Evidence for a spin-aligned neutron-proton paired phase from the level structure of (92)Pd

4 páginas, 4 figuras.-- El Pdf es la versión pre-print.-- et al.

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

New collective structures in Au179 and their implications for the triaxial deformation of the Pt178 core

Lifetimes of core-excited states in semi-magic $^{95}$Rh

Lifetimes of negative-parity states have been determined in the neutron deficient semi-magic (N = 50) nucleus 95Rh. The fusion-evaporation reaction 58Ni(40Ca,3p) was used to populate high-spin states in 95Rh at the Grand Accélérateur National d’Ions Lourds (GANIL) accelerator facility. The results were obtained using the Doppler Shift Attenuation Method (DSAM) based on the Doppler broadened line shapes produced during the slowing down process of the residual nuclei in a thick 6mg/cm2 metallic target. B(M1) and B(E2) reduced transition strengths are compared with predictions from large-scale shell-model calculations. 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…

γ-ray linear polarization measurements and(g9/2)−3neutron alignment in91Ru

The authors would like to thank the operators of the GANIL cyclotrons for providing the 36Ar beam. We would also like to thank the EXOGAM Collaboration for use of the clover Ge detector array, the DIAMANT Collaboration for use of the charged particle detector system, and the European gamma-ray Spectroscopy Pool for use of the neutron detector system. We acknowledge funding support from the French-Polish LEA COPIGAL and the IN2P3-Polish laboratories COPIN Agreement No. 06-122, from the UK STFC, from the Swedish Research Council (Contracts No. 2007-4067 and No. 2008-5793), from the Goran Gustafsson Foundation, from the OTKA under Contract No. K100835, and from the Bolyai Janos Foundation. AG …

Rich band structure and multiple long-lived isomers in the odd-odd 118Cs nucleus

One of the largest sets of collective excitations built on two-quasiparticle configurations in odd-odd nuclei of the proton-rich A≈120 mass region is reported in 118Cs. Several new rotational bands and long-lived isomers have been identified. The 8+ bandhead of the πh11/2⊗νh11/2 band is a short-lived isomer with a half-life in the nanosecond range, while the 7+ state below it is a long-lived isomer with a half-life of T1/2=0.55(6)μs. Two other long-lived isomers have been identified: a 66-keV transition detected at the MARA focal plane depopulates one of them, indicating a half-life in the microsecond range, while no depopulating transitions have been identified for the other, indicating a …

Backbending in the pear-shaped 223(90)Th nucleus: Evidence of a high-spin octupole to quadrupole shape transition in the actinides

International audience; Relatively neutron-rich thorium isotopes lie at the heart of a nuclear region of nuclei exhibiting octupole correlation effects. The detailed level structure of Th223 has been investigated in measurements of γ radiation following the fusion-evaporation channel of the Pb208(O18,3n)Th223 reaction at 85 MeV beam energy. The level structure has been extended up to spin 49/2, and 33 new γ rays have been added using triple-γ coincidence data. The spins and parities of the newly observed states have been confirmed by angular distribution ratios. In addition to the two known yrast bands based on a K=5/2 configuration, a non-yrast band has been established up to spin 35/2. We…

In-beam spectroscopy with intense ion beams: Evidence for a rotational structure in246Fm

The rotational structure of ${}^{246}$Fm has been investigated using in-beam $\ensuremath{\gamma}$-ray spectroscopic techniques. The experiment was performed using the JUROGAMII germanium detector array coupled to the gas-filled recoil ion transport unit (RITU) and the gamma recoil electron alpha tagging (GREAT) focal plane detection system. Nuclei of ${}^{246}$Fm were produced using a 186 MeV beam of ${}^{40}$Ar impinging on a ${}^{208}$Pb target. The JUROGAMII array was fully instrumented with Tracking Numerical Treatment 2 Dubna (TNT2D) digital acquisition cards. The use of digital electronics and a rotating target allowed for unprecedented beam intensities of up to 71 particle-nanoamper…

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

Stability of the heaviest elements : K isomer in 250No

Decay spectroscopy of 250No has been performed using digital electronics and pulse-shape analysis of the fast nuclear decays for the first time. Previous studies of 250No reported two distinct fission decay lifetimes, related to the direct fission of the ground state and to the decay of an isomeric state but without the possibility to determine if the isomeric state decayed directly via fission or via internal electromagnetic transitions to the ground state. The data obtained in the current experiment allowed the puzzle to finally be resolved, attributing the shorter half-life of t1/2 = 3.8 ± 0.3 μs to the ground state and the longer half-life t1/2 = 34.9+3.9 −3.2 μs to the decay of an isom…

