Search

The unbound proton-rich nuclei $$^{16}$$ F and $$^{15}$$ F are investigated experimentally and theoretically. Several experiments using the resonant elastic scattering method were performed at GANIL with radioactive beams to determine the properties of the low lying states of these nuclei. Strong asymmetry between $$^{16}$$ F– $$^{16}$$ N and $$^{15}$$ F– $$^{15}$$ C mirror nuclei is observed. The strength of the $$nucleon-nucleon$$ effective interaction involving the loosely bound proton in the $$s_{1/2}$$ orbit is significantly modified with respect to their mirror nuclei $$^{16}$$ N and $$^{15}$$ C. The reduction of the effective interaction is estimated by calculating the interaction energies with a schematic zero-range force. It is found that, after correcting for the effects due to changes in the radial distribution of the single-particle wave functions, the mirror symmetry of the $$n-p$$ interaction is preserved between $$^{16}$$ F and $$^{16}$$ N, while a difference of 63% is measured between the $$p-p$$ versus $$n-n$$ interactions in the second excited state of $$^{15}$$ F and $$^{15}$$ C nuclei. Several explanations are proposed.

The emission of the 4.439-MeV $\ensuremath{\gamma}$ ray in proton inelastic scattering off $^{12}\mathrm{C}$ has been investigated in detail. For this, two independent descriptions of the correlated scattering and emission process have been used: one for the direct reaction mechanism and the other for the compound-nucleus (CN) component. Direct reactions were calculated in the framework of the coupled-channels formalism, while the CN component was described as a superposition of separate resonances with definite spin and parity, treated with the angular momentum coupling theory. Both components were incoherently added and compared to a comprehensive data set on measured $\ensuremath{\gamma}$-ray line shapes and angular distributions in the proton energy range ${E}_{p}=5.44--25.0$ MeV. In the range ${E}_{p}\ensuremath{\approx}14--25$ MeV, good agreement with data was obtained with a dominating direct reaction component. At lower energy, an important CN component was required to describe line shape and angular distribution data. In general, a good description of the data could be found for a CN component with spin and parity corresponding to a known nearby resonance. The new calculation was found to improve significantly the agreement with line shape data in particular in the region of dominating CN resonances compared to previous calculations. Based on these results, predictions for $\ensuremath{\gamma}$-ray line shapes and angular distributions up to ${E}_{p}=100$ MeV were made and applied to $\ensuremath{\gamma}$-ray emissions in solar flares and proton radiotherapy.

The angular distributions of $^{8}\mathrm{Be}$ states in the excitation energy region ${E}_{x}\ensuremath{\sim}(16.5\text{--}18.2)$ MeV produced in the $^{7}\mathrm{Li}(^{3}\mathrm{He},d)^{8}\mathrm{Be}$ proton transfer reaction have been measured at the Orsay $14.8\ensuremath{-}\mathrm{MV}$ tandem accelerator for $^{3}\mathrm{He}^{2+}$ ion bombarding energy, ${E}_{\text{lab}}\phantom{\rule{4pt}{0ex}}=20$ MeV, and forward angular range, ${\ensuremath{\theta}}_{\text{lab}}=5{}^{\ensuremath{\circ}}\text{--}50{}^{\ensuremath{\circ}}$. A high energy resolution detection system composed of a split-pole magnetic spectrometer and a $\mathrm{\ensuremath{\Delta}}E\ensuremath{-}E$, position-sensitive drift chamber was used to record the energy spectra of outgoing deuterons. The measured cross section data for the direct reaction component have been separated from the compound nucleus one, then analyzed in the framework of the nonlocal, finite-range (FR)--distorted-wave Born approximation (DWBA) theory. New values of the ${C}^{2}S$ and (${S}_{p1/2},\phantom{\rule{4pt}{0ex}}{S}_{p3/2})$ proton absolute and partial spectroscopic factors and related ${\ensuremath{\gamma}}_{p}^{2}(a)$ proton reduced widths versus the $p+^{7}\mathrm{Li}$ channel radius have been extracted for the ${2}^{+}(16.626)$ and ${2}^{+}(16.922),T=0+1$ isospin-mixed loosely bound states of astrophysical interest and the ${1}^{+}(17.640)$, $T=1$ unbound state of $^{8}\mathrm{Be}$. They are compared to sparse earlier experimental values and to shell-model-predicted ones from the literature, and are discussed. In particular, the status of the spectroscopic information on the ${2}^{+}$ isospin-mixed doublet is reviewed and updated. The application in nuclear astrophysics of the DWBA derived results is emphasized.

