First Spectroscopy of 40Mg

• P. Fallon (Lawrence Berkeley National Laboratory, Berkeley CA 94720, USA)

Room: AG66 The study of nuclei far from stability is one of the most active and challenging areas of nuclear structure physics. One of the most exotic neutron-rich nuclei currently accessible to experiment is 40Mg, which lies at the intersection of the nucleon magic number N=28 and the dripline, and is expected to have a large prolate deformation similar to that observed in neighboring isotopes 32-38Mg. In addition, the occupation of the weakly bound low-l p3/2 state may lead to the appearance of a neutron halo structure. 40Mg offers an exciting possibility and rare opportunity to investigate the coupling of weakly bound valence particles outside a deformed core, and the influence of collective rotational motion near to particle threshold. I will discuss the results of an experiment carried out at RIBF (RIKEN) to study excited states in 40Mg produced by a 1-proton removal reaction from a ~240 MeV/u 41Al secondary beam. 40Mg and other final products were separated and identified using the Zero Degree Spectrometer. Prompt gamma rays were detected using the DALI2 array. The observed excitation spectrum is compared to theory and shown to reveal unexpected properties compared to predictions and to those observed in neighboring, more bound, Mg isotopes.

Systematics of Band Termination at High-Spin in N~90 Nuclei: How Robust and Pure Are These Special States?

• M. Riley (1Department of Physics, Florida State University, Tallahassee, FL 32306, U.S.A.)

Room: AG66 The light rare-earth nuclei near N = 90, are textbook examples (Refs. 1-10) of the evolution of nuclear structure with excitation energy and angular momentum. They display a variety of different phenomena, such as, multiple backbends, dramatic prolate to oblate shape changes associated with band termination plus a spectacular return to collectivity extending discrete gamma-ray spectroscopy into the so-called ``ultrahighspin regime`` (I = 50-70). Band termination represents a clear manifestation of mesoscopic physics, since the underlying finite-particle basis of the nuclear angular momentum generation is revealed. In 158Er, terminating states at values Ip = 40+, 43-, 46+ , 48−, and 49−, have been observed, Other neighbouring nuclei have also been found to exhibit similar fully aligned states providing stringent tests of nuclear models since the wavefunctions for these special states are extremely pure. The present work has been triggered by a comprehensive high-spin analysis of data from Gammasphere on 157Ho90 which showed remarkable similarities to the known band termination states in 158Er90. A systematic analysis of favoured band terminations in neighboring nuclei has subsequently been carried out and will be discussed. [1] Szymanski Z 1983 Fast Nuclear Rotation (Clarendon Press, Oxford, England) [2] Ring P and Schuck P 1980 The Nuclear Many-Body Problem (Springer-Verlag, Heidelberg) [3] Krane K S 1988 Introductory Nuclear Physics (John Wiley and Sons, New York) [4] Ejiri H and de Voigt M J A 1989 Gamma-Ray and Electron Spectroscopy in Nuclear Physics (Clarendon Press) [5] Nilsson S G, Ragnarsson I 1995 Shapes and Shells in Nuclear Structure (Cambridge University Press, Cambridge, England) [6] Heyde K 1999 Basic Ideas and Concepts in Nuclear Physics (Institute of Physics, Bristol) [7] Pancholi S C 2011 Exotic Nuclear Excitations (New York: London: Springer, - Springer tracts in modern physics) [8] Casten R F 2001 Nuclear Structure from a Simple Perspective (Oxford Studies in Nuclear Physics, Oxford University Press; 2 edition) [9] Wang X, Riley M A, Paul E S and Simpson J 2013 McGraw-Hill Yearbook of Science and Technology (McGraw-Hill) [10] by Zelevinsky V and Volya A 2017 Physics of Atomic Nuclei (Wiley_VCH).

Probing the structure of isotopically identified fission fragments @ VAMOS

• A. Navin (Grand Accélérateur National d'Ions Lourds, 14000 Caen, France)

Room: AG66 The characteristic -decay of the excited states of the long chains of isotopes of fission fragments provides fingerprints of the evolution of the underlying nuclear configurations of individual and collective motion of the nucleons as a function neutron-proton asymmetry and angular momentum. The characterization of the -decay of the excited states of these nuclei, especially those far from stability received a boost due to increased selectivity and sensitivity, primarily arising from the isotopic identification of the fission fragments produced in fusion-fission and transfer-induced fission, at energies around the Coulomb barrier @GANIL using a large acceptance spectrometer coupled with a large gamma–ray detector array. The talk will give an overview of the study of the evolution of nuclear structure in isotopic chains of various M,Z identified fission fragments at energies around the Coulomb barrier using the VAMOS spectrometer and EXOGAM $\gamma$-array at GANIL. Further improvements in both selectivity and sensitivity, with a further upgraded VAMOS++ spectrometer and its combination with the next generation AGATA array, for prompt and delayed $\gamma$-rays will also be presented.

Seniority and Generalized Seniority: How far can we stretch these quantum numbers?

