In this issue:
- How the Neutron Gets its Spin – The search is underway
- Dawn of a New Era in Neutrino Detection Technology
- Mapping Distributed Radiation Sources Quantitatively
- Inclusion, Diversity, Equity, and Accountability Moments
The building blocks of matter, protons, and neutrons, are made of quarks and held together by gluons. (See Figure 1.) Each of these objects – quarks, gluons, protons, and neutrons – has spin. Quarks and gluons have an internal spin, with values of 1/2 and 1 in particle physics units. They can also orbit around each other – this type of spin is called orbital angular momentum and has integer values – 1, 2, etc. Protons and neutrons are very complicated objects in one sense – they are made of 3 “valence” quarks – quarks that set the quantum identifiers of the nucleon – as well as a sea of quark-antiquark pairs and gluons. All of it spinning in a variety of ways. From the outside, however, protons and neutrons are very simple spin-1/2 objects and so a fundamental question is how do they get their spin? How do they end up with spin-1/2 when they contain within themselves any number of spin-1 and spin-1/2 objects, which may also be spinning around each other? This is a question for theorists and experimentalists at the future Electron-Ion Collider (EIC) accelerator.
Recently, a team from the Berkeley Lab, Jefferson Lab, Brookhaven, MIT, and industry laid out a roadmap  for discovering the spin structure of the neutron by probing it with an electron beam. Oddly enough, the key to this work is making sure we know that the neutron is the target of the probe. Why is it so hard to know that we probed a neutron with the electron beam? Because building a pure neutron target is not easy. Free neutrons have a half-life of about 15 minutes so any bottle of neutrons left alone in the laboratory will be gone quickly. We need to stabilize the neutrons in order to keep them longer. This is done in Nature by combining neutrons with protons – i.e., by binding them in a nucleus such as helium-3.
The team’s roadmap proposes to do an EIC experiment using helium-3 as the target because helium-3 contains two protons and one neutron and, most importantly, the neutron is accessible and stable. By putting silicon detectors (nicknamed “Roman Pots”) very close to the axis of the beam, the team will be able to detect the protons kicked out of the helium nucleus. (See Figure 2). So, when two simultaneous protons are detected coming from the target (called “double-spectator tagging”), the team will know that the neutron was hit. It is a very simple and effective technique. From this knowledge, a set of spin observables can be measured to obtain the valence quark contribution to the neutron’s spin that is 3 to 10 times more precise than our best experiments to date. If the experiment can be successfully carried out, then we will be taking a mighty leap forward in understanding how the neutron gets its spin.
Jennifer Rittenhouse West from the Nuclear Theory group in NSD was the principal theorist on this work.
 I. Friscic et al., Physics Letters B, Volume 823, 10 December 2021, 136726
Monolithic optical detectors have a long history of success in neutrino physics, from water Cherenkov detectors such as Super-Kamiokande and the Sudbury Neutrino Observatory, to liquid scintillator detectors such as Borexino, KamLAND, and Daya Bay. While those two worlds have existed in parallel for decades, the next generation of detectors is about to exploit the best of both worlds by detecting Cherenkov and scintillation signals simultaneously. In the past, Prof. Orebi Gann and her team at the Berkeley Lab have made critical advances towards this goal by researching novel photon detectors and liquid scintillators such as the water-based liquid scintillator developed at Brookhaven National Lab. Using the CHESS  setup at the Lab, the team was able to achieve a separation of Cherenkov and scintillation light in both pure liquid scintillator (LS) and water-based liquid scintillator (WbLS) utilizing ultra-fast light detectors.
The EOS experiment seeks to perform the first-ever data-driven demonstration of event reconstruction using both Cherenkov and scintillation signals. The Berkeley team’s ground breaking effort is now reflected in the allocation of $10M in funding from the National Nuclear Security Administration (NNSA) to build the EOS experiment. EOS is named for the Titan Goddess of Dawn, and would be a precursor to the multi-kiloton THEIA detector . EOS will be constructed in Berkeley over the next three years. The collaboration includes 14 institutes with a strong contribution from the United States, but also involves international partners from Europe. Building upon the success of CHESS, EOS will go one step further to demonstrate the simultaneous use of Cherenkov and scintillation signals for precision event reconstruction at the few-ton scale. Its data will allow the team to validate and refine event simulations and the design of future instruments. EOS will permit the development of production and handling strategies for WbLS in large-scale detectors. Several variants of WbLS and other novel LS techniques will be investigated with EOS. After the initial phase in Berkeley, a re-deployment of the apparatus can be done at a reactor, accelerator beamline, or at an underground site for additional studies of neutrino events.
The EOS demonstrator results will constitute valuable input for the design of future kiloton and larger detectors like THEIA . These technologies have the potential to impact a broad program of fundamental science, including searches for neutrino-less double beta decay, detection of solar and cosmic neutrinos, and measurements of fundamental symmetry violation if deployed in a neutrino beam. Moreover, the technologies studied with EOS can facilitate the use of neutrinos for remote reactor monitoring.
Stefan Schoppmann and Gabriel Orebi Gann contributed to this news note. Dr. Schoppmann led the studies to explore the possibility of deploying EOS at a reactor in the future. Prof. Orebi Gann is the PI for the EOS project.
