Search

Neutron-rich Pm ( Z = 61 ) isotopes were studied by delayed γ -ray spectroscopy at RIBF, RIKEN Nishina Center using the in-flight fission of a 345 MeV/nucleon U 238 beam. A cluster-type Ge detector array, EURICA, was used to measure the delayed γ rays from stopped ions. Isomeric γ decays were observed in Pm 159 and Pm 161 with half-lives of 4.97(12) μ s and 0.79(4) μ s , respectively. Level schemes for Pm 159 and Pm 161 were constructed in this study. The isomeric states of Pm 159 and Pm 161 could be interpreted as two quasiparticle excitations of neutrons with the configurations of ν ( 7 / 2 [ 633 ] ⊗ 5 / 2 [ 523 ] ) and ν ( 7 / 2 [ 633 ] ⊗ 1 / 2 [ 521 ] ) , respectively. They are analogous to the isomers that have been observed systematically in other even-mass N = 98 and N = 100 isotones in this region. A projected shell model calculation was performed and it reproduced the order of three-quasiparticle states only if new Nilsson parameters with an N -dependent spin-orbit interaction were used. This work demonstrates that the strength of spin-orbit interactions in standard Nilsson parameters needs to be modified to study the properties of neutron-rich rare-earth nuclei around A = 165 , and provides new evidence supporting the existence of the deformed N = 98 subshell gap in odd-mass nuclei for the first time.

6 pags., 4 figs., 2 tabs., The change of the shell structure in atomic nuclei, so-called “nuclear shell evolution”, occurs due to changes of major configurations through particle-hole excitations inside one nucleus, as well as due to variation of the number of constituent protons or neutrons. We have investigated how the shell evolution affects Gamow-Teller (GT) transitions that dominate the β decay in the region below 132Sn using the newly obtained experimental data on a long-lived isomer in 127Ag. The T1/2=67.5(9) ms isomer has been identified with a spin and parity of (27/2+) at an excitation energy of 1942−20+14 keV, and found to decay via an internal transition of an E3 character, which competes with the dominant β-decay branches towards the high-spin states in 127Cd. The underlying mechanism of a strong GT transition from the 127Ag isomer is discussed in terms of configuration-dependent optimization of the effective single-particle energies in the framework of a shell-model approach., Part of the WAS3ABi was supported by the Rare Isotope Science Project which is funded by MSIP and NRF of Korea. This work was supported by the Priority Centers Research Program in Korea (2009-0093817), OTKA contract number K100835, the U.S. DOE, Office of Nuclear Physics (Contract No. DE-AC02-06CH11357), NRF2016R1A5A1013277 and NRF-2013M7A1A1075764, the Spanish Ministerio de Economía y Competitividad under contract FPA2017- 84756-C4-2-P, the European Commission through the Marie Curie Actions call FP7-PEOPLE-2011-IEF (Contract No. 300096), German BMBF under Contract No: 05P12PKFNE, JSPS KAKENHI Grant No. 24740188 and 25247045, the National Natural Science Foundation of China (Nos. 11505302, 11575112, 11775316), the National Key Program for S&T Research and Development (No. 2016YFA0400501), and STFC (UK).

Structure of the neutron-rich nucleus $^{30}\mathrm{Mg}$, which is located close to the region of the $N=20$ ``island of inversion,'' has been investigated by $\ensuremath{\beta}\text{\ensuremath{-}}\ensuremath{\gamma}$ spectroscopy of spin-polarized $^{30}\mathrm{Na}$. From the detailed $\ensuremath{\gamma}\text{\ensuremath{-}}\ensuremath{\gamma}$ coincidence relations, nine new states have been established in $^{30}\mathrm{Mg}$. The spin-polarization of $^{30}\mathrm{Na}$ enabled firm spin-parity assignments for seven states in $^{30}\mathrm{Mg}$ by means of the spatial asymmetry of $\ensuremath{\beta}$-ray counts in coincidence with the $^{30}\mathrm{Mg}\phantom{\rule{4pt}{0ex}}\ensuremath{\gamma}$ rays. Based on the experimental information, it is shown that various characteristic structures coexist in $^{30}\mathrm{Mg}$: (i) the ground-state vibrational-like band, (ii) the deformed band built on the ${0}_{2}^{+}$ state at 1.788 MeV, (iii) the $\ensuremath{\gamma}$-vibrational band built on the ${2}_{3}^{+}$ state at 3.543 MeV, and (iv) four states around 5 MeV associated with large $\ensuremath{\beta}$-transition probabilities: ${1}^{+}$ and ${2}^{+}$ states with spherical nature, ${1}^{+}$ and ${2}^{+}$ states with collective nature. The experimental results are compared with three theoretical calculations of the CHFB $+$ LQRPA, the AMD $+$ GCM, and the large-scale shell model with the EEdf1 interaction. All these theories reasonably reproduce the three bands.

The gyromagnetic factor of the low-lying E=251.96(9) keV isomeric state of the nucleus ^{99}Zr was measured using the time-dependent perturbed angular distribution technique. This level is assigned a spin and parity of J^{π}=7/2^{+}, with a half-life of T_{1/2}=336(5) ns. The isomer was produced and spin aligned via the abrasion-fission of a ^{238}U primary beam at RIKEN RIBF. A magnetic moment |μ|=2.31(14)μ_{N} was deduced showing that this isomer is not single particle in nature. A comparison of the experimental values with interacting boson-fermion model IBFM-1 results shows that this state is strongly mixed with a main νd_{5/2} composition. Furthermore, it was found that monopole single-particle evolution changes significantly with the appearance of collective modes, likely due to type-II shell evolution.

