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 lifetimes of first excited 2 + , 4 + and 6 + states in 98 Zr were measured with the Recoil-Distance Doppler-Shift method in an experiment performed at GANIL. Excited states in 98 Zr were populated using the fission reaction between a 6.2 MeV/u 238 U beam and a 9 Be target. The γ rays were detected with the EXOGAM array in correlation with the fission fragments identified in mass and atomic number in the VAMOS++ spectrometer. Our result shows very small B(E2; 2 + 1 → 0 + 1 ) value in 98 Zr thereby confirming the very sudden onset of collectivity at N = 60. The experimental results are compared to large-scale Monte Carlo Shell model and beyond mean field calculations. The present results indicate coexistence of two additional deformed shapes in this nucleus along with the spherical ground state.The study of various modes of excitations and the associated evolution of nuclear shapes along spin and isospin axes in atomic nuclei is one of the fundamental quests in nuclear physics. While nuclei with "magic numbers" of protons and/or neutrons have spherical ground states, as one moves away, the polarizing effect of added nucleons leads to deformation. Throughout the nuclear landscape, this onset of deformation is usually a gradual process, however in neutron rich nuclei around mass A ∼ 100 the shape change is rather drastic and abrupt. The ground states of Sr and Zr isotopes with N ranging from the magic number N = 50 up to N < 60 are weakly deformed, however, they undergo a rapid shape transition from nearly spherical to well deformed prolate deformations as N = 60 is approached. The sudden nature of shape transition in Sr and Zr isotopes is evident from the abrupt changes in the two neutron separation energies [1] and mean-square charge radii [2, 3], but also from the excitation energies of 2 + 1 states and B(E2) values [4]. On the other hand, in isotopes with Z ≥ 42 the shape change is rather gradual [1,5] showing also characteristic signatures of triaxiality. This strong dependence of the observed spectroscopic properties, both on the number of protons and neutrons, makes the neutron-rich A ∼ 100 nuclei an excellent mass region for testing various theoretical models.Many experimental and theoretical studies have already been reported on the structure of these nuclei. More specifically for the Zr isotopes, the onset of deformation at N = 60 has been described by a number of theoretical models [6][7][8][9][10][11][12][13][14][15][16][17][18][19], however, none of the models have been able to successfully reproduce the aforementioned rapid change. Very recently, the abrupt shape changes were correctly described by large-scale Monte-Carlo Shell Model (MCSM) calculations [20,21]. In the so-called type-II shell evolution scenario, the (prolate) deformed states in the isotopes with N ≥ 60 are associated with proton excitations to the 0g 9/2 orbital. Driven by the central and tensor components of the effective (proton-neutron) interactions, these excitations result in a lowering and subsequent filling of the neutron 0g ...

A record number of 100 Sn nuclei was detected and new isotopic species toward the proton dripline were discovered at the RIKEN Nishina Center. Decay spectroscopy was performed with the high-efficiency detector arrays WAS3ABi and EURICA. Both the half-life and the β-decay end point energy of 100 Sn were measured more precisely than the literature values. The value and the uncertainty of the resulting strength for the pure 0 þ → 1 þ Gamow-Teller decay was improved to B GT ¼ 4.4 þ0.9 −0.7 . A discrimination between different model calculations was possible for the first time, and the level scheme of 100 In is investigated further.Sn and its neighboring nuclei comprise a unique testing ground for modern large scale shell model (LSSM) calculations with realistic nuclear interactions. 100 Sn is the heaviest doubly magic N ¼ Z nucleus that is particle stable and decays via a pure and very fast Gamow-Teller (GT) β decay. The 100 Sn region is located in the nuclear chart close to the end of the astrophysical rapid proton capture process path. Thus, it is of particular interest concerning fundamental challenges in both nuclear physics and astrophysics [1].According to the extreme single particle model (ESPM) [2], 100 Sn decays via a pure GT transition of a proton (π) from the completely filled π0g 9=2 orbital into a neutron (ν) in the empty spin-orbit partner, the ν0g 7=2 orbital of 100 In. The ESPM GT strength is predicted to be B GT ¼ 17.78 [1]. However, the experimental values obtained up to now are smaller: 9.1 þ3.0 −2.6 [3] and 5.8 þ5.5 −3.2 [4,5]. These experiments [3,5,6] revealed the smallest log(ft) value-even smaller than the values of nuclei which decay by a Superallowed Fermi decay-throughout the nuclear chart. However, the PHYSICAL REVIEW LETTERS 122, 222502 (2019) 0031-9007=19=122 (22)=222502(6) 222502-1

Half-lives and energies of γ rays emitted in the decay of isomeric states of nuclei in the vicinity of the doubly magic 100 Sn were measured in a decay spectroscopy experiment at Rikagaku Kenkyusho (The Institute of Physical and Chemical Research) of Japan Nishina Center. The measured half-lives, some with improved precision, are consistent with literature values. Three new results include a 55-keV E2 γ ray from a new (4 + ) isomer with T 1/2 = 0.23(6) μs in 92 Rh, a 44-keV E2 γ ray from the (15 + ) isomer in 96 Ag, and T 1/2 (6 + ) = 13(2) ns in 98 Cd. Shell-model calculations of electromagnetic transition strengths in the (p 1/2 ,g 9/2 ) model space agree with the experimental results. In addition, experimental isomeric ratios were compared to the theoretical predictions derived with an abrasion-ablation model and the sharp cutoff model. The results agreed within a factor of 2 for most isomers. From the nonobservation of time-delayed γ rays in 100 Sn, new constraints on the T 1/2 , γ -ray energy, and internal conversion coefficients are proposed for the hypothetical isomer in 100 Sn.

The revised European Directive from 2013 regarding basic safety standard oblige EU Member States to establish a national action plan regarding the exposure to radon. At the same time, International Atomic Energy Agency started technical projects in order to assist countries to establish and implement national radon action. As a consequence, in recent years, in numerous countries national radon surveys were conducted and action plans established, which were not performed before. In this paper, a qualitative overview of radon surveys performed in Europe is given with a special attention to the qualitative and conceptual description of surveys, representativeness and QA/QC (quality assurance/quality control).