Probing the Skin of a Lead Nucleus
April 27, 2021•
Physics 14, 58
Researchers make the most precise measurement yet of the neutron distribution in a heavy nucleus, with implications for the structure of neutron stars.
Figure 1: A cartoon image of a lead-208 nucleus, showing the mixed proton-neutron core and the neutron “skin” (left). Measuring the thickness of the neutron skin offers clues about how neutron stars are structured (right).×
Popular cartoon visualizations depict the protons and neutrons in a nucleus as colored marbles packed randomly into a sphere. In reality, heavy nuclei in which neutrons tend to outnumber protons are more differentiated, with the neutrons nudged radially outward. At the outer limits of such nuclei, the neutrons form a thin “skin” enclosing a core of mixed neutrons and protons (Fig. 1). Now, the Lead Radius Experiment (PREX) Collaboration at the Thomas Jefferson National Accelerator Facility in Virginia has determined the thickne
Scientific American
Upgrades to the SuperNova Early Warning System (SNEWS) detection system offer advance notice of impending blasts
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Discovered in 1987, Supernova 1987A is the closest exploding star to Earth to be detected since 1604. It resides in the nearby Large Magellanic Cloud, a dwarf galaxy adjacent to our own Milky Way. Credit: NASA, ESA, K. France
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Sky watchers both amateur and professional will soon have a new system to alert them to the spectacular death throes of stars in our galaxy. A revamped version of the SuperNova Early Warning System (SNEWS), a software program hosted on servers at Brookhaven National Laboratory on Long Island, New York, will soon provide more reliable, precise and timely notice of any star going supernova in the Milky Way an event that promises to be a once-in-a-lifetime display.
, observed that low-energy neutrinos interact with an argon nucleus through the weak nuclear force in a process called coherent elastic neutrino-nucleus scattering, or CEvNS, which is pronounced “sevens.” Like a ping-pong ball bombarding a softball, a neutrino that hits a nucleus transfers only a small amount of energy to the much larger nucleus, which recoils almost imperceptibly in response to the tiny assault.
Laying the groundwork for the discovery made with the argon nucleus was a 2017 studypublished in
Science in which COHERENT collaborators used the world’s smallest neutrino detector to provide the first evidence of the CEvNS process as neutrinos interacted with larger and heavier cesium and iodine nuclei. Their recoils were even tinier, like bowling balls reacting to ping-pong balls.