Search

Measurements of the cross sections are conducted for coherent photoproduction of the neutral pion and eta meson on the d, gamma deutron to pi0 eta deutron, at the incident energy in the range of the reaction threshold to 1.15 GeV. A rapidly increasing trend below 1 GeV is observed in the total cross section. The data are effectively reproduced by theoretical calculations incorporating the meson-deutron final-state interactions. However, the measured deutron angular distribution d sigma/d Omegad in the center-of-mass frame (gamma d) is rather flat, and it differs significantly from the strong backward-peaking behavior expected in the kinematics of d formation after pi0 eta photoproduction on an initial bound nucleon. In addition, the d sigma/dMeta d differential cross section exhibits a prominent enhancement near the eta d threshold, while d sigma/dMpi d exhibits an enhancement near the known pi d resonance with I=1 and JP=2+. From these observations, we have concluded that two reaction sequences occur; gamma d to pi0 D01 to pi0 eta d and eta D12 to pi0 eta d, where DIJ denotes a state with a baryon number of 2, an isospin of I, and a spin of J. The enhancement corresponding to D01 is expected to be a theoretically predicted eta NN bound state with I=0 and JP=1- or a virtual state of eta d. It is found that attraction between eta d is certainly very strong.

Coherent photoproduction of the neutral pion and eta meson on the deuteron, $\gamma{d}${$\to$}$\pi^0\eta{d}$, has been experimentally studied at incident photon energies ranging from the reaction threshold to 1.15 GeV. The total cross section demonstrates a rapid rise below 1 GeV. The data are underestimated by the existing theoretical calculations based on quasi-free $\pi^0 \eta$ photoproduction on the nucleon followed by deuteron coalescence. At the same time, the data are rather well reproduced by the calculations taking into account the final-state interaction. We have also measured for the first time the differential cross sections: the $\pi^0 \eta$ invariant-mass distribution $d\sigma/dM_{\pi \eta}$, the $\pi^0 d$ invariant-mass distribution $d\sigma/dM_{\pi d}$, the $\eta d$ invariant-mass distribution $d\sigma/dM_{\eta d}$, and the distribution over the deuteron emission angle $d\sigma/d\Omega_d$ in the overall center-of-mass frame. The measured cross section $d\sigma/d\Omega_d$ does not exhibit strongly backward-peaking behavior predicted by the calculations. At all incident energies, an increase in $d\sigma/dM_{\eta d}$ near the $\eta d$ threshold is observed, which indicates a bound or virtual $\eta d$ state resulting from a strong attraction between $\eta$ and a deuteron. The possibilities of using coherent $\pi^0\eta$ photoproduction on a nucleus to study the $\eta$-nuclear interaction are also discussed., Comment: 15 pages, 9 figures

Coulomb screening in nuclear reactions is considered to play an important role in cold fusion, since the screening effect causes considerable enhancement of reaction rates in the ultra-low energy region. This chapter is an overview of results obtained so far in low energy beam experiments of the d + d and Li + d reactions in metal environments. In various metals, extraordinary large screening effects were found in the d + d reaction. The observed enhancement in the low energy region was interpreted as electronic screening, mainly due to conduction electrons in metal. In the Li + d reaction, ionic screening was found in addition to the electronic one, by using liquid Li target. Comparing the obtained screening energy with the expected one from simple models, we found the following. The screening energy due to conduction electrons is several times larger than the calculation by the Thomas-Fermi model. On the other hand, the screening energy due to Li+ ions is about 60% of the prediction by the Debye model, which explains observed temperature dependence of the screening energy. Irradiation of liquid metals with a deuteron molecular beam has led to the discovery of a new process, a cooperative collision mechanism (CCM) of the d + d reaction, by which the screening energy was determined for several metals. Since the CCM is effective in accurately estimating the number of deuterons involved in the d + d reaction, it is expected to determine the screening energy more reliable.

