P. Tidemand-Petersson

Alpha decay of neutron-deficient mercury isotopes and their daughters

Abstract Half-lives, decay energies and branching ratios have been measured for the α-decay of neutron- deficient mercury isotopes and their daughters. The lightest mercury isotope, 177 Hg( E α = 6.580MeV), has a half-life of 0.17±0.05sec. The heaviest observed α-emitter is 188 Hg. Coincidences between α-particles and γ-rays were measured and weak transitions to excited states could be determined. The spectroscopic results are interpreted as evidence for rotational structure in the light odd-mass platinum isotopes. The existence of a pronounced even-odd variation in the Q -values for α-decay of mercury isotopes has been confirmed.

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.

Alpha decay studies of tellurium, iodine, xenon and cesium isotopes☆

Abstract Very neutron-deficient isotopes in the trans-tin region were produced by reactions of 290 MeV 58 Ni ions on 58 Ni targets, and studied by on-line mass separation at GSI. Twelve α-emitters — 107–110 Te, 110–113 I, 111–113 Xe, 114 Cs — were identified. Systematics of Q α values and reduced α-widths for this new island of α-emission are discussed.

Alpha decay of neutron-deficient ytterbium isotopes and their daughters

Abstract Ytterbium isotopes with mass numbers 153–158 have been produced at the ISOLDE on-line mass separator facility. The a-decay energies, half-lives and α-branching ratios were measured. The previously unknown nuclide, 153 Yb, was found to decay with a half-life of 4.0 ± 0.5 sec. Alpha emission was observed for the first time from 158 Yb. For the remaining isotopes, earlier mass assignments were confirmed. The α-decay properties of nuclides that were found as daughters of the ytterbium isotopes were also investigated. Alpha-branching ratios were derived for the nuelides 153 Tm, 152, 153 Er, 152 Hoand 150 Dy. The systematics of α-energies and α-widths are discussed.

Beta-delayed proton emission from 97Cd and 99Cd

Abstract Two new β-delayed proton precursors, 97,99 Cd, have been identified at the ISOLDE on-line isotope separator. The proton branching ratio for 99 Cd is (1.7 +1.1 −0.5 ) × 10 −3 . The 99 Cd proton spectrum is discussed in terms of the statistical model with Porter-Thomas fluctuations. The half-life of 99 Cd was determined to be 16±3 sec. A search for 98 Cd was also performed and it was found to be a pure β-emitter with a probable half-life of ≈ 8 sec.

Properties of the lighest known caesium isotopes 114–118Cs

Abstract Neutron-deficient caesium isotopes with mass numbers from 114 to 118 have been studied at the ISOLDE facility. Half-lives have been determined from counting of β-particles, β-delayed protons, and γ-rays. A short-lived isomer ( T 1 2 = 0.7 sec ) in 116Cs has been observed and the new delayed-particle precursors 116Cs (protons and α-particles), 115Cs (protons), and 114Cs (protons and α-particles) have been identified. Coincidences between delayed particles and γ-rays have been measured for 118Cs (pγ and αγ) and 116Cs (pγ). A search for the possible proton-radioactive isotope 113Cs has been performed and an upper limit for its production yield is given.

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.

Staggering of the moments of inertia of very neutron-deficient platinum isotopes

Abstract Rotational states in the lightest isotopes of platinum (Z=78) have been located through the fine structure in α-decay. For 176Pt the first 2+ level is at 263 keV. The favoured α-transitions in the decay of the odd isotopes 181–185Hg unambiguously identify the bandhead of the 1 2 − [521] Nilsson states in the platinum daughters. In the region N = 98–104 the moments of inertia show a dramatic even-odd staggering amounting to a factor of 2; this behaviour parallels the staggering in 〈r2〉 in the mercury (Z = 80) isotopes.

Alpha decay studies of new neutron-deficient francium isotopes and their daughters

Neutron-deficient francium isotopes were produced by proton-induced spallation reactions and investigated by alpha spectroscopy following on-line mass separation. The new isotopes201, 202Fr were identified and their half-lives measured. An improved value for the half-life of203Fr was obtained. Alpha branching ratios were determined for198m, g, 199At. The derivation of the mass excess of202Fr and the systematics of alpha energies and reduced widths 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.