A D V A N C E D M A T E R I A L S & P R O C E S S E S | M A R C H 2 0 2 3 9 zigzag pattern, the material can withstand substantial deformation without reaching a breaking point. Second, when the cuts pull open, this forces the electrical signal to travel further, moving up and down the zigzag. “The sensor can be easily incorporated into existing wearable materials such as fabrics and athletic tapes, convenient for practical applications,” says researcher Yong Zhu. www.ncsu.edu. MEASURING THIN SKIN OF CALCIUM NUCLEI Studying the rare calcium-48 isotope, physicists determined how its 20 protons and 28 neutrons are distributed inside the nucleus. Measurements took place at the DOE’s Jefferson Lab, Newport News, Va. The researchers found that calcium’s protons and neutrons aren’t simply sprinkled throughout the nucleus—instead, they form a neutron-rich thin skin around a core of more-evenly distributed protons and neutrons. The researchers found that the calcium-48 neutron-rich skin is just 0.121 femtometers thick, a femtometer being just one billionth of a meter. This is thinner than many models predicted and is somewhat surprising in comparison with the thick neutron skin seen in lead. This is because existing theoretical models predicted that calcium-48 should have a thicker skin than it does, while these same models predicted a thinner neutron skin for lead than was measured. This new measurement is an exciting development for nuclear physics. It warrants further exploration of the thin skins of other heavy nuclei to determine why there’s a large discrepancy between nuclei of calcium, which has a medium mass, and more massive lead nuclei. Combining the data from these experiments will provide scientists with important constraints on future models of nuclear structure. The results also have implications for the neutron matter equation of state, which describes the structures of neutron stars and the dynamics of neutron-star mergers. energy.gov. In Jefferson Lab’s Experimental Hall A, scientists measured the distribution of protons and neutrons inside calcium-48 nuclei.
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