Interaction of relativistic alpha particles in emulsion at 2.1 GeV/c/nucleon

An analysis for 2,000 events produced by 2.1 GeV/c/n alpha particles in nuclear emulsion has been carried out. Multiplicity and angular distributions of charged secondaries have been measured and correlation among them are discussed. The presented data are compared with relevant values from proton and¹⁴N interactions with nuclei. The multiplicity distribution of showers has been tested by a modified independent nucleon-nucleus multiple scattering model (INAM) of reference [8], and by the model of reference [12].     

Collinear ternary cluster decay of hyperdeformed <Superscript>60</Superscript>Zn at high angular momentum

Binary and ternary cluster decay of ⁶⁰Zn compound nuclei at high angular momentum, formed in the ³⁶Ar + ²⁴Mg reaction at E _lab(³⁶Ar) = 195 MeV, has been measured in a unique kinematic coincidence setup consisting of two large area position sensitive (x, y) gas detector telescopes with Bragg-ionization chambers (BRS). The BRS provides the opportunity to measure the reaction angles in-and out-of-plane, and through Bragg-curve spectroscopy to achieve a complete identification of the nuclear charge for different final channels. We observed very narrow out-of-plane angular correlations for two heavy fragments emitted either in purely binary events or in events with a missing mass consisting of 2 and 3α particles. These narrow correlations are interpreted as ternary fission decay from compound nuclei at high angular momenta through an elongated (hyperdeformed) shape with a very large moment of inertia. In these stretched configurations, the lighter mass in the neck region remains at rest or with very low momentum in the center of mass. The text was submitted by the authors in English.     

Proton polarization in the14N(3He,p)16O reaction near 10 MeV and reaction mechanisms

The angular distribution of the proton polarization has been measured between 30° and 110° in the CM system near 10 MeV laboratory energy. It provides a sensitive test of theoretical fits to the cross section angular distribution. The reaction mechanism is largely direct below 70° and evidence has been found for a deuteron-cluster transfer. Nuclear Reactions¹⁴N³(He,p),E=9.8 MeV; measuredP(E,θ), σ(E,θ); DWBA and deuteron transfer analysis; deduced dominant mechanism of forward angle amplitudes.     

Understanding the anomalous fragment anisotropies in heavyion induced fission in the dynamical trajectory model

Dynamical trajectory model has been used to calculate the fusion and non-fusion trajectories in ¹⁰ B, ¹² C, ¹⁶ O, ¹⁹ F +²³² Th, ²³⁷ Np reactions. It is seen that in some of the above systems, there exists an l-window (above fusion l-value) for which the trajectories are characterised by large mass exchange and energy relaxation (fission-like) before the system undergoes symmetric split, without formation of a shape equilibrated compound nucleus. These events would correspond to a small value of the variance of the K-distribution, thereby leading to large fragment angular anisotropies. The fission fragment angular distributions, calculated as an admixture of these two classes of events (fusion and non-fusion), are able to explain the anomalous angular anisotropies observed experimentally for some systems at the above barrier energies.     

Fission and ternary cluster decay of hyper-deformed 56Ni

Coincidences between two heavy fragments have been measured from the fission of ⁵⁶Ni compound nuclei formed in the ³²S + ²⁴Mg reaction at E _lab( ^32S ) = 165.4 MeV. A unique experimental set-up consisting of two large-area position-sensitive (x, y) gas detector telescopes has been used allowing the complete determination of the observed fragments and their momentum vectors. In addition to binary fission events with subsequent particle evaporation, narrow out-of-plane correlations are observed for two fragments emitted in purely binary events and in events with a missing charge consisting of 2α - and 3α -particles (¹²C). These events are interpreted as ternary cluster decay from ⁵⁶Ni nuclei at high angular momenta through hyper-deformed shapes.     

12C + 7Li Reaction measurements and the 12C(7Li,t)16O reaction

A measurement of the residues from the ¹²C + ⁷Li reaction has been obtained for ⁷Li energies from 10 to 38 MeV. From these measurements the fusion cross sections and critical angular momenta for the ¹²C + ⁷Li system have been deduced. Cross sections for the ⁷Li(¹²C, t)¹⁶O reaction have been obtained for ¹²C energies from 54 to 62 MeV at θ_lab = 2.7°. The critical angular momenta obtained from the fusion cross sections have been used to perform Hauser-Feshbach calculations for the ¹²C(⁷Li, t)¹⁶O reaction. These calculations have been compared to measured angular distributions over a wide energy range. By comparing the fusion cross sections required by the Hauser-Feshbach calculations to fit the ¹²C(⁷Li, t)¹⁶O(8.87 MeV) reaction and the measured residue cross section it is estimated that at least 80 % of the measured residues are fusion products. The calculations also indicate that direct processes dominate the population of many ¹⁶O levels at forward angles and the 10.35 MeV state at backward angles. The necessity for using a critical angular momentum in Hauser-Feshbach calculations is discussed.     

