Search

We study the new type of big‐bang nucleosynthesis (BBN) reactions that are catalyzed by a hypothetical long‐lived negatively charged, massive leptonic particle (called X−) such as the supersymmetric (SUSY) particle stau, the scalar partner of the tau lepton. It is known that if the X− particle has a lifetime of τX≳103 s, it can capture a light element previously synthesized in standard BBN and form a Coulombic bound state and induces various types of reactions in which X− acts as a catalyst. Some of these X− catalyzed reactions have significantly large cross sections so that the inclusion of the reactions into the BBN network calculation can markedly change the abundances of some elements. We use a high‐accuracy three‐body calculation method developed by the authors and provide precise cross sections and rates of these catalyzed BBN reactions for use in the BBN network calculation.

Properties of medium mass nuclei having excitation energies of 1.5 to 6 MeV/u have been probed in measurements of the multiplicities and energy spectra of emitted particles and fragments. The particle spectra indicate a progressive reduction of both the level density parameter, a, and the emission barriers as the excitation energy is increased. The evolution of the dominant de-excitation modes, observed with increasing excitation energy, is found to be qualitatively consistent with the predictions of statistical models. There is, however, evidence that dynamics may play an important role in fragment emission processes. At energies of 6 MeV/u multifragment emission is an important process. Varying theoretical models predict such multifragment events but differ in their predictions of the probability of such events.

Photoneutron cross sections were measured for $^{117}\mathrm{Sn}$ and $^{116}\mathrm{Sn}$ near the neutron thresholds at $6.94$ and $9.56$ MeV, respectively, with quasi-monochromatic laser-Compton scattering $\ensuremath{\gamma}$ rays. The $^{117}\mathrm{Sn}$ cross section, which is strongly enhanced near the low threshold, provides evidence for the presence of extra $\ensuremath{\gamma}$ strength in the low-energy tail of the giant dipole resonance. A coherent analysis of the photoneutron data for $^{117}\mathrm{Sn}$ together with the neutron capture on $^{116}\mathrm{Sn}$ shows that the $\ensuremath{\gamma}$-ray strength function is balanced in the photoneutron and neutron capture channels in terms of the microscopic Hartree-Fock-Bogoliubov plus quasiparticle random-phase approximation model of $E1$ strength combined with a pygmy $E1$ resonance at $8.5$ MeV. The high-energy part of the pygmy resonance is also suggested in the photoneutron cross section for $^{116}\mathrm{Sn}$.

Photoneutron cross sections were measured for $^{80}\mathrm{Se}$ immediately above the neutron separation energy with quasimonochromatic $\ensuremath{\gamma}$-ray beams to experimentally constrain the $E1$ $\ensuremath{\gamma}$ strength function for $^{80}\mathrm{Se}$. Two sets of the $\ensuremath{\gamma}$ strength function and the level density that equally meet the experimental constraint predict largely different neutron capture cross sections for $^{79}\mathrm{Se}$. Based on the Maxwellian-averaged cross sections of the latest compilation complemented with the predicted cross sections for $^{79}\mathrm{Se}$, we calculated $\ensuremath{\sigma}N$ values of the main $s$-process component using a phenomenological model and deduced empirical abundances of the weak $s$-process component. An attempt is made of considering the implications of the abundance ratios of $^{80}\mathrm{Kr}$ and $^{82}\mathrm{Kr}$ within the framework of phenomenological models for the weak $s$ process.

International audience; An IN2P3‐JINR collaboration has launched a project called GABRIELA at the Flerov Laboratory for Nuclear Reactions (FLNR) within the Joint Institute for Nuclear Research (JINR) in Dubna (Russia). The goal of the project is to perform gamma‐ray and internal conversion electron spectroscopy of heavy nuclei produced in fusion‐evaporation reactions and transported to the focal plane of the recoil separator VASSILISSA. During five experimental campaigns of GABRIELA, the detection system has gained in sensitivity and new spectroscopic information has been obtained for 249Fm, 251Fm, 253No and 255Lr. In this contribution new results for 253No will be discussed. © 2010 American Institute of Physics

