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The 11C(α,p)14N reaction is an important α-induced reaction competing with β-limited hydrogen-burning processes in high-temperature explosive stars. We directly measured its reaction cross sections both for the ground-state transition (α,p0) and the excited-state transitions (α,p1) and (α,p2) at relevant stellar energies 1.3-4.5 MeV by an extended thick-target method featuring time of flight for the first time. We revised the reaction rate by numerical integration including the (α,p1) and (α,p2) contributions and also low-lying resonances of (α,p0) using both the present and the previous experimental data which were totally neglected in the previous compilation works. The present total reaction rate lies between the previous (α,p0) rate and the total rate of the Hauser-Feshbach statistical model calculation, which is consistent with the relevant explosive hydrogen-burning scenarios such as the νp process. [ABSTRACT FROM AUTHOR]

In the standard Big-Bang nucleosynthesis (BBN) model, the primordial 7Li abundance is overestimated by about a factor of 2 to 3 compared to astronomical observations; this is the so-called pending cosmological lithium problem. The 7Be(n,α)4He reaction was regarded as the secondary important reaction in affecting the 7Li abundance by destructing the 7Be nucleus in BBN. However, the reaction rate of 7Be(n,α)4He has not been well studied so far. This reaction rate was first estimated by Wagoner in 1969, which has been primarily adopted in the current BBN simulations. This simple estimate involved only a direct reaction contribution, but the resonant component should also be considered according to the later experimental results. In the present work, we revised this rate based on the indirect cross-section data available for the 4He(α,n)7Be and 4He(α,p)7Li reactions by applying the charge symmetry and the principle of detailed balance. Our new result shows that the previous rate (acting as an upper limit) is overestimated by about a factor of ten. The BBN simulation shows that the present rate leads to a 1.2% increase in the final 7Li abundance compared with the result using the Wagoner rate and, hence, the present rate even worsens the 7Li problem. By the present estimation, the role of 7Be(n,α)4He in destroying 7Be is weakened from the second most importance to the third and, in turn, the 7Be(d,p)24He reaction becomes of secondary importance in destroying 7Be. [ABSTRACT FROM AUTHOR]

Background: Type I x-ray bursts are the most frequently observed thermonuclear explosions in the galaxy, resulting from thermonuclear runaway on the surface of an accreting neutron star. The 30S(α,p) reaction plays a critical role in burst models, yet insufficient experimental information is available to calculate a reliable, precise rate for this reaction. Purpose: Our measurement was conducted to search for states in 34Ar and determine their quantum properties. In particular, natural-parity states with large α-decay partial widths should dominate the stellar reaction rate. Method: We performed the first measurement of 30S+α resonant elastic scattering up to a center-of-mass energy of 5.5 MeV using a radioactive ion beam. The experiment utilized a thick gaseous active target system and silicon detector array in inverse kinematics. Results: We obtained an excitation function for 30S(α,α) near 150° in the center-of-mass frame. The experimental data were analyzed with R-matrix calculations, and we observed three new resonant patterns between 11.1 and 12.1 MeV, extracting their properties of resonance energy, widths, spin, and parity. Conclusions: We calculated the resonant thermonuclear reaction rate of 30S(α,p) based on all available experimental data of 34Ar and found an upper limit about one order of magnitude larger than a rate determined using a statistical model. The astrophysical impact of these two rates has been investigated through one-zone postprocessing type I x-ray burst calculations. We find that our new upper limit for the 30S(α,p)33Cl rate significantly affects the predicted nuclear energy generation rate during the burst. [ABSTRACT FROM AUTHOR]

