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7 pags., 5 figs., 2 tabs., The single-particle properties of Mg29 have been investigated via a measurement of the Mg28(d,p)Mg29 reaction, in inverse kinematics, using the ISOLDE Solenoidal Spectrometer. The negative-parity intruder states from the fp shell have been identified and used to benchmark modern shell-model calculations. The systematic data on the single-particle centroids along the N=17 isotones show good agreement with shell-model predictions in describing the observed trends from stability toward O25. However, there is also evidence that the effect of the finite geometry of the nuclear potential is playing a role on the behavior of the p orbitals near the particle-emission threshold., This work wassupported by the U.K. Science and Technology Facilities Council [Grants No. ST/P004598/1, No. ST/N002563/1, No. ST/M00161X/1 (Liverpool), No. ST/P004423/1 (Manchester), No. ST/P005314/1 (Surrey), the ISOL-SRS Grant (Daresbury), No. ST/R004056/1 (Ernest Rutherford Fellowship - Gaffney), and No. ST/T004797/1 (Ernest Rutherford Fellowship - Sharp)], the U.S. Department of Energy, Office of Science, Office of Nuclear Physics, under Contracts No. DE-AC02-06CH11357 (ANL) and No. DE-SC-0014552 (UConn), the European Union’s Horizon 2020 Framework research and innovation program under Grant Agreement No. 654002 (ENSAR2), the Marie Skłodowska-Curie Grant Agreement No. 665779, the Research Foundation Flanders (FWO, Belgium), the European Research Council under the European Union’s Seventh Framework Programme (FP7/2007-2013)/ERC Grant Agreement No. 617156, and the Spanish Ministry of Science and Innovation under Grants No. PGC2018-095640- B-I00“ELEGANT” and No. PID2019-104390GB-I00. This research used targets provided by the Center for Accelerator Target Science at Argonne National Laboratory. The FSU shell-model calculations were performed using the computational facility of the nuclear physics theory group, Florida State University, supported by grants from the U.S. Department of Energy, Office of Science (DE-SC-0009883 (FSU).

A systematic study of neutron-hole strength in the N = 81 nuclei 137Ba, 139Ce, 141Nd and 143Sm is reported. The single-neutron removal reactions (p,d) and (3He,) were measured at energies of 23 and 34 MeV, respectively. Spectroscopic factors were extracted from measured cross sectionsthrough a distorted-wave Born approximation analysis and centroids of single-particle strength have been established. The change in these centroid energies as a function of proton number have been compared to calculations of the monopole shift for the s1=2 and h11=2 orbitals, where the majorityof the strength has been observed. Signicant fragmentation of strength was observed for the d and g7=2 orbitals, particularly for the latter orbital which is deeply bound, with summed strengths that indicate a signicant amount lies outside of the measured excitation energy range.

The pairing properties of the neutrinoless double-$\beta$ decay candidate $^{116}$Cd have been investigated. Measurements of the two-neutron removal reactions on isotopes of $^{114,116}$Cd have been made in order to identify 0$^+$ strength in the residual nuclei up to $\approx$3 MeV. No significant $L=0$ strength has been found in excited states indicating that the Bardeen-Cooper-Schrieffer (BCS) approximation is a reasonable basis to describe the neutrons in the ground state. This approximation avoids complications in calculations of double-$\beta$ decay matrix elements that use the quasiparticle random-phase approximation (QRPA) techniques. However this is not the case for the protons, where pair vibrations are prevalent and the BCS approximation is no longer valid, complicating the use of traditional QRPA techniques for this system as a whole.

The neutron-deficient mercury isotopes serve as a classical example of shape coexistence, whereby at low energy near-degenerate nuclear states characterized by different shapes appear. The electromagnetic structure of even-mass 182-188 Hg isotopes was studied using safe-energy Coulomb excitation of neutron-deficient mercury beams delivered by the REX-ISOLDE facility at CERN. The population of $ 0^{+}_{1,2}$01,2+, $ 2^{+}_{1,2}$21,2+and $ 4^{+}_{1}$41+states was observed in all nuclei under study. Reduced E2 matrix elements coupling populated yrast and non-yrast states were extracted, including their relative signs. These are a sensitive probe of shape coexistence and may be used to validate nuclear models. The experimental results are discussed in terms of mixing of two different configurations and are compared with three different model calculations: the Beyond Mean Field model, the Interacting Boson Model with configuration mixing and the General Bohr Hamiltonian. Partial agreement with experiment was observed, hinting to missing ingredients in the theoretical descriptions. The neutron-deficient mercury isotopes serve as a classical example of shape coexistence, whereby at low energy near-degenerate nuclear states characterized by different shapes appear. The electromagnetic structure of even-mass 182-188 Hg isotopes was studied using safe-energy Coulomb excitation of neutron-deficient mercury beams delivered by the REX-ISOLDE facility at CERN. The population of $ 0^{+}_{1,2}$01,2+, $ 2^{+}_{1,2}$21,2+and $ 4^{+}_{1}$41+states was observed in all nuclei under study. Reduced E2 matrix elements coupling populated yrast and non-yrast states were extracted, including their relative signs. These are a sensitive probe of shape coexistence and may be used to validate nuclear models. The experimental results are discussed in terms of mixing of two different configurations and are compared with three different model calculations: the Beyond Mean Field model, the Interacting Boson Model with configuration mixing and the General Bohr Hamiltonian. Partial agreement with experiment was observed, hinting to missing ingredients in the theoretical descriptions. ispartof: The European Physical Journal A - Hadrons and Nuclei vol:55 issue:8 pages:130-130 status: published

The energy levels and γ-ray decay scheme of the positive-parity states in the Tz=12 nucleus As67 have been studied by using the Ca40(Ar36,2αp)As67 reaction at a beam energy of 145 MeV. Two new band structures have been identified which can be connected to the previously known levels. The results for these bands are compared with configuration-dependent cranked Nilsson-Strutinsky calculations. The good level of agreement between theory and experiment suggests that these structures can be interpreted in terms of configurations that involve three g92 particles and that both possess noncollective terminating states.

