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.

Background: Mg 24 is a strongly deformed nucleus in the ground state. Deformation effects can be observed in the structure of the isoscalar giant monopole and quadrupole resonances. Mg 24 is also a nucleus that is well known to present different types of cluster-oscillation modes. Both giant resonances and cluster states are strongly populated by isoscalar transitions. Purpose: To extract the E 0 , E 1 , and E 2 transition strengths via Li 6 scattering. The Li 6 probe is a powerful tool for investigating the isoscalar nuclear response with a very favorable ratio of resonance-to-continuum background. Method: Double-differential cross sections of Li 6 inelastic scattering, at the beam energy of 100 MeV/u, were measured in the excitation-energy range 10 – 40 MeV and scattering angles 0 − 3 ∘ . A multipole-decomposition analysis was performed for extracting the isoscalar E 0 , E 1 , and E 2 strength distributions. Results: The extracted multipole strengths were compared with predictions from consistent quasiparticle random phase approximation calculations. The theoretical predictions are in fair agreement with the experimental data. The E 0 strength was also compared with results from antisymmetrized molecular dynamics calculations found in the literature. A few peaks in the experimental data might be associated with clustering in Mg 24 . Conclusions: Ground-state deformation effects were observed in the isoscalar giant monopole resonance (ISGMR) and isoscalar giant quadrupole resonance (ISGQR) distributions. The ISGMR strength is split in two peaks around 19 and 28 MeV. The ISGQR exhibits a pronounced peak at 20 MeV with a broadening at the low-energy region, similar to predictions from microscopic calculations. Signatures of excitation of cluster states were observed in the E 0 response. Further studies including particle-decay measurements will be required to confirm the nature of the observed peaks.

The Research Center for Nuclear Physics (RCNP) was founded in 1971 at Osaka University to promote nuclear physics research using a variable-energy, multiparticle azimuthally varying field (AVF) cyc...

A resonant state at 3.21-0.04+0.12MeV, located just above the one-neutron separation threshold, was observed for the first time in Be12 from the Be11(d,p)Be12 one-neutron transfer reaction in inverse kinematics. This state is assigned a spin-parity of 0- according to the systematics of the level scheme of the N=8 isotones and decay-width analysis. Gamow coupled-channel and Gamow shell-model calculations show the importance of the continuum coupling, which dramatically influences the excitation energy and ordering of low-lying states. Various exotic structures associated with cross-shell intruding configurations in Be12 and in its isotonic nucleus Li11 are comparably discussed.

Inelastic ${}^{6}$Li scattering at 100 MeV/u on ${}^{12}$C and ${}^{93}$Nb have been measured with the high-resolution magnetic spectrometer Grand Raiden. The magnetic-rigidity settings of the spectrometer covered excitation energies from 10 to 40 MeV and scattering angles in the range $0^\circ < \theta_{\text{lab.}}< 2^\circ$. The isoscalar giant monopole resonance was selectively excited in the present data. Measurements free of instrumental background and the very favorable resonance-to-continuum ratio of ${}^{6}$Li scattering allowed for precise determination of the $E0$ strengths in ${}^{12}$C and ${}^{93}$Nb. It was found that the monopole strength in ${}^{12}$C exhausts $52 \pm 3^\text{(stat.)} \pm 8 ^\text{(sys.)}$\% of the energy-weighted sum rule (EWSR), which is considerably higher than results from previous $\alpha$-scattering experiments. The monopole strength in ${}^{93}$Nb exhausts $92 \pm 4^\text{(stat.)} \pm 10 ^\text{(sys.)}$\% of the EWSR, and it is consistent with measurements of nuclei with mass number of $A\approx90$. Such comparison indicates that the isoscalar giant monopole resonance distributions in these nuclei are very similar, and no influence due to nuclear structure was observed.

Local allergic rhinitis (LAR) represents a diagnostic and therapeutic challenge for clinicians. Even though it affects a considerable number of chronic rhinitis patients and a significant number of articles regarding prevalence, evolution, diagnosis, and treatment have been published, the condition remains still largely unrecognized and therefore misdiagnosed and mistreated. LAR is a unique form of chronic rhinitis; it is neither classical allergic rhinitis (AR) nor non-allergic rhinitis (NAR). The symptoms, duration, severity, and complications of LAR are similar to those of AR and can affect adults and children. Thus, a portion of patients diagnosed with NAR or chronic rhinitis of unknown etiology may have LAR. The relationship between LAR inflammation and systemic allergic inflammation is unclear. Patients are frequently misdiagnosed with idiopathic NAR, and distinguishing between both entities is difficult without specific diagnostic tests. Underdiagnosis of LAR has implications on the management of these patients, as they are deprived of allergen immunotherapy (AIT) that has been demonstrated to modulate the immune mechanisms underlying allergic diseases. This review aims to comprehensively summarize the current knowledge on LAR and address unmet needs in the areas of disease diagnosis and treatment.

