The β-decay of the even-even nucleus 70Kr with Z=N+2, has been investigated at the Radioactive Ion Beam Factory (RIBF) of the RIKEN Nishina Center using the BigRIPS fragment separator, the ZeroDegree Spectrometer, the WAS3ABI implantation station and the EURICA HPGe cluster array. Fifteen γ-rays associated with the β-decay of 70Kr into 70Br have been identified for the first time, defining ten populated states below Eexc=3300 keV. The half-life of 70Kr was derived with increased precision and found to be t1/2=45.19±0.14 ms. The β-delayed proton emission probability has also been determined as εp=0.545(23)%. An increase in the β-strength to the yrast 1+ state in comparison with the heaviest Z=N+2 system studied so far (62Ge decay) is observed that may indicate increased np correlations in the T=0 channel. The β-decay strength deduced from the results is interpreted in terms of the proton-neutron quasiparticle random-phase approximation (pnQRPA) and also with a schematic model that includes isoscalar and isovector pairing in addition to quadrupole deformation. The application of this last model indicates an approximate realization of pseudo-SU(4) symmetry in this system.

S. D. Olorunfunmi, R. Neveling, J. Carter, P. von Neumann-Cosel, I. T. Usman, P. Adsley, A. Bahini, L. P. L. Baloyi, J. W. Brümmer, L. M. Donaldson, H. Jivan, N. Y. Kheswa, K. C. W. Li, D. J. Maŕin-Lámbarri, P. T. Molema, C. S. Moodley, G. G. O’Neill, P. Papka, L. Pellegri, V. Pesudo, E. Sideras-Haddad, F. D. Smit, G. F. Steyn, A. A. Aava, F. Diel, F. Dunkel, P. Jones, and V. Karayonchev School of Physics, University of the Witwatersrand, Johannesburg 2050, South Africa iThemba Laboratory for Accelerator Based Sciences, Somerset West 7129, South Africa Institute für Kernphysik, Technische Universität Darmstadt, D-64289 Darmstadt, Germany Department of Physics, University of Stellenbosch, Matieland 7602, South Africa Institut de Physique Nucléaire d’Orsay, IN2P3-CNRS, Université Paris Sud, Orsay, France Department of Physics, University of the Western Cape, Bellville 7535, South Africa Institute für Kernphysik, Universität zu Köln, 50937 Köln, Germany

S. E. A. Orrigo, ∗ B. Rubio, W. Gelletly, 2 P. Aguilera, 3 A. Algora, 4 A. I. Morales, J. Agramunt, D. S. Ahn, P. Ascher, B. Blank, C. Borcea, A. Boso, R. B. Cakirli, J. Chiba, G. de Angelis, G. de France, F. Diel, P. Doornenbal, Y. Fujita, N. Fukuda, E. Ganioğlu, M. Gerbaux, J. Giovinazzo, S. Go, T. Goigoux, S. Grévy, V. Guadilla, N. Inabe, G. Kiss, T. Kubo, S. Kubono, T. Kurtukian-Nieto, D. Lubos, C. Magron, F. Molina, A. Montaner-Pizá, D. Napoli, D. Nishimura, S. Nishimura, H. Oikawa, Y. Shimizu, C. Sidong, P.-A. Söderström, T. Sumikama, H. Suzuki, H. Takeda, Y. Takei, M. Tanaka, P. Vi, J. Wu, and S. Yagi Instituto de F́ısica Corpuscular, CSIC-Universidad de Valencia, E-46071 Valencia, Spain Department of Physics, University of Surrey, Guildford GU2 7XH, Surrey, UK Comisión Chilena de Enerǵıa Nuclear, Casilla 188-D, Santiago, Chile Inst. of Nuclear Research of the Hung. Acad. of Sciences, Debrecen, H-4026, Hungary RIKEN Nishina Center, 2-1 Hirosawa, Wako, Saitama 351-0198, Japan Centre d’Etudes Nucléaires de Bordeaux Gradignan, CNRS/IN2P3 Université de Bordeaux, 33175 Gradignan Cedex, France National Institute for Physics and Nuclear Engineering IFIN-HH, P.O. Box MG-6, Bucharest-Magurele, Romania INFN Sezione di Padova and Dipartimento di Fisica, Universitá di Padova, I-35131 Padova, Italy Department of Physics, Istanbul University, Istanbul, 34134, Turkey Department of Physics, Tokyo University of Science, Noda, Chiba 278-8510, Japan Laboratori Nazionali di Legnaro INFN, I-35020 Legnaro, Padova, Italy Grand Accélérateur National d’Ions Lourds (GANIL), CEA/DRF-CNRS/IN2P3, Bvd Henri Becquerel, 14076 Caen, France Institute of Nuclear Physics, University of Cologne, D-50937 Cologne, Germany Department of Physics, Osaka University, Toyonaka, Osaka 560-0043, Japan Department of Physics and Astronomy, University of Tennessee, Knoxville, Tennessee 37996-1200, USA Physik Department E12, Technische Universität München, D-85748 Garching, Germany Department of Natural Sciences, Tokyo City University, 1-28-1 Tamazutsumi, Setagaya-ku, Tokyo 158-8557, Japan (Dated: August 25, 2020)

