Low background screening facility at Boulby for rare event search experiments

Lead Research Organisation: University College London
Department Name: Physics and Astronomy

Abstract

Scientists around the world are closing in on two of the biggest challenges in physics: understanding the nature of dark matter and the properties of the neutrino. Dark matter accounts for 85% of the mass of the Universe yet we do not know what it is since it has never been observed, and although we do know neutrinos have mass we do not know precisely how much nor if they are their own anti-particles. If they are it could explain the tiny imbalance between matter and antimatter shortly after the Big Bang. These questions have profound impact on our understanding of the Universe and its evolution - answering them is amongst the highest priorities in science.

Experiments that hope to observe dark matter particle interactions or neutrinoless double beta decay events that will tell us about the neutrino share a common requirement. Since both of these processes are extremely rare the detectors need to be shielded from all sources of background radiation that might mask the signal. The first line of defence is to place the detectors deep underground in mines or under mountains - this reduces the rate of cosmic rays from space that bombard the surface of the Earth. Next the detectors are surrounded with copper, lead, plastics and water to block the radiation emitted by the underground rock. Although this is natural low-level radiation that causes no harm to humans, it is catastrophic for our extremely sensitive rare-event searches! The final and most difficult step is to construct the detectors themselves from only the purest materials that are exceptionally 'clean' in terms of trace contaminants that may emit radiation.

The UK has a very strong track record and international standing in rare-event underground physics, going back several decades, and we continue to take leading roles in the most advanced experiments. We now stand on the edge of discovery with the next generation of dark matter and neutrino experiments. Unfortunately, here in the UK, our capability to screen materials to check their radio-purity before using them to build detectors is no longer sufficient. As detectors have become ever more sensitive, so has the requirement for the materials to be ever cleaner and free from even the smallest amount of radiation. Whereas previously we could rely on a germanium detector located at the Boulby Underground Laboratory to perform our screenings, it can no longer keep up with the sensitivity requirements of the dark matter and neutrino-less double beta decay experiments. This is doubly problematic because in addition to vetting material before accepting it in detector construction, we must also understand precisely the amount of radiation expected from each and every component. Only if we know what we expect from all of these materials can we hope to observe an excess and claim discovery of an exceptional signal. Very few facilities exist worldwide with germanium detectors with sufficient sensitivity to satisfy these needs.

We will install a new facility at Boulby with a state-of-the art germanium detector that will be used by 15 institutes across the UK in their low background screening campaigns for the leading dark matter and neutrino-less double beta decay experiments. With this much needed capability to deliver amongst the world's most sensitive material screening tests, the Boulby facility will be reinstated as a leader in the field, and we will be able to construct the next generation of experiments that will help unravel the mysteries of the Universe.

Such a facility would be very useful to a wide variety of applications well beyond particle physics and cosmology. It would significantly improve environmental radioactivity studies already in progress at Boulby, and would provide capability for studying the climate with aerosol growth and cloud formation, and next generation electronics. Internationally there is an industrial and commercial demand for such instruments with the sensitivity we would provide.

Planned Impact

Across the world, the ability to assess the uranium and thorium content of materials at the part-per-trillion level is becoming ever more important. In particular, such measurements are vital for determining acceptable components to be incorporated in key next-generation science projects, most critically the ultra-rare event searches of direct dark matter detection and neutrinoless double beta decay. These are the breakthrough projects that will take us beyond the Higgs, beyond the standard model, and into scientific terra incognita.

The 15 UK institutions supporting this proposal are seeking to establish major roles in such upcoming projects, including responsibilities for radioactive purity of construction materials. However, at present, the UK has no facility with sufficient sensitivity to conduct materials screening at the requisite level, and instead we have to rely on our international partners.

Funding of this project will enable UK leadership in this important area. Moreover, without sufficient control of radioactive backgrounds, these projects become critically compromised, and as a consequence, leadership and responsibility for material screening provides a gateway to scientific leadership of the projects as a whole. A world-class screening facility is an enabler of scientific leadership in the breakthrough physics projects of the next decade.

The impact of such a facility goes well beyond particle physics and cosmology. The UK has expertise and world recognition in environmental gamma ray spectroscopy research. Indeed, the Boulby facility is already being used for environmental radioactivity studies with dedicated detectors. A new BEGe facility would significantly enhance this capability with well over an order of magnitude improvement in sensitivity. The screening facility will also be used for a variety of further applications including, but not limited to, climate (aerosol growth and cloud formation), next generation electronics (single event upsets) and environmental research (radio-ecology, landscape evolution). Similar modes of operation and exploitation already exist at other international underground laboratories. There is a high industrial and commercial demand for such measurements and therefore running the facility may become self-funding on the timescale of a year.

