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Low-lying states in neutron-deficient astatine and francium nuclei have been studied by means of in-beam and delayed spectroscopy. The 13/2+ state has been observed in francium nuclei with a similar down-sloping trend as in neighbouring astatine and bismuth isotopes, as a function of decreasing neutron number. A systematic trend can also now be seen for the 1/2+ state both in astatine and francium nuclei, where the level energy decreases steeply as a function of neutron number when moving further away from the neutron shell closure. This trend is very similar between astatine nuclei and their francium isotones. Moreover, shape coexistence has been observed between the 13/2+ state and the spherical 9/2- ground state in 203Fr and 205Fr. [ABSTRACT FROM AUTHOR]

The Recoil-Distance Doppler-shift method has been combined with Recoil-Decay Tagging for the first time to measure a lifetime in the proton-unbound nucleus 109I. The lifetime value was determined using the Differential Decay-Curve method in singles mode. The result has been compared to theoretical shell-model calculations in order to better understand the nature of unbound valence nucleons at the proton drip line. [ABSTRACT FROM AUTHOR]

Excited states in the extremely neutron-deficient isotope 172Hg have been established for the first time. The 96Ru(78Kr,2n) reaction was employed to populate excited states in 172Hg with a cross section σ ≈ 15 nb. The highly selective Recoil-Decay Tagging (RDT) technique was used to obtain clean in-beam γ-ray spectra for 172Hg. The yrast ground-state band has tentatively been established up to I = 6h. The data have been interpreted within the framework of total Routhian surface and quasiparticle random phase approximation calculations. In addition to the well-known features of shape coexistence previously observed in light Hg isotopes, the systematic trends in the energy of the yrast 2+ and 4+ states in the chain of Hg isotopes indicate a pronounced vibrational collectivity which is reduced in strength, but at the same time shows a higher degree of harmonicity, as the neutron number decreases below the neutron midshell. [ABSTRACT FROM AUTHOR]

Several strongly coupled bands in the neutron-deficient nucleus 161Ta have been identified and quasiparticle configuration assignments have been made on the basis of rotational alignments and cranked shell model calculations. The level scheme elucidated for 161Ta highlights the competition between the ν(h9/2) and ν(i13/2) orbitals to form the yrast spectrum. The band structures in 161Ta also provide new insights into the structural features of other heavy odd-A nuclei populated with much lower reaction cross sections in this region at the proton drip line. [ABSTRACT FROM AUTHOR]

The structure of 246Fm has been investigated using in-beam γ-ray spectroscopy. The experiment was performed at the University of Jyväskylä using JUROGAM 2 coupled to RITU and GREAT. The 246Fm nuclei were produced using a 186 MeV beam of 40Ar impinging on a target of 208Pb. JUROGAM 2 was fully instrumented with TNT2D digital acquisition cards. The use of digital acquisition cards and a rotating target allowed for unprecedented beam intensities up to 71 particle-nanoamperes for prompt γ-ray spectroscopy. With all these major advances for spectroscopy a rotational band is observed for the first time in 246Fm and discussed here. [ABSTRACT FROM AUTHOR]

For the first time, the excited states in the extremely neutron-deficient nucleus 180Pb have been observed in an in-beam γ-ray measurement employing the recoil-decay tagging technique. Deduced level energies follow the trend of prolate intruder band level energies derived from heavier lead isotopes and reflect the persistence of magicity of the closed Z = 82 proton shell when approaching the proton drip line. [ABSTRACT FROM AUTHOR]

In this paper we discuss the discovery of an isomeric state in 252No and a recent experiment studying the rotational band built upon this isomeric state. Results from the later experiment help to assign the structure of the isomer on the basis of purely experimental data, and to disentangle between different theoretical interpretations. Comparison with similar states in 250Fm and 254No provides important information and helps the development of self -consistent theories. [ABSTRACT FROM AUTHOR]

Selective tagging techniques have been used to establish new band structures in the transitional isobars 163Re and 163W. These nuclei were produced in the 106Cd(60Ni, xp yn γ) reaction at a bombarding energy of 270 MeV. Prompt γ rays were detected at the target position using the JUROGAM spectrometer while recoiling ions were separated by the RITU separator and implanted into the GREAT spectrometer. At low spin, the yrast band of 163Re is shown to be a strongly coupled collective band based on a proton h11/2 configuration. In 163W, the decay path of the 13/2+ isomeric state to the ground state has been identified and negative parity structures based on the ground state established. [ABSTRACT FROM AUTHOR]

