Isomeric 13/2+ state in 201Fr

We have identified an isomeric state in 201Fr for which we propose a spin and parity of 13/2 +, and interpret it as arising from the π(i13/2 ) configuration. A half-life of 720(40) ns was measured, corresponding to B(M2) = 0.17(2) W.u., in good agreement with those of other 13/2 + → 9/2 − [π(i13/2 ) → π(h9/2 )] transitions observed in other nuclei in the region. The nuclei of interest were produced in a fusion-evaporation reaction and their decay properties were investigated using the GREAT spectrometer at the focal plane of the RITU gas-filled recoil separator. peerReviewed

In-beam and decay spectroscopy of very neutron deficient iridium nuclei

Iridium nuclei at and beyond the proton drip line have been studied via fusion evaporation reactions. A reaction of 92Mo(78Kr, p2n) at a beam energy of 360 MeV and target thickness 500 µg cm−2 was employed to study 167,167mIr. A reaction of 112Sn(58Ni, p2n) at a beam energy of 266 MeV and target thickness 500 µg cm−2 was used to study 169,169mIr. The experiments were performed at the University of Jyvaskyla utilizing the RITU separator in conjunction with the focal plane GREAT spectrometer and the JUROGAM Ge array at the target position. Excited states feeding both the ground state and isomeric state in 169Ir, excited states feeding the ground state of 167Ir and the ground state alpha decay…

Evidence for prolate structure in light Pb isotopes from in-beamγ-ray spectroscopy ofPb185

For the first time, excited states in {sup 185}Pb have been observed in in-beam {gamma}-ray spectroscopic measurements using the recoil-decay tagging method. The resulting level scheme reveals a strongly coupled yrast band structure that originates from coupling of the i{sub 13/2} quasineutron to a prolate deformed core. The band is also observed to de-excite via the spherical {alpha}-decaying 13/2{sup +}isomeric state.

Isomeric 13/2+ (νi13/2−1) state in 211Th

Using a fusion-evaporation reaction and a gas-filled recoil separator, an isomeric state [T12=83(8)μs] with a most likely spin and parity of 132+ has been identified in Th211. The isomeric state is mainly depopulated via a hindered internal M2 transition [B(M2)=0.0025(5) W.u.], but also a weak α-decay branch of 4(3)% was observed. The present observations fit well to the systematic pattern set by the previously identified states of the same spin and parity in this region of the nuclear chart. peerReviewed

The design of a new gas-filled separator at JYFL

Abstract A new gas-filled recoil separator, intended mainly for the study of reaction products in mass region of 100–200 produced in symmetric or nearly symmetric reactions, is under design at the Department of Physics in the University of Jyvaskyla. The separator will be of the type DQQ where a horizontally focusing dipole (D) is followed by a quadrupole (Q) doublet. The bending radius of the dipole magnet will be 1850 mm and the bending angle 50°.

Exploring the boundaries of the nuclear landscape : α-decay properties of 211Pa

Employing the recoil ion transport unit (RITU) and a fusion-evaporation reaction, the α decay of 211Pa has been identified via the implantation-decay correlation technique through observation of chains up to four consecutive decays. An α-particle energy and half-life of 8320(40) keV and 3.8+4.6−1.4 ms, respectively, were measured, corresponding to favored α decay. In addition, more precise α-decay properties of 212Pa and 213Pa were obtained due to accumulated statistics. The present data were compared to those predicted by selected atomic mass models and it was used to estimate the possibility of observing proton emission from these isotopes. peerReviewed

Structure of rotational bands in 253No

In-beam gamma-ray and conversion electron spectroscopic studies have been performed on the 253 No nucleus. A strongly coupled rotational band has been identified and the improved statistics allows an assignment of the band structure as built on the $\ensuremath 9/2^-[734]_{\nu}$ ground state. The results agree with previously known transition energies but disagree with the tentative structural assignments made in earlier work.

Isomeric and ground-state properties of78171Pt,76167Os, and74163W

Decay paths, half-lives, and excitation energies of the i(13/2) bandheads of the neutron-deficient nuclei Pt-171, Os-167, and W-163 have been established for the first time. Gamma-ray transitions, ...

