New Mass Measurements Of Neutron Rich Nuclei Near N

Extensive new mass measurement capabilities have evolved with the development of recoil spectrometers. In the Z = 3 to 9 neutron-rich region alone, 12 neutron-rich nuclei have been determined for the first time by the fast-recoil direct mass measurement method. A recent experiment using the TOFI spectrometer illustrates this technique. A systematic investigation of nuclei that lie along or near the neutron-drip line has provided a valuable first glimpse into the nuclear structure of such nuclei. No evidence for a large single-particle energy gap at N = 14 is observed; however, a change in the two-neutron separation model calculations, and is interpreted in terms of the smaller 1s12 - 1s12 interaction compared to that of the 0d52 - 0d52 neutron-neutron interaction. 18 refs., 7 figs., 1 tab.

This experiment has demonstrated that direct mass measurements can be performed (albeit of low precision in this first attempt) using the M proportional to ET2 method. This technique has the advantage that many particle-bound nuclei, produced in fragmentation reactions can be measured simultaneously, independent of their N or Z. The main disadvantage of this approach is that both energy and time-of-flight must be measured precisely on an absolute scale. Although some mass walk with N and Z was observed in this experiment, these uncertainties were largely removed by extrapolating the smooth dependence observed for known nuclei which lie closer to the valley of .beta.-stability. Mass measurements for several neutron-rich light nuclei ranging from 17C to 26Ne have been performed. In all cases these measurements agree with the latest mass compilation of Wapstra and Audi. The masses of 2°N and 24F have been determined for the first time.

Presenting more than 100 papers devoted to the understanding of fission processes and neutron-rich nuclei, this book covers all forms of fission, from spontaneous fission of 252Cf to high-energy fragmentation. Together with studies on properties of neutron-rich nuclei and astrophysics, the book also features new experimental techniques, directions and the emerging new radioactive beam facilities.

This project was directed toward the study of neutron-rich nuclei using the experimental facilities at LAMPF, which is a part of LANL. The principal results of the investigation include the discovery of many new isotopes along with a measurement of their masses and in particular those nuclides in the Z = 7--19 and 14 --26 regions of the chart of the nuclides. Thirty-four new nuclides were detected and studied with their masses being measured with relatively high accuracy, and an additional twenty-six that were previously known and measured were remeasured to an improved accuracy. Besides providing new information about the mass surface in new and extended redons of the chart of the nuclides, this investigation enabled properties and previously unknown structure of some of the nuclei to be determined such as nuclear deformation among some of the nuclides. Also a study of the neutron pairing gaps and the proton pairing gaps among these nuclides was made. Other developments also achieved included instrument (TOFI) improvements and upgrades and theoretical investigations into the masses of the hadrons.

A small revolution in our ability to perform mass measurements of light-mass, neutron-rich nuclei has occurred during the last five years with the extension of the direct, total mass measurement method to fast recoiling nuclei. To date the work of two groups, one using the SPEG spectrometer at GANIL and the other using the TOFI spectrometer at LAMPF, has yielded over 85 mass measurements of which 62 had not been reported previously. Extending from the neutron-halo nucleus 11Li up to 66Fe, a region relevant to the astrophysical r-process, these measurements have provided a valuable first glimpse into the interesting nuclear structure present in many of these exotic nuclei. Herein we highlight the nuclear structure insight which as been gained from these measurements, especially that learned from a comparison to recent shell model calculations. Attention is given to: (1) the binding of loosely-bound neutron halo nuclei; (2) the N=14--16 region in the neutron-rich isotopes of O, F, and Ne where the strong two-body interaction plays an important role; (3) the deformed intruder state region around 31Na of long standing interest; (4) the neutron-rich isotopes of sulfur and chlorine; and (5) the question of the isospin dependence (or independence) of neutron and proton pairing energies in the fp shell. Only the briefest account of this work can be given here; emphasis is placed on the most recent results. 24 refs., 3 figs.