Alpha-gamma decay studies of <Superscript>251, 253</Superscript>No and their daughter products <Superscript>247, 249</Superscript>Fm

The isotopes ²⁵¹No and ²⁵³No were produced in nuclear reactions ²⁰⁶Pb(⁴⁸Ca,3n)²⁵¹No and ²⁰⁷Pb (⁴⁸Ca,2n)²⁵³No. Radioactive decay of these isotopes and their daughter products has been investigated by means of - and - - spectroscopy. An isomeric state ^251m No, having a half-life of s and decaying by emission of particles of keV was identified. The measured decay data allowed for the construction of partial level schemes for ²⁵¹No, ^247,249Fm and ^243,245Cf and an extrapolation of energy systematics of single particle levels of N = 145, 147 and 149 isotones with even Z towards higher atomic numbers up to Z = 102.PACS: 23.60. + e decay - 27.90. + b - 21.10.-k Properties of nuclei; nuclear energy levels     

Cluster structure of <Superscript>16</Superscript>O

A folding potential describing the -scattering on ¹⁶O over a broad energy range 25.8-146.0 MeV is constructed on the basis of -like cluster and unclustered-nucleon configurations of ¹⁶O. The resulting potential does not need any renormalization to fit the angular distribution of elastic cross-sections. The effects of the repulsive part of - and -nucleon interactions are investigated. The analysis suggests that both the - repulsive potential and the unclustered nucleonic configuration in the target are important to describe the scattering data over a broad range of incident energies. The root-mean-square radius for the ¹⁶O nucleus is deduced.Received: 5 December 2002, Published online: 9 October 2003PACS: 25.55.Ci Elastic and inelastic scattering - 24.10.Ht Optical and diffraction models - 21.60.Gx Cluster models     

Remeasurement of the half-life of the 615 keV level in <Superscript>181</Superscript>Ta

The lifetimes of the 615 and 619 keV levels in ¹⁸¹Ta have been remeasured by using a - delayed coincidence set up with fast plastic (Pilot U) and BaF₂ detectors. The presently measured values for both levels have been found to be in strong disagreement with results reported earlier. For the 615 keV level, the half-life has been found to be ns in striking contrast to the earlier reported value of 17.6 s. The half-life of the 619 keV level has been found to be ps, whereas values of 0.87 ns and 2.4 ns were reported previously. The nanosecond half-life of the 615 keV level has been confirmed from a separate measurement by employing a NaI(Tl)-Pilot U detector combination. The importance of lifetime measurements for the 615 keV level in perturbed angular correlation studies is discussed.Received: 17 December 2003, Revised: 19 April 2004, Published online: 19 October 2004PACS: 23.20.-g Electromagnetic transitions - 21.10.Tg Lifetimes     

First decay study of the new isotope <Superscript>129</Superscript>Pm near the proton drip line

The very neutron-deficient nuclide ¹²⁹Pm was produced via the ⁹²Mo(⁴⁰Ca, p2n) reaction and identified for the first time by using the X- coincidence in combination with a He jet tape transport system. According to the decay curve of a 99 keV -ray which corresponds to the known transition in the daughter nucleus ¹²⁹Nd of the ¹²⁹Pm decay, the half-life of ¹²⁹Pm was determined to be 2.4(9) s. Based on the nuclear potential energy surface (PES) calculations, the ground-state spin-parity of ¹²⁹Pm was predicted as 5/2^- which is favorable to feed a 5/2^- low-lying state in the daughter nucleus ¹²⁹Nd via the (EC ) decay.Received: 20 November 2003, Revised: 7 January 2004, Published online: 29 June 2004PACS: 23.40.Hc Relation with nuclear matrix elements and nuclear structure - 21.10.Hw Spin, parity, and isobaric spin - 24.10.Pa Thermal and statistical models - 27.60. + j      

Study of thermally excited nuclei through <Emphasis Type="Italic">E</Emphasis>1 and <Emphasis Type="Italic">E</Emphasis>2 decay from collective modes

