Neutron dose measurements with the GSI ball at high-energy accelerators

Abstract

A moderator-type neutron monitor containing pairs of TLD 600/700 elements (Harshaw) modified with the addition of a lead layer (GSI ball) for the measurement of the ambient dose equivalent from neutrons at medium- and high-energy accelerators, is introduced in this work. Measurements were performed with the Gesellschaft für Schwerionenforschung (GSI) ball as well as with conventional polyethylene (PE) spheres at the high-energy accelerator SPS at European Organization for Nuclear Research [CERN (CERF)] and in Cave A of the heavy-ion synchrotron SIS at GSI. The measured dose values are compared with dose values derived from calculated neutron spectra folded with dose conversion coefficients. The estimated reading of the spheres calculated by means of the response functions and the neutron spectra is also included in the comparison. The analysis of the measurements shows that the PE/Pb sphere gives an improved estimate on the ambient dose equivalent of the neutron radiation transmitted through shielding of medium- and high-energy accelerators.

Optimization of a neutron dosimeter for the high energy accelerators

“…The energy dependence of the capture cross sections for 3 He and 6 Li are pretty similar and our simulations showed that exchange of a TLD card with a 3 He proportional counter is possible. Exchanging the sensitive element of the dosimeter in studied layouts should provide close relative read-out.…”

“…The method calculating the amount of e.g. 3 H -particles is very suitable to estimate the dose reading of active detectors, where the dose is calculated as a number of pulses. Each pulse corresponds to a neutron capture event.…”

“…As a couple of tests we have also performed some simulations for active 3 He dosimeters where neutrons are detected in the 3 He(n, p) 3 H reaction. Again we used also the absorption energy for detection and as usually both methods of isotope counting and energy deposition calculations gave the same response characteristics of the investigated dosimeter layouts.…”

“…Exchanging the sensitive element of the dosimeter in studied layouts should provide close relative read-out. Of course the response characteristics are influenced by the size of the 3 He tube as well as by the gas pressures of the counter. The active dosimeter prototypes are to be tested in the near future.…”

“…The position of the ion losses in the beam line are often unpredictable and time dependent thus an accumulative dose measurement of the ambient dose is preferred for monitoring over a wide area. This and necessity in a reliable measurements during a long period, for instance one year, can be provided with thermoluminescence detector (TLD) based dosimeters [2,3]. In the TLD cards the neutrons are detected via a 6 Li(n, α) 3 H reaction whose cross section increases for low energy neutrons.…”