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Register a new userDirect mass measurements beyond the proton drip-line
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First on-line mass measurements were performed at the SHIPTRAP Penning trap mass spectrometer. The masses of 18 neutron-deficient isotopes in the terbium-to-thulium region produced in fusion-evaporation reactions were determined with relative uncertainties of about $7cdot 10^{-8}$, nine of them for the first time. Four nuclides ($^{144, 145}$Ho and $^{147, 148}$Tm) were found to be proton-unbound. The implication of the results on the location of the proton drip-line is discussed by analyzing the one-proton separation energies.
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We report on the observation of excited states in the neutron-deficient phosphorus isotopes $^{26,27,28}$P via in-beam gamma-ray spectroscopy with both high-efficiency and high-resolution detector arrays. In $^{26}$P, a previously-unobserved level has been identified at 244(3) keV, two new measurements of the astrophysically-important 3/2$^+$ resonance in $^{27}$P have been performed, gamma decays have been assigned to the proton-unbound levels at 2216 keV and 2483 keV in $^{28}$P, and the gamma-ray lineshape method has been used to make the first determination of the lifetimes of the two lowest-lying excited states in $^{28}$P. The expected Thomas-Ehrman shifts were calculated and applied to levels in the mirror nuclei. The resulting level energies from this procedure were then compared with the energies of known states in $^{26,27,28}$P.
In a previous letter (Phys. Rev. Lett. 96, 072502 (2006)), the multi-channel algebraic scattering (MCAS) technique was used to calculate spectral properties for proton-unstable $^{15}$F and its mirror, $^{15}$C. MCAS achieved a close match to the then-new data for $p+^{14}$O elastic scattering and predicted several unusually narrow resonances at higher energies. Subsequently, such narrow resonance states were found. New cross section data has been published characterising the shape of the $J^pi =frac{1}{2}^-$ resonance. Herein we update that first MCAS analysis and its predictions. We also study the spectra of the set of mass-15 isobars, ${}^{15}$C, ${}^{15}$N, ${}^{15}$O, and ${}^{15}$F, using the MCAS method and seeking a consistent Hamiltonian for clusterisation with a neutron and a proton, separately, coupled to core nuclei ${}^{14}$C and ${}^{14}$O.
The a-decay chains originating from the s1/2 and h11/2 states in 173Au have been investigated following fusion-evaporation reactions. Four generations of a radioactivities have been correlated with 173Aum leading to a measurement of the a decay of 161Tam. It has been found that the known a decay of 161Ta, which was previously associated with the decay of the ground state, is in fact the decay of an isomeric state. This work also reports on the first observation of prompt g rays feeding the ground state of 173Au. This prompt radiation was used to aid the study of the a-decay chain originating from the s1/2 state in 173Au. Three generations of a decays have been correlated with this state leading to the observation of a previously unreported activity which is assigned as the decay of 165Reg. This work also reports the excitation energy of an a-decaying isomer in 161Ta and the Q-value of the decay of 161Tag.
Properties of particle-unstable nuclei lying beyond the proton drip line can be ascertained by considering those (usually known) properties of its mirror neutron-rich system. We have used a multi-channel algebraic scattering theory to map the known properties of the neutron-${}^{14}$C system to those of the proton-${}^{14}$O one from which we deduce that the particle-unstable ${}^{15}$F will have a spectrum of two low lying broad resonances of positive parity and, at higher excitation, three narrow negative parity ones. A key feature is to use coupling to Pauli-hindered states in the target.
The very neutron-rich oxygen isotopes 25O and 26O are investigated experimentally and theoret- ically. In this first R3B-LAND experiment, the unbound states are populated at GSI via proton- knockout reactions from 26F and 27F at relativistic energies around 450 MeV/nucleon. From the kinematically complete measurement of the decay into 24O plus one or two neutrons, the 25O ground- state energy and lifetime are determined, and upper limits for the 26O ground state are extracted. In addition, the results provide evidence for an excited state in 26O at around 4 MeV. The ex- perimental findings are compared to theoretical shell-model calculations based on chiral two- and three-nucleon (3N) forces, including for the first time residual 3N forces, which are shown to be amplified as valence neutrons are added.
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