Nuclear data development at the European Spallation Source

Abstract

Transport calculations for neutronic design require accurate nuclear data and validated computational tools. In the Spallation Physics Group, at the European Spallation Source, we perform shielding and neutron beam calculations to help the deployment of the instrument suite for the current high brilliance (top) moderator, as well for the design of the high intensity bottom moderator, currently under study for the facility. This work includes providing the best available nuclear data in addition to improving models and tools when necessary. In this paper we present the status of these activities, which include a set of thermal scattering kernels for moderator, reflector, and structural materials, the development of new kernels for beryllium considering crystallite size effects, nanodiamonds, liquid hydrogen and deuterium based on path integral molecular dynamics, and the use of the software package NCrystal to assist the development of nuclear data in the framework of the new HighNESS project.

The neutron cross section of low-temperature heteronuclear diatomic fluids

“…its TCS σ with varying incident neutron energy, since this effort would anyway help assessing the critical issues and envisaging possible improvements for applications to neutron moderation as those announced in Ref. [4]. In such an attempt, a fundamental step consists in evaluating the performance of the simplest analytical model available for the translational dynamics: the ideal gas (IG) law.…”

“…As far as hydrogen (H 2 ) and deuterium (D 2 ) are concerned, a significant progress has been possible a few years ago when crucial experimental work has been dedicated to accurate measurements of the total cross section (TCS) of para-H 2 [1] and, at the same time, quantum calculation methods have been employed, in place of classical evaluations of the translational dynamics, in the DDCS algorithms for these low-mass molecules undergoing nonnegligible delocalisation effects [2,3]. Very recently, the latter approach, which gives the unique opportunity to get rid of adjustable parameters in DDCS evaluations, has been successfully adopted in moderator design and nuclear data processing codes [4] implemented at the European Spallation Source (ESS, Sweden). Therefore, concerning the homonuclear representatives of the hydrogen family, we can be rather satisfied with the capabilities acquired from a scientific point of view, now permitting well-grounded and safe applications to forthcoming and existing neutron sources.…”

“…Nonetheless, another member among the hydrogen liquids, namely hydrogen deuteride (HD), has not deserved in the years the same attention of its homonuclear partners, either from a scientific point of view, or in applications, although some of its midway properties between H 2 and D 2 might be conveniently exploited also in neutron moderation processes, as suggested in Ref. [4]. For instance, it combines a still low absorption (i.e., an advantageous property typical of D 2 ) with a still interesting lowmass-related moderation efficiency (i.e., the key property of H 2 ), and all of this at the same (manageable) low temperatures of liquid H 2 and D 2 (∼ 20 K).…”

HighNESS conceptual design report: Volume I

“…The other possibility is to implement the ND calculation directly in the Monte-Carlo code and use a modified .ACE SANS file, as was done in [83]. This work has been presented in earlier papers [50,166].…”

“…al. [82,83] and was implemented prior to the beginning of this project [50]. The idea is to fit a simple model to the SANS structure factor measured by Teshigawara et.…”