In this study we present the preliminary results about the lifetimes of the 22+ , 41+ states of 208Po and the upper limit of the lifetime of the 21+ state. For measuring the lifetimes of the 21+ and 41+ states the Recoil Distance Doppler Shift (RDDS) method and for the lifetime of the 22+ state the Doppler Shift Attenuation method (DSAM) were used. The resulting absolute transition strength B(M1;22+→21+)≥0.122(20)μN2 reveals the predominant isovector nature of the 22+ state of 208Po.

Beta-decay of the very neutron-deficient Kr isotope, Kr-70, was studied at RIKEN-RIBF using the EURICA cluster array. The experiment significantly increased our knowledge of the beta-decay of this isotope. Namely, 16 new gamma-ray transitions were identified and the half-life was derived from time correlations of the beta particles (t(1/2)(i beta) = (44.99 +/- 0.16) ms) and from the decay curves of the observed gamma-ray transitions (t(1/2)(i beta gamma) = (45.16 +/- 0.71) ms), respectively.

Beta-decay of the very neutron-deficient Kr isotope, Kr-70, was studied at RIKEN-RIBF using the EURICA cluster array. The experiment significantly increased our knowledge of the beta-decay of this isotope. Namely, 16 new gamma-ray transitions were identified and the half-life was derived from time correlations of the beta particles (t(1/2)(i beta) = (44.99 +/- 0.16) ms) and from the decay curves of the observed gamma-ray transitions (t(1/2)(i beta gamma) = (45.16 +/- 0.71) ms), respectively.

The 2019 Mazurian Lakes Conference on Physics was held in Piaski, a vacation resort located at the lake of Bełdany in the heart of the Great Mazurian Lakes District, from the 1 st to 7 th of September 2019.It was the 36 th meeting in a series initiated over 50 years ago, in 1968, by Professor Zdzisław Wilhelmi and his students and collaborators.Throughout these years, the Mazurian conferences have gained a world-wide reputation for their high scientific merit and a unique atmosphere.

The Gamow-Teller strength distributions of 116Sb and 122Sb were measured with the 116,122Sn(3He,t)116,122Sb charge-exchange reactions at 140 MeV/u. The measurements were carried out at the Research Center for Nuclear Physics (RCNP) at Osaka University in Osaka, Japan using the Grand Raiden spectrometer. The data were analysed by Multipole-Decomposition Analysis (MDA). The Gamow-Teller strengths summed up to 28 MeV are (38 +/- 7)% and (48 +/- 6)% of the Ikeda sum rule for 116Sb and 122Sb, respectively, if the quasi-free scattering (QFS) contribution is not subtracted. These percentages are (29 +/- 7)% and (35 +/- 5)%, respectively, if the QFS contribution is maximally subtracted. These results were compared to those from previous measurements of the same isotopes, to recent measurements of 150Pm, and to a Quasi-particle Random-Phase Approximation (QRPA) calculation with Quasi-Particle Vibration Coupling (QPVC). The data suggest that the true QFS contribution is small for 116Sb, but are inconclusive about whether the QFS contribution is small or significant for 122Sb. Therefore, these data may provide an interesting test for the general quenching phenomenon of the Gamow-Teller Resonance (GTR). However, more research to reveal the nature of the QFS contribution is still needed on both the experimental and the theoretical side.

We report on the observation of Kr-67 that has been produced in an experiment performed at the RIKEN/BigRIPS facility. The two-proton decay of Kr-67 has been evidenced and this nucleus is thus the fourth observed long lived ground-state two-proton emitter, after Fe-45, Ni-48 and Zn-54. In addition, the decay of several isotopes in the mass region has been investigated. While for previous cases of two-proton radioactivity, the theoretical models could reproduce the measured data, this is not the case anymore for Kr-67. Two interpretations have been proposed to explain this discrepancy: a transition between real two-proton and sequential decay or the influence of deformation. These hypotheses will be tested in future experiments by measuring the angular and energy correlations of the emitted protons.

