Search

In the first half of the paper, the nuclear astrophysics activities in Japan, especially in experimental studies are briefly overviewed. A variety of beams have been developed and used for nuclear astrophysics experiments in Japan. The activities include the RI beam facilities at low energies by the in-flight method at the Center for Nuclear Study (CNS), University of Tokyo and by the ISOL-based method at the JAERI tandem facility, and the RI beam facility at intermediate energies at RIKEN. Other activities include a study of the 12C(α, γ)16O reaction exclusively at the tandem accelerator at the Kyushu University, and studies at the neutron facility at Tokyo Institute of Technology and at the photon facility at AIST (Sanso-ken). Research opportunities in the future at RIBF, J-PARC, and SPRING8 are also discussed. A discussion on the research activities at CNS has been specifically extended in the latter half, including various possibilities in collaboration at the RI beam factory at RIKEN [ABSTRACT FROM AUTHOR]

The paper reports on the test of the newly developed RIKEN-ATOMKI CsI(Tl) array. It is demonstrated that high-quality detectors with excellent light collection efficiency and narrow resolution distribution could be produced. The setup has been commissioned in the study of the reaction of 22O + CD2. In the present paper, we summarize the results mainly on the (d, d′) channel. From the cross section for the transition between the ground state and the first 2+ state, we could deduce the "matter" deformation parameter to be βM=0.23±0.02 by distorted wave analysis. Comparing this data with previous measurements it can be concluded that 22O isotope has moderate and similar neutron and proton deformations. [ABSTRACT FROM AUTHOR]

Well-established data on production-rates of long-lived radionuclides are important for the understanding and calculation of various nucleosynthesis processes. However, lack of information exists for a list of nuclides as pointed out by nuclear-data requests. In addition, the search for supernova (SN)-produced radionuclides will give an improved insight into explosive scenarios. Accelerator mass spectrometry (AMS) represents a technique, which is capable to quantify such long-lived radionuclides using mass spectrometric methods. The potential of AMS is presented here as a powerful tool for probing nucleosynthesis. Applications of AMS are exemplified for a few specific cases: the detection of extraterrestrial radioactivity on Earth in terrestrial archives as a signature of nearby SN explosions, and the measurement of cross-sections, as an important ingredient for stellar as well as nuclear model calculations. [ABSTRACT FROM AUTHOR]

TACTIC (TACTIC web site: http://tactic.triumf.ca) is a new detector for low-energy nuclear reactions currently under development at TRIUMF. The cylindrical ionization chamber allows three-dimensional reconstruction of particle tracks by means of a two-dimensional anode array combined with a TOF measurement of the drift electrons. In addition, the integrated charge for each pulse provides information about the energy loss of the particle and therefore allows a better identification of the nuclear species producing the track. The geometry of TACTIC covers a large angular range permitting the measurement of differential cross-sections over a large solid angle. It will be ideal for investigations of nuclear processes pertinent to the field of nuclear astrophysics. [ABSTRACT FROM AUTHOR]

The structure of the neutron-rich nucleus 47Ar has been investigated through the d(46Ar,47Ar)p transfer reaction. The radioactive beam of 46Ar at 10 A · MeV was provided by the SPIRAL facility at GANIL. The protons corresponding to a neutron pick-up on bound or unbound states mechanism in 47Ar nuclei were detected at backward angles by the position-sensitive Si array-detector MUST. The transfer-like ejectiles were detected in the SPEG spectrometer. Level scheme, spin assignments and spectroscopic factors have been deduced for 47Ar and compared to shell model predictions. They suggest a slight erosion of the N=28 shell gap from the weakening of the spin-orbit interaction arising from the f and p orbitals. These spectroscopic information are subsequently used to infer (n, γ) reaction rates in the Ar isotopic chain to understand the origin of the 48Ca/46Ca abnormal isotopic ratio observed in certain inclusions of meteorites. [ABSTRACT FROM AUTHOR]

Conventionally, reaction rates relevant to nova nucleosynthesis are determined by performing the relevant proton capture reactions directly for stable species, or as has become possible more recently in inverse kinematics using short-lived accelerated radioactive beams with recoil separators. A secondary approach is to compile information on the properties of levels in the Gamow window using transfer reactions. We present a complementary technique where the states of interest are populated in a heavy-ion fusion reaction and their gamma decay studied with a state-of-the-art array of high-purity germanium detectors. The advantages of this approach, including the ability to determine resonance energies with high precision and the possibility of determining spins and parities from gamma-ray angular distributions are discussed. Two specific examples related to the 22Na(p, γ) and 30P(p, γ) reactions are presented. [ABSTRACT FROM AUTHOR]

The usual neutron-proton BCS wave function is simultaneously projected on both the good neutron and proton numbers using a discrete projection operator. The projected energy of the system is deduced as a limit of rapidly convergent sequence. It is numerically studied for the N=Z nuclei of which "experimental" pairing gaps may be deduced from the experimental odd-even mass differences. It then appears that the particle-number fluctuation effect is even more important than in the case of pairing between like-particles. [ABSTRACT FROM AUTHOR]