Identification of excited states in doubly odd63140Eu77by recoil-isomer tagging

The 36Ar + 107Ag fusion-evapn. reaction was used to search for isomeric states in the N = 77 isotope 140Eu near the proton-drip line. The recoiling nuclei were implanted into a Si detector, at the focal plane of a gas-filled separator, where prompt and delayed g-ray transitions were correlated across isomeric states using recoil-isomer tagging. The feeding and decay of a new 299(3) ns isomeric state was established. This measurement represents the first observation of excited high-spin states in 140Eu. The behavior of the new states above the isomer is discussed in terms of theor. calcns. based upon the cranked-shell model and upon the exptl. systematics of other N = 77 isotones. Within thi…

γ-Ray Spectroscopy at the Limits: First Observation of Rotational Bands inLr255

The rotational band structure of Lr-255 has been investigated using advanced in-beam gamma-ray spectroscopic techniques. To date, Lr-255 is the heaviest nucleus to be studied in this manner. One ro ...

Collectivity and Configuration Mixing inPb186,188andPo194

Lifetimes of prolate intruder states in {sup 186}Pb and oblate intruder states in {sup 194}Po have been determined by employing, for the first time, the recoil-decay tagging technique in recoil distance Doppler-shift lifetime measurements. In addition, lifetime measurements of prolate states in {sup 188}Pb up to the 8{sup +} state were carried out using the recoil-gating method. The B(E2) values have been deduced from which deformation parameters vertical bar {beta}{sub 2} vertical bar =0.29(5) and vertical bar {beta}{sub 2} vertical bar =0.17(3) for the prolate and the oblate bands, respectively, have been extracted. The results also shed new light on the mixing between different shapes.

Decay of aπh11/2⊗νh11/2microsecond isomer in61136Pm75

An experiment has been performed to populate several extremely neutron-deficient nuclei around the mass-140 region of the nuclear chart, using a beam of {sup 54}Fe on a {sup 92}Mo target at an energy of 315 MeV. Analysis of these data using recoil-isomer tagging has established that the yrast {pi}h{sub 11/2} x {nu}h{sub 11/2},J{sup {pi}}=(8{sup +}), bandhead state in {sup 136}Pm is isomeric with a half-life of 1.5(1) {mu}s. This isomeric state decays via a 43-keV, probable-E1 transition to a J{sup {pi}}=(7{sup -}) state. Consideration of the theoretical Nilsson orbitals near the Fermi surface suggests that the J{sup {pi}}=(8{sup +}) state has a {nu}h{sub 11/2}[505](11/2){sup -} x {pi}h{sub …

Level structure above the 17+ isomeric state in Tm8369152

Competing Decay Modes of a High-spin Isomer in the Proton-unbound Nucleus $^{158}$Ta

An isomeric state at high spin and excitation energy was recently observed in the proton-unbound nucleus 158Ta. This state was observed to decay by both α and γ decay modes. The large spin change r ...

Precision measurements of proton emission from the ground states of 156Ta and 160Re

The decays of the πd3/2 ground states of 156Ta and 160Re have been studied in detail using the GREAT spectrometer. More than 7000 160Re nuclei were produced in reactions of 290- and 300-MeV 58Ni ions with an isotopically enriched 106Cd target and separated in flight using the RITU separator. The proton and α decays of the πd3/2 level were confirmed and the half-life and branching ratios of this state were determined with improved precision to be t1/2=611±7 μs and bp=89±1% and bα=11±1%, respectively. The α-decay branch populated the ground state of 156Ta, allowing improved values for the proton-decay energy and half-life to be obtained (Ep=1011±5 keV; t1/2=106±4 ms). The β decay of this leve…

Decay of the high-spin isomer in 160Re: Changing single-particle structure beyond the proton drip line

WOS: 000286708700015

Blurring the Boundaries: Decays of Multiparticle Isomers at the Proton Drip Line

A multiparticle spin-trap isomer has been discovered in the proton-unbound nucleus Ta85 73158. The isomer mainly decays by γ-ray emission with a half-life of 6.1(1) μs. Analysis of the γ-ray data shows that the isomer lies 2668 keV above the known 9+ state and has a spin 10 higher and negative parity. This 19- isomer also has an 8644(11) keV, 1.4(2)% α-decay branch that populates the 9+ state in Lu154. No proton-decay branch from the isomer was identified, despite the isomer being unbound to proton emission by 3261(14) keV. This remarkable stability against proton emission is compared with theoretical predictions, and the implications for the extent of observable nuclides are considered. © …

