No abstract

The fragment mass analyzer at the ATLAS facility has been used to unambiguously identify the mass number associated with different decay modes of the nobelium isotopes produced via 204 Pb(48 Ca, xn) 252−x No reactions. Isotopically pure (>99.7%) 204 Pb targets were used to reduce background from more favored reactions on heavier lead isotopes. Two spontaneous fission half-lives (t 1/2 = 3.7 +1.1 −0.8 and 43 +22 −15 µs) were deduced from a total of 158 fission events. Both decays originate from 250 No rather than from neighboring isotopes as previously suggested. The longer activity most likely corresponds to a K isomer in this nucleus. No conclusive evidence for an α branch was observed, resulting in upper limits of 2.1% for the shorter lifetime and 3.4% for the longer activity.

Abstract. The observation of neutrinoless double-beta decay (0νββ) would show that lepton number is violated, reveal that neutrinos are Majorana particles, and provide information on neutrino mass. A discovery-capable experiment covering the inverted ordering region, with effective Majorana neutrino masses of 15 − 50 meV, will require a tonne-scale experiment with excellent energy resolution and extremely low backgrounds, at the level of ∼0.1 count /(FWHM·t·yr) in the region of the signal. The current generation 76 Ge experiments GERDA and the Majorana Demonstrator, utilizing high purity Germanium detectors with an intrinsic energy resolution of 0.12%, have achieved the lowest backgrounds by over an order of magnitude in the 0νββ signal region of all 0νββ experiments. Building on this success, the LEGEND collaboration has been formed to pursue a tonne-scale 76 Ge experiment. The collaboration aims to develop a phased 0νββ experimental program with discovery potential at a half-life approaching or at 10 28 years, using existing resources as appropriate to expedite physics results.

-The spallation residues produced in the bombardment of 56 F e at 1.5, 1.0, 0.75, 0.5 and 0.3 A GeV on a liquid-hydrogen target have been measured using the reverse kinematics technique and the Fragment Separator at GSI (Darmstadt). This technique has permitted the full identification in charge and mass of all isotopes produced with cross-sections larger than 10 −2 mb down to Z = 8. Their individual production cross-sections and recoil velocities at the five energies are presented. Production cross-sections are compared to previously existing data and to empirical parametric formulas, often used in cosmic-ray astrophysics. The experimental data are also extensively compared to different combinations of intra-nuclear cascade and de-excitation models. It is shown that the yields of the lightest isotopes cannot be accounted for by standard evaporation models. The GEMINI model, which includes an asymmetric fission decay mode, gives an overall good agreement with the data. These experimental data can be directly used for the estimation of composition modifications and damages in materials containing iron in spallation sources. They are also useful for improving high precision cosmic-ray measurements.

Nuclear fission of several neutron-deficient actinides and pre-actinides from excitation energies around 11 MeV was studied at GSI Darmstadt by use of relativistic secondary beams. The characteristics of multimodal fission of nuclei around 226 Th are systematically investigated and interpreted as the superposition of three fission channels. Properties of these fission channels have been determined for 15 systems. A global view on the properties of fission channels including previous results is presented. The positions of the asymmetric fission channels are found to be constant in element number over the whole range of systems investigated.2 data of 15 of the systems, which show features of multi-modal fission. The systematic survey of fissioning systems in the transition from single-humped to double-humped element distributions around 226 Th extends the systematic view on how the intensities and other relevant parameters of the fission channels vary as a function of the nuclear composition of the fissioning nucleus. EXPERIMENTAt GSI Darmstadt, a new technique to investigate low-energy fission has been developed [4,5]. Relativistic secondary projectiles are produced via fragmentation of a 1 A GeV primary beam of 238 U and identified in nuclear mass and charge number by the fragment separator FRS [6]. In a dedicated experimental set-up, the giant resonances, mostly the giant dipole resonance, are excited by electromagnetic interactions in a secondary lead target, and fission from excitation energies around 11 MeV is induced. The fission fragments are identified in nuclear charge, and their velocity vectors are determined. From these data, the element yields and the total kinetic energies are deduced. Details of the experimental technique are given elsewhere [1].

In this Letter, we reported a study of the Snð; tÞ reaction at 40 MeV, on the seven stable, even Sn isotopes, to study the pattern of 11=2 À and 7=2 þ single-particle states as the neutron excess changes. The interpretation of the data relied only on the relative cross sections for these 14 transitions. The absolute cross sections given in Table I, columns 2 and 3, have now been found to be in error. This error has no impact on the rest of the paper, which utilized only the relative values of the cross sections. A numerical error in a measured quantity should, however, be corrected.In the experiment, the cross sections were normalized to the yield for elastic scattering in a monitor detector placed at 9.1 . The collimator in front of the detector had a diameter of 1 mm. In the analysis, it was mistakenly assumed to have had a 1-mm radius.The problem came to light in a recent experiment where the same reaction was studied at 37.5 MeV and significantly different cross sections were found [1], lower by a factor of $3:7 if corrected for a small energy dependence, than those in the Letter. This factor is reasonably constant, showing a rms variation of 8.6% among the 14 transitions. This fluctuation is consistent with the estimated uncertainties from other sources.In all subsequent experiments by our group, utilizing the spectrograph at the Yale tandem facility (e.g., Ref.[2]), a different technique for determining the absolute cross sections was used, a method that did not depend on a monitor at small angles. Instead, the target thicknesses were calibrated by measuring scattering at low bombarding energies and at larger scattering angles. This calibration was done directly with the spectrograph, using the same aperture as in the rest of the measurements. Therefore, the mistake reported here has no effect on the results reported from our subsequent measurements at Yale. *schiffer@anl.gov [1] A. J. Mitchell, Ph.D. thesis, University of Manchester, 2012; the data will be submitted to XUNDL, http://www.nndc.bnl.gov/ xundl/. [2] J. P. Schiffer et al., Phys. Rev. Lett. 108, 022501 (2012).

The possibility of observing neutrinoless double beta decay offers the opportunity of determining the effective neutrino mass if the nuclear matrix element were known. Theoretical calculations are uncertain, and measurements of the occupations of valence orbits by nucleons active in the decay can be important. The occupation of valence neutron orbits in the ground states of 76Ge (a candidate for such decay) and 76Se (the daughter nucleus) were determined by precisely measuring cross sections for both neutron-adding and removing transfer reactions. Our results indicate that the Fermi surface is much more diffuse than in theoretical calculations. We find that the populations of at least three orbits change significantly between these two ground states while in the calculations, the changes are confined primarily to one orbit.

We present an extensive overview of production cross sections and kinetic energies for the complete set of nuclides formed in the spallation of 136 Xe by protons at the incident energy of 1 GeV per nucleon. The measurement was performed in inverse kinematics at the GSI fragment separator. Slightly below the BusinaroGallone point, 136 Xe is the stable nuclide with the largest neutron excess. The kinematic data and cross sections collected in this work for the full nuclide production are a general benchmark for modeling the spallation process in a neutron-rich nuclear system, where fission is characterized by predominantly mass-asymmetric splits.