Shape coexistence in $^{178}$Hg

Lifetime measurements of excited states in 178 Hg have been performed using the 103 Rh ( 78 Kr , p 2 n ) reaction at a beam energy of 354 MeV. The recoil-decay tagging (RDT) technique was applied to select the 178 Hg nuclei and associate the prompt γ rays with the correlated characteristic ground-state α decay. Lifetimes of the four lowest yrast states of 178 Hg have been determined using the recoil distance Doppler-shift (RDDS) method. The experimental data are compared to theoretical predictions with focus on shape coexistence. The results confirm the shift of the deformed prolate structures to higher lying states but also indicate their increasing deformation with decreasing neutron numb…

In-beam gamma-ray and electron spectroscopy of $^{249,251}$Md

The odd-Z Md251 nucleus was studied using combined γ-ray and conversion-electron in-beam spectroscopy. Besides the previously observed rotational band based on the [521]1/2− configuration, another rotational structure has been identified using γ-γ coincidences. The use of electron spectroscopy allowed the rotational bands to be observed over a larger rotational frequency range. Using the transition intensities that depend on the gyromagnetic factor, a [514]7/2− single-particle configuration has been inferred for this band, i.e., the ground-state band. A physical background that dominates the electron spectrum with an intensity of ≃60% was well reproduced by simulating a set of unresolved ex…

De-excitation of the strongly coupled band in 177Au and implications for core intruder configurations in the light Hg isotopes

International audience; Excited states in the proton-unbound nuclide $^{177}$Au were populated in the $^92}$Mo($^{88}$Sr, p2n) reaction and identified using the Jurogam-II and GREAT spectrometers in conjunction with the RITU gas-filled separator at the University of Jyväskylä Accelerator Laboratory. A strongly coupled band and its decay path to the 11/2−α-decaying isomer have been identified using recoil-decay tagging. Comparisons with cranked Hartree-Fock-Bogoliubov (HFB) calculations based on Skyrme energy functionals suggest that the band has a prolate deformation and is based upon coupling the odd 1h11/2 proton hole to the excited 02+ configuration in the $^{178}$Hg core. Although these…

Spectroscopy on the proton drip-line: Probing the structure dependence of isospin nonconserving interactions

J. Henderson et al. ; 4 pags. ; 4 figs. ; PACS number(s): 21.10.Re, 21.60.Cs, 23.20.Lv, 27.50.+e

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

First observation of excited states inHg17595

Excited states of the neutron-deficient nucleus Hg-175, populated using fusion-evaporation reactions, are reported for the first time. The spin and parity of the ground state has been determined to ...

Lifetime measurements of excited states in $^{162}$W and $^{164}$W and the evolution of collectivity in rare-earth nuclei

International audience; Lifetimes of the first excited 2+ states in the extremely neutron-deficient $^{162}$W and $^{164}$W nuclei have been measured using the recoil distance Doppler shift technique. Experimental B(E2) data for the isotopic chains of hafnium, tungsten, and osmium, from the midshell region near the β-stability line towards the N=82 closed shell and the most neutron-deficient nuclides, are compared with predictions of nuclear deformations and 21+→0g.s.+ reduced transition strengths from different classes of state-of-the-art theoretical model calculations. The results reveal striking differences and deficiencies in the predictive power of current nuclear structure models.

Rich band structure and multiple long-lived isomers in the odd-odd Cs118 nucleus

α-spectroscopy studies of the new nuclides 165Pt and 170Hg

The new nuclides 165Pt and 170Hg were produced in the reactions 92Mo(78Kr,5n) and 96Ru(78Kr,4n) at bombarding energies of 418 MeV and 390 MeV, respectively. For 170Hg an α-particle energy of Eα=7590(30)keV and half-life of t1/2=0.08+0.40−0.04ms were deduced, while for 165Pt the corresponding values were 7272(14) keV and 0.26+0.26−0.09ms. Comparison of the reduced α-decay widths with systematics indicates that both α decays are unhindered. Although combining the measured α-decay Q values with extrapolated masses suggests that both new nuclides are unbound to two-proton emission by more than 1 MeV, their α-decay half-lives are too short for this decay mode to compete. Improved data were also …

Characterizing the atomic mass surface beyond the proton drip line via a-decay measurements of the s1/2 ground state of 165Re and the h11/2 isomer in 161Ta

The a-decay chains originating from the s1/2 and h11/2 states in 173Au have been investigated following fusion-evaporation reactions. Four generations of a radioactivities have been correlated with 173Aum leading to a measurement of the a decay of 161Tam. It has been found that the known a decay of 161Ta, which was previously associated with the decay of the ground state, is in fact the decay of an isomeric state. This work also reports on the first observation of prompt g rays feeding the ground state of 173Au. This prompt radiation was used to aid the study of the a-decay chain originating from the s1/2 state in 173Au. Three generations of a decays have been correlated with this state lea…

Shell-Structure and Pairing Interaction in Superheavy Nuclei: Rotational Properties of the Z=104 Nucleus (256)Rf

