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Development of a neutron monitor for pulsed fields

In pulsed radiation fields, accurate determination of neutron radiation is often underestimated by saturation effects in the detectors. At the PTB, a moderator-type neutron monitor has been developed, which registers delayed beta rays from neutron-induced silver activation. The monitor uses four silicon diodes in the centre of a polyethylene moderator, 30 cm in diameter. Two of the diodes are covered by natural silver foils and two of them by tin foils. The latter are used to subtract photon-induced pulses. For registering signals, a pulse height threshold is set at 662 keV, which minimizes the effect of 137Cs and lower energy radiation and - in addition - enhances the detection of beta rays from the shorter half-life silver isotope 110Ag (25 s) as compared to the longer half-life isotope 108Ag (144 s).

A measurement using the prototype monitor AGREM (Fig. 1) in a high-intensity pulsed radiation field at the PSI accelerator showed that the monitor measured dose equivalent for pulses with high peak dose rates which are underestimated by commercial neutron monitors by several orders of magnitudes (Fig. 2).

The principal ideas are protected by patents. A battery-operated prototype with low-power microelectronics is under development. PTB is looking for a partner who overtakes the instrument via an industry transfer.

PTB prototype neutron monitor AGREM (Fig. 1) and results of measurements at PSI (Fig. 2)

References

  • Caresana, M., Denker, A., Esposito, A., Ferrarini, M., Golnik, N., Hohmann, E., Leuschner, A., Luszik-Bhadra, M., Manessi, G., Mayer, S., Ott, K., Röhrich, J., Silari, M., Trompier, F., Vilnhals, M. and Wielunski, M.:
    Intercomparison of radiation protection instrumentation in a pulsed neutron field
    Nucl. Instr. and Meth. A 737 (2014) 203 - 213

  • Luszik-Bhadra, M.; Hohmann, E.; Otto, Th.:
    A new neutron monitor with silver activation
    Radiat. Meas. 45 (2010) 1258 - 1262

  • Luszik-Bhadra, M. and Hohmann, E.:
    A new neutron monitor for pulsed fields at high-energy accelerators
    Proceedings of the IRPA Congress 2008, Buenos Aires, 20 - 24 October 2008

Patents

  • Luszik-Bhadra, M.; Hohmann, E.:
    Neutron dosimeter
    EP000002332985A2
  • Luszik-Bhadra, M.; Hohmann, E.:
    Neutronendosimeter
    DE 102008050731A1.
  • Luszik-Bhadra, M.; Hohmann, E.:
    Neutron dosimeter
    US020110180718A1
  • Luszik-Bhadra, M.; Hohmann, E.:
    Neutron dosimeter
    WO002010040330A3.