The direct component of the 60Fe(n,γ)61Fe cross section was investigated by populating the bound states of the 61Fe nucleus through the (d,pγ) transfer reaction in inverse kinematics using a radioactive beam of 60Fe at 27A MeV. The experiment was performed at GANIL using the MUST2 array and an annular double-sided silicon strip detector for the detection of the light charged particle in coincidence with the photons measured in the EXOGAM γ-ray detectors. For the first time, the spectroscopic factors of the first 3/2−, 5/2−, 1/2−, and 9/2+ states of 61Fe were deduced experimentally from an adiabatic distorted wave approximation analysis of the data. The obtained results show a very good agreement with the shell-model predictions. The calculated direct component of the (n,γ) cross section was found negligible and of about 2% of the total, indicating a dominant resonant component.

We have measured the cross section of the 7Be(p,gamma)8B reaction for E_cm = 185.8 keV, 134.7 keV and 111.7 keV using a radioactive 7Be target (132 mCi). Single and coincidence spectra of beta^+ and alpha particles from 8B and 8Be^* decay, respectively, were measured using a large acceptance spectrometer. The zero energy S factor inferred from these data is 18.5 +/- 2.4 eV b and a weighted mean value of 18.8 +/- 1.7 eV b (theoretical uncertainty included) is deduced when combining this value with our previous results at higher energies. Comment: Accepted for publication in Phys. Rev. Lett

A Coulomb excitation experiment has been performed in order to study the subshell closure atN = 40 for neutron-rich nuclei. This subshell effect is thought to be enhanced when largeN/Z ratios are encountered. Therefore, theZ = 2868Ni is of particular interest in order to test this behaviour. Some experimental information is already available for68Ni at low excitation energy: a 0+ 2 isomer, a 2+ state and a long-lived 5- state. The high energy of the 2+ state suggests the shell closure though its reduced transition probabilityB(E2) has never been mesured. The nuclei68Ni,70,72Zn,76Ge have been produced in the fragmentation of a86Kr beam at 60 MeV/A. The selection of these secondary beams has been performed by LISE3 spectrometer at GANIL. Performances of the detector system “Château de Cristal” and preliminary results on reduced transition probabilitiesB(E2) are presented and discussed.

Fragment angular correlations in projectile breakup reactions are very sensitive to interference between different multipolarities entering in the excitation-dissociation process of the projectile. In particular, it was proposed to disentangle L = 1 and L = 2 contributions in direct breakup reactions of 16 O with low relative energy between the α and 12 C fragment, which are of astrophysical interest. We studied the experimental aspects of extracting those angular correlations in extreme kinematical conditions usually encountered in breakup experiments of astrophysical interest. The breakup of 95 MeV/ A 16 O projectiles induced by a 208 Pb target was measured using the high-resolution spectrometer SPEG at Ganil for the coincident detection of the fragments. Sequential breakup via the 12.53 MeV level of 16 O is analyzed in this framework and it favors an one-step M2 excitation of this level.

Cross sections for the ${}^{7}\mathrm{Be}(p,\ensuremath{\gamma}{)}^{8}\mathrm{B}$ reaction have been measured for ${E}_{\mathrm{c}.\mathrm{m}.}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}0.35--1.4\mathrm{MeV}$ using radioactive ${}^{7}\mathrm{Be}$ targets. Two independent measurements carried out with different beam conditions, different targets, and detectors are in excellent agreement. A statistical comparison of these measurements with previous results leads to a restricted set of consistent data. The deduced zero-energy $S$ factor $S(0)$ is found to be 15%--20% smaller than the previously recommended value. This implies a ${}^{8}\mathrm{B}$ solar neutrino flux lower than previously predicted in various standard solar models.