• A.K. Jain (Department of Physics, Indian Institute of Technology, Roorkee 247667)

Room: AG66 We present an overview of the seniority and generalized seniority approaches and the various experimental signatures of their validity. We also discuss how the seniority isomers arise and under what conditions. We test the validity of the seniority quantum number with increasing j and in the presence of many j-orbitals. We find that the generalized seniority quantum number retains its applicability, although in an approximate manner, to angular momenta much higher than expected.

Evolution of collectivity and symmetry in nuclei

• Muralithar S (IUAC)

Room: AG66 Evolution of collectivity and symmetry in nuclei S. Muralithar (on behalf of INGA group at IUAC) Inter University Accelerator Centre, New Delhi, 110067, India Studies of extreme nuclear shapes fascinated scientists and are pursued over decades. Nuclei present themselves with interesting shapes and structures at different spin, excitation energy and also with number of neutrons and protons present. Gradual alignment of single particle states in presence of collective excitational modes give rise to rich nuclear structure phenomena as a function of angular momentum in nuclei. Results from in beam fusion evaporation reaction experiments give insight to variety of nuclear structure and give opportunity to test nuclear models. A large number of research groups have carried out such studies using the INGA array of 24 suppressed clover detectors at IUAC in recent years. Few of the recent spectroscopic studies done using Indian National Gamma Array at Inter Uiniversity Accelerator Centre, New Delhi, on -vibrational band, Octupole correlation, Chirality, magnetic and anti magnetic rotation will be presented. Some of the ancillary devices such as plunger (for lifetime measurement), charged particle detector array developed at IUAC will be coupled to INGA in coming months. INGA would also be coupled to mass spectrometer HYbrid Recoil Analyser (HYRA) for next experimental campaign at IUAC.

Fission Fragment Spectroscopy: Challenges and opportunities

• D.C. Biswas (Bhabha Atomic Research Centre)

Room: AG66 Nuclear fission process offers an opportunity to study the interplay of the nuclear structure and dynamics in the fission process. In nuclear fission, a large number of neutron-rich nuclei are produced and the shape of the fissioning nucleus evolves in the multidimensional space of relative separation, neck opening, mass asymmetry and deformation of the fragments. In this talk the role of nuclear shell structure as well as importance of shape deformations in the fission fragment mass distribution will be discussed. Some recent investigations on the fission fragment mass measurement using thermal neutrons from reactors will be presented. The possible experiments that can be carried out of utilizing a new setup being developed at Dhruva reactor using clover germanium detectors and LaBr3 will be discussed.

Probing nuclei near shell closure using alpha beam

• S. Bhattacharya (Variable Energy Cyclotron Center)

Room: AG66 Nuclei near shell closures provide the opportunity to probe the various aspects of excitations of single particle orbitals and their shape driving effects. Collectivity can be induced in near spherical nuclei close to shell closure due to the high-j intruder single particle orbitals. The nuclei near Z=50, N=82 and Z=82, N=126 shell closure is difficult to access by heavy ion reactions and light ion induced reactions are most suitable to populate them with large cross section. Both yrast and non-yrast states are possible to be excited in these light ion induced reaction and one can probe the single particle excitations by horizontal spectroscopy. The single particle and collective excitations of some of the nuclei near shell closure have been probed recently at VECC using alpha beams and Compton suppressed Clover detector setup of VENUS and INGA. The advantages of using alpha beams and some of the related physics results of these measurements will be presented.

Nuclear symmetries: critical observation through measurement of short lifetimes

• Pragya Das (IIT Bombay)

Room: AG66 Nuclei at high angular momentum states exhibit various symmetries. The underlying physics which describe these symmetries are often model dependent. Therefore, it is difficult to find a unique set of experimental observables. Originally, Chiral symmetry was recognized by two nearly degenerate bands. A stringent test of Chirality now is the observation of a regular pattern of reduced transition probabilities- identical B(E2) values for the two Chiral bands and alternating sequence of B(M1), between low and high values, for intra-band as well as inter-band transitions [1]. While 128Cs showed the expected behavior, 132La deviated significantly [2]. We have performed an experiment at IUAC (New Delhi) using reaction 116Cd(19F, 5n)130La to measure B(E2) and B(M1) for the two bands which were already qualified as Chiral partners on the basis of near degeneracy. Short lifetimes (in ps) have been measured using Doppler shift attenuation method (DSAM). Our results on the reduced transition probability will finally decide if 130La qualifies for the Chiral symmetry or not. If not, the question will still remain to find an alternative explanation- possibly a different kind of symmetry. Many early studies were devoted to finding different nuclear shapes e.g. axial (prolate or oblate) and triaxial. With the observation of signature splitting and signature inversion, it was possible to assign different shapes at low and high spins. Whenever there remained ambiguity in explanation, measurement of lifetimes was required. Earlier, we proposed a change in the axis of rotation for the doubly odd 126I at inversion point [3]. However, after we performed lineshape analysis using DSAM, a different picture has emerged. A detailed discussion will be presented. [1] I. Hamamoto, Int. J. Mod. Phys. E 20, 373 (2011). [2] E. Grodner et al., Phys. Rev. Lett. 97, 172501 (2006). [3] Bhushan Kanagalekar et al., Phys. Rev. C 88, 054306 (2013).

