The 130Nd↦130Pr↦130Ce decay chain revisited

An investigation of low-lying energy levels of ¹³⁰Pr and ¹³⁰Ce has been made via β-decay. The radioactive parent nuclei were produced via ^94,96Mo + ⁴⁰Ca reactions at 6.8 MeV/nucleon and transported by a He-jet system. Gamma-γ-t, γ-X-t, γ-e^--t coincidence measurements were performed. Internal conversion coefficients have been measured with a magnetic spectrometer. The new β-decay half-life of ¹³⁰Nd has been determined to be 21(3) s. A partial level scheme of ¹³⁰Pr at low-spin has been constructed. The β-decay of ¹³⁰Pr to ¹³⁰Ce suggests the existence of three β-instable isomeric states in ¹³⁰Pr, while only one half-life T _1/2 = 40(4) s has been measured. Based on the present work and low-lying excited states in neighbouring odd-mass nuclei, the spins and parities of isomeric states in ¹³⁰Pr are proposed to be 2⁺, (4,5)⁺ and (7,8^±). The ground state in ¹³⁰Pr is still undetermined. Received: 20 August 2001 / Accepted: 6 November 2001     

Radioactive decay of 217Pa

The radioactive decay of ²¹⁷Pa was investigated by means of α-γ-spectroscopy. Fine structure in the ground-state α-decay was established. Ambiguities in the fine structure of the α-decay of the previously known isomeric state could be clarified by α-γ-coincidence measurements. A previously unknown α-transition of E _α = (8306 ± 5) keV was detected and identified by means of delayed α-α- and α-γ-γ-coincidence measurements. A second isomeric state decaying by α-emission was not observed. The quality of the previously reported data of the α-decay fine structure of ²¹⁷Th was improved. Received: 29 April 2002 / Accepted: 17 June 2002 / Published online: 19 November 2002 RID="a" ID="a"e-mail: f.p.hessberger@gsi.de Communicated by J. ?yst?     

First measurement of β-decay properties of the proton drip-line nucleus 60Ga

By using the fusion-evaporation reaction ²⁸Si(³⁶Ar,p3n) and spectroscopy of β-delayed γ-rays and charged particles on mass-separated sources, β-decay properties of the neutron-deficient isotope ⁶⁰Ga were studied for the first time. The half-life of ⁶⁰Ga was determined to be 70(15) ms, and, based on βγγ coincidences, the isobaric-analogue state in ⁶⁰Zn was identified at 4851.9(7) keV. A semiempirical proton separation energy value of 40(70) keV was deduced for ⁶⁰Ga. The experimental results on half-life, mass excess, proton separation energy, and structure of the ⁶⁰Zn daughter states are discussed in comparison with various model predictions, including large-scale shell model calculations. Received: 4 September 2001 / Accepted: 12 November 2001     

Nonmesonic decay of the Λ-hyperon in hypernuclei produced by p + Au collisions

The β-delayed proton precursor ¹⁴⁹Yb was synthesized in the reaction ¹¹²Sn(⁴⁰Ca, 3n) and identified by using a proton-gamma coincidence measurements in combination with a helium-jet fast tape transport system. Its β-delayed proton spectrum was observed. The half-life of ¹⁴⁹Yb was determined to be 0.7±0.2 s. The 253, 101, and 365 keV γ transitions in ¹⁴⁷Dy, following β-delayed proton emission of ¹⁴⁸Ho decay, were reported for the first time. Received: 14 March 2001 / Accepted: 26 September 2001     

(EC + β+) decay of 133Sm and 1.1 s isomer of 133Pr

The very neutron-deficient isotope ¹³³Sm was produced by irradiation of an enriched target of ⁹⁶Ru with ⁴⁰Ca and studied by using a helium-jet fast tape transport system in combination with X-γ and γ-γ coincidence measurements. A simple ( EC + β⁺) decay scheme of ¹³³Sm was proposed for the first time. As a by-product ¹³³Pr was produced simultaneously because of the ^98-102Ru content of the ruthenium target. The half-life of a 11/2^- low-lying isomeric state in ¹³³Pr was measured to be 1.1±0.2 s. Received: 22 March 2001 / Accepted: 18 July 2001     

Mirror decay of 75Sr

The β-decay of ⁷⁵Sr to its mirror nucleus ⁷⁵Rb was studied at the ISOLDE PSB facility at CERN by means of β-delayed γ and proton spectroscopy. The decay Q-value and β-delayed γ intensity were measured for the first time. These results, 10.60±0.22 MeV and 4.5^+1.9 _-0.7%, together with accurate measurements of the β-decay half-life and β-delayed proton branching ratio yielded the Gamow-Teller strength 0.35±0.05 for the mirror transition. Implications of the results on studies of deformation effects and on the path of the rapid proton capture process are discussed. Received: 26 September 2002 / Accepted: 30 October 2002 / Published online: 18 February 2003 RID="a" ID="a"e-mail: jussi.huikari@phys.jyu.lfi Communicated by D. Schwalm     

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.     

