Silicon detectors for the n-TOF neutron beams monitoring

TL;DR

This paper presents silicon-based neutron beam diagnostic devices with neutron converter foils for monitoring flux and profile across a wide energy range at CERN's n-TOF facility, overcoming gamma flash issues.

Contribution

Introduction of two silicon detector-based devices for neutron beam monitoring, capable of energy-resolved flux and profile measurements, suitable for high-intensity neutron beams at CERN.

Findings

Devices successfully characterized with radioactive sources.

Effective operation in high-intensity neutron environments.

Immediate deployment at CERN's n-TOF experimental areas.

Abstract

During 2014 the second experimental area EAR2 was completed at the n-TOF neutron beam facility at CERN. As the neutrons are produced via spallation, by means of a high-intensity 20 GeV pulsed proton beam impinging on a thick target, the resulting neutron beam covers an enormous energy range, from thermal to several GeV. In this paper we describe two beam diagnostic devices, designed and built at INFN-LNS, both exploiting silicon detectors coupled with neutron converter foils containing 6Li. The first one is based on four silicon pads and allows to monitor the neutron beam flux as a function of the neutron energy. The second one, based on position sensitive silicon detectors, is intended for the reconstruction of the beam profile, again as a function of the neutron energy. Several electronic setups have been explored in order to overcome the issues related to the gamma flash, namely a huge pulse present at the start of each neutron bunch which may blind the detectors for some time. The two devices have been characterized with radioactive sources at INFN-LNS and then tested at n-TOF. The wide energy and intensity range they proved capable of sustaining, made them quite attractive and suitable to be used in both EAR1 and EAR2 n-TOF experimental areas, where they became immediately operational.