Recoil-isomer tagging techniques at RITU

Techniques have been developed to study isomeric states in nuclei with the use of RITU (gas filled separator) at the University of Jyvaskyla. The first was the recoil-isomer tagging technique initially, utilised by D.M. Cullen to study the K π = 8− isomeric state in 138Gd [1]. The juro-sphere array was employed in conjunction with ritu and a focal plane array which consisted of several Compton-suppressed Germanium detectors, placed in close geometry around a multi wire proportional counter (mwpc) and a silicon strip detector used for the implantation of recoiling nuclei. This technique correlates prompt and delayed γ-ray transitions across isomeric states and identifies the lifetime of the …

Low-lying excited states in the neutron-deficient isotopes163Os and165Os

Excited states in the neutron-deficient isotopes Os-163 and Os-165 were identified using the JUROGAM and GREAT spectrometers in conjunction with the RITU gas-filled separator. The Os-163 and Os-165 nuclei were populated via the Cd-106(Ni-60,3n) and Mo-92(Kr-78,2p3n) reactions at bombarding energies of 270 MeV and 357 MeV, respectively. Gamma-ray emissions from these nuclei have been established unambiguously using the recoil-decay tagging technique and a coincidence analysis has allowed level schemes to be established. These results suggest that the yrast states are based upon negative-parity configurations originating from the f(7/2) and h(9/2) orbitals.

Spectroscopy of the neutron-deficient nuclide 171Pt

A number of previously unobserved gamma-rays emitted from the neutron-deficient nuclide Pt-171 have been identified using the recoil decay tagging technique. The level scheme has been updated using ...

Mass-140 isomers near the proton dripline

An experiment has been performed in Jyvaskyla, Finland, using Jurogam in conjunction with RITU and GREAT. This experiment populated several extremely neutron-deficient nuclei around the mass-140 region of the nuclei chart, using the 92Mo(54Fe, α2n) reaction at 245 MeV. Analysis of these data has revealed several previously unobserved isomeric states, in several nuclei. One of these has been assigned to 143Dy with a half-life of 1.2 ± 0.3 µs. The energies of the prompt γ rays in the band built upon the isomer are in agreement with those previously observed.

Decay studies ofAu170,171,Hg171–173, andTl176

The $^{170,171}\mathrm{Au}$ isotopes were produced in the fusion-evaporation reaction of a $^{78}\mathrm{Kr}$ ion beam with a $^{96}\mathrm{Ru}$ target. For $^{170}\mathrm{Au}$ the proton and $\ensuremath{\alpha}$ emission from the ground state were observed for the first time and the decay of the isomeric state was measured with improved accuracy. In addition, the decay of $^{171}\mathrm{Au}$ was measured with high statistics. A new $\ensuremath{\alpha}$-emitting nucleus $^{171}\mathrm{Hg}$ and the previously known $^{172}\mathrm{Hg}$ and $^{167,168,169,170}\mathrm{Pt}$ isotopes were also studied. The ground-state proton emission was identified for a new proton emitter $^{176}\mathrm{Tl}$ …

α-decay studies of the francium isotopes198Fr and199Fr

Very neutron deficient francium isotopes have been produced in fusion evaporation reactions using ${}^{60}$Ni ions on ${}^{141}$Pr targets. The gas-filled recoil separator RITU was employed to collect the fusion products and to separate them from the scattered beam. The activities were implanted into a position sensitive silicon detector after passing through a gas-counter system. The isotopes were identified using spatial and time correlations between the implants and the decays. Two $\ensuremath{\alpha}$-particle activities, with ${E}_{\ensuremath{\alpha}}=7613(15)$ keV and ${T}_{1/2}$ $=$ (${15}_{\ensuremath{-}5}^{+12}$) ms and ${E}_{\ensuremath{\alpha}}=7684(15)$ keV and ${T}_{1/2}$ $=$…

Multiparticle configurations of excited states in Lu155

Excited states in the neutron-deficient N = 84 nuclide Lu-155 have been populated by using the Pd-102(Ni-58, alpha p) reaction. The Lu-155 nuclei were separated by using the gas-filled recoil ion t ...

