R. Kirchner

Alpha decay of neutron-deficient isotopes with 52 ≦ Z ≦ 55, including the new isotopes 106Te (T12 = 60 μs) and 110Xe

Abstract Using 58Ni(58Ni,.xpγn) reactions and on-line mass separation, the α-decays of very neutron-deficient isotopes of tellurium, iodine, xenon and cesium were studied. The new isotopes 106 Te (T 1 2 = 60 − + μ s ) and 110Xe were identified by their α-lines of 4160 ± 30 keV and 3737 ± 30 keV energy, respectively, with the genetic relationship between the two successive α-decays being verified experimentally, while for several other α-decaying isotopes more precise data were obtained. The observed α-decay properties are discussed within the systematics of energy and reduced width.

Coupling a total absorption spectrometer to the GSI on-line mass separator

Abstract A total absorption spectrometer, constructed and briefly operated at the on-line isotope separator OASIS at Lawrence Berkeley Laboratory, has been moved and installed at the on-line mass separator of GSI Darmstadt. At GSI, the spectrometer has been used for β-decay strength function measurements of nuclei in the vicinity of 100 Sn and 146 Gd.

Decay studies of neutron-rich isotopes of manganese, iron, cobalt, nickel, copper and zinc

Abstract A 46 mg/cm2 thick natW target was irradiated with an 11.5 MeV/u 82Se beam. On-line massseparated samples of projectile-like neutron-rich products from multi-nucleon transfer reactions were investigated by βγ spectroscopy in the mass region A = 52–79. Decay properties of the nuclei 61Mn (0.71 s), 64Fe (2.0 s), 65Co (1.25 s), 69Ni (10 s) and 73mZn (5.8 s) were measured for the first time. For 67Ni a decay scheme could be constructed using information from new γ-transitions. The known decay schemes of 60Mn, 63Fe, 63Co and 69Cu were extended. New half-life values of neutron-rich isotopes are compared with theoretical predictions.

Comparison of radioactive ion-beam intensities produced by means of thick targets bombarded with neutrons, protons and heavy ions

Abstract Target and ion-source techniques which allow rapid separation of thermalized radioactive nuclei from 1–500 g cm 2 thick irradiated target material and continuously convert them into a mono-isotopic ion beam have been proven to be a powerful method of radiochemical separation. These techniques combine nuclear reactions with high-temperature chemistry, metallurgy, solid-state diffusion, and ionization phenomena. Developed at the many mass separators on-line to various accelerators or reactors they are today widely used to produce low-energy (10–60 keV) radioactive ion-beams for physics experiments. Since some years they have reached a stage of development that allows the production of high-intensity beams of up to 1012 ions/s of radioactive isotopes of most elements in the periodic system. Such on-line mass separators seem to be excellent injectors to a second accelerator which accelerates up to 20 MeV/u. This paper discusses the radioactive beam intensities that may be injected into proposed or working European radioactive ion-beam facilities which make use of such injectors. First a short introduction is given to the technique of on-line mass separation. This is followed by a detailed discussion of the three factors that determine the production rates in the target, i.e. reaction cross-sections, primary beam properties, and target thicknesses, and by a discussion of the more decisive factors that control the efficiency with which the radioactive nuclei produced in the target can be transformed into an injection ion-beam of typically 10–60 keV energy. Throughout the discussion the influence of new developments is assessed. Finally, selected examples of realistic beam intensities are given, which are used for intercomparison of the different production methods used by the various European projects.

Decay studies of neutron-rich products from 76Ge induced multinucleon transfer reactions including the new isotopes 62Mn, 63Fe and 71, 72, 73Cu

Abstract By irradiating a nat W target with 9 MeV/u 76 Ge ions, neutron-rich isotopes in the chromiumgermanium region were produced. On-line mass-separated samples were investigated. The new isotopes 62 Mn, 71 Cu, 72 Cu and 73 Cu were identified and their half-lives measured to be 0.88(15), 19.5(16), 6.6(1) and 3.9(3) s, respectively. The half-life of 63 Fe, a nucleus which has previously been detected using particle-identification techniques, was measured to be 4.9(5) s. Decay schemes were derived in most cases. Additional spectroscopic information was obtained on the decays of 73 Zn and 74 Zn. We give evidence that the earlier reported γ-ray activity attributed to 67 Ni belongs to the decay of the 70 Cu isomers. At A = 67 we observed a new β-ray activity of 21(1) s half-life which is here assigned to the decay of 67 Ni.