A new type of neutron detector, named Stack Structure Solid organic Scintillator (S 4 ), consisting of multi-layer plastic scintillators with capability to suppress low-energy γ rays under high-counting rate has been constructed and tested. To achieve n - γ discrimination, we exploit the difference in the ranges of the secondary charged particles produced by the interactions of neutrons and γ rays in the scintillator material. The thickness of a plastic scintillator layer was determined based on the results of Monte Carlo simulations using the Geant4 toolkit. With layer thicknesses of 5 mm, we have achieved a good separation between neutrons and γ rays at 5 MeV ee threshold setting. We have also determined the detection efficiencies using monoenergetic neutrons at two energies produced by the d + d → n + 3 He reaction. The results agree well with the Geant4 simulations implementing the Li e ge Intranuclear Cascade hadronic model (INCL++) and the high-precision model of low-energy neutron interactions (NeutronHP).

Low lying states of neutron-rich 32Ne were populated by means of one- and two-proton knock- out reactions at the RIKEN Radioactive Isotope Beam Factory. A new transition is observed at 1410(15) keV and assigned to the 4+ 1 → 2+ 1 decay. With this energy the R4/2 ratio is calculated to be 2.99(6), lying close to the rigid rotor limit and suggests a high degree of collectivity and strongest deformation among neutron-rich Neon isotopes. Comparisons of experimental inclusive and exclu- sive reaction cross sections with shell model and eikonal reaction dynamical calculations reveals considerable quenching for this highly asymmetric system and contributes to systematic trends.

We have constructed and tested a novel plastic-scintillator-based solid-state active proton target for use in nuclear spectroscopic studies with nuclear reactions induced by an ion beam in inverse kinematics. The active target system, named Stack Structure Solid organic Scintillator Active Target (S4AT), consists of five layers of plastic scintillators, each with a 1-mm thickness. To determine the reaction point in the thickness direction, we exploit the difference in the energy losses due to the beam particle and the charged reaction product(s) in the scintillator material. S4AT offers the prospect of a relatively thick target while maintaining a good energy resolution. By considering the relative energy loss between different layers, the energy loss due to unreacted beam particles can be eliminated. Such procedure, made possible by the multi-layer structure, is essential to eliminate the effect of unreacted accompanying beam particles, thus enabling its operation at a moderate beam intensity of up to a few Mcps. We evaluated the performance of S4AT by measuring the elastic proton-proton scattering using a 70-MeV proton beam at Cyclotron and Radioisotope Center (CYRIC), Tohoku University., Comment: 32 pages, 14 figures

The isospin character of p-n pairs at large relative momentum has been observed for the first time in the ^{16}O ground state. A strong population of the J,T=1,0 state and a very weak population of the J,T=0,1 state were observed in the neutron pickup domain of ^{16}O(p,pd) at 392 MeV. This strong isospin dependence at large momentum transfer is not reproduced by the distorted-wave impulse approximation calculations with known spectroscopic amplitudes. The results indicate the presence of high-momentum protons and neutrons induced by the tensor interactions in the ground state of ^{16}O.

Our research goal is to measure the cross section of the 7Be(d, p) reaction to find a solution for the cosmological the 7Li problem, which is an overestimation of the primordial 7Li abundance in the standard Big-Bang nucleosynthesis (BBN) model. We developed a method to produce an unstable 7Be target to measure the reaction in normal kinematics in a high-resolution measurement. We performed an experiment to produce the 7Be target and also to measure the cross section of the 7Be(d, p)8Be reaction with the produced 7Be target at the tandem facility, Kobe University. A 2.36 MeV proton beam irradiated a Li target to transmute 7Li particles to 7Be particles via the 7Li(p, n)7Be reaction. We produced 2.6×1013 7Be particles in the target after two days’ proton irradiation. After the target production, the beam ion was changed to deuterons with energies of 0.6, 1.0, and 1.6 MeV to measure the 7Be(d, p) reaction. The outgoing protons were measured by two ΔE-E silicon telescopes placed at 30° and 45°. We report the preliminary results of this experiment, including the 7Be(d, p) cross section.

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.