Photoneutron cross sections were measured for 91Zr, 92Zr, and 94Zr near the neutron separation energy with quasimonochromatic gamma rays. The data exhibit some extra components around the neutron threshold. A coherent analysis of the photoneutron data for 92Zr together with the neutron capture on 91Zr based on the microscopic Hartree-Fock-Bogoliubov plus quasiparticle random-phase approximation model for the E1 strength has revealed the presence of an M1 resonance at 9 MeV. The microscopic approach systematically shows the same M1 strength in the photoneutron cross section for 91Zr and 94Zr. The total M1 strength is about 75% larger than the strength predicted by the systematics, being qualitatively consistent with the giant M1 resonance observed in the inelastic proton scattering.

Charged-particle decay from the dipole resonances at ${E}_{x}=24$ MeV in $^{6}\mathrm{He}$ and at ${E}_{x}=18$ MeV in $^{7}\mathrm{He}$ was studied via the $^{6,7}\mathrm{Li}$($^{7}\mathrm{Li}$,$^{7}\mathrm{Be}$ $x$) coincidence experiment at 455 MeV and at ${0}^{\ifmmode^\circ\else\textdegree\fi{}}$. These resonances are those that were interpreted as the analogs of the dipole resonances in the \ensuremath{\alpha} clusters of $^{6}\mathrm{Li}$ and $^{7}\mathrm{Li}$ in our previous work. The dominant decay channels (branching ratios) of the dipole resonances are found to be $d+t+n$ ($26~32%$) and $\ensuremath{\alpha}+2n$ ($47~69%$) for $^{6}\mathrm{He}$ and $t+t+n$ ($47~55%$) and $\ensuremath{\alpha}+3n$ ($38~47%$) for $^{7}\mathrm{He}$. The branching ratios measured for the $d+t+n$ and $t+t+n$ channels in $^{6}\mathrm{He}$ and $^{7}\mathrm{He}$, respectively, are larger than those calculated in a simple statistical model by a factor of $~100$. These results are consistent with the picture that the observed dipole resonances are analogs of the corresponding dipole resonances in the \ensuremath{\alpha} clusters of $^{6}\mathrm{Li}$ and $^{7}\mathrm{Li}$.

Light charged-particle emission and neutron emission have been measured for the fusion-evaporation and fusion-fission channels in the $^{60}\mathrm{Ni}$${+}^{100}$Mo reaction at 550 and 655 MeV bombarding energies. Temperatures, emission barriers, and multiplicities for the particles detected in coincidence with evaporation residues and fission fragments have been determined. For the evaporation residue data, the ``first-chance'' spectra of particles emitted from the compound nucleus have been isolated and the same initial temperature for the different evaporated particles has been extracted. The inverse level density parameter K=A/a reaches a value of 13.8\ifmmode\pm\else\textpm\fi{}0.7 MeV at ${\mathit{E}}_{\mathrm{th}}$\ensuremath{\simeq}236 MeV. A decrease of the apparent emission barriers for the charged-particle emission at high excitation energy suggests dynamical effects on the de-excitation process. Analysis of the fissionlike events shows a saturation of light particle emission from the fission fragments. Using the average energies and multiplicities of the emitted neutrons, and charged particles, it has been found that for both initial excitation energies, 251 and 293 MeV, scission occurs at an excitation energy \ensuremath{\simeq}140 MeV. For both fusion evaporation and fusion fission, the light charged particles are preferentially emitted during the early part of the de-excitation cascade. Statistical models and dynamical calculations have been used in an attempt to interpret the experimental data.

