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Nuclear Science Division

Semiconductor Detector Lab Reaches for the Stars

For decades, the LBNL Semiconductor Detector Lab (SDL) has been at the forefront of advancements in gamma-ray detector technology. Amongst the technologies pioneered at the SDL are double-sided high-purity germanium (HPGe) strip detectors with amorphous germanium (a-Ge) contacts [1] (Fig. 1). These devices find application in a range of areas including basic science, nuclear security, medical imaging, and gamma-ray astronomy. Using this technology, SDL researchers have designed, developed, and built detectors for multiple instruments for astrophysics projects led by the Space Sciences Laboratory at UC Berkeley [2]. These include the Compton Spectrometer and Imager (COSI) [3-6] and the Gamma-Ray Imager/ Polarimeter for Solar Flares (GRIPS) [7-9], which were successfully flown on balloon missions for NASA.

Figure 1: One of the HPGe strip detectors made in the SDL for the COSI instrument prototype.

Currently, the SDL is abuzz with activity as researchers work on the next iteration of the COSI instrument [10]. Fig. 2 shows a diagram of this instrument. This gamma-ray telescope is scheduled for launch in 2025 and will be flown on a spacecraft in low Earth orbit for at least two years. An artist’s rendering of the spacecraft is shown in Fig. 3. The primary objective of the COSI instrument is to explore where the production of heavy elements in the Milky Way occurs. It will also map the distribution of positron-electron annihilations, providing valuable insights into the distribution of antimatter. At the heart of this exciting mission to improve our understanding of our galaxy, and at the heart of the instrument, lie SDL detectors.

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Figure 2: Rendering of COSI instrument design. The instrument consists of 16 HPGe detectors, each 8 x 8 x 1.5 cm3. Surrounding the detector is a scintillator anti-coincidence shield that is 46 x 46 x 20 cm3. Each detector has a separate power connection and an ASIC for readout. Figure from [11].

NSD’s Joanna Szornel and Mark Amman have recently fabricated the first set of detectors, which are intended for the device prototype. One of these devices is shown in Fig. 1. Soon, they will begin the production of flight detectors for the final instrument.

Figure 3: Artist’s rendering of the COSI-SMEX satellite. Image by Jim Willis, courtesy of Northrop Grumman Corporation ½ Space Systems. Background Image courtesy of European Southern Observatory. Overall concept: COSI team.

Connecting Nuclear Quark Distributions to Dense Configurations in Nuclei

The strong interactions between protons and neutrons (nucleons) in the dense interior of heavy nuclei are believed to be responsible for modifying the internal quark structure of the nucleon. This modification, known as the “EMC effect” [1,2], was observed to scale with nuclear density, yielding a modest A dependence in medium-to-heavy nuclei. Measurements of the EMC effect at Jefferson Lab [2,3] showed that this picture breaks down in light nuclei, with the EMC effect in 9Be, an anomalously low-density nucleus, being much larger than predicted. 

As part of the commissioning run in Hall C after the 12 GeV upgrade data were taken on light nuclei including, for the first time, 10B and 11B [5]. These new results confirm the initial conclusion that the EMC effect does not scale with nuclear density. A global analysis of all light nuclei is consistent with the hypothesis that the EMC effect scales with the overlap between neighboring nucleons. This is consistent with the observation of a correlation between the EMC effect and Short-Range Correlations (SRCs), which generate highly-relativistic nucleons in nuclei when these nucleons interact at very short distances. Measurements of SRCs in 10B and 11B were also made, and will allow us to extend the observation of the EMC-SRC correlation to additional light nuclei.

These data were taken as part of a much broader program, initiated by NSD scientist John Arrington, head of the Relativistic Nuclear Collisions Program, and completed earlier this year. The program included two experiments to map out both the EMC effect and the contribution of SRCs across all stable light nuclei [6]. These experiments also included measurements on a variety of heavier nuclei, including 40Ca and 48Ca, to see how these effects change as a function of the neutron excess in nuclei, providing the first opportunity to try and separate density-dependent effects from potential isospin-dependent contributions.

[1] J. Aubert, et al., Phys. Lett. B 123 (1983) 275
[2] J. Gomez, et al., Phys. Rev. D 49 (1994) 4348
[3] J. Seely, et al., Phys. Rev. Lett. 103 (2009) 202301
[4] J. Arrington, et al., Phys. Rev. C 104 (2021) 065203
[5] A. Karki, et al., Phys. Rev. C 108 (2023) 035201
[6] JLab experiments E12-06-105 and E12-10-008

Figure 1: World’s data on the EMC effect in light nuclei including the new measurements (red circles).  The data from this result are shown relative to carbon in the bottom panel and compared to curves showing scaling with the average nuclear density and with the relative amount of short-distance NN configurations [3].