In-flight fission of a 345 MeV per nucleon 238U primary beam on a 2 mm thick 9Be target has been used to produce and study the decays of a range of neutron-rich nuclei centred around the doubly mid-shell nucleus 170Dy at the RIBF Facility, RIKEN, Japan. The produced secondary fragments of interest were identified eventby- event using the BigRIPS separator. The fragments were implanted into the WAS3ABI position sensitive silicon active stopper which allowed pixelated correlations between implants and their subsequent β-decay. Discrete γ-ray transitions emitted following decays from either metastable states or excited states populated following beta decay were identified using the 84 coaxial high-purity germanium (HPGe) detectors of the EURICA spectrometer, which was complemented by 18 additional cerium-doped lanthanum bromide (LaBr3)

The structure of excited states in the neutron-rich nucleus 31 Mg, which is in the region of the “island of inversion” associated with the neutron magic number N = 20 , is studied by β – γ spectroscopy of spin-polarized 31 Na. Among the 31 Mg levels below the one neutron separation energy of 2.3 MeV, the spin values of all five positive-parity levels are unambiguously determined by observing the anisotropic β decay. Two rotational bands with K π = 1 / 2 + and 1 / 2 − are proposed based on the spins and energies of the levels. Comparison on a level-by-level basis is performed between the experimental results and theoretical calculations by the antisymmetrized molecular dynamics (AMD) plus generator coordinate method (GCM). It is found that various nuclear structures coexist in the low excitation energy region in 31 Mg.

Physics letters / B 762, 404 - 408 (2016). doi:10.1016/j.physletb.2016.09.058, Published by North-Holland Publ., Amsterdam

The β-delayed γ-ray spectroscopy of neutron-rich 123;125Ag isotopes is investigated at the Radioactive Isotope Beam Factory of RIKEN and the long-predicted 1/2¯ β-emitting isomers in 123;125Ag are identified for the first time. With the new experimental results, the systematic trend of energy spacing between the lowest 9/2+ and 1/2¯ levels is extended in Ag isotopes up to N = 78, providing a clear signal for the reduction of the Z = 40 subshell gap in Ag towards N = 82. Shellmodel calculations with the state-of-the-art VMU plus M3Y spin-orbit interaction give a satisfactory description of the low-lying states in 123;125Ag. The tensor force is found to play a crucial role in the evolution of the size of the Z = 40 subshell gap. The observed inversion of the single particle levels around 123Ag can be well interpreted in terms of the monopole shift of the π1g9/2 orbitals mainly caused by the increasing occupation of ʋ1h11/2 orbitals.

The level structure of $^{31}\mathrm{Mg}$, which is located close to the region of the $N$ = 20 ``island of inversion'' in the nuclear chart, has been studied by $\ensuremath{\beta}\text{\ensuremath{-}}\ensuremath{\gamma}$ spectroscopy with spin-polarized $^{31}\mathrm{Na}$. In $^{31}\mathrm{Mg}$, shape coexistence is expected as a result of subtle competition between the spherical mean field and the nuclear correlation which favors deformed configurations. In the present work, our unique method utilizing the anisotropic $\ensuremath{\beta}$ decay of spin-polarized $^{31}\mathrm{Na}$ enables us to firmly assign the spins of all positive-parity excited levels in $^{31}\mathrm{Mg}$ below the neutron separation energy at 2.3 MeV. Furthermore, by constructing a very detailed decay scheme, including two newly found levels, the spins of negative-parity levels are restricted. The examination of the spectroscopic information shows that the deformed rotational bands with ${K}^{\ensuremath{\pi}}=1/{2}^{+}$ and $1/{2}^{\ensuremath{-}}$, which have very similar structures to those observed in a higher excitation energy region of $^{25}\mathrm{Mg}$, appear as the ground-state and low-lying bands, respectively, in $^{31}\mathrm{Mg}$. The experimental levels of $^{31}\mathrm{Mg}$ are compared, on the level-by-level basis, with two types of theoretical calculations. These are, first, the antisymmetrized molecular dynamics (AMD) plus generator coordinate method (GCM) and, second, the shell model with the EEdf1 interaction, which is microscopically derived from chiral effective field theory. It is understood that 8 levels among the experimental 11 levels are the members of four types of largely deformed rotational bands and 2 levels are of spherical nature. The $1/{2}^{+}$ 2.244-MeV level is successfully reproduced by the shell-model calculation with a dominant 4p4h configuration. The present work clearly demonstrates that various structures coexist in a low excitation energy region of $^{31}\mathrm{Mg}$.

The neutron-rich isotopes of palladium have attracted considerable interest in terms of the evolution of the N=82 neutron shell closure and its influence on the r-process nucleosynthesis. In this Letter, we present the first spectroscopic information on the excited states in Pd and Pd studied using the EURICA γ-ray spectrometer, following production via in-flight fission of a high-intensity U beam at the RIBF facility. New isomeric states with half-lives of 144(4) ns and 39(6) μs have been assigned spins and parities of (23/2 ) and (19/2 ) in Pd and Pd, respectively. The observed level properties are compared to a shell-model calculation, suggesting the competition between proton excitations and neutron excitations in the proton-hole and neutron-hole systems in the vicinity of the doubly magic nucleus Sn.