A newly developed technique has been used to probe a previously inaccessible region of the continuum in the at channels of 7 Li breakup reactions. This was used to investigate reactions of 63 MeV 7 Li with 58 Ni, 120 Sn, 144 Sm, and 208 Pb targets. Breakup pairs of α-particles and tritons emitted within a finite opening angle were analyzed according to their magnetic rigidity using a K = 150 Enge split-pole spectrograph. The αt coincidences were taken with two single-wire proportional counters mounted at different positions along the focal plane of the spectrograph. The large energy acceptance ( E max / E min ≈ 8) of the spectrograph is crucial to the present coincidence measurements involving two particles with different q / m values. Very small relative energy components were studied without any detection threshold. A pronounced bump was observed immediately above the αt particle threshold. No strong indication of the post Coulomb acceleration was observed. The excitation of the continuum states as well as the 7 − 2 state in 7 Li is discussed in terms of the distorted-wave Born approximation. The astrophysical implications of the data are also discussed regarding the Coulomb excitation of the continuum. The present technique offers the promise of very high sensitivity at small relative energies if it were applied in conjunction with ray-tracing, a thin target, and a dispersion-matched beam.

The {sup 20}Ne(p,t)h{sup 18}Ne reaction has been studied in order to investigate the properties of {sup 18}Ne excited states. A missing 3{sup +} state of {sup 18}Ne, which could have a great influence on the {sup 17}F(p,{gamma})h{sup 18}Ne reaction rate, was searched for, but the existence of this state was not clearly verified. The spins and parities of the 5.11- and 5.15-MeV states were assigned tentatively by angular distribution measurements, as 2{sup +} and 3{sup {minus}}, respectively. We were able to resolve the doublets at 4.5, 5.1, and 6.3 MeV clearly for the first time due to our high precision system, which allowed us to determine the widths of some critical states above the proton threshold of {sup 18}Ne more precisely. {copyright} {ital 1999} {ital The American Physical Society}

The gamma-ray mass attenuation coefficients of important materials for gamma-ray detection have been measured using the laser-Compton backscattering gamma-rays (LCS gamma-rays) and the high-resolution high-energy photon spectrometer (HHS). The preliminary results performed for materials (Ge and BGO) are presented for gamma-ray energy of 5.1 MeV. The measured data are compared with tabulated theoretical calculations.

Photon-induced reactions play a key role in the nucleosynthesis of rare neutron-deficient p-nuclei. The paper focuses on (gamma,alpha), (gamma,p), and (gamma,n) reactions which define the corresponding p-process path. The relation between stellar reaction rates and laboratory cross sections is analyzed for photon-induced reactions and their inverse capture reactions to evaluate various experimental approaches. An improved version S_C(E) of the astrophysical S-factor is suggested which is based on the Coulomb wave functions. S_C(E) avoids the apparent energy dependence which is otherwise obtained for capture reactions on heavy nuclei. It is found that a special type of synchrotron radiation available at SPring-8 that mimics stellar blackbody radiation at billions of Kelvin is a promising tool for future experiments. By using the blackbody synchrotron radiation, sufficient event rates for (gamma,alpha) and (gamma,p) reactions in the p-process path can be expected. These experiments will provide data to improve the nuclear parameters involved in the statistical model and thus reduce the uncertainties of nucleosynthesis calculations., 13 pages, 6 figures, EPJA, accepted

Photodisintegration cross sections were measured for 80Se with laser Compton scattering γ beams at Eγ=9.98–11.80 MeV near the neutron separation energy. The stellar neutron capture rate for 80Se was evaluated by using the photodisintegration data as constraints on the E1 γ strength function for 80Se within the framework of the Hauser‐Feshbach statistical model. It was found that the rate at 30 keV is 0.7–1.1 times that of Bao and Kappeler. s‐process temperatures deduced from the empirical solar abundances of the s‐only nuclei 79Se and 80Kr with this neutron capture rate are 17–25 keV in the neutron density rage of (0.8–1.9)×103/cm3.

The characteristics of the nuclear photo-absorption spectroscopy using the laser Compton scattering (LCS) photons and the high-resolution high-energy photon spectrometer (HHS) are presented in this paper. The maximum energy of a LCS photon was increased up to 30MeV, and the response functions of the HHS were improved. By taking advantage of these achievements, the 16 O(γ,abs) cross section was measured in the giant resonance region, that is, 20 to 25MeV. The preliminary result with the energy resolution of about 0.1% is presented and compared with the preceding data.