 CHESS collaboration – Phys. Rev. C 95, 055801 (2017) and Eur. Phys. J. C 80, 867 (2020)
 THEIA collaboration – Eur. Phys. J. C 80, 416 (2020)
Mapping distributed radiation sources is vital for radiological emergency response, for example, in reactor accidents such as Chernobyl or Fukushima. In particular, quantitative maps of radioactivity concentrations can inform path-planning methods for keeping the dose to first responders below established thresholds. The task of radiation mapping, quantitatively, is challenging and requires a knowledge of absolute detector efficiencies, accurate models of the 3D scene being mapped, and quantitatively-correct image reconstruction algorithms. Moreover, producing distributed radiological sources with known ground truth for developing the techniques is challenging from an operational perspective. Distributing radioactive material in a liquid, powder, or aerosol form can be difficult to do in a configurable, repeatable fashion, and can present a substantial human and environmental safety hazard.
To overcome these concerns, scientists from LBNL’s Applied Nuclear Physics program developed a method for emulating true distributed sources with arrays of sealed point sources. This technique avoids the risk of inhaling or ingesting radioactive material, and allows for easier ground-truthing and reconfiguration of source patterns during measurements. The Berkeley Lab team partnered with Washington State University and Idaho National Laboratory to irradiate copper pellets in the WSU nuclear reactor to produce hundreds of sealed ~5 mCi Cu-64 sources. The sources were arranged on a field in various patterns, each covering approximately 100 square meters, and radiation detectors were then flown over the source patterns on an unmanned aerial system (UAS)—see Figure 1.
Analysis is ongoing to compare the measured results against the known ground truth source distributions. Preliminary results show that the shapes of the source distributions can be accurately reconstructed, and that the overall intensity can be determined to within the systematic uncertainties of the measurements. The measurements will also form the basis for radiation mapping uncertainty quantification studies, with a focus on accurate methods that can be computed in near-real time on edge computers, and will stimulate future work on training UAS swarms to efficiently and autonomously map sources during radiological emergencies.
Jayson Vavrek led the experimental design and analysis team for this work. Jayson, along with Brian Quiter, Mark Bandstra, and Daniel Hellfeld collected the experimental data in August 2021. Tenzing Joshi is PI of the project supporting the work.
The majority of us in NSD can directly testify to the important role of mentoring in our professional development and careers. It is a key way to support employees, especially new hires or people transitioning into new roles. The advice and support that mentoring provides can be key to navigating the workplace effectively and minimizing the stresses which can come with this. Whether through a formal mentoring program, such as the Physical Sciences Mentoring Program at LBNL, or via more informal avenues, mentorship provides benefits to all involved, mentors and mentees alike.
Mentorship is not always easy, and we can always be improving our skills as mentors. The February 22, 2022 IDEA presentation put forward some suggestions and resources to help in doing exactly this. Following the DOE workshop on “Mentorship at the Laboratories Across All Levels and Career Types”, we have compiled a number of resources that you may consider exploring if you are interested in continuing to develop your skills as a mentor.
- The Science of Effective Mentorship in STEMM (Online Guide V1.0)
- Mentoring Guides for Research Advisors by National Academies of Science
- Culturally Aware Mentoring Resources from the Center for Improvement of Mentored Experiences in Research
Reflections on TDoV
The International Transgender Day of Visibility (TDoV) is recognized each March 31, as a response to the lack of recognition of transgender people and to raise awareness of the burden of discrimination faced by this community. On March 29th, 2022, the Lambda Alliance and the Nuclear Science Division IDEA Council co-sponsored a TDoV event, with a presentation from Prof. Gwen Grinyer of the Department of Physics at the University of Regina (Saskatchewan, Canada). Gwen discussed her physics career, as well as her work and research on the topic of representation of the 2SLGBTQ+ community in STEM fields. Punctuated with heartfelt personal anecdotes, this well-attended seminar was truly a moment of visibility, and we are very proud to have had Gwen join us. For those who were unable to attend her seminar, Gwen’s slides are available here.
Recent DEI topics @ NSD Staff Meetings
March 8, 2022 – Women’s History Month 2022
February 22, 2022 – Mentoring
February 8, 2022 – Active Listening
January 25, 2022 – The NSD Luminary Card Program
January 11, 2022 – IDEA Council Updates for 2022
December 14, 2021 – Winter Break 2021
You may recognize your co-workers with a Luminary Card for any action fostering inclusion, diversity, equity, and accountability within our LBNL community. The following people received a Luminary Card this quarter:
Barbara Jacak and Ren Cooper
Reiner Kruecken has been selected to be the next Division Director for the Nuclear Science Division at the Berkeley Lab. It is anticipated that he will join the Laboratory in May. Congratulations Reiner!
Volker Koch has been the interim NSD Director since Barbara Jacak stepped down to return to research. Volker will be returning to research after Dr. Kruecken arrives and is settled. Thank you, Volker, for a job well done!
2022 Service Awards
Peter Jacobs has reached the milestone of 35 years of service.
Mario Cromaz has reached the milestone of 25 years of service.
Bethany Goldblum has reached the milestone of 10 years of service.
Congratulations Peter, Mario, and Bethany!
Outstanding Referee Recognition
I-Yang Lee has been selected as an Outstanding Referee of the Physical Review journals, and was chosen by the journal editors for his distinguished service. The award will be recognized at an upcoming APS meeting. Congratulations, I-Yang!