Direct and beta-delayed proton decay of very neutron-deficient rare-earth isotopes produced in the reaction58Ni+92Mo

Using on-line mass separation of evaporation residues from the reaction58Ni +92Mo→150Yb*, a proton line of 1,055±6 keV energy and 0.42±0.10 s half-life was observed at mass number 147. The origin of this activity is very likely the direct proton decay of147Tm. Beta-delayed protons registered at the same mass position show a pronounced peak structure in their energy distribution. A lower limit of their half-life was set to 1 s.

Beta- and gamma-decay studies of neutron-rich chromium, manganese, cobalt and nickel isotopes including the new isotopes 60Cr and 60gMn

Abstract A 36 mg cm 2 thick natW target was irradiated with 11.5 MeV/u 76Ge of 15 to 20 particle-nA beam intensity. On-line mass-separated samples of projectile-like neutron-rich products from multi-nucleon transfer-reactions were investigated in the region of mass 58–69 by β and γ-ray spectroscopy. The new isotope 60Cr was identified with a half-life of 0.57 (6) s and for the 60Mn ground state a half-life value of 51 (6) s was obtained. Decay schemes were constructed for 58Cr, 58Mn ( t 1 2 = 3 s ), 65,66,67Co and 69Ni. One new γ-ray was found in the decay of 59Cr. The Qβ value of 66Co was measured yielding 9.7 (5) MeV. The comparison of the measured new β half-life of 60Cr with the most recent predictions gave again an enhancement of the experimental value.

New neutron-rich 179Yb and 181,182Lu isotopes produced in reactions of 9 MeV/u 136Xe ions on tantalum and tungsten targets

Abstract The new neutron-rich isotopes 179 Yb and 181,182 Lu were produced in multinucleon transfer reactions by irradiating nat W/Ta targets with 9 MeV/u 136 Xe ions, and identified by mass separation and decay spectroscopy. The measured half-lives of 179 Yb, 181 Lu and 182 Lu are 8.1±0.8, 3.5±0.3 and 2.0±0.2 min, respectively. The properties of the excited states of 181,182 Hf are discussed. The possibility of studying neutron-rich nuclei outside the classical fission-product regions is demonstrated.

Decay studies of neutron-rich radium and actinium isotopes, including the new nuclides 232Ra and 232,234Ac☆

Abstract Isotopes of the elements francium to neptunium were produced in multinucleon-transfer reactions of 11.4 MeV/u 238 U ions with nat W/Ta targets. On-line mass-separated samples were investigated by γ, X and β singles and coincidence measurements. New spectroscopic information was gained on the 231 Ac decay. For the first time, β-delayed γ-rays from 232 Ra and 232,233,234 Ac were observed. Decay schemes for these isotopes are presented, and half-lives of the latter four nuclides were determined to be 250(50) s, 119(5) s, 145(10) s and 44(7) s, respectively. The comparison with theoretical half-life predictions gave remarkable agreement with gross-theory calculations.

Investigation of neutron-rich rare-earth nuclei including the new isotopes 177Tm and 184Lu☆

Abstract Decays of neutron-rich isotopes in the rare-earth region were studied by means of on-line mass separation and β − γ spectroscopy using multinucleon-transfer reactions between beams of 136 Xe (9 and 11.7 MeV/u), 186 W (11.7 and 15 MeV/u) and 238 U (11.4 MeV/u) and targets of nat W and Ta. The higher beam energies appear to be advantageous for the production of such isotopes. Two new isotopes were identified: 177 Tm with a half-life T 1 2 = 85 −15 +10 s , and 185 Lu with T 1 2 ≈ 18 s . A new 47 s activity found at A = 171 is tentatively assigned to the decay of the new isotope 171 Ho. The properties of the ground and excited states of neutron-rich lanthanide isotopes are interpreted within the shell model using the deformed Woods-Saxon potential. A change of the ground-state configuration for odd-mass neutron-rich lutetium isotopes from π 7 2 + [404] to π 9 2 − [514] is suggested, this change being due to the influence of a large hexadecapole deformation. The role of the possible isomeric state in 180 Lu for the nucleosynthesis of 180m Ta is discussed.