The D+D reactions in Ti metal were investigated for the deuteron incident energies between 4.7 and 18 keV. Observed were protons, tritons and 3 He particles emitted in the deuteron bombardment on TiD x . Thick target yields for the D(d, p)T and D(d, n) 3 He reactions were measured at bombarding energies down to 4.7 and 5.4 keV, respectively, for the first time. They were well explained with the reported astrophysical S-factors which were deduced from gas target measurements at E d >6 keV for the D(d, p)T reaction and E d >13.3 keV for the D(d, n) 3 He reaction. The cross section ratio σ(d, p)/σ(d, n) was obtained down to 6.4 keV, and was found to be constant at around 1.0 for E d

In order to study entrance channel and angular momentum effects on the pre-ecission time, light charged particle multiplicities were measured in coincidence with binary decay fragments in the reactions 58 Ni(580 MeV) + 56 Fe and 86 Kr(890 MeV) + 27 Al , which lead to similar composite systems with almost the same excitation energy. It is observed that the lifetime of the composite system decreases as the entrace channel spin increases.

Energetic charged particles have been measured in the bombardment of 150-keV deuterons on deuterated Ti. Protons and α particles were observed with energies up to ~17 and ~6.5 MeV, respectively, which can never be attained in the D+D reaction. A bump structure at around 14 MeV seen in the proton spectrum can be well explained as emitted in the sequential reaction involving three deuterons. However, protons and α particles distributed continuously up to the maximum energies can never be understood as products of the conceivable nuclear reactions.

Properties of the giant dipole resonances (GDR) in very hot nuclei have been discussed based on γ-ray data measured in fusion reactions producing nuclei with E x = 90 – 500 MeV. It has been shown that there exists a limiting temperature of nuclei for the GDR γ-ray decay; the γ-ray emission cannot be observed above the limiting temperature. Although this fact simply suggests that the collective motion disappears when the nucleus is heated up, the characteristic time required for the formation of the GDR motion should be considered. We show the result of a sophisticated analysis which includes the effect of the time evolution of the GDR. The new analysis shows that the GDR width increases as the temperature increases but not so rapidly as previously reported.

A phoswich detector which consists of thin plastic and thick BaF2 scintillators has been tested using heavy ion reactions. It was found that gamma-rays, neutrons and charged particles with an atomic number up to 8 can be clearly distinguished. Based on the obtained resolution of particle identification, practical use of the detector has been discussed.

Neutron spectra are measured by the time-of-flight method at laboratory angles from 15 to 120 degfor the reaction Ag(14N,n) at 50 MeV/nucleon. All spectra are fitted with a moving-source model. The...

We report the Li+d reaction with liquid Li target and the D+D reaction in liquid Li with ultrasonic cavitation. The screening potential of the Li+d reaction has been deduce from the thick target yields of α particles emitted in the 6Li(d,α)4 He reaction in the solid and liquid phase. The deduced screening potential for the liquid Li is about 180 eV larger than for the solid. This difference is considered to attributed to the effect of liquefied Li+ ions. It is found out that the D+D reaction in liquid Li with ultrasonic cavitation is enhanced very much; the enhancement corresponds to effective energy increase of about 2000 eV.

The 6 Li(α, 2α) 2 H breakup reaction has been measured at E α = 77−119 MeV in coplanar, symmetric geometry. The projected energy spectra of the 2α correlation maps on the E 1 axis were obtained and analyzed with DWIA and PWIA calculations. The positions of the quasifree-scattering peaks are well reproduced by both calculations, which at the higher incident energies reproduced well the widths of the experimental peaks. At lower energies, the widths obtained from the DWIA calculation are wider than those observed. Spectroscopic factors, S α d , for breakup into α + d deduced from the DWIA calculation averaged 0.58. Effective numbers of α-clusters, N eff , deduced from the PWIA calculation averaged 0.22.

In order to study the properties of hot nuclei, neutrons emitted in the {sup 40}Ar+Ni, {sup 92}Mo, {sup 122}Sn reactions at {ital E}/{ital A}=26 MeV were measured in coincidence with fusion residues. The neutron spectra obtained for different residue velocities were analyzed with the moving source model. The spectra are well reproduced with two sources; one corresponds to preequilibrium emission and the other to the decay of fusion nuclei. The extracted neutron multiplicity and initial temperature of the fusion nuclei indicate the formation of thermally equilibrated nuclei with excitation energy up to 5.0 MeV/nucleon. The extracted relation between the temperature and the excitation energy shows that the level densities of the hot nuclei are well described with the level density parameter {ital a}={ital A}/(9{plus minus}1) for excitation energies from 2.5 to 5.0 MeV/nucleon.

