Head of Press and Information Office
Dr. Dr. Jens Simon
Phone: +49 531 592-3005
Email:
jens.simon(at)ptb.de
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:
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.
Literature:
Patents:
Dr. Dr. Jens Simon
Phone: +49 531 592-3005
Email:
jens.simon(at)ptb.de
Karin Conring
Phone: +49 531 592-3006
Fax: +49 531 592-3008
Email:
karin.conring(at)ptb.de
Physikalisch-Technische Bundesanstalt
Bundesallee 100
38116 Braunschweig