Super-allowed α decay above doubly-magic <Superscript>100</Superscript>Sn and properties of <Superscript>104</Superscript>Te = <Superscript>100</Superscript>Sn ⊗ α

α-decay half-lives for ^{104, 105, 106}Te and ^{108, 109, 110}Xe close above the doubly-magic ¹⁰⁰Sn are calculated from systematic double-folding potentials. The derived α preformation factors are compared to results for ^{212, 213, 214}Po and ^{216, 217, 218}Rn above the doubly-magic ²⁰⁸Pb. α-decay energies of Q _α = 5.42±0.07MeV and 4.65±0.15MeV are predicted for ¹⁰⁴Te and ¹⁰⁸Xe; the corresponding half-lives are T _1/2 ≈ 5ns for ¹⁰⁴Te and of the order of 60μs for ¹⁰⁸Xe. Additionally, the properties of rotational bands in ¹⁰⁴Te are analyzed, and the first excited 2⁺ state in ¹⁰⁴Te is predicted at E _x = 650±40keV; it decays preferentially by γ emission with a reduced transition strength of 10 Weisskopf units to the ground state of ¹⁰⁴Te and with a minor branch by α emission to the ground state of ¹⁰⁰Sn.     

Mapping of the <Superscript>12</Superscript>C* states via the <Superscript>10</Superscript>B(<Superscript>3</Superscript>He,pααα) reaction

We have studied ¹²C in full kinematics via the ¹⁰B(³He,pααα) reaction at an energy of 2.45 MeV. In our data we have identified states in ¹²C from the ground state up to about 18 MeV, with spins ranging from 0 to 4. Due to the very good resolution, we are able to determine properties of these ¹²C resonances, such as their energy, width, and spin. In this contribution preliminary results from the ongoing analysis are presented. Main focus on the precise determination of the breakup spectra for all resonances.     

High-spin states in <Superscript>36</Superscript>Ar and their underlying shell model configurations

Eight high-spin states in ³⁶Ar below 10MeV excitation energy, among them a prospective J ^π = 8^- state at 9408keV and the J? 8 levels of the recently discovered superdeformed rotational band, have been observed by n-γ coincidence measurements with the ³³S(α, nγ) reaction at E _α = 14.4 and 13.4MeV. High-spin assignments of, respectively, J ^π = 6⁺ and 5^- were obtained for the E _p = 1209 and 1462keV (E _x = 9682 and 9927keV) resonances of the ³⁵Cl (p,γ) reaction by a measurement of γ-ray angular distributions. The spectrum of the high-spin and of the E _x? 7.4MeV levels is decomposed according to the underlying shell model configurations with n = 0, 1, 2, 4 particles excited from the N = 2 into the N = 3 major shell. The role of four-particle excitations, all connected with large prolate distortions, is elucidated for the entire A = 36-40 mass region. Received: 21 December 2001 / Accepted: 25 March 2002     

Indication for hyperdeformed cluster states in <Superscript>233</Superscript>Th

An activation technique was used to investigate relative yields of fission products from the reaction ²³²Th(n, f ) for neutron energies between 1.3 and 1.8MeV covering the region around the first hyperdeformed resonances. Intensities of characteristic γ-ray transitions were analyzed to search for changes in the mass distribution for neutron energies corresponding to the resonances and below the resonances. Relative increases in yield between 7 and 23% are observed for A ≈ 100 and 132 in the resonance region around 1.6MeV. It is proposed that the yield enhancement of daughter nuclei of the preformed fragments ¹³²Sn and ¹⁰¹Zr arises from cold fission of a di-cluster configuration. The experimental results support theoretical predictions for the existence of hyperdeformed octupole shapes based on the di-nuclear configuration ¹³²Sn + ¹⁰¹Zr.     

Effective three-body interactions in the α-cluster model for the <Superscript>12</Superscript>C nucleus

Properties of the lowest 0⁺ states of ¹²C are calculated to study the role of three-body interactions in the α-cluster model. An additional short-range part of the local three-body potential is introduced to incorporate the effects beyond the α-cluster model. There is enough freedom in this potential to reproduce the experimental values of the ground-state and excited-state energies and the ground-state root-mean-square radius. The calculations reveal two principal choices of the two-body and three-body potentials. Firstly, one can adjust the potentials to obtain the width of the excited 0₂⁺ state and the monopole 0₂⁺↦0₁⁺ transition matrix element in good agreement with the experimental data. In this case, the three-body potential has strong short-range attraction supporting a narrow resonance above the 0₂⁺ state, the excited-state wave function contains a significant short-range component, and the excited-state root-mean-square radius is comparable to that of the ground state. Next, rejecting the solutions with an additional narrow resonance, one finds that the excited-state width and the monopole transition matrix element are insensitive to the choice of the potentials and both values exceed the experimental ones.     

