The last decades brought impressive progress in synthesizing and studying properties of nuclides located very far from the beta stability line. Among the most fundamental properties of such exotic nuclides, the ones usually established first are the half-life, possible radioactive decay modes, and their relative probabilities. When approaching limits of nuclear stability, new decay modes set in. First, beta decays are accompanied by emission of nucleons from highly excited states of daughter nuclei. Second, when the nucleon separation energy becomes negative, nucleons start being emitted from the ground state. A review of the decay modes occurring close to the limits of stability is presented. The experimental methods used to produce, identify, and detect new species and their radiation are discussed. The current theoretical understanding of these decay processes is reviewed. The theoretical description of the most recently discovered and most complex radioactive process---the two-proton radioactivity---is discussed in more detail.

Radioactive decays at limits of nuclear stability

The interaction of an E/A = 57.6-MeV Ne-17 beam with a Be target is used to populate levels in Ne-16 following neutron knockout reactions. The decay of 16Ne states into the three-body O-14 + p + p continuum is observed in the High Resolution Array (HiRA). For the first time for a 2p emitter, correlations between the momenta of the three decay products are measured with sufficient resolution and statistics to allow for an unambiguous demonstration of their dependence on the long-range nature of the Coulomb interaction. Contrary to previous measurements, our measured limit Gamma < 80 keV for the intrinsic decay width of the ground state is not in contradiction to the small values (of the order of keV) predicted theoretically.

http://publications.lib.chalmers.se/records/fulltext/209794/local_209794.pdf

Observation of Long-Range Three-Body Coulomb Effects in the Decay of Ne 16

Linking the exotic structure of 17 C to its unbound mirror 17 Na

Recent observations of the late ($t=10^8$--$10^9$ s) emission of supernovae (SNe) associated to GRBs (GRB-SN) show a distinctive emission in the X-ray regime consistent with temperatures $10^7$--$10^8$ K. Similar features have been also observed in the two Type Ic SNe SN 2002ap and SN 1994I that are not associated to GRBs. We advance the possibility that the late X-ray emission observed in GRB-SN and in isolated SN is associated to a hot neutron star (NS) just formed in the SN event, here defined as a neo-NS. We discuss the thermal evolution of neo-NS in the age regime that spans from $\sim 1$ minute (just after the proto-NS phase) up to ages <10-100 yr. We examine the key factor governing the neo-NS cooling emphasizing on the neutrino emission. A phenomenological heating source and new boundary conditions are introduced to mimic the high-temperature atmosphere of young NSs. We match the neo-NS luminosity to the late X-ray emission of the GRB-SN events URCA-1 in GRB980425-SN1998bw, URCA-2 in GRB030329-SN2003dh, and URCA-3 in GRB031203-SN2003lw. By calibrating our additional heating source at early times to $\sim 10^{12}$--$10^{15}$ erg/g/s, we find a striking agreement of the luminosity obtained from the cooling of neo-NSs with the late ($t=10^{8}$--$10^{9}$ s) X-ray emission observed in GRB-SN. It is therefore appropriate to revise the boundary conditions used in the cooling theory of NSs, to match the proper conditions of the atmosphere at young ages. Additional heating processes that are still not studied within this context, such as e+e- pair creation by overcritical fields and nuclear fusion and fission energy release, might also take place under such conditions and deserve further analysis. Observation of GRB-SN has shown the possibility of witnessing the thermal evolution of neo-NSs. A new campaign of dedicated observations is recommended both of GRB-SN and of isolated Type Ic SN.

/pdf/cooling-of-young-neutron-stars-in-grb-associated-to-4iik2ubiyl.pdf

Cooling of young neutron stars in GRB associated to Supernova

A survey of the available single-proton data in $A\ensuremath{\le}17$ nuclei was completed. These data, along with calculations using a Woods-Saxon potential, show that the ordering of the $0{d}_{5/2}$ and $1{s}_{1/2}$ proton orbitals are determined primarily by the proximity of the $s$-state proton energy to the Coulomb barrier. This is analogous to the dependence of the corresponding neutron orbitals in proximity to the neutron threshold, which was previously discussed.

Ordering of the 0 d 5 / 2 and 1 s 1 / 2 proton levels in light nuclei

A powerful method of investigating proton-unbound nuclear states by tracking their decay products in flight is discussed in detail. To verify the method, four known levels in 
15
F
, 
16
Ne
, and 
19
Na
 were investigated by measuring the angular correlations between protons and the respective heavy-ion fragments stemming from the precursor decays in flight. The parent nuclei of interest were produced in nuclear reactions of one-neutron removal from 
17
Ne
 and 
20
Mg
 projectiles at energies of 410–450 
A
 MeV. The trajectories of the respective decay products, 
14
O
 
+
 p 
+
 p and 
18
Ne
 
+
 p 
+
 p, were measured by applying a tracking technique with microstrip detectors. These data were used to reconstruct the angular correlations of the fragments, which provided information on energies and widths of the parent states. In addition for reproducing properties of known states, evidence for hitherto unknown excited states in 
15
F
 and 
16
Ne
 was found. This tracking technique has an advantage in studies of exotic nuclei beyond the proton drip line measuring the resonance energies and widths with a high precision although by using low-intensity beams and very thick targets.

/pdf/spectroscopy-of-proton-unbound-nuclei-by-tracking-their-4l921hecac.pdf

Spectroscopy of proton-unbound nuclei by tracking their decay products in-flight: One- and two- proton decays of F15, Ne16, and Na19

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Spectroscopy of proton-unbound nuclei by tracking their decay products in-flight: One- and two- proton decays of F15, Ne16, and Na19