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We report on an attempt to reproduce the observation of beta-minus-delayed proton emission from ¹¹Be through detection of the final state nucleus ¹⁰Be with accelerator mass spectrometry. Twelve samples were collected at the ISOLDE facility at CERN at different separator settings, allowing tests of different sources of contamination to be carried out. The observed amounts of ¹⁰Be per collected ¹¹Be rule out several contamination sources, but do not agree internally. Formation of BeH molecular ions in the ion source may explain our data, in which case an upper limit of the beta p branching ratio of 2.2 x10-6 can be derived.

Using a hybrid Gammasphere array coupled to 25 LaBr3(Ce) detectors, the lifetimes of the first three levels of the yrast band in Pd114, populated via Cf252 decay, have been measured. The measured lifetimes are τ2+=103(10)ps, τ4+=22(13)ps, and τ6+≤10ps for the 21+, 41+, and 61+ levels, respectively. Palladium-114 was predicted to be the most deformed isotope of its isotopic chain, and spectroscopic studies have suggested it might also be a candidate nucleus for low-spin stable triaxiality. From the lifetimes measured in this work, reduced transition probabilities B(E2;J→J-2) are calculated and compared with interacting boson model, projected shell model, and collective model calculations from the literature. The experimental ratio RB(E2)=B(E2;41+→21+)/B(E2;21+→01+)=0.80(42) is measured for the first time in Pd114 and compared with the known values RB(E2) in the palladium isotopic chain: the systematics suggest that, for N=68, a transition from γ-unstable to a more rigid γ-deformed nuclear shape occurs.

GSI Scientific Report 2014 - GSI Report 2015-1

TVIVL OMKRING J. H. KUSK - AFKLARES MED KARSTEN RIISAGER

Riisager, Karsten et al., We have observed β−β−-delayed proton emission from the neutron-rich nucleus 11Be by analyzing a sample collected at the ISOLDE facility at CERN with accelerator mass spectrometry (AMS). With a branching ratio of (8.3±0.9)⋅10−6(8.3±0.9)⋅10−6 the strength of this decay mode, as measured by the BGTBGT-value, is unexpectedly high. The result is discussed within a simple single-particle model and could be interpreted as a quasi-free decay of the 11Be halo neutron into a single-proton state., We acknowledge support from the European Union Seventh Framework through ENSAR (contract No. 262010), from Austrian Science Fund (FWF) P22164-N20, from Spanish MINECO through projects FPA2010-17142 and FPA2012-32443, and CPAN ConsoliderCSD-2007-00042.

INPC 2013 – International Nuclear Physics Conference; 4 pags.; 3 figs.; Open Access funded by Creative Commons Atribution Licence 2.0, The astrophysical S-factor for the 3He(α,γ)7Be reaction plays an important role in the Solar Standard Model and in the Big Bang Nucleosynthesis scenario. The advances from two recent experiments performed using complementary techniques at center of mass (C.M.) energies between 1 and 3 MeV are discussed., The work was partly financed by the Spanish Research Funding Agency CICYT under Project FPA2012-32443 and was supported by the UK STFC. Further M.C.G. acknowledges his CSICJAEpredoc grant partly funded by the European Social Funds.

A multi-hit capacity setup was used to study the decay of the dripline nucleus 31Ar, produced at the ISOLDE facility at CERN. A spectroscopic analysis of the beta-delayed three-proton decay of 31Ar is presented for the first time together with a quantitative analysis of the beta-delayed two-proton-gamma-decay. A new method for determination of the spin of low-lying levels in the beta-proton-daughter 30S using proton-proton angular correlations is presented and used for the level at 5.2 MeV, which is found to be either a 3+ or 4+ level, with the data pointing towards the 3+. The half-life of 31Ar is found to be 15.1(3) ms. An improved analysis of the Fermi beta-strength gives a total measured branching for the beta-3p-decay of 3.60(44) %, which is lower than the theoretical value found to be 4.24(43) %. Finally the strongest gamma-transitions in the decay of 33Ar are shown including a line at 4734(3) keV associated to the decay of the IAS, which has not previously been identified., Comment: 12 pages, 14 figures

