Structure of 136Te and the problem of mass of 134Te

Neutron-rich, N=84 nuclei from the ₁₃₂Sn region, populated in spontaneous fission of ₂₄₈Cm, have been studied with EUROGAM 2. Excited states and their spins and parities in the ₁₃₆Te nucleus were established up to 17ħ. OXBASH code calculations support the experimental identification of maximum aligned configurations in ₁₃₆Te. Empirical shell model calculations for the I_π= 14₊ level in ₁₃₆Te indicate that the adopted mass of the ₁₃₄Te nucleus should be lowered by 200(80) keV. Received: 3 August 1998     

Identification of the 109Xe and 105Te α-decay chain

The α-decay chain ¹⁰⁹Xe → ¹⁰⁵Te → ¹⁰¹Sn was identified at the Holifield Radioactive Ion Beam Facility. Advances in digital electronics have made possible the identification of both alpha emitters in the same experiment despite the disparate half-lives of 13 ±2 ms and 620 ±70 ns for ¹⁰⁹Xe and ¹⁰⁵Te, respectively. Two α-decay transitions were observed from ¹⁰⁹Xe with Q_α values of 4067 ±10 and 4217 ±8 keV. One transition between the ground states of ¹⁰⁵Te and ¹⁰¹Sn was observed with a Q_α value of 4889 ±6 keV. Using the measured half-lives, branching ratios, and Q_α values the reduced α-decay widths, δ², were determined. Comparison of the δ² value for ¹⁰⁵Te with ²¹³Po indicates a “superallowed" character in the α emission of ¹⁰⁵Te.     

Search for β-delayed fission of the heavy neutron-rich isotope 230Ac

The ²³⁰Ra has been produced via multinucleon transfer reaction and dissipative fragmentation by 60 MeV/u ¹⁸O ion irradiation of ²³²Th targets. The radium was radiochemically separated from the mixture of thorium and reaction products. Thin Ra sources were prepared and exposed to the mica fission track detectors, and measured by a HPGe gamma detector. It is likely that the β-delayed fission of ²³⁰Ac was observed for the first time and the β-delayed fission probability of ²³⁰Ac was tentatively found to be (1.19±0.40)×10^-8. Received: 2 November 2000 / Accepted: 30 January 2001     

New limits on the ββ decay of 130Te to excited states of 130Xe

Experimental limits on half-lives of the (0ν + 2ν)ββ decay of ¹³⁰Te to excited states of ¹³⁰Xe are obtained using low-background HPGe detectors. At the 90% CL, these limits are equal to 1.6 ^. 10²¹ y, 2.7 ^. 10²¹ y and 2.3 ^. 10²¹ y for transitions to the 2⁺ ₁, 2⁺ ₂ and 0⁺ ₁ levels, respectively. Received: 16 March 2001 / Accepted: 18 June 2001     

New isomeric states in 152,154,156Nd produced by spontaneous fission of 252Cf

Isomeric states have been observed in fission-fragments produced by spontaneous fission of ²⁵²Cf. These states are found in neutron rich nuclei of different structure and deformations. About 50 isomeric nuclei have been observed using coincidences between γ-rays identified in EUROGAM II and fission fragments detected in photovoltaic cells (SAPhIR). Lifetimes in the range from 20 ns to 2μs have been measured. Presented calculations based on HFB +D1S force on new measured isomeric states in the ^152,154,156Nd show evidence for K-isomers. Received: 3 November 1997 / Revised version: 15 December 1997     

High-spin isomers in 183Os

High-spin states in ¹⁸³Os have been studied by means of in-beam γ-ray spectroscopy. Two isomers with I ^π= ((43/2)⁻) and (43/2)⁺ have been identified at excitation energies of E _x = 5.068 and 5.168 MeV. The half-lives are determined as T _1/2= 27 ± 3 and 24 ± 2 ns. Received: 22 December 1997     

Properties of N=84, even-even nuclei populated in the spontaneous fission of 248Cm

Excited states in the neutron-rich, N=84 nuclei ¹³⁴Sn, ¹³⁶Te and ¹³⁸Xe, populated in the spontaneous fission of ²⁴⁸Cm, were studied to medium spins using the EUROGAM2 array. OXBASH code calculations support the experimental identification of maximum aligned configurations in these isotopes. Empirical shell model calculations agree with the proposed excitation energy of the neutron h_9/2 excitation in the ¹³²Sn region. A discrepancy between the observed and calculated excitation energy of the I^π= 12⁺ level in ¹³⁶Te indicates possible admixtures of collective excitations in this nucleus. Clear signs of collective excitations are observed in ¹³⁸Xe. Received: 10 November 1999 / Revised version: 22 December 1999     