Band structure of <Superscript>146</Superscript>Ce studied through γ-γ angular correlation measurements

The β-decay of ¹⁴⁶La was studied using the on-line isotope separator KUR-ISOL. Gamma-gamma angular correlation measurements were performed with a 4-Ge detectors system. Spin assignments of three levels were made: 3⁺ for the 1576.5 keV level, 4⁺ for the 1627.1 keV level and 5⁺ for the 1810.2 keV level. The mixing ratios (E2/M1) were deduced to be δ_183.2= 0.25 ± 0.08, δ_638.9= 0.33 ± 0.05, δ_959.0= 1.19^+0.16 _−0.14, δ_1015.9= 5.4^+3.1 _−1.5 and δ_1318.1= 6.5^+1.7 _−1.1. These were compared to the calculated values obtained in three cases involving different Majorana force parameter values. The band structure of ¹⁴⁶Ce is discussed based on the results of calculation using the IBM-2 theory. Received: 20 September 1999 / Revised version: 8 February 2000     

The β+-electron capture decay of 73Kr

The β⁺– electron capture decay of ⁷³Kr, produced at the ISOLDE CERN facility, has been studied by β-delayed proton and gamma emission. The established decay scheme involves 15 up to now unreported gamma emitting levels in ⁷³Br. The total proton branching ratio has been measured to be 0.0025 ± 0.0003. From this work, a spin and parity 3/2⁻ is assigned to the ⁷³Kr ground state, on the basis of the allowed β branch to the ⁷³Br J^π= 1/2⁻ ground state and the feeding of the 5/2⁺ level located at 286 keV in ⁷³Br. Received: 17 September 1998 / Revised version: 25 January 1999     

Ionization of iridium ions in the Dresden EBIT studied by X-ray spectroscopy of direct excitation and radiative recombination processes

Ir^q+ ( 41≤q≤64) ions with open-shell configurations have been produced in the electron beam of the room-temperature Dresden Electron Beam Ion Trap (Dresden EBIT) at electron excitation energies from 2 keV to 13 keV. X-ray emission from direct excitation processes and radiative capture in krypton-like to aluminium-like iridium ions is measured with an energy dispersive Si(Li) detector. The detected X-ray lines are analyzed and compared with results from multiconfigurational Dirac-Fock (MCDF) atomic structure calculations. This allows to determine dominant produced ion charge states at different electron energies. The analysis shows that at the realized working gas pressure of 5×10^-9mbar for higher charged ions the maximum ion charge state is not preferently determined by the chosen electron beam energy needed for ionization of certain atomic substates, but by the balance between ionization and charge state reducing processes as charge exchange and radiative recombination. This behaviour is also discussed on the basis of model calculations for the resulting ion charge state distribution. Received 12 July 2001 and Received in final form 10 September 2001     

Decay studies of N ≈ Z nuclei from 75Sr to 102Sn

Neutron deficient nuclei near ¹⁰⁰Sn have been produced by fragmentation of a 1 ^. AGeV ¹¹²Sn beam. The fragments were separated, identified and stopped in a highly segmented silicon strip detector stack. This detector measured the total energy of emitted β⁺-particles. γ-radiation was measured with surrounding detectors. The half-lives for many nuclides have been determined for the first time and give important information for the following topics: For the heaviest particle-stable odd-odd nuclei ⁹⁰Rh, ⁹⁴Ag and ⁹⁸In we observed for the first time fast β-decays, compatible with superallowed Fermi transitions and confirmed such decays for ⁷⁸Y, ⁸²Nb and ⁸⁶Tc. We have also observed long-lived T = 0 states in some of these nuclei. We measured the half-lives of all rp-process waiting-point nuclei from ⁸⁰Zr up to ^{92, 93}Pd. In addition we find the proton drip line nucleus ⁷⁷Y to decay dominantly via β-decay. To study the Gamov-Teller strength in the β-decay near the doubly magic ¹⁰⁰Sn we measured the half-life, β- and γ-spectrum of ¹⁰²Sn. We propose a level scheme for the daughter nuclide ¹⁰²In and deduce the Gamov-Teller strength (B _GT = 4.0±0.6). This is one of the largest values known. Received: 21 March 2002 / Accepted: 16 May 2002 / Published online: 31 October 2002 RID="a" ID="a"e-mail: thomas.faestermann@ph.tum.de     

Gamow-Teller transitions from 58Ni to discrete states of 58Cu

Under the assumption that isospin is a good quantum number, symmetry is expected for the transitions from the ground states of T = 1, T _z = ±1 nuclei to the common excited states of the T _z = 0 nucleus situated between the two nuclei. The symmetry can be studied by comparing the strengths of Gamow-Teller (GT) transitions obtained from a (p, n)-type charge-exchange reaction on a target nucleus with T _z = 1 with those from the β-decay of the T _z = - 1 nucleus. The A = 58 system is the heaviest for which such a comparison is possible. As a part of the symmetry study, we measured the GT transitions from ⁵⁸Ni (T _z = 1) to ⁵⁸Cu (T _z = 0) by using the zero-degree (³ He, t) reaction at 150 MeV/nucleon. With the achieved resolution of 50 keV, many hitherto unresolved GT states have been identified. The GT transition strengths were obtained for states up to 8 MeV excitation, i.e., near to the Q window limitation ( Q _EC = 9.37 MeV) of the β-decay from ⁵⁸Zn (T _z = - 1) to ⁵⁸Cu. The strength distribution is compared with that from shell-model calculations. Received: 24 November 2001 / Accepted: 30 January 2002     

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     

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?     