GSI Scientific Report 2013 - GSI Report 2014-1

ITO International Research Center, on the campus of the University of Tokyo, June 1 to 6, 2014; http://ribf.riken.jp/ARIS2014/index.html, Due to its relevance to the Standard Solar Model and to the Big Bang Nucleosynthesis calculations, the cross section of the 3He(α, γ)7Be reaction have been widely studied both from the theoretical and the experimental fronts. We report here on cross section measurements in the energy region Ec.m.=1- 3 MeV using the direct recoil counting method in an attempt to solve the discrepancies among the previous data sets and calculations in this energy region and thus to constrain the extrapolations of the S34(E) curve to astrophysical energies.

The abstract is available here: https://uscholar.univie.ac.at/o:467402

G. T. Koldste et al. ; 10 pags. ; 14 figs. ; 4 tabs. ; PACS number(s): 23.40.Hc, 27.30.+t, A multihit capacity setup was used to study the decay of the dripline nucleus 31Ar, produced at the ISOLDE facility at CERN. A spectroscopic analysis of the β-delayed three-proton decay of 31Ar is presented for the first time together with a quantitative analysis of the β-delayed 2pγ decay. A new method for determination of the spin of low-lying levels in the βp daughter 30S using proton-proton angular correlations is presented and used to determine that the spin of the 5.2-MeV level is most likely 3+ with 4+ also possible. The half-life of 31Ar is found to be 15.1(3) ms. An improved analysis of the Fermi β strength including the β3p-decay mode gives a total measured branching ratio of 3.60(44)%, which is lower than the theoretical value found to be 4.24(43)%. Finally, a previously unidentified γ transition from the isobaric analog state in the decay of 33Ar has been found. © 2014 American Physical Society., This work was supported by the European Union Seventh Framework through ENSAR (Contract No. 262010). This work was partly supported by the Spanish Funding Agency under Projects No. FPA2009-07387, No. FPA2010-17142, and No. AIC-D-2011- 0684, by the French ANR (Contract No. ANR-06-BLAN- 0320).

Resonances just above the proton threshold in 30S affect the 29P(p,gamma)30S reaction under astrophysical conditions. The (p,gamma)-reaction rate is currently determined indirectly and depends on the properties of the relevant resonances. We present here a method for finding the ratio between the proton and gamma partial widths of resonances in 30S. The widths are determined from the beta-2p and beta-p-gamma decay of 31Ar, which is produced at the ISOLDE facility at the European research organization CERN. Experimental limits on the ratio between the proton and gamma partial widths for astrophysical relevant levels in 30S have been found for the first time. A level at 4688(5) keV is identified in the gamma spectrum, and an upper limit on the proton to gamma width of 0.26 (95 % C.L.) is found. In the two-proton spectrum two levels at 5227(3) keV and 5847(4) keV are identified. These levels are previously seen to gamma decay and upper limits on the gamma to proton width of 0.5 and 9, respectively, (95 % C.L.) are found, where the latter differs from previous calculations., 6 pages, 4 figures

5 p.: gráf., A measurement of the final state distribution of the 8B decay, obtained by implanting a 8B beam in a double-sided silicon strip detector, is reported here. The present spectrum is consistent with a recent independent precise measurement performed by our collaboration at the IGISOL facility, Jyväskylä[O. S. Kirsebom et al., Phys. Rev. C 83, 065802 (2011)]. It shows discrepancies with previously measured spectra, leading to differences in the derived neutrino spectrum. Thanks to a low detection threshold, the neutrino spectrum is for the first time directly extracted from the measured final state distribution, thus avoiding the uncertainties related to the extrapolation of R-matrix fits. Combined with the IGISOL data, this leads to an improvement of the overall errors and the extension of the neutrino spectrum at high energy. The new unperturbed neutrino spectrum represents a benchmark for future measurements of the solar neutrino flux as a function of energy., Supported by FWO-Vlaanderen(Belgium), the IUAP-Belgian State Belgian Science Policy (BriX network P6/23), the Dutch FOM program 114 (TRI P), the European Union—Research Infrastructure Action under the FP6 ‘‘Structuring theEuropean Research Area’’ Program, and the Spanish projects FPA2009-07387, FPA2010-17142 and CSD2007-00042.