Isomeric state of 80Y and its role in the astrophysical rp-process

A careful investigation of the isomeric transition of the long-lived state at 228.5 keV excitation energy in ⁸⁰Y has been done. The HIGISOL facility at the Jyv?skyl? isochronous cyclotron has been used. We used the electron magnetic transporter to prepare an appropriate source and to measure the electron spectra in clean background conditions. The measured internal conversion coefficient α_K = 0.50±0.07 allows unambiguous 1^- identification for the 228.5 keV first excited isomeric state in ⁸⁰Y. With a “bare" half-life of 6.8±0.5 s found in this work, this state is strongly populated in the rp-process during X-ray bursts and has therefore to be taken into account in X-ray burst model calculations. However, because of the similarity of the β-decay half-lives of isomeric and ground states, we find a maximum reduction in the effective β-decay lifetime of ⁸⁰Y of only 17±2%. Our results pave the way for a future investigation of the impact of the isomeric state on the “effective" ⁸⁰Y proton capture rate. Received: 14 March 2001 / Accepted: 10 July 2001     

Decay study of neutron-rich zirconium isotopes employing a Penning trap as a spectroscopy tool

A new technique to produce isobarically pure ion beams for decay spectroscopy by using a gas-filled Penning trap was commissioned at the ion guide isotope separator on-line facility, IGISOL. β-decays of neutron-rich ¹⁰⁰Zr, ¹⁰²Zr and ¹⁰⁴Zr isotopes were studied with this technique. In addition, the values of ^100,102,104Zr β-decays were determined from the direct mass measurements of zirconium and niobium isotopes performed with a high-precision Penning trap. The mass of ¹⁰⁴Nb was directly measured for the first time and the obtained mass excess value for the longer-living (1⁺) state is -71823±10 keV. For the ground states of ¹⁰⁰Nb and ¹⁰²Nb the obtained mass excess values were -79802±20 keV and -76309±10 keV, respectively. The observed distribution of the β strength supports a prolate deformation assignment for ^100,102,104Zr isotopes.     

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.     

A new high-spin isomer in 145Sm

A new high-spin isomer in ¹⁴⁵Sm was observed by in-beam γ-ray spectroscopy with the reaction ¹²²Sn(²⁷Al,3np) at 127 MeV performed at the Nordball multi-detector array in Roskilde. The excitation energy of the isomer was determined to be E _x= 11147 keV, and using the generalized centroid-shift method its half-life was found to be T _1/2= (7.4 ± 1.0) ns. Received: 23 October 1998     

β-delayed proton decays of 93Pd and 92Rh

β-delayed proton precursors ⁹³Pd and ⁹²Rh were produced by the irradiation of ⁵⁸Ni with a ⁴⁰Ca beam, and identified using proton-gamma coincidence measurements in combination with a helium-jet fast tape transport system. The half-lives of ⁹³Pd and ⁹²Rh were determined to be 1.3(2), 3.0(8) s, respectively. The measured energy spectrum of β-delayed protons and the estimated relative branching ratios to the final states in the daughter nuclei were fitted by a statistic model calculation, and then the ground-state spin and parity of ⁹³Pd were assigned as 9/2^±. Received: 13 April 2001 / Accepted: 22 August 2001     

The neutron and proton two-particle nucleus 134Sb: New low-spin states observed in the decay of 134Sn and an estimate of the energy of the 7- isomer

Excited states in the ¹³⁴Sb nucleus, populated in the β^--decay of ¹³⁴Sn, have been studied at the mass separator OSIRIS. The ¹³⁴Sn activity was produced via fast neutron-induced fission of ²³⁸U target. A main result was the discovery of a very low-lying first-excited state of ¹³⁴Sb, at 13keV, which has led to a strong revision of the level scheme. The new results are compared with different theoretical calculations and with the known data for the analogous neutron and proton two-particle nucleus in the ²⁰⁸Pb region. On the basis of this comparison, the energy of the ( πg _7/2νf _7/2)_7- isomer is estimated to be about 250keV, some 100keV lower than previously reported. Received: 21 March 2002 / Accepted: 16 May 2002 / Published online: 31 October 2002 RID="a" ID="a"e-mail: anovak@fuw.edu.pl     

High spin states and evidence for octupole correlations in 117Xe

High-spin states of ¹¹⁷Xe were investigated by means of in-beam γ-ray spectroscopic techniques via the reaction of ²⁸Si bombarding a ⁹²Mo target at beam energies of 100-120 MeV. A positive-parity rotational band decaying into the yrast negative-parity band by a series of enhanced E1 transitions was observed for the first time, implying the existence of octupole correlations in ¹¹⁷Xe. The B(E1) values increase with spin. The νd_5/2 band was firmly established up to 27/2⁺ and the B(M1)/B(E2) ratios were extracted from the relative intensities of γ-rays in this band. The previously known νh_11/2 and νg_7/2 [413]5/2⁺α=−1/2 bands were confirmed and extended up to high spins and two bandcrossings are observed in the latter at ħω=0.33 and 0.44 MeV, respectively. The bandcrossings and configurations of these bands are discussed by TRS and CSM calculations. In a γ–γ–t measurement, the 11/2⁻ and 7/2⁻ levels were identified as two isomers with half-lives of 59.4±20 ns and 16.5±8.0 ns, respectively. Received: 17 June 1997 / Revised version: 29 September 1997     