Positive pion production at threshold on A 10B target

The angular distribution of low-energy positive pions (E_π ≈ 11 MeV) produced by 154 MeV protons on a ¹⁰B target has been measured between 16.2° and 54.8° c.m. angles. Only pions corresponding to the ground state of ¹¹B were observed. The data have been compared with theoretical angular distributions calculated in the framework of the one-nucleon mechanism using the DWBA formalism.     

Direct and compound nuclear contributions to the 13C(6Li,t) reaction at Elab = 25 MeV

The reaction ¹³C(⁶Li, t)¹⁶O has been studied in the incident energy range 24–26 MeV. Complete angular distributions have been measured at E_⁶Li, = 25 MeV in the angular range θ_lab = 8°–172°, with the reaction ⁶Li(¹³C, t)⁶O being used for the backward angle measurements. Cross sections for evaporation residues from the fusion of the ⁶Li + ¹³C system have been measured in the incident ⁶Li energy range 9.2–35.1 MeV. Compound nuclear contributions to the transfer cross sections have been calculated using the Hauser-Feshbach statistical theory with the assumption that the compound-nucleus formation cross section is equal to the measured fusion cross section. By comparison of the compound nuclear calculations with backward angle data it is found that the sharp cutoff approximation commonly used to represent the initial angular momentum distribution of the compound nucleus is not adequate for the ¹³C(⁶Li, t)¹⁶O reaction. Good fits to the backward angle data can be obtained by using a smooth cutoff approximation. The forward angle cross sections have been compared with exact finite-range distorted-wave Born approximation calculations to extract transferred angular momenta and spectroscopic strengths. The present results differ from those of an earlier study. These differences are due to the inclusion of forward angle data in the present study.     

Proton-hole states in 115In observed in the 116Sn(d, 3He) reaction

The ¹¹⁶Sn(d, ³He)¹¹⁵In reaction has been investigated at E_d = 50 MeV. Thirteen transitions to states up to 3 MeV excitation energy were studied. The measured angular distributions were compared with DWBA calculations and transferred angular momenta and spectroscopic factors were deduced. Levels at 1.04, 2.23 and 2.52 MeV were found to be excited most likely by l = 3 angular momentum transfer in contrast to previous investigations at lower incident energies in which no l = 3 transitions have been observed.     

Two- and three-point energy correlations in Hadronice + e − annihilation

Correlations between the energies incident on two or three detectors arounde ⁺ e ^? annihilation events are considered as a probe of the QCD structure of the events. Practical methods for deducing two-detector energy correlations (which give the mean product of energies incident on two detectors as a function of their angular separation) from measured events are devised. Analytical formulae for energy correlations from QCD perturbation theory are given, but it is found that large corrections from hadron formation obscure these symptotic predictions at available energies. Correlations between the final state and the incominge ^± beam direction are discussed, and observables are presented which measure the angular distributions of planes of final particles with respect to the beam axis (but do not require explicit determination of the planes). Finally, three-detector energy correlatons and their moments are treated, and methods for investigating planar structures ine ⁺ e ^? annihilation events are devised.     

Direct α particle emission in incomplete fusion reaction on a spherical target124Sn

Direct α particles cross sections and angular distributions have been measured when bombarding a¹²⁴Sn target with various projectiles:¹⁶O (90, 105, 125 MeV)¹⁹F (104 MeV)²⁰Ne (112, 156 MeV). Results have been found independant of the projectile structure. In the same reactions, gamma multiplicity measurements have shown that direct α particles are emitted in collisions with intermediate impact parameters. The angular momentum is found to be about half of the valuel _cr for complete fusion.     

The study of the (α, α'f) reaction at 120 MeV on 232Th and 238U: (I). Fission probabilities and angular distributions in the region of the giant quadrupole resonances

The fission decay channel of ²³²Th and ²³⁸U has been investigated, using the (α, α'f) reaction at 120 MeV bombarding energy. The angular distributions of the fission fragments and the fission probabilities up to around 15 MeV excitation have been measured. No evidence for the fission decay of the giant quadrupole resonance has been found, although for ²³⁸U, a weakly excited structure is seen in the (α, α'f) spectrum at about 9.5 MeV excitation at backward angles with respect to the recoil axis. This effect is similar to what has been found in a (⁶Li, ⁶Li'f) experiment reported recently. The over-all feature of the fission probability for excitation energies above the fission barrier are well reproduced by statistical calculations.     