Background: The 14O(α,p) 17F reaction plays an important role as the trigger reaction for the x-ray burst. Purpose: The direct measurement of 14O(α,p) 17F was made for studying the resonant states in 18Ne and determining the reaction rate of 14O(α,p) 17F at astrophysical temperatures. Methods: The differential cross section of the 14O(α,p) 17F reaction was measured using a 2.5-MeV/u 14O radioactive beam and the thick target method in inverse kinematics. Three sets of ΔE-E Si telescopes were installed and coincidence measurements were performed. We analyzed single-proton decay events using the time-of-flight (TOF) information of the recoiling protons. Results: The excitation function of 14O(α,p) 17F was acquired for excitation energies between 7.2 and 10.4 MeV in 18Ne by considering the two channels which decay to the ground state and first excited state of 17F. Several new, as well as previously known, states in 18Ne were observed and their resonance parameters were extracted from R-matrix analysis. The contributions of four resonances over the excitation energy range, 7 < Ex < 8.2 MeV, to the 14O(α,p) 17F reaction rate were calculated. Conclusions: We observed very strong single-proton decay events, but did not observe strong double-proton decay events as in a previous study by Fu et al. The reaction rates contributed by the 7.35-, 7.58-, and 7.72-MeV states were estimated to be dominant at temperatures T9 > 2. Among these three states, the 7.35-MeV state was found to enhance the reaction rate by a factor of 10 greater than the other two resonance states. [ABSTRACT FROM AUTHOR]

Measurement of nuclear cross sections at astrophysical energies involving unstable species is one of the most challenging tasks in experimental nuclear physics. The use of indirect methods is often unavoidable in this scenario. In this paper the Trojan horse method is applied for the first time to a radioactive ion beam-induced reaction studying the 18F(p,α)15O process at low energies relevant to astrophysics via the three-body reaction ²H(18F,α15O)n. The knowledge of the 18F(p,α)15O reaction rate is crucial to understand the nova explosion phenomena. The cross section of this reaction is characterized by the presence of several resonances in Ne19 and possibly interference effects among them. The results reported in literature are not satisfactory and new investigations of the 18F(p,α)15O reaction cross section will be useful. In the present work the spin-parity assignments of relevant levels have been discussed and the astrophysical S factor has been extracted considering also interference effects. [ABSTRACT FROM AUTHOR]

Background: The properties of resonances in 26Si are important to better constrain the 25Al(p,γ)26Si reaction rate relevant to the synthesis of galactic 26Algs and energy generation in explosive stellar environment at higher temperature. Purpose: 21Al + p elastic scattering was measured to further constrain and investigate disagreements in resonance parameters for the high-lying excited states of 26Si with high statistics and without background contamination within the target. Methods: The experiment was performed by bombarding a thick H2 target with an 25Al radioactive ion beam. The resonances at excitation energies of 6.6-8.3 MeV in the 26Si compound nucleus were studied at the low-energy radioactive-ion beam facility CRIB (Center for Nuclear Study Radioactive Ion Beam separator) at the University of Tokyo. Results: Six resonant states were observed and their resonance parameters were extracted by an R-matrix analysis. Our resonance parameters for two levels are in good agreement with the results of previous studies, while for four others, excitation energy, proton partial width, and spin-parity assignment disagree with the results of recent study via elastic scattering of 25Al + p. Conclusion: The parameters of resonant states in 26Si determined in the present work for the 25Al(p,γ)26Si reaction rate are consistent with that of the previous result, solving spin-parity assignment discrepancies between experiments, relevant at higher temperatures. [ABSTRACT FROM AUTHOR]

The 14O(αp)17F reaction is one of the key reactions involved in the breakout from the hot-CNO cycle to the rp-process in type-I x-ray bursts (XRBs). The resonant properties in the compound nucleus 18Ne have been investigated through resonant elastic scattering of 17F+p. The radioactive 17F beam was separated by the Center for Nuclear Study radioactive ion beam separator (CRIB) and bombarded a thick H2 gas target at 3.6 MeV/nucleon. The recoiling hght particles were measured by three Δ E-E silicon telescopes at laboratory angles of Θ1ab ≈3°, 10°, and 18°. Five resonances at Ex = 6.15, 6.28, 6.35, 6.85, and 7.05 MeV were observed in the excitation functions, and their spin-parities have been determined based on an R-matrix analysis. In particular, Jπ = 1- was hrmly assigned to the 6.15-MeV state which dominates the thermonuclear 140 (αp)17F rate below 2 GK. As well, a possible new excited state in 18Ne was observed at Ex = 6.85 ± 0 .1 1 MeV with tentative 7 = 0 assignment. This state could be the analog state of the 6.880 MeV (0-) level in the mirror nucleus 180, or a bandhead state (0+) of the six-particle four-hole (6p-4h) band. A new thermonuclear 140 (α,p)17F rate has been determined, and the astrophysical impact of multiple recent rates has been examined using an XRB model. Contrary to previous expectations, we find only a modest impact on predicted nuclear energy generation rates from using reaction rates differing by up to several orders of magnitude. [ABSTRACT FROM AUTHOR]