In order to investigate the evolution of the GDR from low to high excitation energies, a series of experiments, in which high energy gamma-rays were measured in heavy ion fusion reactions, have been performed at JAERI and at RIKEN. It has been confirmed that the width of the GDR increases rapidly for Ex greater-than-or-equal-to 100 MeV and our previously introduced GAMMA(E(x)) can explain the data well for 80 less-than-or-equal-to E(x) less-than-or-equal-to 120 MeV. The limiting temperature of the nucleus for existing of the GDR has been deduced for A approximately 70, 105 and 130. The GDR seems to disappear at the temperature of about a quarter of the resonance energy.

Screening for nuclear reactions plays an important role in enhancing reaction cross sections at low energy region. In the present work, results so far obtained in experiments of the D+D reactions in metal environment is overviewed and the origin of the screening potential is discussed; i.e., electronic and ionic screening. For the ionic screening we have performed Li+p,d reactions in liquid Li metal which can be regarded as a low‐temperature dense plasma. In such a condition, the classical ions contribute to the screening more strongly than the quantum electrons do. The effects of the solid‐liquid phase transition are clearly seen in these reactions. It can be concluded that the ionic Debye screening is much stronger than the electronic screening in a low‐temperature dense plasmas.

We have measured the inclusive neutron cross section as a function of neutron energy and angle at 15\ifmmode^\circ\else\textdegree\fi{}, 30\ifmmode^\circ\else\textdegree\fi{}, 45\ifmmode^\circ\else\textdegree\fi{}, 60\ifmmode^\circ\else\textdegree\fi{}, 120\ifmmode^\circ\else\textdegree\fi{}, and 160\ifmmode^\circ\else\textdegree\fi{} for the system Ag${(}^{36}$Ar,n) at 35 MeV/nucleon. All spectra can be fitted with a moving-source model consisting of a projectilelike source, an intermediate-rapidity source, and a targetlike source. Temperatures for the targetlike and intermediate-rapidity sources were found to be about 4 and 11 MeV, respectively. Neutron multiplicities for each were 5.6 and 1.0. These parameters are compared with those from the neutron inclusive measurement of Ag${(}^{14}$N,n) at 35 MeV/nucleon and with proton exclusive data from the reaction $^{32}\mathrm{S}$+Ag at 30 MeV/nucleon.

The populations of neutron-unbound states and of bound states in intermediate-mass fragments have been measured at 15{degree}, 31{degree}, and 64{degree} from the {sup 14}N+Ag reaction at {ital E}/{ital A}=35 MeV. We did this for eleven neutron-unbound states in seven isotopes whose bound-state populations we were also able to measure. The data are identified in terms of the reaction mechanism producing them, which is either a deep-inelastic mechanism or a quasielastic mechanism. In order to test the assumption that the deep-inelastic data are produced from a thermal source, the unbound-state--bound-state population ratios of deep-inelastic fragments are compared to the predictions of a thermal sequential decay model. Most, but not all, of the deep-inelastic population ratios are fitted with model calculations that assume a source temperature between 2.5 and 3.5 MeV. In the case of {sup 13}C we were able to measure four deep-inelastic populations, and in the case of {sup 12}B we were able to measure three such populations. To further test the assumption of emission from a thermal source, attempts were made to fit all of the populations from each of these two isotopes with the sequential decay model using a single temperature.

An alignment of the nuclear spin has been observed for a secondary radioactive beam of $^{14}\mathrm{B}$ produced in the fragmentation of a 60 MeV/nucleon $^{18}\mathrm{O}$ beam impinging onto a $^{9}\mathrm{Be}$ target. The fragments were separated and analyzed in momentum by means of the doubly achromatic spectrometer LISE. The spin alignment was determined through a measurement of the anisotropy of the \ensuremath{\beta}-delayed \ensuremath{\gamma}-ray emission. The alignment is found to be small in the momentum region corresponding to the peak of the fragmentation yield, whereas it takes a large negative value for the high-momentum tail. This result is discussed in terms of a simple model of projectile fragmentation. The relevance of this result for the determination of nuclear moments far from stability is considered.

Thick target yields of α particles emitted in the 6Li(d,α)4He and 7Li(p,α)4He reactions were measured for Li target in the solid and liquid phase. Observed reaction rates for the liquid Li are always larger than those for the solid. This suggests that the stopping power of hydrogen ion in the liquid Li metal might be smaller than in the solid. Using the empirically obtained stopping power for the liquid Li, we have deduced the screening potentials of the Li+p and Li+d reactions in both phases. The deduced screening potential for the liquid Li is about 500 eV larger than for the solid. This difference is attributed to the effect of liquefied Li+ ions. It is concluded that the ionic screening is much stronger than the electronic screening in a low‐temperature dense plasmas.