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     

The new isotope 217U

The new neutron deficient isotope ²¹⁷U was produced in the bombardment of the ¹⁸²W target with ⁴⁰Ar ions and identified using a recoil-- correlation method. The -decay energy and the half-life of ²¹⁷U were determined to be 8005 ± 20 keV and 15.6 ^+21.3 _-5.7 ms, respectively. Received: 18 May 2000 / Accepted: 21 June 2000     

New insights into neutron-rich nuclei at high spin

With new high statistic data, new isotopes and new high-spin structures are observed in neutron-rich nuclei populated in the spontaneous fission of ²⁵²Cf. The ¹³⁵Te levels are extended, and many new levels in ^139,141Ba observed. The coexistence of collective and single particle-hole states is found in ¹³⁵Te. The N = 83 ¹³⁵Te and ¹³⁹Ba show marked differences associated with differences in their particle and hole states. New levels in ¹⁴¹Ba complete evidence for two opposite-parity doublets characteristic of stable octupole deformation. In ^114,116Pd a second backbend is observed for the first time in this mass region and the backbend in ¹¹⁸Pd occurs earlier than in ^112-116Pd because of a reduction in pairing. Gamma-type vibrational bands are seen up to 13⁺ to 15⁺ in ^104,106Mo, ^108-112Ru, and ^112-116Pd. Their behavior reflects prolate to triaxial shapes in these nuclei. The levels of ^162,164Gd are observed for the first time. As N increases toward mid-shell at 104, the moments of inertia in N = 100 ¹⁶⁴Gd show an unexpected decrease compared to N = 98 ¹⁶²Gd. The levels in ^162,164Gd form remarkable shifted identical bands with nuclei separated by 2n, 2p, α, and 2α. Received: 21 March 2002 / Accepted: 16 May 2002 / Published online: 31 October 2002 RID="a" ID="a"e-mail: j.h.hamilton@vanderbilt.edu     

Synthesis and decay properties of superheavy atoms in nuclear reactions induced by stable and radioactive ion beams

This talk consists of two parts. The first one presents the results of investigations performed in 1998-2000 in Dubna on the synthesis of superheavy nuclei in reactions induced by ⁴⁸Ca ions. The radioactive decay properties of the nuclei, indicating a considerable increase in the α-decay and spontaneous fission half-lives of the isotopes of elements 110-116 when approaching the closed neutron shell at N = 184, are given. In the second part the possible ways of advancing into the region of more neutron-rich nuclei, using stable and radioactive ion beams, are discussed. Since so far no intense radioactive ion beams are available, some experiments with stable beams are considered as a test for the suggested ideas. Received: 1 May 2001 / Accepted: 4 December 2001     

Conversion electron measurements of 152Nd

Abstact: Multipolarities of γ-rays in ¹⁵²Nd have been studied by conversion electron measurements in the β⁻ decay of ¹⁵²Pr. The praseodymium activities were obtained by the thermal neutron fission of ²³⁵U and followed with the on-line isotope separator KUR–ISOL. Conversion electrons and γ-rays were measured with a Si(Li) detector and a HPGe detector, respectively. The two γ-rays, 226 keV and 285 keV, were decided to have the multipolarities of the E1 transition. The spins and parities of the 1600 keV and 1542 keV levels were determined to be 3⁺ and 2⁺, respectively. Received: 14 April 1998     

Conversion electron measurement in the β<Superscript>-</Superscript>-decay of <Superscript>151</Superscript>Pr

The β^--decay of ¹⁵¹Pr produced by the thermal neutron-induced fission of ²³⁵U has been studied using an on-line isotope separator. From an internal-conversion electron measurement with a Si(Li) detector, K-conversion coefficients were obtained for 20 γ-transitions. Spins and parities of 6 excited levels in ¹⁵¹Nd were newly determined from the deduced multipolarities: even parities for the 543 and 627 keV levels, odd parities for 250 and 599 keV, (3/2, 5/2)⁺ for 685 keV, and (1/2, 3/2)⁺ for 880 keV. The level structure was compared with the rotation-vibration coupling Nilsson model. Received: 28 June 2002 / Accepted: 31 October 2002 / Published online: 25 February 2003 RID="a" ID="a"e-mail: ykojima@hiroshima-u.ac.jp Communicated by J. ?yst?