P.G. Hansen

The essential decay of pandemonium: A demonstration of errors in complex beta-decay schemes

Abstract The β-decay of a fictional nuclide, Pandemonium, is created numerically using a statistical model. By analyzing its simulated γ-ray spectrum as experimental data, we find that much γ-ray intensity actually remains unobserved under normal experimental conditions. This results - illustrated for the case of 145Gd - casts doubt on many decay schemes determined from such spectra.

Studies of the α-active isotopes of mercury, gold and platinum

Abstract Neutron-deficient isotopes of mercury were produced by isotope-separation-on-line techniques. Alpha-emission was established from all mass numbers 179–187. The α-decay energies were measured, as were the half-lives except for 179Hg. Fine structure in the α-spectra was observed in 6 cases. The partial α-lifetime was determined for 11α-transitions from mercury isotopes. The α-decay was also studied for isotopes of gold and platinum, which were found as daughters of the mercury isotopes. Previous assignments of α-decay energies and half-lives to mass numbers were confirmed. Alpha-emission was found for the first time from 184Au and, tentatively, from 182Au. Fine structure was seen in the α-spectra from 184Au, 178Pt and 177Pt. The α-lifetime was determined for 9 transitions from isotopes of gold and platinum. The measured α-decay energies were compared to recent mass calculations. The energy of the first excited 2+ level was determined in the even nuclei 180 Pt (159 ± 5 keV ), 178 Pt (169 ± 5 keV ) and 174 Os (152 ± 5 keV ) . A systematic dependence of α-transition rates on neutron and proton number is pointed out.

ALPHA DECAY OF NEUTRON-DEFICIENT RADON AND POLONIUM ISOTOPES.

Abstract The use of mass-separated samples of neutron-deficient radon isotopes, produced at the ISOLDE on-line mass-separator facility at the CERN 600 MeV synchro-cyclotron, has permitted precise half-life determinations and unambiguous mass assignments for a range of light radon isotopes. Alpha/EC-branching ratios are extracted for several radon and polonium isotopes through the use of genetic relationships. The systematics of the α-widths is discussed.

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.

BETA-DELAYED PROTON EMISSION FROM HEAVY NUCLEI. II. THE CALCULATION OF SPECTRAL SHAPES AND INTENSITIES IN A COMPOUND-NUCLEUS MODEL.

Abstract Beta-delayed proton emission from isotopes of xenon and mercury is investigated in a statistical calculation. The absolute proton intensities, the branching ratios to final levels, and the approximate spectral shapes are in good agreement with experiment if the β-strength function is assumed to be a constant with a low-energy cut-off. For the xenon isotopes an improved fit is obtained if the β-strength function is taken to have a broad peak centred at 5 MeV. This peak is tentatively interpreted as evidence for intermediate structure involving the ( g p 9 2 ) −1 g n 7 2 state.

Alpha-decay widths of neutron-deficient francium and astatine isotopes

Abstract The use of mass-separated samples of neutron-deficient francium isotopes, produced at the ISOLDE on-line mass-separator facility at the CERN 600 MeV synchro-cyclotron, has permitted precise determinations through genetic relationships of α /(EC+ β + ) branching ratios for a range of light francium and astatine isotopes. The experiments verify previous mass assignments and provide improved values for the half-lives. The systematics of α-widths and of β-strength functions is surveyed.

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.

The strongly deformed nucleus 100Sr

Abstract Two γ-rays of 129.2 and 288.4 keV observed in the β-decay of 55 ms 100Rb are interpreted as representing the two lowest transitions in the 100Sr ground-state rotational band. The energy ratio of the two levels, 3.23, approaches the value for a rigid rotator. The half-life of the 2+ state is 5.15 ± 0.20 ns corresponding to a deformation parameter ϵ of 0.29. The theoretical implications of these results are discussed on the basis of a Nilsson-Strutinsky calculation.

Widths for s- and d-wave α-decay of neutron-deficient isotopes with Z ≦ 82

Abstract The α-decay of the nucleides 188–192Pb, 180Hg, and 176Pt has been studied after on line mass separation of spallation products from reactions with 600 MeV protons. For the lead isotopes, the K X-ray/α ratios were determined, and from these partial α half-lives were deduced. In the decay of 6 sec 176Pt, a 1.4% α-branch was found to the 228 keV 2+ level of 172Os, while for 180Hg an upper limit of 10−3 (relative to the ground-state α-branch) could be put on the intensity of an assumed rotational fine-structure component. The systematics of reduced s-wave (0+ → 0+) α-widths is discussed. The lead isotopes show a surprising trend: the reduced s-widths vary from a very small value for 186Pb (deduced from the heavy-ion cross sections of Gauvin et al.) to a quite large value for 192Pb. The systematics of d-wave (0+ → 2+) hindrance factors (relative to the ground-state branch) shows that these range from 1 to 4 for the actinides, while for platinum and mercury one finds 8 and ≈ 50, respectively.

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.