Experimental signatures of the dynamical correlations of a core with a single-particle neutron have been found in light neutron-rich nuclei investigated via the (7Li,7Be)c harge-exchange reactions at around 8MeV/u. Of particular astrophysical relevance are low-lying narrow resonances (Γ ∼ 200 keV FWHM) BSEC (Bound States Embedded in the Continuum). Because of their long lifetime BSEC states are likely to effect the capture rates in any scenario for nucleosynthesis in neutron-rich environment. They have been observed in the continuum of 11Be and 15C nuclei. A microscopic nuclear structure model based on QRPA theory, which takes into account Dynamical Core Polarisation (DCP) correlations, gives a suitable description of these resonances as well as single-particle states of the studied systems. In this context, high-energy narrow structures populated in nuclei having an integer number of α-particles plus three neutrons are good BSEC candidates and can be systematically investigated. [ABSTRACT FROM AUTHOR]

The relativistic invariant approach is applied to analyzing the 3.3 A GeV 22Ne fragmentation in a nuclear track emulsion. New results on few-body dissociations have been obtained from the emulsion exposures to 2.1 A GeV 14N and 1.2 A GeV 9Be nuclei. It can be asserted that the use of the invariant approach is an effective means of obtaining conclusions about the behavior of systems involving a few He nuclei at a relative energy close to 1 MeV per nucleon. The first observations of fragmentation of 1.2 A GeV 8B and 9C nuclei in emulsion are described. The presented results allow one to justify the development of few-body aspects of nuclear astrophysics. [ABSTRACT FROM AUTHOR]

The single-particle structure and shell gap of 100Sn as inferred from previous in-beam γ-ray spectroscopy has been confirmed in recent studies of seniority and spin-gap isomers by γγ, βγ, βpγ, pγ and 2pγ spectroscopy. The results for 94,95Ag, 98Cd and its N=50 isotones 96Pd and 94Ru stress the importance of large-scale shell model calculations employing realistic interactions for the isomerism, np-nh excitations, seniority mixing and E2 polarisation of the 100Sn core. The strong monopole interaction of the Δl=0, 1 spin/isospin-flip partners πg9/2-νg7/2 along the N=50 isotones and the πf5/2-νg9/2 pair of nucleons along the Z=28 Ni isotopes are decisive for the evolution of the shell structure towards 100Sn and 78Ni. It can be traced back to the tensor force in the effective nucleon-nucleon interaction and provides a straightforward explanation for new shells in neutron-rich light nuclei, implying qualitative predictions for new N=32, 34 subshells in Ca isotopes, persistence of the 78Ni proton and neutron shell gaps and non-equivalence of the g9/2 valence mirror Ni isotopes and N=50 isotones. This is corroborated by recent experimental data on 56,58Cr and 70-76Ni. The implication of monopole driven shell evolution for apparent spin-orbit splitting towards N ≫ Z and structure along the astrophysical r-path between N=50 and N=82 is discussed [ABSTRACT FROM AUTHOR]

We study the equation of state of strongly interacting matter at large densities and vanishing temperature. The hadronic matter equation of state is computed in a relativistic mean-field model and the quark matter equation of state is computed using a NJL-type model which takes into account the possibility of formation of the gapless color flavor locked phase. We focus in particular on the possible phase transition from hadronic matter to quark matter using both Maxwell and Gibbs constructions. We finally discuss the relevance of the equation of state in the context of compact stars and we propose some astrophysical signatures of the presence of quark matter in compact stars. [ABSTRACT FROM AUTHOR]

A simple approach is presented to estimate the position of the first opposite-parity state for p- and sd-shell nuclei. The approach is based on the assumption that the quadrupole-quadrupole interaction determines the energy of the lowest-lying states, and they are a mixture of a few leading SU(3) irreps even in the presence of further symmetry-breaking interactions. The quadrupole-quadrupole interaction together with the indirect effect of the Pauli exclusion principle will then lead to a rich structure in the trends of observables along Z, N and A chains. A comparison with the experimental data is given, with the carbon chain as illustrative example. The findings suggest that the changing shell structure near the neutron drip line might be explained by the appearance of low-lying highly deformed 2ħω states. [ABSTRACT FROM AUTHOR]

It has been realised recently that charge symmetry of the nucleon-nucleon interaction leads to a certain relation between Asymptotic Normalization Coefficients (ANCs) in mirror-conjugated one-nucleon overlap integrals. This relation can be approximated by a simple analytical formula that involves mirror neutron and proton separation energies, the core charge and the range of the strong nucleon-core interaction. We perform detailed microscopic multi-channel cluster model calculations and compare their predictions to the simple analytical formula as well as to calculations within a single-particle model in which mirror symmetry in potential wells and spectroscopic factors are assumed. The validity of the latter assumptions is verified on the basis of microscopic cluster model calculations. For mirror pairs in which one of the states is above the proton decay threshold, a link exists between the proton partial width and the ANC of the mirror neutron. This link is given by an approximate analytical formula similar to that for a bound-bound mirror pair. We compare predictions of this formula to the results of microscopic cluster model calculations. Mirror symmetry in ANCs can be used to predict cross sections for proton capture at stellar energies using neutron ANCs measured with stable or "less radioactive" beams. [ABSTRACT FROM AUTHOR]