A. Jungclaus et al. -- 6 pags., 5 figs., 2 tabs. -- Open Access funded by Creative Commons Atribution Licence 4.0, A new high-spin isomer in the neutron-rich nucleus Cd was populated in the projectile fission of a U beam at the Radioactive Isotope Beam Factory at RIKEN. A half-life of T=6.3(8) ms was measured for the new state which was tentatively assigned a spin/parity of (15). The experimental results are compared to shell model calculations performed using state-of-the-art realistic effective interactions and to the neighbouring nucleus Cd. In the present experiment no evidence was found for the decay of a 18 E6 spin-trap isomer, based on the complete alignment of the two-neutron and two-proton holes in the 0h and the 0g orbit, respectively, which is predicted to exist by the shell model., We thank the staff of the RIKEN Nishina Center accelerator complex for providing stable beams with high intensities to the experiment. We acknowledge the EUROBALL Owners Committee for the loan of germanium detectors and the PreSpec Collaboration for the readout electronics of the cluster detectors. This work was supported by the Spanish Ministerio de Ciencia e Innovación under contract FPA2011-29854-C04 and the Spanish Ministerio de Economía y Competitividad under contract FPA2014-57196-C5-4-P, the Generalitat Valenciana (Spain) under grant PROMETEO/2010/101, the National Research Foundation of Korea (NRF) grant funded by the Korea government (MEST) (NRF-2014S1A2A2028636, 2016K1A3A7A09005579, 2016R1A5A1013277), the Priority Centers Research Program in Korea (2009-0093817), OTKA contract number K-100835, JSPS KAKENHI (Grant No. 25247045), the European Commission through the Marie Curie Actions call FP7-PEOPLE-2011-IEF under Contract No. 300096, the U.S. Department of Energy, Office of Nuclear Physics, under Contract No. DE-AC02-06CH11357, the STFC (UK), the “RIKEN foreign research program”, the German BMBF (No. 05P12RDCIA, 05P12RDNUP and 05P12PKFNE), HIC for FAIR, the DFG cluster of excellence “Origin and Structure of the Universe” and DFG (Contract No. KR2326/2-1).

The decay of a new four-quasiparticle isomeric state in 160Sm has been observed using γ-ray spectroscopy at the RIBF, RIKEN. The four-quasiparticle state is assigned a 2 π ⊗ 2 ν π 5 2 − [ 532 ] , π 5 2 + [ 413 ] , ν 5 2 − [ 523 ] , ν 7 2 + [ 633 ] configuration. The half-life of this ( 11 + ) state is measured to be 1.8(4) μs. The ( 11 + ) isomer decays into a rotational band structure, based on a ( 6 − ) ν 5 2 − [ 523 ] ⊗ ν 7 2 + [ 633 ] bandhead, consistent with the g K − g R values. This decays to a ( 5 − ) two-proton quasiparticle state, which in turn decays to the ground state band. Potential energy surface and blocked-BCS calculations were performed in the deformed midshell region around 160Sm. They reveal a significant influence from β 6 deformation and that 160Sm is the best candidate for the lightest four-quasiparticle K isomer to exist in this region. The relationship between reduced hindrance and isomer excitation energy for E1 transitions from multiquasiparticle states is considered with the new data from 160Sm. The E1 data are found to agree with the existing relationship for E2 transitions.

The first fast-timing measurements from nuclides produced via the in-flight fission mechanism are reported. The lifetimes of the first 2+states in 104,106Zr nuclei have been measured via β-delayed γ-ray timing of stopped radioactive isotope beams. An improved precision for the lifetime of the 2+1state in 104Zr was obtained, τ(2+1) =2.90+25−20ns, as well as a first measurement of the 2+1state in 106Zr, τ(2+1) =2.60+20−15ns, with corresponding reduced transition probabilities of B(E2; 2+1→0+g.s.) =0.39(2)e2b2and 0.31(1)e2b2, respectively. Comparisons of the extracted ground-state deformations, β2=0.39(1)(104Zr) and β2=0.36(1)(106Zr) with model calculations indicate a persistence of prolate deformation. The data show that 104Zr is the most deformed of the neutron-rich Zr isotopes measured so far.

The decay of an isomeric state in the neutron-rich nucleus 129 Cd has been observed via the detection of internal conversion and Compton electrons providing first experimental information on excited states in this nucleus. The isomer was populated in the projectile fission of a 238 U beam at the Radioactive Isotope Beam Factory at RIKEN. From the measured yields of γ -rays and internal conversion electrons, a multipolarity of E 3 was tentatively assigned to the isomeric transition. A half-life of T 1 / 2 = 3.6 ( 2 ) ms was determined for the new state which was assigned a spin of ( 21 / 2 + ) , based on a comparison to shell model calculations performed using state-of-the-art realistic effective interactions.

Excited states have been studied in \iso{159}{Sm}, \iso{161}{Sm}, \iso{162}{Sm} (Z~=~62), \iso{163}{Eu} (Z~=~63), and \iso{164}{Gd} (Z~=~64), populated by isomeric decay following 238U projectile fission at RIBF, RIKEN. The isomer half-lives range from 50 ns to 2.6 \mus. In comparison with other published data, revised interpretations are proposed for \iso{159}{Sm} and \iso{163}{Eu}. The first data for excited states in \iso{161}{Sm} are presented, where a 2.6 \mus isomer is assigned a three-quasiparticle, K^\pi = 17/2^- structure. The interpretation is supported by multi-quasiparticle Nilsson-BCS calculations, including the blocking of pairing correlations. A consistent set of reduced E1 hindrance factors is obtained. Limited evidence is also reported for isomeric decay in 163Sm, 164Eu and 165Eu.