The energy of the vh9/2 orbital in nuclei above N = 82 drops rapidly in energy relative to the vf7/2 orbital as the occupancy of the πh11/2 orbital increases. These two neutron orbitals become nearly degenerate as the proton drip line is approached. In this work, we have discovered the new nuclides 161Os and 157W, and studied the decays of the proton emitter 160Re in detail. The 161Os and 160Re nuclei were produced in reactions of 290, 300 and 310 MeV 58Ni ions with an isotopically enriched 106Cd target, separated in-flight using the RITU separator and implanted into the GREAT spectrometer. The 161Os α a decays populated the new nuclide 157W, which decayed by β-particle emission. The β decay fed the known α-decaying 1/2+ and 11/2- states in 157Ta, which is consistent with a vf7/2 ground state in 157W. The measured α-decay energy and half-life for 161Os correspond to a reduced α-decay width that is compatible with s-wave α-particle emission, implying that its ground state is also a vf7/2 state. Over 7000 160Re nuclei were produced and the γ decays of a new isomeric state feeding the πd3/2 level in 160Re were discovered, but no evidence for the proton or a decay of the expected πh11/2 state could be found. The isomer decays offer a natural explanation for this non-observation and provides a striking example of the influence of the near degeneracy of the vh9/2 and vf7/2 orbitals on the properties of nuclei in this region. [ABSTRACT FROM AUTHOR]

This report details the status of an experimental research programme which has studied isomeric states in the mass 130–160 region of the nuclear chart. Several new isomers have been established and characterised near the proton drip line using a recoil isomer tagging technique at the University of Jyväskylä, Finland. The latest experiments have been performed with a modified setup where the standard GREAT focal-plane double-sided silicon-strip detector was changed to a dual multi-wire proportional-counter arrangement. This new setup has improved capability for short-lived isomer studies where large focal-plane rates can be tolerated. The results of key recent experiments for nuclei situated above (153Yb, 152Tm) and below (144Ho, 142Tb) the N = 82 shell gap were presented. These studies have charted the evolution of isomeric states across the neutron shell from K-Isomers at N = 74, to shape isomers at N = 77 and shell-model isomers at N = 82, 83. The excitation energies for some of the lowest-lying excited states in these isomeric nuclei show behaviour which is characteristic of an X(5) symmetry falling midway between the limits expected for pure vibrational and rotational behaviour. The future prospects for studies of these nuclei were discussed using an isomer-tagged differential-plunger setup. This technique will be capable of establishing the deformation of the states above the isomers and will aid in determining whether their behaviour is indeed well described by the X(5) symmetry limit. [ABSTRACT FROM AUTHOR]

A series of recoil distance Doppler-shift lifetime measurements have been carried out to probe collectivity and configuration mixing of different shapes in the vicinity of neutron mid-shell Pb nuclei. Lifetime measurements of 186Pb and 194Po, the first ever utilizing the recoil-decay tagging method, probed the collectivity of coexisting prolate and oblate shapes in this region. Futher lifetime measurements of excited states in 180Hg, 182Hg and 196Po have been carried out. [ABSTRACT FROM AUTHOR]

Advances in spectroscopic techniques have meant that heavy nuclei in the upper right-hand corner of the nuclear chart have become amenable to detailed study. This detailed spectroscopic data can provide a stringent test for current nuclear structure theories. Experiments to investigate the structure of nuclei in the region of 254No can yield information concerning moments of inertia, stability against fission with rotation, single-particle properties, excitation energies of two quasi-particle states, and so on. A brief overview of the techniques used and recent results from studies in the region of 254No are presented, along with a summary of future developments which will allow further advances to be made. [ABSTRACT FROM AUTHOR]

Single-particle energies have been investigated in the closed neutron shell proton emitter 155Ta. The 155Ta nuclei were populated through the α decay of 159Re, which has been observed for the first time. The 159Re nuclei were produced in reactions of 300 MeV 58Ni ions with an isotopically enriched 106Cd target, separated in-flight using the RITU separator and implanted into the GREAT spectrometer. The 159Re α decay emanates from the proton-emitting πh11/2 state and populates a state in 155Ta which decays by the emission of a proton from a πh11/2 orbital. The results fit in with the systematics of proton and α-particle separation energies in the region, but disagree with the previously reported decay properties of 155Ta. [ABSTRACT FROM AUTHOR]

