the telescope instead of the reaction target due to the long lifetime of the expected isomer.

The fragment and beam detectors, as well as the CAESAR array, were all integrated into a digital data acquisition system (DDAS). The coincidence between all the decay products required the synchronization of DDAS with the MoNA-LISA VME based electronics. The first preliminary results show a good identification for the fragment PID and a clean separation between neutrons and charged fragments in the neutron detector (Figure 2). This experiment also enables a sweeperless MoNA-LISA setup as a complementary alternative regarding invariant mass spectroscopy for neutron unbound isotopes.

Figure 2: Separation of the different decay products in the MoNA-LISA array

SOMETHING TO HANG YOUR HAT ONContributed by Lijie Sun and Chris Wrede

Most radioactive isotopes decay by a process called beta decay. In 1963, it was discovered that the beta decay of the isotope silicon-25 is sometimes followed by the emission of a proton. Since then, this process of “beta delayed proton emission” has been observed in the decays of approximately 200 isotopes, and silicon-25 decay has been measured in many different experiments. Because its decay is so extensively studied, silicon-25 was chosen for the 2018 commissioning of the Gaseous Detector with Germanium Tagging (GADGET) system, which is designed to detect beta delayed proton emission.

MONA'S LAST RUN AT NSCLContributed by Belen Monteagudo Godoy

The spectroscopy of the neutron unbound beryllium-13 nucleus is key to understanding the evolution of the N=8 shell gap, yet its structure is not well understood. Invariant mass spectra from different experiments display similar structures but, even using the same reaction mechanism, quite different interpretations have been proposed. In particular, the location of the 1/2- p-wave is still uncertain. This p-wave resonance is expected to strongly decay to a long-lived 02

+ state in beryllium-12 with a mean lifetime of 331(12) nanoseconds, instead of directly to the ground state. Its decay scheme has a 20% branch through the beryllium-12(2+) to the ground state (2.1 MeV) and an 80% branch for an E0 transition giving two 511 keV gamma rays from positron annihilation.

A new experiment has been performed by the MoNA Collaboration at the NSCL to study exclusively the neutron decay of beryllium-13 to this isomer state in beryllium-12. The experiment took place in the S2 vault with a sweeperless MoNA-LISA setup (Figure 1). States in beryllium-13 were populated following a one-neutron removal reaction from a ~76 MeV/u beryllium-14 beam. The detection of the beryllium-12 fragment was achieved with a new telescope detector composed of a stack of 5 thin (500 µm) silicon detectors and a 30 mm thick CsI. Fragment identification was based on energy loss and total energy. The coincident emitted neutrons were measured with 96 modules of the MoNA-LISA neutron detector array. The gamma rays were measured with CAESAR, placed around

October 23, 2020 | VOLUME 41 NUMBER 40

Figure 1: Sweeperless setup in S2

This short experiment turned out to be more sensitive than previous measurements of silicon-25 decay, thanks to the intense NSCL beam and the high efficiency and resolution of GADGET. A new proton peak was observed in the energy spectrum along with several new gamma-ray peaks, and instances where both protons and gamma rays are emitted together were observed in detail for the first time (see figure below). Moreover, the uncertainty associated with the half-life was reduced and the Doppler effect of emitted protons on gamma rays was used to provide complementary measurements of the proton energies and intensities. The results are in excellent agreement with theoretical nuclear structure calculations and enhance the utility of silicon-25 as a calibration standard for future experiments.

Figure: Coincidences between proton and gamma-ray emissions in the decay of silicon-25.

CCF UPDATEThe cyclotrons are having a difficult week. Last Friday, the cyclotrons were running a germanium-76 primary beam into the home stretch of the second AT-TPC experiment in S3, when first the CCF radiation safety system malfunctioned and then the K1200 main magnet power supply (MMPS) failed. A quick repair was successful for some hours, but ultimately, a major effort was required that went on for several days. The K500 was switched to a calcium-48 beam on Tuesday, and in the early morning hours of Wednesday, the K1200 main magnet could be ramped and the RF turned on. At that time, the beam chamber vacuum deteriorated and the K1200 had to be turned off again. Regenerating the helium cryo panels fixed the vacuum issue on Thursday, and early Friday morning, the calcium beam was tuned up, only to have the MMPS fail again. A repair effort is underway.

REA UPDATEReA3 delivered tin-120 beam for a JANUS/SeGA experiment, which run till Tuesday morning. New beams of xenon-126 and 128 are being prepared for the forthcoming experiment using the same set-up and that should start Monday. One of the quadrupoles of ReA high energy beam line showed a water leak that cannot be easily fix at this time, as the leak is in one of the coils of the magnet. Therefore a new beam optics of ReA high energy beam line is being calculated to allow running the following experiment without this magnet.

#BLACKINPHYSICS WEEK ON OCTOBER 25 - 31Black In Physics (https://www.blackinphysics.org) will organize seven topical days that cover different aspects of physics. The week will include professional and social events, as well as community-building activities on twitter. Additionally, each day will also feature an article written by black physicists regarding different aspects of black identities. Each of the following physics disciplines will have one day of #BlackInPhysics week dedicated to them: physics education research, high energy and astro-physics, AMO physics, condensed matter and materials physics, soft condensed matter physics, as well as nuclear and medical physics.

• 10/25/20 - Open Mic Night• 10/26/20 - C3: Coffee, Cookie, Chat: Postdoc/Jr

Faculty Mixer• 10/28/20 - Gabbing and Games A UG/Grad Mixer• 10/29/20 - Ask-a-Scientist• 10/30/20 - Let’s Get Quarky DJ/All mixer• 10/31/20 - Virtual Murder Mystery Halloween Party

SEMINARS• THURSDAY, OCT 29-NOV 1

Online via ZoomDNP 2020 Virtual Conference Oct 29 - Nov 1'Division of Nuclear Physics 2020 Fall Meeting'

• FRIDAY, OCTOBER 30 AT 3:00 PMOnline via Zoom, Passcode: 785073Guimei Wang, Brookhaven National Laboratory' National Synchrotron Light Source II (NSLS-II): Present status and upgrade plans'

EDITOR: ERIN O’DONNELL | 517-908-7198 | ODONNELL@NSCL.MSU.EDUTHE GREENSHEET ARCHIVE IS AVAILABLE HERE

Operation of NSCL as a national

user facility is supported by the

Experimental Nuclear Physics Program

of the U.S. National Science Foundation

National Superconducting Cyclotron Laboratory

Michigan State University

640 S. Shaw Lane, East Lansing, Michigan 48824-1321

Phone 517-355-9671 www.nscl.msu.edu