The rotational band structure of the Z ¼ 104 nucleus 256Rf has been observed up to a tentative spin of 20@ using state-of-the-art -ray spectroscopic techniques. This represents the first such measurement in a superheavy nucleus whose stability is entirely derived from the shell-correction energy. The observed rotational properties are compared to those of neighboring nuclei and it is shown that the kinematic and dynamic moments of inertia are sensitive to the underlying single-particle shell structure and the specific location of high-j orbitals. The moments of inertia therefore provide a sensitive test of shell structure and pairing in superheavy nuclei which is essential to ensure the val…

Lifetime measurements of excited states in ¹⁶³W and the implications for the anomalous B(E2) ratios in transitional nuclei

This letter reports lifetime measurements of excited states in the odd-N nucleus $^{163}$W using the recoil-distance Doppler shift method to probe the core polarising effect of the i13/2 neutron orbital on the underlying soft triaxial even-even core. The ratio B(E2:21/2+→17/2+)/B(E2:17/2+→13/2+) is consistent with the predictions of the collective rotational model. The deduced B(E2) values provide insights into the validity of collective model predictions for heavy transitional nuclei and a geometric origin for the anomalous B(E2) ratios observed in nearby even-even nuclei is proposed.

Identification of sub-μs isomeric states in the odd-odd nucleus 178Au

The neutron-deficient gold (Z=79) isotopes in the vicinity of the neutron midshell N=104 provide prolific examples of shape coexistence and isomerism at low excitation energy. They can be probed via a number of different experimental techniques. In this study, two new isomeric states with half-lives of 294(7) and 373(9) ns have been observed in the neutron-deficient odd-odd nuclide 178Au (N=99) in an experiment at the RITU gas-filled separator at JYFL, Jyväskylä. This result was achieved due to the use of a segmented planar germanium detector with a high efficiency at low energies. By applying the recoil-decay tagging technique, they were assigned to decay to two different long-lived α-deca…

Neutron excitations in 119Ba

The neutron-deficient 119Ba nucleus has been studied using the 58Ni(64Zn,2pn) reaction and the JUROGAM 3 γ-ray detector array coupled to the MARA recoil-mass separator setup. One new rotational band and several low-lying states are newly identified. A half-life of T1/2=0.36(2)μs has been measured for the 5/2− bandhead of the νh11/2 band. The two previously known rotational bands are confirmed, except for the higher part of the +1/2 signature partner of the positive-parity band. Configurations are assigned based on the analysis of the observed quasiparticle alignments whose nature is unveiled by the calculations using the particle number conserving cranked shell model. peerReviewed

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, ...

Decay of a 19(-) isomeric state in Lu-156

A multiparticle spin-trap isomeric state having a half-life of 179(4) ns and lying 2601 keV above the yrast 10(+) state in Lu-156 has been discovered. The Lu-156 nuclei were produced by bombarding isotopically enriched Cd-106 targets with beams of Ni-58 ions, separated in flight using the gas-filled separator RITU and their decays were measured using the GREAT spectrometer. Analysis of the main decay path that populates yrast states observed previously suggests a spin-parity assignment of 19(-) for the isomeric state, which is consistent with isomeric states identified in the N = 85 isotones. Comparison with other decay paths in Lu-156 indicates that the [pi h(11/)(2)(-1) circle times nu h(…

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.

Signatures of enhanced octupole correlations at high spin in 136Nd

Experimental signatures of moderately enhanced octupole correlations at high spin in 136Nd are indicated for the first time. The extracted dipole moments of two negative-parity bands are only two times smaller than those of the lanthanide nuclei with N≈90 which present well-established octupole correlations. Calculations using the cranked quasiparticle random phase approximation and a model of quadrupole-octupole rotations with octupole vibrations reveal the structure of the bands and the enhanced octupole correlations at high spin in 136Nd. peerReviewed

In-beam γ-ray spectroscopy of 94Ag

A recoil-beta-tagging experiment has been per formed to study the excited T = 0 and T = 1 states in the odd–odd N = Z nucleus 94Ag, populated via the 40Ca(58Ni,1p3n)94Ag reaction. The experiment was con ducted using the MARA recoil separator and JUROGAM3 array at the Accelerator Laboratory of the University of Jyväskylä. Through correlating fast, high-energy beta decays at the MARA focal plane with prompt γ rays emitted at the reaction target, a number of transitions between excited states in 94Ag have been identified. The timing characteris tics of these transitions confirm that they fall within decay sequences that feed the short-lived T = 1 ground state of 94Ag. The transitions are propo…

Complete set of proton excitations in 119Cs

The very neutron-deficient strongly deformed 119Cs nucleus has been studied using the 58Ni(64Zn,3p) reaction and the JUROGAM 3 γ-ray detector array coupled to the MARA recoil-mass separator setup. The excitation energies of all observed bands have been determined, spins and parities have been firmly assigned to most of the observed states. The previously known and the newly identified rotational bands have been extended to very high spin and excitation energy. The configurations of the observed bands are discussed using the particle number conserving cranked shell model. The present study establishes the largest set of rotational bands observed in the proton-rich A≈120 mass region. peerRevi…

