W.-D. Schmidt-Ott

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

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.

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.

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.

Beta-decay half-lives of new neutron-rich chromium-to-nickel isotopes and their consequences for the astrophysical r-process

Abstract Beta-decay studies of the new neutron-rich isotopes 58,59Cr, 63Mn, 66,67Co and 69Ni, yielding distinctly shorter half-lives than the corresponding theoretical predictions, are presented. The influence of the short half-lives on the r-process calculations of nuclear abundances is discussed. It is concluded that a significantly higher neutron density than the one obtained from explosive helium burning in supernovae is need to reproduce the observe abundances around A=80.

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

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.

Identification of μs-isomers produced in the fragmentation of a 112Sn beam

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.

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.

Measurement of the magnetic moments of 14B and 15B using projectile fragmentation spin polarization

Abstract By making use of the phenomenon of ejectile spin polarization in the projectile fragmentation reaction as a tool to produce polarized radioactive nuclei, the magnetic moments of 14B and 15B have been determined by the β-NMR measurement, to be μ( 14 B ) = (1.185±0.005) μn and μ( 15 B ) = (2.659±0.015) μn where μn is the nuclear magneton. The comparison of the results with shell model calculations suggests that the single-particle energy of the neutron s 1 2 orbit shifts downwards considerably compared with the d 5 2 orbit in 14B, and also indicates the importance of Jπ = 2+ configurations of neutrons in the sd shell. Thus, it is demonstrated that the measurement of magnetic moments provides useful information on the nuclear structure in the newly accessible region of light-mass unstable nuclei.

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.

Evidence of new isotopes:169, 170Ir,166, 167, 168Re

At the Darmstadt UNILAC newα-emitting nuclei were produced in the bombardment of89Y and93Nb targets using84Kr ions with energies in the range of 5.1 to 5.5 MeV/u, and 5.8 to 6.4 MeV/u, and using86Kr ions with energies in the range of 5.6 to 6.0 MeV/u. Reaction recoils emitted from the targets were stopped and transported with argon to a collection site. Using three alpha detectors and spectrum multiscaling, energies and half-lives were measured. Ir and Re isotopes were identified by cross bombardments, excitation function data andα-systematics. The decay characteristics of the new species are as follows: Estimates onα-branching ratios have been obtained for169, 170Os and166, 167, 168Re.