The 18Ne(α,p)21Na reaction is thought to be one of the key breakout reactions from the hot CNO cycles to the rp process in type I x-ray bursts. In this work, the resonant properties of the compound nucleus 22Mg have been investigated by measuring the resonant elastic scattering of 21Na + p. An 89-MeV 21Na radioactive beam delivered from the CNS Radioactive Ion Beam Separator bombarded an 8.8 mg/cm² thick polyethylene (CH2)n target. The 21Na beam intensity was about 2 × 105 pps, with a purity of about 70% on target. The recoiled protons were measured at the center-of-mass scattering angles of θc.m. ≈ 175.2°, 152.2°, and 150.5° by three sets of ΔE-E telescopes, respectively. The excitation function was obtained with the thick-target method over energies Ex(22Mg) = 5.5-9.2 MeV. In total, 23 states above the proton-threshold in 22Mg were observed, and their resonant parameters were determined via an R-matrix analysis of the excitation functions. We have made several new Jα assignments and confirmed some tentative assignments made in previous work. The thermonuclear 18Ne(α,p)21Na rate has been recalculated based on our recommended spin-parity assignments. The astrophysical impact of our new rate has been investigated through one-zone postprocessing x-ray burst calculations. We find that the 18Ne(α,p)21Na rate significantly affects the peak nuclear energy generation rate, reaction fluxes, and onset temperature of this breakout reaction in these astrophysical phenomena. [ABSTRACT FROM AUTHOR]

The 18Ne(a,p)21Na reaction provides a pathway for breakout from the hot CNO cycles to the rp process in type-I x-ray bursts. To better determine this astrophysical reaction rate, the resonance parameters of the compound nucleus 22Mg have been investigated by measuring the resonant elastic scattering of 21Na+p. An 89 MeV 21Na radioactive ion beam was produced at the CNS Radioactive Ion Beam Separator and bombarded an 8.8 mg/cm2 thick polyethylene target. The recoiled protons were measured at scattering angles of θc.m.~175° and 152¯ by three θE-E silicon telescopes. The excitation function was obtained with a thick-target method over energies Ex(22Mg) = 5.5-9.2 MeV. The resonance parameters have been determined through an R-matrix analysis. For the first time, the Jπ values for ten states above the a threshold in 22Mg have been experimentally determined in a single consistent measurement. We have made three new Jπ assignments and confirmed seven of the ten tentative assignments in the previous work. The 18Ne(a,p)21Na reaction rate has been recalculated, and the astrophysical impact of our new rate has been investigated through one-zone postprocessing x-ray burst calculations. We find that the 18Ne(a,p)21Na rate significantly affects the peak nuclear energy generation rate and the onset temperature of this breakout reaction in these phenomena. [ABSTRACT FROM AUTHOR]