Resonances just above the proton threshold in $^{30}$S affect the $^{29}$P$(p,\gamma)^{30}$S reaction under astrophysical conditions. The ($p,\gamma$)-reaction rate is currently determined indirectly and depends on the properties of the relevant resonances. We present here a method for finding the ratio between the proton- and $\gamma$- partial widths of resonances in $^{30}$S. The widths are determined from the $\beta -2p$ and $\beta -p-\gamma$-decay of $^{31}$Ar, which is produced at ISOLDE, CERN. Experimental limits on the ratio between the proton- and $\gamma$- partial widths for astrophysical relevant levels in $^{30}$S have been found for the first time. A level at 4689.2(24)keV is identified in the $\gamma$-spectrum, and an upper limit on the $\Gamma_{p}/\Gamma_{\gamma}$ ratio of 0.26 (95% C.L.) is found. In the two-proton spectrum two levels at 5227(3)keV and 5847(4)keV are identified. These levels were previously seen to $\gamma$-decay and upper limits on the $\Gamma_{\gamma}/\Gamma_{p}$ ratio of 0.5 and 9, respectively, (95% C.L.) are found, where the latter differs from previous calculations. Resonances just above the proton threshold in 30S affect the 29P(p,γ)30S reaction under astrophysical conditions. The (p,γ)-reaction rate is currently determined indirectly and depends on the properties of the relevant resonances. We present here a method for finding the ratio between the proton and γ partial widths of resonances in 30S. The widths are determined from the β2p- and βpγ-decay of 31Ar, which is produced at the ISOLDE radioactive ion beam facility at the European research organization CERN. Experimental limits on the ratio between the proton and γ partial widths for astrophysical relevant levels in 30S have been found for the first time. A level at 4689.2(24)keV is identified in the γ spectrum, and an upper limit on the Γp/Γγ ratio of 0.26 (95% C.L.) is found. In the two-proton spectrum two levels at 5227(3)keV and 5847(4)keV are identified. These levels were previously seen to γ decay and upper limits on the Γγ/Γp ratio of 0.5 and 9, respectively, (95% C.L.) are found, where the latter differs from previous calculations. Resonances just above the proton threshold in 30S affect the 29P(p,gamma)30S reaction under astrophysical conditions. The (p,gamma)-reaction rate is currently determined indirectly and depends on the properties of the relevant resonances. We present here a method for finding the ratio between the proton and gamma partial widths of resonances in 30S. The widths are determined from the beta-2p and beta-p-gamma decay of 31Ar, which is produced at the ISOLDE facility at the European research organization CERN. Experimental limits on the ratio between the proton and gamma partial widths for astrophysical relevant levels in 30S have been found for the first time. A level at 4688(5) keV is identified in the gamma spectrum, and an upper limit on the proton to gamma width of 0.26 (95 % C.L.) is found. In the two-proton spectrum two levels at 5227(3) keV and 5847(4) keV are identified. These levels are previously seen to gamma decay and upper limits on the gamma to proton width of 0.5 and 9, respectively, (95 % C.L.) are found, where the latter differs from previous calculations.

Preliminary studies in preparation for an absolute cross-section measurement of the radiative capture reaction 3He(α,γ)7Be with the DRAGON recoil separator have demonstrated beam suppression >1014 at the 90% confidence level. A measurement of this cross section by observation of 7Be recoils at the focal plane of the separator should be virtually background free. & 2012 Elsevier B.V.