Shape evolution in neutron-rich Zr nuclei

• Purnima Singh (Irfu, CEA, Universite Paris-Saclay, F-91191 Gif-sur-Yvette, France)

Room: AG66 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 quest in nuclear physics. In this regard, the neutron rich nuclei with Z~40 and N~60 have attracted considerable attention recently. While the ground states of Sr, Zr, and Mo isotopes with N ranging from the magic number N = 50 up to N<60 are weakly deformed, they undergo a shape transition from nearly spherical to well deformed prolate deformations as N = 60 is approached. This shape transition is rapid in Sr and Zr isotopes as evident from the abrupt changing of lifetimes and excitation energies of 2+ 1 states. Whereas, in isotopes with Z≥42 the shape change is rather gradual showing characteristic signatures of triaxiality. This strong dependence of observed spectroscopic properties on the number of protons and neutrons, makes the neutron-rich A~100 nuclei a very good region for testing various theoretical models. Several experimental and theoretical efforts have been made to investigate the structural evolution in these nuclei, however, a satisfactory description is still far from being complete. Further experimental information, especially lifetime and static quadrupole moments of these nuclei is an important step towards providing a firmer understanding of their properties through comparisons with modern theoretical models. Some recent results from our experimental program to study these nuclei using fusion-fission experiment performed at GANIL will be presented and the future prospects will be discussed.

High Spin Spectroscopy: Microscopic Theory and Perspectives

• C.R. Praharaj (Institute of Physics, Bhubaneswar 751005)

Room: AG66 We emphasise the role of interacting Neutrons and Protons in large Shell Model Spaces, interacing by effective two-body interactions , in determining nuclear properties, deformations and spectra. Theoretical formalism to study the many-body interacing system will be discussed. Deformed Hartree-Fock theory and Angular Momentum Projection (along with diagonalisation for band mixing will be discussed. Results of theoretical calculations and comparison with available experimental data will be presented. Some theoretical predictions and expectations will be given for future studies. Some of these will be: High Spin phenomena in including heavy nuclei (rare-earths, Hf, Hg etc) Deformed structures and excited rotational bands in closed shall nuclei (82Ge, 84 Se, 56 Ni, 78Ni etc) Future perspectives: Band structures in exotic nuclei Need for gamma-ray spectroscopy of multiquasiparticle excited configurations References: 1. Zashmir Naik and C .R. Praharaj, Phys. Rev. C67,054318 (2003) 2. S.K. Ghorui and C.R. Praharaj, Pramana 82, 659-669 (2014); S.K Ghorui et. al., IJMP E21, 1250070 (2012)

Isomers from multi-nucleon hole configurations near doubly-magic 208Pb

• S.K. Tandel (UM-DAE Centre for Excellence in Basic Sciences, Mumbai, India)

Room: AG66 Nuclei with Z < 82 and multiple nucleons in hole states with respect to the heaviest doubly-magic nucleus 208Pb are near-spherical, and have high-j valence orbitals: neutron i13/2 and proton h11/2, present near the respective Fermi surfaces. These are suitable conditions for the realization of high-spin isomers with configurations having dominant contributions from high-j orbitals. Several isomers have been identified in the isotopes 201-203Tl with half-lives in the nanoseconds-microseconds range. Excited states in Tl isotopes were populated through fusion-evaporation and multi-nucleon transfer reactions. Gamma-ray coincidence data, recorded using the INGA and Gammasphere detector arrays at the Inter-University Accelerator Centre and Argonne National Laboratory, respectively, were used to establish detailed decay schemes and half-lives of isomers. Many new gamma rays have been identified in each of these isotopes. In addition to isomers, multi-quasiparticle states involving two to seven nucleons have been established in various Tl isotopes along with core excitation of possible octupole character. These data provide an opportunity to understand nuclear structure in the vicinity of 208Pb and allow for stringent tests of modern-day, large-scale shell model calculations and associated interactions.

Nuclear structure studies in the vicinity of shell closure

• S. Sihotra (Department of Physics, Panjab University, Chandigarh-160014, India.)