Alpha-heavy-ion angular correlations from 28Si + 12C

Alpha particles have been measured in coincidence with heavy recoil nuclei from the ²⁸Si + ¹²C reaction. At E_lab = 87 MeV angular correlations for alphas between 15° and 55° and heavy ions at angles ?9°, ?12° and ?15° have been taken. An excitation function of coincidence events with θ_α = 30° and θ_HI = ?12° has been measured for 84 MeV < E_lab < 91.5 MeV. The results are well described by a statistical-model calculation for compound nucleus decay. No evidence is found for additional processes.     

High-spin states in154Er

High-spin states in¹⁵⁴Er have been populated by bombarding¹⁴⁷Sm and¹⁴⁸Sm with¹²C particles. Excitation functions, lifetimes, angular distributions andγ-γ coincidences were measured. AT _1/2=35ns isomeric state atE _x～3 MeV has been found and is interpreted as a two-quasi-particle state with aligned angular momenta. A cascade of intense individual lines from states with spin up to at least 26 (excitation energy up to 8.543 MeV) was found to feed the isomeric state. The level sequence above this yrast trap exhibits an irregular pattern which cannot be easily interpreted in terms of collective modes.     

Incomplete deep-inelastic scattering in20Ne+197Au collisions at 20 MeV/nucleon

Correlations between emission angles and energies of coincidentα-particle projectile-fragment pairs have been measured for the²⁰Ne+¹⁹⁷Au system at 390 MeV beam energy. Theα-particles observed close to the direction of the projectile-like fragment were found to result essentially from sequential projectile decay. Starting from the close-geometry data, the contribution of sequentially emittedα-particles was calculated by Monte Carlo simulations for the entire angular range. For deep inelastic events, the measured angular correlations exhibit a spectacular excess over the calculated correlation. This excess is centred close to the beam direction but on the opposite side of it with respect to the detected projectile-like fragment. The correspondingα-particles have velocities around 85% of the projectile velocity indicating emission in an early reaction phase.     

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.     

Multiparticle production of doubly charged fragments in the fragmentation of relativistic nuclei

Features of angular distributions of events involving two or more doubly charged fragments of relativistic nuclei ²²Ne, ²⁴Mg, ¹⁴N, ¹¹B, and ¹⁰B in photoemulsions are studied. It is found that, in all cases, with the exception of the case of the intermediate-state decay ⁸Be → 2α, the fragments in these events are independent of one another. The inclusive angular distributions of fragments of relativistic nuclei ²²Ne for events in which the number of particles ranges between one and five are identical. Thus, the emission angle of each fragment of a relativistic nucleus does not depend either on other fragments or on the presence or absence of product particles and target-nucleus fragments in an event.     

The (d, α) reaction viewed as a two-step process

The ^{98, 97, 94}Mo(d, α)^{96, 95, 92}Nb and ⁹³Nb(d, α)⁹¹Zr reactions have been studied at 12 MeV bombarding energy. A DWBA analysis using one- and two-step processes has been carried out. The two-step process is found, in general, to dominate the one-step and together give rise to cross-section predictions within a factor of 10 of experiment. The angular distribution patterns are found to be best reproduced by DWBA predictions based on certain L-transfers (“parity violating”) associated with only the two-step process and which play but a minor role in their contribution to the overall cross section.     

The compensation of the noise due to angular oscillations of the laser beam in the Precision Laser Inclinometer

An experimental method for the compensation of the noise originated by the laser ray angular oscillations was proposed and experimentally proved for the Precision Laser Inclinometer (PLI). The PLI noise spectral density was reduced by factor 30× and reached 10^–8 rad/Hz^1/2 level at the frequency of 5 × 10^–5 Hz. The angular noise of a laser ray leaving the one-mode optical fiber in the vacuum and in stabilized temperature conditions has been measured. The amplitude of the oscillations for one-day observation reached 0.46 μrad.     

Investigation of 91Zr by high resolution (d,p), (p,p′) and (p,d) reactions

Energy spectra and angular distributions of light particles (Z = 3–8) produced in the reactions ¹³C+^{58, 60, 64}Ni have been measured at 105 MeV. Coincidence events between light outgoing particles Li, Be, B and α, p have been observed for the first time in the ¹³C+⁵⁸Ni and ¹³C+⁶⁴Ni reactions. The results show that at least part of the ‘deep-inelastic’ events are due to many-particle reactions.