Lifetime Measurements of Excited States in $^{172}$Pt and the Variation of Quadrupole Transition Strength with Angular Momentum

Lifetimes of the first excited 2 + and 4 + states in the extremely neutron-deficient nuclide 172 Pt have been measured for the first time using the recoil-distance Doppler shift and recoil-decay tagging techniques. An unusually low value of the ratio B ( E 2 : 4 + 1 → 2 + 1 ) / B ( E 2 : 2 + 1 → 0 + gs ) = 0.55 ( 19 ) was found, similar to a handful of other such anomalous cases observed in the entire Segré chart. The observation adds to a cluster of a few extremely neutron-deficient nuclides of the heavy transition metals with neutron numbers N ≈ 90 – 94 featuring the effect. No theoretical model calculations reported to date have been able to explain the anomalously low B ( E 2 : 4 + 1 → …

Lifetime measurements of yrast states in ¹⁷⁸ Pt using the charge plunger method with a recoil separator

Abstract Lifetime measurements in \(^{178}\)Pt with excited states de-exciting through \(\gamma\)-ray transitions and internal electron conversions have been performed. Ionic charges were selected by the in-flight mass separator MARA and measured at the focal plane in coincidence with the \(4^{+}_{1}→2^{+}_{1}\) 257 keV γ-ray transition detected using the JUROGAM 3 spectrometer. The resulting charge-state distributions were analysed using the differential decay curve method (DDCM) framework to obtain a lifetime value of 430(20) ps for the \(2^{+}_{1}\) state. This work builds on a method that combines the charge plunger technique with the DDCM analysis. As an alternative analysis, ions were…

Refined description of the positive-parity bands and the extent of octupole correlations in 120Ba

Three new negative-parity bands have been identified in 120Ba, two of them forming a strongly coupled band. The previously known negative-parity band is significantly extended to high spin, while the lower part of the yrare positive-parity band has been modified. From the analysis of the band properties and comparison with the neighboring nuclei a coherent description of all bands is achieved. In particular, a simple explanation of the evolution of the positive-parity bands at high spin is proposed, including the possible occupation of the νf7/2[541]1/2− intruder orbital. Cranked Nilsson-Strutinsky calculations reveal similar quadrupole deformations but different triaxiality of the bands, w…

Production cross section and decay study of $^{243}$Es and $^{249}$Md

In the study of the odd-$Z$, even-$N$ nuclei $^{243}$Es and $^{249}$Md, performed at the University of Jyv\"askyl\"a, the fusion-evaporation reactions $^{197}$Au($^{48}$Ca,2$n$)$^{243}$Es and $^{203}$Tl($^{48}$Ca,2$n$)$^{249}$Md have been used for the first time. Fusion-evaporation residues were selected and detected using the RITU gas-filled separator coupled with the focal-plane spectrometer GREAT. For $^{243}$Es, the recoil decay correlation analysis yielded a half-life of $24 \pm 3$s, and a maximum production cross section of $37 \pm 10$ nb. In the same way, a half-life of $26 \pm 1$ s, an $\alpha$ branching ratio of 75 $\pm$ 5%, and a maximum production cross section of 300 $\pm$ 80 nb…

New collective structures in 179Au and their implications for the triaxial deformation of the 178Pt core

The extremely neutron-deficient isotope 179Au has been studied by a combination of in-beam γ-ray and isomeric-decay spectroscopy. For in-beam spectroscopy, the recoil-isomer tagging technique was employed, using the known 3/2−, T1/2=328 ns isomer. A new rotational band, associated with the unfavored signature band of the 1h9/2⊕2f7/2 proton-intruder configuration, was revealed. A previously unknown, high-spin isomeric state with an excitation energy of 1743(17) keV and T1/2=2.16(8)µs was discovered. Five decay paths were identified, some of them feeding previously unknown non-yrast excited states, associated with the 1i13/2 proton-intruder configuration. Calculations based on the particle-pl…

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.

α-Decay branching ratios measured by γ-ray tagging

Abstract The nuclides 168–170Pt were produced by bombarding isotopically enriched 92,94Mo targets with 336, 348 MeV 78Kr ions. Prompt γ rays were detected at the target position and provided a selection criterion for the 168–170Pt nuclei. This technique enables the problem of the background from higher-energy α decays in the spectrum to be circumvented. The Pt nuclei were separated in flight using the gas-filled separator RITU and implanted into the GREAT spectrometer, which was used to study subsequent α decays. The α -decay branching ratios of 164–166Os were deduced from the fraction of selected 168–170Pt nuclei correlated with α decays of 164–166Os. The resulting branching ratios agree w…

