Facilities and Methods: Heavy Element Spectroscopy at JYFL

Abstract

A central theme throughout the history of experimental nuclear physics has been the pursuit of nuclei at the extremes. These extremes, be they in terms of mass, proton-to-neutron ratio, or spin and excitation energy, provide the most stringent tests for our current nuclear structure theories. The pursuit of these extremes also provides impetus to develop and exploit new techniques and instrumentation. At the Department of Physics of the University of Jyväskylä (JYFL), a major part of the experimental program is devoted to the study of heavy nuclei along the proton dripline and superheavy nuclei in the transfermium region. This program was initiated in the mid-1990s when a small array of TESSA-type germanium detectors known as DORIS (DOdecahedral aRray In Suomi) was coupled to the gas-filled recoil separator RITU [1]. Using the Recoil-Decay Tagging (RDT) technique [2], whereby the delayed charged particle radiation measured at the focal plane of the recoil separator is used to identify the gamma-rays of interest, it was possible to observe gamma-rays from the yrast band of the neutron-deficient nucleus 192Po for the first time [3]. The production cross-section of 192Po was on the order of 10 microbarns. This should be compared to the gamma-ray background from fission that is produced with a cross-section of the order of one barn. Over the decade or so since these initial studies, the instrumentation and range of techniques used at JYFL has evolved steadily such that currently in-beam studies of nuclei produced with cross-sections below 100 nanobarns are possible [4]. An overview of the developments in spectroscopic studies of deformed superheavy nuclei was given in the earlier Nuclear Physics News article of Butler and Leino [5]. This article reports on developments at JYFL since that time.