Probing structural changes in the very neutron-deficient Os isotopes with recoil-decay tagging

In recent years, the exploitation of the iecoil-decay tagging (RDT) technique with,large arrays of germanium detectors has revealed much information about the structure of heavy nuclei approaching the proton drip line. The yrast bands of the N <= 93 osmium isotopes have been identified in a campaign of tagging experiments using various spectrometer arrays coupled to the RITU gas-filled separator based at the University of Jyvaskyla. Trends in the yrast state excitation energies have indicated a transition from gamma-soft triaxial to near-spherical shapes with decreasing neutron number. Recent experimental results for Os-162 obtained with the JUROGAM and GREAT spectrometers also indicate the…

Recoil decay tagging ofγrays in the extremely neutron-deficient nucleusOs162

The neutron-deficient nucleus $^{162}\mathrm{Os}$, produced in the $^{106}\mathrm{Cd}(^{58}\mathrm{Ni},2n)$ reaction, has been studied using the JUROGAM $\ensuremath{\gamma}$-ray spectrometer in conjunction with the RITU gas-filled separator and the GREAT focal plane spectrometer. $\ensuremath{\gamma}$-ray transitions in $^{162}\mathrm{Os}$ have been assigned for the first time through the application of the recoil decay tagging technique. The excitation energy of the ${2}^{+}$ state and the tentative energy of the ${8}^{+}$ state are discussed in terms of the systematic energy trends as the $N=82$ shell gap is approached.

Spectroscopy at the two-proton drip line: Excited states in 158W

Abstract Excited states have been identified in the heaviest known even-Z N = 84 isotone 158W, which lies in a region of one-proton emitters and the two-proton drip line. The observation of γ-ray transitions feeding the ground state establishes the excitation energy of the yrast 6+ state confirming the spin-gap nature of the α-decaying 8+ isomer. The 8+ isomer is also expected to be unbound to two-proton emission but no evidence for this decay mode was observed. An upper limit for the two-proton decay branch has been deduced as b 2 p ≤ 0.17% at the 90% confidence level. The possibility of observing two-proton emission from multiparticle isomers in nearby nuclides is considered.

High-spin states beyond the proton drip-line: Quasiparticle alignments in 113 Cs

Abstract Excited states have been studied in the deformed proton emitter 113Cs. Gamma-ray transitions have been unambiguously assigned to 113Cs by correlation with its characteristic proton decay, using the method of recoil-decay tagging. Two previously identified rotational bands have been observed and extended to tentative spins of 45/2 and 51 / 2 ħ , with excitation energies over 8 MeV above the lowest state. These are the highest angular momenta and excitation energies observed to date in any nucleus beyond the proton drip-line. Transitions in the bands have been rearranged compared to previous work. A study of aligned angular momenta, in comparison to the predictions of Woods–Saxon cra…

Isomeric states in proton-unbound 187, 189Bi isotopes

Prompt and delayed gamma-ray spectroscopy of very neutron-deficient bismuth isotopes 187, 189Bi has been performed using the Recoil Decay Tagging (RTD) method. The isomeric i 13/2 states have been identified and their lifetimes have been measured. The systematics of these long-lived M2 isomers has been extended to the proton-unbound isotopes. The general behaviour of single-proton states is discussed within the systematics and interpreted within the shell-model framework.

Discovery of 157W and 161Os

The nuclides W-157 and Os-161 have been discovered ill reactions of Ni-58 ion beams with a Cd-106 target. The Os-161 alpha-decay energy and half-life were 6890 +/- 12 keV and 640 +/- 60 mu s. The d ...

Probing the limit of nuclear existence: Proton emission from 159Re

WOS: 000240847400007

Lifetimes of intruder states in 186Pb, 188Pb and 194Po

Abstract Lifetimes of prolate intruder states in 186Pb and 188Pb and oblate intruder states in 194Po have been determined through recoil distance Doppler-shift lifetime measurements. Deformation parameters of | β 2 | = 0.29 ( 5 ) and | β 2 | = 0.17(3) have been extracted from experimental B ( E 2 ) values for the prolate and the oblate bands, respectively. The present study addresses the phenomenon of shape coexistence typical for the nuclei near Z = 82 and N = 104 , providing information on configuration mixing of intrinsic structures of the nuclei of interest. The results are compared with the available lifetime data and theoretical results for neutron-deficient Po, Pb, Hg and Pt nuclei. …