Room: AG66 The nuclei approaching the neutron and proton major shell closure at N=Z=50 provide a unique opportunity to study interplay between the single particle and collective degree of freedom and the influence of the valence orbitals on deformation. Theoretical interpretation of band structures observed in the nuclei approaching major shell closures at N=Z=50 have revealed diversity in the deformation-generating mechanisms. The proton particle-hole excitations across major shell gap are energetically possible due to the strong proton-pair correlations and proton-neutron interaction between the spin-orbit partner orbitals. As one approaches , N =54 the h11=2 subshell intruder orbital is likely to be occupied. The Neutron Fermi level lie at the bottom in the h11=2 sub shell or the low- h11=2 orbitals are accesible at low excitation energies, the shape is driven to prolate deformation. The active intruder orbitals lie near the top in the high- g9=2orbitals which drives shapes towards oblate deformation. The delicate interplay of strongly shape-driving g9=2 and h11=2 orbitals result in the soft (triaxial) shapes with modest deformation. Intriguing relevant phenomena such as magnetic rotation and degenerate twin bands have been reported in this mass region. The limited number of valence particles (holes) in the nuclei in this mass region, are able to break the spherical symmetry and induce, albeit small, nuclear deformation. Because the small (prolate) deformation requires high angular velocity to generate collective angular momentum, specific noncollective \aligned" states with the nuclear spin made up completely from single particle angular momentum contributions, are able to compete energetically with the weakly deformed collective structures. In the nuclides in the A100 region, there is existence of isomers due to the presence of low energy states based on the p1=2 and g9=2 orbitals, with widely dierent angular momentum where the $\gamma$-decay is slow. The identication of isomers has been a difficult task, considerable effort has been devoted to the study of isomers in nuclides. For the even -Z and odd -A nuclei in this mass region, the presence of nearby h11=2, g7=2, d5=2 neutron orbitals usually give rise to dierent one-quasiparticle band structures, and further rearrangements of neutrons and protons is expected to add richness to the structure.

FAIR and NUSTAR - Status and opportunities

• J. Gerl (FAIR/GSI Darmstadt Germany)

Room: AG66 The international FAIR project at GSI aims for an unprecedented facility for research with stable and radioactive ion and anti-proton beams. It will comprise of ion beam accelerators, storage rings, an anti-proton source, a fragment separator and experimental set-ups for four research pillars. These pillars are organized in large collaborations involving almost 3000 scientists: APPA for atomic and plasma physics, biology and material science, CBM for studies of compressed baryonic matter, NUSTAR for nuclear structure, reactions and astrophysics investigations, and PANDA for anti-proton studies. After a reorganisation in 2015 the FAIR project is progressing vigorously. Construction of the buildings and production of the machine and experiment components have started. Moreover, preparations for a scientific phase-0 program are on-going. From 2018 almost until 2024/25, when the full FAIR facility will become operational, experiments can be performed with the upgraded GSI accelerators and the already available FAIR sub-systems, e.g. the many NUSTAR set-ups. NUSTAR is the largest collaboration for nuclear structure, astrophysics and reactions studies in the world. It was founded 12 years ago to develop a science programme and build instrumentation for the planned FAIR facility at GSI Darmstadt, Germany. A versatile suite of state-of-the-art detection system has been developed and is being employed already now at GSI and other facilities in the world. NUSTAR relies primarily on the availability of exotic rare isotope beams produced by fragmentation reactions and fission of relativistic heavy ions. The fragment separator FRS and a versatile set of instruments, including gamma arrays, particle spectrometers and a storage ring enable unique experiments at GSI. The Super-FRS at the FAIR facility will provide several orders of magnitude stronger beams, enabling access to the extremes of nuclear stability. Continuous R&D efforts result in improved detectors and enable the NUSTAR collaboration to steadily enhance the sensitivity and selectivity limit of their experiments. The status of FAIR and NUSTAR will be reported and the opportunities for NUSTAR experiments in FAIR phase-0 at GSI and at Day-1 at GSI will be discussed.

Nuclear structure studies with brilliant gamma beams at ELI-NP

• D.L. Balabanski (Extreme Light Infrastructure – Nuclear Physics, Horia Hulubei National Institute for R&D in Physics and Nuclear Engineering, Reactorului Str. 30, 077125 Bucharest – Magurele, Romania)

Room: AG66 he emerging experimental program with brilliant gamma beams at the Extreme Light Infrastructure – Nuclear Physics facility (ELI-NP), which is under construction in Magurele, Romania will be presented with emphasis on the prepared day-one experiments. Experiments at ELI-NP will cover nuclear resonance fluorescence (NRF) measurements, studies of large-amplitude motions in nuclei, photofission and photonuclear reactions of astrophysics interest, and measurements of photonuclear reaction cross sections. The physics cases of the flagship experiments at ELI-NP will be discussed, as well as the performance of the related instruments which are under construction for their realization. *Work supported by the Extreme Light Infrastructure Nuclear Physics (ELI-NP) Phase II, a project co-financed by the Romanian Government and the European Union through the European Regional Development Fund – the Competitiveness Operational Programme (1/07.07.2016, COP, ID 1334)

CAGRA Project at RCNP, Osaka University

• Eiji Ideguchi (RCNP, Osaka University)

Room: AG66 We have started a CAGRA (Clover Array Gamma-ray spectrometer at RCNP/RIBF for Advanced research) project at RCNP, Osaka Univeristy. This project constructs a Compton-suppressed Germanium clover array (CAGRA) by an international collaboration (U.S.-Japan-China-Italy, …). It consists of 16 Ge Clover detectors with BGO Compton shields. and a digital data acquisition system employing GRETINA digitizers is used, which enables high-rate data taking. At RCNP cylclotron facility, there are various experimental capabilities such as high-resolution spectrometer, Grand Raiden, low-energy RI beam facility, EN beam line, and the DC muon beam facility, MuSIC. By combining the CAGRA with these devices, many physics opportunities will be provided. So far, CAGRA campaign experiments at EN beam line and Grand Raiden were successfully performed. It is also planned to bring the CAGRA array to RIBF for further experimental studies using unstable nuclear beams. In this talk, an overview of the CAGRA project and recent experimental results in the studies of mass 40 region obtained from the CAGRA experiment ar RCNP will be presented.

