High energy particle background at neutron spallation sources and possible solutions

N Cherkashyna,G Greene,P M Bentley,R Connatser,U Filges,J Carpenter,K Herwig,G Ehlers,R Hall-Wilton,T Kittelmann,K Kanaki,P Deen

doi:10.1088/1742-6596/528/1/012013

Abstract

Modern spallation neutron sources are driven by proton beams ~ GeV energies. Whereas low energy particle background shielding is well understood for reactors sources of neutrons (~20 MeV), for high energies (100s MeV to multiple GeV) there is potential to improve shielding solutions and reduce instrument backgrounds significantly. We present initial measured data on high energy particle backgrounds, which illustrate the results of particle showers caused by high energy particles from spallation neutron sources. We use detailed physics models of different materials to identify new shielding solutions for such neutron sources, including laminated layers of multiple materials. In addition to the steel and concrete, which are used traditionally, we introduce some other options that are new to the neutron scattering community, among which there are copper alloys as used in hadronic calorimeters in high energy physics laboratories. These concepts have very attractive energy absorption characteristics, and simulations predict that the background suppression could be improved by one or two orders of magnitude. These solutions are expected to be great benefit to the European Spallation Source, where the majority of instruments are potentially affected by high energy backgrounds, as well as to existing spallation sources.

Highlights

The European Spallation Source combines a powerful spallation source with the instrumental goal of being able to measure weak processes with cold neutrons
The data spike that can be detected as the pulse arrives is a high energy physics phenomenon that has been called a “prompt pulse”, because those neutrons possess such high energy that they appear at virtually zero time-of-flight as measured by the neutron instruments
As one can see from figure 5, the number of particles developed by particle showers in copper has a similar qualitative shape to that of iron, but reaches the initial number (106) of neutrons when the thickness of the block is about 110 cm

Summary

Introduction

The European Spallation Source combines a powerful spallation source with the instrumental goal of being able to measure weak processes with cold neutrons. The prompt pulse is accompanied by a long tail of fast neutron spectra; which is likely to be caused by energetic neutrons being moderated by instrument and it’s surroundings Another evidence of the problem is the data measured at CNCS instrument, the cold neutron chopper spectrometer at the Spallation Neutron Source (SNS, Oak Ridge National Laboratory, USA), see figure 1. The spatial extent of a particle shower depends on the energy of incoming particles (that dependence is logarithmic) and on the material they hit This is why examining different materials in order to know how they can produce and/or stop particle showers is important for building a solution which will reduce high energy background

Geant4 simulation idea

Findings

Conclusions