Publications

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Dobson J (2018) Ultra-low background mass spectrometry for rare-event searches in Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment

 
Title Perspectives On The Unknown 
Description Perspectives on the Unknown is a short documentary film that investigates a scientific discovery known as dark matter and dark energy, which fills up over 95% of the Universe and yet remains as the unknown. The film tries to present different perspectives on this invisible matter by questioning how scientists deal with this mysterious matter, and how artists interpret this unknown. The film features two artists, Alison Gill and Julie Mecoli, with a physics academic, Dr. Chamkaur Ghag from department Physics and Astronomy at the University College London. This project is a collaborative project with Roger Stabbins and Thomas Deacon. 
Type Of Art Film/Video/Animation 
Year Produced 2015 
Impact This work has led to further enquiries from students in the arts, and organisation of a visit tot the Boulby Underground Laboratory in 2016 where several national artists will group and develop proposals for further collaborative work. The intention is that this would result in a travelling exhibit. 
URL https://vimeo.com/123613759
 
Description Chair of STFC's Particle Astrophysics Advisory Panel
Geographic Reach National 
Policy Influence Type Participation in a advisory committee
 
Description International Exchanges Award
Amount £11,029 (GBP)
Funding ID IE141517 
Organisation The Royal Society 
Sector Academic/University
Country United Kingdom
Start 03/2015 
End 02/2017
 
Title Development of lead shields 
Description In partnership with UK industry (Lead Shield Engineering) we have developed new designs for low background radiation shields for use with gamma spectroscopy detectors. 
Type Of Material Improvements to research infrastructure 
Year Produced 2015 
Provided To Others? Yes  
Impact These designs have been realised with lead and copper shields manufactured by Lead Shield Engineering UK for the Boulby Underground Laboratory, the AWE, and others. 
URL http://www.lead-shield.co.uk/
 
Title Trace radioactivity analyses with ICP-MS 
Description Development of methods for trace uranium and thorium radioactivity analyses with ICP-MS using microwave digestion 
Type Of Material Technology assay or reagent 
Year Produced 2016 
Provided To Others? Yes  
Impact We have been able to assay materials to levels of less than 10 ppt (g/g) for uranium-238 and thorium-232 
 
Title Trace radioactivity measurements 
Description Improvements to trace radioactivity measurements in material samples using underground gamma spectroscopy and surface mass spectrometry. 
Type Of Material Improvements to research infrastructure 
Year Produced 2015 
Provided To Others? Yes  
Impact We have provided low level radioactivity measurements for rare event search experiments with UK involvement but also to industry; in particular SSI, and Photek Ltd for the enhancement of their products supplied commercially to UK and international consumers. 
URL http://www.boulby.stfc.ac.uk/Boulby/Projects/39343.aspx
 
Description LUX-ZEPLIN 
Organisation Lyngby-Taarbæk Municipality
PI Contribution I am the co-lead of the LZ 'Background and Screening' Work Package (WBS1.10), one of 11 in the international project, and lead for the equivalent Work Package (WP4) in the UK project. These contain tasks related to the radio-assay of all materials for construction of the instrument to meet low-background requirements unprecedented in the field to-date, and characterization of the experiments radiation field from materials and the environment to provide accurate input for the background model. These are crucial tasks necessary for LZ to achieve its science reach in terms of Dark Matter sensitivity, and to assess any potential signal in case of discovery. In addition to overall leadership and management of these Work Packages, UCL is specifically responsible for delivery of approximately half of all project radio-assays together with radio-content characterization and modeling. This is performed with state-of-the-art technologies and infrastructure I have been developing in the UK since 2012.
Collaborator Contribution All other activities in this international collaboration, from design through to construction.
Impact Construction of the LZ dark matter experiment
Start Year 2012
 
Description Event Horizon Cafe Scientifique 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach Local
Primary Audience Undergraduate students
Results and Impact 30 people attended a Cafe Scientifique event organised by UCL undergraduate students where I talked about the search for Dark Matter in our Universe. Impact that has arisen since includes requests for more information on how to conduct further studies or apply for PhD and postgraduate positions in the field of Dark Matter and particle physics in general.
Year(s) Of Engagement Activity 2015
URL https://www.facebook.com/events/197495787252785/
 
Description Article in Cosmos magazine 
Form Of Engagement Activity A magazine, newsletter or online publication
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Public/other audiences
Results and Impact Featured in a Cosmos Magazine article about the search for Dark Matter.
Year(s) Of Engagement Activity 2015
URL https://cosmosmagazine.com/physical-sciences/ghost-traps-hunt-dark-matter
 
Description BBC Today programme feature 
Form Of Engagement Activity A press release, press conference or response to a media enquiry/interview
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Public/other audiences
Results and Impact Radio feature discussing UK particle physics and involvement in 'Beyond Standard Model' experiments including Dark Matter searches.
Year(s) Of Engagement Activity 2013
URL http://www.bbc.co.uk/programmes/b03kpnjl
 
Description Forbes magazine article 
Form Of Engagement Activity A magazine, newsletter or online publication
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Public/other audiences
Results and Impact 5000 views of this article discussing Dark Matter experiments with UK involvement, where I discuss the implications of new results. This article led to changes in opinion of the readers as documented by the comments on the website, and further enquiries.
Year(s) Of Engagement Activity 2013
URL http://www.forbes.com/sites/bridaineparnell/2013/11/07/why-the-lux-results-matter-to-dark-matter-and...
 