Identification of excited states in 107,52Te55

Excited states in the extremely neutron-deficient nucleus 107Te have been identified from two separate experiments using the recoil-decay tagging technique. Two connected structures were observed on the basis of γγ-coincidence relations and tentatively assigned as built on the mixed-parentage νg7/2d5/2 and νh11/2 intruder configurations. The observed structures were compared with large-scale shell-model calculations and total Routhian surface calculations. Collective behavior was discovered to persist in the νh11/2 band of 107Te which highlights the shape-polarizing effect of a single valence neutron occupying the h11/2 intruder orbit as the N=50 shell closure is approached. peerReviewed

Excited states in the proton-unbound nuclide Ta-158

Excited states in the neutron-deficient odd-odd proton-unbound nuclide $^{158}\mathrm{Ta}$ have been investigated in two separate experiments. In the first experiment, $^{166}\mathrm{Ir}$ nuclei were produced in the reactions of 380 MeV $^{78}\mathrm{Kr}$ ions with an isotopically enriched $^{92}\mathrm{Mo}$ target. The $\ensuremath{\alpha}$-decay chain of the ${9}^{+}$ state in $^{166}\mathrm{Ir}$ was analyzed. Fine structure in the $\ensuremath{\alpha}$ decay of the ${9}^{+}$ state in $^{162}\mathrm{Re}$ established a 66 keV difference in excitation energy between the lowest-lying ${9}^{+}$ and ${10}^{+}$ states in $^{158}\mathrm{Ta}$. Higher-lying states in $^{158}\mathrm{Ta}$ were popul…

Decay spectroscopy of 171,172Os and 171,172,174Ir

We report on a study of the α-decay fine structure and the associated Eα−Eγ correlations in the decays of 171,172Os and 171,172,174Ir. In total, 13 new α-decay energy lines have been resolved, and three new γ-ray transitions have been observed following the new decay branches to 168Re and 167W. The weak α-decay branch from the bandhead of the νi13/2 band in 171Os observed in this work highlights an unusual competition between α, β, and electromagnetic decays from this isomeric state. The nucleus 171Os is therefore one of few nuclei observed to exhibit three different decay modes from the same excited state. The nuclei of interest were produced in 92Mo(83Kr,xpyn) fusion-evaporation reactions…

A charge plunger device to measure the lifetimes of excited nuclear states where transitions are dominated by internal conversion

A charge plunger device has been commissioned based on the DPUNS plunger (Taylor et al., 2013) using the in-flight mass separator MARA at the University of Jyväskylä. The 152Sm(32S,4n)180Pt reaction was used to populate excited states in 180Pt. A lifetime measurement of the 21+ state was performed by applying the charge plunger technique, which relies on the detection of the charge state-distribution of recoils rather than the detection of the emitted γ rays. This state was a good candidate to test the charge plunger technique as it has a known lifetime and depopulates through a converted transition that competes strongly with γ-ray emission. The lifetime of the 21+ state was measured to be…

Identification of Excited States in theTz=1NucleusXe110: Evidence for Enhanced Collectivity near theN=Z=50Double Shell Closure

Gamma-ray transitions have been identified for the first time in the extremely neutron-deficient (N=Z+2) nucleus {sup 110}Xe, and the energies of the three lowest excited states in the ground-state band have been deduced. The results establish a breaking of the normal trend of increasing first excited 2{sup +} and 4{sup +} level energies as a function of the 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.

Nuclear levels in proton-unboundI109: Relative single-particle energies beyond the proton drip line

A level scheme has been constructed for the proton-unbound, T-z=3/2 nuclide I-109(53)56 following a recoil-decay-tagging experiment using the Ni-58(Fe-54, p2n gamma) reaction at a beam energy of 19 ...

Coulomb shifts and shape changes in the mass 70 region

The technique of recoil beta tagging has been developed which allows prompt gamma decays in nuclei from excited states to be correlated with electrons from their subsequent short-lived beta decay. This technique is ideal for studying nuclei very far from stability and improves in sensitivity for very short-lived decays and for high decay Q-values. The method has allowed excited states in 78Y to be observed for the first time, as well as an extension in the knowledge of T=1 states in 74Rb. From this new information it has been possible to compare Coulomb energy differences (CED) between T=1 states in 70Br/70Se, 74Rb/74Kr, and 78Y/78Sr. The A=70 CED exhibit an anomalous behavior which is inco…

Spectroscopy of proton-rich 66^Se up to J^{\pi} = 6^+: isospin-breaking effect in the A = 66 isobaric triplet

Candidates for three excited states in the 66^Se have been identified using the recoil-{\beta} tagging method together with a veto detector for charged-particle evaporation channels. These results allow a comparison of mirror and triplet energy differences between analogue states across the A = 66 triplet as a function of angular momentum. The extracted triplet energy differences follow the negative trend observed in the f_7/2 shell. Shell-model calculations indicate a continued need for an additional isospin non-conserving interaction in addition to the Coulomb isotensor part as a function of mass.