One of the most exotic light neutron-rich nuclei currently accessible for experimental study is ^{40}Mg, which lies at the intersection of the nucleon magic number N=28 and the neutron drip line. Low-lying excited states of ^{40}Mg have been studied for the first time following a one-proton removal reaction from ^{41}Al, performed at the Radioactive Isotope Beam Factory of RIKEN Nishina Center with the DALI2 γ-ray array and the ZeroDegree spectrometer. Two γ-ray transitions were observed, suggesting an excitation spectrum that shows unexpected properties as compared to both the systematics along the Z=12, N≥20 Mg isotopes and available state-of-the-art theoretical model predictions. A possible explanation for the observed structure involves weak-binding effects in the low-lying excitation spectrum.

Background: Inelastic neutrino-nucleus scattering is important for understanding core-collapse supernovae and the detection of emitted neutrinos from such events in earth-based detectors. Direct measurement of the cross sections is difficult and has only been performed on a few nuclei. It is, therefore, important to develop indirect techniques from which the inelastic neutrino-nucleus scattering cross sections can be determined. Purpose: This paper presents a development of the (Li-6,Li-6*[T = 1, T-z = 0, 0(+), 3.56 MeV]) reaction at 100 MeV/u as a probe for isolating the isovector spin-transfer response in the inelastic channel (Delta S = 1, Delta T = 1, Delta T-z = 0) from which the Gamow-Teller transition strengths from nuclei of relevance for inelastic neutrino-nucleus scattering cross sections can be extracted. Method: By measuring the Li-6 ejectile in a magnetic spectrometer and selecting events in which the 3.56 MeV gamma ray from the decay of the Li-6*[3.56 MeV] state is detected, the isovector spin-transfer selectivity is obtained. High-purity germanium clover detectors served to detect the gamma rays. Doppler reconstruction was used to determine the gamma energy in the rest frame of Li-6. From the Li-6 and 3.56 MeV gamma-momentum vectors the excitation energy of the residual nucleus was determined. Results: In the study of the C-12(Li-6,Li-6*[3.56 MeV]) reaction, the isovector spin-transfer excitation-energy spectrum in the inelastic channel was successfully measured. The strong Gamow-Teller state in C-12 at 15.1 MeV was observed. Comparisons with the analog C-12(Li-6,He-6) reaction validate the method of extracting the Gamow-Teller strength. In measurements of the Mg-24, Nb-93(Li-6,Li-6*[3.56 MeV]) reactions, the 3.56 MeV gamma peak could not be isolated from the strong background in the gamma spectrum from the decay of the isoscalar excitations. It is argued that by using a gamma-ray tracking array instead of a clover array, it is feasible to extend the mass range over which the (Li-6,Li-6*) reaction can be used for extracting the isovector spin-transfer response up to mass numbers of similar to 25 and perhaps higher. Conclusions: It is demonstrated that the (Li-6,Li-6*[3.56 MeV]) reaction probe can be used to isolate the inelastic isovector spin-transfer response in nuclei. Application to nuclei with mass numbers of about 25 or more, however, will require a more efficient gamma-ray array with a better tracking capability.

The (^{12}N, ^{12}C) charge-exchange reaction at 175 MeV/u was developed as a novel probe for studying the isovector spin giant monopole resonance (IVSMR), whose properties are important for better understanding the bulk properties of nuclei and asymmetric nuclear matter. This probe, now available through the production of ^{12}N as a secondary rare-isotope beam, is exothermic, is strongly absorbed at the surface of the target nucleus, and provides selectivity for spin-transfer excitations. All three properties enhance the excitation of the IVSMR compared to other, primarily light-ion, probes, which have been used to study the IVSMR thus far. The ^{90}Zr(^{12}N,^{12}C) reaction was measured and the excitation energy spectra up to about 70 MeV for both the spin-transfer and non-spin-transfer channels were deduced separately by tagging the decay by γ emission from the ^{12}C ejectile. Besides the well-known Gamow-Teller and isobaric analog transitions, a clear signature of the IVSMR was identified. By comparing with the results from light-ion reactions on the same target nucleus and theoretical predictions, the suitability of this new probe for studying the IVSMR was confirmed.

We report on the in-beam gamma spectroscopy of Sn102 and Cd100 produced via two-neutron removal from carbon and CH2 targets at about 150 MeV/nucleon beam energy. New transitions assigned to the decay of a second 2+ excited state at 2470(60) keV in Sn102 were observed. Two-neutron removal cross sections from Sn104 and Cd102 have been extracted. The enhanced cross section to the 22+ in Sn102 populated via the (p,p2n) reaction is traced back to an increase of shell-model structure overlaps, consistent with the hypothesis that the proton-induced two-deeply bound-nucleon removal mechanism is of direct nature.

