Isotopic dependence of electron screening in fusion reactions

The fusion reactions⁶Li(p, )³He,⁶Li(d, )⁴He, and⁷Li(p, )⁴He have been studied over the c.m. energy rangeE=10 to 1450 keV. Each reaction involved the use of hydrogen projectiles and LiF solid targets as well as Li projectiles and hydrogen molecular gas targets. In all cases the effects of electron screening on the low-energy fusion cross sections (exponential enhancement) have been observed; the effects are somewhat stronger in the case of atomicp ord projectiles compared to the case of molecularH ₂ orD ₂ gas targets. If isotopic effects on electron screening are negligible, all three reactions should exhibit the same enhancements for each set of experimental techniques. The measurements confirmed this expectation to a large extent.Supported in part by the Landesamt Nordrhein-Westfalen (IVA5-10600387), the Deutsche Forschungsgemeinschaft (Ro429/ 18-2 and Ro429/21-1), and the Comision Interministerial de Ciencia y Tecnologia (AEN90-0932)     

Langevin dynamic simulation of hysteresis in a field-swept Landau potential

Numerical simulations are done of Langevin dynamics for a uniform-orderparameter, field-swept Landau model,= –|a/2|m ²+|b/4|m ⁴–mh(t) , to study hysteresis effects. The field is swept at a constant rateh(t)=h(0)+ht. The stochastic jump values of the field {h_J from an initially prepared metastable minimumm(0) are recorded, on passage to a global minimum m(). The results are: (a) The mean jump¯h _J(h) increases (hysteresis loop widens) with h, confirming a previous theoretical criterion based on rate competition between field-sweep and inverse mean first-passage time (FPT); (b) The broad jump distribution(h _J,h) is related to intrinsically large FPT fluctuations ( ²–²)/ ² O(1), and can be quantitatively understood. Possible experimental tests of the ideas are indicated.     

Ricci collineations of the Bianchi type II,VIII, and IX space-times

Ricci and contracted Ricci collineations of the Bianchi type II, VIII, and IX space-times, associated with the vector fields of the form (i) one component of ^a (x ^b ) is different from zero and (ii) two components of ^a (x ^b ) are different from zero, fora, b=1, 2, 3, 4, are presented. In subcase (i.b), which is ^a = (0, ¹(x ^a ),0,0), some known solutions are found, and in subcase (i.d), which is ^a =(0, 0, 0, ⁴(x ^a )), choosingS(t) = const.×R(t), the Bianchi type II, VIII, and IX spacetime is reduced to the Robertson-Walker metric.     

A study of the ϱ0 meson polarization in π− p reaction at 5 GeV/c

Experimental data on ⁰ meson polarization in ^– p reaction at 5 GeV/c are presented. Change in ⁰ meson polarization for mesons produced at smallP ² and atP ² 0·3 or produced in backward direction in CMS is demonstrated. Natural explanation of these phenomena is one pion exchange mechanism and mechanism of quark-antiquark annihilation as observed for ⁰ meson production in¯pp reactions.The authors are indebted to Ján Piút, Richard Lednický, V. S. Rumiancev and N. K. Koutsidi for discussions and critical comments.     

Low energy antiproton annihilation on nuclei

Data obtained in the study of the antiproton interaction on⁴He, Ne and photographic emulsion nuclei are reported. Charged prong multiplicities, branching ratios and reaction cross-section values are given. Some features of¯p annihilation deep inside the nuclear matter are described. Cosmological restrictions deduced from³He production in¯p ⁴He reactions are discussed.Presented at the symposium Mesons and Light Nuclei, Bechyn, Czechoslovakia, May 27–June 1, 1985.     

Dynamics of low-energy nuclear forces for electromagnetic and weak reactions with the deuteron in the Nambu-Jona-Lasinio model of light nuclei

A dynamics of low-energy nuclear forces is investigated for low-energy electromagnetic and weak nuclear reactions with the deuteron in the Nambu-Jona-Lasinio model of light nuclei by example of the neutron-proton radiative capture (M1-capture) n + p → D + γ, the photomagnetic disintegration of the deuteron γ + D → n + p and weak reactions of astrophysical interest. These are the solar proton burning p + p → D + e⁺ + ν _e, the pep-process p + e⁻ + p → D + ν _e and the neutrino and antineutrino disintegration of the deuteron caused by charged ν _e + D → e⁻ + p + p, + D → e⁺ + n + n and neutral ν _e() + D → ν _e() + n + p weak currents.     