Evidence for direct elastic breakup of 16 O into the α- 12 C continuum with relative energies ranging from 900 to 1800 keV has been obtained in the scattering of 1527 MeV 16 O projectiles off 208 Pb. An interpretation of E2 breakup including nuclear and Coulomb contributions leads to reduced electromagnetic transitions probabilities and astrophysical S e 2 factors in reasonable agreement with direct measurements, showing that the method can be applied to extract the E2 part of the 12 C(α, γ) reaction rate.

In the present work we attempted to determine excitation energies and widths of proton unbound states in 32 Cl. These states may contribute as resonances to the 31 S(p,γ) reaction and will determine the reaction rate. Results were used to evaluate the reaction flow in the Si to Ar region obtained by nova outbursts in the case of an ONeMg white dwarf of 1.35 M ⊙ .

We have studied the ionic charge state dependence of the nuclear lifetime of the 35.5-keV first excited state of {sup 125}Te. We found for the 47{sup +} and 48{sup +} ions, 400 and 670{percent} variations with respect to the neutral-atom half-life (1.49 ns). These unusually large effects are due to the energetic blocking of the K-shell internal conversion as the charge state increases past 47{sup +}. For the 46{sup +}, we suggest a new internal conversion mode without any electron emission into the energy continuum. {copyright} {ital 1997} {ital The American Physical Society}

The observed primordial ${}^{7}$Li abundance in metal-poor halo stars is found to be lower than its Big-Bang nucleosynthesis (BBN) calculated value by a factor of approximately three. Some recent works suggested the possibility that this discrepancy originates from missing resonant reactions which would destroy ${}^{7}$Be, parent of ${}^{7}$Li. The most promising candidate resonances which were found include a possibly missed 1${}^{\ensuremath{-}}$ or 2${}^{\ensuremath{-}}$ narrow state around 15 MeV in the compound nucleus ${}^{10}$C formed by ${}^{7}$Be+${}^{3}$He and a state close to 7.8 MeV in the compound nucleus ${}^{11}$C formed by ${}^{7}$Be+${}^{4}$He. In this work, we studied the high excitation energy region of ${}^{10}$C and the low excitation energy region in ${}^{11}$C via the reactions ${}^{10}$B(${}^{3}$He,$t$)${}^{10}$C and ${}^{11}$B(${}^{3}$He,$t$)${}^{11}$C, respectively, at the incident energy of 35 MeV. Our results for ${}^{10}$C do not support ${}^{7}$Be+${}^{3}$He as a possible solution for the ${}^{7}$Li problem. Concerning ${}^{11}$C results, the data show no new resonances in the excitation energy region of interest and this excludes the ${}^{7}$Be+${}^{4}$He reaction channel as an explanation for the ${}^{7}$Li deficit.

Nucleosynthesis of fluorine in the context of helium burning occurs through the 15 N(α,γ) 19 F reaction. At temperatures where fluorine formation takes place in most astrophysical models, the narrow resonance associated with the 4.378 MeV level of 19 F is expected to dominate the reaction rate, but its strength is not known. We used a 15 N confined gas target to study this level by means of the transfer reaction 15 N 7 Li,t) 19 F at 28 MeV. Reaction products products were analysed with a split pole magnetic spectrometer and the angular distributions for the first 16 levels of 19 F were extracted. These distributions are fairly well reproduced by FR-DWBA calculations in the framework of an α-cluster transfer model with a compound-nucleus contribution obtained by Hauser-Feshbach calculations. α-spectroscopic factors were deduced and, for unbound levels, the α-widths were determined and compared with the existing direct measurements. The α-width of the level of astrophysical interest ( E x = 4.378 MeV) was found to be Γ α = 1.5 × 10 −9 eV, a value 60 times smaller than the commonly used one. The astrophysical consequences for 19 F production in AGB stars are discussed.

