J. Żylicz

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.

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.

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.

Yrast levels of 220Ra populated in the 208Pb(14C, 2n) reaction

Abstract Yrast states in the nucleus 220 Ra were studied by means of the 208 Pb( 14 C, 2n) reaction at 61 and 64 MeV. A staggering sequence of levels of positive and negative parity has been observed up to spin and parity I π = 16 + (18 + ) and from I π = 5 − to I π = 17 − , respectively. These states are connected by strong E1 transitions competing with the stretched E2 transitions, the B( E 1) B( E 2) ratio being ~ 10 −6 fm −2 . The ratio of the excitation energy of the 4 + state to that of the 2 + state is close to the vibrational limit. The moment of inertia associated with the negative-parity yrast states is slightly increasing with the rotational frequency ω. It is considerably higher than that of the positive-parity states at lower spins, the difference decreasing monotonically with increasing ω. The data are discussed with reference to the octupole vibrational picture as well as to the results of recent models predicting reflection-asymmetric shapes in the Ra-Th region.

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.

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.

Alpha decay of 114Ba

The neutron-deficient isotope 114Ba was produced in a fusion evaporation reaction at the GSI On-Line Mass Separator. We measured the α-particle energy of 114Ba, the half-life of its daughter nucleus 110Xe, and the α-decay branching ratios for 114Ba, 110Xe and 106Te.

The Gamow-Teller transitions in the96Pd→96Rh decay

Using the40Ca(4.2 MeV/u) +60Ni reaction and on-line mass separation, the decay properties of4696Pd50 were reinvestigated. From a comparison of experimental and theoreticalβ+/(EC +β+) probability ratios, theQEC value was deduced to be 3,450 ± 150 keV. The strength was determined for four 0+→1+ Gamow-Teller beta transitions and found to be quenched as compared to predictions of the single-particle shell model. For96Pd and94Ru the sources of this quenching are discussed.

Measurements of proton separation-energies close to the proton drip line in the antimony—cesium region

Abstract Mass-excesses and proton separation energies are determined for 114Cs, 110I and 106Sb - the lightest known isotopes of cesium, iodine and antimony. The localization of the proton drip line is discussed.

Decay properties of very neutron-deficient isotopes of silver and cadmium

Abstract The β-decay properties of the lightest known silver and cadmium isotopes are investigated. Data for β-delayed γ-ray emission of 95–97Ag and for β-delayed proton emission of 96Ag and 97Cd are presented. The experimental findings are compared with predictions of shell-model calculations in which a variety of model spaces and effective interactions are considered.