Radiation Shielding Group

This group study on how long radiation reaches in matter and how the radiation changes in matter.

Purpose and Vision

For the purpose of protection of human body and machine from radiation generated in accelerator, and application of radiation for medical and industrial areas, research on behavior of radiation in matter, such as scattering, penetration, absorption of radiation, and generation of heat and radioactivity by radiation, is indispensable. Development and improvement of a calculation system to simulate behavior of radiation in matter and precise measurement to verify the accuracy of the system are performed in collaboration with researchers in universities. These calculation systems are widely utilized in wide fields such as medical radiation area, accelerator engineering, and space engineering.


Development of general purpose electron and photon transport code EGS

This calculation code is developed to simulate electron and photon transport in an international collaboration between KEK, University of Michigan, and Stanford University. For the purpose of user support, workshop of 100 participants is held annually. Also, short course of 30-70 participants is held for beginner and advanced users at domestic places and overseas. Also, X ray scattering measurement using synchrotron is performed to improve the accuracy of low energy photon transport simulation.

image001.jpg Fig.1 A photograph of EGS short course held annually at KEK. Participants for medical application increase in recent years.

image002.jpg Fig.2 An example of EGS simulation on a behavior of electrons and photons in an X ray tube. Electron trajectory curves due to the effect of electric field.

Development of general purpose particle and heavy ion transport code PHITS
This calculation code is developed in a collaboration of JAEA、KEK、RIST. PHITS code simulates behavior of proton, neutron and heavy ion. An example of detailed calculation on particle therapy is shown in Fig.3. 12C of 400 MeV/u and its secondary particle generated in water is displayed in 100 pico second interval. Fig.3 shows a timing when 12C is stopped (1.55 nano second from z=0cm ), and particles after 300 pico second is shown in Fig.4. 1000 12C ions are entered in a beam of 5 mm diameter. Neutrons and protons are dominant at large angle, whereas 4He, neutron and proton are main component at forward direction.
Among many kind of radiation generated in accelerator, high energy neutron is the most difficult radiation to stop. For the purpose of measurement on performance of shielding with good precision and comparison with simulation, mono energy neutron is indispensable. Research Center for Nuclear Physics (RCNP) in University of Osaka has a facility to generate neutron of quasi mono energy at 100-400 MeV. Utilizing this facility, RCNP perform a research in collaboration with researchers from KEK, AIST, University of Kyoto, University of Tohoku, Riken, and University of Osaka. Also, calibration of neutron detector is performed, while researchers from CERN and other foreign institutes participate in this calibration activity. Snapshot of RCNP shielding experiment is shown in Fig.5. In Fig.6, neutron dose at a point of 1766 cm apart from Li target and its attenuation against shielding thickness is displayed for 250, 400 MeV Li(p,n) quasi mono energy neutron. Neutron dose is measured using several standard spectrometers and dosimeters which are used domestic and at overseas. Calculation is a tentative result (2011/2) in which dose is obtained from neutron energy spectrum after penetration of shielding.

Also, secondary neutron measurement was performed using 120 GeV proton at Fermi National Accelerator Laboratory in USA in collaboration with JAEA, KEK, University of Kyoto, and Shimizu cooperation for the purpose of measurement of accelerator shielding performance in a realistic geometry and verification of accuracy of simulation. Setup of JASMIN project and an example of result is shown in Fig 7 and Fig. 8, respectively. The analysis is on the secondary neutron from 120 GeV proton at Pbar target station at Fermi National Accelerator Laboratory. Measured value is amount of 203Bi, 204Bi, 205Bi, 206Bi which is produced by spallation reaction by secondary neutron inside 209Bi sample which locates on the 5 points above target. Measured value is compared with PHITS calculation. Calculation geometry is shown in Fig.7. Threshold energy for 209Bi is 23 MeV and 45 MeV for production of 203Bi, 206Bi, respectively. Thus amount of 203Bi, 206Bi is related to the amount of neutron above these energies. Good agreement of measurement and calculation regarding production and attenuation of neutron above these energies is shown in Fig. 8.