Background: The uncertainty in the 29P(p, ɣ )30S reaction rate over 0.1 ≤ T ≤ 1.3GK was previously determined to span approximately four orders of magnitude due to the uncertain location of two previously unobserved 3+ and 2+ resonances in the Ex = 4.7-4.8 MeV region in 30S. Therefore, the abundances of silicon isotopes synthesized in novae, which are relevant for the identification of presolar grains of putative nova origin, were uncertain by a factor of 3. Purpose: (a) To investigate the level structure of 30S above the proton threshold [4394.9(7) keV] via chargedparticle spectroscopy using the 32S(p, t)30S reaction and in-beam y-ray spectroscopy using the 28Si(³He, ny)30S reaction to calculate the 29P(p, ɣ)30S reaction rate, (b) To explore the impact of this rate on the abundances of silicon isotopes synthesized in novae. Methods: Differential cross sections of the 32S(p, t)30S reaction were measured at 34.5 MeV. Distorted-wave Bom approximation calculations were performed to constrain the spin-parity assignments of the observed levels, including the two astrophysically important levels. An energy-level scheme was deduced from ɣ-ɣ coincidence measurements using the 28Si(³He, nɣ)30S reaction. Spin-parity assignments based on measurements of ɣ-ray angular distributions and ɣ-ɣ directional correlation from oriented nuclei were made for most of the observed levels of 30S. Results: The resonance energies corresponding to the states with 4.5 MeV ≤ Ex ≤ 6 MeV, ncluding the two astrophysically important states predicted previously, are measured with significantly better precision than before. The spin-parity assignments of both astrophysically important resonances are confirmed. The uncertainty in the rate of the 29P(p, ɣ)30S reaction is substantially reduced over the temperature range of interest. Finally, the influence of this rate on the abundance ratios of silicon isotopes synthesized in novae are obtained via ID hydrodynamic nova simulations. Conclusions: The uncertainty in the 29P(p, ɣ)30S reaction rate is reduced to the point that it no longer affects the silicon isotopic abundance ratios significantly, and, thus, the results of our nova hydrodynamic simulation for the nucleosynthesis in the Si-Ca mass region are more reliable than before. [ABSTRACT FROM AUTHOR]

Background: The resonance structure in 11C is of particular interest with regard to the astrophysical 7Be(α,γ) reaction, relevant at high temperature, and to the α-cluster structure in 11C. Purpose: The measurement was made to determine the unknown resonance parameters for the high excited states of 11C. In particular, the α-decay width can be useful information to discuss the α-cluster structure in 11C. Methods: New measurements of 7Be+α resonant scattering and the 7Be(α,p)10B reaction in inverse kinematics were performed for center-of-mass energy up to 5.5 MeV, and the resonances at excitation energies of 8.9-12.7 MeV in the compound 11C nucleus were studied. Inelastic scattering of 7Be+α and the 7Be(α,p1)10B* reaction were also studied with a simultaneous γ-ray measurement. The measurements were performed at the low-energy radioactive ion beam facility CRIB (CNS Radioactive Ion Beam separator) of the Center for Nuclear Study, the University of Tokyo. Results: We obtained excitation functions of 7Be(α,α0)7Be (elastic scattering), 7Be(α,α1)7Be* (inelastic scattering), 7Be(α,p0)10B, and 7Be(α,p1)10B*. Many resonances including a new one were observed and their parameters were determined by using an R-matrix analysis. Conclusions: The resonances we observed possibly enhance the 7Be(α,γ) reaction rate but with a smaller magnitude than the lower-lying resonances. A new negative-parity cluster band, similar to the one previously suggested in the mirror nucleus 11B, is proposed. [ABSTRACT FROM AUTHOR]

The evolution of massive stars with very low-metallicities depends critically on the amount of CNO nuclides which they produce. The 12N(p, γ)130 reaction is an important branching point in the rap processes, which are believed to be alternative paths to the slow 3a process for producing CNO seed nuclei and thus could change the fate of massive stars. In the present work, the angular distribution of the 2H(12N, 130)n proton transfer reaction at Ec.m. = 8.4 MeV has been measured for the first time. Based on the Johnson-Soper approach, the square of the asymptotic normalization coefficient (ANC) for the virtual decay of 13Og s. --> 12N 4- p was extracted to be 3.92 ± 1.47 fm-' from the measured angular distribution and utilized to compute the direct component in the 12N(p, γ)130 reaction. The direct astrophysical S factor at zero energy was then found to be 0.39 ±0.15 keV b. By considering the direct capture into the ground state of 130, the resonant capture via the first excited state of 130 and their interference, we determined the total astrophysical S factors and rates of the 12N(p, γ130 reaction. The new rate is two orders of magnitude slower than that from the REACLIB compilation. Our reaction network calculations with the present rate imply that 12N(p, γ)130 will only compete successfully with the ß+ decay of 12N at higher (~2 orders of magnitude) densities than initially predicted. [ABSTRACT FROM AUTHOR]