The nuclear system at the limit of excitation energy and angular momentum is here studied in the case of the superdeformed nucleus ¹⁴³Eu using -spectroscopy techniques. The data are based on a EUROBALL experiment using the reaction ³⁷Cl + ¹¹⁰Pd Eu + 4n. The influence of thermal energy on superdeformed configurations is investigated through the analysis of the quasi-continuum spectra formed by E2 transitions among states of excited rotational bands with energy extending up to 4-5 MeV above the yrast line. In particular, the effective lifetimes of the discrete rotational bands forming ridge structures in - coincidence matrices is measured by a Doppler Shift Attenuation Method. The deduced quadrupole deformation of 10 eb indicates that the nucleus maintains its collectivity with increasing excitation energy, supporting the superdeformed character of the excited nuclear rotation. The obtained number of superdeformed discrete bands forming the ridge structures is found in good agreement with microscopic cranked shell model calculations including the decay-out process into the lower deformation minimum. In addition, the nuclear properties at higher excitation energies are investigated through the E1 -decay of the giant dipole resonance (GDR). It is found that the intensity of the superdeformed yrast and excited bands increases by a factor of approximately 1.6 when a coincidence with a high-energy -ray is required, showing the importance of the E1 cooling in the feeding mechanism of the superdeformed states.Received: 2 December 2002, Published online: 2 March 2004PACS: 21.10.Tg Lifetimes - 21.10.Re Collective levels - 23.20.Lv transitions and level energies - 27.60. + j      

Excited states in 163,164Ho populated through incomplete-fusion reactions

High-spin states in ^163,164Ho were investigated by means of in-beam -ray spectroscopy techniques using the multidetector array GASP. Excited states in ^163,164Ho were populated predominantly through the incomplete-fusion mechanism in the ¹⁶⁰Gd (¹¹B reaction at a beam energy of 61 MeV. Known rotational bands in ¹⁶³ Ho have been extended to higher spins and a three-quasiparticle band has been observed in this nucleus. Rotational bands have been identified in ¹⁶⁴Ho and their configurations have been discussed. Empirical Gallagher-Moszkowski (GM) splitting energies were extracted from the and GM doublets. Alignments, band crossing frequencies, and electromagnetic properties have been analyzed in the framework of the cranking model.Received: 13 February 2004, Revised: 18 March 2004, Published online: 14 September 2004PACS: 21.10.Re Collective levels - 21.60.Ev Collective models - 23.20.Lv transitions and level energies - 27.70. + q      

Decay properties of isomeric states in radium isotopes close to N = 126

Isomeric states in ^210-215Ra have been populated by the decay of the compound nuclei ^216,220Ra produced in irradiations of ^204,208Pb with ¹²C at MeV. Published values for -ray energies and half-lives were confirmed for Ra. Our data for Ra agree with the -energies and the half-life measured at the RITU separator, University of Jyväskylä (Finland). Its decay pattern is complex. Two series of -rays of keV and keV were observed. A half-life of s was measured. The isomeric state is attributed to an 8 ⁺ state at E ^* = 2053.8keV. A previously unknown isomeric state was assigned to Ra. It has a half-life of ( ) and it decays by emission of -rays with energies of 396.1keV and 802.0keV. It is attributed to a 13/2 ⁺ state at E ^* = 1198.1 keV.PACS: 23.60. + e decay - 27.90. + b      

First structure information on the exotic 149 La from the $\beta^-$-decay of 149 Ba

The -decay of ¹⁴⁹Ba to ¹⁴⁹La has been investigated by means of - and X-ray spectroscopy, and a partial level scheme of ¹⁴⁹La has been constructed for the first time. It includes thirteen -rays and ten excited states. The exotic ¹⁴⁹La is the heaviest lanthanum for which spectroscopic information is now available. We have applied the shell correction approach with the axially deformed Woods-Saxon potential in order to calculate the deformation energy for the ¹⁴⁹La ground state. The deformed ground state was found at 0.23, 0 and 0.12.Received: 18 July 2003, Revised: 12 January 2004, Published online: 26 May 2004PACS: 27.60. + j - 29.30.Kv X- and -ray spectroscopy     