The rearrangements of protons and neutrons amongst the valence single-particle orbitals during double-$\ensuremath{\beta}$ decay of $^{100}\mathrm{Mo}$ have been determined by measuring cross sections in ($d,p$), ($p,d$), ($^{3}\mathrm{He},\ensuremath{\alpha}$), and ($^{3}\mathrm{He},d$) reactions on $^{98,100}\mathrm{Mo}$ and $^{100,102}\mathrm{Ru}$ targets. The deduced nucleon occupancies reveal significant discrepancies when compared with theoretical calculations; the same calculations have previously been used to determine the nuclear matrix element associated with the decay probability of double-$\ensuremath{\beta}$ decay of the $^{100}\mathrm{Mo}$ system.

Author(s): Vogt, A; Siciliano, M; Birkenbach, B; Reiter, P; Hadynska-Klȩk, K; Wheldon, C; Valiente-Dobon, JJ; Teruya, E; Yoshinaga, N; Arnswald, K; Bazzacco, D; Blazhev, A; Bracco, A; Bruyneel, B; Chakrawarthy, RS; Chapman, R; Cline, D; Corradi, L; Crespi, FCL; Cromaz, M; De Angelis, G; Eberth, J; Fallon, P; Farnea, E; Fioretto, E; Fransen, C; Freeman, SJ; Fu, B; Gadea, A; Gelletly, W; Giaz, A; Gorgen, A; Gottardo, A; Hayes, AB; Hess, H; Hetzenegger, R; Hirsch, R; Hua, H; John, PR; Jolie, J; Jungclaus, A; Karayonchev, V; Kaya, L; Korten, W; Lee, IY; Leoni, S; Liang, X; Lunardi, S; MacChiavelli, AO; Menegazzo, R; Mengoni, D; Michelagnoli, C; Mijatovic, T; Montagnoli, G; Montanari, D; Muller-Gatermann, C; Napoli, D; Pearson, CJ; Podolyak, Z; Pollarolo, G; Pullia, A; Queiser, M; Recchia, F; Regan, PH; Regis, JM; Saed-Samii, N; Sahin, E; Scarlassara, F; Seidlitz, M; Siebeck, B; Sletten, G; Smith, JF; Soderstrom, PA; Stefanini, AM; Stezowski, O; Szilner, S; Szpak, B; Teng, R; Ur, C; Warner, DD; Wolf, K; Wu, CY; Zell, KO | Abstract: The transitional nuclei Xe132 and Xe133 are investigated after multinucleon-transfer (MNT) and fusion-evaporation reactions. Both nuclei are populated (i) in Xe136+Pb208 MNT reactions employing the high-resolution Advanced GAmma Tracking Array (AGATA) coupled to the magnetic spectrometer PRISMA, (ii) in the Xe136+Pt198 MNT reaction employing the GAMMASPHERE spectrometer in combination with the gas-detector array CHICO, and (iii) as an evaporation residue after a Te130(α,xn)Xe134-xn fusion-evaporation reaction employing the HORUS γ-ray array at the University of Cologne. The high-spin level schemes are considerably extended above the Jπ=(7-) and (10+) isomers in Xe132 and above the 11/2- isomer in Xe133. The results are compared to the high-spin systematics of the Z=54 as well as the N=78 and N=79 chains. Furthermore, evidence is found for a long-lived (T1/2â‰1μs) isomer in Xe133 which closes a gap along the N=79 isotones. Shell-model calculations employing the SN100PN and PQM130 effective interactions reproduce the experimental findings and provide guidance to the interpretation of the observed high-spin features.

The high-spin structures of the N = 81 isotones 135Xe and 137Ba are investigated after multinucleontransfer (MNT) and fusion-evaporation reactions. Both nuclei are populated in (i) 136Xe+238U and (ii) 136Xe+208Pb MNT reactions employing the high-resolution Advanced Gamma Tracking Array (AGATA) coupled to the magnetic spectrometer PRISMA, (iii), in the 136Xe+198Pt MNT reaction employing the -ray array GAMMASPHERE in combination with the gas detector array Chico, and (iv) via a 11B+130Te fusion-evaporation reaction. The high-spin level schemes of 135Xe and 137Ba are considerably extended to higher energies. The 2058-keV (19=2 ) state in 135Xe is identified as an isomer, completing the systematics for the N = 81 isotones. Its half-life is measured to be 8.6(10) ns, corresponding to a transition probability of B(E2; 19=2 ! 15=2 ) = 0:539(69) W.u. Latest shell model calculations considering 132Sn as a closed core reproduce the experimental findings and provide guidance to the interpretation of the new levels. The experimentally deduced reduced quadrupole transition probabilities of the isomeric states are compared to shell-model predictions.

Multi-quasiparticle high-K states, several of which are isomeric, were observed in Hf-180 with the Gammasphere array. We determined the lifetimes in the ns-μs range using centroid-shift and decay measurements within a mu s coincidence time window. The configurations of high-K states involve two and four quasiparticles, with states up to Kπ = (18-) established. High-K excitations are found to be progressively more favored with increasing excitation energy. The K quantum number is quite robust up to the highest spins observed, as evidenced by the large values of the reduced hindrance for isomeric decays. Furthermore, rotational bands built on three high-K states are identified, and the measured branching ratios in these sequences enable the assignment of underlying configurations. Multi-quasiparticle calculations using the Lipkin-Nogami approach for pairing, with blocking included, reproduce the observed high-K energies quite well.