Evidence for enhanced collectivity in Te-I-Xe nuclei near the N = Z = 50 double shell closure

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 hi…

Isomer spectroscopy in254No

Isomeric states in No-254 were investigated using a calorimetric method. Two different isomers were found with half-lives of T-1/2 = 266 +/- 2 ms and T-1/2 = 184 +/- 3 mu s, respectively. The domin ...

Lifetime Measurements with the Doppler Shift Attenuation Method Using a Thick Homogeneous Production Target — Verification of the Method

International audience; Doppler Shift Attenuation Method (DSAM) analysis of excited-state lifetimes normally employs thin production targets mounted on a thick stopper foil (“backing”) serving to slow down and stop the recoiling nuclei of interest in a well-defined manner. Use of a thick, homogeneous production target leads to a more complex analysis as it results in a substantial decrease in the energy of the incident projectile which traverses the target with an associated change in the production cross section of the residues as a function of penetration depth. Here, a DSAM lifetime analysis using a thick homogeneous target has been verified using the Doppler broadened lineshapes of γ ra…

In-beam γ-ray and electron spectroscopy of Md249,251

The odd-Z 251Md nucleus was studied using combined γ-ray and conversion-electron in-beam spectroscopy. Besides the previously observed rotational band based on the [521]1/2− configuration, another rotational structure has been identified using γ−γ coincidences. The use of electron spectroscopy allowed the rotational bands to be observed over a larger rotational frequency range. Using the transition intensities that depend on the gyromagnetic factor, a [514]7/2− single-particle configuration has been inferred for this band, i.e., the ground-state band. A physical background that dominates the electron spectrum with an intensity of ≃60% was well reproduced by simulating a set of unresolved ex…

Spectroscopy of Kr 70 and isospin symmetry in the T=1 fpg shell nuclei SPECTROSCOPY of Kr 70 and ISOSPIN SYMMETRY ... D. M. DEBENHAM et al.

The recoil-β tagging technique has been used in conjunction with the Ca40(S32,2n) reaction at a beam energy of 88 MeV to identify transitions associated with the decay of the 2+ and, tentatively, 4+ states in the nucleus Kr70. These data are used, along with previously published data, to examine the triplet energy differences (TED) for the mass 70 isobars. The experimental TED values are compared with shell model calculations, performed with the JUN45 interaction in the fpg model space, that include a J=0 isospin nonconserving (INC) interaction with an isotensor strength of 100 keV. The agreement is found to be very good up to spin 4 and supports the expectation for analog states that all t…

Evidence against the wobbling nature of low-spin bands in 135Pr

International audience; The electromagnetic character of the ΔI=1 transitions connecting the 1- to 0-phonon and the 2- to 1-phonon wobbling bands should be dominated by an E2 component, due to the collective motion of the entire nuclear charge. In the present work it is shown, based on combined angular correlation and linear polarization measurements, that the mixing ratios of all analyzed connecting transitions between low-lying bands in 135Pr interpreted as 0-, 1-, and 2-phonon wobbling bands, have absolute values smaller than one. This indicates predominant M1 magnetic character, which is incompatible with the proposed wobbling nature. All experimental observables are instead in good agr…

In-beam spectroscopic study of $^{244}$Cf

The ground-state rotational band of the neutron-deficient californium ( Z = 98 ) isotope 244 Cf was identified for the first time and measured up to a tentative spin and parity of I π = 20 + . The observation of the rotational band indicates that the nucleus is deformed. The kinematic and dynamic moments of inertia were deduced from the measured γ -ray transition energies. The behavior of the dynamic moment of inertia revealed an up-bend due to a possible alignment of coupled nucleons in high- j orbitals starting at a rotational frequency of about ℏ ω = 0.20 MeV . The results were compared with the systematic behavior of the even-even N = 146 isotones as well as with available theoretical c…

Tilted precession bands in $^{135}$Nd

International audience; Two new excited bands built on the πh11/2 configuration have been identified in Nd135 in addition to the known πh11/2 band. The energy spectra of the excited bands and the available electromagnetic transition probabilities are in good agreement with theoretical results obtained using quasiparticle-plus-triaxial-rotor model calculations. The properties of the bands identify them as tilted precession bands instead of wobbling bands. Our results give a new insight into the interpretation of the low-lying bands in odd-A mass nuclei, and can stimulate future studies to address the nuclear triaxiality.