The low-energy, bare-nucleus cross section for 15N(p, α)12C is extracted by means of the Trojan-Horse Method applied to the 2H(15N, α12C)n reaction at Ebeam = 60 MeV. The astrophysical S-factor is compared to the direct data in the same energy region. A nice agreement shows up down to 100 keV, while the low-energy behaviour of the S-factor suggests a smaller rate than is reported in the literature. [ABSTRACT FROM AUTHOR]

We discuss the use of one-nucleon breakup reactions of loosely bound nuclei at intermediate energies as an indirect method in nuclear astrophysics. These are peripheral processes, therefore we can extract asymptotic normalization coefficients (ANC) from which reaction rates of astrophysical interest can be inferred. To show the usefulness of the method, three different cases are discussed. In the first, existing experimental data for the breakup of 8B at energies from 30 to 1000 MeV/u and of 9C at 285 MeV/u on light through heavy targets are analyzed. Glauber model calculations in the eikonal approximation and in the optical limit using different effective interactions give consistent, though slightly different results, showing the limits of the precision of the method. The results lead to the astrophysical factor S17(0) = 18.7 ± 1.9 eV · b for the key reaction for solar neutrino production 7Be(p, γ)8B. It is consistent with the values from other indirect methods and most direct measurements, but one. Breakup reactions can be measured with radioactive beams as weak as a few particles per second, and therefore can be used for cases where no direct measurements or other indirect methods for nuclear astrophysics can be applied. We discuss a proposed use of the breakup of the proton drip line nucleus 23Al to obtain spectroscopic information and the stellar reaction rate for 22Mg(p, γ)23Al. [ABSTRACT FROM AUTHOR]

The Coulomb dissociation of 27P was studied experimentally using 27P beams at 57 MeV/nucleon with a lead target. The E2 gamma decay width of the first excited state in 27P was determined to be (2.8 ± 0.5) × 10−5 eV. The total (M1+E2)gamma decay width of the state, which is of astrophysical interest, is estimated by combining the experimental result and a shell model calculation. The reaction rate of 26Si(p, γ)27P is deduced from the estimated total gamma decay width. The astrophysical implication derived from estimated gamma decay width is discussed. [ABSTRACT FROM AUTHOR]

The Trojan Horse Method (THM) was applied to the 3He+7Li interaction in order to investigate the quasi-free 7Li(p, α)4He reaction. The three-body experiment was performed at 33 MeV corresponding to a 7Li-p relative energy ranging from 50 keV to 7 MeV. The extracted 7Li(p, α)4He quasi-free cross-section was compared with the behavior of direct data, as well as with the result of a previous THM investigation on the 7Li(p, α)4He reaction off the neutron in 2H. A good agreement between data sets shows up throughout the energy range investigated, providing a very important validity test of the pole approximation for the THM. [ABSTRACT FROM AUTHOR]

In this paper we present first results from a 8Li electromagnetic neutron-breakup experiment. Specific reactions studied were Pb(8Li,7Li+n)Pb and C(8Li,7Li+n)C at 41 MeV/nucleon beam energy. This is an effort to compare the results of a Coulomb dissociation experiment with the well determined (n, γ) reaction cross sections at astrophysical energies. The angular dependence of the cross section above 7 degree, which is the grazing angle of 8Li-Pb system, is similar in shape for lead and carbon and approximately proportional to A2/3 in magnitude indicating that the nuclear dissociation is the main component in this region. At very forward angles the angular distributions differ significantly and the electromagnetic dissociation dominates for the lead, although the nuclear contribution is not negligible. [ABSTRACT FROM AUTHOR]

The Trojan Horse Method has been applied to the 2H(9Be, 6Liα)n three-body reaction in order to investigate the 9Be(p, α)6Li two-body reaction, which is involved in the study of light element abundances (lithium, beryllium and boron). A coincidence measurement was performed in order to identify the presence of the quasi-free mechanism in the three-body reaction, needed for the application of the method. The astrophysical S(E)-factor was extracted and compared to direct data. No information about electron screening effects can be extracted due to the poor resolution of the indirect data. [ABSTRACT FROM AUTHOR]

An exclusive measurement of the Coulomb breakup of 8B into 7Be+p at 254 AMeV was used to infer the low-energy 7Be(p, γ)8B cross section. Particular emphasis was placed on the angular correlations of the breakup particles which demonstrate clearly that E1 multipolarity dominates within the angular cuts selected for the analysis. The deduced astrophysical S17 factors exhibit good agreement with the most recent direct 7Be(p, γ)8B measurements. [ABSTRACT FROM AUTHOR]