First observation of gamma-rays from the proton emitter 171Au

Gamma-rays from the alpha- and proton-unstable nuclide 171Au have been observed for the first time. The gamma-rays were correlated with both a proton- and an alpha-particle decay branch, confirming that the nucleus decays by alpha and proton emission from a single (11/2-) state. The measurement confirms the previously determined half-lives for these particle decays but the present values are of higher precision. In addition, a longer half-life than determined in previous work was measured for the proton-unstable tentative ground state. The results are discussed in relation to structures in neighbouring nuclei and compared with a Strutinsky-type TRS calculation.

α decay studies of the nuclidesU218andU219

Very neutron deficient uranium isotopes were produced in fusion evaporation reactions using $^{40}\mathrm{Ar}$ ions on $^{182}\mathrm{W}$ targets. The gas-filled recoil separator RITU was employed to collect the fusion products and to separate them from the scattered beam and other reaction products. The activities were implanted into a position sensitive silicon detector after passing through a gas-counter system. The isotopes were identified using spatial and time correlations between the implants and the decays. Two $\ensuremath{\alpha}$-decaying states, with ${E}_{\ensuremath{\alpha}}=(8612\ifmmode\pm\else\textpm\fi{}9)$ keV and ${T}_{1/2}=(0.{51}_{\ensuremath{-}0.10}^{+0.17})$ ms for t…

Yrast structures in the light Pt isotopes169–173Pt

The exploitation of the recoil-decay tagging (RDT) technique has reinvigorated experimental investigations of the shape coexistence phenomenon in heavy neutron-deficient nuclei. In a recent experiment using the JUROGAM and GREAT spectrometers in conjunction with the RITU gas-filled separator, excited states have been investigated in the light platinum isotopes. In addition to extending the yrast sequences in 170Pt and 172Pt, the first observation of excited states in the odd-N isotopes, 169Pt and 173Pt, is reported. The bands are discussed in terms of trends in level excitation energies as a function of neutron number.

Nuclear isomers in superheavy elements as stepping stones towards the island of stability

The stability of an atomic nucleus is determined by the outcome of a tug-of-war between the attractive strong nuclear force and the repulsive electrostatic force between the protons in the nucleus. If 100 protons and about 150 neutrons or more are assembled into a nucleus, the repulsion usually becomes dominant and causes the nucleus to fission. For certain 'magic numbers' of protons and neutrons this repulsion can be overcome and the nucleus stabilized. In particular an 'island of stability' is predicted beyond the actinides, where long-lived or even stable superheavy elements can exist, but its precise limits are unknown. Experiments can help determine where this island lies, however. Spe…

αdecay studies of very neutron-deficient francium and radium isotopes

Very neutron-deficient francium and radium isotopes have been produced in fusion evaporation reactions using $^{63}\mathrm{Cu}$ and $^{65}\mathrm{Cu}$ ions on $^{141}\mathrm{Pr}$ targets and $^{36}\mathrm{Ar}$ ions on $^{170}\mathrm{Yb}$ targets. The gas-filled recoil separator RITU was employed to collect the fusion products and to separate them from the scattered beam. The activities were implanted into a position-sensitive silicon detector after passing through a gas-counter system. The isotopes were identified using spatial and time correlations between the implants and decays. Two new \ensuremath{\alpha} decaying radium isotopes, $^{201}\mathrm{Ra}$ and $^{202}\mathrm{Ra}$, were identi…

Application of ultra-fast timing techniques to the study of exotic and weakly produced nuclei

Ultra-fast time-delayed techniques have been recently applied in a number of studies where exotic nuclei were identified using advanced selection techniques. These include large Compton-suppressed Ge arrays, in-flight separators or recoil separators. Some of the new results are discussed in this presentation. Besides the results for $^{32}$Mg and $^{96}$Pd, they include the first determination of the half-life of the $8^+$ state in $^{80}$Ge, $T_1/2$ = 2.95(6) ns, and significantly more precise results for $^{51}$Mn (3680 keV level) and $^{48}$V (421 keV level), $T_1/2$ = 1760(40) ps and $T_1/2$ $\leq$ 135 ps, respectively. Development of new scintillators will steadily improve precision an…