High energy γ-rays were measured with a large BaF2 detector in coincidence with fusion residues produced in the 92 Mo+ 40 Ar reactions at E A=21 and 26 MeV . The obtained γ-ray spectra were compared with statistical calculations for γ-ray transitions from highly excited nuclei. Contributions of bremsstrahlung in the early stages of the reaction were subtracted. The evolution of the GDR γ-ray yields and the shape of the γ-ray spectra are well reproduced by calculations in which the width of the GDR increases with the excitation energy.

The electron-capture (EC) decay rate of (7)Be in C(60) at the temperature of liquid helium (T=5 K) was measured and compared with the rate in Be metal at T=293 K. We found that the half-life of (7)Be in endohedral C(60) ((7)Be@C(60)) at a temperature close to T=5 K is 52.47+/-0.04 d, a value that is 0.34% faster than that at T=293 K. In this environment, the half-life of (7)Be is nearly 1.5% faster than that inside Be metal at room temperature (T=293 K). We then interpreted our observations in terms of calculations of the electron density at the (7)Be nucleus position inside the C(60); further, we estimate theoretically the temperature dependence (at T=0 K and 293 K) of the electron density at the Be nucleus position in the stable center inside C(60). The theoretical estimates were almost in agreement with the experimental observations.

The decay rate of 7Be electron capture was measured in C60 and Be metal with a reference method. The half-life of 7Be endohedral C60 ((7)Be@C(60)) and 7Be in Be metal (Be metal (7Be)) is found to be 52.68+/-0.05 and 53.12+/-0.05 days, respectively. This amounts to a 0.83% difference in electron-capture decay half-life between (7)Be@C(60) and Be metal (7Be). Our result is a reflection of the different electron wave functions for (7)Be@C(60) inside C60 compared to the situation when 7Be is in a Be metal.

Publisher Summary The Laboratory of Nuclear Science (LNS) at Tohoku University has contributed to nuclear science research with electron beams in the last three decades. It has recently completed construction of the stretcher-booster ring (STB ring). The STB ring is now producing a continuous electron beam with energies up to 250 MeV for external target stations, and is ready to deliver a tagged photon beam with energies up to 1.1 GeV. This chapter describes the present experimental programs for nuclear physics with the STB ring at LNS-Tohoku. The ring has two functions; the pulse-beam stretcher ring and the boost and storage ring. In the boost and storage mode operation, electrons are accelerated up to 1.2 GeV to be stored in the ring. They can be used for internal target experiments including high-energy tagged photon production.

The transverse and longitudinal components of collective flow have been measured for the nuclear reactions 27Al(40Ar, X), E = 25–85 MeV/nucleon and Ni(40Ar, X), E = 36 and 65 MeV/u with the 4π array Mur+Tonneau. Monte Carlo simulations show that, even for peripheral reactions, the transverse-momentum analysis method gives a better determination of the reaction plane than the method which uses only the projectile-like fragments. The measured in-plane transverse-flow values reach −30 MeV/c at low energies for Z = 2 particles and tends to zero around 85 MeV/u. Flow-angle values are in the range −65° to −35°. The azimuthal distributions of the measured charged products show that there is no squeeze-out of nuclear matter, but the reaction system has a rotation-like behaviour which increases with the impact-parameter value.

Temperatures and excitation energies have been independently determined for hot nuclei formed in the 40Ar + 27Al reaction at energies ranging from 36 to 65 MeV/u. Charged products have been measured in a geometry close to 4π in the center of mass with the multidetectors MUR and TONNEAU. Events were sorted as a function of the impact parameter and the products emitted from equilibrated nuclei were separated from both pre-equilibrium and target-like products. Temperature (slope parameter) and excitation energy values were deduced from the kinetic energies of particles in the frame of the reconstructed equilibrated nucleus. Both have been found to increase with decreasing impact parameter. For the most central collisions impact parameters — less than 2 fm — the temperature was seen to increase with incident energy (slowly above 45 MeV/u) and reach a value of 7 MeV at 65 MeV/u. The excitation energy per nucleon exhibited a similar behaviour. The correlation between excitation energy and temperature was found to remain compatible with the statistical theory.

