Constructing and commissioning of a Multi-Grid neutron detector prototype for the European Spallation Source

Abstract

A prototype of a novel 10B-based neutron detector called the Multi-Grid detector has been constructed, tested and commissioned for the European Spallation Source (ESS). The detector is constructed after the specifications set by the CSPEC instrument at ESS and is therefore called the CSPEC Multi-Grid detector. The detector uses multiple layers of solid coating containing 10B4C on the edges of a voxelated proportional counter gas detector. The detector was constructed at the ESS detector workshop Utgård in Lund. Initial tests were also performed at Utgård to ensure the functionality and initial state of the detector. It was then moved to the Source Testing Faculty at the Division of Nuclear Physics at Lund University to test the detector with moderated neutrons and with gamma-rays from radioactive sources. Lastly the detector was commissioned at LET, ISIS, for comparison between the detector and the 3He detectors used in the LET instrument. The tests performed in Lund demonstrated that the Data Acquisition System (DAQ) of the detector and the detector itself was functioning, a discrimination threshold for discriminating gamma-rays was found, as well as that the detector is sensitive to neutrons. The tests performed in LET confirmed that the detector can be used for time-of-flight measurements in the energy range required by the CSPEC instrument, furthermore both line-shape and signal to background ratio of the CSPEC Multi-Grid detector was comparable to the 3He detectors.

Popular Abstract

Similar to the way X-rays can expose the atomic structures in the body, revealing broken bones, neutrons can be used to expose the nuclear composition of matter. A vital yet challenging part of using neutrons in science is to detect them. In this work a neutron detector prototype based on a novel technique has been constructed, tested and commissioned.

Neutrons are uncharged particles with about the same mass as protons. Due to its lack of electrical charge it will almost exclusively interact with the nuclei of the atoms it encounters. This means that neutrons can be used to study materials on a nuclear level. However, since the nuclei radius only spans a factor 0.0001 of the radius of an atom, the neutron can encounter a lot of atoms before it hits a nucleus allowing deep penetration into sample materials. This either means that the neutron has to encounter a lot of atoms to increase the likelihood of an interaction, alternatively to use more neutrons so that there are more neutrons available to hit the nucleus.

This creates the need for neutron sources that can provide a lot of neutrons. One facility that will produce an unprecedented number of neutrons is the European Spallation Source (ESS), which is still under construction at the time of writing this paper. ESS is a neutron source placed at the outskirts of Lund and will be one of the neutron facilities creating the most number of neutrons per second when it is up and running.

When studying nuclei with the help of neutrons, the path and velocity of the neutron before and after colliding with nuclei are vital. Imagine a billiard ball. If the billiard ball hits the edge of the billiards table it will bounce out with the same angle, however mirrored, and same velocity as it entered with. If the billiard ball instead hits another billiard ball the path will be harder to anticipate. It will however not exit with the same, but mirrored angle and same velocity as it initially had. Information about what the billiard ball has collided with can therefore be gained from looking at the path and velocity before and after the collision. The same is true for neutrons colliding with nuclei.

If the path and velocity of the neutron is known before and after the interaction with a nucleus, information about the collision can be gained. This information on the collision can in turn give information on properties of the nuclei collided with. To determine the exiting path of the neutron a neutron detector must be used. This is not straightforward since the neutrons, as described above, can travel far before interacting with any nuclei. The goal of this work was to construct, test and commission a novel state-of-the-art neutron detector prototype called the CSPEC Multi-Grid detector for the ESS.

The prototype detector was built at the ESS detector workshop Utg˚ard in Lund. It was first tested at Utgård and at the Source Testing Facility at Lund University. The initial tests showed that the electronics used, and all parts of the detector were working as expected. The detector was then sent to the LET instrument at ISIS, a facility in UK similar to ESS, to compare its performance to another well-established neutron detector type, the 3He detector. The detector clearly detected neutrons even after the long transport to the UK!

• author: Wahlén, Rebecka
• supervisor: Hanno Perrey; Ramsey Al Jebali
• organization: Nuclear physics; Department of Physics; European Spallation Source ESS AB
• alternative title: From welding to detection
• course: PHYM01 20221
• year: 2022
• type: H2 - Master's Degree (Two Years)
• subject: Physics and Astronomy
• language: English
• id: 9100956
• date added to LUP: 2022-09-27 16:33:57
• date last changed: 2022-09-27 16:33:57