ANNUAL REPORT 2011 - Instituto de Estructura de la Materia

show an enormous reduction that could only be explained considering dipolepolarizability effects and coupling tothe continuum. These results have been presented at various conferences this year (FUSION11 Saint-Malo, France,Rutherfors Centenial Conference – Manchester UK), and they are now being summarized in an article.On November of 2011 our group performed an experiment at CMAM Madrid dedicated to measure the elasticscattering cross section of 3 He on a heavy target. The aim of this work is to extract the dipole polarizability of 3 He,and to compare it to previous measurements, which are in disagreement. A beam of 3 He was accelerated at the 5 MVTandem at CMAM and impinged upon a 208 Pb target, covering the energy range between 9 and 15 MeV. The setupconsisted of two Double-sided Silicon Strip Detectors (DSSD) placed at backward angles, plus one Si surface barrierdetector placed at 60º. Analysis of the data from this measurement is currently being carried out by our postdoc A.Becerril.BETA DECAY STUDY OF THE N=Z NUCLEUS 72 KrThe beta decay of N=Z nucleus 72 Kr was measured at ISOLDE (CERN) with “Lucrecia”, a Total Absorption gammaSpectrometer (TAS) with the aim of determining the sign of the deformation from the Gamow-Teller strengthdistribution. The analysis of the data showed up the need for further information on the competence betweenconversion electrons and gamma emission of low energy transitions. This is why we performed complementarymeasurements in order to determine the conversion coefficients of low energy transitions in the daughter nucleus,72 Br. Of special interest was to determine the half--life of the isomeric state at 101 keV in 72 Br and the multipolarityof the gamma transition connecting with the ground state as the spin of the latter has been debated and it is still notfirmly established.The analysis of the electron conversion data has been performed and the results are in progress to be published. Theconversion coefficients of several low energy transitions in the beta decay of 72 Kr have been determined, allowing toextract valuable information on the spin-parity of several excited states in the daughter nucleus. In particular, themultipolarity of the transition connecting the isomeric state with the ground state has been determined as well as anew measurement of the half-life of the isomeric state through the study of the time evolution of the gammaemission of this deexcitation.These results on the level scheme at low excitation energy of 72 Br allow us to face the analysis of the data taken withthe TAS “Lucrecia” which is currently in progress. The experimental distribution of Gamow-Teller strength in ourdecay will be obtained from the beta feeding distribution to excited levels in 72 Br through the beta decay of 72 Kr.This complete study of the beta decay of N=Z nucleus 72 Kr is the main topic of the Ph. D. work of the student JoséA. Briz (PhD Fellowship-FPI).TRANSFER REACTIONS ON EXOTIC NEUTRON-RICH BEAMS AT REX-ISOLDESingle-nucleon transfer reactions constitute an excellent tool to study single-particle properties of nuclear states. Inparticular they provide essential data to study the evolution of shell structure and of effective single-particle energiesaway from the line of beta stability. Dr. Riccardo Orlandi, member of our group since June 2010 (and since January2011 on a CPAN Postgraduate contract), is involved in the study of single-nucleon transfer reactions at REX-ISOLDE. The experiments exploit the coupling of the T-REX Si array to the MINIBALL germanium detector array.In 2011 R. Orlandi and A. Jungclaus were actively involved in the setup and running of one such experiment:72 Zn(t,p) 74 Zn, which took place in October 2011. R. Orlandi is currently carrying on the data analysis for the78 Zn(d,p) 79 Zn experiment which was performed at ISOLDE at the end of 2010. Preliminary results from these datahave already been presented as oral contributions to three international conferences during 2011 (ARIS – Leuven,NCNP – Stockholm, Rutherford Centennial Conference – Manchester).EVIDENCE FOR A SPIN-ALIGNED NEUTRON-PROTON PAIRED PHASE FROM THE LEVELSTRUCTURE OF 92 PdIn an experiment performed at GANIL (Caen, France), the excitation scheme of the extremely neutron deficientnucleus 92 Pd has been studied for the first time within an international collaboration. The Pd nuclei were producedusing a fusion-evaporation reaction and identified using the gamma spectrometer EXOGAM, the CsI arrayDIAMANT for charge particle detection and a neutron wall comprising 50 liquid scintillators. The study was aimedat investigating a long standing question that has received considerable attention in nuclear physics – whether a newtype of pair correlations between neutrons and protons (“isoscalar pairing” where the proton and neutron spins arefully aligned) could appear in nuclei with equal numbers of neutrons and protons. In all atomic nuclei studied untilnow, the low-lying structures are generally characterized by pair correlations between like-nucleon pairs, i.e. pairs ofneutrons and pairs of protons. Since these are identical particles they must, according to the Pauli Principle, have57