International audience; Excited states in the neutron-rich nucleus 150Ba have been observed via β–γ spectroscopy at the Radioactive Isotope Beam Factory, RIKEN Nishina Center. The 150Ba ions were produced by the in-flight fission of a 238U beam with an energy of 345 MeV/nucleon. The E(2+) energy of 150Ba was identified at 100 keV, which is the lowest known in the neutron-rich Ba isotopes. A γ -ray peak was also observed at 597 keV. A mean-field calculation with a fully 3D real space was performed and a static octupole deformation was obtained for the Ba isotopes. Kπ = 0− and 1− excited states with significant octupole collectivity were newly predicted at around or lower than 1 MeV on the ground state of 150Ba by a random-phase approximation calculation. The 597 keV γ ray can be interpreted as a negative-parity state, showing that 150Ba may possess octupole collectivity.

The low-lying structure of 55Sc has been investigated using in-beam \gamma-ray spectroscopy with the 9Be(56Ti,55Sc+\gamma)X one-proton removal and 9Be(55Sc,55Sc+\gamma)X inelastic-scattering reactions at the RIKEN Radioactive Isotope Beam Factory. Transitions with energies of 572(4), 695(5), 1539(10), 1730(20), 1854(27), 2091(19), 2452(26), and 3241(39) keV are reported, and a level scheme has been constructed using \gamma\gamma coincidence relationships and \gamma-ray relative intensities. The results are compared to large-scale shell-model calculations in the sd-pf model space, which account for positive-parity states from proton-hole cross-shell excitations, and to {\it ab initio} shell-model calculations from the in-medium similarity renormalization group that includes three-nucleon forces explicitly. The results of proton-removal reaction theory with the eikonal model approach were adopted to aid identification of positive-parity states in the level scheme; experimental counterparts of theoretical 1/2+1 and 3/2+1 states are suggested from measured decay patterns. The energy of the first 3/2- state, which is sensitive to the neutron shell gap at the Fermi surface, was determined. The result indicates a rapid weakening of the N=34 subshell closure in pf-shell nuclei at Z>20, even when only a single proton occupies the \pi f7/2 orbital.

Two-proton relative momentum ($q_{pp}$) and opening angle ($\theta_{pp}$) distributions from the three-body decay of two excited proton-rich nuclei, namely $^{23}$Al $\rightarrow$ p + p + $^{21}$Na and $^{22}$Mg $\rightarrow$ p + p + $^{20}$Ne, have been measured with the projectile fragment separator (RIPS) at the RIKEN RI Beam Factory. An evident peak at $q_{pp}\sim20$ MeV/c as well as a peak in $\theta_{pp}$ around 30$^\circ$ are seen in the two-proton break-up channel from a highly-excited $^{22}$Mg. In contrast, such peaks are absent for the $^{23}$Al case. It is concluded that the two-proton emission mechanism of excited $^{22}$Mg is quite different from the $^{23}$Al case, with the former having a favorable diproton emission component at a highly excited state and the latter dominated by the sequential decay process.

By using para-hydrogen and a mechanical press made of neodymium magnets, we have succeeded in making a 1-mm-thick and 30-mm-diameter solid hydrogen target (SHT), and have measured elastic scattering of protons with radioactive ion beams at 300 MeV/u. We also succeeded in making not only a 0.5-mm-thick and 10-mm-diameter SHT but also a 2-mm-thick and 30-mm-diameter SHT to study excited-state properties of nuclei via (p,p′) reactions, and quasi-free (p,pα) reactions at intermediate energies. The ortho–para converter and the simple mechanical press show possibilities for making SHTs which have various radii and thicknesses.

One-neutron knockout from 24O leading to the first excited state in 23O has been measured for a proton target at a beam energy of 62 MeV/nucleon. The decay energy spectrum of the neutron unbound state of 23O was reconstructed from the measured four momenta of the 22O fragment and emitted neutron. A sharp peak was found at E decay = 50 ± 3 keV , corresponding to an excited state in 23O at 2.78 ± 0.11 MeV , as observed in previous measurements. The longitudinal momentum distribution for this state was consistent with d-wave neutron knockout, providing support for a J π assignment of 5 / 2 + . The associated spectroscopic factor was deduced to be C 2 S ( 0 d 5 / 2 ) = 4.1 ± 0.4 by comparing the measured cross section ( σ − 1 n exp = 61 ± 6 mb ) with a distorted wave impulse approximation calculation. Such a large occupancy for the neutron 0 d 5 / 2 orbital is in line with the N = 16 shell closure in 24O.

