Characterization of high-energy neutron calibration fields on external facilities

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At PTB’s accelerator facility PIAF, neutrons with a maximum energy of 20 MeV are produced. For many purposes, neutrons of higher energies are required. Among these are, for example, the development of measuring instruments for the improvement of radiation protection at high-energy accelerators, for radiation therapy with high-energy particles or for space missions. Another example is the investigation of nuclear reactions which contribute to the background caused by cosmogenic neutrons in the experiments of neutrino physics.

For such tasks, PTB utilizes the accelerator facility at the iThemba Laboratory for Accelerator Based Sciences (iThemba LABS) in Cape Town. There, collimated neutron beams can be produced in the energy range from approx. 35 MeV to 200 MeV using the ⁷Li(p,n) reaction. In contrast to the monoenergetic calibration fields at PTB, the neutron beams at the iThemba LABS are quasi-monoenergetic, i.e., they have a high-energy intensity maximum and an adjacent low-energy continuum.

Quasi-mono-energetic energy distribution of high-energy neutron fields produced at the facility of iThemba LABS. The width of the high-energy maximum is partly determined by the time resolution of the time-of-flight measurement.

Due to the large distance and the considerable logistic effort, experiments at the facility in Cape Town can be carried out at larger time intervals only. They are only realized in cooperation with the South-African partners and after a positive assessment by the programme committee of iThemba LABS.

PTB is putting effort into the modernization of the neutron beam facility at iThemba LABS in cooperation with the French metrology institute IRSN and iThemba LABS. Furthermore the operation of the beam line is to be placed on a new contractual basis.

Literature

• H. Harano and R. Nolte:
  Quasi-monoenergetic neutron standards above 20 MeV
  Metrologia 48 (2011) S292-S303
  
  
• M. Mosconi, E. Musonza, A. Buffler, R. Nolte, S. Röttger, F.D. Smit:
  Characterisation of the high-energy neutron beam at iThemba LABS
  Radiat. Meas. 45 (2010) 1342-1345