Decay of 1.643 h <Superscript>95</Superscript>Ru and its daughter's level structure

The decay of ⁹⁵Ru has been investigated by means of γ-ray spectroscopy. The ⁹⁵Ru nuclei were produced by the reaction ⁹²Mo( α, n) ⁹⁵Ru at a beam energy of 17MeV. High-purity Ge detectors have been used singly and in coincidence to study γ-rays in the decay of ⁹⁵Ru to ⁹⁵Tc. 132 γ-rays are reported, among them, energies and intensities for 127 transitions have been determined. A decay scheme of ⁹⁵Ru with 31 levels is proposed which accommodates 127 of these transitions. Spins and parities for three new levels are proposed from calculated log ft values, measured γ-ray branching ratios, and in-beam experiment results of the daughter nucleus ⁹⁵Tc. Combining with the high-spin states observed by in-beam γ-ray spectroscopy of previous decay works, the structure of the excited states of ⁹⁵Tc is discussed in the framework of the projected shell model.     

Nuclear deformation and the two-neutrino double- β decay in <Superscript>124, 126</Superscript>Xe , <Superscript>128, 130</Superscript>Te , <Superscript>130, 132</Superscript>Ba and <Superscript>150</Superscript>Nd isotopes

The two-neutrino double-beta decay of ^{124, 126}Xe , ^{128, 130}Te , ^{130, 132}Ba and ¹⁵⁰Nd isotopes is studied in the Projected Hartree-Fock-Bogoliubov (PHFB) model. Theoretical 2ν β^-β^- half-lives of ^{128, 130}Te , and ¹⁵⁰Nd isotopes, and 2ν β⁺β⁺ , 2ν β⁺ EC and 2ν ECEC for ^{124, 126}Xe and ^{130, 132}Ba nuclei are presented. Calculated quadrupolar transition probabilities B(E2 : 0⁺ → 2⁺) , static quadrupole moments and g -factors in the parent and daughter nuclei reproduce the experimental information, validating the reliability of the model wave functions. The anticorrelation between nuclear deformation and the nuclear transition matrix element M _2ν is confirmed.     

Inelastic excitation of <Superscript>187</Superscript>Re

Excited states in ¹⁸⁷Re populated by inelastic scattering of a 500 MeV ⁸²Se beam have been studied by means of in-beam γ-ray spectroscopy. Levels built on the 5/2⁺[402] and 9/2^-[514] one-quasiparticle states were measured up to I ^π = (21/2⁺) and (21/2^-), respectively. In addition, several new levels including an isomer at 1682 keV with a half-life of 114(23) ns have been found. Quasiparticle configurations of the levels and the transition rates are discussed. Received: 12 December 2002 / Accepted: 13 March 2003 / Published online: 13 May 2003     

Observation of M3 isomeric transition from <Superscript>156m</Superscript>Pm through the βdecay of <Superscript>156</Superscript>Nd

An M3 transition in a doubly odd nucleus of ¹⁵⁶Pm was identified by internal conversion electron measurement through the β-decay of ¹⁵⁶Nd which was separated from the fission products of ²³⁵U using the on-line mass separator KUR-ISOL. The isomeric state at 150.3keV de-excites to the ground state with the M3 transition, and the spin-parity is considered to be 1^-. Nilsson configurations are also discussed on the basis of the systematics.     

Dynamic polarization potential of 12C+12C system at molecular-resonance energies

The nuclear reaction dynamics leading to the formation of recently discovered resonance in the mutual-0₂ ⁺ channel of the ¹²C+¹²C inelastic scattering around E _c.m.≃ 32 MeV is studied in terms of the dynamic polarization potential (DPP) induced by the channel coupling among various excited states in ¹²C. The microscopic 3α cluster-model wave functions are used to generate the ¹²C−¹²C diagonal and coupling potentials in the double-folding model. It is found that DPP for the 0₂ ⁺+ 0₂ ⁺ channel is an unusually strong attractive potential which even exceeds the zeroth-order folding-model potential of this channel around the nuclear surface region and that the strong coupling between the 0₂ ⁺ and 2₂ ⁺ states is predominantly responsible for the unusual DPP in this channel. The effective potential, the sum of the original folding-model potential and the attractive DPP, is found to generates resonance states in the same energy region as that of the resonance states generated by the original folding-model potential but the former states are found to be higher-nodal states having four additional radial nodes. Similar but more moderate property of DPP is also found in the entrance (elastic) channel. These results suggest that the reaction dynamics of generating the resonance in the ¹²C(0₂ ⁺) +¹²C(0₂ ⁺) channel may rather differ from that of the simple crossing of the zeroth-order molecular band generated by the potentials in the entrance and exit channels suggested by the standard band-crossing model. Received: 17 December 1998 / Revised version: 1 March 1999     