This work was performed to understand the structure of neutron-rich fission fragments around the 130 mass region. A thin 235U target was bombarded by a 14N beam with 10 MeV/A from the Separated Sector Cyclotron at the iThemba Laboratory for Accelerator Based Sciences, Cape Town, South Africa. The main goal was to detect and identify fission fragments and to obtain their mass distribution by using solar cell detectors in the AFRODITE (African Omnipurpose Detector for Innovative Techniques and Experiments) spectrometer. The X-rays emitted from fission fragments were detected by LEP (Low Energy Photon) detectors and γ-rays emitted from excited states of the fission fragments were detected by CLOVER detectors in the spectrometer. [ABSTRACT FROM AUTHOR]

The elastic scattering cross section of 106Cd(α, α)106Cd has been measured with high accuracy at energies of Ec.m. ≈ 15.5, 17, and 19MeV. The optical potential for the system 106Cd ⊗α has been derived at energies above and below the Coulomb barrier. Predictions for the 106Cd(α, γ)110Sn capture cross section at astrophysically relevant energies are presented and compared to the experimental data measured recently. [ABSTRACT FROM AUTHOR]

Owing to the presence of the Coulomb barrier at astrophysically relevant kinetic energies it is very difficult, or sometimes impossible, to measure astrophysical reaction rates in the laboratory. That is why different indirect techniques are being used along with direct measurements. Here we address two important indirect techniques, the asymptotic normalization coefficient (ANC) and the Trojan Horse (TH) methods. We discuss the application of the ANC technique for calculation of the astrophysical processes in the presence of subthreshold bound states, in particular, two different mechanisms are discussed: direct capture to the subthreshold state and capture to the low-lying bound states through the subthreshold state, which plays the role of the subthreshold resonance. The ANC technique can also be used to determine the interference sign of the resonant and nonresonant (direct) terms of the reaction amplitude. The TH method is unique indirect technique allowing one to measure astrophysical rearrangement reactions down to astrophysically relevant energies.We explain why there is no Coulomb barrier in the sub-process amplitudes extracted from the TH reaction. The expressions for the TH amplitude for direct and resonant cases are presented. [ABSTRACT FROM AUTHOR]

7Be decays via electron capture and therefore its half-life is expected to depend on the electron density at the nucleus. We measured the 7Be half-life in palladium, tungsten, zirconium and tantalum metals, in order to investigate the influence of the quasi-free electrons in metals on the probability of electron capture. The 7Be samples were obtained implanting a 4.85MeV pure radioactive 7Be ion beam. The 7Be half-life was determined measuring the 478 keV gamma decay following the electron capture by means of HPGe detectors. In order to reduce systematic errors, we planned to perform independent measurements in three different laboratories: Naples (Italy), Bochum (Germany) and Debrecen (Hungary). On the basis of the first results, we do not find a 7Be half-life change within the experimental errors of 0.4%. [ABSTRACT FROM AUTHOR]

Interaction of radiation with helium atoms and/or ions is of interest in various astrophysical applications. The reverse reactions of fast 150 MeV/amu 3He++ ions with solid C targets have been studied at the isochronous cyclotron of the RCNP in Osaka. The singly ionized helium ions resulting from capture of the target electrons to the projectile were observed with the use of large magnetic spectrograph, Grand Raiden, set at θ=0° with respect to the beam. The yield ratios of singly-to-doubly ionized helium ions emerging from thin carbon foils, He+/He++, have been measured as a function of the foil thickness. Extrapolating the results to zero target thickness permits to determine the cross section values separately for electron stripping from 3He+ ions and for electron capture to 3He++ ions. The radiative and non-radiative contributions to the capture cross section were determined in a separate experiment in which the 84 keV (C.M.) photons were observed in coincidence with the He+ ejectiles. The results are compared with theoretical predictions. Need for improved calculations is noted for all the three processes involved, i.e. for the radiative and non radiative electron capture as well as for the electron stripping. [ABSTRACT FROM AUTHOR]

Angular distributions and the neutron-proton branching ratio of the mirror reactions 2H(d, p)3H and 2H(d, n)3He have been investigated using different self-implanted deuterized metallic targets at projectile energies between 5 and 60 keV. Whereas the experimental results obtained for the transition metals Zr, Pd, Ta and also Al do not differ from those known from gas-target experiments, an enhancement of the angular anisotropy in the neutron channel and an attenuation of the neutron-proton branching ratio have been observed for the (earth)alkaline metals Li, Sr and Na at deuteron energies below 20 keV. Experimental results are discussed with consideration of the special problems arising from the properties of these chemically very reactive target materials. A first theoretical effort explaining simultaneously both n/p asymmetry effects based on an induced polarization of the reacting deuterons within the crystal lattice is presented. [ABSTRACT FROM AUTHOR]

