Among the dozens of papers being presented by Berkeley Lab researchers is a new technique for the study of unstable atomic nuclei developed by I-Yang Lee and his colleagues in the Nuclear Science Division. It's a new way of studying this kind of nuclei, and we've had some interesting surprises.
Z stands for atomic number, the number of protons in a nucleus.
But smaller neutron-rich nuclei exist only fleetingly in nature and must be created to be studied, typically by bombarding a target with an accelerated beam of ions. But when we split a vanadium nucleus with a beam of carbon ions, one of the fragments is heavy magnesium, with high excitation. As this fragment decays we can observe the energy and distribution of the emitted gamma rays to learn about its nuclear shell properties, angular momentum, shape, and so on. The catch is, Lee explains, typically the nuclei of interest are studied as fragments in the cyclotron beam, meaning they are traveling at high velocity relative to the gamma-ray detector. The resulting gamma-ray spectrum is smeared by the Doppler effect, because gamma rays traveling in the same direction of the fragment have more energy when they hit the detector, while gamma rays in the opposite direction have less.