We have studied the atomic charge state dependence of the nuclear lifetime of the 35.5-keV first excited state of {sup 125}Te. For the 47{sup +} and 48{sup +} ions, 300% and 640% increases, respectively, of the half-life were found with respect to the neutral-atom value (1.49 ns). These unusually large effects are due to the energetic blocking of {ital K}-shell internal conversion as the charge state increases past 47{sup +}.

Charge transfer of 4.3 MeV/u chlorine ions passing through a discharge plasma target is used as a probe to determine the plasma density and the ratio of impurities inside the plasma column. Charge-state distributions of 2 MeV/u chlorine ions passing through the plasma are then measured and compared to corresponding measurements in the cold gas. Stopping power measurements are also performed in both cases.

We present some preliminary calculations on cross sections for the breakup of {sup 16}O around 100 MeV/nucleon with emphasis on the effect of nuclear breakup on the angular distributions. Underlying the results of these calculations, the possibilities and problems of extracting the astrophysical {ital S} factor for the {sup 12}C({alpha},{gamma}){sup 16}O reaction at very low energies are discussed. Some considerations on the experimental conditions for a {sup 16}O breakup experiment aiming at this astrophysical information are given.

The unbound nucleus 18 Na , the intermediate nucleus in the two-proton radioactivity of 19 Mg , is studied through the resonant elastic scattering 17 Ne ( p ,17 Ne ) p . The spectroscopic information obtained in this experiment is discussed and put in perspective with previous measurements and the structure of the mirror nucleus 18 N .

In stellar-evolution models, the 13N(p, γ)14O reaction plays an important role in the hot CNO cycle. Its reaction rate depends directly on the magnitude of the radiative width of the 5.17 MeV level in 14O. That width has been measured using the Coulomb break-up technique. A 70 MeV u 14O beam was excited in the Coulomb field of a 208Pb target, the 13N and proton fragments being recorded using a magnetic spectrometer and CsI scintillators, respectively. The experimental value Γγ = 2.4 ± 0.9 eV is in overall agreement with other recent measurements.

INTEGRAL and RHESSI spacecrafts recently detected the 1.173 and 1.333 MeV γ‐ray lines coming from the 60Fe—60Co—60Ni radioactive decay chain. The long lived isotope 60Fe (T1/2 = 1.5 106y) is believed to be primarily produced in core‐collapse supernovae. However the interpretation of the observations is difficult because of the large uncertainties concerning 59Fe(n,γ)60Fe and 60Fe(n,γ)61Fe cross sections, involved in 60Fe nucleosynthesis.The direct component of the 60Fe(n,γ)61Fe reaction was studied indirectly via the d(60Fe,pγ)61Fe transfer reaction. The experiment performed in GANIL in spring 2009 will allow to determine the excitation energies of the populated excited states of 61Fe and for the first time their spectroscopic factors as well as their transfer angular momentum.I will first give an overview of the astrophysical context, then I will describe the experimental setup and finally present some preliminary results of the ongoing analysis.

The 12C(α,γ)16O reaction plays an important role in helium burning in massive stars and their evolution. However, despite many experimental studies, the low‐energy cross section of 12C(α,γ)16O still highly uncertain. The extrapolation of the measured cross sections to stellar energies (E∼300 keV) is made difficult by the presence of the two sub‐threshold states at 6.92 and 7.12 MeV of 16O. In order to further investigate the contribution of these two‐subthreshold resonances to the 12C(α,γ)16O cross section, we performed a new determination of the α ‐reduced widths via a measurement of the transfer reaction 12C(7Li,t)16O at two incident energies, 34 and 28 MeV. The measured and calculated differential cross sections will be presented as well as the obtained spectroscopic factors and the α ‐reduced widths.