Properties of <Superscript>152</Superscript><Emphasis Type="Italic">Gd</Emphasis> collective states

The decays of ¹⁵²Tb (T _1/2 = 17.5 h) and ¹⁵²Gd excited states have been investigated by the analysis of -rays and -coincidences measured with the use of high-resolution HPGe detectors. The source of ¹⁵²Tb was prepared by chromatographic isolation followed by electromagnetic separation from a tantalum target irradiated by an internal proton beam of the LNP JINR phasotron. New and more precise data on the -transitions and excited states of ¹⁵²Gd are reported. Using previously published data on internal-conversion electrons many transition multipolarities are suggested, some of them with E0 admixture. The ratio was found for a number of low-lying levels, for most of the levels their spins, parities, and are given. The excited levels of ¹⁵²Gd were deduced from the analysis of -coincidences. The experimental level energies and reduced transition probabilities are compared with the calculations by phenomenological formulae as well as in the frameworks of theoretical models.Received: 21 May 2002, Revised: 26 May 2003, Published online: 18 November 2003PACS: 29.30.Kv X- and gamma-ray spectroscopy - 23.20.-g Electromagnetic transitions - 21.10.-k Properties of nuclei; nuclear energy levels - 21.60.-n Nuclear structure models and methodsJ. Adam: On leave from Nuclear Physics Institute of ASCR, e, Czech Republic.V.S. Pronskikh: On leave from Saint Petersburg State Institute of Technology, Russia     

Systematics of deformed states around doubly-magic <Superscript>40</Superscript>Ca

The low-lying rotational bands of A = 36-48 nuclei are consistently explained by starting from the recently discovered, superdeformed intrinsic state of ³⁶Ar as the core, filling successively the first three Nilsson orbits above the Fermi border. The critical single-particle energies were obtained from experimental data as were the residual interactions in the parametrization of Brink and Kerman. Implicit are the rearrangement energies due to configuration-dependent equilibrium deformations. The binding energies of 20 experimental bandheads were used to derive the parameters while another 38 bandheads were subsequently predicted and identified almost completely. The Racavy expression reduced by 20% reproduces or predicts the values of the deformation parameter . The empirical Nilsson model amended by -vibrational and rotation-aligned bands accounts completely for the multi-particle excitations from the N = 2 into the N = 3 major shell which are not accessible by shell-model calculations. In the case of ⁴⁰Ca a spectrum of 42 states below E _x = 8 MeV is explained.PACS: 21.60.Ev Collective models - 21.10.Dr Binding energies and masses - 27.30. + t - 27.40. + z      

Some physics highlights from the EUROBALL spectrometer

Exotic, neutron-rich proton-induced spallation products of ²³²Th and ²³⁸U obtained from the PS Booster ISOLDE facility have been investigated by - , - coincidence and spectrum-multiscaling measurements. A new method for the reduction of isobaric contamination enabled to study the unknown region beyond ²⁰⁸Pb for the decay chain A = 217. A new isotope ²¹⁷Bi with a half-life of s was discovered and its -decay studied. For the first time, a half-life value of s for the -decay of ²¹⁷Po was measured.Received: 3 March 2003, Revised: 13 May 2003, Published online: 30 September 2003PACS: 23.20.Lv transitions and level energies - 23.60.+e decay - 27.80.+w 190 A 219 - 29.30.Kv X- and -ray spectroscopyV. Fedoseyev: Present address: ISOLDE, CERN-PPE, CH-1211, Geneva 23, Switzerland.M. Górska: Present address: GSI, Darmstadt, D-64220, Germany.M. Huhta: Present address: Nokia, Tampere, Finland.     

