New Neutron Rich Nuclei Near 28pb

The level properties near the stable doubly-magic nuclei formed the experimental grounds for the theoretical description of nuclear structure. However with a departure from the beta-stability line, the classical well-established shell structure might be modified. In particular, it may even vanish for extremely exotic neutron-rich nuclei near the neutron-drip line. Presently, it is impossible to verify such predictions by a direct experimental studies of these exotic objects. However, one may try to observe and understand the evolution of the nuclear structure while departing in the experiment as far as possible from the stable nuclei. An extension of experimental nuclear structure studies towards the nuclei characterized by high neutron excess is crucial for such verifications as well as for the [tau]-process nucleosynthesis scenario. Heavy neutron-rich nuclei, south-east of doubly-magic 2°8Pb, were always very difficult to produce and investigate. The nuclei like 218Po and 214Pb or 21°Tl marked the border line of known nuclei from the beginning of the radioactivity era for over ninety years. To illustrate the difficulties, one can refer to the experiments employing the on-line mass separator technique. A spallation of heavy targets like 232Th and 238U by high-energy protons was proven as a source of heavy neutron-rich nuclei. The isotopes near and beyond doubly-magic 2°8Pb were produced too. However, such studies often suffered from an isobaric contamination of much more strongly produced and efficiently released elements like francium or radon and their decay products. A new experimental technique, based on the pulsed release element selective method recently developed at the PS Booster-ISOLDE at CERN [7,8,9] greatly reduces the contamination of these very short-lived [alpha]-emitters (Z ≥ 84) for the isobaric mass chains A=215 to A=218.

The level properties near the stable doubly-magic nuclei formed the experimental grounds for the theoretical description of nuclear structure. However with a departure from the beta-stability line, the classical well-established shell structure might be modified. In particular, it may even vanish for extremely exotic neutron-rich nuclei near the neutron-drip line. Presently, it is impossible to verify such predictions by a direct experimental studies of these exotic objects. However, one may try to observe and understand the evolution of the nuclear structure while departing in the experiment as far as possible from the stable nuclei. An extension of experimental nuclear structure studies towards the nuclei characterized by high neutron excess is crucial for such verifications as well as for the[tau]-process nucleosynthesis scenario. Heavy neutron-rich nuclei, south-east of doubly-magic[sup 208]Pb, were always very difficult to produce and investigate. The nuclei like[sup 218]Po and[sup 214]Pb or[sup 210]Tl marked the border line of known nuclei from the beginning of the radioactivity era for over ninety years. To illustrate the difficulties, one can refer to the experiments employing the on-line mass separator technique. A spallation of heavy targets like[sup 232]Th and[sup 238]U by high-energy protons was proven as a source of heavy neutron-rich nuclei. The isotopes near and beyond doubly-magic[sup 208]Pb were produced too. However, such studies often suffered from an isobaric contamination of much more strongly produced and efficiently released elements like francium or radon and their decay products. A new experimental technique, based on the pulsed release element selective method recently developed at the PS Booster-ISOLDE at CERN[7,8,9] greatly reduces the contamination of these very short-lived[alpha]-emitters (Z[ge] 84) for the isobaric mass chains A=215 to A=218.

The monograph describes the properties of the lightest nuclei with large excess of neutrons. The results of theoretical and experimental studies of neutron-rich isotopes with 1

The recently developed methods allowing the experimental studies on new neutron-rich nuclei beyond doubly-magic 2°8Pb are briefly described. An identification of new neutron-rich isotopes 215Pb and 217Bi, and new decay properties of 216Bi studied by means of a pulsed release element selective technique at PS Booster-ISOLDE are reported.

Radioactive beam experiments have made it possible to study the structure of nuclei at the neutron drip line. Pair correlations play a crucial role in such nuclei and characteristic features include an extended neutron halo density and a large dipole strength near threshold. The most detailed studies have been performed for 11Li. I will present a 3-body model that explains the main features of the data obtained for this nucleus.