On kaonic deuterium. Quantum field-theoretic and relativistic covariant approach

We study kaonic deuterium, the bound K^-d state A_{K d}. Within a quantum field-theoretic and relativistic covariant approach we derive the energy level displacement of the ground state of kaonic deuterium in terms of the amplitude of K^-d scattering for arbitrary relative momenta. Near threshold our formula reduces to the well-known DGBT formula. The S-wave amplitude of K^-d scattering near threshold is defined by the resonances (1405), (1750) and a smooth elastic background, and the inelastic channels K^-d NY and K^-d NY, where Y = ^±,^{0} and ^{0}, where the final-state interactions play an important role. The Ericson-Weise formula for the S-wave scattering length of K^-d scattering is derived. The total width of the energy level of the ground state of kaonic deuterium is estimated using the theoretical predictions of the partial widths of the two-body decays A_Kd NY and experimental data on the rates of the NY pair production in the reactions K^-d NY. We obtain _{1s} = (630±100)eV. For the shift of the energy level of the ground state of kaonic deuterium we predict _{1s} = (325±60)eV.     

Excited levels of111In and113In

Levels and transitions in¹¹¹In and¹¹³In have been studied in the¹¹¹Cd(p, n)¹¹¹In and¹¹³Cd(p, n)¹¹³In reactions. By means of- coincidences,-angular distributions, relative excitation functions and conversion electron measurements more than 20 levels below 2 MeV have been established in each nucleus. Several negative-parity states were found above 1 MeV. Two low-spin positive-parity states with features similar to the possible rotational band in the heavier In nuclei are observed below 1,400 keV in both nuclei.     

16, 18O induced transfer reactions on122, 120Sn

The reactions¹²⁰Sn+72 MeV¹⁸O and¹²²Sn+74 MeV¹⁶O were investigated with time of-flightE-E-telescopes. Data are presented for all quasi-elastic reaction channels. The two neutron stripping and pickup reactions (¹⁸O,¹⁶O), (¹⁸O,²⁰O) and (¹⁶O,¹⁸O) are analyzed in detail. It is shown that these heavy ion induced two neutron transfer reactions proceed with essentially the same type of selectivity as the corresponding light ion induced reactions. The differential cross sections for transfer reactions leaving the^{120, 122}Sn nuclei in their 2⁺ first excited states are shown to be influenced by interference effects due to additional inelastic excitations.     

On the Possible Mechanisms of Activation Changes of Enzymes under Pulsed Irradiation

Classical radiation biology, radiation treatment of patients, and pulsed radiation chemistry usually deal with weak beams of radiation and operate in terms of dose (D). In this case, only the absolute number of ionizing particles or photons interacting with the object independently of one another is important. In this work, we resume our previous investigations of enzyme activation/inactivation produced by pulsed ionizing radiation from a dense plasma focus (DPF) device at a very short and intense irradiation process, when the concentrations of spurs and blobs are sufficiently dense to allow the micro-volumes to overlap each other. The time interval is small compared with the corresponding biochemical process. It is shown that the irradiation of biological objects for a few nanoseconds by beams of x-ray photons with a low dose (D 10^-6–10^-3 Gy) but at a high dose power (D/10³–10⁵ Gy/s) may be of a collective nature and result in synergetic effects. In particular, it was found that a remarkable activation/inactivation of enzymes (horseradish peroxidase, angiotensin-converting-enzyme) takes place at low doses in these regimes. The results of irradiating the above-mentioned enzymes in vitro with x-rays of nanosecond pulse duration coming from a dense plasma focus are presented here. Neutrons (2.5 MeV, 10³–10⁵ n/cm² and x-ray photons of different energy ranges (7–9 keV and 20–200 keV) together with dose power factors are analyzed as possible reasons for the activation/inactivation of enzymes in various dose ranges. Our results are compared to those of the same experiments conducted with continuous x-ray sources based on a classical x-ray tube and on a ¹³⁷Cs-isotope source (D10^-3–10² Gy).     