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.

Neutron-proton pairing correlations are investigated in detail via $np$ transfer reactions in $N=Z\phantom{\rule{4pt}{0ex}}sd$-shell nuclei. In particular, we study the cross-section ratio of the lowest ${0}^{+}$ and ${1}^{+}$ states as an observable to quantify the interplay between $T=0$ (isoscalar) and $T=1$ (isovector) pairing strengths. The experimental results are compared to second-order distorted-wave Born approximation calculations with proton-neutron amplitudes obtained in the shell-model formalism using the universal $sd$-shell interaction B. Our results suggest underestimation of the nonneglible isoscalar pairing strength in the shell-model descriptions at the expense of the isovector channel.

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.

Recent investigations of exotic nuclei with $N=32$ and $34$ have highlighted the presence of sizable subshell closures at these neutron numbers that are absent in stable isotones. Indeed, the development of the shell gap at $N=32$ is now well established from studies along the calcium, titanium, and chromium isotopic chains and, more recently, below the $Z=20$ core in potassium and argon isotones. The onset of a new subshell closure at $N=34$ was reported in $^{54}$Ca owing to the relatively high energy of its first $2^{+}$ state. On the theoretical side, the development of these neutron subshell gaps has been discussed, for example, in the framework of tensor-force-driven shell evolution; as protons are removed from the $\pi f_{7/2}$ orbital, the $\nu f_{5/2}$ state becomes progressively less bound and shifts up in energy relative to the $\nu p_{3/2}$--$\nu p_{1/2}$ spin-orbit partners. However, it was also reported that no significant $N=34$ subshell gap exists in titanium, despite the fact that an inversion of the $\nu f_{5/2}$ and $\nu p_{1/2}$ orbitals has been noted. Thus, the strength of the $N=34$ subshell closure in the scandium isotopes, which lie between calcium and titanium, provides additional insight on the migration of the $\nu f_{5/2}$ orbital in exotic nuclei. In the present work, the low-lying structures of the neutron-rich isotopes $^{54}$Sc, $^{55}$Sc, and $^{56}$Sc---investigated using in-beam $\gamma$-ray spectroscopy with fast radioactive projectiles---will be presented, and the evolution of the $N=34$ subshell closure will be further examined. The results will be compared to modern shell-model calculations applied within the $pf$ shell.

The two odd-even fluorine isotopes $^{27,29}\mathrm{F}$ were studied via in-beam $\ensuremath{\gamma}$-ray spectroscopy at the RIKEN Radioactive Isotope Beam Factory. A secondary beam of $^{30}\mathrm{Ne}$ was used to induce one-proton and one-proton--two-neutron removal reactions on carbon and polyethylene targets at midtarget energies of 228 MeV/$u$. Excited states were observed at 915(12) keV for $^{27}\mathrm{F}$ and at 1080(18) keV for $^{29}\mathrm{F}$. Both were assigned a $1/{2}_{1}^{+}$ spin and parity. The low transition energy for $^{29}\mathrm{F}$ largely disagrees with shell model predictions restricted to the $sd$ model space. Calculations using effective interactions that include the neutron $pf$ shell indicate that the $N=20$ gap is quenched for $^{29}\mathrm{F}$, thus extending the ``island of inversion'' to isotopes with proton number $Z=9$. Variations of the $N=20$ gap further reveal a strong correlation to the $1/{2}_{1}^{+}$ level energy in $^{29}\mathrm{F}$ and suggest a persistent reduced neutron gap for $^{28}\mathrm{O}$.

The elastic scattering and breakup reactions of the halo nucleus $^{11}\mathrm{Be}$ on deuterons at an incident energy of $26.9A$ MeV are reported for the first time. Special attention has been paid to the determination and subtraction of the proton contaminations in the deuterated polyethylene ${({\mathrm{CD}}_{2})}_{n}$ target (where ${\mathrm{D}}_{2}$ denotes $^{2}\mathrm{H}_{2}$). The cross sections for elastic scattering are analyzed with the systematic optical potentials of Daehnick et al. and DA1p, as well as with single-folding potentials, derived from the Jeukenne-Lejeune-Mahaux effective nucleon-nucleon interaction. An extended version of the continuum-discretized coupled-channels (XCDCC) formalism, including dynamic core excitation (DCX) effects, is applied to analyze the elastic scattering and breakup data. Comparisons of the full XCDCC calculation with that omitting DCX effects indicate that the core excitation plays a remarkable role in reproducing breakup reactions of $^{11}\mathrm{Be}+d$.

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.