Background: Neutron-rich, even-mass chromium and iron isotopes approaching neutron number $N=40$ have been important benchmarks in the development of shell-model effective interactions incorporating the effects of shell evolution in the exotic regime. Odd-mass manganese nuclei have received less attention, but provide important and complementary sensitivity to these interactions.Purpose: We report the observation of two new $\ensuremath{\gamma}$-ray transitions in $^{63}\mathrm{Mn}$, which establish the $(9/{2}^{\ensuremath{-}})$ and $(11/{2}^{\ensuremath{-}})$ levels on top of the previously known $(7/{2}^{\ensuremath{-}})$ first-excited state. The lifetime for the $(7/{2}^{\ensuremath{-}})$ and $(9/{2}^{\ensuremath{-}})$ excited states were determined for the first time, while an upper limit could be established for the $(11/{2}^{\ensuremath{-}})$ level.Method: Excited states in $^{63}\mathrm{Mn}$ have been populated in inelastic scattering from a $^{9}\mathrm{Be}$ target and in the fragmentation of $^{65}\mathrm{Fe}$. $\ensuremath{\gamma}\ensuremath{\gamma}$ coincidence relationships were used to establish the decay level scheme. A Doppler line-shape analysis for the Doppler-broadened $(7/{2}^{\ensuremath{-}})\ensuremath{\rightarrow}5/{2}^{\ensuremath{-}}$, $(9/{2}^{\ensuremath{-}})\ensuremath{\rightarrow}(7/{2}^{\ensuremath{-}}),$ and $(11/{2}^{\ensuremath{-}})\ensuremath{\rightarrow}(9/{2}^{\ensuremath{-}})$ transitions was used to determine (limits for) the corresponding excited-state lifetimes.Results: The low-lying level scheme and the excited-state lifetimes were compared with large-scale shell-model calculations using different model spaces and effective interactions in order to isolate important aspects of shell evolution in this region of structural change.Conclusions: While the theoretical $(7/{2}^{\ensuremath{-}})$ and $(9/{2}^{\ensuremath{-}})$ excitation energies show little dependence on the model space, the calculated lifetime of the $(7/{2}^{\ensuremath{-}})$ level and calculated energy of the $(11/{2}^{\ensuremath{-}})$ level reveal the importance of including the neutron ${g}_{9/2}$ and ${d}_{5/2}$ orbitals in the model space. The LNPS effective shell-model interaction provides the best overall agreement with the new data.

Yrast and near-yrast states in 30 Al and 30 Si have been populated to high spin with the O 18 + C 14 fusion–evaporation reaction in inverse kinematics. The level schemes for these two isobars have been extended up to J ∼ 9 ℏ at 9.4 and 15.5 MeV, respectively. Their decay schemes indicate that cross-shell excitations dominate at high spin, where negative-parity structures exist. Positive-parity states are compared to the results of shell-model calculations using the USD, USDA, and USDB effective interactions. The negative-parity levels are compared to predictions of the WBP interaction and the recently-developed WBP-a Hamiltonian, by allowing 1p–1h excitations to fp -shell orbitals. The results suggest that single-neutron excitations to the 0 f 7 / 2 orbital play a significant role at high spin.

Background: Shape coexistence in heavy nuclei poses a strong challenge to state-of-the-art nuclear models, where several competing shape minima are found close to the ground state. A classic region for investigating this phenomenon is in the region around Z=82 and the neutron midshell at N=104. Purpose: Evidence for shape coexistence has been inferred from α-decay measurements, laser spectroscopy, and in-beam measurements. While the latter allow the pattern of excited states and rotational band structures to be mapped out, a detailed understanding of shape coexistence can only come from measurements of electromagnetic matrix elements. Method: Secondary, radioactive ion beams of Rn202 and Rn204 were studied by means of low-energy Coulomb excitation at the REX-ISOLDE in CERN. Results: The electric-quadrupole (E2) matrix element connecting the ground state and first excited 21+ state was extracted for both Rn202 and Rn204, corresponding to B(E2;21+→01+)=29-8+8 and 43-12+17 W.u. respectively. Additionally, E2 matrix elements connecting the 21+ state with the 41+ and 22+ states were determined in Rn202. No excited 0+ states were observed in the current data set, possibly owing to a limited population of second-order processes at the currently available beam energies. Conclusions: The results are discussed in terms of collectivity and the deformation of both nuclei studied is deduced to be weak, as expected from the low-lying level-energy schemes. Comparisons are also made to state-of-the-art beyond-mean-field model calculations and the magnitude of the transitional quadrupole moments are well reproduced., 0, SCOPUS: ar.j, info:eu-repo/semantics/published

Excited states up to I π = 8 + in the neutron-rich nucleus 58Cr have been identified by using a new experimental setup composed of the large acceptance magnetic spectrometer PRISMA and the highly efficient γ-detector array CLARA. Interestingly, the excitation energy sequence of the ground-state band follows the one expected by the E ( 5 ) dynamical symmetry for a nucleus at the critical point of the shape phase transition from a spherical vibrator ( U ( 5 ) ) to a γ-soft rotor ( O ( 6 ) ). For the first time, in the same physical system, large scale shell-model calculations in the full fp shell are compared to the E ( 5 ) analytical model results and to the Interacting Boson Model. The theoretical results are in excellent agreement with the present data.

Excited states have been identified in the very neutron-deficient 122Ce nucleus. This is the first observation of this nucleus and its excited states. The ground-state rotational band has been observed up to spin 14 ℏ. The band has been assigned to 122Ce by detecting gamma rays in coincidence with evaporated charged particles and neutrons. The E ( 2 1 + ) value suggests a rather large ground-state deformation of β 2 = 0.35 , in good agreement with Hartree–Fock–Bogoliubov (HFB) mean-field calculations. The aligned angular momentum of the band has been studied and is compared with those of the neighboring even–even cerium isotopes, and to Woods–Saxon cranking calculations. The non-observation of the π ( h 11 / 2 ) 2 alignment until at least 0.4 MeV/ℏ is consistent with the extracted value of β 2 .

The low-lying levels in 59,60Cr have been populated with 13,14C(48Ca, 2p) reactions using a beam energy of 130 MeV. Prompt electromagnetic radiation was detected using the Gammasphere array, in coincidence with recoiling ions measured with the Fragment Mass Analyzer. The residues were selected and identified on the basis of charge-to-mass ratio, energy-loss and time-of-flight measurements. Preliminary results for 60Cr, when compared to lighter even-even isotopes, indicate a softness in shape which increases with neutron number. The low-lying structure of 59Cr is clearly inconsistent with the results of a spherical shell-model calculation and requires the inclusion of the νg9/2 orbital. The sequence of states can be understood within the Nilsson model assuming a moderate oblate ground-state deformation. This is in contrast to lighter odd-Cr nuclei where there is evidence for prolate deformation after excitation of g9/2 neutrons.