Nuclear physics studies at the Legnaro National Laboratories

• Francesco Recchia (Dipartimento di Fisica ed Astronomia "Galileo Galilei" Universita' degli Studi di Padova)

Room: AG66 The SPES Radioactive Ion Beam facility at INFN-LNL is presently in the construction phase. The facility is based on the Isol (Isotope separation on-line) method with an UCx Direct Target able to sustain a power of 10 kW. The primary proton beam is provided by a high current Cyclotron accelerator with energy of 35-70 MeV and a beam current of 0.2-0.5 mA. Neutron-rich radioactive ions are produced by proton induced Uranium fission at an expected fission rate of the order of 10^13 fissions per second. After ionization and selection the exotic isotopes are re-accelerated by the ALPI superconducting Linac at energies of 10 AMeV for masses in the region A = 130. The expected secondary beam rates are of the order of 10^7 - 10^9 pps. Aim of the SPES project is to provide a facility for high intensity radioactive ion beams for nuclear physics research as well as to develop an interdisciplinary research center based on the cyclotron proton beam. An overview of the planned instrumentation for the SPES facility will be presented together with some examples of perspective future studies.

Beta-delayed neutron emitters and advances in fast neutron spectroscopy

• P. Chowdhury (Radiation Laboratory Pinanski 201 University of Massachusetts Lowell Lowell, MA 01854)

Room: AG66 The talk will focus on (a) high-resolution gamma-ray spectroscopic studies of beta-delayed neutron-emitters far from stability at the the Californium Rare Isotope Breeder Upgrade (CARIBU) facility at Argonne National Lab; and (b) advances in fast neutron spectroscopic techniques with CLYC scintillators at Los Alamos National Lab and at the Radiation Laboratory at UMass Lowell.

Short presentation Room: AG66

Systematic study of fission fragment de-excitation depending on compound system and excitation energy

• Andreas Oberstedt (Extreme Light Infrastructure - Nuclear Physics (ELI-NP))

Room: AG66 Nuclear fission is a complex process, which – after almost 80 years since its discovery – is still not fully understood. One field of research is for instance studies of the de-excitation process of fission fragments, which in the early stages, i.e. within a few nanoseconds after scission, takes place through the successive emission of prompt neutrons and gamma rays. For nuclear applications, information about the prompt neutrons is crucial for calculating the reactivity in reactors, while precise knowledge about the prompt gamma rays is important for the assessment of the prompt heat released in the reactor core. Concerning the latter we have contributed in the past years with a number of precise measurements of prompt gamma-ray spectra from spontaneous as well as thermal and fast neutron-induced fission of various compound systems. From those we determined average characteristics like multiplicity, mean energy per photon and total gamma-ray energy released in fission. The obtained results were investigated for their dependence of mass and atomic numbers of the fissioning system as well as the dissipated excitation energy. The purpose of this endeavor was to find a description that allows predicting prompt gamma-ray spectra characteristics for cases that cannot be studied experimentally. In this talk we will give an overview on the latest measurements of prompt fission gamma ray spectra. We will also present first results from a recent angular correlation measurement between these gamma rays and fission fragments from the spontaneous fission of 252Cf and infer what can be learned from the observed angular distributions. For instance, the relative contributions of dipole and quadrupole photons were deduced and compared to results of very recent calculations with the Monte Carlo Hauser-Feshbach code FIFRELIN, developed at CEA Cadarache.

Measurement of gamma rays from both hadronic and electromagnetic decay of giant resonance of 12C and 16O

• Makoto Sakuda (Physics Department, Okayama University, Japan)

Room: AG66 We have carried out an experiment E398 at RCNP (Osaka) to measure gamma rays from both hadronic decay and direct electromagnetic decay of giant resonance of 12C and 16O using 392-MeV proton beam, high-resolution magnetic spectrometer Grand-Raiden and an array of NaI(Tl) counters. We first confirmed the consistency of our cross section of the known levels (12.71MeV, 15.11MeV) with the previous measurements. Then, we measure the gamma emission probability \Gamma_{\gamma}/\Gamma at each 2 MeV step for 16<Ex<34MeV. The gamma emission probability for the giant resonance of 12C increases from 0 at Ex=16MeV to 0.7 at Ex=27 MeV and then begins to decrease. The measurement is compared to the statistical model calculation. We also observe the direct electromagnetic decay from the giant resonance of 12C to be about 0.28+-0.04(stat) % for 22<Ex<26MeV, where GDR resonances are known to be there, while we observe no significant direct decays for 16<Ex<22MeV, where there are higher multipole resonances (JP=2-, 3-). This is the first systematic measurement of gamma rays from both hadronic decay and electromagnetic (direct) decay of the giant resoance of 12C (and 16O) over the excitation energy 16MeV<Ex<34MeV. We apply our measurement for the estimation of gamma rays induced by neutrino bursts from supernova explosion.