The (ν 5 2 [532] ⊗ 3 2 [411]) 4− state in 102Zr, populated in the β-decay of 102Y, has been measured to be isomeric with a mean lifetime of 9.5(7) ns. It decays via four transitions, two of which are ∆K = 2 (to the 3+ and 4+ members of the 2+ γ band) and one is ∆K = 4 (to the 4+ member of the ground state 0+ band). The fourth (low-energy) transition is inferred to decay to an as-yet unassigned state. Hindrances of 106 were derived for the ∆K = 2 transitions compared to Weisskopf estimates and the ∆K = 4 transition hindered by a factor of 109 . These values are consistent with the decay pattern of the analogous isomeric state in the neighbouring N = 62 nucleus 100Sr and with the broader systematics of such transitions. A comparison of the hindrances for the ∆K = 4 transitions suggests that 102Zr is hardened against the γ degree of freedom compared to 100Sr.

We report for the first time the β-decay scheme of Te140 (Z=52) to I140 (Z=53), with a specific focus on the Gamow-Teller strength along N=87 isotones. These results were obtained in an experiment performed at the Radioactive Ion Beam Factory (RIBF), RIKEN, where the parent nuclide, Te140, was produced through the in-flight fission of a U238 beam at 345 MeV per nucleon impinging on a Be9 target. Based on data from the high-efficiency γ-ray spectrometer, EUROBALL-RIKEN Cluster Array (EURICA), we constructed a decay scheme of I140. The half-life of Te140 has been determined to be 350(5) ms. A level at 926 keV has been assigned as a (1+) state based on the logft value of 4.89(6). This (1+) state, commonly observed in odd-odd nuclei, can be interpreted in terms of the πh11/2νh9/2 configuration formed by the Gamow-Teller transition between a neutron in the h9/2 orbital and a proton in the h11/2 orbital. We observe a sharp contrast to this type of β-decay branching to the lower-lying 1+ states between I140 and I136, where we see a large reduction as the number of neutrons increases. This is in contrast to the prediction by large-scale shell model calculations. To investigate this type of the suppression, results of the Nilsson model calculations will be discussed. Along the isotones with N=87, we discuss a characteristic feature of the Gamow-Teller distributions at 1+ states with respect to the isospin difference.

Excited states in Re186 with spins up to J=12 were investigated in two separate experiments using W186(d,2n) reactions at beam energies of 12.5 and 14.5 MeV. Two- and threefold γ-ray coincidence data were collected using the CAESAR and CAGRA spectrometers, respectively, each composed of Compton-suppressed high-purity germanium detectors. Analysis of the data revealed rotational bands built on several two-quasiparticle intrinsic states, including a long-lived Kπ=(8+) isomer. Configuration assignments were supported by an analysis of in-band properties, such as gK-gR values. The excitation energies of the observed intrinsic states were compared with results from multi-quasiparticle blocking calculations, based on the Lipkin-Nogami pairing approach, that included contributions from the residual proton-neutron interactions.

The level structure of the neutron-rich ^{77}Cu nucleus is investigated through β-delayed γ-ray spectroscopy at the Radioactive Isotope Beam Factory of the RIKEN Nishina Center. Ions of ^{77}Ni are produced by in-flight fission, separated and identified in the BigRIPS fragment separator, and implanted in the WAS3ABi silicon detector array, surrounded by Ge cluster detectors of the EURICA array. A large number of excited states in ^{77}Cu are identified for the first time by correlating γ rays with the β decay of ^{77}Ni, and a level scheme is constructed by utilizing their coincidence relationships. The good agreement between large-scale Monte Carlo shell model calculations and experimental results allows for the evaluation of the single-particle structure near ^{78}Ni and suggests a single-particle nature for both the 5/2_{1}^{-} and 3/2_{1}^{-} states in ^{77}Cu, leading to doubly magic ^{78}Ni.

One of the most successful descriptions of the structure of atomic nuclei is the spherical shell model. It, however, becomes impractical when moving away from closed-shell nuclei. Instead, it is the interplay between the macroscopic shape degrees of freedom and the microscopic nature of the underlying single-particle structure in a deformed basis that determines the nuclear structure. Being the heaviest nucleus precisely in the middle of, known, closed proton and neutron shells, $^{170}$Dy has become a central calibration point for tests of collective models of nuclear physics. However, besides one candidate transition from a previous experiment in Legnaro, Italy, no experimental information is available for this nucleus. Using the EURICA setup at RIKEN, which couples the worlds highest intensity in-flight fission facility with a high-efficiency HPGe array, an experiment in November 2014 produced $^{170}$Dy nuclei by in-flight fission of a $^{238}$U beam. The results from this experiment provide a wealth of information on this elusive nucleus, including the evolution of quadrupole collectivity, rigidity and higher order deformations, as well as the long sought for isomeric $K=6^+$ state, predicted to be exceptionally pure at mid-shell. These results provide us with a rich level scheme for discussing both single-particle and collective structures at mid-shell.

