Angular correlations in ternary fission induced by polarized neutrons

Ternary fission induced by cold polarized neutrons was studied for the two isotopes ²³³U and ²³⁵U at the Institut Laue-Langevin in Grenoble, France. In particular two types of angular correlations between the spin of the incoming neutrons and the emission directions of both, the fission fragments (FF) and the ternary particles (TP), were investigated. For FF and TP detectors facing the target at right angles to the neutron beam, first, for longitudinally polarized neutrons a triple correlation between spin and the emission of outgoing particles was explored and, second, for transversally polarized neutrons parity violating asymmetries in the emission of FFs and TPs were analyzed. Nonzero expectation values for the triple correlation were oberserved in the present experiments for the first time.     

Angular momentum bearing modes and nuclear structure effects in12C-induced fission

The angular momenta of the fragments produced in several 100 and 180 MeV¹²C induced fission reactions have been investigated usingγ-ray multiplicity (M _λ) techniques. The averageM _λ increases with both the bombarding energy and the total mass of the system. The dependence ofM _λ on mass asymmetry is generally rather weak, except in regions near shell closures, where local minima are observed. The magnitudes ofM _λ tend to be larger than expected on the basis of rigid rotation, possibly due to the excitation of collective modes. A comparison is made with a statistical model.     

Angular distribution in ternary fission

The angular distribution of long-range alpha particles emitted in keV-neutron induced fission of²³⁵U has been measured using a technique which employs only a particle telescope to derive the angular information. The neutron energy region investigated is 100 keV-1 MeV. The angular distribution oflras has been found to be peaked perpendicular to the neutron-direction with a substantial amount of anisotropy near 200 keV.     

Angular correlations in pair creation

We present the Monte Carlo analysis of angular correlations in electron-positron pair production by the laser field-heavy ions impact process. It is shown that, for linearly polarized laser fields, pairs are created mainly in the plane spanned by the polarization vector and the laser photon momentum, and that the angular distribution of created electrons and positrons is anticorrelated.     

Angular distribution in ternary cold fission

We describe the spontaneous ternary cold fission of ²⁵²Cf, accompanied by ⁴He, ¹⁰Be and ¹⁴C. The light cluster decays from the first resonant eigenstate in the Coulomb potential plus a harmonic oscillator potential. We have shown that the angular distribution of the emitted light particle is strongly connected with its deformation and the equatorial distance.     

Angular momentum of fission fragments

We continue the discussion on the respective roles of individual and collective motion in the angular momentum distribution in fission fragments. As in our prior publications on the subject, the role of individual nucleon motion in fragments in the postscission configuration is underlined, and the central part in the discussion concerns phenomena observed in the spontaneous fission of even-even nuclei. A formalism is prepared to study the spin distribution of fragments in induced fission from high-spin states.     

Angular momenta of fission fragments in the α-accompanied fission of 252Cf

For the first time, average angular momenta of the ternary fission fragments ^{100, 102}Zr, ¹⁰⁶Mo, ^{144, 146}Ba and ^{138, 140, 142}Xe from the α-accompanied fission of ²⁵²Cf were obtained from relative intensities of prompt γ-ray transitions with the use of the statistical model calculation. Average values of the angular momenta were compared with the corresponding values for the same fission fragments from the binary fission of ²⁵²Cf. Results indicate the presence of a decreasing trend in the average values of angular momenta induced in ternary fission fragments compared to the same binary fission fragments. On the average, the total angular momentum extracted for ternary fission fragments is ∼1.4 ℏ lower than in binary fission. Consequently, results indicate that the mechanism of the ternary α-particles emission may directly effect an induction of angular momenta of fission fragments, and possible scenarios of such mechanisms are discussed. Further, the dependence of the angular momenta of ¹⁰⁶Mo and ¹⁴⁰Xe on the number of emitted neutrons from correlated pairs of primary fragments was obtained also showing a decreasing dependence of average angular momenta with increasing number of emitted neutrons. Consequences are briefly discussed.     