On the unusual properties of the 282 keV state in <Superscript>135</Superscript>Sb

Recently the first excited state in ¹³⁵Sb has been observed at the unexpectedly low excitation energy of only 282keV and interpreted as mainly d _5/2 proton coupled to the ¹³⁴Sn core. Based on theoretical considerations it was suggested that its low excitation energy is related to a relative shift of the proton d _5/2 and g _7/2 orbits induced by the neutron excess. We have measured the lifetime of the 282keV state by the advanced time-delayed βγγ(t) method. The measured half-life, T _1/2 = 6.1(4)ns, yields exceptionally low limits of B(M1;5/2₁ ⁺→7/2₁ ⁺)≤3.0×10^-4 μ ² _N and B(E2;5/2₁ ⁺→7/2₁ ⁺)≤54e ² fm ⁴. These strongly hindered M1 and slow E2 transition rates are similar to those for the transition de-populating the first excited state at 405keV in ²¹¹Bi. Results of shell model calculations with realistic interactions are presented. The M1 decay rate was found to be extremely sensistive both to the wave function and to the M1 effective operator.     

Covariant tensor formalism for partial-wave analyses of ψ decays into γB¯, γγV and ψ(2s)↦γχ<Subscript>c0,1,2</Subscript> with χ<Subscript>c0,1,2</Subscript>↦K¯πand 2π<Superscript>+</Superscript>2π<Superscript>-</Superscript>

With accumulation of high statistics data at BES and CLEO-c, many new interesting channels can get enough statistics for partial-wave analysis (PWA). Among them, ψ↦γpˉ,γΛˉ,γΣˉ,γΞˉ channels provide a good place for studying baryon-antibaryon interactions; the double radiative decays ψ↦γγV with V ≡ ρ,ω,φ have a potential to provide information on the flavor content of any meson resonances (R) with positive charge parity (C = +) and mass above 1 GeV through ψ↦γR↦γγV; ψ(2s)↦γχ_c0,1,2 with χ_c0,1,2↦Kˉπ⁺π^- and 2π⁺2π^- decays are good processes to study χ_cJ charmonium decays. Using the covariant tensor formalism, here we provide theoretical PWA formulae for these channels.     

Multiple particle break-up study of low excited states in <Superscript>9</Superscript>Be: The ghost peak in the <Superscript>8</Superscript>Be excitation energy spectrum visited

The aim of this work is to find out the origin of the anomalous resonance in ⁸Be seen in the reactions through excited states in ⁹Be. We have populated the ⁹Be excited states by β-decay of ⁹Li. Energy and direction of the two α particles has been detected and the neutron spectra reconstructed. In our work we identified the “anomalous resonance" in ⁸Be observed in several reaction studies as coming from the decay of the 2.43 and 2.78 MeV states in ⁹Be. This anomalous resonance appears when the two detected α particles are assumed to form a resonance in ⁸Be. We argued that the main decaying channels for these two levels in ⁹Be do not involve ⁸Be.     

Low-spin states in <Superscript>182</Superscript>Os and K<Superscript>π</Superscript> = 0<Superscript>+</Superscript>, 2<Superscript>+</Superscript> excited bands

Excited states in ¹⁸²Os were populated by the β⁺/EC decay of ¹⁸²Ir following mass separation. Gamma-ray and conversion electron spectroscopy techniques were employed. Monopole (E0) contributions were determined in transitions populating the ground-state band. A systematic study of the low-spin structures in the Os isotopes is presented and a detailed analysis in the framework of a microscopic configuration mixing approach is performed.     

