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Neutron monitor AGREM – test measurements in pulsed radiation fields

  • Metrology for Society

The AGREM neutron monitor [1] records the delayed beta radiation of neutron-induced silver activation. The monitor uses four silicon diodes in the centre of a polyethylene moderating sphere of 30 cm in diameter. Two of these diodes are surrounded with silver foil and the other two with tin foil. The diodes covered in silver foil are sensitive to neutron and photon radiation. The diodes covered in tin foil are only sensitive to photon radiation and serve to subtract the photon-induced signals from the results obtained by the diodes covered in silver foil. In addition, low-energy photon radiation (< 662 keV) is suppressed over a threshold in the pulse-height spectrum of the diodes. Furthermore, by setting the pulse-height threshold, the detection of the beta radiation of the silver isotope 110Ag (half-life: 25 s, Emax = 2.9 MeV), which has a slightly higher energy – compared to the beta radiation of the silver isotope 108Ag (half-life: 144 s, Emax = 1.7 MeV), is enhanced. For the principle of this procedure (see Patents 1 to 4), a patent application has been filed.

Figure 1 shows the prototype of the AGREM neutron monitor. The pulse-height signals are pre-amplified in the detector capsule in the centre of the moderator and are then processed further via a conventional nuclear electronic unit (main amplifier, pulse-height analyzer). A battery-operated monitor, equipped with a low-consumption microelectronic unit, is being developed.

Over the past few years, several test measurements have been carried out with the prototype of the AGREM neutron monitor:

  • At the PSI in Villigen (Switzerland), irradiations were carried out where a proton beam (590 MeV, current: from 0.01 mA to 1.0 mA) hit a tungsten target of 1 mm thickness. The pulse was applied for a duration from 5 ms to 25 ms. The monitors (AGREM and the commercially available device LB6411) were located at a distance of 60 cm from the target, vertically to the beam direction. Figure 2 shows the results displayed by the monitors. The AGREM monitor shows a practically linear behaviour at increasing current, whereas the LB6411 monitor underestimates the neutron dose by several orders of magnitude [2].
  •  At the electron storage rings BESSY and MLS (both located in Berlin), irradiations were performed in which electrons (1.7 GeV at BESSY and 100 MeV at the MLS) hit a closed valve (6 mm steel at BESSY and 20 mm aluminium at the MLS) with a repetition rate of 10 Hz. The pulse widths were in the ns range. The neutron monitors (the commercially available device BIOREM: versions A and B with different amplifiers, LB6419 and AGREM) were mounted vertically to the beam direction at a distance of 1 m from the target. Whereas BIOREM A, for instance, underestimated the dose equivalent by up to a factor of 20, the AGREM monitor did not underestimate the dose equivalent [3].
  • At the HZB, irradiations were carried out where a proton beam (68 MeV, 100 Hz, pulse widths from 1 µs to 40 µs) hit a tungsten target of 20 mm thickness. The neutron monitors (14 different devices) were irradiated at a distance of 50 cm from the target in forward direction. The AGREM neutron monitor and the REM-2 recombination chamber exhibited a linear behaviour at increasing charge per pulse. A monitor based on a current amplifier (LUPIN) showed a nearly linear behaviour, whereas all the other monitors deviated strongly from the linear behaviour [4].



Fig. 1:  Prototype of the AGREM neutron monitor.


Fig. 2:  Measurement of the dose equivalent H*(10) as a function of the proton current, with the neutron monitors AGREM and LB6411.


  1. Luszik-Bhadra, M. und 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,
    (http://www.irpa12.org.ar/fullpapers/FP3384.pdf), letzter Zugriff am 21.11.2013.
  2. Luszik-Bhadra, M.; Hohmann, E. and Otto, Th.:
    A new neutron monitor with silver activation
    Radiat. Meas. 45 (2010) 1258-1262
  3. Ott, K.; Helmecke, M.; Luszik-Bhadra, M.; Martin, M. und Weber A.:
    Dead-time effects of neutron detectors due to pulsed radiation
    Radiation Prot. Dosim. 155 (2013) 125-140
  4. 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.; Volnhals, M.; Wielunski, M.:
    Intercomparison of radiation protection instrumentation in a pulsed neutron field
    Nucl. Instr. and Meth. A, submitted (2013).


  1. Luszik-Bhadra, M.; Hohmann, E.: Neutronendosimeter, DE 102008050731A1.
  2. Luszik-Bhadra, M.; Hohmann, E.: Neutron dosimeter, EP000002332985A2
  3. Luszik-Bhadra, M.; Hohmann, E.: Neutron dosimeter, US020110180718A1
  4. Luszik-Bhadra, M.; Hohmann, E.: Neutron dosimeter, WO002010040330A3.


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