Spectroscopy of the neutron-deficient isobars 163 Re and 163 W using tagging techniques

Bozok University;Erciyes University;et al.;Istanbul University;Nigde University;The Turkish Atomic Energy Authority (TAEK)

Experimental observation of the M1 scissors mode in $^{254}No$

Physics letters / B 834, 137479 (2022). doi:10.1016/j.physletb.2022.137479

Evidence for octupole collectivity in 172Pt

Excited states in the extremely neutron-deficient nucleus 172Pt were populated via 96Ru(78Kr,2p) and 92Mo(83Kr,3n) reactions. The level scheme has been extended up to an excitation energy of  ~ 5 MeV and tentative spin-parity assignments up to Iπ = 18+. Linear polarization and angular distribution measurements were used to determine the electromagnetic E1 character of the dipole transitions connecting the positive-parity ground-state band with an excited side-band, firmly establishing it as a negative-parity band. The lowest member of this negative-parity structure was firmly assigned spin-parity 3-. In addition, we observed an E3 transition from this 3- state to the ground state, providing…

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 ...

Lifetime measurements of excited states in W-162 and W-164 and the evolution of collectivity in rare-earth nuclei

WOS: 000400140500006

Spectroscopy of the neutron-deficient nucleusOs16791

Excited states of the nucleus Os-167 have been populated by the reaction Mo-92(Kr-78,2pn). The JUROGAM gamma-ray detector array has been used in conjunction with the RITU gas-filled separator and the GREAT spectrometer to observe prompt gamma rays in coincidence with recoiling fusion-evaporation residues and their subsequent decay by alpha particle emission. By correlating prompt gamma radiation with the characteristic alpha radioactivity of Os-167, it has been possible to extend the level scheme for this nucleus significantly. In particular, an extension of the yrast band and four previously unobserved bands are reported. In addition, the recoil distance Doppler-shift method was used to de…

γ-ray spectroscopy approaching the limits of existence of atomic nuclei: A study of the excited states ofPt168andPt169

Excited states in the $N=90$ and $N=91$ Pt nuclei have been investigated using the JUROGAM and GREAT spectrometers in conjunction with the RITU gas-filled separator. These nuclei were populated via the reactions $^{92}\mathrm{Mo}(^{78}\mathrm{Kr},2n)$ and $^{94}\mathrm{Mo}(^{78}\mathrm{Kr},3n)$ at 335 and 348 MeV, respectively. The recoil-decay tagging technique has been used to correlate prompt $\ensuremath{\gamma}$ radiation with the characteristic $\ensuremath{\alpha}$ decays of $^{168}\mathrm{Pt}$ and $^{169}\mathrm{Pt}$. A $\ensuremath{\gamma}\text{\ensuremath{-}}\ensuremath{\gamma}$ analysis has allowed a level scheme for $^{168}\mathrm{Pt}$ to be reported for the first time and the l…

Investigation of 246Fm : in-beam spectroscopy at the limits\u2028

Identification of isomeric states in the N=73 neutron-deficient nuclei 132Pr and 130La

Decays from isomeric states in the neutron-deficient N=73 nuclei 132Pr and 130La have been observed for the first time. Half-lives of 486(70) ns and 2.46(4) μs were measured for two isomeric states in 132Pr. The decay from the 486ns (8 -) isomer has been interpreted as a hindered E1 transition from the bandhead state of the excited πh 11/2νg 7/2 configuration. The decay from the 2.5 μs (8 +) isomer is consistent with the Weisskopf estimate for a low-energy E2 transition. An analogous 0.74(3) μs decay from an (8 +) isomer in the neighboring isotone 130La has also been observed which similarly can be explained if the transition has E2 character. The Weisskopf interpretation for the isomer hin…

Neutron excitations in Ba119

Excited states in 217Ra populated in the α decay of 221Th

Fine structure in the α decay of 22190Th, populating excited states in 21788Ra, was studied using αγ-coincidence spectroscopy. Two α-decay branches from 221Th have been newly observed, with Eα(keV)[bα(%)]=7951(8)[0.14(3)] and 8247(3)[1.51(12)], together with three previously known branches. Also, two new states in 217Ra were identified at E = 177 and 227 keV. The ground-state configurations of the odd-A, N = 131 transitional isotones above 208Pb are interpreted from their α-decay fine structure systematics and considered in terms of predictions using spherical shell and reflection-asymmetric models. peerReviewed

α-decay spectroscopy of the N = 130 isotones 218Ra and 220Th: Mitigation of α-particle energy summing with implanted nuclei

An analysis technique has been developed in order to mitigate energy summing due to sequential short-lived α decays from nuclei implanted into a silicon detector. Using this technique, α-decay spectroscopy of the N=130 isotones 218Ra (Z=88) and 220Th (Z=90) has been performed. The energies of the α particles emitted in the 218Ra→214Rn and 220Th→216Ra ground-state-to-ground-state decays have been measured to be 8381(4) keV and 8818(13) keV, respectively. The half-lives of the ground states of 218Ra and 220Th have been measured to be 25.99(10) μs and 10.4(4) μs, respectively. The half-lives of the ground states of the α-decay daughters, 214Rn and 216Ra, have been measured to be 259(3) ns and …