Total gamma absorption cross sections are the most important data used in various fields related to the application of gamma rays. However, the measurements of the total gamma absorption cross section were difficult for high energy gamma rays since there were no suitable gamma ray sources. Recently, the nuclear photo-absorption measurement system using the laser-Compton backscattering (LCS) gamma rays and the high-resolution high-energy photon spectrometer (HHS) were developed. We have utilized the system to measure the total gamma absorption cross section, that is, the sum of the atomic and nuclear interactions. The total gamma absorption cross sections at 10MeV for Al and Cu have been measured with the system. The preliminary results show that the obtained values agree fairly with the theoretical ones. Total gamma absorption cross sections are the most impor- tant data used in various fields related to the application of gamma rays. However, the measurements of the total gamma absorption cross section were difficult for high energy gamma rays since there were no suitable gamma ray sources. The gamma sources for such experiments in the past were

Cross sections of the $^{139}\mathrm{La}$$(\ensuremath{\gamma},n)$ and $^{141}\mathrm{Pr}$($\ensuremath{\gamma},n$) reactions were measured using quasi-monochromatic \ensuremath{\gamma}-ray beams from laser Compton scattering. The results are compared to the predictions of Hauser-Feshbach statistical calculations using different models for the \ensuremath{\gamma}-ray strength function. The model parameters are constrained by the present experimental data and used to estimate the stellar photoneutron rates and their associated uncertainties and to study the implication for the production of the rare odd-odd nuclide $^{138}\mathrm{La}$ by the p process. No evidence for a large thermonuclear p-process contribution to the solar $^{138}\mathrm{La}$ is found. The need to further explore the photodestruction rate of $^{138}\mathrm{La}$ is emphasized.

The isovector dipole resonances (DR's) consisting of the giant dipole resonance and spin dipole resonance (SDR) in $^{4}\mathrm{He}$ were investigated by using the ($p,{p}^{'}$) reaction at an incident energy of 300 MeV. We compared the excitation energy, width, resonance shape and the differential cross sections for the DR in $^{4}\mathrm{He}$ with those for the DR's in $^{6}\mathrm{Li}$ and $^{7}\mathrm{Li}$ which had been observed and interpreted in earlier work as the DR's in the \ensuremath{\alpha} clusters of $^{6}\mathrm{Li}$ and $^{7}\mathrm{Li}$. The DR's in $^{4}\mathrm{He}$ and in the \ensuremath{\alpha} clusters of $^{6,7}\mathrm{Li}$ were observed at ${E}_{x}=25.1\ifmmode\pm\else\textpm\fi{}0.5,28.0\ifmmode\pm\else\textpm\fi{}0.5$, and $30.5\ifmmode\pm\else\textpm\fi{}0.5$ MeV with the widths of $11.0\ifmmode\pm\else\textpm\fi{}2.0,11.7\ifmmode\pm\else\textpm\fi{}1.5$, and $11.3\ifmmode\pm\else\textpm\fi{}2.0$ MeV, respectively. The peaks corresponding to the 2${}^{\ensuremath{-}}$ SDR in the \ensuremath{\alpha} cluster were not as dominant as that observed in $^{4}\mathrm{He}$ at ${E}_{x}=22.1$ MeV. The resonance shapes for the \ensuremath{\alpha} cluster in $^{6,7}\mathrm{Li}$ were reproduced well with the DR shape without including the 2${}^{\ensuremath{-}}$ SDR in $^{4}\mathrm{He}$. The excitation energies for the DR's in the \ensuremath{\alpha} clusters slightly increase with the number of the surrounding nucleons. The cross sections for the excitation of the DR's in the \ensuremath{\alpha} clusters of $^{6,7}\mathrm{Li}$, normalized to the spectroscopic factors for the \ensuremath{\alpha} particle in $^{6,7}\mathrm{Li}$, are comparable to the cross section for the excitation of the DR in $^{4}\mathrm{He}$.