The differential cross sections for the 3H(7Li, n0)9Be reaction were measured at 5 angles in the energy range E(c.m.)=0.2–0.9 MeV using a pulsed 7Li beam and time-of-flight technique. Absolute values of the cross section were obtained by comparison with the well-known cross section of 3H(d, n)4He at Ed=1.0 MeV. The resulting reaction rates are obtained at temperatures relevant to big-bang nucleosynthesis, and consequences for primordial 9Be abundances are discussed.

Coulomb dissociation of light nuclear projectiles in the electric field of heavy target nuclei has been experimentally investigated as an alternative access to radiative capture cross sections at low relative energies of the fragments, which are of astrophysical interest. As a pilot experiment the breakup of 156 MeV {sup 6}Li projectiles at {sup 208}Pb with small emission angles of the {alpha} particle and deuteron fragments has been studied. Both fragments were coincidentally detected in the focal plane of a magnetic spectrograph at several reaction angles well below the grazing angle and with relative angles between the fragments of 0{degree}--2{degree}. The experimental cross sections have been analyzed on the basis of the Coulomb breakup theory. The results for the resonant breakup give evidence for the strong dominance of the Coulomb dissociation mechanism and the absence of nuclear distortions, while the cross section for the nonresonant breakup follows theoretical predictions of the astrophysical {ital S} factor and extrapolations of corresponding radiative capture reaction cross section to very low c.m. energies of the {alpha} particle and deuteron. Various implications of the approach are discussed.

The $^{13}\mathrm{C}$($\ensuremath{\alpha},n$)$^{16}\mathrm{O}$ reaction is considered the main neutron source for the s process in low mass asymptotic giant branch (AGB) stars. In the Gamow peak, the cross section sensitively depends on the $1/{2}^{+}$ subthreshold state of $^{17}\mathrm{O}$ (${E}_{x}=6.356$ MeV). In this work, we determined the astrophysical $S$ factor through an evaluation of the \ensuremath{\alpha} spectroscopic factor and the corresponding asymptotic normalization factor (ANC) of the 6.356 MeV state using the transfer reaction $^{13}\mathrm{C}$($^{7}\mathrm{Li}$,$t$)$^{17}\mathrm{O}$ at two different incident energies. Our result confirms that the contribution of the $1/{2}^{+}$ state is dominant at astrophysical energies. Our reaction rate at $T=0.09$ GK is slightly lower than the value adopted in the Nuclear Astrophysics Compilation of REaction rates (NACRE), but two times larger than the one obtained in a recent ANC measurement.

The reaction 13C(α,n)16O is considered as the main neutron source for s‐process in low‐mass asymptotic giant branch stars. At low energies of astrophysical interest, the contribution of the subthreshold state 6.356 MeV of 17O to the 13C(α,n)16O cross section should be taken into account. However, the results of previous studies of this contribution lead to different conclusions.Hence, we investigated the effect of this resonance on the astrophysical S‐factor through a new precise measurement of the alpha spectroscopic factor, Sα, of the 6.356 MeV state using the transfer reaction 13C(7Li,t)17O at two different incident energies. The measured angular distributions and the obtained spectroscopic factors will be presented as well as their impact on C(α,n)16O cross section and reaction rate.

The ground state of particle‐unbound nuclei is observed as a resonance. According to the Heisenberg's uncertainty principle, the shorter is the lifetime of the state the broader is the resonance. The Breit‐Wigner formalism describes perfectly the shape of the resonance when energy‐dependent partial‐widths are used. In the low energy tail of a ground state resonance near the particle‐emission threshold, the partial‐width for the emission of a charged particle through the Coulomb barrier is drastically reduced. The fact that the proton decay is strongly hindered seems to be equivalent to the assertion that the decay of the proton is strongly delayed. In this interpretation and as an example, possible consequences are discussed in astrophysical context. Two reactions 15O(p,β+)16O and 15O(p,γ)(β+)16O are proposed as new pathways to bypass the 15O waiting point. Cross‐sections were calculated after precise measurements of energies and widths of the proton‐unbound 16F low lying states, obtained using the H(15O,...

