Resonance Excitations in Be 7 (d,p) Be∗ 8 to Address the Cosmological Lithium Problem

6 pags., 5 figs., 3 tabs.The anomaly in lithium abundance is a well-known unresolved problem in nuclear astrophysics. A recent revisit to the problem tried the avenue of resonance enhancement to account for the primordial Li7 abundance in standard big-bang nucleosynthesis. Prior measurements of the Be7(d,p)Be∗8 reaction could not account for the individual contributions of the different excited states involved, particularly at higher energies close to the Q value of the reaction. We carried out an experiment at HIE-ISOLDE, CERN to study this reaction at Ec.m.=7.8 MeV, populating excitations up to 22 MeV in Be8 for the first time. The angular distributions of the several excited states have been measured and the contributions of the higher excited states in the total cross section at the relevant big-bang energies were obtained by extrapolation to the Gamow window using the talys code. The results show that by including the contribution of the 16.63 MeV state, the maximum value of the total S factor inside the Gamow window comes out to be 167 MeV b as compared to earlier estimate of 100 MeV b. However, this still does not account for the lithium discrepancy.D. G. acknowledges research funding from the European Union’s Horizon 2020 research and innovation programme under Grant Agreement No. 654002 (ENSAR2) and ISRO, Government of India under Grant No. ISRO/RES/2/378/ 15–16. O. T. would like to acknowledge the support by the Spanish Funding Agency (AEI/FEDER, EU) under the project PID2019–104390GB-I00. I. M. would like to acknowledge the support by the Ministry of Science, Innovation and Universities of Spain (Grant No. PGC2018-095640-B-I00). J. C. acknowledges grants from the Swedish Research Council (VR) under Contracts No. VR-2017-00637 and No. VR-2017-03986 as well as grants from the Royal Physiographical Society. J. P. would like to acknowledge the support by Institute for Basic Science (IBS-R031-D1). S. S. acknowledges support by the Academy of Finland (Grant No. 307685)

Study of elastic and inelastic scattering of 7Be + 12C at 35 MeV

6 pags., 5 figs., 2 tabs.The elastic and inelastic scattering of Be from C have been measured at an incident energy of 35 MeV. The inelastic scattering leading to the 4.439 MeV excited state of C has been measured for the first time. The experimental data cover an angular range of θ = 15-120. Optical model analyses were carried out with Woods-Saxon and double-folding potential using the density dependent M3Y (DDM3Y) effective interaction. The microscopic analysis of the elastic data indicates breakup channel coupling effect. A coupled-channel analysis of the inelastic scattering, based on collective form factors, shows that mutual excitation of both Be and C is significantly smaller than the single excitation of C. The larger deformation length obtained from the DWBA analysis could be explained by including the excitation of Be in a coupled-channel analysis. The breakup cross section of Be is estimated to be less than 10% of the reaction cross section. The intrinsic deformation length obtained for the C (4.439 MeV) state is δ = 1.37 fm. The total reaction cross section deduced from the analysis agrees very well with Wong's calculations for similar weakly bound light nuclei on C target.D. Gupta acknowledges research funding from the European Union's Horizon 2020 research and innovation programme under grant agreement no. 654002 (ENSAR2) and ISRO, Government of India under grant no. ISRO/RES/2/378/15-16. O. Tengblad would like to acknowledge the support by the Spanish Funding Agency (AEI / FEDER, EU) under the project PID2019-104390GB-I00. I. Martel would like to acknowledge the support by the Ministry of Science, Innovation and Universities of Spain (Grant No. PGC2018-095640-B-I00). J. Cederkall acknowledges grants from the Swedish Research Council (VR) under contract numbers VR-2017-00637 and VR-2017-03986 as well as grants from the Royal Physiographical Society. J. Park would like to acknowledge the support by Institute for Basic Science (IBS-R031-D1). S. Szwec acknowledges support by the Academy of Finland (Grant No. 307685). A.M.M. is supported by the I+D+i project PID2020-114687GB-I00 funded by MCIN/AEI/10.13039/501100011033, by the grant Group FQM-160 and by project P20_01247, funded by the Consejería de Economía, Conocimiento, Empresas y Universidad, Junta de Andalucía (Spain) and by “ERDF A way of making Europe”

Study of elastic and inelastic scattering of 7^7Be + 12^{12}C at 35 MeV

The elastic and inelastic scattering of $^7$Be from $^{12}$C have been measured at an incident energy of 35 MeV. The inelastic scattering leading to the 4.439 MeV excited state of $^{12}$C has been measured for the first time. The experimental data cover an angular range of $\theta_{cm}$ = 15$^{\circ}$-120$^{\circ}$. Optical model analyses were carried out with Woods-Saxon and double-folding potential using the density dependent M3Y (DDM3Y) effective interaction. The microscopic analysis of the elastic data indicates breakup channel coupling effect. A coupled-channel analysis of the inelastic scattering, based on collective form factors, show that mutual excitation of both $^7$Be and $^{12}$C is significantly smaller than the single excitation of $^{12}$C. The larger deformation length obtained from the DWBA analysis could be explained by including the excitation of $^7$Be in a coupled-channel analysis. The breakup cross section of $^7$Be is estimated to be less than 10$\%$ of the reaction cross section. The intrinsic deformation length obtained for the $^{12}$C$^*$ (4.439 MeV) state is $\delta _2$ = 1.37 fm. The total reaction cross section deduced from the analysis agrees very well with Wong's calculations for similar weakly bound light nuclei on $^{12}$C target.Comment: 8 pages, 5 figure

