M. Lewitowicz

New mass measurements of neutron-rich nuclei near N= 20

Abstract The masses of 39 neutron-rich nuclei in the mass range 17–37 have been measured using a direct time-of-flight technique following the fragmentation of a 48 Ca beam at 55 MeV/nucleon. The masses of 29,30 Ne, 34,35 Mg and 36,37 Al are reported for the first time. The very neutron-rich nuclei, 31–33 Na, are found to be 2–4 MeV less bound than previously believed. A comparison is made with recently available large scale shell model calculations encompassing the deformed A ∼32 nuclei. Conclusions are drawn regarding the extent of the region of deformation, which is found to include 30 Ne.

On the discovery of doubly magic Ni-48

The paper reports on the first observation of doubly-magic Nickel-48 in an experimental at the SISSI/LISE3 facility of GANIL. Four Nickel-48 isotopes were identified. In addition, roughly 100 Nickel-49, 50 Iron-45, and 290 Chromium-42 isotopes were observed. This opens the possibility to search for two-proton emission from these nuclei.

The program LISE: a simulation of fragment separators

This paper describes the program LISE which simulates the operation of fragment separators used to produce radioactive beams via fragmentation. Various aspects of the physical phenomena involved in the production of such radioactive beams are discussed. They include fragmentation cross-sections, energy losses in materials, ionic charge-state distributions, as well as ion optics calculations and acceptance effects. This program is highly user-friendly, and is designed not only to forecast intensities and purities for planning future experiments, but also for beam tuning during experiments where its results can be quickly compared to on-line data. In addition, several general-purpose tools such as a physical parameters calculator, a database of nuclear properties, and relativistic two-body kinematics calculations make it useful even for experiments with stable beams. After a general description of fragment separators, the principles underlying the calculations are presented, followed by a practical description of the program and its features. Finally, a few examples of calculations are compared to on-line data, both qualitatively and quantitatively.

Search for 28O and study of neutron-rich nuclei near the N = 20 shell closure

Abstract A search for 28 O with a 78 AMeV beam of the neutron-rich isotope 36 S has been performed for the first time. Evidence for the unbound character of 28 O was obtained. In the same experiment the half-lives of the very neutron-rich isotopes 27,29 F and 30 Ne were measured and those for 28,29 Ne and 30,31 Na reexamined. The results are compared to shell-model predictions and conclusions drawn regarding the extent of the region of deformation around N = 20.

On the discovery of doubly-magic

The paper reports on the first observation of doubly-magic Nickel-48 in an experimental at the SISSI/LISE3 facility of GANIL. Four Nickel-48 isotopes were identified. In addition, roughly 100 Nickel-49, 50 Iron-45, and 290 Chromium-42 isotopes were observed. This opens the possibility to search for two-proton emission from these nuclei.

^{48}

Abstract We report on the production of the doubly-magic nucleus 100 Sn and other proton-rich nuclei in the A ∼ 100 region in the reaction 112 Sn + nat Ni at 63 MeV/nucleon. The experiment was carried out using the high acceptance device SISSI and the Alpha and LISE3 spectrometers at GANIL. The identification of the reaction products ( A , Z and Q ) was made using the measurements of time-of-flight, energy-loss and kinetic energy.

Ni

The neutron drip line in a neon–magnesium region has been explored by the projectile fragmentation of a 59.8 A MeV 48Ca beam using the new fragment separator LISE 2000 at GANIL. New neutron-rich isotopes, 34Ne and 37Na, have been observed together with some evidence for the particle instability of 33Ne and 36Na.

Identification of the doubly-magic nucleus 100Sn in the reaction 112Sn+natNi at 63 MeV/nucleon

Abstract Very neutron-rich isotopes have been produced by the fragmentation of 55 MeV/u 48 Ca projectiles from GANIL onto a 181 Ta target. The nuclei were separated by means of the doubly achromatic spectrometer LISE and implanted into a semiconductor telescope for identification in Z and A . Their β-delayed neutron radioactivity is observed by means of a 4π β -n coincidence detector. The results include first measurements of the half-life T 1 2 and the neutron emission probability P n for the isotopes 20 C, 40,41,42 p and 43,44 S. They are compared to current theoretical predictions.

Experimental evidence for the particle stability of 34Ne and 37Na

Abstract Decays of over forty short-lived ( T 1 2 from ≈ 50 ns to 70 μs) isomeric states including a new isomer 66mAs produced in the fragmentation of a 112Sn beam (58 A·MeV, 63 A·MeV) on a natNi target were observed at the final focus of the LISE3 spectrometer at GANIL. Their detection, based on the slow (≈ 10 μs) time correlation of identified ions with the characteristic γ-radiation, represents a novel method to search for new isomers and can be used for unambiguous isotope identification for projectile fragment separator experiments. Isomeric yields and isomer-to-total production ratios were determined.

β-Delayed neutron emission of the isotopes 20C, 40,41,42P, 43,44S☆

Abstract At the projectile-fragment separator FRS at GSI, longitudinal momentum distributions and production cross-sections were investigated for reactions between a 500 A× MeV 86 Kr beam and beryllium, copper and tantalum targets. Fragments in a wide A Z range were studied. For fragments close to the projectile the measured longitudinal momentum distributions agree qualitatively with a semi-empirical parametrization. Deviations from this simple picture are found, however, for the momentum widths of light fragments and for the momentum transfer to those fragments that differ in their A Z ratio from the most probable value. The experimental data on production cross-sections are used for testing the predictions obtained from a semi-empirical parametrization, a geometrical abrasion model and an intranuclear-cascade model. The cross-section for the formation of the doubly magic nucleus 78Ni in 86Kr fragmentation is estimated to be 17 pb.