The angular distributions for low lying states of 16O produced in the 12C(6Li, d)16O α-transfer reaction at E Li 6 ( lab ) = 48.2 MeV have been measured using a high energy resolution position sensitive detection system. The measured cross section data have been analyzed by the FRDWBA theory with a particular emphasis put on the states of astrophysical interest mainly the 1 − (7.12 MeV) state. Extracted values of nuclear level parameters (excitation energy, E x , line width, Γ c . m . , α-spectroscopic factor, S α , and reduced α-width, γ α 2 or θ α 2 ) are reported and discussed in comparison to previous ones. The used binding potential corresponds to a long nuclear interaction range (up to a channel radius a = 7.7 fm ), suggesting that the channel radius a = 6.5 fm is likely suitable for the calculations of reduced α-widths near the nuclear surface. However, given that previous DWBA results are available for comparison only near the channel radius a = 5.5 fm , calculations have been carried out here for both three preceding a values. Formal values, 0.0036 ⩽ θ α 2 ( 7.12 ) ⩽ 0.152 and 0.019 ⩽ θ α 2 ( 6.92 ) ⩽ 0.096 of the reduced α-widths ( a = 6.5 fm ) of the 1 − (7.12 MeV) and 2 + (6.92 MeV) states have thus been derived. Furthermore, the R-matrix analysis of various data sets of importance to the 12C( α , γ )16O direct capture reaction has been carried out, leading to the range of values for the 1 − (7.12 MeV) state, 0.0096 ⩽ θ α 2 ( 7.12 ) ⩽ 0.0166 , which is consistent with the preceding DWBA interval, and to a result for the E1 component of the reaction astrophysical factor, S E 1 ( 0.3 ) = 80.6 −16 +17 keV b , very consistent with most constrained values previously reported in the literature.

The F-18, produced during nova explosions, is the main responsible for the 511 keV gamma-ray emitted during the outburst that could be detected with satellite missions or future gamma-ray telescopes. In spite of many experimental efforts, the amount of F-18 synthesized still suffers from large uncertainties concerning mainly the F-18(p, alpha)O-15 reaction. We report here on a new direct measurement of the F-18(p, alpha)O-15 cross section recently carried out at the RIB facility at Louvain-la-Neuve. Cross section data down to a center-of-mass energy of 400 keV have been obtained using an isobarically pure F-18 beam ( averaged intensity of the order of 10(6) pps) and a thin polyethylene target. The reaction products were detected using the multi-strip detector array LEDA. The cross section data are analysed in the framework of the R-matrix model. Our main aim is to determine the interference sign between three 3/2(+) resonances above threshold that can significantly affect the extrapolation of the F-18(p, alpha)O-15 cross section to the energies relevant for novae, and thus, the modeling of nova explosions.

A new experiment to determine the thermonuclear cross section of the C-12(alpha,gamma)O-16 reaction has been performed in regular kinematics using an intense alpha-particle beam of up to 340 mu A from the Stuttgart DYNAMITRON. For the first time, a 4 pi-germanium-detector setup has been used to measure the angular distribution of the gamma rays at all angles simultaneously. It consisted of an array of nine EUROGAM high-purity Ge detectors in close geometry, actively shielded individually with bismuth germanate crystals. The C-12 targets were isotopically enriched by magnetic separation during implantation. The depth profiles of the implanted carbon in the C-12 targets were determined by Rutherford backscattering for purposes of cross-section normalization and absolute determination of the E1 and E2 S factors. Angular distributions of the gamma decay to the O-16 ground state were measured in the energy range E-c.m.=1.30-2.78 MeV and in the angular range (lab.) 30 degrees-130 degrees. From these distributions, astrophysical E1 and E2 S-factor functions vs energy were calculated, both of which are indispensable to the modeling of this reaction and the extrapolation toward lower energies. The separation of the E1 and E2 capture channels was done both by taking the phase value phi(12) as a free parameter and by fixing it using the results of elastic alpha-particle scattering on C-12 in the same energy range.