Search for Double Beta Decay in 94Zr

• V. Nanal (Tata Institute of Fundamental Research)

Room: AG66 Double beta decay (DBD) is a rare second-order weak nuclear transition, first suggested by Maria Goeppert-Mayer in 1935 [1]. Generally, in the case of a beta unstable parent nucleus it is extremely difficult to distinguish the rare DBD from an intensive single beta decay background. There are 35 even-even nuclides with single beta decay either energy forbidden or spin suppressed, which makes it possible to search for the DBD transformation in these nuclides. In the two-neutrino double beta decay (2$\nu\beta\beta$) mode, two neutrons simultaneously undergo beta decay producing two protons, two electrons and two anti-neutrinos in the final state. The 2$\nu\beta\beta$ process has been experimentally observed in 12 nuclei so far with a half-life range of T1/2~ 10^18-10^24 y [2]. Neutrinoless Double Beta Decay is a phenomenon of fundamental interest for particle physics. For a number of nuclei, double beta decays to excited states in their daughter nuclei are also energetically possible and can provide supplementary information for the calculation of NTME for the process. These processes can be probed at low background facilities and limits of the order of T1/2~ 10^18-10^25 y have been reached using different experimental techniques for some nuclei. In the present work, double beta decay of 94Zr to the 2+ excited state of 94Mo at 871.1 keV is studied using TIFR low background counting setup. No evidence of this decay was found with a 232 g.y exposure of natural Zirconium. The lower half-life limit for the double beta decay is significantly improved over the existing experimental limit [3]. Challenges in the measurement and results will be discussed in this talk. References: [1] M. Goeppert-Mayer, Phys. Rev. 48 (1935) 512. [2] R. Saakyan, Annu. Rev. Nucl. Part. Sci. 63 (2013) 503. [3] N. Dokania et al. Eur. Phys. J. A 53, 74 (2017)

Nuclear Deformation and the search for neutrinoless double beta decay $(0\nu\beta\beta)$: A case study of $^{76}$Ge

• D. Ayangeakaa (United States Naval Academy, Department of Physics, 572 Holloway Road, Annapolis, MD 21402 USA.)

Room: AG66 Observation of neutrinoless double-beta decay $(0\nu\beta\beta)$ would both demonstrate the Majorana nature of the neutrino and provide experimental access to its absolute mass scale. A great deal of experimental effort is, therefore, being dedicated to the detection of this rare process. However, results of nuclear structure calculations of nuclear matrix elements which mediate the decay differ by up to a factor of three, depending on the methodology. This translates into an order of magnitude variation when considered in terms of the decay lifetime. Experimental input from a nuclear structure perspective to constrain these calculations is, thus, imperative and significant experimental work (e.g., studies of transfer reactions, gamma-ray spectroscopy, etc.) has already been done in this context. In this talk, results of a high-precision Coulomb excitation measurement of $^{76}$Ge, performed at Argonne National Laboratory using GRETINA and CHICO2 will be presented. The results will be compared with state-of-the-art Shell Model calculations and recently obtained $(n,n’\gamma)$, with emphasis on demonstrating the importance of nuclear deformation in determining the nuclear decay matrix element.

Of Signals, Shapes and Shells: Nuclear Structure Studies at the Consortium

• S. S. Ghugre (UGC DAE CSR Kolkata Centre, Kolkata 700098)

Room: AG66 The Kolkata Centre of the UGC-DAE Consortium for Scientific Research has been contributing to the nuclear structure research in the ountry for around two decades starting with setting up a modest clover array at TIFR in 1999 and later working towards conception and installation of the Indian National Gamma Array (INGA). The Consortium has been one of the key partners in the use, operation, maintenance and evolution of the facility over the period. Recently the group at the Consortium has been active while working in collaboration with TIFR, VECC, IUAC and Universities in the domain of instrumentation for the data acquisition and sorting and the data analysis codes and the pursuits in nuclear physics in the vicinity of shell closures. Consortium has been able to incorporate the use of a unique digitizer based pulse processing and data acquisition system at the ongoing campaign of INGA at the room temperature K130 cyclotron of the Variable Energy Cyclotron Centre (VECC), Kolkata. A versatile package of codes, IUCPIX, for reducing the acquired data from the digital DAQ has been developed. The nuclear lifetime analysis code has been extended to the applicability of the Doppler Shift Attenuation Method (DSAM) beyond the conventional thin-target-on-thick-backing setups to atypical configurations involving thick elemental or even molecular targets required, at times, to cater to specific experimental aspirations. The particular physics interest of the Group centers around nuclei in the vicinity of shell closures and systematic studies of the same have been undertaken in the A~30, 60, 200 regions. The experimental results are interpreted from large basis shell model calculations that feature as one of the principal components of the aforementioned pursuits. These various R & D efforts of the Consortium in domain of gamma ray spectroscopy shall be elaborated in the conference.