5 pags., 3 figs., 2 tabs., Neutron-rich nuclei in the vicinity of Ni78 were produced using a U238 beam at the RIKEN Radioactive Isotope Beam Factory. The particle-identification plot for the in-flight fission fragments highlights the first observation of eight new isotopes: Mn73, Fe76, Co77,78, Ni80,81,82, and Cu83. Although the β-decay half-lives of Co77 and Ni80 were recently reported by Xu [Phys. Rev. Lett. 113, 032505 (2014)]PRLTAO0031-900710.1103/PhysRevLett.113.032505 using data from the same experiment, the current work provides the first direct, quantitative evidence for the existence of these isotopes. The experimental production cross sections are reproduced in a satisfactory manner by theoretical predictions. An odd-even staggering of the cross sections was observed, and the effect appears to become more pronounced for the most exotic nuclei that were investigated. The staggering effect was interpreted as an increase of the neutron-evaporation probability for odd-N isotopes, owing to the decrease of the neutron-separation energy, Sn. The predicted cross section for Ni80 is significantly overestimated, which may be related to a weak binding of the neutron pair above the N=50 shell closure., This work was supported by JSPS KAKENHI (25247045, 25800130), the Spanish Ministerio de Ciencia e Innovación under Contracts No. FPA2009-13377-C02 and No. FPA2011- 29854-C04, OTKA Contract No. K-100835, U.S. DOE Contract No. DE-FG02-91ER40609, and the Priority Centers Research Program in Korea (2009-0093817).

The neutron-rich nuclei $^{158,160}\mathrm{Nd}$ have been studied via delayed $\ensuremath{\gamma}$-ray spectroscopy of $\ensuremath{\mu}\mathrm{s}$ isomeric states at the RIBF facility, RIKEN. These nuclei were produced following the projectile fission of a 345 $A\phantom{\rule{0.16em}{0ex}}\mathrm{MeV}\phantom{\rule{4pt}{0ex}}^{238}\mathrm{U}$ beam and delayed $\ensuremath{\gamma}$ rays were detected by the EURICA cluster Ge array. The isomeric states have measured half-lives of 339(20) ns and 1.63(21) $\ensuremath{\mu}\mathrm{s}$ for $^{158}\mathrm{Nd}$ and $^{160}\mathrm{Nd}$, respectively. From the observed $\ensuremath{\gamma}$ decays and the systematics of levels in the neighboring Nd isotopes first level schemes were constructed for these nuclei. The isomeric states of $^{158,160}\mathrm{Nd}$ have been assigned spins of $({6}^{\ensuremath{-}})$ and $({4}^{\ensuremath{-}})$, with proposed $\ensuremath{\nu}5/2[523]\ensuremath{\bigotimes}\ensuremath{\nu}7/2[633]$ and $\ensuremath{\nu}1/2[521]\ensuremath{\bigotimes}\ensuremath{\nu}7/2[633]$ configurations, respectively.

Spin-polarized radioactive nuclear beams at TRIUMF enable a new spectroscopic method which efficiently assigns spins and parities of the daughter levels by taking advantage of the asymmetric β-decay of the polarized parent nucleus. This method was successfully applied to structure studies of 29Mg and 30Mg in connection with the physics of the “island of inversion”. In 29Mg, two low-lying levels with intruder configuration were assigned. In 30Mg, coexistence of spherical shape, prolate shape and γ-collectivity was strongly suggested.

The doubly-odd nucleus $^{136}\mathrm{La}$ is theoretically studied in terms of a large-scale shell model. The energy spectrum and transition rates are calculated and compared with the most updated experimental data. The isomerism is investigated for the first ${14}^{+}$ state, which was found to be an isomer in the previous study [Phys. Rev. C 91, 054305 (2015)]. It is found that the ${14}^{+}$ state becomes an isomer due to a band crossing of two bands with completely different configurations. The yrast band with the ($\ensuremath{\nu}{h}_{11/2}^{\ensuremath{-}1}\ensuremath{\bigotimes}\ensuremath{\pi}{h}_{11/2}$) configuration is investigated, revealing a staggering nature in $M1$ transition rates.

For the first time, the γ decay of excited states has been observed in a nucleus situated in the quadrant south-east of doubly magic Sn132, a region in which experimental information so far is limited to ground-state properties. Six γ rays with energies of 50, 86, 103, 227, 357, and 602 keV were observed following the β-delayed neutron emission from Cd85133, populated in the projectile fission of a U238 beam at the Radioactive Isotope Beam Factory at RIKEN within the EURICA project. The new experimental information is compared to the results of a modern realistic shell-model calculation, the first one in this region very far from stability, focusing in particular on the π0g9/2-1 - ν1f7/2 particle-hole multiplet in In83132. In addition, theoretical estimates based on a scaling of the two-body matrix elements for the πh11/2-1 - νg9/2 analog multiplet in Tl127208, one major proton and one major neutron shell above, are presented. © 2016 American Physical Society.