Photoneutron cross sections for (181)Ta(y, n) (180)Ta(m) were determined from simultaneous measurements of total cross sections (sigma(tot) and ground-state cross sections (sigma(gs)) for (180)Ta in photodisintegration of with laser Compton-backscattered rays. Techniques of direct neutron counting and photoactivation were used for the measurement of sigma(tot) and sigma(gs), respectively. The partial cross sections for the isomeric state serves as a novel probe of the nuclear level density of (180)Ta. Implications for the p- and s-process nucleosynthesis of (180)Ta(m) are given.

NACRE, the ‘nuclear astrophysics compilation of reaction rates’, has been widely utilized in stellar evolution and nucleosynthesis studies since its publication in 1999. We describe here the current status of a Konan‐Universite Libre de Bruxelles (ULB) joint project that aims at its update and extension.

Direct determination of photodisintegration cross sections with quasi‐monochromatic γ rays from laser Compton scattering has shed new light on nucleosynthesis. Presented here are results of photoneutron cross‐section measurements dedicated to investigating the origin of 180Tam, the only naturally occurring isomer and the rarest isotope in the solar system.

NACRE, the ‘nuclear astrophysics compilation of reaction rates’, has been widely utilized in stellar evolution and nucleosynthesis studies. Its update and extension programme started within a Konan‐Universite Libre de Bruxelles (ULB) collaboration. At the present moment, experimental data in refereed journals have been collected, and their theoretical extrapolations are being performed using the R‐matrix or potential models. For the 3H(d,n)4He and 2H(p,γ)3He reactions, we present preliminary results that could well reproduce the experimental data.

Cross sections of the $^{186}\mathrm{W}$, $^{187}\mathrm{Re}$, $^{188}\mathrm{Os}$($\ensuremath{\gamma},n$) reactions were measured using quasimonochromatic photon beams from laser Compton scattering with average energies from 7.3 to 10.9 MeV. The results are compared with the predictions of Hauser-Feshbach statistical calculations using four different sets of input parameters. In addition, the inverse neutron capture cross sections were evaluated by constraining the model parameters, especially the $E1$ strength function, on the basis of the experimental data. The present experiment helps to further constrain the correction factor ${F}_{\ensuremath{\sigma}}$ for the neutron capture on the 9.75 keV state in $^{187}\mathrm{Os}$. Implications of ${F}_{\ensuremath{\sigma}}$ for the Re-Os cosmochronology are discussed with a focus on the uncertainty in the estimate of the age of the galaxy.

The di-trinucleon clustering resonances of $^{3}\mathrm{He}+^{3}\mathrm{He}$ in $^{6}\mathrm{Be}$ and $t+t$ in $^{6}\mathrm{He}$ were studied via the $^{6}\mathrm{Li}(^{3}\mathrm{He},t\phantom{\rule{0.3em}{0ex}}^{3}\mathrm{He})$ and $^{6}\mathrm{Li}(^{7}\mathrm{Li},^{7}\mathrm{Be}\phantom{\rule{0.3em}{0ex}}t)$ reactions at incident energies of 450 and 455 MeV, respectively. A new resonance in $^{6}\mathrm{Be}$ was found at ${E}_{x}=18.0\ifmmode\pm\else\textpm\fi{}1.2\phantom{\rule{0.3em}{0ex}}\text{MeV}$ with a width of $9.2\ifmmode\pm\else\textpm\fi{}1.0\phantom{\rule{0.3em}{0ex}}\text{MeV}$ in the binary decay channel of $^{6}\mathrm{Be}\ensuremath{\rightarrow}^{3}\mathrm{He}+^{3}\mathrm{He}$. The resonance in $^{6}\mathrm{He}$ previously reported was also observed at ${E}_{x}=18.0\ifmmode\pm\else\textpm\fi{}1.0\phantom{\rule{0.3em}{0ex}}\text{MeV}$ with a width of $9.5\ifmmode\pm\else\textpm\fi{}1.0\phantom{\rule{0.3em}{0ex}}\text{MeV}$ in the binary decay channel of $^{6}\mathrm{He}\phantom{\rule{0.3em}{0ex}}\ensuremath{\rightarrow}t+t$. The branching ratios of the resonances for each binary decay were both $0.7\ifmmode\pm\else\textpm\fi{}1.0$, which was larger than the branching ratio calculated in a statistical model by two orders of magnitude. The angular correlations measured for t and $^{3}\mathrm{He}$ particles in the binary decay show a contribution dominantly from the multipolarity of $L=1$. We suggest that the resonances are the members of the isobaric triplet of the ${}^{3}P$ resonances in $A=6$ nuclei.

