N. Kaffrell

Identification of Short-lived Isotopes of Zirconium, Niobium, Molybdenum, and Technetium in Fission by Rapid Solvent Extraction Techniques

Einige mehr orientierende Versuche mit anderen Nukliden sollten schließlich noch zeigen, daß das hier eingehend untersuchte System kein Sonderfall ist. Dazu wurden wägbare Mengen an radioaktiv markiertem Kobalt, Zink, Thallium oder Blei gemeinsam mit Wismut aus komplexalkalischem, borsäurehaltigem Medium abgeschieden; die Wismutschicht war 1,0 mg/cm, die der Fremdkomponente 0,2 mg/cm dick. Nach der Abscheidung wurde die Schicht bei einem Potential von 0 , 0 5 bis 0 , 1 5 V in 0,5 η Salzsäure (Zn, Tl) oder 0,5 η Salpetersäure (Co, Pb) von 70 °C gebracht. Innerhalb von 2-3 min waren 97 + 4% des Zinks, 98 + 2 % des Thalliums und 90% des Bleis abgelöst, während die Ablösung des Kobalts langsam verlief und nach 20 min erst 75% umfaßte.

Collective excitations in the transitional nuclei 224, 226Ra

Abstract The γ-rays following the β − decay of 224,226 Fr have been investigated by means of γ-ray singles including multispectrum analysis and γ-γ coincidence measurements using Ge(Li) spectrometers. Most of the observed transitions could be placed in level schemes comprising 40 excited states of 224 Ra and 40 excited states of 226 Ra. The properties of the collective states of 224,226 Ra are discussed. It is concluded that the ground states of these nuclei possess a non-zero octupole deformation.

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.

Collective states fed by weak α-transltions in the 232U chain

Abstract The 232 U decay chain has been investigated down to 212 Pb using Ge(Li) spectrometers in singles and coincidence measurements. In the decay of 232 U and 228 Th some 10 −5 −10 −6 % α-branchings to collective states at ⪆ 400 keV in 228 Th and 224 Ra, respectively, have been identified. Hindrance factors (HF) calculated for all α-transitions are discussed in terms of nuclear models. In particular, for the K π = 0 + bands with the heads at 831.4 and 916.4 keV in 228 Th and 224 Ra, respectively, the low HF values are consistent with the quadrupole-pairing vibrational nature of these states indicated by previous (p, t) reaction studies. No evidence has been found (branching ratio −6 %, HF > 10 5 ) for an α-transition to a hypothetical two-phonon 0 + state in 224 Ra which should be expected at ≈ 430 keV, if the 215.98 keV 1 − state were due to harmonic octupole vibrations. The alternative interpretation of this 1 − state as a shape isomer is not supported by the analysis of the half-lives of the 3 − and 5 − rotational states. For the decay of 224 Ra and its descendants, one new transition and improved energies for the leves are reported.

SISAK 3 – An Improved System for Rapid Radiochemical Separations by Solvent Extraction

SISAK is a well established radiochemical technique used for studies of nuclides with half-lives down to ~ 1 s. The method is based on multistage solvent extraction steps applying specially designed centrifuges for fast phase separation. The equipment has been improved to gain access to even shorter half-lives, and to decrease the amount of liquid used. The new minisystem, SISAK 3, consists of a degassing unit to separate the gases from the liquid and of one to four centrifuges for rapid separation of the two phases after solvent extraction. The degasser and the centrifuges have volumes of about 0.1 and 0.3 ml, respectively. The liquid flow-rate per phase can be varied from about 0.1 ml/s up to about 3 ml/s, and the jet gas flow-rate from about 10 ml/s up to some hundred ml/s. The properties of the new system and its application to fast separations are briefly outlined.

Structure of high-spin states in 232Th, 234U and 236U

Abstract Multiple Coulomb excitation of 232 Th, 234 U and 236 U by 5.3 MeV u 208 Pb ions has been studied using γ-ray spectroscopy. Excitation of ground-band levels is observed up to spin I π = 26 + (tentatively 28 + ) in 232 Th and 234 U and I π = 28 + (tentatively 30 + )in 236 U. High-spin levels of the K π = 0 − octupole-vibrational bands are also observed in these nuclei. The measured transition energies between ground-band levels suggest that at I≈ 28 h several units of angular momentum are carried by single particles aligned with the rotation axis.This result can be understood in terms of a super band built on aligned two-quasiparticle configurations which crosses the ground-state rotational band at a rotational frequency of h ω ≳ 0.25 MeV (I ≳ 28 h ) . The E2 transition-matrix elements deduced from the experimental γ-yields agree within their errors with the rigid-rotor predictions up to the highest spins observed.The experimental results are discussed using the concept of rotation alignment and are compared with predictions of the rotation-vibration model and the interacting-boson model.

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.

The combination of the gas jet recoil technique with the fast chemical on-line separation system SISAK

The fast chemical on-line separation system SISAK has been connected to a gas jet recoil transport arrangement. Pure fractions of short-lived La, Ce and Pr nuclides have been isolated from complex mixtures of reaction products obtained by thermal-neutron-induced fission of 235U.

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.