The proton capture cross-sections of the two most proton-rich, stable isotopes of cadmium have been measured for the first time in the energy range relevant to the astrophysical p-process. The 106Cd(p, γ)107Inan d 108Cd(p, γ)109In cross-sections have been determined using the activation technique. Highly enriched as well as natural Cd targets have been irradiated with proton beams from both the Van de Graaff and Cyclotron accelerators of the ATOMKI. The cross-sections have been derived by measuring the γ-radiationfollo wing the β-decay of the 107Inan d 109In reaction products. The measurements were carried out in the energy range between 2.4 and 4.8MeV which is the relevant energy region (Gamow window) for the astrophysical p-process. Preliminary results are presented here and are compared with the predictions of the Hauser-Feshbach statistical model calculations using the NON-SMOKER code. [ABSTRACT FROM AUTHOR]

The 3He(4He, γ)7Be reaction is the key process for the production of 7Be and 8B neutrinos in the Sun. We have designed a new experimental setup to study this reaction with high accuracy at low energies using two different experimental techniques. The first method consists in measuring the prompt capture gamma-ray transitions with an ultra-low background germanium detector heavily shielded and placed at close distance from a 3He windowless gas target. With another fully shielded large-volume germanium detector we will also measure the β-decay of the 7Be residual nuclei. The aim of the experiment is to reduce the error on the astrophysical factor S3,4 to 4%. [ABSTRACT FROM AUTHOR]

The availability of exotic beams has produced great opportunities for advances in our understanding of the nucleosynthesis occurring in stellar burning and stellar explosions such as novae, X-ray bursts, and supernovae. In these extreme environments, synthesized radioactive nuclei can undergo subsequent nuclear processing before they decay, and thus to understand these events, we must understand reaction rates involving radioactive nuclei. At the ORNL Holifield Radioactive Ion Beam Facility (HRIBF), we have made a number of measurements using proton-rich beams such as 18F and 7Be and neutron-rich beams such as 82Ge and 84Se that help clarify the structure of astrophysically-important nuclei. We are also poised to begin studies with doubly-magic 132Sn. The experimental methods and results are discussed. [ABSTRACT FROM AUTHOR]

In stars, four hydrogen nuclei are converted into a helium nucleus in two competing nuclear fusion processes, namely the proton-proton chain (p-p chain)and the carbon-nitrogen-oxygen (CNO) cycle. For temperatures above 20 million kelvin, the CNO cycle dominates energy production, and its rate is determined by the slowest process, the 14N(p, γ)15O radiative capture reaction. This reaction proceeds through direct and resonant capture into the ground state and several excited states in 15O. High energy data for capture into each of these states can be extrapolated to stellar energies using an R-matrix fit. The results from several recent extrapolation studies are discussed. A new experiment at the LUNA (Laboratory for Underground Nuclear Astrophysics) 400 kV accelerator in Italy's Gran Sasso laboratory measures the total cross section of the 14N(p, γ)15O reaction with a windowless gas target and a 4π BGO summing detector, down to center of mass energies as low as 70 keV. After reviewing the characteristics of the LUNA facility, the main features of this experiment are discussed, as well as astrophysical scenarios where cross section data in the energy range covered have a direct impact, without any extrapolation. [ABSTRACT FROM AUTHOR]

The distribution of electromagnetic dipole strength in 92, 98, 100Mo has been investigated by photon scattering using bremsstrahlung from the new ELBE facility. The experimental data for well-separated nuclear resonances indicate a transition from a regular to a chaotic behaviour above 4 MeV of excitation energy. As the strength distributions follow a Porter-Thomas distribution much of the dipole strength is found in weak and in unresolved resonances appearing as fluctuating cross section. An analysis of this quasi-continuum —here applied to nuclear resonance fluorescence in a novel way— delivers dipole strength functions, which are combining smoothly to those obtained from (γ, n) data. Enhancements at 6.5 MeV and at ∼ 9 MeV are linked to the pygmy dipole resonances postulated to occur in heavy nuclei. [ABSTRACT FROM AUTHOR]

Direct determination of photoneutron cross sections of astrophysical importance has recently become possible with use of quasi-monochromatic γ beams produced in laser Compton backscattering (LCS) from relativistic electrons at AIST. The astrophysics to be discussed with the photodisintegration cross section are both stellar and big bang nucleosyntheses regarding the production of p-process and s-process nuclei as well as light elements. Synchrotron radiations from a 10 tesla superconducting wiggler (SCW) at SPring-8 serve as an ideal photon source to determine photoreaction rates. This paper covers the latest cross section measurements with the LCS photon beams and a feasibility study of determining (γ,x) (x = n, p, α) reaction rates with the SCW radiation. [ABSTRACT FROM AUTHOR]