Nuclear matrix elements (NMEs) for double beta decays (DBDs) are crucial for studying the neutrino mass and other neutrino properties beyond the standard electro-weak model by measuring neutrino-less DBDs. The spin-dipole (SD) J(pi) = 2(-) NME is one of the major components associated with the DBD NME. The SD NME for Ge-76 was derived for the first time by using the (74,76) Ge (He-3, t) at RCNP Osaka. The obtained SD NME for the Ge-76 -> As-76 ground-state transition is divide M EXP-(SD) ivide = 1.5 x 10-3 k 0.2 with respect to the quasi-particle model NME divide MQP-(SD) divide <i. The impact of the reduced (quenched) SD NME on DBD neutrino studies is discussed.

The Gamow–Teller strength distributions of and were measured with the charge-exchange reactions at . The measurements were carried out at the Research Center for Nuclear Physics (RCNP) at Osaka University in Osaka, Japan using the Grand Raiden spectrometer. The data were analysed by Multipole-Decomposition Analysis (MDA). The Gamow–Teller strengths summed up to are and of the Ikeda sum rule for and , respectively, if the quasi-free scattering (QFS) contribution is not subtracted. These percentages are and , respectively, if the QFS contribution is maximally subtracted. These results were compared to those from previous measurements of the same isotopes, to recent measurements of , and to a Quasi-particle Random-Phase Approximation (QRPA) calculation with Quasi-Particle Vibration Coupling (QPVC). The data suggest that the true QFS contribution is small for , but are inconclusive about whether the QFS contribution is small or significant for . Therefore, these data may provide an interesting test for the general quenching phenomenon of the Gamow–Teller Resonance (GTR). However, more research to reveal the nature of the QFS contribution is still needed on both the experimental and the theoretical side.

Lifetimes of excited states in At-211 were measured using the electronic gamma-gamma fast timing technique. The nucleus of interest was populated in a Pb-208(Li-6, 3n)(211) At fusion-evaporation reaction at the FN Tandem accelerator of the Institute for Nuclear Physics, University of Cologne. The lifetimes of the 17/2(1)(-) and 23/2(1)(-) states were determined, together with an upper limit for the 13/2(1)(-) state. The experimental results are compared to two shell-model calculations, one using a semiempirical interaction for three particles in a single j = 9/2 shell and the other using the modified Kuo-Herling interaction in a multi- j model space.

The two-proton radioactivity is a unique tool to study the nuclear structure beyond the proton drip-line. Since its discovery in 2002, the known emitters have been Mg-19, Fe-45, Ni-48, Zn-54 and Kr-67. Kr-67 was observed for the first time at the RIKEN Nishina Center in 2015. Its decay energy was measured at 1690(17) keV with a branching ratio of 37(14) %. The halflife, 7.4(30) ms, was found in contradiction with theoretical calculations, pointing out effects of decay dynamics and nuclear deformation.

The beta decay of the Tz=-2 nucleus 64Se has been studied in a fragmentation reaction at RIKEN-Nishina Center. 64Se is the heavies Tz=-2 nucleus that decays to bound states in the daughter nucleus and the heaviest case where the mirror reaction 64Zn(3He,t)64Ga on the Tz=+2 64Zn stable target exists and can be compared. Beta-delayed gamma and proton radiation is reported for the 64Se and 64As cases. New levels have been observed in 64As, 64Ge (N=Z), 63Ge and 63Ga. The associated T1/2 values have been obtained.

Gamow-Teller (GT) transitions starting from the ${T}_{z}=+2$ nucleus $^{64}\mathrm{Zn}$ to the ${T}_{z}=+1$ nucleus $^{64}\mathrm{Ga}$ were studied in a ($p,n$)-type ($^{3}\mathrm{He},t$) charge-exchange reaction at a beam energy of 140 MeV/nucleon and scattering angles close to ${0}^{\ensuremath{\circ}}$. Here, ${T}_{z}$ is the $z$ component of the isospin $T$. The experiment was conducted at the Research Center for Nuclear Physics (RCNP) in Osaka, Japan. An energy resolution of $\ensuremath{\approx}34$ keV was achieved by applying beam matching techniques to the Grand Raiden magnetic spectrometer system. With our good resolution, we could observe GT strength fragmented in many states up to an excitation energy of $\ensuremath{\approx}11$ MeV. By performing angular distribution analysis, we could identify states in $^{64}\mathrm{Ga}$ excited by GT transitions. The reduced GT transition strengths [$B$(GT) values] were calculated assuming the proportionality between the cross sections and the $B$(GT) values. Shell-model calculations using the GXPF1J interaction reproduced the $B$(GT) strength distribution throughout the spectrum. States with isospin $T=3$ were identified by comparing the $^{64}\mathrm{Zn}\text{(}{}^{3}\text{He,}t{\text{)}}^{64}\text{Ga}$ spectrum with a $^{64}\mathrm{Zn}(d,^{2}\mathrm{He})^{64}\mathrm{Cu}$ spectrum. Relative excitation energies of the corresponding structures are in good agreement, supporting the robustness of isospin symmetry in the mass number $A=64$ nuclei.

