Search for the 1/2+ intruder state in P 35

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

Experimental study of Ar 38 +α reaction cross sections relevant to the Ca 41 abundance in the solar system

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

Invariant-mass spectroscopy of 14^{14}O excited states

International audienceExcited states in O14 have been investigated both experimentally and theoretically. Experimentally, these states were produced via neutron-knockout reactions with a fast O15 beam and the invariant-mass technique was employed to isolate the 1p and 2p decay channels and determine their branching ratios. The spectrum of excited states was also calculated with the shell model embedded in the continuum that treats bound and scattering states in a unified model. By comparing energies, widths, and decay branching patterns, spin and parity assignments for all experimentally observed levels below 8 MeV are made. This includes the location of the second 2+ state that we find is in near degeneracy with the third 0+ state. An interesting case of sequential 2p decay through a pair of degenerate N13 excited states with opposite parities was found where the interference between the two sequential decay pathways produces an unusual relative-angle distribution between the emitted protons

Spin alignment following inelastic scattering of 17^{17}Ne , lifetime of 16^{16}F , and its constraint on the continuum coupling strength

International audienceThe sequential two-proton decay of the second excited state in Ne17, produced by inelastic excitation at intermediate energy, is studied. This state is found to be highly spin aligned, providing another example of a recently discovered alignment mechanism. The fortuitous condition that the second decay step is slightly more energetic than the first, permits the lifetime of the one-proton daughter, the ground state of F16, to be determined from the magnitude of the final-state interactions between the protons. This new method gave a result [Γ=20.6(57) keV] consistent with that obtained by directly measuring the width of the state [Γ=21.3(51) keV]. This width allows one to determine the continuum coupling constant in this mass region. Real-energy continuum-shell-model studies yield a satisfactory description of both spectra and widths of low-energy resonances in F16 and suggest an unusual large ratio of proton-proton to proton-neutron continuum couplings in the vicinity of the proton drip line

Two-proton decay of the 6Be ground state and the double isobaric analog of 11Li

Two-proton decay is discussed in a number of light isobaric multiplets. For the lightest two-proton emitter, 6Be, the momentum correlations between the three decay products were measured and found to be consistent with quantum-mechanical three-cluster-model calculations. Two-proton decay was also found for two members of the A=8 and A=11 quintets. Finally, a third member of the A=11 sextet, the double isobaric analog of the halo nucleus 11Li in 11B was observed by its two-proton decay

Two-proton decay of the 6Be ground state and the double isobaric analog of 11Li

Two-proton decay is discussed in a number of light isobaric multiplets. For the lightest two-proton emitter, 6Be, the momentum correlations between the three decay products were measured and found to be consistent with quantum-mechanical three-cluster-model calculations. Two-proton decay was also found for two members of the A=8 and A=11 quintets. Finally, a third member of the A=11 sextet, the double isobaric analog of the halo nucleus 11Li in 11B was observed by its two-proton decay