Detector requirements and simulation for HISPEC/DESPEC experiments at Super-FRS

• Sudipta Saha (GSI Helmholtzzentrum Für Schwerionenforschung)

Room: AG66 The HISPEC/DESPEC experiments will explore the problems related to nuclear structure, reaction and astrophysics far from the valley of stability using γ-ray spectroscopy techniques. The experiments will be carried out after successful production, separation, and selection of these exotic nuclei at Super-FRS of FAIR. Based on the physics requirement various tracking and identification detectors will be required at the focal planes of Low Energy Branch (LEB) relevant for H/D experiments. Simulations have been carried out for specification of the H/D tracking detectors as well as arrays planned for γ-ray spectroscopy. The physics cases, related detector development and some simulation results related to H/D experiment will be discussed.

Wobbling Motion in A$\sim$130 Nuclei

• U. Garg (University of Notre Dame)

Room: AG66 Wobbling of triaxial even-even nuclei represents the quantized oscillations of the principal axes of an asymmetric top relative to the space-fixed angular momentum vector or, in the body fixed frame of reference, the oscillations of the angular momentum vector about the axis of the largest moment of inertia [1]. In transverse wobbling, the odd quasiproton, with predominantly particle nature, aligns its angular momentum vector j along the short axis of the triaxial rotor, i.e., perpendicular to the axis with the largest moment of inertia [2]. The result is a pair of bands corresponding to wobbling phonons nw=0 and nw=1. In a series of measurements with Gammasphere and INGA, we had identified “wobbler partner” bands in the nucleus $^{135}$Pr, the first observation of wobbling in a mass region other than near A~160 [3]. The nature of wobbler bands is confirmed by verifying the Delta-I=1, E2 character of the inter-band transitions via angular distribution and polarization measurements. The transverse nature of wobbling is evidenced by the characteristic decrease in E_{wobb} [2]. In the isotone $^{133}$La, one observes longitudinal wobbling instead. These observations are in accordance with Quasiparticle-triaxial-rotor (QTR) and Tilted-axis-cranking (TAC) calculations. [1] A. Bohr and B. R. Mottelson, Nuclear Structure II (Benjamin, 1975). [2] S. Frauendorf and F. Dönau, Phys. Rev. C 89, 014322 (2014). [3] J. T. Matta et al., Phys. Rev. Lett. 114, 082501 (2015).

Consistent description of shell gaps and deformed states around $^{16}$O and $^{40}$Ca

• Yutaka Utsuno (Japan Atomic Energy Agency, Tokai, Japan)

Room: AG66 From the early days of nuclear-structure physics, the nature of the second 0+ state in $^{16}$O has been an attracting issue. This nucleus is a typical doubly magic nucleus, and its second 0+ state is interpreted as a four-particle four-hole state. The excitation energy of this state, however, looks too low, considering the large shell shell gap that is naively estimated to be about 11 MeV. In fact, the previous large-scale shell-model calculations (Haxton and Johnson; Warburton et al.) assumed a quenched shell gap from this value. One of the primary aim of the present srudy is how the use of the narrow gap is justified. We focus on the role of correlation energy due to particle-hole excitation, and find that the actual shell gap must be narrower owing to correlation energy compared to a simple estimate from the separation energies. We then achieve a consistent description of the "shell gap" and deformed states around $^{16}$O. The same idea has recently been applied to the $^{40}$Ca region. The N=Z=20 shell gap is determined in the same way, and the resulting shell-model Hamiltonian well reproduces four-particle four-hole bands that appear systematically around $^{40}$Ca.

Studies of extremely deformed nuclei near 40Ca

• Piotr Bednarczyk (IFJ PAN, Krakow)

Room: AG66 The medium light nuclei situated in the nuclear chart between the double magic nuclei 40Ca and 58Ni exhibit many features characteristic for well deformed heavier nuclei. Although in this regions close to the stability line the ground states are predominantly spherical or oblate, at higher values of spin well developed rotational bands are present. This happens in particular when the intruder f7/2 or g9/2 proton- and neutron- shells are partially filled. Such SD-like bands, resulted from the multiple particle-hole excitations across the magic N,Z=20 shells, were observed so far in several isotopes of Ar, Ca and Ti, but this knowledge is limited to rather moderate spins I ≤16. The effective interactions derived for the sdfp active orbitals allowed for reasonable description of the collectivity developed in these nuclei, from low lying band heads up to the maximum aligned spin, within the spherical shell model. On the other hand, recent calculations performed in the framework of the EDF theory [1] foresee extremely deformed, high spin cluster states, that become yrast beyond the SD termination. I will discuss plans to investigate very deformed rotational bands in these nuclei. Application of complementary methods: Coulomb excitation and gamma spectroscopy in the continuum will provide opportunity to track the shape evolution in the full range of the available angular momentum. [1] D.Ray and V.Afanasjev, PhysReV C94, 014310(2016)

Reinforce in low and intermediate states of the beta stable Ba and Xe nuclei near N=82 shell closure

• Kumar Suresh (University of Delhi)

