Measurement of the 16O(n, α)13C cross-section using a Double Frisch Grid Ionization Chamber

Sebastian Urlass,Stefan Müller,David Weinberger,Roland Beyer,Laurent-Got Tassan,Arnd R Junghans,Andreas Wagner,Andreas Hartmann,Daniela Scheibler,Toni Kögler,Steffen Turkat,Katja Römer,Sebastian Hammer,The N_Tof Collaboration ,Daniel Stach,Tamás Szücs,Federica Mingrone,Benjamin Lutz

doi:10.1051/epjconf/202023901030

Abstract

The 16O(n, α)13C reaction was proposed to be measured at the neutron time-of-flight (n_TOF) facility of CERN. To this purpose, a Double Frisch Grid Ionization Chamber (DFGIC) containing the oxygen atoms as a component in the counting gas coupled with a switch device in order to prevent the charge collection from the so-called γ-flash has been developed at Helmholtz-Zentrum Dresden-Rossendorf (HZDR), in Germany. The first 16O(n, α)13C measurement without seeing the charge of the γ-flash at n_TOF has been performed in November 2018. After the electronics did not suffer from the y-flash any more, another huge charge collection was discovered. Due to the high instantaneous flux at the n_TOF facility [1] the amount of that induced charge from neutron induced background reactions was piling up so much that the recognition of 16O(n, α)13C reactions from that background was very difficult. For that reason another 16O(n, α)13C measurement at the time-of-flight facility nELBE at HZDR which has a low instantaneous flux [2], has been performed in April 2019. Both measurements from n_TOF and nELBE will be presented here.

Highlights

The 16O(n, α)13C cross-section reaction measurement plays an important role for nuclear technology, as pointed out by the CIELO Collaboration [3]
A Double Frisch Grid Ionization Chamber (DFGIC) containing the oxygen atoms as a component in the counting gas coupled with a switch device in order to prevent the charge collection from the so-called γ-flash has been developed at Helmholtz-Zentrum Dresden-Rossendorf (HZDR), in Germany
In November 2017 the first test of a prototype DFGIC, which has been produced at HZDR, has been performed at neutron time-of-flight (n_TOF) in the experimental area called EAR1 - with a horizontal flight path of 185 m

Summary

Introduction

The 16O(n, α)13C cross-section reaction measurement plays an important role for nuclear technology, as pointed out by the CIELO Collaboration [3]. The layers of matter in the beam of the new prototype DFGIC were kept as minimal as possible, it was clear that the saturation of the charge sensitive preamplifiers (CSP) due to the γ-flash makes a time-of-flight measurement in the high-energy region impossible. Due to the high instantaneous neutron flux of the facility the pile-up of neutron induced background reactions induces charges in the DFGIC with up to two orders of magnitude higher than one induced by α-particles. In order to reduce neutron induced background both chambers were operated with reduced pressure of 1.3 bar and neutron filters (3 cm thick lead and 8 cm thick sulfur) has been put in beam Under this condition signals from fission fragments (coming from the 235U containing chamber part) which are depicted as an example, could be analysed. Α-particles from the decay of 235U could be identified, the disturbance of the neutron induced background is still so large that a proper analysis of the 16O(n, α) reactions in the fast neutron region is not possible

Experiment at nELBE

Findings

Summary and Outlook