The two-proton radioactivity is a unique tool to study the nuclear structure beyond the proton drip-line. Since its discovery in 2002, the known emitters have been 19Mg, 45Fe, 48Ni, 54Zn and 67Kr. 67Kr was observed for the first time at the RIKEN Nishina Center in 2015. Its decay energy was measured at 1690(17) keV with a branching ratio of 37(14)%. The half-life, 7.4(30) ms, was found in contradiction with theoretical calculations, pointing out effects of decay dynamics and nuclear deformation.

Gamow-Teller (GT) transitions starting from the T-z = +2 nucleus Zn-64 to the T-z = +1 nucleus Ga-64 were studied in a (p, n)-type (He-3,t) charge-exchange reaction at a beam energy of 140 MeV/nucleon and scattering angles close to 0 degrees. Here, T-z is the z component of the isospin T. The experiment was conducted at the Research Center for Nuclear Physics (RCNP) in Osaka, Japan. An energy resolution of approximate to 34 keV was achieved by applying beam matching techniques to the Grand Raiden magnetic spectrometer system. With our good resolution, we could observe GT strength fragmented in many states up to an excitation energy of approximate to 11 MeV. By performing angular distribution analysis, we could identify states in Ga-64 excited by GT transitions. The reduced GT transition strengths [B(GT)values] were calculated assuming the proportionality between the cross sections and the B(GT)values. Shell-model calculations using the GXPF1J interaction reproduced the B(GT)strength distribution throughout the spectrum. States with isospin T = 3 were identified by comparing the Zn-64(He-3,t)Ga-64 spectrum with a Zn-64(d, He-2)Cu-64 spectrum. Relative excitation energies of the corresponding structures are in good agreement, supporting the robustness of isospin symmetry in the mass number A = 64 nuclei.

F. Diel,1,* Y. Fujita,2,3,† H. Fujita,3 F. Cappuzzello,4,5 E. Ganioğlu,6 E.-W. Grewe,7 T. Hashimoto,3 K. Hatanaka,3 M. Honma,8 T. Itoh,3 J. Jolie,1 Bin Liu,3 T. Otsuka,9 K. Takahisa,3 G. Susoy,6 B. Rubio,10 and A. Tamii3 1Institut für Kernphysik, Universität zu Köln, D-50937 Cologne, Germany 2Department of Physics, Osaka University, Toyonaka, Osaka 560-0043, Japan 3Research Center for Nuclear Physics, Osaka University, Ibaraki, Osaka 567-0047, Japan 4Istituto Nazionale di Fisica Nucleare, Laboratori Nazionali del Sud, I-95125 Catania, Italy 5Dipartimento di Fisica e Astronomia, Universitá di Catania, I-95125 Catania, Italy 6Department of Physics, Istanbul University, Istanbul 34134, Turkey 7Institut fur Kernphysik, Westfälische Wilhelms-Universität Münster, Germany 8Center for Mathematical Science, University of Aizu, Aizu-Wakamatsu, Fukushima 965-8580, Japan 9Department of Physics, University of Tokyo, Hongo, Bunkyo, Tokyo 113-0033, Japan 10Instituto de Física Corpuscular, CSIC-Universidad de Valencia, E-46071 Valencia, Spain

The lifetimes of the first 2(+) excited states of Po-212,Po-210 were measured in two transfer reactions Pb-208(C-12, Be-8)Po-212 and Pb-208(C-12, Be-10)Po-210 by the Recoil Distance Doppler Shift (RDDS) method and by the Doppler Shift Attenuation method (DSAM), respectively. The derived absolute B(E2) values of 2.6(3) W.u. for Po-212 and 1.83(28) W.u. for Po-210 indicate low collectivity. It is shown that the properties of the yrast 2(1)(+), 4(1)(+), 6(1)(+) and 8(1)(+) states in both nuclei cannot be described consistently in the framework of nuclear shell models. It is also demonstrated in the case of Po-210 that Quasi-particle Phonon Model (QPM) calculations cannot overcome this problem thus indicating the existence of a peculiarity which is neglected in both theoretical approaches.