E Sahin et al. ; 7 págs.; 4 figs.; Presented at the XXXIV Mazurian Lakes Conference on Physics, Piaski, Poland, September 6–13, 2015., The level structure of the 77Cu nucleus has been studied by means of -delayed -ray spectroscopy at RIKEN Nishina Center. Secondary beamparticles in the region near 78Ni were produced via in-flight fission of 238U on a thick 9Be target at a primary beam energy of 345 MeV/nucleon. After identification in atomic number (Z) and mass-to-charge ratio (A=Q) in the BigRIPS fragment separator, the fission products were delivered to the final focal plane through the ZeroDegree Spectrometer. The WAS3ABI silicon stack array was used for the implantation of the ions, while de-excitation rays were detected with the EURICA -ray spectrometer at the focal plane. Beta-correlated particle identification of 77Ni allowed to obtain the -ray spectrum of the daughter 77Cu in a selective way. Experimental details and first results on the excited states in 77Cu nucleus will be presented in this contribution., This work was supported by the Research Council of Norway under project Grants Nos. 213442 and 240104. V.W. was supported by the U.S. Department of Energy Grant No. DE-FG02-91ER-40609.

We have been studying the structure of Mg isotopes in the region of the N = 20 island of inversion, to clarify the structure change as a function of the neutron number. The experiments are being performed by our unique method of β-decay spectroscopy taking advantage of highly-spin-polarized radioactive nuclear beams at TRIUMF. The β-decay asymmetry in the Na-isotope decay enables unambiguous spin-parity assignments of the levels in the daughter Mg isotope, and it becomes possible to compare the experimental data and theoretical predictions on a level-by-level basis. The present paper reports on the results of the β decay of 30Na→30Mg. From the detailed decay scheme of Na, it is suggested that the Mg levels at 1.788 MeV [(0+2 )], 3.460 MeV [(2) ], 4.967 MeV [1], and 5.414 MeV [2] have deformed shapes with intruder configurations, whereas the level at 2.466 MeV [(2+2 )] has different nature both from the spherical ground state and the deformed four levels. It is proposed that the 2+2 level is the band-head of the predicted γ-band.

In the EURICA campaign aimed at exploration of the $^{78}\mathrm{Ni}$ region, an isomeric state of $^{76}\mathrm{Co}$ has been observed via $\ensuremath{\gamma}$-ray spectroscopy. The nuclei were produced by in-flight fission of a $^{238}\mathrm{U}$ beam at the Radioactive Isotope-Beam Factory. Two coincident $\ensuremath{\gamma}$ rays of $192.02(30)$ and $446.4(7)$ keV from the decay of a ${t}_{1/2}=2.96{(}_{25}^{29})\phantom{\rule{4pt}{0ex}}\ensuremath{\mu}\mathrm{s}$ isomeric state of $^{76}\mathrm{Co}$ have been observed. The decay of the isomer was assigned to an $E1$ transition with a reduced transition probability of $B(E1;{3}^{+}\ensuremath{\rightarrow}{2}^{\ensuremath{-}})=1.79(16)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}8}$ W.u. A $\ensuremath{\beta}$-decaying state with spin-parity ${1}^{\ensuremath{-}}$ and a half-life of $16(4)$ ms was also observed in the data, and the known state with a half-life of $22{(}_{5}^{7})$ ms was assigned to have a spin-parity of ${8}^{\ensuremath{-}}$. Furthermore, the isomer of $^{76}\mathrm{Ni}$ has been remeasured to $547.8(33)$ ns giving a $B(E2;{8}^{+}\ensuremath{\rightarrow}{6}^{+})$ value of $0.786(5)$ W.u. A new excited state at $2994.6(5)$ keV, decaying via a $\ensuremath{\gamma}$ ray of 2004.5(4) keV, has also been observed. This is in agreement with either of the predicted ${0}_{2}^{+}$ or ${2}_{2}^{+}$ states. These results are discussed in terms of the shell model and the interaction of the $\ensuremath{\nu}{p}_{1/2}$ and $\ensuremath{\pi}{f}_{7/2}$ orbitals.

The level structures of 28 Mg and 29 Mg have been investigated by the β-decay of spin-polarized28 Na and 29 Na at ISAC, TRIUMF. The detailed β-γ and γ-γ coincidence measurements were performed. New γ rays and β transitions were observed both in 28 Mg and 29 Mg . We have succeeded in assigning spins and parities of many levels in 28 Mg and 29 Mg . Comparison with shell model calculations using USD Hamiltonian suggest that the structure of 28 Mg and 29 Mg are well explained in the sd-shell configurations, except for two levels at 1.095 and 1.430 MeV in 29 Mg . This suggests negative parity assignments for these levels. The evolution of sd-pf shell is discussed.

Experiments based on the isomer-spectroscopy method were performed using the secondary beam line at RCNP, Osaka University. Recently, a new γ-ray spectroscopy method was established using fusion reaction induced by low-energy RI beam. This method enables us to study high-spin states of nuclei in wider mass region where it is difficult to populate them by using the combination of stable beams and stable targets. This method works well although low production of nuclei, because (1) the combination of beams and targets can be selected with large-reaction cross section and (2) high-S/N measurement can be performed by the event-by-event detection to select the events correlated with RI beam, which reduces background γ rays, competing with γ rays emitted from fusion products. As the first step, high-spin states of 142 Pr were studied using fusion reaction induced by low-energy 17 N RI beam. Large cross section was obtained by the 130 Te (17 N ,5 n ) reaction with 4.9 MeV/u 17 N beam. Event selection, which was carried out by the event-by-event detection with low-beam intensity of 2×104 pps, enables high-S/N measurement.

