Towards nuclear astrophysics measurements at the NEW Birmingham High-Flux Accelerator-Driven Neutron Facility (HF-ADNeF)

Lead Research Organisation: University of Birmingham

Abstract

Neutrons are uncharged particles that exist in the tightly bound nucleus at the core of atoms. Together with charged protons they make up most of the mass that we see around us. In the Universe, most of the elements that we find on earth have been produced in stars by a combination of neutron capture and subsequent beta decay. These processes convert light elements to heavier elements in giants stars - those many times the size of our sun. In such environments there can be billions of neutrons passing through every square centimetre every second. Although this sounds like a huge number, the probability of elements capturing neutrons, even in such an environment, is quite low and so it is referred to as the slow-neutron capture process - or s-process for short. There are many things we don't understand about the s-process, for example, details about where the process splits into several branches and the precise rates of the beta decay process etc. These gaps in our knowledge mean we don't have a full understanding of how the elements were made (nucleosynthesis) and what the abundances of each element in giant stars were - material from which the earth was formed. To find out, we can study the s-process in the laboratory to measure the missing information. However, because neutrons are uncharged, it is not possible to accelerate them using electric and magnetic fields. This makes beams of neutrons for research more difficult to produce. However, at Birmingham we are building a next-generation neutron source that generates neutrons by bombarding a lithium target with protons. This machine will come on line in early 2022. The energies of the neutrons produced will closely mimic those found in giant stars. Furthermore, the intensity of the new neutron beam will one of the highest of its kind in the world (capable of producing more than a 10 trillion neutrons per second). This unique combination of energy and intensity makes the study of the s-process possible. To facilitate these studies, this proposal is to test the feasibility of building a detector end-station that is sufficiently well shielded that the detectors won't be damaged by the neutron beam. The added complexity is that the neutron beam needs to be focused on to a reaction target without diminishing the intensity of the beam significantly. The reactions between the target and neutrons could then be observed and measured.
To fully exploit this rare opportunity for exploring the potential of making a UK laboratory for astrophysics requires undertaking this feasibility study when the machine is installed.

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