Director’s Corner

Fall is kicking off with major developments. The Nuclear Science community is rolling out its new Long Range Plan for Nuclear Science with ambitious scientific and technical goals and clear priorities for the years ahead. Berkeley Lab’s Nuclear Science Division is well aligned with the community’s priorities and will continue to make leading contributions in support of the Long Range Plan and its recommendations. 

Additional exciting news comes from CERN, where heavy ion running for LHC Run 3 has commenced and the ALICE experiment is taking  data. All detector systems, including the inner tracker system to which LBNL made major contributions, are working as designed and we are looking forward to further revelations on the properties of the quark gluon plasma ahead.

This issue of the NSD newsletter features other exciting examples of NSD science aiming to unravel the nature of the strong force and how technologies pioneered by Berkeley Lab are applied to enable multimessenger astrophysics. In particular, this issue reports on how recent measurements at Jefferson lab are challenging our understanding on how the nuclear interaction between protons and neutrons (nucleons) is modified inside light nuclei. The data seems to indicate that the so-called EMC effect, which measures the modification of the strong interaction inside the nucleus, scales with the overlap between neighboring nucleons. In this issue  we also learn about how the LBNL Semiconductor Detector Lab (SDL) is deploying double-sided high-purity germanium (HPGe) strip detectors, a technology pioneered at the SDL, for the next iteration of the NASA  Compton Spectrometer and Imager (COSI) mission. 

These are just a few examples of the broad spectrum of exciting science and advanced technological developments led by NSD. Some other highlights are featured in the Fragments.

The newsletter also provides a summary of how the Nuclear Science Division continues its strong engagement in outreach and in advancing the IDEA culture within the Division and the broader community. In addition, last month Berkeley Lab’s team, including a sizable contingent from the Nuclear Science Division, was awarded “Absolutely Fabulous Overall Contingent” in the San Francisco Pride Parade. Most recently, the Lab welcomed 200 scouts for the 11th annual Nuclear Science Day for Scouts.  It was fantastic to see everyone’s curiosity and fascination with the various facets of nuclear science [photo]. I would like to express my deep appreciation to the many volunteers making this event happen. The badge for this year features the Electron Ion Collider [see photo]. See this Elements article leading up to the event.

Sincerely,

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200 Scouts Head for the Hill this Saturday

Berkeley Lab will host the 11th annual Nuclear Science Day for Scouts this Saturday, Sept. 30. Learn how boys and girls will get hands-on experience from a cadre of volunteers, including Lab physicist Alan Poon, who was at the first event in 2009 as a way to give back to the community.

2024 DNP Dissertation Award Awarded to Evan Rule

Evan Rule, a former graduate student in the UC Berkeley Physics Department has been awarded the 2024 Dissertation Award in Nuclear Physics by the American Physical Society (APS).  Dr. Rule conducted his graduate research at UC Berkeley under the supervision of Prof. Wick Haxton who is a faculty member in the UC Berkeley Physics Department, and a Faculty Senior Scientist in LBNL’s Nuclear Science Division.

Dr. Rule, who is currently a postdoctoral fellow at the Network for Neutrinos, Nuclear Astrophysics, and Symmetries (N3AS), received the award “For the timely development of a flexible and fully general effective theory of muon-to-electron conversion. The formulation establishes an interface between the nuclear and particle physics components of this process that will encourage coordination between the two communities.“

Further details can be found in the APS announcement here.

Photo of Dr. Evan Rule

New DOE funding for AI/ML projects in the Nuclear Science Division

Berkeley Lab’s Nuclear Science Division has received two Department of Energy (DOE) funding awards for two-year projects focused on artificial intelligence and machine learning (AI/ML).

A collaboration of Nuclear Science Division (NSD) scientists from the Low-Energy Nuclear Physics,  88” Cyclotron, and Applied Nuclear Physics programs will develop new methods to optimize a large gamma-ray spectrometer and an ion source for low-energy nuclear physics. The primary goal of this project is to explore the best applications of ML approaches and data analytics techniques to automate online optimization and tuning during operation, building on an existing ML project, started in 2021.