The neturon rich nucleus 13B was studied via the proton transfer reaction 4He(12Be,13B \gamma) at 50AMeV. The known 4.83-MeV excited state was strongly populated and its spin and parity were assigned to 1/2+ by comparing the angular differential cross section data with DWBA calculations. This low-lying 1/2+ state is interpreted as a proton intruder state and indicates a deformation of the nucleus., Comment: 16 pages, 3 figures

Mean lifetime tau of the isomeric O-2(+) state in Be-12 has been determined by measuring decay spectra of delayed y-rays from stopped Be-12 2 nuclei produced by the projectile fragmentation of O-18 at 100 A MeV. A consistent value of tau = 331 +/- 12 ns was obtained from the time spectra of the E2 gamma decay to the 2(1)(+) state and the positron annihilation following the E0 decay to the ground state. Based on the observed branching ratio between the E2 and E0 decays, transition strengths of the two decay modes were deduced to be B(E2; O-2(+) -> 2(1)(+)) = 7.0 +/- 0.6 e(2) fm(4) and 2 1 1 (O-2(+) Sigma(i) e(i) r(i)(2) O-1(+)), = 0.87 +/- 0.03 e fM(2), respectively. (C) 2007 Elsevier B.V. All rights reserved.

Single-particle properties of low-lying resonance levels in 14O have been studied efficiently by utilizing a technique of proton elastic resonance scattering with a 13N secondary beam and a thick proton target. The excitation functions for the N 13 + p elastic scattering were measured over a wide energy range of E CM = 0.4 – 3.3 MeV and fitted with an R-matrix calculation. A clear assignment of J π = 2 − has been made for the level at E x = 6.767 ( 11 ) MeV in 14O for the first time. The excitation functions show a signature of a new 0 − level at E x = 5.71 ( 2 ) MeV with Γ = 400 ( 100 ) keV . The excitation energies and widths of the 14O levels are discussed in conjunction with the spectroscopic structure of A = 14 nuclei with T = 1 .

Shell-model calculations are performed for even-even, odd-mass, and doubly-odd nuclei of Sn, Sb, Te, I, Xe, Cs, and Ba isotopes around mass 130 using the single-particle space made up of valence nucleons occupying the $0{g}_{7/2},\phantom{\rule{0.16em}{0ex}}1{d}_{5/2},\phantom{\rule{0.16em}{0ex}}2{s}_{1/2},\phantom{\rule{0.16em}{0ex}}0{h}_{11/2}$, and $1{d}_{3/2}$ orbitals. The calculated energies and electromagnetic transitions are compared with the experimental data. In addition, several typical isomers in this region are investigated.

We report new data on the $^{136}\mathrm{Sb}\phantom{\rule{4pt}{0ex}}{6}^{\ensuremath{-}}$ yrast isomer with ${T}_{1/2}=489(40) \mathrm{ns}$ and $\ensuremath{\pi}{g}_{7/2}^{1}\ifmmode\times\else\texttimes\fi{}\ensuremath{\nu}{f}_{7/2}^{3}$ configuration, populated in the projectile fission of $^{238}\mathrm{U}$ on a $^{9}\mathrm{Be}$ target. The analysis confirms the lifetime, providing a good accuracy measurement. In addition, the decay of the isomer to the ground state is newly suggested. Our result for the isomeric decay scheme is in a good agreement with shell-model calculations.

In this contribution the low-excitation structural properties of the doubly mid-shell nucleus 170Dy are discussed, with a special empasis on the evolution of the ground state rotational band within the dysprosium isotopic chain. Recent results from an experiment with the EURICA setup at RIKEN are shown in the context of previous measurements at the PRISMA+CLARA as well as the PRISMA+AGATA setups at Laboratori Nazionali di Legnaro. A brief outlook on future planned measurements is also given.

The thermo-emf ΔV and thermoelectric current ΔI generated by imposing a temperature gradient alternating at a period of T on a thermoelectric (TE) generator were measured as a function of t, where t is the lapsed time and 1/T was varied from 0 to 1/30 s-1. A TE generator was sandwiched between two Peltier modules connected in series. The alternating temperature gradients were produced by imposing an alternating voltage V on two Peltier modules, where V was varied from 1.0 to 3.7 V. Both ΔV and ΔI generated by the TE generator oscillate at a period of T but their amplitudes tend to increase monotonically with an increase of V. The effective thermo-emf ΔVeff and current ΔIeff calculated from ΔV and ΔI increase abruptly with an increase of 1/T and have a local maximum at 1/T=1/120 or 1/240 s-1. The generating power ΔWeff(=ΔVeffΔIeff) tends to increase proportionally with an increase of input power Winput, owing to the increase in the temperature difference. The rate of ΔWeff to Winput at 1/T=1/240 s-1 reached approximately 3.2 times as large as that obtained for the steady temperature gradient corresponding to 1/T=0 s-1. It was thus found that the generating power of the TE generator operating under the temperature gradient alternating at an optimum period is remarkably increased compared to that of a TE generator working under a conventional steady temperature gradient.

Excited states in the N=102 isotones 166Gd and 164Sm have been observed following isomeric decay for the first time at RIBF, RIKEN. The half-lives of the isomeric states have been measured to be 950(60) and 600(140) ns for 166Gd and 164Sm, respectively. Based on the decay patterns and potential energy surface calculations, including β6 deformation, a spin and parity of 6- has been assigned to the isomeric states in both nuclei. Collective observables are discussed in light of the systematics of the region, giving insight into nuclear shape evolution. The decrease in the ground-band energies of 166Gd and 164Sm (N=102) compared to 164Gd and 162Sm (N=100), respectively, presents evidence for the predicted deformed shell closure at N=100.