The response function of a high-resolution high-energy photon spectrometer (HHS), consisting of a twin Ge detector and BGO (Bi 3 Ge 4 O 12 ) anti-coincidence shields, has been measured for 10.763 MeV monochromatic γ-rays generated in a resonant reaction 27 Al(p,γ) 28 Si. The experimental response functions measured with and without the anti-coincidence were compared with results by Monte Carlo simulations, in which a pulse-height degradation effect associated with a surface channel of the twin Ge detector has been included. Excellent agreement was obtained between the experimental response functions and the simulations.

The neutron capture cross section of the unstable s-process branching nucleus 185W has been derived from experimental data of the inverse 186W(g,n)185W photodisintegration taken with monochromatic photon beams from laser Compton scattering. The result of sigma = 553 +- 60 mb at kT = 30 keV leads to a relatively high effective neutron density in the classical s-process of N_n = 4.7 \times 10^8 cm^-3. A realistic model for the s-process in thermally pulsing AGB stars overestimates the abundance of 186Os significantly because of the relatively small neutron capture cross section of 185W.

Photodisintegration cross sections were measured for deuterium with Laser Compton scattering γ beams at Eγ = 2.3 – 4.6 MeV. The experimental evaluation of R(E) = Naσv for the p(n,γ)D reaction was performed in the energy region relevant to big bang nucleosynthesis (BBN) by using the present data combined with the preceding data. The result confirms the past theoretical evdaluation with 6% uncertainty. The reaction rate for the p(n,γ)D reaction is presented for the BBN in the precision era.

γ‐ray beams at synchrotron radiation facilities will give us unprecedented opportunities to study photonuclear reactions of astrophysical interest. We report our photonuclear reaction studies and give a prospect of a fertile research field to be pioneered in the next 5 years.

In the p‐process production of 180Tam, not only photo‐production cross sections of 181Ta(γ,n)180Ta but also photo‐destruction cross sections of 180Tam(γ,n)179Ta are needed. We propose to measure the destruction cross section with high‐energy synchrotron radiation generated from a 10 tesla super‐conducting wiggler at SPring‐8.

Photodisintegration cross sections were measured for deuterium with Laser-Compton scattering $\ensuremath{\gamma}$ beams at seven energies near threshold. Combined with the preceding data, ${R(E)=N}_{a}\ensuremath{\sigma}v$ for the $p(n,\ensuremath{\gamma})\mathrm{D}$ reaction is for the first time evaluated based on experimental data with 6% uncertainty in the energy region relevant to the big bang nucleosynthesis (BBN). The result confirms the theoretical evaluation on which the BBN in the precision era relies.

Resonances above the t+t threshold in ${}^{6}\mathrm{He}$ have been studied via the ${}^{6}\mathrm{Li}$${(}^{7}\mathrm{Li},$ ${}^{7}\mathrm{Be}$ $t)$${}^{3}\mathrm{H}$ reaction at $0\ifmmode^\circ\else\textdegree\fi{}$ taken with a ${}^{7}\mathrm{Li}$ beam of 65 MeV/nucleon. By observing the binary triton decay, a new prominent resonance is found at ${E}_{x}=18.0\ifmmode\pm\else\textpm\fi{}0.5\mathrm{MeV}$ with a width of $7.7\ifmmode\pm\else\textpm\fi{}1.0\mathrm{MeV}.$ The branching ratio for the binary triton decay from this resonance is deduced to be $90\ifmmode\pm\else\textpm\fi{}10%,$ suggesting that the resonance at 18 MeV has a di-triton molecular structure.