Observation of bound excited states in 15B

The structure of the A/Z = 3 nucleus ¹⁵B has been investigated using the in-beam -spectroscopy technique with a fragmentation reaction of a ³⁶S beam on a ⁹Be target at 77.5 . The fragments were identified and selected by their energy loss and time of flight using the SPEG spectrograph. -ray energies and intensities have been measured in coincidence with the projectile-like fragments. From this information as well as from the -coincidence relationships a level scheme is proposed for ¹⁵B up to the neutron separation energy. The experimental results have been interpreted using shell model calculations in the psd valence space. Effects of the weakly bound nature of the valence neutrons have been observed.Received: 4 May 2004, Revised: 2 September 2004, Published online: 19 October 2004PACS: 25.70.Mn Projectile and target fragmentation - 23.20.Lv transitions and level energies - 27.20. + n - 21.60.Cs Shell model     

Delayed crossing in the \pi h_{9/2} 1/2-[541] band of 173 Lu

High-spin states in the odd-proton nucleus ¹⁷³Lu have been populated in a ¹⁷⁰Er(⁷Li,4n) reaction and the emitted -radiation was detected with the GASP array. The favoured and unfavoured sequences of the band have been considerably extended. The favoured sequence does not show any indication of a band crossing up to a rotational frequency of 0.45 MeV. This is the largest crossing frequency ever observed for 1/2^- [541] bands of odd-proton nuclei with and . Previous Cranked Shell Model (CSM) calculations underestimate the crossing frequency by 100 keV.Received: 19 May 2003, Published online: 11 November 2003PACS: 21.10.-k Properties of nuclei; nuclear energy levels - 21.10.Re Collective levels - 23.20.Lv transitions and level energies - 27.70. + q      

\alpha-decay spectroscopy of light odd-odd Bi isotopes - II: 186Bi and the new nuclide 184Bi

Alpha-decay of the new nuclide ¹⁸⁴Bi has been studied in the complete-fusion reaction ⁹³Nb(⁹⁴Mo, 3n)¹⁸⁴Bi at the velocity filter SHIP. The evaporation residues were separated in-flight and subsequently identified on the basis of recoil- , recoil- - analysis and excitation functions measurements. Two -decaying isomeric states in ¹⁸⁴Bi with half-life values of 13(2) ms and 6.6(1.5) ms were identified. The -branching ratio of ¹⁸⁰Tl was deduced for the first time as . Improved data on the fine-structure -decay of ¹⁸⁶Bi were obtained in the ⁹³Nb(⁹⁵Mo, 2n)¹⁸⁶Bi reaction. A similarity of the decay energies and half-life values of ^184,186Bi is pointed out and a possible explanation for this effect is suggested.Received: 14 March 2003, Revised: 29 April 2003, Published online: 2 September 2003PACS: 23.60.+e decay - 27.70.+q - 27.80.+w K. Heyde: Present address: EP-ISOLDE, CERN, CH-1211, Geneva 23, Switzerland.     

A new isomer in 136 Ba populated by deep inelastic collisions

Excited states in ¹³⁶Ba, populated in deep inelastic collisions by the interaction of 450 MeV ⁸²Se ions with a ¹³⁹La target, have been studied by means of in-beam -ray spectroscopy. A new isomer with has been identified at an excitation energy E_x = 3.357 MeV. The half-life was determined as ns. The extracted B(E2) value is much smaller than those in ¹³²Te and ¹³⁴Xe. This hindrance is investigated by a shell model calculation.Received: 22 September 2003, Revised: 11 November 2003, Published online: 6 April 2004PACS: 21.10.Tg Lifetimes - 23.20.Lv transitions and level energies - 27.60. + j      

High-resolution in-beam particle-gamma coincidence spectroscopy

A short summary of the present status of prompt particle decays in the mass region is presented. It includes recent results from a GAMMASPHERE experiment, which aimed at the combined high-resolution spectroscopy of light charged particles and -rays to allow for more detailed studies of known decays and the identification of new cases of discrete prompt proton and -particle emission from highly and superdeformed states.Received: 10 October 2002, Published online: 17 February 2004PACS: 23.50. + z Decay by proton emission - 23.60. + e decay - 27.40. + z - 27.50. + e      