The g-factor of the 27− isomer state of 152Dy has been measured using the Time- Integral Perturbed Angular Distribution (TIPAD) method. The high-spin states of 152Dy have been populated by 141Pr(16O,p4n)152Dy reaction at E = 115 MeV from the AVF cyclotron at CYRIC. The paramagnetic correction factor of Dy ions in Pr has been determined to be 4.2(5) by the Time- Differential Perturbed Angular Distribution (TDPAD) measurement of the 21− state of 152Dy. As a result, the g-factor of the 27− isomer state of 152Dy has been obtained to be +0.09(5). This shows the smaller value than the expected one of +0.39 deduced from a fully aligned configuration of π(h 11 2/2 ) ⊗ v(f 7 2/2 h 9/2 i 13/2).

With using low-energy RI beams from an in-flight RIB separator, CRIB, the most crucial stellar reaction 14 O( α ,p) 17 F for the onset of the high-temperature rp-process was directly investigated and the transitions through the states at around 6.2 MeV in 18 Ne were first observed, confirming the importance predicted before. The ( α ,p) reaction leading to the first excited state in 17 F was also found to have a large contribution. A proton resonance search experiment of 23 Mg + p was also discussed, which is a part of our series of resonance search studies relevant to the early stage of the rp-process.

The high-spin states of 93Mo have been studied by a 82Se( 16O, 5n) 93Mo reaction at a beam energy of 100 MeV using techniques of in-beam γ-ray spectroscopy. Measurements of γ-t, γ-γ-t coincidences, γ-ray angular distributions and γ-ray linear polarizations were performed. The high-spin isomer was found as a (39/2-) state at about 9.7 MeV. The near-yrast states in 93Mo were interpreted using the weak-coupling picture of a d5/2 neutron to a neutron magic core nucleus 92Mo.

The stellar reaction 14 O( α ,p) 1 7F, that critically determines the onset of the high-temperature rp-process, has been studied through a direct measurement with a low-energy radioactive 14 O beam and a gaseous helium target cooled down to 30 K. The reaction cross section was measured directly by means of a thick target technique in the energy range of E c.m. ( 14 O+ α ) = 0.8-3.8 MeV. The 14 O( α ,p) 17 F * reaction leading to the first excited state in 17 F was clearly observed for the first time, suggesting an increase of about 50% for the stellar reaction rate through resonance at around 7.1 MeV in 18 Ne.

A new high-spin isomer in 150Dy has been observed at an excitation energy of 10.3 MeV by combining the inverse-kinematic reaction induced by a pulsed beam of 132Xe and the $\gamma$ -ray recoil-shadow technique. The half-life of this isomeric state has been determined to be $T_{1/2} = 1.6 \pm 0.6$ ns using the conventional centroid-shift method with the 141Pr(16O, p6n)150Dy reaction at 165 MeV. The mechanism producing high-spin isomers in N = 83,84 isotones is qualitatively discussed in terms of the difference of the neutron particle-hole configuration between the high-spin isomer and the lower-lying state.

The first evidence for excited states in Ag-95 is presented. Ag-95 is the heaviest T-z = 1/2 nucleus for which gamma-rays have been identified. The reaction Ca-40(Ni-58, 1p2n)Ag-95 was used in the ...

High-spin states in the odd-odd 168Lu nucleus, populated in the 154Sm(19F,5n) reaction at a beam energy of 96 MeV, were investigated using in-beam γ-ray spectroscopy techniques. The BC neutron crossing in the yrast band, based on πg7/2[404]7/2+⊗νi13/2[642]5/2+ configuration, occurs at ħω= 0.31 MeV. The two side bands, based on πh11/2[514]9/2−⊗νi13/2[642]5/2+ and πh9/2[541]1/2−⊗νi13/2[642]5/2+ configurations, show anomalous signature-splitting and signature-inversion in the first one, to occur at ħω= 0.24 MeV. A moderately delayed BC-crossing is anticipated in the second one.

A high-spin isomeric beam line has been constructed at RIKEN based on the inverse kinematics of fusion–evaporation reactions. The beam line provides high-spin isomers as secondary beams, whose intensity is more than 10 5 sec −1 . The characteristics and the present status of the beam line are described.

We present information on the excited states in the prolate-deformed, neutron-rich nuclei 165;167Tb100;102. The nuclei of interest were synthesised following in-flight fission of a 345 MeV per nucleon 238U primary beam on a 2 mm 9Be target at the Radioactive Ion-Beam Factory (RIBF), RIKEN, Japan. The exotic nuclei were separated and identified event-by-event using the BigRIPS separator, with discrete energy gamma-ray decays from isomeric states with half-lives in the s regime measured using the EURICA gamma-ray spectrometer. Metastable-state decays are identified in 165Tb and 167Tb and interpreted as arising from hindered E1 decay from the 7 2 [523] single quasi-proton Nilsson configuration to rotational states built on the 3 2 [411] single quasi-proton ground state. These data correspond to the first spectroscopic information in the heaviest, odd-A terbium isotopes reported to date and provide information on proton Nilsson configurations which reside close to the Fermi surface as the 170Dy doubly-midshell nucleus is approached.