Excited states in 57 Cr have been populated to high spin in the C 14 ( Ca 48 , α n ) reaction at a beam energy of 130 MeV. A regular sequence of stretched quadrupole transitions has been established above the yrast 9 / 2 + level. This sequence is interpreted as a rotational band associated with prolate deformation induced by the excitation of the odd neutron into the 1 / 2 + [ 440 ] orbital. Total Routhian surface calculations, which follow this configuration to high spin, reproduce the observed features of the band. They are also able to account for a similar, but less well developed structure in 55 Cr. In contrast, the isomeric yrast 9 / 2 + state in 59 Cr appears to be a band-head state dominated by the 9 / 2 + [ 404 ] configuration, which is favoured at oblate deformations. Such a marked difference presents a significant challenge for theoretical descriptions, but is consistent with features exhibited by the low-lying negative-parity states in 59 Cr.

A study of high spin states in the odd-neutron isotones 239 Pu and 237 U is reported. Striking differences were found in the high-spin properties of rotational bands built on the 1 /2 + [631] ground states in these two nuclei. These differences mirror those observed in the even–even Pu and U immediate neighbors and appear to be related to the strength of octupole correlations.

A seven-quasiparticle isomer with $K^{\pi} = (49 /2^ + )$ and T 1/2 = 53 ( + 3 -7) ns has been identified in 179Ta. By comparing its excitation energy with results from multi-quasiparticle calculations that include the effects of blocking and residual nucleon-nucleon interactions, the isomer is assigned the $\pi^{3}$ (5/2 + [402], 7/2 + [404], $9/2^{-}[514]) \otimes \nu^{4}$ (5/2-[512], 7/2-[514], 7/2-[503], 9/2 + [624]) configuration. The decay of this isomer is found to be unusually fast, a feature that is attributed to a mixing with a specific collective level. The interaction strength is found to be orders of magnitude lower than that observed between interacting collective levels.

A multi-nucleon transfer reaction using an 850 MeV 136Xe beam incident on a 198Pt target was used to populate high-spin states in 184W, 14 nucleons from the target. A 4-quasiparticle isomer with \(t_{1/2} = 188 \pm 38\) ns has been observed for the first time and its de-excitation through collective and intrinsic structures studied. The results are compared with predictions of blocked BCS Nilsson calculations. Observation of this metastable state completes the tungsten 4-quasiparticle isomer systematics from A = 176 to 186. Mapping out the most yrast 4-quasiparticle isomers in these even-even tungsten isotopes suggests the existence of a highly favoured state in 188W, within reach of current experimental set-ups.

The fusion–evaporation reaction 10 B( 12 C, 2 n ) was used to make the first observation of in-beam γ decays from the astrophysically important nucleus 20 Na, lying adjacent to the proton drip-line. All states below the proton threshold in 20 Na were populated and identified in the experiment. These include new levels, previously unresolved levels, and states located with improved energy precision. The level structure of 20 Na, and its γ transitions, are compared to the mirror partner 20 F measured simultaneously in this experiment. In particular, a high degree of energy stability is found for all negative parity states. These results are discussed in the context of the nuclear shell model.

This paper reports on recent work using multi-nucleon transfer reactions to populate metastable states in neutron-rich, rare-earth and transitional nuclei with A∼180-200. The use of a position sensitive gas-filled detector, CHICO, allowed the directions of the binary fragments to be measured, thereby enabling event-by-event Doppler corrections to be made for the prompt, in-beam transitions depopulating the nuclei of interest. By using the temporal calibration provided by (i) the measurement of the binary reaction fragments and (ii) the natural pulsing of the cyclotron beam, transitions from metastable states with lifetimes in the nano-to-microsecond regime could be identified. The complementarity of this technique with the novel use of relativistic projectile fragmentation reactions is outlined, together with potential future avenues for this research, with a particular emphasis on the population of exotic isomeric states at high angular momentum and excitation energy values.

Long-lived high- K states have been identified in 177 Lu, including an isomer with τ >10 μs, placed at 3530 keV and associated with the yrast K π =39/2 − , 5-quasiparticle state predicted in multi-quasiparticle-state calculations. The γ -decay of the isomer exposes the rotational band based on the 160-day 23/2 − isomer, 177m Lu , with band properties which support its proposed configuration. A 90-ns isomer at 1325 keV is associated with the predicted 3-quasiparticle K π =25/2 + state while a 5-quasiparticle 33/2 + , 902-ns isomer with highly-hindered decays is identified at 2771 keV. Both exhibit rotational bands whose properties are used to support the assigned configurations. The possibility that the K π =39/2 − isomer found in this work should be identified with a β -decaying isomer, proposed recently to populate the 51-min 37/2 − isomer in 177 Hf, is discussed in terms of the implied log ft values, configuration changes, and hindrances for K -forbidden γ -decays.

Lifetime measurements have been performed for yrast rotational states of 100Zr and 104Mo using a 252Cf source in a differential plunger arrangement, together with the EUROBALL and SAPHIR multi-detector arrays. The system has been proved capable of covering a range of lifetimes from a nanosecond to a picosecond. The transition quadrupole moments are found to decrease by around 20% between I = 4 and I = 8 in the case of 104Mo while remaining constant in 100Zr. The origin of this effect lies either in a rotation-induced shape change, or in the strong mixing between the ground and s-bands in 104Mo.

High-spin states in the neutron-deficient isotope Cd-104 were populated using the Cr-50(Ni-58,4p)Cd-104 reaction at a beam energy of 250 MeV The level scheme has been extended using triple gamma-ray coincidences to a spin of 29h and an excitation energy of 18.2 MeV. Several collective structures involving the excitation of h(11/2) neutrons have been observed to spins approaching 30h. The high-spin structure has been compared to the results of cranked Nilsson-Strutinsky calculations.