We investigated the proton‐capture reactions on 17O occuring in classical nova explosions. We observed a previously undiscovered resonance at ERlab=194.1±0.6 keV in the 17O(p,α)14N reaction, with a measured resonance strength ωγpα=1.6±0.2 meV. We studied in the same experiment the 17O(p,γ)18F reaction by an activation method and the resonance‐strength ratio was found to be ωγpα/ωγpγ=470±50. The corresponding excitation energy in the 18F compound nucleus was determined to be 5789.8±0.3 keV by γ‐ray measurements using the 14N(α,γ)18F reaction. These new resonance properties have important consequences for 17O nucleosynthesis and γ‐ray astronomy of classical novae.

International audience; The possibility that big-bang nucleosynthesis (BBN) may produce nontrivial amounts of 6Li is under study since the recent observations of this element in old halo stars. However, the interpretation of these observations needs a precise knowledge of the reaction rate of D(alpha, gamma)6Li which, at present, is extremely uncertain (a factor of 20) at the energies of astrophysical interest (Ecm

Gamma-ray production cross sections have been measured for gamma-ray lines copiously emitted in the $^3$He bombardment of $^{16}$O nuclei: the 937, 1042 and 1081 keV lines of $^{18}$F and the 1887 keV line of $^{18}$Ne. Four Ge detectors with BGO shielding for Compton suppression were used to measure the angular distributions of the gamma-rays. The excitation functions have been obtained for $^3$He bombarding energies from 3.7 to 36 MeV. Total cross sections are tabulated for calculations relevant to gamma-ray astronomy. The importance of these lines as diagnosis for the presence and properties of accelerated $^3$He in solar flares is discussed in light of the measured cross sections.

The neutron-rich ${}^{66,68}\mathrm{Ni}$ have been produced at GANIL via interactions of a $65.9A\mathrm{MeV}$ ${}^{70}\mathrm{Zn}$ beam with a ${}^{58}\mathrm{Ni}$ target. Their reduced transition probability $B({E2;0}_{1}^{+}\ensuremath{\rightarrow}{2}^{+})$ has been measured for the first time by Coulomb excitation in a ${}^{208}\mathrm{Pb}$ target at intermediate energy. The $B(E2)$ value for ${}^{68}{\mathrm{Ni}}_{40}$ is unexpectedly small. An analysis in terms of large scale shell model calculations stresses the importance of proton core excitations to reproduce the $B(E2)$ values and indicates the erosion of the $N\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}40$ harmonic-oscillator subshell by neutron-pair scattering.

The structure of nuclei far from stability can be investigated by means of in-beam gamma spectroscopy using both stable and radioactive beams. Two such experiments have been recently performed at GANIL. i) Secondary beams of neutron-rich Ge, Zn and Ni isotopes around N=40 were produced from the fragmentation of a primary 86 Kr beam, and analyzed by means of the LISE3 spectrometer. For the transitions between the 0+ ground state and the first 2+ state, B(E2) values have been extracted from Coulomb excitation cross-section measurement. Some of the obtained results related to the effectiveness of the N=40 spherical sub-shell closure are discussed. ii) In-beam γ-spectroscopy of neutron-rich nuclei around 32Mg produced by fragmentation of 36S have been performed recently. Gamma decay of relatively higher excited states have been measured in a large number of exotic light nuclei. Preliminary results obtained in a number of neutron-rich nuclei around N=20 are presented.

NESTER; International audience

The Coulomb break-up technique has been used to determine the radiative width of one excited level in 12 N and the direct capture contribution to 11 C(p,γ) 12 N. The 12 N radioactive beam was produced through transfer and fragmentation reactions of a primary 95.5 MeV/u 14 N beam at GANIL. From the extracted cross section we deduce the rate of the 11 C+p reaction. Consequences for the hot pp chain are analysed.

The reaction 15Na(α,γ)19F is of great importance for fluorine nucleosynthesis. At temperatures where 19F is expected to be produced, the narrow resonance associated with the 4.377 MeV level of 19F yields the dominant contribution to cross section. We have extracted its width by using the alpha‐transfer reaction 15N(7Li,t)19F and finite range DWBA analysis.