A measurement of the final state distribution of the B-8 beta decay, obtained by implanting a 8B beam in a double-sided silicon strip detector, is reported here. The present spectrum is consistent with a recent independent precise measurement performed by our collaboration at the IGISOL facility, Jyvaskyla [O. S. Kirsebom et al., Phys. Rev. C 83, 065802 ( 2011)]. It shows discrepancies with previously measured spectra, leading to differences in the derived neutrino spectrum. Thanks to a low detection threshold, the neutrino spectrum is for the first time directly extracted from the measured final state distribution, thus avoiding the uncertainties related to the extrapolation of R-matrix fits. Combined with the IGISOL data, this leads to an improvement of the overall errors and the extension of the neutrino spectrum at high energy. The new unperturbed neutrino spectrum represents a benchmark for future measurements of the solar neutrino flux as a function of energy.

3 pags., 1 tab. -- Nuclear Physics in Astrophysics V 3–8 April 2011, Eilat, Israel, The astrophysical S factor for the He-4(He-3,gamma)Be-7 direct capture reaction plays a major role in the context of solar neutrino flux and primordial Li-7 abundances that demand accurate information on the reaction. We report here our recent cross section measurements using the activation method in the region of E-CM=900-2800 keV, that aim to shed light on the discrepancies in the existing data and lead to a more accurate extrapolation of the S factor.

We report on a new cross-section measurement for the 3He(α, γ)7Be reaction at three medium energies of E c.m. between 1 and 3 MeV. The interest stems from the significant role played by the reaction in calculating an accurate solar neutrino flux and the primordial 7Li abundance. The energy dependence of the astrophysical S 34 factor observed in the present work, especially above 1 MeV, highlights the need to constrain theories in order to obtain a precise extrapolated value for S 34(0). In this context, a comparison with the recent theoretical work in a fully microscopic fermionic molecular dynamics approach and a few other representative calculations emphasize the need for further experimental as well as theoretical work to resolve the existing conflicts. ©2012 American Physical Society., Supported by the UK STFC and was partly financed by the Spanish Research Funding Agency CICYT under Project FPA2009-07387. Further, M.C.G. acknowledges his CSIC-JAEpredoc grant partly funded by the European Social Funds.

Submitted to J. Phys. G: Nucl. Phys; Expérience GANIL-SPIRAL; Beta-delayed proton and $\gamma$-ray emission from the 32Ar decay has been studied at the low-energy identi cation station of SPIRAL at GANIL. The study of $\beta$ -delayed charged-particle emission and electromagnetic radiation allowed us to achieve a nearly complete decay scheme of the 32Ar nucleus. With the distinction between $\beta$-delayed protons emitted to the ground and to the rst excited state in 31S and the new values of half-life and QEC we have deduced the Gamow-Teller strength distribution over a large part of the QEC window. The GT strength is compared to advanced shell-model calculations. The experimental Gamow-Teller strength is wider distributed than theoretically predicted and the onset of the Gamow-Teller Giant Resonance happens at lower energy. This explains why the deduced value for the quenching factor depends strongly on the explored excitation energy in the daughter nucleus. When the energy window is chosen large enough the standard quenching factor for the sd-shell is recovered.

In stellar helium burning, 16O represents the endpoint of the helium-burning sequence due to the low rate of 16O(α,γ)20Ne. We present a new direct measurement of the total capture reaction rate of 16O(α,γ)20Ne at Ec.m.=2.26MeV employing the DRAGON recoil separator. For the first time, the total S factor and its contributing direct capture transitions could be determined in one experiment. © 2011 American Physical Society., We would like to thank the beam delivery and ISAC operations groups at TRIUMF. The authors gratefully acknowledge funding from the Natural Sciences and Engineering Research Council of Canada and the US DOE Office of Nuclear Physics