Coulomb-excitation experiments to study electromagnetic properties of radioactive even-even Hg isotopes were performed with 2.85 MeV/nucleon mercury beams from REX-ISOLDE. Magnitudes and relative signs of the reduced E2 matrix elements that couple the ground state and low-lying excited states in Hg182-188 were extracted. Information on the deformation of the ground and the first excited 0(+) states was deduced using the quadrupole sum rules approach. Results show that the ground state is slightly deformed and of oblate nature, while a larger deformation for the excited 0(+) state was noted in Hg-182; 184. The results are compared to beyond mean field and interacting-boson based models and interpreted within a two-state mixing model. Partial agreement with the model calculations was obtained. The presence of two different structures in the light even-mass mercury isotopes that coexist at low excitation energy is firmly established.

Excited states have been identified in the very neutron-deficient 112 Xe nucleus. The ground-state band has been observed up to spin 12 ℏ, and a negative-parity side band has been observed up to 13 ℏ. The bands have been assigned to 112 Xe by detecting gamma rays in coincidence with evaporated charged particles and neutrons. The energy of the 2 + 1 state in 112 Xe is lower than would be expected from both calculations and from systematics of the neighboring xenon isotopes, which indicates a larger than expected ground-state deformation. The observations of a low-lying 3 − state and large deduced B (E1) values are suggestive of increased octupole correlations, which may explain the apparently large ground-state deformation. Constrained Hartree–Fock+BCS calculations have been performed which show qualitative agreement with the trend in deformation of the very neutron-deficient xenon isotopes.

For many nuclei beyond the proton drip line in the Z > 72, N > 82 region, both proton and α emission are energetically allowed. In the case of some proton emitters, there are α-decay chains emanating from both parent and daughter nuclei. This means that if the mass excess of one member of an α-decay chain is known, then the mass excesses for all members of both chains can be obtained. In addition, proton separation energies may be derived for nuclei in the α-decay chain of the proton emitter. The method of time- and space-correlations also allows the identification of isomeric states in these nuclei. As an example, a large number of mass excesses and proton separation energies for ground and metastable states have been derived from Q α and Q p values obtained from the proton emitters 165,166,167Ir, 171Au, 177Tl and their daughters.

Measurements of g-factors of excited states in barium and cerium fission fragments have been performed using time-integral perturbed angular correlations between secondary-fragment gamma rays. Larmor precession angles have been obtained for the first I-pi = 2(+) states in Ba-144,Ba-146 and Ce-146,Ce-148 as well as for the 9/2(-) state at 117 keV in Ba-143, the 7/2(-) state at 114 keV in Ba-145 and the first 4(+) state in Ce-150. The deduced g-factor fur the 2(+) state in Ba-146 provides substantiating evidence for a downward trend in 2(+) g-factors with increasing neutron number, in line with Interacting Boson Model predictions for the neutron-rich barium isotopes, assuming the quenching of the Z = 64 shell gap for N>88. The static hyperfine fields for implanted barium and cerium isotopes are found to be opposite in sign. These results constitute the first use of secondary-fragment gamma-ray emission in the determination of g-factors of excited states in fission fragments. (C) 1999 Elsevier Science B.V. All rights reserved.

The low-lying level structure of the neutron-deficient isotope ${}^{198}\mathrm{Rn}$ has been studied for the first time, using the ${}^{166}\mathrm{Er}{(}^{36}\mathrm{Ar},4n)$ reaction at a beam energy of 175 MeV. Evaporation residues were selected using an in-flight gas-filled separator, RITU, and implanted at the focal plane into a 16-element position-sensitive, passivated ion-implanted planar silicon detector. Prompt $\ensuremath{\gamma}$ rays in ${}^{198}\mathrm{Rn}$ were observed at the target position using the JUROSPHERE array of 24 Compton-suppressed germanium detectors, and were identified by the subsequent radioactive decay of associated recoiling ions in the silicon detector. Isotopic assignments of the nuclei produced were made on the basis of the energy and half-life of their $\ensuremath{\alpha}$ decay. The estimated production cross section for ${}^{198}\mathrm{Rn}$ in this reaction was 180 nb. The excitation energy of the ${2}_{1}^{+}$ state indicates inconsistency with theoretical predictions of large stable ground-state deformation in this isotope. The systematics of other low-lying excited states suggests the presence of deformed intruder states falling in energy with increasing neutron deficiency.

Rotational bands in the odd-proton nucleus 171 Lu have been populated with the 160 Gd( 19 F, α4n) reaction. High-spin states were observed to a maximum spin of 73 2 − using the NORD-BALL array. Several new three-quasiparticle bands were observed, including one based on the π 1 2 − [541]⊗ν 7 2 + [633]⊗ν 1 2 − [521] configuration. The signature splitting of this band is inverted from the expected splitting, and this is interpreted as being due to a residual proton-neutron interaction. The contribution of this interaction to the increased crossing frequency observed for the alignment of i 13 2 neutrons in the π 1 2 − [541] band is considered. Strong E1 transitions from high-spin levels in the π 1 2 + [411] band to the π 1 2 − [541] band are observed.

Six rotational bands in the odd-odd nucleus 174Ta have been populated with the 160Gd(19F,5n) reaction. High-spin states were identified using the NORDBALL array. Both signatures of the doubly decoupled π 1 2 − [541] ⊗ ν 1 2 − [521] band and semi-decoupled π 1 2 − [541] ⊗ ν 7 2 − [633] band are observed, in addition to the high-K couplings of the π 9 2 − [514] ⊗ ν 7 2 + [633] , π 9 2 − [514] ⊗ ν 5 2 − [512] , π 7 2 + [404] ⊗ ν 7 2 + [633] , and π 5 2 + [402] ⊗ ν 5 2 − [512] configurations. The signature splitting of the π 1 2 − [541] ⊗ ν 7 2 + [633] band is inverted from the expected splitting, and this is interpreted as being due to a residual proton-neutron interaction. It is shown empirically that this interaction, together with deformation changes, can account for the increased crossing frequency associated with the alignment of i 13 2 neutrons in the π 1 2 − [541] bands of odd-Z nuclei.