Gamma-ray transitions have been identified for the first time in the extremely neutron-deficient Tz = 1 nuclide 110Xe and the energies of the three lowest excited states in the ground-state band have been deduced. A level scheme has also been constructed for the proton-unbound, Tz = 3/2 nuclide 109I, exhibiting band structures built on g7/2 and h11/2 states in a weakly deformed, triaxial nucleus. In addition, a third band is proposed to be built on a g7/2 orbital coupled to an octupole-vibrational phonon of the 108Te core. The results were obtained in a recoil-decay tagging experiment using the 58Ni(54Fe,2n/p2n) reaction at a beam energy of 195 MeV. The experiment was performed using the highly efficient JUROGAM γ-ray spectrometer in conjunction with the RITU gas-filled recoil separator and the GREAT focal-plane spectrometer. The results on 110Xe establish a breaking of the normal trend of increasing first excited 2+ and 4+ level energies as a function of decreasing neutron number as the N = 50 major shell gap is approached for the neutron-deficient Xe isotopes. This unusual feature is suggested to be an effect of enhanced collectivity, possibly arising from isoscalar n-p interactions becoming increasingly important close to the N = Z line. Features in the low-lying levels of 106Te and 109I, showing similar trends, are also discussed. [ABSTRACT FROM AUTHOR]

The neutron-deficient isotope 189Bi has been studied at the University of Jyväskylä using alpha-decay, isomer and prompt gamma-ray spectroscopy. The structure of 189Bi can be understood by the coupling of an unpaired proton to the 188Pb core, in which spherical, prolate, and oblate shapes were found to coexist. Improved data on alpha-decay and prompt gamma-ray spectroscopy have been obtained, giving further insight into the shape coexistence phenomenon in the neutron-deficient lead region. [ABSTRACT FROM AUTHOR]

This report details the status of an experimental research programme which has studied isomeric states in the mass 130–160 region of the nuclear chart. Several new isomers have been established and characterised near the proton drip line using a recoil isomer tagging technique at the University of Jyväskylä, Finland. The latest experiments have been performed with a modified setup where the standard GREAT focal-plane double-sided silicon-strip detector was changed to a dual multi-wire proportional-counter arrangement. This new setup has improved capability for short-lived isomer studies where high focal-plane rates can be tolerated. The results of key recent experiments for nuclei situated above (153Yb,152Tm) and below (136Pm,142Tb) the N = 82 shell gap were presented along with an interpretation for the isomers. Finally, the future prospects of the technique, using an isomer-tagged differential-plunger setup, were discussed. This technique will be capable of establishing the deformation of the states above the isomers and will aid in the process of assigning underlying single-particle configurations to the isomeric states. [ABSTRACT FROM AUTHOR]

The observation of the new nuclide 159Re provides important insights into the evolution of single-particle structure in heavy nuclei beyond the proton drip line. The nuclide 159Re was synthesised in the reaction 106Cd(58Ni,p4n) and identified via its proton radioactivity using the RITU gas-filled separator and the GREAT focal-plane spectrometer. Comparisons of the measured proton energy (Ep = 1805±20 keV) and decay half-life (t1/2 = 21±4 μs) with values calculated using the WKB method indicate that the proton is emitted from an h11/2 state. The implications of these results for future experimental investigations into even more proton unbound Re isotopes using in-flight separation techniques are considered. [ABSTRACT FROM AUTHOR]

This paper reviews the past, present and future status of recoil-isomer tagging at the University of Jyväskylä. The main focus of this research has been to access isomeric states at and beyond the mass ≈140 proton drip line. Recoil-isomer tagging was first used at the University of Jyväskylä in 1998 to establish the prompt rotational band built upon a Kπ = 8- isomeric state in 138Gd. Since that time a series of experiments have been performed which have studied isomeric states in the N = 77 isotones 63140Eu77, 65142Tb77 and 67144Ho77, and in the N = 74 K-isomer chain, 64138Gd74 and 66140Dy74. These experiments have revealed valuable first information about deformations, single-particle excitation energies and hindrance factors in nuclei at and beyond the proton drip line where little or no information previously existed. The results of the most-recent experiments were discussed. These experiments established new isomeric states in 66143Dy77, 61136Pm75, and 64137Gd73 and a further two isomers which are currently unplaced. The paper concludes with a discussion of the future prospects for this research including the increased efficiency of the recoil-isomer tagging technique with a new Multi-Wire Proportional Counter (MWPC) detector which was designed and built at the University of Manchester. The first results from this new setup were shown. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

The gas-filled recoil separator ritu has been used to study neutron-deficient nuclei above the N=82 neutron shell closure and beyond the proton drip line. New information about the proton emitting nuclei in Ir, Au and Tl isotopes was obtained including the identification of two new proton emitters. The systematics of low-lying states in odd-mass At isotopes beyond the proton drip line were studied down to 191At using alpha-decay. A new low-lying state associated with an oblate π(2p - 1h) configuration was also observed in the corresponding Bi daughter nuclei. In order to realise these studies at the extreme limit of experimental devices, several technical developments at the ritu separator were required. © 2003 American Institute of Physics [ABSTRACT FROM AUTHOR]