The α-decay energies and halflives of 195g,mAt and 199Fr

The α-decay energy and halflife of ^195mAt were determined to be 6960±20 keV and 385⁺⁶⁹ ₋₅₁ ms respectively, on the basis of genetic correlations in the ¹⁶⁹Tm(³⁶Ar, α6n)¹⁹⁵At reaction, while those of ^195gAt measured simultaneously were 7105±30 keV and 146⁺²¹ ₋₁₇ ms respectively, reconfirming the previously reported values. A new isotope ¹⁹⁹Fr was also produced and identified in the same way in the ¹⁶⁹Tm(³⁶Ar, 6n)¹⁹⁹Fr reaction, yielding E_α= 7655±40 keV and T_1/2= 12⁺¹⁰ ₋₄ ms. Received: 26 March 1999     

Investigations into the alpha-decay of <Superscript>195</Superscript>At

The low-energy nuclear structure and decay properties of the neutron-deficient isotopes ¹⁹⁵At and ¹⁹¹Bi have been studied. ¹⁹⁵At was produced in the reaction ¹⁴²Nd(⁵⁶Fe,p2n)¹⁹⁵At and ¹⁹¹Bi as the daughter activity of ¹⁹⁵At. The activities were implanted in a position-sensitive silicon detector after being separated from the primary beam by a gas-filled recoil separator. The 1/2⁺ intruder state was determined to be the ground state in ¹⁹⁵At with an alpha-decay energy of E _α = 6953(3) keV and a half-life T _1/2 = 328(20) ms. Another state with an alpha-decay energy E _α = 7075(4) keV and a half-life T _1/2 = 147(5) ms was found to decay to a 148.7(5) keV excited state in ¹⁹¹Bi for which a spin and parity of 7/2^- were deduced. Consequently, the same 7/2^- character was assigned to the initial state at 32(7) keV in ¹⁹⁵At on the basis of unhindered alpha-decay. The 9/2^- state, being the ground state in heavier odd-mass astatine isotopes, was not observed. Received: 16 September 2002 / Accepted: 19 December 2002 / Published online: 25 March 2003 RID="a" ID="a"e-mail: heikki.kettunen@phys.jyu.fi RID="b" ID="b"Present address: Laboratory of Radiochemistry, P.O. Box 55, FIN-00014, University of Helsinki, Finland. RID="c" ID="c"Present address: Radiation and Nuclear Safety Authority, P.O. Box 14, FIN-00881 Helsinki, Finland. Communicated by W. Henning     

Search for hyperdeformed structures populated in the <Superscript>37</Superscript>Cl+<Superscript>120</Superscript>Sn reaction by using EUROBALL III

The ridge structure with ΔE_γ=±30 keV, observed in the past in coincidence with protons emitted in the reaction 187 MeV ³⁷Cl +¹²⁰Sn and attributed to an hyperdeformed nuclear shape in ¹⁵²Dy, has been studied in a new experiment performed with the EUROBALL III array. The ridge is now observed in coincidence with transitions in the yrast superdeformed band of ¹⁵²Dy but no discrete rotational bands have been identified. Received: 7 February 2000     

Search for superheavy hydrogen isotopes <Superscript>6</Superscript>H and <Superscript>7</Superscript>H in stopped π-absorption reactions

Experimental search for superheavy hydrogen isotopes ⁶H and ⁷H was performed in the stopped pion absorption on ⁹Be and ¹¹B nuclei. The structures in the missing-mass spectra were observed in the reaction channels ⁹Be(π^-, pd )X and ¹¹B(π^-, p⁴He)X . Four states of ⁶H were proposed. Evidences for ⁷H formation were obtained in the reaction channels ⁹Be(π^-, pp)X and ¹¹B(π^-, p³He)X .     

Nuclear quadrupole moments of 5/2<Superscript>-</Superscript> and 9/2<Superscript>-</Superscript> states in <Superscript>169</Superscript>Ta

The nuclear spectroscopic quadrupole moments for the πh_9/25/2^-, 1/2^-[541] and the πh_11/29/2^-, 9/2^-[514] isomeric states in ¹⁶⁹Ta have been measured employing the time differential perturbed angular-distribution technique following the nuclear reaction ¹⁵⁹Tb(¹⁶O, 6nγ)¹⁶⁹Ta at beam energy 104 MeV. The ratio of the intrinsic quadrupole moments has been derived as 1.87(13) from the measured quadrupole precession frequencies of the corresponding states. The model-independent analysis of the equilibrium deformation indicates strong prolate- and oblate-driving nature of the 1/2^-[541] and 9/2^-[514] orbitals in ^169,171Ta isotopes, respectively.     

The low-spin structure of <Superscript>115</Superscript>Xe

The low-spin band structure of neutron-deficient ¹¹⁵ ₅₄Xe has been studied following a low-energy (212.3 MeV) ⁶⁰Ni(⁵⁸Ni,2pnγ) reaction performed at IReS, Strasbourg, with the Garel⁺ spectrometer. The relative excitation energies of νh_11/2 (isomeric), νg_7/2, and νd_5/2 bandheads have been established. Received: 23 March 2000