New measurements of the photoneutron reaction on ${}^{181}\mathrm{Ta}$ have been conducted with the AIST-LCS (laser Compton scattering) beam in the $7.8\ensuremath{\lesssim}E[\mathrm{MeV}]\ensuremath{\lesssim}12$ energy range. The major advantage of the present $\ensuremath{\gamma}$-ray experiment is its intense peaking in the energy window of astrophysical interest, i.e., close to the neutron threshold. Details on photon beams from the laser Compton scattering, neutron counting, and experimental determination of the ${}^{181}\mathrm{Ta}$ photoneutron cross section are given. The present experimental data are in good agreement with the IAEA evaluation. Reaction rate calculations in the Hauser-Feshbach statistical model are performed and confronted with the experimental data. The data provide constraints on the low-energy tail of the dipole strength function. It is found that among the three different models for the $E1$-strength considered, only the microscopic quasiparticle random phase approximation model can reproduce the extra strength observed in the ${}^{181}\mathrm{Ta}(\ensuremath{\gamma}{,n)}^{180}\mathrm{Ta}$ reaction at energies of about 8.5 MeV. Such an experiment helps to improve the determination of the corresponding stellar photodisintegration rate of ${}^{181}\mathrm{Ta}$ which directly influences the p-process production of ${}^{180}\mathrm{Ta}.$

The γ-strength functions and level densities of 73,74Ge have been extracted from particle-γ coincidence data using the Oslo method. In addition the γ-strength function of 74Ge above the neutron separation threshold, Sn = 10.196 MeV has been extracted from photoneutron measurements. When combined, these two experiments give a γ-strength function covering the energy range of ∼1-13 MeV for 74Ge. This thorough investigation of 74Ge is a part of an international campaign to study the previously reported low energy enhancement in this mass region in the γ-strength function from ∼3 MeV towards lower γ energies. The obtained data show that both 73,74Ge display an increase in strength at low γ energies., SCOPUS: cp.p, info:eu-repo/semantics/published

The Extreme Light Infrastructure - Nuclear Physics, one of the three pillars of the Extreme Light Infrastructure Pan-European initiative, is a new large scale facility dedicated to nuclear physics with extreme electromagnetic fields. ELI-NP will host two 10 PW lasers and a very brilliant Gamma beam system with unprecedented intensity and energy resolution parameters. We propose to perform photon induced nuclear reactions using the very brilliant γ -ray beams provided by the Gamma beam system to examine in detail the photon absorption process and its decay modes. Here the experimental program related to nuclear research on reactions above the neutron separation threshold, which is under preparation at ELI-NP, is presented.

A new Coulomb breakup experiment was performed for ${}^{7}\mathrm{Li}$ with an improved experimental technique and theoretical treatment. Energy spectra of $\ensuremath{\alpha}$ particles and tritons were examined to find the signature of post-Coulomb acceleration in the breakup of ${}^{7}\mathrm{Li}$ at ${E}_{\ensuremath{\alpha}t}=0.$ The data revealed the delayed nature of nonresonant breakup of astrophysical relevance that stems from quantum tunneling. Semiclassical discussions are presented of the lifetime of continuum states in ${}^{7}\mathrm{Li}$ and distortion of relative kinetic energies between $\ensuremath{\alpha}$ and t by post-Coulomb acceleration. Dynamical calculations of Coulomb breakup were performed by solving a time-dependent Schr\"odinger equation. A simple potential model of ${}^{7}\mathrm{Li}$ was employed. The dynamical calculations reasonably reproduced experimental cross sections for both resonant and nonresonant breakup with two key ingredients: higher order effects and mixture of $E1$ and $E2$ multipoles. Considering the dominant role of the first-order $E1$ nature in adiabatic Coulomb breakup, cross sections in the ${v}_{\ensuremath{\alpha}}g~{v}_{t}$ branch at $7\ifmmode^\circ\else\textdegree\fi{}$--$15\ifmmode^\circ\else\textdegree\fi{}$ for ${}^{64}\mathrm{Zn}$ and ${}^{90}\mathrm{Zr}$ were used to deduce astrophysical S factors $S(E)$ for $t(\ensuremath{\alpha},\ensuremath{\gamma}{)}^{7}\mathrm{Li}.$ They exhibit a moderate energy dependence at small energies. The strongly energy-dependent $S(E)$ resulted from the previous Coulomb breakup experiment based on cross sections with ${v}_{\ensuremath{\alpha}}l~{v}_{t};$ they are most likely Coulomb distorted and are revised in the present work.