Proton resonant states in 27P were studied by the resonant elastic scattering of 26Si + p with a 26Si radioactive ion beam bombarding a thick H2 gas target with the inverse kinematics method. The properties of these resonance states are important to better constrain the production rates of the 26Si(p,γ)27P reaction. This is one of the astrophysically important reactions needed to understand proton-rich nucleosynthesis such as the galactic production of 26Al and energy generation in explosive stellar environments. Although there are recent studies on the resonant structure in 27P, large uncertainties remain, and only a few levels are known. In this work, resonant states were observed over the excitation energies range of 2.3 to 3.8 MeV with high statistics and without background contamination within the target. The resonance parameters were extracted by an R-matrix analysis of the excitation function. The 26Si(p,γ )27P stellar reaction rate has been evaluated, including high-lying resonances found in this work. [ABSTRACT FROM AUTHOR]

Neutron single-particle states in the neutron-rich nucleus 35Si, which is located beside the N = 20 shell breaking nucleus 32Mg, were investigated through their isobaric analog resonances. The excitation function for 34Si+p elastic scattering was measured around 0d in the laboratory frame by the thick target inverse kinematics method with a 34Si beam around 5 MeV/nucleon and a thick polyethylene target. Eight resonances were successfully observed. Angular momenta and proton and total widths of the resonances were assigned using R-matrix analysis. With the help of information of the β decay study, six isobaric analog resonances were identified. Spectroscopic factors and spin-parities of the corresponding parent states in 35Si are presented. [ABSTRACT FROM AUTHOR]

25A1 + p elastic scattering in inverse kinematics was measured to explore the level structure of 26Si above its proton threshold. The 2H(24Mg, n) 25A1 reaction was used to produce a 3.4 MeV/nucleon 25A1 radioactive beam with intensities of about 106 ions per second on target. By using a thick target of (CH2)n, a center-of-mass energy range of 3 MeV was scanned, reaching up to about 8.5 MeV in excitation energy in 26Si. This energy range covered the region of importance for the 25Al(p, &ggr;)26Si at temperatures characteristic of explosive nucleosynthesis. Level parameters of six strong s-wave 25Al + p resonances in 26Si were extracted from fits to the measured excitation functions using the R-matrix formalism. Two new levels have been discovered, while for two others, our spin-parity assignments disagree with the results of some previous studies. Lastly, our resonance parameters for the remaining two levels are in good agreement with past experimental work, and with recent shell-model calculations. [ABSTRACT FROM AUTHOR]

A new measurement of α resonant scattering on 7Li was performed over the excitation energy of 10.2-13.0 MeV in 11B at the low-energy RI beam facility CNS Radioactive Ion Beam separator (CRIB) of the Center for Nuclear Study (CNS), University of Tokyo. The excitation function of 7Li+α at 180° in the center-of-mass system was successfully measured for the first time with the inverse kinematics method, providing important information on the α cluster structure in 11B and the reaction rate of 7Li(α,γ), which is relevant to the 11B production in the ? process in core-collapse supernovae. The excitation function of the 7Li(α,p) reaction cross section for 11.7-13.1 MeV was also measured. [ABSTRACT FROM AUTHOR]

The structure of proton-unbound 30S states strongly determines the thermonuclear 29P(p,γ)30S reaction rate at temperatures characteristic of explosive hydrogen burning in classical novae and type I x-ray bursts. Specifically, the rate had been previously predicted to be dominated by two low-lying, unobserved, levels in the Ex= 4.7-4.8 MeV region, with spin and parity assignments of 3+ and 2+. In recent experimental work, two candidate levels were observed with energies of 4.699 MeV and 4.814 MeV, but no experimental information on their spins and parities was obtained. We have performed an in-beam γ-ray spectroscopy study of 30S with the 28Si(3He, nγ)30S reaction. By constructing the decay schemes of proton-unbound states with a γ-γ coincidence analysis of their decay γ rays, their Jπ values were inferred from a comparison to the known decay schemes of the corresponding mirror states in 30Si. For the two aforementioned states, our results strongly corroborate the spin-parity assignments assumed in recent evaluations of the 29P(p,γ)30S reaction rate. [ABSTRACT FROM AUTHOR]