Delayed or absent π(h11/2)2 alignment in 111Xe

Excited states have been identified in the very neutron-deficient N = Z + 3 nucleus 111Xe for the first time, using the 58Ni(58Ni, αn) heavy-ion fusion-evaporation reaction. γ -ray transitions have been unambiguously assigned to 111Xe by correlation with the characteristic 111Xe → 107Te → 103Sn α-decay chain using the method of recoil-decay tagging. Inspection of γ γ -coincidence data has shown that five of the transitions form a rotational-like sequence. Excitation-energy systematics suggest that the sequence could be the favored signature partner of a band built on an h11/2 neutron. Aligned angular momenta of states in the band have been compared to analogous bands in neighboring xenon is…

Population of a low-spin positive-parity band from high-spin intruder states in Au: The two-state mixing effect

The extremely neutron-deficient isotopes $^{177,179}$Au were studied by means of in-beam γ-ray spectroscopy. Specific tagging techniques, α-decay tagging in $^{177}$Au and isomer tagging in $^{179}$Au, were used for these studies. Feeding of positive-parity, nearly spherical states, which are associated with 2d3/2 and 3s1/2 proton-hole configurations, from the 1i13/2 proton-intruder configuration was observed in $^{177}$Au. Such a decay path has no precedent in odd-Au isotopes and it is explained by the effect of mixing of wave functions of the initial state.

Transmission Efficiency of the SAGE Spectrometer Using GEANT4

The new SAGE spectrometer allows simultaneous electron and γ-ray in-beam studies of heavy nuclei. A comprehensive GEANT4 simulation suite has been created for the SAGE spectrometer. This includes both the silicon detectors for electron detection and the germanium detectors for γ-ray detection. The simulation can be used for a wide variety of tests with the aim of better understanding the behaviour of SAGE. A number of aspects of electron transmission are presented here.

Nanosecond-Scale Proton Emission from Strongly Oblate-Deformed ^{149}Lu.

Using the fusion-evaporation reaction ^{96}Ru(^{58}Ni,p4n)^{149}Lu and the MARA vacuum-mode recoil separator, a new proton-emitting isotope ^{149}Lu has been identified. The measured decay Q value of 1920(20) keV is the highest measured for a ground-state proton decay, and it naturally leads to the shortest directly measured half-life of 450_{-100}^{+170}  ns for a ground-state proton emitter. The decay rate is consistent with l_{p}=5 emission, suggesting a dominant πh_{11/2} component for the wave function of the proton-emitting state. Through nonadiabatic quasiparticle calculations it was concluded that ^{149}Lu is the most oblate deformed proton emitter observed to date.

Single-particle states and parity doublets in odd-Z 221Ac and 225Pa from α-decay spectroscopy

Low-lying states in the odd-Z isotopes 22189Ac132 and 22591Pa134 have been studied using α-particle and αγ-coincidence spectroscopy in the 225Pa→221Ac→217Fr decay chain. Ground-state spin and parity assignments of Iπ = 5/2− are proposed for both 221Ac and 225Pa, with the odd proton occupying the Ω = 5/2 orbital of the quadrupole-octupole deformed shell model in both nuclei. In 221Ac, excited states in the bands based on the Ω = 5/2 and Ω = 3/2 orbitals have been identified, including proposed parity-doublet states. The results suggest that reflection-asymmetric deformation of the ground state persists in the odd-A members of the isotope chains down to N = 132 for Ac and N = 134 for Pa, befo…

Experimental study of 1/2(+) isomers in At-199,At-201

Using fusion-evaporation reactions, a gas-filled recoil separator, and recoil-electron and recoil-electron-alpha tagging techniques, a new isomeric 1/2(+) state [T-1/2 = 45(3) ms] in At-201 is identified, and an earlier reported corresponding state [T-1/2 = 273(9) ms] in At-199 is confirmed. The 1/2(+) state is suggested to originate from an intruder pi(s(1/2))(-1) configuration. In addition, nuclear structure of states below and above this 1/2(+) state are studied in both nuclei. The isomer decays through a cascade of an E3 transition followed by a mixed M1/E2 transition to the 9/2(-) ground state, and it is interpreted to be fed from nearly spherical 3/2(+) and 5/2(+) states originating f…

The influence of quasineutron configurations on 161Ta and nearby odd-A Nuclei

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.

Chirality of $^{135}$Nd reexamined: Evidence for multiple chiral doublet bands

One new pair of positive-parity chiral doublet bands have been identified in the odd-$A$ nucleus $^{135}$Nd which together with the previously reported negative-parity chiral doublet bands constitute a third case of multiple chiral doublet (M$\chi$D) bands in the $A\approx130$ mass region. The properties of the M$\chi$D bands are well reproduced by constrained covariant density functional theory and particle rotor model calculations. The newly observed M$\chi$D bands in $^{135}$Nd represents an important milestone in supporting the existence of M$\chi$D in nuclei.