We have measured for the first time the charge-changing cross sections $({\ensuremath{\sigma}}_{\text{CC}})$ of $^{12\text{--}16}\mathrm{C}$ on a $^{12}\mathrm{C}$ target at energies below $100A$ MeV. To analyze these low-energy data, we have developed a finite-range Glauber model with a global parameter set within the optical-limit approximation which is applicable to reaction cross section $({\ensuremath{\sigma}}_{\text{R}})$ and ${\ensuremath{\sigma}}_{\text{CC}}$ measurements at incident energies from $10A$ to $2100A$ MeV. Adopting the proton-density distribution of $^{12}\mathrm{C}$ known from the electron-scattering data, as well as the bare total nucleon-nucleon cross sections and the real-to-imaginary-part ratios of the forward proton-proton elastic scattering amplitude available in the literatures, we determine the energy-dependent slope parameter ${\ensuremath{\beta}}_{pn}$ of the proton-neutron elastic differential cross section so as to reproduce the existing ${\ensuremath{\sigma}}_{\text{R}}$ and interaction cross-section data for $^{12}\mathrm{C}+\phantom{\rule{4pt}{0ex}}^{12}\mathrm{C}$ over a wide range of incident energies. The Glauber model thus formulated is applied to calculate the ${\ensuremath{\sigma}}_{\text{R}}$'s of $^{12}\mathrm{C}$ on a $^{9}\mathrm{Be}$ and $^{27}\mathrm{Al}$ targets at various incident energies. Our calculations show excellent agreement with the experimental data. Applying our model to the ${\ensuremath{\sigma}}_{\text{R}}$ and ${\ensuremath{\sigma}}_{\text{CC}}$ for the so-called neutron-skin $^{16}\mathrm{C}$ nucleus, we reconfirm the importance of measurements at incident energies below $100A$ MeV. The proton root-mean-square radii of $^{12\text{--}16}\mathrm{C}$ are extracted using the measured ${\ensuremath{\sigma}}_{\text{CC}}$'s and the existing ${\ensuremath{\sigma}}_{\text{R}}$ data. The results for $^{12\text{--}14}\mathrm{C}$ are consistent with the values from the electron scatterings, demonstrating the feasibility, usefulness of the ${\ensuremath{\sigma}}_{\text{CC}}$ measurement, and the present Glauber model.

Atomic nuclei are finite quantum systems composed of two distinct types of fermion--protons and neutrons. In a manner similar to that of electrons orbiting in an atom, protons and neutrons in a nucleus form shell structures. In the case of stable, naturally occurring nuclei, large energy gaps exist between shells that fill completely when the proton or neutron number is equal to 2, 8, 20, 28, 50, 82 or 126 (ref. 1). Away from stability, however, these so-called 'magic numbers' are known to evolve in systems with a large imbalance of protons and neutrons. Although some of the standard shell closures can disappear, new ones are known to appear. Studies aiming to identify and understand such behaviour are of major importance in the field of experimental and theoretical nuclear physics. Here we report a spectroscopic study of the neutron-rich nucleus (54)Ca (a bound system composed of 20 protons and 34 neutrons) using proton knockout reactions involving fast radioactive projectiles. The results highlight the doubly magic nature of (54)Ca and provide direct experimental evidence for the onset of a sizable subshell closure at neutron number 34 in isotopes far from stability.

The triple α reaction rate in stars is quite important in many astrophysical scenarios including the stellar evolution and carbon synthesis in stars. Recently the non-resonant triple α reaction rate has been reevaluated using a calculation with the continuum-discretized coupled-channels (CDCC) method, which dramatically increased the rate at low temperature compared to the widely-used NACRE compilation. Since the enhancement influences strongly on astrophysical model simulations, we have planned an experiment for drawing conclusion on the non-resonant triple α reaction rate at low temperature by measuring the three-α continuum state in 12C. We report the present situation of the experiment.

Tensor correlations in 4He were studied via the (p, dp) reaction at the incident energy of 392 MeV with a focus on spin configurations of correlated pn pairs in 4He at high relative momenta \({(P_{\rm rel}^{\rm cor})}\). The preliminary results show that the correlated pn pair at \({P_{\rm rel}^{\rm cor} = 310 {\rm MeV/c}}\) predominantly has the channel spin S = 1, which is consistent with the characteristics of tensor correlations.