A detailed feasibility study on deducing the high-lying single particle components (HLSPCs), which are important but used to be ignored, in the ground and low-lying excited states of even-even light nuclei is performed by analyses of (p,d) reactions with 12C, 24Mg, 28Si, and 40Ca targets at 51.93 MeV. Coupled reaction channel analyses have been made for (p,d) transitions to the j-forbidden excited states in 11C (5-/2; 4.32 MeV), 23Mg (7+/2; 2.05 MeV), 27Si (7+/2; 2.16 MeV), and 39Ca (9-/2; 3.64 MeV), including the major allowed transition components together with direct components of HLSPCs. Spectroscopic amplitudes of the HLSPCs are deduced by fitting the angular distributions of the ground and the j-forbidden excited states simultaneously. The present analysis demonstrates for the first time that information about HLSPCs in atomic nuclei can be obtained from analysis of (p,d) reactions. [ABSTRACT FROM AUTHOR]

Masses of 52g,52mCo were measured for the first time with an accuracy of ~10 keV, an unprecedented precision reached for short-lived nuclei in the isochronous mass spectrometry. Combining our results with the previous β−γ measurements of 52Ni, the T=2, Jπ=0+ isobaric analog state (IAS) in 52Co was newly assigned, questioning the conventional identification of IASs from the β-delayed proton emissions. Using our energy of the IAS in 52Co, the masses of the T=2 multiplet fit well into the isobaric multiplet mass equation. We find that the IAS in 52Co decays predominantly via γ transitions while the proton emission is negligibly small. According to our large-scale shell model calculations, this phenomenon has been interpreted to be due to very low isospin mixing in the IAS. [ABSTRACT FROM AUTHOR]

The β-delayed one- and two-neutron emission probabilities (P&#95;{1n} and P&#95;{2n}) of 20 neutron-rich nuclei with N≥82 have been measured at the RIBF facility of the RIKEN Nishina Center. P&#95;{1n} of ^{130,131}Ag, ^{133,134}Cd, ^{135,136}In, and ^{138,139}Sn were determined for the first time, and stringent upper limits were placed on P&#95;{2n} for nearly all cases. β-delayed two-neutron emission (β2n) was unambiguously identified in ^{133}Cd and ^{135,136}In, and their P&#95;{2n} were measured. Weak β2n was also detected from ^{137,138}Sn. Our results highlight the effect of the N=82 and Z=50 shell closures on β-delayed neutron emission probability and provide stringent benchmarks for newly developed macroscopic-microscopic and self-consistent global models with the inclusion of a statistical treatment of neutron and γ emission. The impact of our measurements on r-process nucleosynthesis was studied in a neutron star merger scenario. Our P&#95;{1n} and P&#95;{2n} have a direct impact on the odd-even staggering of the final abundance, improving the agreement between calculated and observed Solar System abundances. The odd isotope fraction of Ba in r-process-enhanced (r-II) stars is also better reproduced using our new data.

The ^{13}C(α,n)^{16}O reaction is the main neutron source for the slow-neutron-capture process in asymptotic giant branch stars and for the intermediate process. Direct measurements at astrophysical energies in above-ground laboratories are hindered by the extremely small cross sections and vast cosmic-ray-induced background. We performed the first consistent direct measurement in the range of E&#95;{c.m.}=0.24 to 1.9 MeV using the accelerators at the China Jinping Underground Laboratory and Sichuan University. Our measurement covers almost the entire intermediate process Gamow window in which the large uncertainty of the previous experiments has been reduced from 60% down to 15%, eliminates the large systematic uncertainty in the extrapolation arising from the inconsistency of existing datasets, and provides a more reliable reaction rate for the studies of the slow-neutron-capture and intermediate processes along with the first direct determination of the alpha strength for the near-threshold state.

We report the first (in)elastic scattering measurement of ^{25}Al+p with the capability to select and measure in a broad energy range the proton resonances in ^{26}Si contributing to the ^{22}Mg(α,p) reaction at type I x-ray burst energies. We measured spin-parities of four resonances above the α threshold of ^{26}Si that are found to strongly impact the ^{22}Mg(α,p) rate. The new rate advances a state-of-the-art model to remarkably reproduce light curves of the GS 1826-24 clocked burster with mean deviation <9% and permits us to discover a strong correlation between the He abundance in the accreting envelope of the photospheric radius expansion burster and the dominance of ^{22}Mg(α,p) branch.