Room: AG66 In A ~ 130 mass region, the nuclei show many interesting phenomena like shape coexistence, MR bands, chiral bands and spin isomers. They are γ-soft in the ground state with triaxial deformation. The 134Ba nucleus has already studied for low-spin states and seen to be one of the best candidate for E(5) critical point symmetry . In the previous experimental study, the 10+, 5- and 7– isomeric states based on the configurations v[h_11/2^2} 10+ and v[s_1/2^1 h_11/2 ^1) 5- or (v[d3/2 h11/2]) 7- are also observed. The other isotone of N=78 have been already studied for the intermediate and high spin states. The 136Ce and 138Nd nuclei exhibit many dipole bands at their high spin states having different shapes and phenomena. Recently, the 132Xe and 133Xe nuclei are investigated through multinucleon-transfer in the AGATA array coupled to the magnetic spectrometer PRISAMA and the GAMMASPHERE array along with CHICO. In the first experiment, the 134Ba nucleus was populated using the reaction 124 Sn(13C, 3n) 134Ba at a beam energy of 48 MeV from the Pelletron accelerator at Tata Institute of Fundamental Research (TIFR), Mumbai. The 124Sn target of thickness 1.5 mg/cm 2 with the Au backing was used. The gamma-rays were detected using the Indian National Gamma Array (INGA). In the present study, the level scheme was extended upto a maximum spin of 20. In the intermediate excitation, three quadrupole bands were observed and the level of the gamma-band was re-confirmed at the low-excitation. In the second experiment, the alpha induced fusion evaporation reaction is used to explore the intermediate states of 132Xe in INGA spectrometer at VEEC, Kolkata using seven HPGe clover clover detectors and one LEPS segmented detector. Both the nuclei (134Ba and 132Xe) have shown similar structure at low and intermediate spin. The theoretical calculations to understand these bands are in progress.

Ab initio shell-model study of nuclear observables

• Praveen Chandra Srivastava (Indian Institute of Technology Roorkee, Roorkee -247667, India.)

Room: AG66 Modern ab initio approaches, like the IM-SRG, the coupled cluster theory and the self-consistent Green’s function method, have been established and provide accurate description of nuclear properties. The ab initio approaches are more fundamental, although in many cases empirical interactions still are used as benchmarks. The ab initio calculations can be used not only for spherical nuclei, but also to predict the ground and excited state energies and deformations for doubly open shell nuclei. With these recent ab initio approaches it is now feasible to perform ab initio calculations for medium and heavier nuclei. In this meeting I will present first ab initio shell-model results of electromagnetic properties [1], GT strengths [2] and spectroscopic factor strengths [3] of sd shell nuclei. For above calculations, the ab initio effective interactions are based on in-medium similarity renormalization group (IM-SRG) and coupled-cluster effective interaction (CCEI) approaches. References [1] A. Saxena and P.C. Srivastava, First-principles results for electromagnetic properties of sd shell nuclei, Phys. Rev. C 96, 024316 (2017). [2] A. Saxena, P.C. Srivastava and T. Suzuki, Ab initio calculations for Gamow- Teller strengths in sd shell, arXiv:1801.04859. [3] P.C. Srivastava and V. Kumar, Spectroscopic factor strengths using ab initio approaches, Phys. Rev. C 94, 064306 (2016).

Short presentation Room: AG66

Evidence of γ-instability in 124Te

• Hariprakash Sharma (BANARAS HINDU UNIVERSITY)

Room: AG66 Investigation of Te-nuclei has been subject of considerable interest because of their transitional character. Particularly, the h11/2 orbital play important role in Te nuclei, because the alignments of low-Ω h11/2 valance protons outside the core drive the nucleus towards prolate shape and the aligned high-Ω neutrons drive the nucleus towards oblate shape and induces tri-axiality. As of this, bands associated with β and γ deformation have been observed in these nuclei. Systematically, band structures associated with particle-hole configurations have been studied up to high spin, however, the structures of low lying non-yrast states are not well studied in these nuclei. The experimental data is very limited in the literature regarding non yrast states, hence, low lying states of 124Te were investigated via 122Sn(9Be, α3n)124Te reaction using INGA facility installed at 15 UD Pelletron accelerator at IUAC, New Delhi. The non-yrast states have been studied up to 12ħ. Results of the investigation will be discussed in the conference.

An overview of recent experiments at VECC-INGA array

• A. Goswami (Saha Institute of Nuclear Physics, HBNI, Kolkata 700064, India)

Room: AG66 Recently a number of experiments were performed at VECC-INGA array with low energy (28-40 MeV) alpha beam. The array consists of six to seven Compton suppressed Clovers and one LEPS along with digital data acquisition system. The primary physics issues addressed in the present campaign is the study of non-yrast excitation modes in nuclei across A 190, 160, 130, 110, 70, 40 mass regions. Dierent properties like multiphonon and mixed symmetry states in odd-A nuclei in A=130 mass region, -vibrational band in mass 110 region, investigation of near yrast band structure of transitional nuclei in A=80 region etc. were studied. Preliminary results of the analysis of dierent experiments will be presented.