High-spin states in the N=Z nucleus 72Kr have been populated in the 40Ca(40Ca, 2α)72Kr fusion–evaporation reaction at a beam energy of 165 MeV and using a thin isotopically enriched 40Ca target. The experiment, performed at Argonne National Laboratory close to Chicago, USA, employed the Gammasphere array for γ-ray detection coupled to the Microball array for charged particle detection. The previously observed bands in 72Kr were extended to a higher excitation energy of ~24 MeV and higher angular momentum of 30. Using the Doppler-shift attenuation method, the lifetimes of high-spin states were measured for the first time in order to investigate deformation changes associated with the g9/2 proton and neutron alignments in this N=Z nucleus. An excellent agreement with theoretical calculations including only standard t=1 np pairing was observed.

Theπh9/2[541 1/2−] band in 167Tm has been studied through the 124Sn(48Ca, p4n)167Tm reaction at E beam = 210 MeV. The favoured signature of the πh9/2[541 1/2−] band is observed to spin 61/2h. A remarkable small gain in aligned angular momentum at the AB-band crossing has been found. The crossing frequency and the gain in aligned angular momentum for 167Tm are compared with data for the N = 98 isotones of Lu, Ta and Re, and contrasted with Cranked Shell Model predictions, based on frequency diabatic configurations. Large deviations are found for the gain in aligned angular momentum.

The new proton radioactivities ${}^{165,166,167}\mathrm{Ir}$ and ${}^{171}\mathrm{Au}$ have been observed. The Ir isotopes were produced via the ${}^{92}\mathrm{Mo}{(}^{78}\mathrm{Kr}{,pxn)}^{165,166,167}\mathrm{Ir}$ reactions at 357 and 384 MeV. ${}^{171}\mathrm{Au}$ was produced via the ${}^{96}\mathrm{Ru}{(}^{78}\mathrm{Kr}{,p2n)}^{171}\mathrm{Au}$ reaction at 389 MeV. The proton emitters were each identified by position, time, and energy correlations between the implantation of a residual nucleus into a double-sided silicon strip detector, the observation of a decay proton, and the subsequent observation of a decay alpha particle from the daughter nucleus (${}^{164,165,166}$Os and ${}^{170}\mathrm{Pt},$ respectively). Both ${}^{166}\mathrm{Ir}$ and ${}^{167}\mathrm{Ir}$ have proton-emitting ground and isomeric states, which also decay by alpha emission. The proton-decay rates have been reproduced by calculations using the WKB barrier penetration approximation and a low-seniority shell-model calculation of the spectroscopic factors. The alpha decays of the four nuclei are followed by chains of alpha decays, allowing the determination of single-particle orbital orderings. Mass information has also been obtained from the alpha-decay chains because a connection to a known mass can be obtained for one of the nuclei. Ground-state mass excesses are reported for ${}^{151}\mathrm{Tm},$ ${}^{154}\mathrm{Yb},$ ${}^{155}\mathrm{Lu},$ ${}^{158}\mathrm{Hf},$ ${}^{159}\mathrm{Ta},$ ${}^{162}\mathrm{W},$ ${}^{163}\mathrm{Re},$ ${}^{166}\mathrm{Os},$ ${}^{167}\mathrm{Ir},$ and ${}^{170}\mathrm{Pt}.$ The mass excess for ${}^{171m}\mathrm{Au}$ is also given. Proton separation energies are also deduced for the odd-$Z$ alpha daughter nuclei of the Ir proton emitters.

Cross sections for proton knockout observed in ($e$,${e}^{\ensuremath{'}}p$) reactions are apparently quenched by a factor of $\ensuremath{\sim}0.5$, an effect attributed to short-range correlations between nucleons. Here we demonstrate that such quenching is not restricted to proton knockout, but a more general phenomenon associated with any nucleon transfer. Measurements of absolute cross sections on a number of targets between $^{16}\mathrm{O}$ and $^{208}\mathrm{Pb}$ were analyzed in a consistent way, with the cross sections reduced to spectroscopic factors through the distorted-wave Born approximation with global optical potentials. Across the 124 cases analyzed here, induced by various proton- and neutron-transfer reactions and with angular momentum transfer $\ensuremath{\ell}=0--7$, the results are consistent with a quenching factor of 0.55. This is an apparently uniform quenching of single-particle motion in the nuclear medium. The effect is seen not only in ($d$,$p$) reactions but also in reactions with $A=3$ and 4 projectiles, when realistic wave functions are used for the projectiles.

Measurements of neutron-adding, neutron-removing, and proton-adding reactions were carried out for the four stable even Ni isotopes. Particular attention was paid to obtaining precise values of the cross sections at the peaks of the angular distributions. Tests with sum rules for the neutron data indicate that the results are self-consistent at the level of a few tenths of a nucleon. Data on proton-adding reactions were also obtained and analyzed with a slightly different method—while these data are also consistent, the ambiguities are larger. The occupancies of the neutron orbits derived from the data, the proton vacancies, and the energy centroids of the neutron, neutron-hole, and proton single-particle excitations are obtained. The data also provide some estimate about the closure of the 0 f 7 / 2 shell. The results are compared to shell-model calculations and may serve as a reference point for future exploration. ispartof: Physical Review C, Nuclear Physics vol:87 issue:3 pages:1-15 status: published