The knowledge of the cross sections for photodissociation reactions like e.g. (λ, n) of neutron deficient nuclei is of crucial interest for network calculations predicting the abundances of the so-called p nuclei. However, only single cross sections have been measured up to now, i.e., one has to rely nearly fully on theoretical predictions. While the cross sections of stable isotopes are accessible by experiments using real photons, the bulk of the involved reactions starts from unstable nuclei. Coulomb dissociation (CD) experiments in inverse kinematics might be a key to expand the experimental database for p-process network calculations. The approach to test the accuracy of the CD method is explained. [ABSTRACT FROM AUTHOR]

The 112Sn(α, γ)116Te reaction cross-section has been measured to test the applicability of statistical models, especially NON-SMOKER in the energy range of importance for the astrophysical p-process nucleosynthesis. The measurements were carried out at the Notre Dame FN Tandem Van de Graaff accelerator by means of the activation method. Enriched self-supporting foils were irradiated with alpha beams over the alpha bombarding energy range of 8MeV to 12MeV in 0.5MeV steps. The induced activity was measured with a pair of large volume Ge Clover detectors in close geometry to maximize the detection efficiency. The preliminary results are compared with recent statistical model predictions using the code NON-SMOKER. [ABSTRACT FROM AUTHOR]

A research program has been started to study experimentally the near-threshold photodissociation of nuclides in the chain of cosmic heavy-element production with bremsstrahlung from the ELBE accelerator. An important prerequisite for such studies is the good knowledge of the bremsstrahlung distribution which was determined by measuring the photodissociation of the deuteron and by comparison with model calculations. First data were obtained for the astrophysically important target nucleus 92Mo by observing the radioactive decay of the nuclides produced by bremsstrahlung irradiation at end-point energies between 11.8MeV and 14.0MeV. The results are compared to recent statistical model calculations. [ABSTRACT FROM AUTHOR]

The nucleosynthesis of elements beyond iron is dominated by the s and r processes. However, a small amount of stable isotopes on the proton-rich side cannot be made by neutron capture and is thought to be produced by photodisintegration reactions on existing seed nuclei in the so-called "p process". So far most of the p-process reactions are not yet accessible by experimental techniques and have to be inferred from statistical Hauser-Feshbach model calculations. The parametrization of these models has to be constrained by measurements on stable proton-rich nuclei. A series of (n, γ) activation measurements on p nuclei, related by detailed balance to the respective photodisintegrations, was carried out at the Karlsruhe Van de Graaff accelerator using the 7Li(p, n)7Be source for simulating a Maxwellian neutron distribution of kT = 25 keV. We present here preliminary results of our extended measuring program in the mass range between A = 74 and A = 132, including first experimental (n, γ) cross-sections of 74Se, 84Sr, 120Te and 132Ba, and an improved value for 130Ba. In all cases we find perfect agreement with the recommended MACS predictions from the Bao et al. compilation. [ABSTRACT FROM AUTHOR]

DAMA is an observatory for rare processes based on the development and use of various kinds of radiopure scintillators; it is operative deep underground at the Gran Sasso National Laboratory of the INFN. Several low background setups have been realized and many rare processes have been investigated. In particular, the DAMA/NaI setup (⋍ 100 kg highly radiopure NaI(Tl)) has effectively investigated the model-independent annual modulation signature; the data of seven annual cycles (total exposure of 107731 kg × d) have offered a 6.3σ C.L. model-independent evidence for the presence of a Dark Matter particle component in the galactic halo. Some of the many possible corollary model-dependent quests for the candidate particle have also been investigated. At present, the second-generation DAMA/LIBRA setup (⋍ 250 kg highly radiopure NaI(Tl)) is in operation deep underground. This paper summarizes the main aspects. [ABSTRACT FROM AUTHOR]

Analyzing the Solar System abundance, we have found two universal scaling laws concerning the p- and s-nuclei with the same atomic number. They are evidence of the p-nucleus origin that has been discussed for long years. The first scaling is the correlation of the isotope abundances between a p-nucleus and an s-nucleus that is two neutron heavier than the p-nucleus. The abundance ratios of the s-nucleus to the p-nucleus are almost constant in a wide range of atomic numbers. This scaling indicates that the p-nucleus is dominantly produced from the s-nucleus by (γ, n) reactions in huge photon bath in supernova explosions. The second scaling indicates that the isotope abundance ratio between two pnuclei with the same atomic number is almost unity. These two scalings are a new useful method to verify nucleosynthesis models for the p-process. We have calculated these ratios by a p-process nucleosynthesis based on a typical core-collapse supernova explosion model. The results are consistent with the scaling in the solar abundances. In addition, the scalings provide new concepts: a universality of the p-process, a rate meter for the s-process and a new nuclear cosmochronometer. [ABSTRACT FROM AUTHOR]

We study the effect of screening by bound electrons in low energy nuclear reactions. We use molecular dynamics to simulate the reactions involving many electrons: D+d, D+D, 3He+d, 3He+D, 6Li+d, 6Li+D, 7Li+p, 7Li+H. Quantum effects corresponding to the Pauli and Heisenberg principles are enforced by constraints in terms of the phase space occupancy. In addition to the well-known adiabatic and sudden limits, we propose a new "dissipative limit" which is expected to be important not only at high energies but in the extremely low energy region. The dissipative limit is associated with the chaotic behavior of the electronic motion. It affects also the magnitude of the enhancement factor. We discuss also numerical experiments using polarized targets. The derived enhancement factors in our simulation are in agreement with those extracted within the R-matrix approach. [ABSTRACT FROM AUTHOR]

