and a systematic comparison between measured and simulated spectra under various lead-shielding conditions. These measurements are expected to establish a basis for future quantitative validation of gas-bremsstrahlung simulations and the associated shielding design at NanoTerasu.
[1] Hayakawa et al., “Energy Calibration of CsI(Tl) Scintillation Detectors for Gas Bremsstrahlung Measurement at NanoTerasu”, Proceedings of the 40th Workshop on Radiation Detectors and Their Uses, KEK Proceedings 2026-3, 108-120 (2026).
| Topics | T4. Shielding and dosimetry |
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