Size matters: how Sheffield physicists are exploring the very small and the very large
The size of the matter
Much of physics deals with extremes of scale, and the research being done within the Department of Physics and Astronomy is no exception. From visualising subatomic particles to modelling the birth of stars, the physical size of the matter to be studied is rarely a matter of size in the eyes of a physicist.
Several particle physicists at the University of Sheffield work at one extreme end of this scale spectrum by looking at neutrinos. These subatomic particles have extremely small masses and are one of the most abundant particles in the Universe but, because they don't interact with matter, they are very hard to detect.
To get around this, neutrino detectors need to be extremely large in size. Most neutrino detectors actually come in the form of water Cherenkov experiments – huge tanks filled with purified water and a small amount of gadolinium. The tanks are lined with sensors called photomultiplier tubes (PMTs) and these pick up on the small amount of radiation emitted when a neutrino collides with a gadolinium-loaded water molecule within the tank.
Because of their hard-to-detect nature, bigger is better when it comes to neutrino detectors. Hyper-Kamiokande (Hyper-K) is the latest neutrino detector being constructed in Japan with an expected completion date of 2027. Hyper-K’s cylindrical tank will be a huge 68 metres in diameter and 71 metres deep, the entirety of which will be buried 650 metres underground.
Hyper-K is the successor to Super-Kamiokande, which University of Sheffield particle physicist Dr Matthew Malek worked on during his own PhD. Since then, Matthew has been involved in many more different neutrino detection experiments, including WATCHMAN, based at Boulby Underground Laboratory in North Yorkshire, and ANNIE, which is based at Fermilab in the USA.
Particle physics students working at extreme scales
Matthew’s involvement with such large and varied projects in the field of neutrino physics has paved the way for University of Sheffield students to take up some very unique research placements within the field.
Matthew said: “I like to find them unusual placements, like those at Fermilab in the US. Being in a real-world facility and surrounded by all the hardware used in neutrino experiments – there’s a real wow-factor for students.”
One such student is Rob Foster, who is conducting his PhD research within Matthew’s research group. Rob first got a taste of neutrino physics research in the summer after his second year, when he approached Matthew and asked if he could do a project with him.
Rob said: “Matthew presented to us a range of different projects and asked which we were interested in. One of these projects was WATCHMAN, and I was really interested in that because of its applications in real life.”
The WATCHMAN project was based on the idea that a water Cherenkov detector could detect antineutrinos (the antimatter counterpart to neutrinos) which are emitted by operating nuclear reactors. If the detector were large enough, it could even detect nuclear reactor operation in another country, hence providing a way to monitor the compliance of other countries to nuclear non-proliferation commitments.
Following his second year summer project, Rob continued to work with Matthew on WATCHMAN in research projects throughout his third and fourth years of undergraduate study. Although a PhD was not on the forefront of Rob’s mind, the experience he had working with WATCHMAN throughout his undergraduate studies spurred him to continue his studies in this area.
Rob said: “The reason I went into a PhD was because I wanted to see WATCHMAN through. When I first did the project in second year, WATCHMAN was just a name on some paper, but I was really interested in using physics to accomplish something in the real world.”
“As well as this, the professional relationship I built up with Matthew over three research projects was a really strong one, and this helped me hit the ground running when it came to starting a PhD.”
This is echoed by Matthew, who said: “A huge advantage of leading undergraduate research projects as an academic is that you get the chance to form a strong mentoring relationship with your students. If they then pursue a PhD, it's easier to dive straight into doing cutting edge research if I'm already confident in our working dynamic.”
Now, after spending the first 18 months of his PhD running simulations, Rob is focussing on the hardware used in neutrino detection. He’s unsure about what he wants to do when he finishes his PhD, but a postdoc in particle physics is not off the cards.
“Since being able to come back to the lab, I’ve had a renewed appreciation that I really enjoy the research I do,” Rob said. “Though I'm also interested in going to work in industry. The photon detectors I work on have a particular application in particle physics, but they also have a lot of applications in medical fields, which is interesting to explore.”
Addressing the big questions in astrophysics
At the other end of the spectrum lies the research of Dr Richard Parker, a lecturer in astronomy. Richard’s research addresses the big questions about the space that surrounds our tiny planet, including how stars, planets and our universe are made.
Richard also has a long history of involving students in his research, some of which have even resulted in published studies.
He said: “There are loads of little ideas or avenues that I’d love to explore but perhaps don't lend themselves to PhD research, however they are perfect for undergraduate student research.”
Many of these projects have resulted in interesting or novel results, which Richard has since been able to convert into published studies.
“I want my students to be really interested and excited in the research that they’re doing, and then also for my benefit I get to see where these new ideas go,” Richard said. “Because this research is very speculative and exploratory, it means that I can follow things up when something new is revealed, and I really believe students should get the credit they deserve for their research.”
Hayley Alcock is one student who undertook two separate research projects with Richard, one being a summer placement and the other a final year project. Both of these resulted in publications, and made a big impact on her university experience.
Interestingly for Hayley, astronomy wasn't always on the cards as an area for research. As a student on the pure physics course, Hayley took a chance on the coding course offered for those wishing to pursue a masters.
Hayley said: “I had never done any coding before and in all honesty I was expecting to grit my teeth and get through it, but soon I realised that the coding was really really fun. It quickly became one of my favourite modules that I took at university.”
After a subsequent module where Hayley used her coding skills to simulate the structure of a young star, she decided she wanted to do some further work in this area. She was put in touch with Richard who helped her secure a summer placement for her as part of the University’s Sheffield Undergraduate Research Experience scheme.
For this first six-week long project, Hayley worked with Richard to investigate how heavier stars in star forming regions emit radiation, destroying the planetary building blocks around smaller stars in that region.
“It was an intensive six weeks, but with Richard's guidance I set up the code for that which he could then integrate into some other research and take it further to produce some publications,” Hayley said.
The enjoyment Hayley got from this summer project led her to pursue an astrophysics placement with Richard for her third year project.
Richard said: “Hayley wanted to get more experienced in writing computer code, and my research was ideal for that. I was so impressed with what Hayley did in the summer placement that I was more than happy to supervise her third year project as well.”
For her third year project, Hayley and Richard looked at how the environment around stellar cores affects their splitting into smaller stars, and how these stars move after their fragmentation. This project once again resulted in a publication.
Hayley said: “We worked to code up a simulation to replicate the process. I really liked that way of working as Richard would give me guidance but didn’t hold my hand through the whole process. The freedom to create my own code was a really refreshing way of learning.”
Richard said: “This publication was only possible thanks to Hayley’s high quality research on the project, which was more in line with what I would expect from a good postgraduate student.”
Now, Hayley is pursuing a career in data analytics and is finding the skills she developed on her student research projects to come in handy with her work.
She said: “Even though data analytics isn’t directly related to physics, a lot of the skills I learned during my placements are transferable to my everyday work. For example, in my first placement I taught myself how to use [programming language] Python in a huge amount of ways that I now use day-to-day in my job.”
“Doing a student placement also really helped me to get the most out of my education because you really see another side to the university,” Hayley said. “Going beyond the structure of lectures made me engage a lot more with the department, and it was really interesting getting to know Richard and being able to contribute to his research.”
As for Richard himself, he, like Matthew, plans to continue engaging students in his work as much as possible. He’s just published a new paper in collaboration with Bridget Marchington, a student on Sheffield’s Astrophysics MSc.
“I’m currently working on writing up the results of some other student projects which could potentially become a published study,” Richard said. “It's something I really enjoy doing and I think it's great for students to see that their work really does contribute to the wider field.”
Written by Louise Elliott
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