Description IOP Physics World article 
Form Of Engagement Activity A magazine, newsletter or online publication
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Public/other audiences
Results and Impact Article in Physics World magazine about underground science including Dark Matter searches. This article highlighted activities at the UK's Boulby Underground Laboratory.
Year(s) Of Engagement Activity 2015
URL http://physicsworld.com/cws/article/indepth/2015/may/07/subterranean-science
 
Description IOP Physics World article 
Form Of Engagement Activity A magazine, newsletter or online publication
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Public/other audiences
Results and Impact Article highlighting the selection of the next generation of experiments in the search for Dark Matter, including LZ.
Year(s) Of Engagement Activity 2014
URL http://physicsworld.com/cws/article/news/2014/jul/15/dark-matter-searches-get-us-government-approval
 
Description Light and Dark TV series 
Form Of Engagement Activity A broadcast e.g. TV/radio/film/podcast (other than news/press)
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Public/other audiences
Results and Impact This was a major BBC production broadcast on TV in two-parts, hosted by Prof. Jim Al-Khalili. It featured a section on Dark Matter where I discussed underground experimental techniques.
Year(s) Of Engagement Activity 2013
URL http://www.bbc.co.uk/programmes/b03jrxhv
 
Description Naked Scientists Radio and Podcast feature 
Form Of Engagement Activity A broadcast e.g. TV/radio/film/podcast (other than news/press)
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Public/other audiences
Results and Impact Radio and Podcast feature by the Naked Scientists discussing Dark Matter searches. This feature led to several further media enquiries and questions from the general public.
Year(s) Of Engagement Activity 2015
URL http://www.thenakedscientists.com/HTML/podcasts/naked-scientists/show/20150602/
 
Description New Scientist Public Event 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Public/other audiences
Results and Impact 270 members of the general public attended a Particle Physics Experts Masterclass organised by New Scientist. I was one of the 5 experts, presenting Dark Matter including the LZ experiment, and I was a member of the panel for a Q&A session. There was significant interest during the ticketed event (£150 per person), and outcomes that have arisen since include contact from schools and students regarding Dark Matter for their school projects, and contact from the media.
Year(s) Of Engagement Activity 2016
URL http://www.eventbrite.co.uk/e/instant-expert-mysteries-of-particle-physics-tickets-19713709235?aff=n...
 
Description Public Lecture at Second Home 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach Regional
Primary Audience Industry/Business
Results and Impact Approximately 70 people that work at or operate from Second Home, London, attended a talk about Dark Matter that focused on technologies. Second Home houses numerous technology firms and businesses and this talk led to several questions about potential socioeconomic impact of particle physics and Dark Matter experiments, and potential areas for collaborative research and spin-offs. It has also led to arrangement of a trip to Boulby Underground Laboratory in 2016, where I will host 10 artists from across the UK on an underground tour of the science facility.
Year(s) Of Engagement Activity 2015
URL https://www.facebook.com/events/1498288067129210/
 
Description Radio 5 Live feature 
Form Of Engagement Activity A broadcast e.g. TV/radio/film/podcast (other than news/press)
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Public/other audiences
Results and Impact Dark Matter feature on Radio 5 live, highlighting UK research. This feature led to enquiries from the general public and other media outlets.
Year(s) Of Engagement Activity 2015
URL http://www.bbc.co.uk/programmes/b043wvt9
 
Description Radio feature on Newsdrive 
Form Of Engagement Activity A press release, press conference or response to a media enquiry/interview
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Public/other audiences
Results and Impact Interview on BBC Newsdrive discussing UK involvement in international Dark Matter search experiments.
Year(s) Of Engagement Activity 2014
URL http://www.bbc.co.uk/programmes/b03zdylq
 
Description School Visit (Newham Collegiate College, London) 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach Local
Primary Audience Schools
Results and Impact Particle physics seminar focussing on searched for beyond the standard model physics, particularly for dark matter signatures. Approximately 40 students attended, and there was considerable interest afterwards with questions, discussion, and follow up emails to me.
Year(s) Of Engagement Activity 2017