In this Letter, the observation of two previously unknown isotopes is presented for the first time: ^{72}Rb with 14 observed events and ^{77}Zr with one observed event. From the nonobservation of the less proton-rich nucleus ^{73}Rb, we derive an upper limit for the ground-state half-life of 81 ns, consistent with the previous upper limit of 30 ns. For ^{72}Rb, we have measured a half-life of 103(22) ns. This observation of a relatively long-lived odd-odd nucleus, ^{72}Rb, with a less exotic odd-even neighbor, ^{73}Rb, being unbound shows the diffuseness of the proton drip line and the possibility of sandbanks to exist beyond it. The ^{72}Rb half-life is consistent with a 5^{+}→5/2^{-} proton decay with an energy of 800-900 keV, in agreement with the atomic mass evaluation proton-separation energy as well as results from the finite-range droplet model and shell model calculations using the GXPF1A interaction. However, we cannot explicitly exclude the possibility of a proton transition between 9^{+}(^{72}Rb)→9/2^{+}(^{71}Kr) isomeric states with a broken mirror symmetry. These results imply that ^{72}Kr is a strong waiting point in x-ray burst rp-process scenarios.

The β-decay half-lives of 94 neutron-rich nuclei ^{144-151}Cs, ^{146-154}Ba, ^{148-156}La, ^{150-158}Ce, ^{153-160}Pr, ^{156-162}Nd, ^{159-163}Pm, ^{160-166}Sm, ^{161-168}Eu, ^{165-170}Gd, ^{166-172}Tb, ^{169-173}Dy, ^{172-175}Ho, and two isomeric states ^{174m}Er, ^{172m}Dy were measured at the Radioactive Isotope Beam Factory, providing a new experimental basis to test theoretical models. Strikingly large drops of β-decay half-lives are observed at neutron-number N=97 for &#95;{58}Ce, &#95;{59}Pr, &#95;{60}Nd, and &#95;{62}Sm, and N=105 for &#95;{63}Eu, &#95;{64}Gd, &#95;{65}Tb, and &#95;{66}Dy. Features in the data mirror the interplay between pairing effects and microscopic structure. r-process network calculations performed for a range of mass models and astrophysical conditions show that the 57 half-lives measured for the first time play an important role in shaping the abundance pattern of rare-earth elements in the solar system.

The cross sections of the ^{7}Be(n,α)^{4}He reaction for p-wave neutrons were experimentally determined at E&#95;{c.m.}=0.20-0.81  MeV slightly above the big bang nucleosynthesis (BBN) energy window for the first time on the basis of the detailed balance principle by measuring the time-reverse reaction. The obtained cross sections are much larger than the cross sections for s-wave neutrons inferred from the recent measurement at the n&#95;TOF facility in CERN, but significantly smaller than the theoretical estimation widely used in the BBN calculations. The present results suggest the ^{7}Be(n,α)^{4}He reaction rate is not large enough to solve the cosmological lithium problem, and this conclusion agrees with the recent result from the direct measurement of the s-wave cross sections using a low-energy neutron beam and the evaluated nuclear data library ENDF/B-VII.1.

Masses of ^{52g,52m}Co were measured for the first time with an accuracy of ∼10  keV, an unprecedented precision reached for short-lived nuclei in the isochronous mass spectrometry. Combining our results with the previous β-γ measurements of ^{52}Ni, the T=2, J^{π}=0^{+} isobaric analog state (IAS) in ^{52}Co was newly assigned, questioning the conventional identification of IASs from the β-delayed proton emissions. Using our energy of the IAS in ^{52}Co, the masses of the T=2 multiplet fit well into the isobaric multiplet mass equation. We find that the IAS in ^{52}Co decays predominantly via γ transitions while the proton emission is negligibly small. According to our large-scale shell model calculations, this phenomenon has been interpreted to be due to very low isospin mixing in the IAS.