The electron screening in the d(d,p)t reaction has been studied for the deuterated metal Pt at a target temperature T = 20 °C to 340 °C, and for Co at T = 20 °C and 200 °C. The enhanced electron screening decreases with increasing temperature, where the data agree with the plasma model of Debye applied to the quasi-free metallic electrons. The data represent the first observation of a temperature dependence of a nuclear cross-section. We also measured the screening effect for the deuterated metal Ti (an element of group 4 of the periodic table) at T = −10 °C to 200 °C: above 50 °C the hydrogen solubility dropped to values far below unity and a large screening effect became observable. Similarly, all metals of groups 3 and 4 and the lanthanides showed a solubility of a few percent at T = 200 °C ( compared to T = 20 °C) and a large screening became also observable. Within the Debye model the deduced number of valence electrons per metallic atom agrees with the corresponding number from the Hall coefficient, for all metals investigated. [ABSTRACT FROM AUTHOR]

Thermonuclear runaways are at the origin of some of the most energetic and frequent stellar cataclysmic events. In this review talk, we outline our understanding of the mechanisms leading to classical nova explosions and X-ray bursts, together with their associated nucleosynthesis. In particular, we focus on the interplay between nova outbursts and the Galactic chemical abundances (where 13C, 15N, and 17O constitute the likely imprints of many nova outbursts during the overall 10Gyr of Galactic history), the synthesis of radioactive nuclei of interest for gamma-ray astronomy (7Be-7Li, 22Na, or 26Al), the endpoint of nova nucleosynthesis, based on theoretical and observational grounds, and the recent discovery of presolar meteoritic grains, both in the Murchison and Acfer 094 meteorites, likely condensed in nova shells. Recent progress in the modeling of X-ray bursts as well as an insight into the input nuclear physics requests, for both novae and X-ray bursts, will also be presented. [ABSTRACT FROM AUTHOR]

The study of the 2H(d, p)3H reaction at very low energies in deuterized metallic targets provides a unique possibility to test models of the electron screening developed for dense astrophysical plasmas. Here, we compare the experimental screening energies obtained by our group as well as by other authors for different target materials with theoretical predictions based on an improved dielectric function theory. The calculations are performed within the self-consistent regime and include polarization of both quasifree and bound electrons. Additionally, the cohesion screening, arising from different binding energies of deuterons and α-particles in crystal lattices, is taken into account. The proposed theory predicts only a weak material dependence of the screening energy in agreement with our experimental results but fails in the absolute strength of the effect by a factor of 2. The projectile-velocity dependence of the screening energy corresponding to the transition from the weak-screening regime to the strong-screening limit is discussed. [ABSTRACT FROM AUTHOR]

The astrophysical reaction rates of the 16O(α, γ)20Ne capture reaction and its inverse 20Ne(γ, α)16O photodisintegration reaction are given by the sum of several narrow resonances and a small direct capture contribution at low temperatures. Although the thermal population of low-lying excited states in 16O and 20Ne is extremely small, the first excited state in 20Ne plays a non-negligible role for the photodisintegration rate. Consequences for experiments with so-called quasi-thermal photon energy distributions are discussed. [ABSTRACT FROM AUTHOR]

Starting from chiral Lagrangians, possessing the SU(2)L × SU(2)R local chiral symmetry, we derive weak axial one-boson exchange currents in the leading order in the 1/M expansion (M is the nucleon mass), suitable for the nuclear physics calculations beyond the threshold energies and with the wave functions, obtained by solving the Schrödinger equation with the one-boson exchange potentials. The constructed currents obey the nuclear form of the partial conservation of the axial current. We apply the space component of these currents in calculations of the cross-sections for the disintegration of deuterons by the low-energy neutrinos. The deuteron and the 1S0 final-state nucleon-nucleon wave functions are derived i) from a variant of the OBEPQB potential and ii) from the Nijmegen 93 and Nijmegen I nucleonnucleon interactions. The extracted values of the constant L1,A, entering the axial exchange currents of the pionless effective field theory (EFT), are in agreement with those predicted by the dimensional analysis. The comparison of our cross-sections with those obtained within the pionless EFT and other potential model calculations shows that the solar neutrino-deuteron cross-sections can be calculated within an accuracy of ≈ 3.3%. [ABSTRACT FROM AUTHOR]

