A. Płochocki

Alpha decay of neutron-deficient isotopes with 78 ⪕ Z ⩽ 83 including the new isotopes 183, 184Pb and 188Bi

Abstract Using on-line mass separation of evaporation residues from heavy-ion-induced fusion reactions, three new isotopes were identified by their alpha decay, E α given in keV: 183 Pb, 6715(20), 184 Pb, 6632(10) and 188 Bi, 6820(20). Half-lives were determined for 184 Pb, 0.55(6)s, 185 Pb, 4.1(3)s and 183 Tl, 0.060(15) s. The alpha branching ratios were re-measured for 182–184 Hg and 178, 179 Pt, the results are discussed within the framework of alpha width systematics.

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.

The decay of 0.57 s114Cs

Fusion reactions between58Ni projectiles and58Ni target nuclei were used to produce114Cs activity, which was studied by on-line mass separation and decay spectroscopy. The obtained half-life of 0.57±0.02 s and the probability ratio of 44±3 between betadelayed proton and beta-delayed alpha emission represent data with improved precision. The absolute branching ratios for both particle decay modes were determined to be (7 ±2)×10−2 and (1.6±0.6)×10−3, respectively. These branching ratios and the shapes of particle spectra are discussed with reference to the statistical model calculations. Groundstate alpha decay of114Cs was observed with an alpha energy of 3,226±30 keV and a branching ratio of (1.8±0.6)×10−4. An upper limit of the branching ratio for a possible ground-state proton decay was set at 5×10−4. Fromγ-ray singles andγ-γ coincidence measurements, excited states in114Xe are proposed.

Beta decay of neutron-deficient even-mass indium isotopes: Evidence for population of highly-excited states in the cadmium-daughter nuclei

Abstract By using mass-separated sources, positrons as well as β-delayed protons and γ-rays were measured from the β-decay of 102 In ( T 1 2 = 22 ± 1 s ) and 100 In ( T 1 2 = 6.1 ± 0.9 s ). In particular, the average β + (β + + EC ) ratio for the decay of 102 In was measured to be 0.76(4) and the level scheme of 102 Cd was extended. Whereas no direct β + EC feeding of the identified 102 Cd levels was observed, there is evidence for population of 102 Cd states at high excitation energy followed by statistical γ-decay. This feature, which has been deduced on the basis of the measured positron spectrum and the measured β + (β + + EC ) ratio of the 102 In decay, is compared to the decay properties of the heavier odd-odd indium isotopes 104 In, 106 In and 108 In, and is also used to interpret the observed β-delayed proton data of 102 In and 100 In. For the first time, large-space shell-model calculations have been performed for the Gamow-Teller decay of heavy odd-odd nuclei. The decay results from these calculations are in good overall agreement with the gross decay properties of 102 In and 100 In deduced from the experiment.

Decay properties of the new isotopes94Ag and95Ag

By using a40Ca beam of the UNILAC accelerator the new isotopes94Ag and95Ag were produced through58Ni(40Ca,p3n) and58Ni(40Ca,p2n) reactions, respectively, and identified by detectingβ-delayed protons from mass-separated sources.94Ag represents the heaviest N=Z nucleus with known decay properties. Theβ-decay half-lives of94Ag and95Ag were determined to be 0.42±0.05 s and 2.0±0.1 s, respectively. The measuredβ-decay properties are compared with model predictions.

New neutron-deficient isotopes of lanthanum and cerium

The short-lived neutron-deficient isotopes of lanthanum and cerium were produced in the 32S+96, 98Ru reactions and separated according to their masses. Seven isotopes 123–125La and 124–127Ce have been first observed and their half-lives and low-energy γ-ray data are reported. In addition, low-energy γ-ray data are given for the 122–125Ba and 127La decays. The β-decay probabilities for Ce, La and Ba isotopes are discussed in terms of the average β-strength function.

Isomerism in 96Ag and non-yrast levels in 96Pd and 95Rh, studied in β decay

The β decay of 96Ag (Z=47,N=49) was investigated by measuring positrons, X rays as well as β-delayed protons and γ rays. The γ radiation was studied by means of germanium detectors and a NaI total-absorption spectrometer. Two β-decaying isomers in 96Ag were established with half-lives of 4.40(6) and 6.9(6) s and tentative spin–parity assignments of (8+) and (2+), respectively. For both isomers, the intensities of β transitions to low-lying levels of 96Pd (Z=46,N=50) and β-delayed proton decays to levels in 95Rh (Z=45,N=50) were measured. Several new 96Pd levels were firmly established. The level energies, their γ decays and the Gamow–Teller decay of 96Ag are compared to shell-model predictions. A new low-lying level in 95Rh was found at 680 keV excitation energy. Through a comparison with low-lying states of N=50 isotones, this level is interpreted as the first excited 7/2+ state built on the proton 9/2+ ground state. The assignments of further excited states in 95Rh are discussed.

β-delayed particle emission from neutron-deficient Te, I, Xe, Cs and Ba isotopes

Abstract Using 58Ni, 63Cu(58Ni, xpyn) reactions and on-line mass separation the β-delayed proton and α-particle emission from neutron-deficient isotopes with 52 ≦ Z ≦ 56 was studied. Half-lives and β-delayed particle branching ratios were determined. Coincidences between β-delayed particles and γ-rays were measured for 113Xe (protons), 114Cs (protons and α-particles) and 117Ba (protons). Coincidences between positons and β-delayed protons were recorded for 113Xe and 114Cs, yielding QEC-Sp values of 7.92(15) and 8.73(15) MeV, respectively. The results are discussed within the statistical model.

Beta decay of 103In: Evidence for the Gamow-Teller resonance near 100Sn

Abstract The β decay of the neutron-deficient isotope 103 In was investigated by using total absorption γ-ray spectrometry on mass-separated sources. The measurement reveals a high-lying resonance of the β-decay strength in striking disagreement with high-resolution γ-ray data. The result is discussed in comparison with shell-model predictions.

A new pulsed release method for element selective production of neutron rich isotopes near 208Pb

Abstract A new method to reduce the isobaric contamination problem for the production of neutron rich Bi, Pb and Tl nuclei at on-line mass separators, based on the pulsed release of these radioactive species, is presented. The results of a feasibility study are reported.