Microsecond isomers in 187Tl and 188Pb

Lifetime measurements of states in nuclei with A=187 and 188 have been performed, using reactions between ¹⁵⁵Gd and ³⁶Ar and following the transport of evaporation residues to the focal plane of a gas-filled recoil separator. In a separate experiment using the ¹⁵⁹Tb(³²S, 4n) reaction the γ-decay of isomeric levels in ¹⁸⁷Tl has been studied using delayed γ-γ coincidence measurements. From observation of their subsequent γ decay, the mean lifetimes were measured to be 1000 ± 55 ns and 1600 ± 100 ns. Although it was not possible to characterize the isomers completely, they are proposed as candidates for one-proton, two-neutron excitations. In the course of this study, the decay of an isomer in ¹⁸⁸Pb was also observed and its lifetime was measured as 1150 ± 30 ns, and limits of 20–600 ns were placed on the meanlife of an isomer conjectured in ¹⁸⁷Pb. Received: 20 August 1999     

Alpha decay of the new isotopes 188,189Po

New neutron-deficient isotopes ^188,189Po have been produced in the complete fusion reaction of ⁵²Cr ions with a ¹⁴²Nd target at the velocity filter SHIP. The evaporation residues were separated in-flight and subsequently identified on the basis of α-γ and α-conversion electron coincidence measurements and of α-α position and time correlations. In ¹⁸⁹Po a ground state to ground state α decay with E_α1= 7540(20) keV, T_1/2= 5(1) ms and two fine structure α-decays at E_α2= 7264(15) keV and E_α3= 7316(15) keV have been observed. In ¹⁸⁸Po (T_1/2= 400⁺²⁰⁰ ₋₁₅₀μs) a ground state to ground state α decay at E_α= 7915(25) keV and a fine structure α decay at E_α= 7350(40) keV have been found. Improved data on the α-decay of ¹⁸⁹Bi were obtained. Received: 15 October 1999     

Analysis of decay data from neutron-rich nuclei

The β-decays of the neutron-rich nuclei ¹²Be and ²⁹Ne have been studied. The statistical correlations between the almost identical half-lives of ¹²Be and its daughter ¹²B are analysed for a large sample of ¹²Be decay data. Stringent mutual bounds are obtained on the parameter set, leading to a precise determination of the ¹²Be half-life of 21.50±0.04 ms. From a simultaneous detection of β-particles and neutrons from the decay of ²⁹Ne the neutron emission probability, P_n, is determined to 17±5%. No indication of two-neutron emission is seen from this nucleus. An upper limit of 2.2% (90% confidence level) is established for P_2n. Received: 3 May 2001 / Accepted: 6 August 2001     

New transitions in the β-decay of 36Ca

The β-decay of the T _z = - 2 nucleus ³⁶Ca was studied at the LISE3 magnetic spectrometer at GANIL. Two new proton-emitting states have been detected and the other nine known βp and βγ transitions have been remeasured with improved resolution. A simulation with the GEANT code has been applied to this experimental setup. A comparison with shell model calculations is given. Received: 19 September 2000 / Accepted: 28 February 2001     

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.     

Nuclear spins, magnetic moments and α-decay spectroscopy of long-lived isomeric states in 185Pb

Alpha-decay properties of the neutron-deficient isotope ¹⁸⁵Pb were studied at the PSB-ISOLDE (CERN) on-line mass separator using the resonance ionisation laser ion source (RILIS). The nuclei of interest were produced in a 1.4 GeV proton-induced spallation reaction of a uranium graphite target. In contrast to previous studies, two α-decaying isomeric states were identified in ¹⁸⁵Pb. The relative production of the isomers, monitored by their α-counting rates, could be significantly changed when a narrow-bandwidth laser at the RILIS setup was used to scan through the atomic hyperfine structure. Based on the atomic hyperfine structure measurements, along with the systematics for heavier odd-mass lead isotopes, the spin and the parity of these states were interpreted as 3/2^- and 13/2⁺ and their nuclear magnetic moments were deduced. The α-decay energy and half-life value for the I ^π = 13/2⁺ isomer are E _α = 6408(5) keV, T _1/2 = 4.3(2) s, respectively; while for the I ^π = 3/2^- isomer ( T _1/2 = 6.3(4) s) two α-decays with E _α1 = 6288(5) keV, I _α1 = 56(2)% and E _α2 = 6486(5) keV, I _α2 = 44(2)% were observed. By observing prompt α-γ coincidences new information on the low-lying states in the daughter isotope ¹⁸¹Hg was obtained. Received: 7 February 2002 / Accepted: 19 February 2002