Prompt and delayed γ rays from in [sup 191,193]Bi have been identified using the recoil-decay tagging (RDT), isomer tagging, and recoil gating techniques, resulting in extensive level schemes for both nuclei. Excitation energies of the isomeric 13/2[sup +] states have been established and rotational bands based on them have been observed. The nearly spherical 9/2[sup -] ground-state bands appear to be crossed by more deformed low-lying structures. TRS calculations have been performed and B(M1)/B(E2) ratios have been extracted for the observed strongly-coupled bands. In [sup 193]Bi, a 3 µs isomer has been interpreted as a h[sub 9/2] proton coupled to the 12[sup +] state of the [sup 192]Pb core. [ABSTRACT FROM AUTHOR]

A Recoil-Beta Tagging (RBT) experiment was recently performed at the accelerator laboratory at the University of Jyväskylä in order to identify T = 1 excited states in the medium-heavy N = Z = 33 nucleus 66As. The fusion-evaporation reaction 28Si(40Ca,pn)66As was employed at a beam energy of 75 MeV. The experiment was carried out utilising the JUROGAM II γ-ray spectrometer in conjunction with the gas-filled recoil separator RITU and the GREAT focal plane spectrometer system. The half-lives and ordering of the two known isomeric states in 66As have been determined. In addition, several new prompt γ-ray transitions from excited states both bypassing and decaying to the isomeric states in 66As have been observed. [ABSTRACT FROM AUTHOR]

Two rotational bands have been found in the transfermium nuclei 251Md and 255Lr, the latter being the heaviest nucleus so far studied in-beam. Both are assigned to a [521]1/2- Nilsson state by comparison to theory. The experiments have been carried out in the Accelerator Laboratory of the University of Jyväskylä (JYFL), where the array of germanium detectors JUROGAM was used in conjunction with the recoil-seperator RITU and the focal-plane setup GREAT for gamma-spectroscopic studies. [ABSTRACT FROM AUTHOR]

For the first time, excitated states in very neutron-deficient odd-mass nucleus 185Pb have been observed in an in-beam γ-ray measurement. The present data provide evidence for a strong-coupling of an odd-neutron hole to the even-mass prolate core in the light Pb isotopes. [ABSTRACT FROM AUTHOR]

Neutron-deficient uranium isotopes 218U and 219U were studied via α spectroscopic methods. The isotopes were produced in fusion evaporation reaction 182W(40Ar,xn)222-xnU. The ground state decay properties of 218U were measured with improved statistics and in addition a low-lying α decaying isomeric state was discovered. The isomer in 218U decays by α emission with an energy of Eα=10 678(17) keV and with a half-life of T1/2=(0.56-0.14+0.26) ms. The new isomeric state was assigned spin and parity IΠ = 8+. The ground state α decay has an energy of Eα=8612(9) keV and a half-life of T1/2=(0.51-0.10+0.17) ms. The ground state decay properties of 219U were determined with improved statistics as Eα=9774(18) keV and a half-life of T1/2= (0.08-0.03+0.10) ms. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

Evidence for the presence of non-yrast states in 254No has been observed in two different in-beam experiments carried out at the University of Jyväskylä. Firstly an in-beam conversion electron spectroscopic study was performed with the SACRED spectrometer, revealing a distribution consisting of high-multiplicity electron cascades. This provides an indirect proof of the presence of high K-bands in 254No. In a more recent in-beam γ-ray spectroscopic measurement, evidence for the decay of non-yrast states in 254No has been observed for the first time. It is speculated that the observation of high-energy γ rays is due to the decay of a K = 3 band-head state. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

Gamma-ray transitions from excited states in 106Te have been identified using the recoil decay tagging technique. The experiment which was the reaction 54Fe(54Fe,2n)106Te* was performed at the JYFL accelerator facility at the University of Jyväskylä, Finland. The production cross section was estimated at 25 nb, a new limit for in-beam γ-ray spectroscopy. A tentative level structure for the ground state band of 106Te is proposed. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

Recoil-decay tagging technique has been employed in the study of non-yrast states in 186Pb. High quality γγ-coincidence data have revealed three new bands and the yrast band has been extended up to Iπ=20+. A low-lying non-yrast band provide evidences for an oblate structure. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

γ-ray transitions in the neutron deficient 190,197Po nuclei have been identified. The yrast band of 190Po has been extended up to a spin and parity of 14+ and is found to display similar systematic behaviour to isotones 186Hg and 188Pb above the 4+ level, thus confirming its prolate nature. In 197Po the band built upon the 13/2+ isomer has been extended up to a spin and parity of 33/2+, while the non-yrast side-band has been observed for the first time. The behaviour of 197Po is found to be similar to that of the nearby even-mass isotopes, which is consistent with the model in which the i13/2 neutron is weakly coupled to the states in the even-even core. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]