Far-infrared absorption of the superionic conductor Li3N. temperature and isotope effects

The far-infrared absorption spectrum (20–250cm^–1) of the superionic conductor Li₃N —with⁶Li- and⁷Li-isotopes in the starting material—has been measured for different polarizations and temperatures (4–150 K). TheE c spectrum yields two lines near 80 and 140 cm^–1, which are not observed forE c. From the isotopic frequency ratio ( ₆/ ₇1.07) and from the comparison to lattice dynamics it is concluded that these lines are due to resonant modes, weakly coupled to the lattice. Measurements of the isotope effects on the dielectric properties (10 Hz to 1 MHz) establish that the local diffusive type motion in shallow potentials and the low lying resonant modes originate from the same defect system (including Li-ions in non-regular positions).     

Study of the Dynamic Properties of Nuclei at Short Nucleon-Nucleon Distances

Results of investigations into the effects of non-nucleonic degrees of freedom and short-range dynamic correlations in nuclei for the reactions of interaction of real photons with light nuclei carried out in the Tomsk synchrotron are reviewed. The measured asymmetry of deuteron photodisintegration upon exposure to linearly polarized photons below the pion production threshold and the measured cross sections of reactions (, ⁺ p) and (, ^{–, 0} p) on p-shell nuclei are examined for a wide range of kinematic variables.     

The influence of the entrance channel dynamics on the evaporation residue formation

The dynamical effects of the entrance channel on the competition between quasifission and fusion processes, and on the evaporation residue formation are investigated. We have analyzed the results and compared our calculations with the experimental data obtained in the ¹⁶ O + ²⁰⁴ Pb and ⁹⁶ Zr + ¹²⁴ Sn reactions having very different mass asymmetries and leading to the ²²⁰ Th ^* compound nucleus. We have found that different partial capture cross-sections for these reactions lead to different fusion-quasifission competitions and, consequently, to different partial fusion cross-sections of the compound nucleus formed in the two reactions. The dynamical conditions also affect the fission-evaporation competition of the excited intermediate nuclei along the CN de-excitation cascade and, consequently, the evaporation residue formation.Received: 8 March 2004, Revised: 5 April 2004, Published online: 25 October 2004PACS: 25.70.Jj Fusion and fusion-fission reactions - 25.70.-z Low and intermediate energy heavy-ion reactions - 27.80. + w - 27.90. + b      

Cosmic Antiproton Spectrum at the Top of the Atmosphere Derived from the New Scaling Model

The new scaling variable model explains the scaling behavior of p + p → p + X inclusive reactions at ISR energies. The cosmic antiproton spectrum has been derived from this model using the primary proton spectrum of RYAN et al. The derived antiproton-proton flux ratio lies within the upper limit value of BOGOMOLOV et al. and CHEN. The estimated antiproton spectrum follows the relation where the antiproton energy E_p is expressed in GeV and the intensity in units (cm² sec sr GeV)^?1.     

Magnetoconductivity of thin epitaxial silver films

The magnetoconductance (MC) of thin epitaxial Ag films on Si(111) surfaces is studied as a function of film thickness (1–125 monolayers (ML)) at 20 K under ultra high vacuum (UHV) conditions. Three different regimes of magnetoconductance are observed depending on the degree of disorder in the films which is controlled by film thickness and annealing procedures. Thick films (d>3 ML) with diffuse electron transport show in the case of large elastic scattering times ₀ a classical, negative MC B ² and in the case of small ₀ a positive MC due to weak localization effects. The MC of thin films (d<2 ML) which have a conductance smaller than e ²/h, i.e. localized electron states, is negative again.     