Isomeric and ground-state decay of 215 Bi

A new high-spin isomer in ²¹⁵Bi, with a half-life of 36.9(6) s, has been identified at the PSB-ISOLDE on-line mass separator using the pulsed-release technique combined with the element selective RILIS source. A decay scheme of Bi was constructed and complemented with the low-spinstructure observed in Bi decay. The population of a cascade on top of the level in ²¹⁵Poprovides evidence for Gamow-Teller -decay of the high-spin ²¹⁵Bi isomer.Received: 3 March 2003, Revised: 10 June 2003, Published online: 9 October 2003PACS: 23.20.Lv transitions and level energies - 27.80.+w - 29.30.Kv X- and -ray spectroscopyV. Fedoseyev: Present address: ISOLDE, CERN-PPE, CH-1211, Geneva 23, Switzerland.M. Górska: Present address: GSI, Darmstadt, D-64220, Germany.M. Huhta: Present address: Nokia, Tampere, Finland.     

Isospin mixing in the 4<Superscript> + </Superscript> doublet of <Superscript>54</Superscript><Emphasis Type="Italic">Co</Emphasis>

The T = 1 admixture into the T = 0 member of a recently discovered isospin-doublet in ⁵⁴Co is obtained from the measured electromagnetic E2/M1 multipole mixing ratio, of the transition. Combining these data with shell model calculations for strong isovector M1 and isoscalar E2 electromagnetic matrix elements one obtains a value for the T = 1 admixture into the T = 0, 4 ⁺ state of . The corresponding mixing matrix element in the 4 ⁺ doublet is keV.Received: 31 October 2002, Published online: 9 March 2004PACS: 21.10.Hw Spin, parity, and isobaric spin - 21.60.Cs Shell model - 23.20.Gq Multipole mixing ratios     

Spectroscopic quadrupole moments of high-spin isomers in 193 Pb

The quadrupole interaction of high-spin isomers in ¹⁹³Pb implanted into solid Hg cooled at a temperature T = 170 K has been investigated by the time-differential perturbed -ray angular-distribution method. Spectroscopic quadrupole moment values of eb and 0.45(4) eb have been deduced for the 21/2^- and 33/2 ⁺ three-neutron states, respectively. A much higher value eb has been determined for the 29/2^- isomer, the band head of a magnetic rotational band.Received: 4 November 2002, Published online: 2 March 2004PACS: 21.10.Ky Electromagnetic moments - 27.80. + w      

\alpha-decay spectroscopy of light odd-odd Bi isotopes - I: 188,190Bi nuclei

Detailed fine-structure -decay studies of ^188,190Bi were performed using the complete-fusion reactions of ^50,52Cr ions with a ¹⁴²Nd target at the velocity filter SHIP. The evaporation residues were separated in-flight and subsequently identified on the basis of recoil- , recoil- - /X-ray and excitation function measurements. Improved data on the -decay of ^188,190Bi were obtained and a number of new low-lying excited states in the daughters ^184,186Tl were observed. An intruder, presumably 10^- state was identified in ¹⁸⁴Tl, extending the systematics of such states in the odd-odd Tl nuclei beyond the neutron mid-shell at N = 104. Some technical aspects of experiment at recoil separators are also discussed.Received: 14 March 2003, Revised: 1 May 2003, Published online: 2 September 2003PACS: 23.60.+e decay - 27.70.+q - 27.80.+w C.D. OLeary: Present address: Department of Physics, University of York, York, UK.M.J. Taylor: Present address: Department of Physics and Astronomy, Rutgers Univesity, NJ, USA.L. Weissman: Present address: NSCL, Michigan State University, East Lansing, MI 48824-1321 USA.K. Heyde: Present address: EP-ISOLDE, CERN, CH-1211, Geneva 23, Switzerland.