The single-neutron properties of N = 51 nuclei have been studied with the ( d , p )and( α , 3 He) reactions, at beam energies of 15 and 50 MeV respectively, on 88 Sr, 90 Zr, and 92 Mo targets. The light reaction products were momentum analyzed using a conventional magnetic spectrometer. Additionally, the 2 H( 86 Kr ,p ) reaction was measured at a beam energy of 10 MeV / u, where outgoing light ions were analyzed using a helical-orbit spectrometer. Absolute cross sections and angular distributions corresponding to the population of different final states in the heavy product were obtained for each reaction. Spectroscopic factors were extracted and centroids of the single-particle strength were deduced. The observations appear consistent with calculations based on an evolution of single-particle structure driven by the nucleon-nucleon forces acting between valence protons and neutrons. ispartof: Physical Review C, Nuclear Physics vol:87 issue:1 status: published

The low-lying level structure of the neutron-deficient isotope $^{200}\mathrm{Rn}$ has been studied using the $^{176}\mathrm{Hf}$${(}^{28}$Si,4n) reaction at a beam energy of 142 MeV. Evaporation residues were selected using an in-flight recoil mass separator, the Argonne Fragment Mass Analyzer, and implanted in a double-sided silicon strip detector. Prompt \ensuremath{\gamma} rays in $^{200}\mathrm{Rn}$ were observed at the target position using the AYEBALL array of 19 Compton-suppressed germanium detectors, and were identified by the subsequent radioactive decay of associated recoiling ions in the strip detector. Isotopic assignments of the nuclei produced were made on the basis of the mass-to-charge ratio of the recoiling ion and the energy and half-life of its \ensuremath{\alpha} decay. Previous results concerning transitions in $^{202}\mathrm{Rn}$ were confirmed. The level scheme deduced for $^{200}\mathrm{Rn}$, compared with those of heavier radon isotopes, is not consistent with the onset of deformation predicted by theoretical calculations. The estimated production cross section for $^{200}\mathrm{Rn}$ in this reaction was 5 \ensuremath{\mu}b. \textcopyright{} 1996 The American Physical Society.

rays depopulating high-spin states in have been detected using the EUROGAM phase-1 array. A crossing which is possibly observed at a rotational frequency of MeV in a quasi-neutron band is interpreted as being due to the alignment of a pair of neutrons.

K-isomers are states in deformed nuclei whose {gamma}-decay is hindered by selection rules involving K, the projection of the angular momentum along the axis of symmetry of the nucleus. Previous work with the Argonne Notre Dame BGO Array delineated the existence of two K-isomers in {sup 176}W, one of which had a very unusual pattern of decay. A short description of this work was published as a letter, and a more complete account is being readied for submission. These results provided evidence that quantum-mechanical fluctuations in the nuclear shape may be responsible for some of the observed K-violating transitions. In addition, hints were present in the data of the existence of another K-isomer with an even higher in. An experiment was performed in September 1994 to observe this isomer, using the reaction {sup 50}Ti({sup 130}Te,4n), and a technique in which recoiling {sup 176}W nuclei were created 17-cm upstream of the center of the array and caught on a Pb catcher foil at the center. Intense ({approximately} 3 pnA) beams of {sup 130}Te were supplied by the ECR source using a new sputtering technique. The recoil-shadow geometry was highly successful at removing the background from non-isomeric decays, allowing the weakly populatedmore » K-isomers to be detected cleanly. In addition, the availability of pulsed beams from ATLAS and the timing data from the BGO array provided a second technique for isolating the decays of interest, by selecting events in which a given number of BGO detectors fired between beam pulses. This method was used in the previous experiment, and was also applied in this experiment as a second level of selection. As a result, gamma-ray transitions were detected in the present experiment with intensities as small as {approximately} 0.02 % of the {sup 176}W reaction channel. The existence of the new isomer was confirmed, and a partial level-scheme was constructed.« less

High-spin properties of rotational bands are studied in 173Ta using the 160Gd(19F,6n) reaction at bombarding energies of 103–105 MeV. With the existing bands being extended, and new bands established, a total of 16 rotational sequences are interpreted in terms of their (multi) quasiparticle structure. Measurements of electromagnetic properties for these bands include E2 M1 mixing ratios, branching ratios and lifetimes of isomeric states close to band heads, for which all energies have now been determined. Particular emphasis is devoted to (i) the band structures related to the 1 2 − [541] intruder configuration, for which both favoured, and unfavoured partners as well as the extended g- and S-bands in the (delayed) crossing region have been established, (ii) the reduced E1 transition strength between the (new) 1 2 + [411] and 1 2 − [541] bands, which is strongly enhanced, most likely due to coupling to octupole degrees of freedom, and show a ΔI = 4 staggering, (iii) the observation of weak interband transitions between the two partners of a pseudo-spin doublet composed of the 5 2 + [402] and 7 2 + [404] bands together with accurately measured intraband mixing ratios enable an analysis of the mixing of these bands through comparisons to particle-rotor calculations, (iv) the observed three-quasiparticle bands which are assigned to specific configurations coupling the lowest protons to lowest two-quasineutrons with negative parity.

The lifetimes of the high-spin states of 157 Ho have been measured using the Doppler shift attenuation method (DSAM). The comparison of the observed shifts following the 124 Sn( 37 Cl, 4n) reaction at a beam energy of 150 MeV, and the 142 Ce( 19 F, 4n) reaction at 85.5 MeV shows that the yrast states above spin 71 2 − are much less collective than the states below. Transition quadrupole moments were obtained for states from spin 45 2 − to 55 2 − h in the yrast band, and from 37 2 − to 53 2 − h in the third lowest negative-parity band. The difference in collectivity agrees with the assignment of these bands to a [523] 7 2 − ( h 11 2 ) and a [541] 1 2 − ( h 9 2 ) quasiproton excitation, respectively. However, it cannot explain the difference in the i 13 2 neutron crossing frequencies of the two bands. The measured Q t values for the [523] 7 2 − configuration are compared to those of other N = 90 isotones.