Nonlinear relaxation at first-order phase transitions: A Ginzburg-Landau theory including fluctuations

Kinetics of phase transitions are investigated in systems with nonconserved one-component order parameter (i.e., generalized time-dependent Ginzburg-Landau models ind dimensions). The correct static critical behavior as well as fluctuation effects on the kinetics are incorporated by a suitable adaptation of the theory on spinodal decomposition by Langer, Baron and Miller. Both the case of quenches from temperaturesT above to below the critical pointT _c and the case of magnetic field changesH from positive to negative values are treated, and both time-dependent order parameter m() and structure factorS(q, ) are obtained numerically ford=2, 3. In the case of quenches atH=0, we find that m()0 andS(q, ) —S(q, ) exp(– ^1/2/7.2) , withS(q, )q ^–2. In the case of field changes we find that forH not exceeding some critical valueH ^* the system is trapped in a metastable state with infinite lifetime. In contrast to the meanfield-spinodal, the susceptibility does not seem to diverge atH ^*. These results are compared with other treatments, in particular the Monte Carlo simulations of kinetic Ising models by Binder and Müller-Krumbhaar. While our theory describes some properties of the metastable states reasonably,H ^* distinctly exceeds the observed limit of metastability. We argue that the present theory does not take into account nucleation fluctuations, and also fails to describe correctly the domain growth in the late stages of the relaxation. Contrary to Langer et al. we suggest that universality holds for nonlinear relaxation and spinodal decomposition nearT _c .Supported in part by the Deutsche Forschungsgemeinschaft, Sonderforschungsbereich 130     

Comparative analysis of (p,d), (d,t) and (3He, α) reactions on13C nucleus

The angular distributions of the (p, d), (d, t) and(³He, ) reactions on¹³C have been analysed within the framework of DWBA in which additional information on nuclear vertex constants was introduced. Although all these reactions seem to be similar single nucleon transfer, their mechanism is shown to be quite different and so is the information extracted thereof. While from the (p, d) reactions spectroscopic factors may be extracted unambiguously, from the (d, t) reactions it is possible to obtain directly the values of vertex constants only, which in turn are consistent with those determined by extrapolation of the experimental cross sections of the (p, d) reactions to the pole.In the case of (³He, ) reactions, however, the analysis indicates inadequacy of the DWBA concerning the calculations of central partial amplitudes. For a more reliable extraction of structural information, besides the correct normalization of peripheral amplitudes, a contribution of more complex mechanisms must be taken into account.     

Magnetic moments of proton drip-line nuclei13O and9C

The magnetic moments of the proton drip-line nuclei¹³O(I = 3/2^–,T _1/2 = 8.6 ms) and 9C(I = 3/2^–,T _1/2 = 126 ms) have been determined for the first time through the combined techniques of polarized radioactive nuclear beams and-NMR detection. The observed magnetic moments are ¦(¹³O)¦ = 1.3891 ±0.0003 _N and ¦(⁹C)¦ = 1.3914 ±0.0005 _N. Spin expectation values are deduced to be 0.76 and 1.44 for¹³O and⁹C, respectively. While the of¹³O is consistent with the systematics from isospinT= 1/2 mirror pairs, the of⁹C is unusually large, even far larger than the single particle value, = 1.     

The Action of √−Δ on Weighted Sobolev Spaces

The action of – on distributions is examined within the context of weighted Sobolev spaces. The results obtained are as follows: (1) – is a continuous map of R ⁿ ), the space of rapidly decreasing functions, to L ^{2, s} (R ⁿ for any s < n/2 +1; (2) if k R and s > –n/2 – 1, then – is a continuous map from H ^{k, s} (R ⁿ ), the weighted Sobolev space, to H ^{k–1, t} (R ⁿ for some t. The results are optimal in a sense.     

Condensed matter effects on nuclear fusion rates in laboratory and astrophysical environments

Previously overlooked condensed matter effects (CME) can significantly influence nuclear fusion rates in both laboratory and astrophysical environments. In dense plasmas, the ensemble of fusing particles has a significant exchange of kinetic and potential energies. Thus, there are diminished effective flux velocities resulting in a significant selective reduction of fusion rates. Our CME predictions are testable in laboratory experiments and have broad-ranging implications on the fusion rates for stellar media in general. By calculating reaction rates forp(p, e ⁺ v _e ) D and⁷Be(p, )⁸B in the sun, we show that CME help to solve the solar neutrino problem.