Clear experimental evidence of plasma stripping enhancement for 1.5 MeV/u chlorine ions is contrasted with its cold gas homologue at the same density (1{times}10{sup 19} {ital e}{sup {minus}}/cm{sup {minus}2}). The plasma is created by an electrical discharge in hydrogen and diagnosed with optical spectroscopic methods and beam probe analysis. The velocity dependence for the charge distributions is modeled both in cold gas and in plasma experiments. The calculations are found to be in good agreement with the hypothesis of a strongly reduced capture rate in the plasma case. Those results document quantitatively the basic mechanisms underlying the enhanced ion projectile charge in a plasma target. They also add credence to currently advocated scenarios for heavy-ion-driven fusion.

Influence of target temperature, density and atomic number on the charge state of swift heavy ions interacting with hot and dense plasma is considered. Hydrogen targets exhibit strong temperature effects and large non-equilibrium charges, whereas interactions with heavy material are more sensitive to the density effect. Our new average correlated hydrogenic atom model (ACHAM) is presented. It enables us to cover the whole range of target densities of interest for swift heavyion-plasma interaction experiments.

Charge exchange of chlorine ions traversing a discharge plasma target is used as a probe to determine the rati of heavy impurities inside a plasma column. The rate coefficient of the recombination process is strongly related to the atomic number of the target atoms. High-Z impurities are much more efficient to modify the charge state distribution of the incoming chlorine ions. The ragne of detection could reach about 1‰ of the total number of atoms.

The differential cross sections for the 3 H( 7 Li,n 0 ) 9 Be reaction were measured at 5 angles in the energy range E CM = 0.2–0.9 MeV using a pulsed 7 Li beam and time-of-flight technique. Absolute values of the cross section were obtained by comparison with the well known cross section of 3 H(d,n) 4 He at E d = 1.0 MeV. The resulting reaction rates are obtained at temperatures relevant to big-bang nucleosynthesis, and consequences for primordial 9 Be abundances are discussed.

Intermediate mass fragment cross-sectionsσ(E, θ, 4≤Z≤11) have been measured in the reaction6Li+46Ti at 156 MeV incident energy. A simple sequential binary decay model describes most of theZ>8 data as evaporation from the compound nucleus. The complete fusion cross-section is also well reproduced. An intermediate velocity source model (β=2β CN, T=7 MeV) has been used in order to explain the small angle and Z≤8 data which indicate aZ −4.1 dependence.

Inclusive alpha particle and deuteron spectra from collisions of 156 MeV6Li-ions with12C and208Pb were measured at extreme forward emission angles including zero degree. The measurements were performed with the Karlsruhe magnetic spectrograph ‘Little John’ and required an efficient reduction of the background from small-angle scattering. The observed double differential cross sections and angular distributions have been analysed on the basis of Serber's spectator break-up model. When going to angles smaller than grazing, where Coulomb effects are expected to be dominating, transitional features may appear. Corresponding effects probably associated with Coulomb break-up are observed with the208Pb-target and require a slight extension of the Serber approach. In the case of the12C-target the break-up cross sections in forward direction seem to reflect the shape of the internal momentum distribution of the alpha particle and deuteron cluster in the6Li-projectile and are in agreement with a 2S-type wave function. However, at larger angles the shape appears to be distorted, possibly by final state interactions.

The triple-differential cross sections for elastic break-up of 156 MeV 6 Li projectiles by the reactions 208 Pb( 6 Li, αd) 208 Pb g.s. and 12 C( 6 Li, αd) 12 C g.s. have been measured with large asymptotic relative momenta of the outgoing fragments. The data exhibit rather unfamiliar shapes of the energy spectra, often replacing the usual bell-shape distributions by double-peaked structures and varying rapidly with the relative emission angles. The origin of these features has been explored and the cross sections have been analysed on the basis of a diffractive disintegration approach.