DOI QR코드

DOI QR Code

Activation Reduction Method for a Concrete Wall in a Cyclotron Vault

  • Received : 2016.10.04
  • Accepted : 2017.08.22
  • Published : 2017.09.30

Abstract

Background: The concrete walls inside the vaults of cyclotron facilities are activated by neutrons emitted by the targets during radioisotope production. Reducing the amount of radioactive waste created in such facilities is very important in case they are decommissioned. Thus, we proposed a strategy of reducing the neutron activation of the concrete walls in cyclotrons during operation. Materials and Methods: A polyethylene plate and B-doped Al sheet (30 wt% of B and 2.5 mm in thickness) were placed in front of the wall in the cyclotron room of a radioisotope production facility for pharmaceutical use. The target was Xe gas, and a Cu block was utilized for proton dumping. The irradiation time, proton energy, and beam current were 8 hours, 30 MeV, and $125{\mu}A$, respectively. To determine a suitable thickness for the polyethylene plate set in front of the B-doped Al sheet, the neutron-reducing effects achieved by inserting such sheets at several depths within polyethylene plate stacks were evaluated. The neutron fluence was monitored using an activation detector and 20-g on de Au foil samples with and without 0.5-mm-thick Cd foil. Each Au foil sample was pasted onto the center of a polyethylene plate and B-doped Al sheet, and the absolute activity of one Au foil sample was measured as a standard using a Ge detector. The resulting relative activities were obtained by calculating the ratio of the photostimulated luminescence of each foil sample to that of the standard Au foil. Results and Discussion: When the combination of a 4-cm-thick polyethylene plate and B-doped Al sheet was employed, the thermal neutron rate was reduced by 78%. Conclusion: The combination of a 4-cm-thick polyethylene plate and B-doped Al sheet effectively reduced the neutron activation of the investigated concrete wall.

References

  1. Fujibuchi T, Nohtomi A, Baba S, Sasaki M, Komiya I, Umedzu Y, Honda H. Distribution of residual long-lived radioactivity in the inner concrete walls of a compact medical cyclotron vault room. Ann. Nucl. Med. 2015;29:84-90. https://doi.org/10.1007/s12149-014-0918-6
  2. Ogata Y, Ishigure N, Mochizuki S, Ito K, Hatano K, Abe J, Miyahara H, Masumoto K, Nakamura H. Distribution of thermal neutron flux around a PET cyclotron. Health Phys. 2011;100:S60-S66. https://doi.org/10.1097/HP.0b013e3182004d89
  3. Masumoto K, Miura T, Bessho K, Matsumura H, Toyoda A, Wang Q, Shibata T. Evaluation of radioactivity in concrete samples obtained from various accelerator facilities. Asian and Oceanic Congress for Radiation Protection (AOCRP)-II. Bejing, China. October 9-13, 2006.
  4. Wang Q, Masumoto K, Bessho K, Matsumura H, Miura T, Shibata T. Evaluation of the radioactivity in concrete from accelerator facilities. J. Radioanal. Nucl. Chem. 2007;273:55-58. https://doi.org/10.1007/s10967-007-0710-3
  5. Masumoto K, Toyoda A, Eda K, Izumi Y, Shibata T. Evaluation of radioactivity induced in the accelerator building and its application to decontamination work. J. Radioanal. Nucl. Chem. 2003;255:465-469. https://doi.org/10.1023/A:1022511811356
  6. Kinno M, Kimura K, Ishikawa T, Nakamura T. Studies on induced activities and target nuclei in low-activation concrete structure for thermal neutron irradiation. J. Nucl. Sci. Technol. 2000;30(1):821-826.
  7. Masumoto K, Toyoda A, Eda K, Ishihara T. Measurement of the spatial distribution of neutrons in an accelerator room by the combination of activation detectors and an imaging plate. Radiat. Safety Manage. 2002;1:12-16. https://doi.org/10.12950/rsm2002.1.12
  8. Masumoto K, Iijima K, Toyoda A, Wang Q. Evaluation of imaging plate technique coupled with activation detector as the passive neutron monitor. J. Radioanal. Nucl. Chem. 2007;271:297-303. https://doi.org/10.1007/s10967-007-0207-0