The 16C nucleus has been investigated by the neutron knockout reaction of 17C on a liquid hydrogen target. Applying the invariant mass method in inverse kinematics and γ-ray spectroscopy, the energy spectrum was reconstructed by triple-coincidence measurement, in which neutrons, charged fragments, and γ rays from the decay of the reaction residue (16C*) were detected. A peak at 0.47 MeV was observed in the invariant mass spectrum in coincidence with a peak at 0.74 MeV in the γ-ray spectrum, which indicates the presence of an unbound state with an excitation energy of 5.46 MeV. Comparison of the experimental cross section with the value derived by a theoretical calculation provided evidence that the spin-parity of this state is 2−.

Spectroscopy for neutron-rich nuclei 9He and 12Be has been performed by means of heavy-ion double charge exchange (HIDCX) (18O, 18Ne) reaction on stable target nuclei 9Be and 12C, respectively. Several clear peaks in 12Be at low excitation energy region even above neutron separation energy have been observed in one-shot measurement, whereas no prominent signals of 9He have been observed owing to the small cross section. It is shown that the HIDCX reaction is a new powerful spectroscopic tool for study of unstable neutron-rich nuclei.

The neutron-rich nucleus Cd132 has been studied at the RIKEN Radioactive Isotope Beam Factory using in-beam γ-ray spectroscopy with two-proton removal reactions from Sn134. A γ-ray transition was observed at 618(8) keV and was assigned to the 21+→0g.s.+ decay. The 21+ state provides the first spectroscopic information from the even-even nuclei located in the region "southeast" of the doubly magic nucleus Sn132. By comparing with the 21+ excitation energies in the semimagic nuclei Sn134 and Cd130, it is found that neutron excitations dominate the 21+ state in Cd132, in a similar manner to Te136. The results are discussed in terms of proton-neutron configuration mixing. © 2016 American Physical Society.

The proton-proton momentum correlation functions ($C_{pp}(q)$) for kinematically complete decay channels of $^{23}$Al $\rightarrow$ p + p + $^{21}$Na and $^{22}$Mg $\rightarrow$ p + p + $^{20}$Ne have been measured at the RIKEN RI Beam Factory. From the very different correlation strength of $C_{pp}(q)$ for $^{23}$Al and $^{22}$Mg, the source size and emission time information were extracted from the $C_{pp}(q)$ data by assuming a Gaussian source profile in the correlation function calculation code (CRAB). The results indicated that the mechanism of two-proton emission from $^{23}$Al was mainly sequential emission, while that of $^{22}$Mg was mainly three-body simultaneous emission. By combining our earlier results of the two-proton relative momentum and the opening angle, it is pointed out that the mechanism of two-proton emission could be distinguished clearly.

The change in the configuration of valence protons between the initial and final states in the neutrinoless double-$\beta$ decay of $^{130}$Te $\rightarrow$ $^{130}$Xe and of $^{136}$Xe $\rightarrow$ $^{136}$Ba has been determined by measuring the cross sections of the ($d$,$^3$He) reaction with 101-MeV deuterons. Together with our recent determination of the relevant neutron configurations involved in the process, a quantitative comparison with the latest shell-model and interacting-boson-model calculations reveals significant discrepancies. These are the same calculations used to determine the nuclear matrix elements governing the rate of neutrinoless double-$\beta$ decay in these systems.

Background: For the deeply bound one-nucleon removal at intermediate energies using a $^{9}\text{Be}$ or $^{12}\text{C}$ target, a strong reduction of cross section was observed relative to the prediction of eikonal theoretical model. The large disagreement has not been explained and the systematic trend is inconsistent with results from transfer reactions. The recently observed asymmetric parallel momentum distribution of the knockout residue indicates the significant dissipative core-target interaction in the knockout reaction with a composite target, implying new reaction mechanisms beyond the eikonal reaction descriptions.Purpose: To investigate the reaction mechanism for deeply bound nucleon removal at intermediate energies.Method: Neutron removal from $^{14}\text{O}$ using a $^{12}\text{C}$ target at 60 MeV/nucleon was performed. Nucleon knockout cross sections were measured. The unbound excited states of $^{13}\text{O}$ were reconstructed by using the invariant mass method with the residues and the associated decay protons measured in coincidence. The measured cross sections are compared with an intra-nuclear cascade (INC) prediction.Results: The measured cross section of ($^{14}\text{O}$, $^{11}\text{C}$) is 60(9) mb, which is 3.5 times larger than that of ($^{14}\text{O}$, $^{13}\text{O}$) channel. This $2pn$-removal cross section is consistent with INC prediction, which is 66 mb with the main contribution being non-direct reaction processes. On the other hand, the upper limit of the cross section for one-neutron removal from $^{14}\text{O}$ followed by proton evaporation is 4.6(20) mb, integrated up to 6 MeV above the proton separation energy of $^{13}\text{O}$. The calculated total cross section for such reaction processes by the INC model is 2.5 mb, which is within the measured upper limit.Conclusions: The data provide the first constraint on the role of core excitation and evaporation processes in deeply bound nucleon removal from asymmetric nuclei. The experiment results suggest that non-direct reaction processes, which are not considered in the eikonal model, play an important role in deeply bound nucleon removal from asymmetric nuclei at intermediate energies.