The leading questions in today neutrino physics concern the transformation properties of neutrinos under charge conjugation, the lepton number conservation hypothesis and the values of neutrino masses. The answers can be obtained if the neutrinoless double beta decay, 0ν2β, is observed and its rate is measured. The mere observation of the process proves the Majorana nature of neutrinos as well as the violation of the lepton number conservation, while the rate is a sensitive measure of the neutrino mass. The search for this effect at present concerns mainly the double β− decay. This paper describes the recent proposal to search for the neutrinoless radiative double electron capture as an attractive alternative to the double β− decay. It is shown, moreover, that the same information which is expected from the 0ν2β studies can in principle be also obtained from experiments using intense νe beams produced by radioactive ions decaying in flight (the "beta beams"). [ABSTRACT FROM AUTHOR]

We show that low-energy beta beams are very well suited to obtain information about supernova-neutrino interactions. Linear combinations of low-energy beta-beam spectra are fitted to supernova-neutrino energy distributions. The resulting synthetic spectra are able to reproduce the response of a nuclear target to an incoming supernova neutrino flux in a very accurate way. This can provide important information about the neutrino response in a terrestrial detector. We illustrate this technique using deuterium and 16O as target material. The procedure provides an easy and straightforward way to apply the results of a beta-beam neutrino-nucleus measurement to a supernova neutrino detector, virtually eliminating potential uncertainties due to nuclear-structure calculations. [ABSTRACT FROM AUTHOR]

After a short introduction on the low background liquid xenon DAMA set-up (DAMA/LXe) and its main previous results, we discuss the search for the nucleon, di-nucleon and tri-nucleon decays into invisible channels (disappearance or decay to neutrinos, Majorons, etc.) in the 136Xe isotope. The obtained limits (90% C.L.) on the lifetimes are: τn > 3.3 · 1023 yr, τp > 4.5 · 1023 yr, τnp > 3.2 · 1023 yr, τpp > 1.9 · 1024 yr, τnnp > 1.4 · 1022 yr, τnpp > 2.7 · 1022 yr and τppp > 3.6 · 1022 yr. In particular, the tri-nucleon decay into invisible channels is investigated here for the first time. [ABSTRACT FROM AUTHOR]

Neutrinos have recently provided us with the first tangible evidence of phenomena beyond the reach of our theory of the laws of particle physics, the remarkably predictive "Standard Model". The positive observation of oscillations in atmospheric and in solar neutrinos gives new motivations for more sensitive searches. Unfortunately, the oscillation experiments can only provide data on the squared mass differences of the neutrino mass eigenstates, while the absolute scale can only be obtained from direct mass measurements, 3H end point measurements for example or, in the case of Majorana neutrinos, more sensitively by neutrinoless double beta decay. In fact, recently published constraints on the mixing angles of the neutrino mixing matrix make a strong case that if neutrinos are Majorana particles, there are many scenarios in which next-generation double beta decay experiments should be able to observe the phenomenon, trying to disentangle the mass scale of the neutrinos. The interest for next-generation double beta decay experiments is growing, for if the mass scale is below ∼ 0.2 eV, double beta decay may be the only hope for measuring it. [ABSTRACT FROM AUTHOR]

The neutrino-nucleon cross-section is calculated in dense nuclear matter at finite temperature, in view of applications to supernovae and protoneutron stars. The main contribution to this parameter is provided by the axial response function. Nuclear correlations play an important role: while the v-N crosssection is usually reduced by correlations, a collective mode in the spin S = 1 channel may be excited. In that case, the cross-section diverges and the neutrino mean free path would be drastically reduced. The predictions of various models of the nuclear force commonly used in the literature are compared in relation with a possible spin instability. While Skyrme or Gogny forces lead to attraction in this channel, variational or Brueckner-Hartree-Fock calculations predict a repulsive contribution. An interesting alternative appears to be the density-dependent M3Y interaction. [ABSTRACT FROM AUTHOR]

The Sudbury Neutrino Observatory is a 1 ktonne heavy-water Čerenkov detector. The first phase of this experiment has shown that neutrinos from the Sun change flavour. For the second phase of the experiment, approximately 2 tonnes of salt (NaCl) was added to the heavy water to enhance the neutral-current detection as well as the neutral-current and charged-current separability. Here the results are presented from the complete salt phase at the Sudbury Neutrino Observatory. The electron energy spectrum is presented for the first time. It is consistent with an undistorted 8B spectral shape. It is also consistent with the Large Mixing Angle (LMA) parameters obtained through a global fit including the data presented in this paper. These parameters are found to be Δm2 = (8.0−0.4+0.6) × 10−5 eV2 and θ = 33.9−2.2+2.4 degrees. The total flux of active-flavour neutrinos from 8B decay in the Sun is found to be 4.94−0.21+0.21(stat)−0.34+0.38(syst), whereas the integral flux of electron neutrinos for an undistorted 8B spectrum is 1.68−0.06+0.0.6(stat)−0.09+0.08(syst), both in units of 106 cm−2s−1. The day-night asymmetry in the observed fluxes is consistent with both absence of matter-enhancement effects in the Earth and with the small level of these effects expected for the LMA model as stated above. [ABSTRACT FROM AUTHOR]