Long cascades of stretched E2 transitions have been observed in $^{143}\mathrm{Eu}$ and $^{144}\mathrm{Eu}$ nuclei which at low excitation exhibit spherical shape. Lifetime experiments demonstrate high collectivity values up to B(E2)\ensuremath{\approxeq}100 W.u. among these E2 cascades. The total Routhian surface calculations indicate many crossing rotational bands of the nucleus with triaxial shape at ${\mathrm{\ensuremath{\beta}}}_{2}$\ensuremath{\approxeq}0.25 and \ensuremath{\gamma}\ensuremath{\approxeq}30\ifmmode^\circ\else\textdegree\fi{}. The E2 cascades in $^{143}\mathrm{Eu}$ are proposed to represent the \ensuremath{\nu}${\mathit{h}}_{11/2}^{2}$\ensuremath{\pi}${\mathit{h}}_{11/2}^{\mathit{n}}$ configurations with an additional \ensuremath{\nu}${\mathit{d}}_{3/2}^{\mathrm{\ensuremath{-}}1}$${\mathit{i}}_{13/2}$ excitation at the highest states.

The decay of the yrast and near-yrast high-spin states in 161Tm has been observed following the reaction 128Te(37Cl,4n). Extension of the known level scheme reveals previously unobserved crossings in the bands built on the 7 2 − [523] , 7 2 + [404] and 1 2 − [541] Nilsson states. The use of both gold- and terbium-backed targets has enabled the measurement by the Doppler shift attenuation method of lifetimes of states in the h 11 2 yrast band in the spin range 41 2 ⩽ I ⩽ 67 2 . The results show little evidence for change in the nuclear deformation over this interval in spin (Qt ≈ 6 eb). From lifetime measurements and B( M1 ) B( E2 ) values in the h 11 2 band, absolute B(M1) values for five transitions (for states with 41 2 ⩽ I ⩽ 51 2 ) were determined. These results provide some evidence for a reduction in the proton spin projection on the deformation axis relative to its value at low rotational frequency. The signature splitting in the Routhians and B( M1 ) B( E2 ) values for the h 11 2 band is discussed in terms of the inclusion of non-axially-symmetric (γ-deformed) components in the nuclear wavefunction.

Isotopes in the light actinide region with [ital N][lt]126, [ital Z][gt]82 have been produced in the reaction of [sup 28]Si on [sup 182]W at beam energies of 164 and 170 MeV. Evaporation residues were selected using an in-flight mass separator, the Argonne Fragment Mass Analyzer, and implanted in a double-sided silicon strip detector. The charge-to-mass ratio of implanted ions, and energies and half-lives of correlated [alpha]-decay events have been used to make isotopic identifications. The [alpha] decay from the ground state of [sup 204]Ra has been observed with an [alpha]-particle energy of 7.488(12) MeV and a half-life of 45[sub [minus]21][sup +55] ms. Previous results concerning the decay of [sup 205]Ra were also confirmed.

The transient-field technique has been used to measure the [ital g] factors of yrast states in [sup 86]Zr over the spin region [ital I]=8[h bar]--14[h bar] in order to ascertain the nature of the alignments at the first and second backbends. The states of interest were populated in the reaction [sup 12]C([sup 77]Se,3[ital n]) at 260 MeV. The results demonstrate that the first crossing at the 8[sub 1][sup +] state involves the alignment of neutron [ital g][sub 9/2] quasiparticles, and that proton [ital g][sub 9/2] quasiparticles align at higher spin.

High-spin states in 167Yb and 168Yb have been investigated using the 124 Sn( 48 Ca, x n ) reaction at a bombarding energy of 210 MeV. The level sequences of the two nuclei were established from a large set of high-fold γ-ray coincidence data detected in the EUROGAM spectrometer. The experimentally observed upbends at high rotational frequency are discussed in terms of the cranked shell model for protons both with and without pairing. An unpaired crossing involving interchange of proton orbitals is tentatively identified. No evidence was found for hyperdeformation.

The pairing properties of the neutrinoless double-$\ensuremath{\beta}$ decay $(0\ensuremath{\nu}2\ensuremath{\beta})$ candidate ${}^{100}$Mo have been studied, along with its daughter ${}^{100}$Ru, to provide input for nuclear matrix element calculations relevant to the decay. The $(p,t)$ two-neutron transfer reaction was measured on nuclei of ${}^{102,100}$Ru and ${}^{100,98}$Mo. The experiment was designed to have particular sensitivity to ${0}^{+}$ states up to excitation energies of $\ensuremath{\sim}3$ MeV with high energy resolution. Measurements were made at two angles and $L=0$ transitions identified by the ratio of yields between the two angles. For the reactions leading to and from ${}^{100}$Ru, greater than $95%$ of the $L=0$ $(p,t)$ strength was in the ground state, but in ${}^{100}$Mo about $20%$ was in excited ${0}^{+}$ states. The measured $(p,t)$ data, together with existing $(t,p)$ data, suggest that ${}^{100}$Mo is a shape-transitional nucleus while ${}^{100}$Ru is closer to the spherical side of that transition. Theoretical calculations of the $0\ensuremath{\nu}2\ensuremath{\beta}$ nuclear matrix element may be complicated by this difference in shape.

Excited states have been identified in the very neutron-deficient $Z=58$ nucleus ${}^{123}$Ce. This is the most neutron-deficient odd-$A$ cerium isotope in which excited states have been identified. The states have been unambiguously assigned to ${}^{123}$Ce by detecting de-excitation $\ensuremath{\gamma}$ rays in coincidence with evaporated charged particles and neutrons. Three rotational bands, each consisting of at least eight $E2$ transitions, have been observed. The bands have tentatively been assigned to be based on neutrons in ${g}_{7/2}$ and ${h}_{11/2}$ orbitals. Two of the bands have been assigned to be signature partners, although no interband transitions have been observed. The aligned angular momenta of the bands have been studied in comparison with neighboring nuclei and with the results of Woods-Saxon cranking calculations. Observation of the deformation-dependent $\ensuremath{\pi}{({h}_{11/2})}^{2}$ quasiparticle alignment at 0.36 MeV/$\ensuremath{\hbar}$ in each of the bands suggests a quadrupole deformation of ${\ensuremath{\beta}}_{2}\ensuremath{\simeq}0.3$, in good agreement with theoretical predictions for the suggested possible configuration assignments.