Production of very neutron-rich nuclei with aGe76beam

Abstract

Production cross sections for neutron-rich nuclei from the fragmentation of a 76 Ge beam at 132 MeV/u were measured. The longitudinal momentum distributions of 34 neutron-rich isotopes of elements 13 ≤ Z ≤ 27 were scanned using a novel experimental approach of varying the target thickness. Production cross sections with beryllium and tungsten targets were determined for a large number of nuclei including 15 isotopes first observed in this work. These are the most neutron-rich nuclides of the elements 17 ≤ Z ≤ 25 ( 50 Cl, 53 Ar, 55,56 K, 57,58 Ca, 59,60,61 Sc, 62,63 Ti, 65,66 V, 68 Cr, 70 Mn). A one-body Qg systematics is used to describe the production cross sections based on thermal evaporation from excited prefragments. Some of the fragments near 58 Ca show anomalously large production cross sections.

Production cross sections from82Se fragmentation as indications of shell effects in neutron-rich isotopes close to the drip-line

“…35 pnA, accelerated by the coupled cyclotrons at the NSCL, was fragmented in a series of beryllium targets and a tungsten target, each placed at the object position of the A1900 fragment separator [30]. In this work we used an identical configuration to our previous experiment with a 76 Ge beam [1], where the combination of the A1900 fragment separator with the S800 analysis beam line [31] formed a two-stage separator system, that allowed a high degree of rejection of unwanted reaction products. At the end of the S800 analysis beam line, the particles of interest were stopped in a telescope of eight silicon PIN diodes (50×50 mm 2 each) with a total thickness of 8.0 mm.…”

“…In our previous cross section measurements in the region around 62 Ti ( 76 Ge primary beam) [2] we observed a systematic variation of the production cross sections that might point to nuclear structure effects, such as an onset of collectivity, that are not included in global mass models that were used to construct the basis of the systematics. The present work, since it is based on isotope production from a different primary beam, covering the same region of the nuclear chart, provides an independent check of this interpretation.…”

“…Indeed, recent measurements at the NSCL [1,[4][5][6] have demonstrated that the fragmentation of 48 Ca and 76 Ge beams can be used to produce new isotopes in the proximity of the neutron dripline. Continuing this work, we report here the next step with a newly developed 82 Se beam towards the fundamental goal of defining the absolute mass limit for chemical elements in the region of calcium.…”

“…A number of production mechanisms have been used to produce neutron-rich isotopes for 20 ≤ Z ≤ 28 [1] but, in the last few years, two reaction mechanisms were the most effective at producing nuclei in this region:…”

“…• projectile fragmentation -an experiment with a 76 Ge (132 MeV/u) beam produced 15 new isotopes of 17 ≤ Z ≤ 25 [2],…”