3He break-up and quasi-free7Li(p, α)4He reaction at low energies

Using the reactions³⁵Cl(¹³⁰Ba;4,5n) and³⁶Ar(¹³³Cs;6,7n), the half-lives of^160,161Ta were measured to be 1.2(3) and 2.7(2) s, respectively, and theα-lines observed at 4.88(1) and 4.63(1) MeV were assigned to¹⁶²Ta and¹⁶³Ta, respectively. Theα-decay branch of¹⁶²Ta was determined to be 0.065(14)%.     

Measurement of the breakup channels in nuclear muon capture by3He and4He

The rates of the breakup reactions _B(³He) and _B(⁴He) in nuclear muon capture by³He and⁴He have been measured. The measurements were performed on the muon beam of PSI with a multi-anode high-pressure ionization chamber filled with isotopically pure³He or⁴He at 120 bar. The chamber was used as a target and detector for both the incoming muons and for the charged reaction products (tritons, deuterons and protons) of the breakup reactions _B(³He) and _B(⁴He). Our statistics, about 5 × 10⁵ of breakup events, provides a possibility to improve the precision of evaluated rates. The preliminary results: _B(³He)=720 ± 70 s^–1, _B(⁴He)=415 ± 40 s^–1 are compared to theoretical predictions and to previous experiments.     

Studying of the neutron halo structure in quasi-free proton scattering from 6He Halo nucleus

An experimental method based on an analysis of the neutron-neutron correlations in reactions induced by halo nuclei in nuclear photoemulsion is proposed for studying the two-neutron halo structure. Photoemulsion stacks were exposed to a beam of radioactive ⁶He nuclei. Preliminary data on interaction of the ⁶He halo nucleus to hydrogen are compared with the results of the kinematic calculation for the reaction of quasi-free proton scattering from clusters making up the ⁶He halo nucleus. A fraction of quasi-free scattering events with “survival” of the dineutron is evaluated for scattering of protons by the dineutron configuration of the ⁶He nucleus.     

Open quasi-free systems

We compute the time evolution of an infinitely extended, open, quasi-free system in the weak coupling limit followed by the thermodynamic limit, and we derive the Onsager relations and the properties of entropy production.On leave of absence from Istituto di Fisica dell'Università, Milan, Italy     

Final-state interactions and quasi-free mechanism in the3He(d,3Hp)p reaction

A measurement of absolute differential cross sections of the³He(d,³Hp)p reaction atE _d=23.083 MeV shows the importance of the quasi-free reaction (QFR) mechanism. The observation of a prominent QFR peak indicates that complicated multiple-scattering processes may not be so important as to prevent a simple phenomenological analysis based on two-body interactions. In this respect we isolate final-state-interaction (FSI) effects related toS andP wave³H-p interactions. In particular, the FSI, associated with the⁴He level at 25.5 MeV of excitation energy, plays a dominant role.     

Halo-nucleus structure obtained from quasi-free scattering

An experimental investigation of drip-line nuclei by using quasi-free knockout is discussed. The reaction formalism reformulated in terms of Mandelstam variables allows extraction of valuable information from measurements with radioactive beams made in inverse kinematics.     

Effective polarization in quasi-free scattering

A simple relation, involving only experimental quantities, for the effective polarizations in quasi-free (p, 2p) scattering on closed shell nuclei is tested for recent TRIUMF (p, 2p) experiments with 200 MeV polarized protons.     

Nucleon-nucleon interaction and meson exchange current effects in3He two-body breakup by polarized photons

Cross sections for the reaction³He(γ, p)d have been calculated with the Faddeev wave functions of the³He nucleus. The parametrized forms of the functions have been used for two different types ofNN interaction, viz., the separable Mongan potential (MP) and the Reid soft-core (RSC) potential. Contributions of meson exchange currents (MEC) to this process have been considered. Constraints imposed by the continuity equation for the nuclear current are discussed. The calculated results are compared with new data obtained recently at Kharkov.     