In the Coulomb dissociation method the electromagnetically induced breakup of light nuclei is studied in order to extract astrophysical S-factors. Possible pitfalls like higher order effects and a mixture of different multipolarities can be avoided by a careful study of the reaction mechanism. As an example a recent breakup experiment of 7 Li is discussed and it is shown that the Coulomb dissociation method is a useful tool for nuclear astrophysics.

We give a summary of the round table discussions on nuclear reactions in hot and explosive burning with emphasis on four topics: primordial nucleosynthesis in relation to the recent Boomerang and Maxima-1 observations, the 15O(α,γ)19Ne reaction in the hot CNO cycle, the p-process, and the Re/Os cosmochronometer.

Photoneutron cross sections were measured for ${}^{9}\mathrm{Be}$ in the energy range from 1.78 to 6.11 MeV with laser-induced Compton backscattered $\ensuremath{\gamma}$ rays. Resonance parameters $[{E}_{R},B(E1),{\ensuremath{\Gamma}}_{n}]$ for the ${1/2}^{+}$ and ${5/2}^{+}$ states were deduced from the least-squares fit to the data, while ${\ensuremath{\Gamma}}_{\ensuremath{\gamma}}$ for the ${5/2}^{\ensuremath{-}}$ state was deduced from the energy-integrated cross section. The reaction rate $〈\ensuremath{\alpha}\ensuremath{\alpha}n〉$ is discussed.

Photoneutron cross sections were measured for 9Be in the energy range from 1.77 to 3.75 MeV using quasi-monochromatic γ-rays produced in laser-induced Compton-backscattering. These cross sections are relevant to the reaction rate of the first step of the α–process of Type II & Type Ib supernovae, i.e., α(α,n,γ)9Be. Results are compared to the data taken with other photon sources like radioactive isotopes and Bremsstrahlung.

The performance of a plastic phoswich (400 μm NE102A + NE115) as an element of the focal plane detector for magnetic spectrographs was studied. When combined with the p/q selection by the spectrograph, the phoswich provides a complete isotope separation for light heavy ions in the energy range of some tens of MeV/nucleon.

Experimental investigation of critical nuclear reactions for the breakout off the Hot-CNO cycle are in progress. One is the 15O(α,γ)19Ne reaction, which could be the limiting reaction of the breakout at relatively low temperature (T

The excitation energy sharing between the two partners of binary dissipative collisions was derived for the Ar-40 + Ag-nat system at 27 and 44 MeV/u. From the eventual equilibration of energy between the two partners, and their separation time obtained from Landau-Vlasov simulations, the energy relaxation time was extracted, and compared with theoretical predictions.

A search was made with a sea water sample taken at a depth of 4000 m for anomalously heavy hydrogen dating from the early Universe. A technique of accelerator mass spectrometry involving a time-of-flight spectrometer was used. A new upper limit for the concentration of heavy particles in hydrogen is set around 4[times]10[sup [minus]17] in the mass range of 5--1600 u at a 95% confidence level.

Intrinsic excitation of α cluster in A = 6 nuclei were searched for by using the 6Li(3He, t) and 6Li(7Li,7Be) charge exchange reactions at the incident energy of 450 and 455 MeV at 0°. Charged particle decay from the dipole resonance at around 25 MeV in 6Be and 6He was measured. The dominant decay channels of the resonance are found to be d+3He+n for 6Be and d+t+p for 6He. The invariant mass spectra for 3He+n and 3H+p show clear enhancement in comparison with phase-space spectra, and suggests that α cluster in 6Be and 6He are excited to 4Li and 4H.