In order to investigate the role of heavy nuclei in the heavy water cluster impact d+d fusion, we have undertaken a series of d+d fusion experiments using atomic and molecular heavy ions (C, O, Ne, Ar, Kr, and Xe) on the deuterated solid targets in the energy range of 0.4–4 MeV. The observed excitation functions of 3 MeV proton yields are well accounted for in terms of the two step knock‐on cascade model. No distinct differences were observed in d+d fusion rate even when the number of atoms in the oxygen molecule (O+, O2+ and O3+) were changed. Extending the calculation of the excitation function of the atomic oxygen impact fusion rate up to the extremely low incident energies (∼keV), it has been found that the estimated proton yields are much smaller than the heavy water cluster impact fusion by 10 orders of magnitude. This indicates that the recent observation of strong enhancement of cluster impact d+d fusion from Brookhaven cannot be explained by the sum of usual elementary processes but must be due t...

The properties of the GDR in hot nuclei were investigated by measuring high energy γ‐rays in heavy ion fusion reactions. It has been confirmed that the width of the GDR increases rapidly for Ex≥100 MeV and our previously introduced Γ(Ex) can explain the data well for 80≤Ex120 MeV. The limiting temperature of the nucleus for existing of the GDR has been deduced for A∼70, 105 and 130, and it is concluded that the GDR disappears above the temperature of about a quarter of the resonance energy.

The multidetector array Mur + Tonneau has been used to perform a 4π detection of charged particles and fragments emitted in reactions between 40 Ar, at energies ranging from 25 to 85 MeV/u, and 27 Al or 58 Ni target. The events have been sorted as a function of the impact parameter value. The collective transverse momentum in the reaction plane (sidewards flow parameter) is observed to strongly vary as a function of impact parameter and incident energy. At low energies, it is shown to be negative. It inverts to positive values at beam energies in the range 70–100 MeV/u depending on the impact parameter value and the mass of the system. These data are compared to dynamical calculations based on LVUU and QMD. In this energy range, the calculated flow values are much more sensitive to the nucleon-nucleon cross section in medium and to the equation of state than at relativistic energies; therefore, quantitative information can be obtained.

Charged particles and fragments emitted in reactions between 40 Ar at energies ranging from 25 to 85 MeV/u and an 27 Al target have been detected in a geometry close to 4π in the center of mass with the 4π array MUR + TONNEAU. A new global variable, the average parallel velocity, has been used to sort the events as a function of the impact parameter value. The multiplicity of particles emitted from the interaction region increases strongly when the impact parameter value decreases, and reaches 7 in head-on reactions. The flow of these particles is attributed to scattering at negative angles. When the energy increases, compression gradually opposes this negative scattering, until the flow falls to zero. This is obtained at a beam energy in the range 70–80 MeV/u for impact parameters below 2 fm and increases with the impact parameter. This study as a function of the impact parameter and the energy should allow information both on the nucleon-nucleon cross section in medium and the EOS of nuclear matter to be obtained. In central reactions, incomplete fusion nuclei are formed at all incident energies. Their excitation energy increases with the incident energy. Above 36 MeV/u no heavy residue is left, the multiplicity of final products increases as well as the emission probability of several heavy fragments.

Several global variables are tested for determining the impact parameter in 4π measurements of charged products. For the system Ar + Al from 25 to 85 MeV/u, simulated reactions are used to study the correlation between the real impact parameter value and the experimentally determined one. Even with a perfect detector, the total multiplicity and the mid-rapidity charge give a poor correlation. Filtering through the acceptance of an actual detector (Mur + Tonneau at GANIL) provides a poor correlation with the total charge, and an acceptable one with the total perpendicular momentum. The average (mass weighted) parallel velocity V av gives the best correlation and is less sensitive to the incident energy and to the mechanisms used in the simulation. Measurements extending to very forward angles are needed to accurately sort events by impact parameter. Real data are used to study the variation of other global variables versus V av : they exhibit the expected average trend, with broad fluctuations. The eccentricity and flow angle allow the evolution of central reactions with the incident energy to be followed. The proportion of relative motion transformed into energy perpendicular to the beam direction decreases when the incident energy increases; its absolute value, however, doubles from 25 to 65 MeV/u. In experimental studies where good separation between participant (pre-equilibrium) and spectator (equilibrium) particles is wanted in addition to good impact parameter sorting, the projectile mass should be in the range 1.2–2.5 times the target mass.