Thermal neutron detection using a silicon pad detector and 6LiF removable converters

Abstract

A semiconductor detector coupled with a neutron converter is a good candidate for neutron detection, especially for its compactness and reliability if compared with other devices, such as (3)He tubes, even though its intrinsic efficiency is rather lower. In this paper we show a neutron detector design consisting of a 3 cm × 3 cm silicon pad detector coupled with one or two external (6)LiF layers, enriched in (6)Li at 95%, placed in contact with the Si active surfaces. This prototype, first characterized and tested at INFN Laboratori Nazionali del Sud and then at JRC Ispra, was successfully shown to detect thermal neutrons with the expected efficiency and an outstanding gamma rejection capability.

Characterization of the silicon+6LiF thermal neutron detection technique

“…We have already proved that this detector can be operated in such a double-converter configuration [10], but for the current tests we have chosen to use it in single-converter configuration to simplify the installation and replacement of the several substrates used. The detector, with and without a converter installed, is shown in Figure 1.…”

“…The layer thickness was measured by means of the change in the oscillation frequency of a quartz as the 6 LiF is evaporated onto it [11]. The reliability of the thickness measurements was checked by measuring the energy loss of alpha particles from a known source when crossing a converter layer deposited onto a suitably thin known substrate [10]. The thickness precision resulted of the order of a few percent, as well as its uniformity, checked on 5 different points.…”

“…One of the possibilities is the use of a semiconductor-based charged particle detector in combination with a neutron reactive film which converts neutrons into other detectable radiation [3]- [9]. Several principle studies have been done about this technique, and we have recently proved its feasibility by using commercial 3cm x 3cm silicon detectors coupled with thin layers of 6 LiF, where the 6 Li acts as converter due to its 940 b cross section to thermal neutrons [10]. The energy spectrum measured by the silicon detectors in such a configuration has a typical shape, and should allow to easily discriminate the capture reaction products from the background gamma rays.…”

HELNED: Helium-3-free low-cost neutron detectors

“…As for the detection efficiency, it depends on the energy loss of the two reaction products inside the converter itself and in the dead layer of the silicon detector, and on the electronic threshold. An accurate calculation was performed in [8], giving a value around 75%. Under the described configuration a thermal neutron impinging on the detector will have a ≈1.5% probability of being detected.…”

Study of silicon+ 6 LiF thermal neutron detectors: GEANT4 simulations versus real data

“…In a previous paper [7] it was shown that the use of a fully depleted silicon charged particle detector, in combination with a 6 LiF neutron converter film, can be successfully exploited to detect thermal neutrons with a reasonable efficiency, as also suggested by other authors [8], [9]. The neutron conversion mechanism is based on the well known reaction (1) which is the only possible decay channel following the neutron capture in 6 Li, and is free of gamma rays.…”