Angular correlations and the tau-neutrino mass

Effects of a nonzero mass for the tau neutrinov _τ as well as a right-handed charged-current contribution to the τ?v _τ coupling are discussed. Angular correlations of the decay products of τ⁺τ^? ine ⁺ e ^? annihilation are calculated as functions of \(m_{v_\tau } \) and the relative amount of right-handed τ?v _τ coupling.     

Interference effects in nuclear fission

Various interference effects governing the character of angular distributions of binary and ternary nuclear fission products and P-odd, P-even, and T-odd asymmetries in these angular distributions have been studied within the quantum theory of spontaneous and low-energy induced nuclear fission.     

Energy partition in nuclear fission

A scission point model (two spheroid model TSM) including semi-empirical, temperature-dependent shell correction energies for deformed fragments at scission is presented. It has been used to describe the mass-asymmetry-dependent partition of the total energy release on both fragments from spontaneous and induced fission. Characteristic trends of experimental fragment energy and neutron multiplicity data as function of incidence energy in the Th — Cf region of fissioning nuclei are well reproduced. Based on model applications, information on the energy dissipated during the descent from second saddle of fission barrier to scission point have been deduced.     

Angular uncertainty of momentum correlations in parametric fluorescence

Uncertainty in determining the emission angles of the signal and idler photons is investigated. The role of the pump beam divergence, the pump-spectrum width, and the crystal size is elucidated. Experimental data obtained using an intensified CCD camera are in good agreement with a numerical model that provides angular and spectral characteristics of the signal and idler fields.     

Angular correlations in peripheral fragmentation of halo nuclei

The angular correlation between momenta of ⁵He and its decay products has been calculated for the peripheral fragmentation of ⁶He using a two-step model in a sudden approximation: (1) One neutron knock-out leading to the unbound nucleus ⁵He. (2) Subsequent decay of ⁵He undisturbed by the target in an α-particle and a neutron. Angular correlations measured in a recent experiment dealing with the peripheral fragmentation of 240 MeV/u ⁶He on a carbon target can be well described by a dominant ⁵He 3/2^? ground state configuration plus a small admixture of ≈ 7% of the first excited 1/2^? state. The influence of an s-state admixture as well as a contribution of the momentum transfer to the correlation function are investigated. The results obtained for ⁶He are then used as a touch stone for a discussion of the methods to investigate peripheral fragmentation of other Borromean halo nuclei like ¹¹Li and ¹⁴Be. It is shown that the evidence on the possible existence of low-lying s-states in ¹⁰Li and ¹³Be can be derived from the corresponding angular correlations.     

Angular and spin distributions of primary fission fragments

It is demonstrated that the formation of the fissile nucleus prescission configuration with two fission prefragments connected by a neck is possible only with the simultaneous appearance of high values of relative orbital moments [(L)\vec]\vec L of the abovementioned prefragments, independently of their form. It is found that conservation of the fissile nucleus spin when its values are low leads to the formation of high values of prefragment spins [(J)\vec]₁\vec J_1, [(J)\vec]₂\vec J_2 that are oriented antiparallel to the moment [(L)\vec]\vec L and perpendicular to the fissile nucleus symmetry axis. It is shown that for two deformed fission prefragments, the pumping mechanism of high values of their relative moments [(L)\vec]\vec L and spins [(J)\vec]₁\vec J_1, [(J)\vec]₂\vec J_2 is due to the combined influence of bending- and wriggling- vibrations, the latter predominating. It is found that the high values of spherical fission prefragments are not related to thermal excitations but is determined by the excitation of the initial high-spin double quasiparticle states, due to the nonadiabatic collective deformation motion of the fissile nucleus in the vicinity of its rupture point.     

Angular correlations for semileptonic D meson decays

We study the exclusive semileptonicD meson decaysD→K+π+l+ν. For this we develop the general formalism for the joint angular distribution of the charged lepton and theK meson and calculate the helicity dependent decay widths which determine the full angular distribution for several models withK ^*(892) andK ₀ ^* (1430) intermediate state with nonresonant background terms calculated from chiral Lagrangians.