Coulomb effects in quasi-free scattering

Using the exact three-body scattering theory for Coulomb-like potentials a new result for the quasi-free breakup amplitude is obtained. It consists in adding an easily calculable factor to the existing expression for the modulus of the quasi-free breakup amplitude. The importance of this factor is discussed by illustrative examples for the breakup reactions.     

Non-factor quasi-free states of the CAR-algebra

A necessary and sufficient condition is given in order that a quasi-free state on the Clifford algebraA(H,s) build on a real separable Hilbert (H, s) be a factor state.On leave of absence of Université d'Aix-Marseille, Fac. Sc. St. Charles, Marseille 3^e (France).     

Completely positive quasi-free maps of the CCR-algebra

The class of completely positive (CP) quasi-free maps on the CCR-algebra is studied. We characterize the pure maps, study invariant states under semigroups, construct a particular dilation and consider the problem of implementation.     

Transfer, breakup, and fusion reactions of 6He with 209Bi near the Coulomb barrier

The fusion of ⁶He with a ²⁰⁹Bi target displays a large enhancement at energies near to and below the Coulomb barrier. Recently, a ⁴He group of remarkable intensity, which dominates the total reaction cross-section, has also been observed in the near-barrier interaction of the same system. It is argued that this transfer/breakup channel acts as a doorway state to fusion. Received: 1 May 2001 / Accepted: 4 December 2001     

On the product form of quasi-free states

The product form of quasi-free states is outlined, and the types of the generated factors are exhibited whenever the states are translation invariant. Among these states some are shown to be involved in the study of Fermi and Bose gases.Attaché de recherche au C.N.R.S.     

Microscopic description of diffractive deuteron breakup by <Superscript>3</Superscript>He nuclei

A microscopic formalism for describing observed cross sections for deuteron breakup by threenucleon nuclei was developed on the basis of the diffraction nuclear model. A general formula that describes the amplitude for the reaction ²H(³He, ³Hep)n and which involves only one adjustable parameter was obtained by using expansions of the integrands involved in terms of a Gaussian basis. This formula was used to analyze experimental data on the exclusive cross sections for deuteron breakup by ³He nuclei at the projectile energy of 89.4MeV. The importance of employing, in calculations, a deuteron wave function that has a correct asymptotic behavior at large nucleon–nucleon distances was demonstrated.     

Quasi-equivalence of quasi-free states on the Weyl algebra

A necessary and sufficient condition for quasi-equivalence of quasi-free factor states over the Weyl algebra is proved. The essential part of this paper is closely related to the work of Powers and Størmer on the Clifford algebra.Aspirant van het Belgisch N. F. W. O. On leave from the University of Louvain (Belgium).     

Automorphisms and quasi-free states of the CAR algebra

We study automorphisms of the CAR algebra which map the family of gauge-invariant, quasi-free states of the CAR algebra onto itself and show (Theorem 3.1) that they are one-particle automorphisms.     

y-scaling in quasi-free electron scattering by nuclei

The origin of the so-calledy-dependences ofd ² σ cross sections for the inclusive (e, e′) reaction on nuclei is studied using the properties of the time structure functions that determine the nuclear dynamic form factor. The validity of the approximations leading to two versions of they-scaling is verified in the framework of the single-particle (s.p.) model. A variant of the model-independent analysis (MIA) of the dependences is offered.     

Transfer and/or breakup modes in the 6He+209Bi reaction near the coulomb barrier

Reaction products from the interaction of 6He with 209Bi have been measured at energies near the Coulomb barrier. A 4He group of remarkable intensity, which dominates the total reaction cross section, has been observed. The angular distribution of the group suggests that it results primarily from a direct nuclear process. It is likely that this transfer and/or breakup channel is the doorway state that accounts for the previously observed large sub-barrier fusion enhancement in this system.