The production of the 26 Al radioisotope in astrophysical environments is not understood, in part, because of large uncertainties in key nuclear reaction rates. The 25 Al(p,␥) 26 Si reaction is one of the most important, but its rate is very uncertain as a result of the lack of information on the 26 Si level structure above the proton threshold. To reduce these uncertainties, we have measured differential cross sections for the 28 Si(p,t) 26 Si reaction and determined excitation energies for states in 26 Si. A total of 21 states in 26 Si were observed, including ten above the proton threshold. One new state at 7019 keV was observed, the excitation energies of several states were corrected, and the uncertainties in the excitation energies of other states were significantly reduced. Spins and parities of several states above the proton threshold were determined for the first time through a distorted-wave Born approximation analysis of the angular distributions. These results substantially clarify the level structure of 26 Si.

The proton drip-line defines the limit at which nuclei become unbound to the emission of a proton from their ground states. Low-Z nuclei lying beyond this limit only exist as short-lived resonances and cannot be detected directly. The location of the drip-line constrains the path of nucleosynthesis in explosive astrophysical scenarios such as novae and X-ray bursters, and consequently controls the rate of energy generation. In higher-Z regions of the drip-line, the potential energy barrier resulting from the mutual electrostatic interaction between the unbound proton and the core can cause nuclei to survive long enough to be detected. This review describes the recent major advances in the study of these exotic nuclei. Particular emphasis is placed on understanding the phenomenon of proton radioactivity and the unique insights it offers into the structure of nuclei lying beyond one of nature's fundamental limits to stability.

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This is an accepted version of a paper published in Nature. This paper has been peer-reviewed but does not include the final publisher proof-corrections or journal pagination.Citation for the published paper: Hinke, C., Boehmer, M., Boutachkov, P., Faestermann, T., Geissel, H. et al. (2012) "Superallowed Gamow-Teller decay of the doubly magic nucleus 100 Sn" Nature, 486 (7403): [341][342][343][344][345] Access to the published version may require subscription.

The new proton radioactivities 165,166,167 Ir and 171 Au have been observed. The Ir isotopes were produced via the 92 Mo( 78 Kr,pxn) 165,166,167 Ir reactions at 357 and 384 MeV. 171 Au was produced via the 96 Ru( 78 Kr,p2n) 171 Au reaction at 389 MeV. The proton emitters were each identified by position, time, and energy correlations between the implantation of a residual nucleus into a double-sided silicon strip detector, the observation of a decay proton, and the subsequent observation of a decay alpha particle from the daughter nucleus ͑ 164,165,166 Os and 170 Pt, respectively͒. Both 166 Ir and 167 Ir have proton-emitting ground and isomeric states, which also decay by alpha emission. The proton-decay rates have been reproduced by calculations using the WKB barrier penetration approximation and a low-seniority shell-model calculation of the spectroscopic factors. The alpha decays of the four nuclei are followed by chains of alpha decays, allowing the determination of single-particle orbital orderings. Mass information has also been obtained from the alpha-decay chains because a connection to a known mass can be obtained for one of the nuclei. Ground-state mass excesses are reported for 151 Tm, 154 Yb, 155 Lu, 158 Hf, 159 Ta, 162 W, 163 Re, 166 Os, 167 Ir, and 170 Pt. The mass excess for 171m Au is also given. Proton separation energies are also deduced for the odd-Z alpha daughter nuclei of the Ir proton emitters.

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Proton radioactivity from 141 Ho and 131 Eu has been identified. The 141 Ho proton transition has an energy E p 1169͑8͒ keV, a half-life t 1͞2 4.2͑4͒ ms, and is assigned to the decay of the 7͞2 2 ͓523͔ Nilsson state. The 131 Eu transition has an energy E p 950͑8͒ keV and a half-life of 26(6) ms, consistent with decay from either the 3͞2 1 ͓411͔ or 5͞2 1 ͓413͔ Nilsson orbital. The proton decay rates deviate significantly from calculations assuming spherical configurations, and thus indicate the onset of large deformations in the region of the proton drip line below Z 69. [S0031-9007(98)

Abstract. The Miniball germanium detector array has been operational at the REX (Radioactive ion beam EXperiment) post accelerator at the Isotope Separator On-Line facility ISOLDE at CERN since 2001. During the last decade, a series of successful Coulomb excitation and transfer reaction studies have been performed with this array, utilizing the unique and high-quality radioactive ion beams which are available at ISOLDE. In this article, an overview is given of the technical details of the full Miniball setup, including a description of the γ-ray and particle detectors, beam monitoring devices and methods to deal with beam contamination. The specific timing properties of the REX-ISOLDE facility are highlighted to indicate the sensitivity that can be achieved with the full Miniball setup. The article is finalized with a summary of some physics highlights at REX-ISOLDE and the utilization of the Miniball germanium detectors at other facilities.