Probing proton halo effects in the 8B+64Zn collision around the Coulomb barrier

Proton halo effects in the 8B+64Zn reaction at an energy around 1.5 times the Coulomb barrier have been studied at HIE-ISOLDE CERN using, for the first time, the only existing postaccelerated 8B beam. This, together with the use of a high granularity and large solid angle detection system, allowed for a careful mapping of the elastic angular distribution, especially in the Coulomb-nuclear interference region. Contrary to what is observed for the one-neutron halo nucleus 11Be on the same target in a similar energy range, the analysis of the elastic scattering angular distribution shows only a modest suppression of the Coulomb-nuclear interference peak, with no remarkable enhancement of the total reaction cross-section. Inclusive angular and energy distributions of 7Be produced in direct reaction processes have also been measured. The comparison of these data with the results of theoretical calculations for the elastic and non-elastic breakup contributions indicate that both processes are important. Overall, the experimental data suggest a 8B collision dynamics at the barrier very different from the one of neutron halo nuclei, showing only modest effects of coupling to continuum. This behaviour can be interpreted as due to the presence of the additional Coulomb interactions halo-core and halo-target together with the presence of the centrifugal barrier felt by the valence proton of 8B

The most accurate determination of the 8B half-life

Beta decay is a primary source of information of the structure of a nucleus. An accurate measurement of the half-life of a nucleus is essential for the proper determination of the reduced Gammow-Teller transition probability B(GT). In this work, we present an experiment using a compact set-up of Si-telescope detectors to measure the half-life of the 8B nucleus. Three independent measurements have been analysed, obtaining the values 771.9(17) ms, 773.9(18) ms, and 770.9(27) ms. The value of the half-life obtained as the weighted averaged with the previous published measures is 771.17(94) ms which is a factor 3.2 of improvement in the uncertainty of the half-life

The experiments to determine the electron capture and β-decay of 8B into the highly excited states of 8Be

The main goal of this work is to study the structure of the highest energy states in 8Be populated following the β+-decay and the electron capture (EC) of 8B. With this aim, two experiments were performed at ISOLDE-CERN in 2017 and 2018. The first experiment had the aim to resolve the 2+ doublet at 16.6 and 16.9 MeV, in order to study their isospin mixing. The second experiment aimed to determine a value or give an experimental upper limit to the branching ratio of the exotic EC-p decay. In this paper, we present the experimental setups and we discuss the analysis and present the preliminary results obtained so far

Searching for ß-delayed protons from 11 Be

ISOLDE Workshop and Usersmeeting. Wednesday 05 December - Friday 07 December 2018 .CERN ( ISOLDE User Support. PH Departmen - CERN/CH-1211 Geneve 23). --.https://indico.cern.ch/event/736872/contributions

Decay studies of the long-lived states in Tl-186

Decay spectroscopy of the long-lived states in Tl-186 has been performed at the ISOLDE Decay Station at ISOLDE, CERN. The a decay from the low-spin (2(-)) state in Tl-186 was observed for the first time and a half-life of 3.4(-0.)(4)(+0.5) s was determined. Based on the alpha-decay energy, the relative positions of the long-lived states were fixed, with the (2(-)) state as the ground state, the 7((+)) state at 77(56) keV, and the 10((-)) state at 451(56) keV. The level scheme of the internal decay of the Tl-186(10((-))) state [T-1/2 = 3.40(9) s], which was known to decay solely through emission of 374-keV gamma-ray transition, was extended and a lower limit for the beta-decay branching b(beta) > 5.9(3)% was determined. The extracted retardation factors for the gamma decay of the 10((-) )state were compared to the available data in neighboring odd-odd thallium isotopes indicating the importance of the pi d(3/2) shell in the isomeric decay and significant structure differences between Tl-184 and Tl-186.Peer reviewe

Simultaneous γ-ray and electron spectroscopy of 182,184,186Hg isotopes

Background: The mercury isotopes around N=104 are a well-known example of nuclei exhibiting shape coexistence. Mixing of configurations can be studied by measuring the monopole strength ρ2(E0), however, currently the experimental information is scarce and lacks precision, especially for the Iπ→Iπ (I≠0) transitions. Purpose: The goals of this study were to increase the precision of the known branching ratios and internal conversion coefficients, to increase the amount of available information regarding excited states in Hg182,184,186, and to interpret the results in the framework of shape coexistence using different models. Method: The low-energy structures in Hg182,184,186 were populated in the β decay of Tl182,184,186, produced at ISOLDE, CERN and purified by laser ionization and mass separation. The γ-ray and internal conversion electron events were detected by five germanium clover detectors and a segmented silicon detector, respectively, and correlated in time to build decay schemes. Results: In total, 193, 178, and 156 transitions, including 144, 140, and 108 observed for the first time in a β-decay experiment, were assigned to Hg182,184,186, respectively. Internal conversion coefficients were determined for 23 transitions, out of which 12 had an E0 component. Extracted branching ratios allowed the sign of the interference term in Hg182 as well as ρ2(E0;02+→01+) and B(E2;02+→21+) in Hg184 to be determined. By means of electron-electron coincidences, the 03+ state was identified in Hg184. The experimental results were qualitatively reproduced by five theoretical approaches, the interacting boson model with configuration mixing with two different parametrizations, the general Bohr Hamiltonian, the beyond mean-field model, and the symmetry-conserving configuration-mixing model. However, a quantitative description is lacking. Conclusions: The presence of shape coexistence in neutron-deficient mercury isotopes was confirmed and evidence for the phenomenon existing at higher energies was found. The new experimental results provide important spectroscopic input for future Coulomb excitation studies