Physics Division Research Highlights

Nuclear Charge Radius of 8He

Helium-8 (8He) is the most neutron-rich matter that can be synthesized on earth: it consists of two protons and six neutrons, and remains stable for an average of 0.2 seconds. Unlike regular helium (3He and 4He), which usually has two and occasionally one neutron that pack closely with two protons, the additional neutrons in 8He form a halo around a compact, 4He like core. Because of its intriguing properties, 8He has the potential to reveal new aspects of the fundamental forces among the constituent nucleons. Argonne physicists have recently succeeded in laser trapping and cooling this exotic helium isotope, produced at the GANIL cyclotron facility in northern France, and have performed precision laser spectroscopy on individual trapped atoms. Based on atomic frequency differences measured along the isotope chain 3He – 4He – 6He – 8He, the nuclear charge radius of 8He has been determined for the first time. The result can now be compared with the values predicted by a number of nuclear structure calculations and is testing their ability to characterize this loosely-bound halo nucleus.

nuclear models of He-4, He-6 and He-8


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