In an experiment with the BigRIPS separator at the RIKEN Nishina Center, we observed two-proton (2p) emission from ^{67}Kr. At the same time, no evidence for 2p emission of ^{59}Ge and ^{63}Se, two other potential candidates for this exotic radioactivity, could be observed. This observation is in line with Q value predictions which pointed to ^{67}Kr as being the best new candidate among the three for two-proton radioactivity. ^{67}Kr is only the fourth 2p ground-state emitter to be observed with a half-life of the order of a few milliseconds. The decay energy was determined to be 1690(17) keV, the 2p emission branching ratio is 37(14)%, and the half-life of ^{67}Kr is 7.4(30) ms.

The half-lives of 20 neutron-rich nuclei with Z=27-30 have been measured at the RIBF, including five new half-lives of (76)Co(21.7(-4.9)(+6.5) ms), (77)Co(13.0(-4.3)(+7.2) ms), (79)Ni(43.0(-7.5)(+8.6) ms), (80)Ni(23.9(-17.2)(+26.0) ms), and (81)Cu(73.2 ± 6.8 ms). In addition, the half-lives of (73-75)Co, (74-78)Ni, (78-80)Cu, and (80-82)Zn were determined with higher precision than previous works. Based on these new results, a systematic study of the β-decay half-lives has been carried out, which suggests a sizable magicity for both the proton number Z = 28 and the neutron number N=50 in (78)Ni.

The low-lying states in ¹⁰⁶Zr and ¹⁰⁸Zr have been investigated by means of β-γ and isomer spectroscopy at the radioactive isotope beam factory (RIBF), respectively. A new isomer with a half-life of 620 ± 150 ns has been identified in ¹⁰⁸Zr. For the sequence of even-even Zr isotopes, the excitation energies of the first 2⁺ states reach a minimum at N = 64 and gradually increase as the neutron number increases up to N = 68, suggesting a deformed subshell closure at N = 64. The deformed ground state of ¹⁰⁸Zr indicates that a spherical subshell gap predicted at N = 70 is not large enough to change the ground state of ¹⁰⁸Zr to the spherical shape. The possibility of a tetrahedral shape isomer in ¹⁰⁸Zr is also discussed.

The β-decay half-lives of 38 neutron-rich isotopes from (36)Kr to (43)Tc have been measured; the half-lives of (100)Kr, (103-105)Sr, (106-108)Y, (108-110)Zr, (111,112)Nb, (112-115)Mo, and (116,117)Tc are reported here. The results when compared with previous standard models indicate an overestimation in the predicted half-lives by a factor of 2 or more in the A≈110 region. A revised model based on the second generation gross theory of β decay better predicts the measured half-lives and suggests a more rapid flow of the rapid neutron-capture process (r-matter flow) through this region than previously predicted.

The 21Na(p,gamma)22Mg reaction is expected to play an important role in the nucleosynthesis of 22Na in oxygen-neon novae. The decay of 22Na leads to the emission of a characteristic 1.275 MeV gamma-ray line. This report provides the first direct measurement of the rate of this reaction using a radioactive 21Na beam, and discusses its astrophysical implications. The energy of the important state was measured to be E(c.m.)=205.7+/-0.5 keV with a resonance strength omegagamma=1.03+/-0.16(stat)+/-0.14(sys) meV.

The reaction rate of the stellar reaction 13C(alpha,n)16O, which is currently considered to be the main neutron source for the slow (s) process at low energies, has been rederived using the direct alpha-transfer reaction 13C(6Li,d)17O leading to the subthreshold state at 6.356 MeV in 17O. The contribution of the subthreshold state is found to be much smaller than the currently accepted predictions for the main neutron source of the s process, indicating less of a role of this reaction as the neutron source for the s-process scenario in low-mass stars at the asymptotic giant branch.

The charge-exchange reaction 60Ni(13C,13N)60Co at E/A=100 MeV has been studied to locate isovector (deltaT=1) non-spin-flip (deltaS=0) giant resonances. Besides the giant dipole resonance at E(x)=8.7 MeV, another resonance has been observed at E(x)=20 MeV with a width of 9 MeV. Distorted-wave Born approximation analysis on the angular distribution clearly indicated the L=2 multipolarity, attributing the E(x)=20 MeV state to the giant isovector quadrupole resonance.