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International audience; Excited states in O13 were investigated using inelastic scattering of an E/A=69.5 MeV O13 beam off of a Be9 target. The excited states were identified in the invariant-mass spectra of the decay products. Both single-proton and sequential two-proton decays of the excited states were examined. For a number of the excited states, the protons were emitted with strong anisotropy where emissions transverse to the beam axis are favored. The measured proton-decay angular distributions were compared to predictions from distorted-wave Born-approximation calculations of the spin alignment which was shown to be largely independent of the excitation mechanism. The deduced O13 level scheme is compared to ab initio no-core shell model with continuum predictions. The lowest-energy excited states decay isotropically consistent with predictions of strong proton 1s1/2 structure. Above these states in the level scheme, we observed a number of higher-spin states not predicted within the model. Possibly these are associated with rotational bands built on deformed cluster configurations predicted by antisymmetrized molecular dynamics calculations. The spin alignment mechanism is shown to be useful for making spin assignments and may have widespread use.

The excitation energy of deformed intruder states (specifically the 2p2h bandhead) as a function of proton number Z along N=20 is of interest both in terms of better understanding the evolution of nuclear structure between spherical Ca40 and the Island of Inversion nuclei, and for benchmarking theoretical descriptions in this region. At the center of the N=20 Island of Inversion, the npnh (where n=2,4,6) neutron excitations across a diminished N=20 gap result in deformed and collective ground states, as observed in Mg32. In heavier isotones, npnh excitations do not dominate in the ground states but are present in the relatively low-lying level schemes. With the aim of identifying the expected 2p2h - s1/2+ state in P35, the only N=20 isotone for which the neutron 2p2h excitation bandhead has not yet been identified, the S36(d,He3)P35 reaction has been revisited in inverse kinematics with the HELical Orbit Spectrometer (HELIOS) at the Argonne Tandem Linac Accelerator System (ATLAS). While a candidate state has not been located, an upper limit for the transfer reaction cross section to populate such a configuration within a 2.5 to 3.6 MeV energy range provides a stringent constraint on the wave function compositions in both S36 and P35.

The detection of the neutrinos produced in the p−p chain and in the CNO cycle can be used to test the Standard Solar Model. The $^{3}$He(α,γ)$^{7}$Be reaction is the first reaction of the 2nd and 3rd branch of the p−p chain, therefore, the uncertainty of its cross section sensitively influences the prediction of the $^{7}$Be and $^{8}$B neutrino fluxes. Despite its importance and the large number of experimental and theoretical works devoted to this reaction, the knowledge on the reaction cross section at energies characterizing the core of the Sun (15 keV - 30 keV) is limited and further experimental efforts are needed to reach the desired (≈ 3%) accuracy. The precise knowledge on the external capture contribution to the $^{3}$He(α,γ)$^{7}$Be reaction cross section is crucial for the theoretical description of the reaction mechanism. In the present work the indirect measurement of this external capture contribution using the Asymptotic Normalization Coefficient (ANC) technique is reported. To extract the ANC, the angular distributions of deuterons emitted in the $^{6}$Li($^{3}$He,d)$^{7}$Be α-transfer reaction were measured with high precision at EH3e = 3.0 MeV and EH3e = 5.0 MeV. The ANCs were then extracted from comparison of DWBA calculations to the measured data and the zero energy astrophysical S-factor for $^{3}$He(α,γ)$^{7}$Be reaction was found to be 0.534 ± 0.025 keVb.

Employing the Argonne Fragment Mass Analyzer and the implantation-decay-decay correlation technique, a weak 0.50(21)% proton decay branch was identified in $^{108}$I for the first time. The $^{108}$I proton-decay width is consistent with a hindered l=2 emission, suggesting a d52 origin. Using the extracted $^{108}$I proton-decay Q value of 597(13) keV, and the Qα values of the $^{108}$I and $^{107}$Te isotopes, a proton-decay Q value of 510(20) keV for $^{104}$Sb was deduced. Similarly to the $^{112,113}$Cs proton-emitter pair, the Qp(I108) value is lower than that for the less-exotic neighbor $^{109}$I, possibly due to enhanced proton-neutron interactions in N≈Z nuclei. In contrast, the present Qp(Sb104) is higher than that of $^{105}$Sb, suggesting a weaker interaction energy. For the present Qp(Sb104) value, network calculations with the one-zone X-ray burst model Mazzocchi et al. (2007) [18] predict no significant branching into the Sn-Sb-Te cycle at $^{103}$Sn.

Employing the Argonne Fragment Mass Analyzer and the implantation-decay-decay correlation technique, a weak 0.50(21)% proton decay branch was identified in 108 I for the first time. The 108 I proton-decay width is consistent with a hindered l=2 emission, suggesting a d [Formula presented] origin. Using the extracted 108 I proton-decay Q value of 597(13) keV, and the Q α values of the 108 I and 107 Te isotopes, a proton-decay Q value of 510(20) keV for 104 Sb was deduced. Similarly to the 112,113 Cs proton-emitter pair, the Q p (I108) value is lower than that for the less-exotic neighbor 109 I, possibly due to enhanced proton-neutron interactions in N≈Z nuclei. In contrast, the present Q p (Sb104) is higher than that of 105 Sb, suggesting a weaker interaction energy. For the present Q p (Sb104) value, network calculations with the one-zone X-ray burst model Mazzocchi et al. (2007) [18] predict no significant branching into the Sn-Sb-Te cycle at 103 Sn.

In massive stars, the Ca41(n,α)Ar38 and K41(p,α)Ar38 reactions have been identified as the key reactions governing the abundance of Ca41, which is considered as a potential chronometer for solar system formation. So far, due to experimental limitations, the Ca41(n,α)Ar38 reaction rate is solely based on statistical model calculations. In the present study, we have measured the time-inverse Ar38(α,n)Ca41 and Ar38(α,p)K41 reactions using an active target detector. The reactions were studied in inverse kinematics using a 133-MeV Ar38 beam and He4 as the active-gas target. Both excitation functions were measured simultaneously in the energy range of 6.8≤Ec.m.≤9.3 MeV. Using detailed balance the Ca41(n,α)Ar38 and K41(p,α)Ar38 reaction rates were determined, which suggested a 20% increase in the Ca41 yield from massive stars.

We report the first observation of the Xe108→Te104→Sn100 α-decay chain. The α emitters, Xe108 [Eα=4.4(2) MeV, T1/2=58-23+106 μs] and Te104 [Eα=4.9(2) MeV, T1/2

A beam containing a substantial component of both the Jπ=5+, T1/2=162 ns isomeric state of F18 and its 1+, 109.77-min ground state is utilized to study members of the ground-state rotational band in F19 through the neutron transfer reaction (d,p) in inverse kinematics. The resulting spectroscopic strengths confirm the single-particle nature of the 13/2+ band-terminating state. The agreement between shell-model calculations using an interaction constructed within the sd shell, and our experimental results reinforces the idea of a single-particle-collective duality in the descriptions of the structure of atomic nuclei.