The feeding probability of 102;104;105;106;107 Tc, 105 Mo, and 101 Nb nuclei, which are important contributors to the decay heat in nuclear reactors, has been measured using the total absorption technique. We have coupled for the first time a total absorption spectrometer to a Penning trap in order to obtain sources of very high isobaric purity. Our results solve a significant part of a long-standing discrepancy in the component of the decay heat for 239 Pu in the 4-3000 s range. DOI: 10.1103/PhysRevLett.105.202501 PACS numbers: 23.40.Às, 27.60.+j, 28.41.Fr, 29.30.Kv Nuclear reactors provide a significant fraction of the world's electricity. A burgeoning population and an associated growth in economic activity suggest that world demand will double by 2050. Until now, the bulk of this has come from the burning of fossil fuels. There is general concern that reserves of fossil fuels are limited and their burning damages the environment. In particular, it contributes to the emission of large amounts of CO 2 . In this context, nuclear power, based on the fission process, will be less damaging to the environment. Accordingly there is now a renaissance in the building of nuclear power stations around the world. Modern reactor designs, based on many years of operating experience, are much more efficient, more economical, and safer than earlier designs. Although the basic principles are well established, we still lack certain information, such as a knowledge of the decay properties of specific nuclei that are important contributors to the heating of the reactor during and after operation. The estimation and control of the heat emitted by the decay of fission products plays a key role in the safe operation of reactors. The primary aim of this work is to study the decay properties of specific nuclei that are important contributors to this source of heat.Approximately 8% of the total energy generated during the fission process is related to the energy released in the natural decay of fission products, and is commonly called decay heat [1]. Once the reactor is shut down, the energy released in radioactive decay provides the main source of heating. Hence, coolant needs to be maintained after termination of the neutron-induced fission process in a reactor, and the form and extent of this essential requirement needs to be specified on the basis of decay-heat summation calculations. Decay heat varies as a function of time after shutdown and can be determined theoretically from known nuclear data. Such computations are based on the inventory of nuclei created during the fission process and after reactor shutdown and their radioactive decay characteristics:where fðtÞ is the power function, E i is the mean decay energy of the ith nuclide ( , , and components), i is the decay constant of the ith nuclide, and N i ðtÞ is the number of nuclide i at cooling time t. These calculations require extensive libraries of cross sections, fission yields, and decay data. Obviously, an accurate assessment of the decay heat is highly relevant...

Quasifree one-proton knockout reactions have been employed in inverse kinematics for a systematic study of the structure of stable and exotic oxygen isotopes at the R^{3}B/LAND setup with incident beam energies in the range of 300-450  MeV/u. The oxygen isotopic chain offers a large variation of separation energies that allows for a quantitative understanding of single-particle strength with changing isospin asymmetry. Quasifree knockout reactions provide a complementary approach to intermediate-energy one-nucleon removal reactions. Inclusive cross sections for quasifree knockout reactions of the type ^{A}O(p,2p)^{A-1}N have been determined and compared to calculations based on the eikonal reaction theory. The reduction factors for the single-particle strength with respect to the independent-particle model were obtained and compared to state-of-the-art ab initio predictions. The results do not show any significant dependence on proton-neutron asymmetry.

A novel method of deducing the deformation of the N=Z nucleus 76 Sr is presented. It is based on the comparison of the experimental Gamow-Teller strength distribution B(GT) from its β-decay with the results of QRPA calculations. This method confirms previous indications of the strong prolate deformation of this nucleus in a totally independent way. The measurement has been carried out with a large Total Absorption gamma Spectrometer, "Lucrecia", newly installed at CERN-ISOLDE.PACS numbers: 21.10. Pc, 23.40.Hc, 27.50.+e, 29.30.Kv, 29.40.Mc The shape of the atomic nucleus is conceptually one of the simplest of its macroscopic properties to visualise. However, it turns out to be one of the more difficult properties to measure. In general terms we now have a picture of how the nuclear shape varies across the Segrè Chart. Nuclei near to the closed shells are spherical. In contrast nuclei with the valence nucleons in between two shells have deformed shapes with axial symmetry and the extent of the quadrupole deformation is quite well described as being proportional to the product N p N n of the numbers of pairs of valence protons (N p ) and neutrons (N n ) [1]. This picture is underpinned by both the Shell and Mean Field models of nuclear structure. Experiment and theory concur that, as the N p N n parameterisation would suggest, nuclei rapidly deform as we add only a small number of valence nucleons to the magic numbers. Thus nuclei in the middle of the f 7/2 shell turn out to be deformed even although the numbers of valence nucleons are relatively small.Experimentally this picture is supported by a mass of independent observations: the strongly enhanced quadrupole transition rates between low-lying states, the strongly developed rotational bands built on low-lying states, and measurements of ground state quadrupole moments. Where we have evidence of the shapes of ground and excited states in the same nucleus they are, in general but not always, the same. It turns out that in some cases nuclear states with different shapes co-exist in the same nucleus [2].The nuclei with N≈Z and A≈70-80 are of particular interest in this context. Such nuclei enjoy a particular symmetry since the neutrons and protons are filling the same orbits. This, and the low single-particle level density, lead to rapid changes in deformation with the addition or subtraction of only a few nucleons. In terms of Mean Field models these rapid changes arise because of the proximity in energy of large energy gaps for protons and neutrons at Z,N=34 and 36 on the oblate and Z,N=38 on the prolate side of the Nilsson diagram. As a result Mean Field calculations predict the existence of several energy minima with quite different shapes in some of these nuclei [3,4]. Evidence of this co-existence has been found for instance in Se and Kr nuclei [5,6], and it is also predicted for the lightest Sr isotopes [7]. Thus it is of considerable interest to map out the deformation of the ground and excited states of nuclei in this region. This is easier said than do...

Beta-delayed proton emission from 20 Mg has been measured at ISOLDE, CERN, with the ISOLDE Decay Station (IDS) setup including both charged-particle and gamma-ray detection capabilities. A total of 26 delayed proton branches were measured including seven so far unobserved. An updated decay scheme, including three new resonances above the proton separation energy in 20 Na and more precise resonance energies, is presented. Beta-decay feeding to two resonances above the Isobaric Analogue State (IAS) in 20 Na is observed. This may allow studies of the 4032.9(2.4) keV resonance in 19 Ne through the beta decay of 20 Mg, which is important for the astrophysically relevant reaction 15 O(α, γ) 19 Ne. Beta-delayed protons were used to obtain a more precise value for the half-life of 20 Mg, 90.9(1.2) ms. PACS. 23.20.Lv γ transitions and level energies-26.30.Ca Explosive burning in accreting binary systems (novae, x-ray bursts)-27.30.+t 20 ≤ A ≤ 38-29.30.Ep Charged-particle spectroscopy