With new-generation facilities able to provide beams of very unstable nuclei, one can explore how the traditional magic numbers and shell closures become fragile and break down in neutron-rich regions of the chart of nuclides. One important such region is near ${}^{32}$Mg, the so-called ''island of inversion'', suggesting a rearrangement of the nuclear shell structure. This study reports on $B(E2)$ transition probabilities for the most neutron-rich nuclei yet measured in that region, ${}^{30}$Ne and ${}^{36}$Mg. The results help map the evolution and extent of anomalous shell structure toward the neutron drip line.

The elastic scattering and breakup of the halo nucleus $^{11}\mathrm{Be}$ on protons at an incident energy of $26.9A$ MeV have been measured. The $^{11}\mathrm{Be}+p$ elastic scattering cross sections at various energies, including the present one, are systematically analyzed with the Chapel Hill 89 (CH89) and Koning-Delaroche (KD) global optical model potentials (OMPs), and the corresponding normalization factors are obtained. An extended version of the continuum-discretized coupled-channels (XCDCC) formalism, including dynamic core excitation effects, is applied to analyze the elastic scattering and breakup data. It is found that the core excitation plays a moderate role in the elastic scattering and breakup reaction of the halo nucleus $^{11}\mathrm{Be}$, being consistent with previous results at higher energies.

The low-lying level structures of nuclei in the vicinity of $^{78}\mathrm{Ni}$ were investigated using in-beam $\ensuremath{\gamma}$-ray spectroscopy to clarify the nature of the nuclear magic numbers $Z=28$ and $N=50$ in systems close to the neutron drip line. Nucleon knockout reactions were employed to populate excited states in $^{80}\mathrm{Zn}$ and $^{82}\mathrm{Zn}$. A candidate for the ${4}_{1}^{+}$ level in $^{80}\mathrm{Zn}$ was identified at 1979(30) keV, and the lifetime of this state was estimated to be ${136}_{\ensuremath{-}67}^{+92}$ ps from a line-shape analysis. Moreover, the energy of the ${2}_{1}^{+}$ state in $^{82}\mathrm{Zn}$ is reported to lie at 621(11) keV. The large drop in the ${2}_{1}^{+}$ energy at $^{82}\mathrm{Zn}$ indicates the presence of a significant peak in the $E({2}_{1}^{+})$ systematics at $N=50$. Furthermore, the $E({4}_{1}^{+})/E({2}_{1}^{+})$ and $B(E2;{4}_{1}^{+}\ensuremath{\rightarrow}{2}_{1}^{+})/B(E2;{2}_{1}^{+}\ensuremath{\rightarrow}{0}_{\mathrm{g}.\mathrm{s}.}^{+})$ ratios in $^{80}\mathrm{Zn}$ were deduced to be $1.32(3)$ and $1.{12}_{\ensuremath{-}60}^{+80}$, respectively. These results imply that $^{80}\mathrm{Zn}$ can be described in terms of two-proton configurations with a $^{78}\mathrm{Ni}$ core and are consistent with a robust $N=50$ magic number along the Zn isotopic chain. These observations, therefore, indicate a persistent $N=50$ shell closure in nuclei far from the line of $\ensuremath{\beta}$ stability, which in turn suggests a doubly magic structure for $^{78}\mathrm{Ni}$.

Interaction cross sections (sigma(1)) for Me isotopes from the stability line to the vicinity of the neutron drip line have been measured at around 240 MeV/nucleon using BigRIPS at RIBF, RIKEN, The sigma(1) for Ne27-32 in every case exceed the systematic mass-number dependence of sigma(1) for stable nuclei, which can be explained by considering the nuclear deformation. In particular the sigma(1) for Ne-29 and Ne-31 are significantly greater than those of their neighboring nuclides. These enhancements of sigma(1) for Ne-29 and Ne-31 cannot be explained by a single-particle model calculation under the assumption that the valence neutron of Ne-29 (Ne-31) occupies the 0d(3/2) (0f(7/2)) orbital, as expected from the standard spherical shell ordering. The present data suggest an s dominant halo structure of Ne-29 and s- or p-orbital halo in Ne-31. (C) 2011 Elsevier B.V. All rights reserved.