Heavy-ion Reaction Studies Research Articles

A kinematic coincidence technique for the study of low-energy heavy-ion reactions

A setup for kinematic coincidences has been developed for the study of low-energy binary heavy-ion reactions. It consists of a position-sensitive silicon detector, and a counter telescope with microchannel plates detectors and a conventional ΔE- E ionization chamber. The solid angle is around 0.6 msr. By measuring the time of flight of one of the ions, and both correlated scattering angles, we achieve mass and Q-value resolutions of ΔA/A⋍ 1 120 FWHM and ΔQ ⋍ 900 keV , respectively, for the elastic scatteri 58Ni + 64Ni near the barrier.

Energy dependence of the nuclear level density at energies above 100 MeV

Level densities are calculated for the nucleus $^{40}\mathrm{Ca}$ using an exact iterative method for noninteracting fermions. Various single-particle energies are tested. It is found that the conventional Fermi-gas energy dependence provides a good representation of the actual level density only up to energies about 100 MeV. Above this point, the deviations rapidly grow, reaching many orders of magnitude at energies above 200 MeV. One calculation has also been made for $^{90}\mathrm{Zr}$. These results are similar, with the point of breakdown of the Fermi-gas form raised to about 200 MeV. The present results should have significant consequences for heavy-ion reaction studies of equilibration and for astrophysics.

Self-calibrating position-sensitive silicon detectors

Position-sensitive silicon detectors with discrete position output signal levels, which have been developed for heavy ion reaction studies at the Lawrence Berkeley Laboratory are discussed. The detectors, both 300- and 5000- mu m thick, for use in Delta E-E telescopes, use a series of high and low conductivity strips on the detector p/sup +/ contact to produce a position signal with 15 discrete levels. Since the position of the signals from the strips is known, the detectors are self-calibrating against position nonlinearities. Some aspects of the fabrication of both the 300- and 5000- mu m detectors are discussed, along with their operating characteristics. Illustrative experimental results of /sup 139/La-induced reactions on /sup 40/Ca targets are presented. >

Performance of the heavy-ion magnetic spectrograph “ENMA” on the kinematic correction

A magnetic spectrograph, named ENMA, has been successfully put into operation for heavy-ion reaction studies at the JAERI tandem accelerator. The spectrograph consists of two dipoles, a quadrupole and three multipoles arranged in the form of Q-M1-D1-M2-D2-M3. The kinematic broadening has been well compensated for over the kinematic parameter range from k = 0.4 to 1.15 mainly with a quadrupole field produced by the multipole magnet M2. The energy resolution obtained as a function of the kinematic parameter k is consistent with the value estimated from the contributions due to the target effects, the beam emittance and the intrinsic energy resolution of the spectrograph.

A broad-range detector system with large geometric efficiency for heavy-ion reaction studies

A detector module sensitive to heavy ions, capable of covering a very large solid angle, and having a broad dynamic range in energy and atomic number has been designed and tested. It is tapered, has a pentagonal cross section and has been constructed to permit close-packing in a spherical array with a minimum of inactive area. The detector consists of a radial-field drift chamber for Bragg-curve spectroscopy, followed by a thin fast-plastic scintillator laminated to a thick slow-plastic scintillator for light-ion detection; the two scintillators are read together in phoswich ΔE — E mode. Mixed-mode operation is also possible, with the drift chamber serving as a ΔE counter and the fast plastic scintillator providing an energy signal. Tests with a beam of 145 MeV 28Si ions have shown that for 83% geometric efficiency (active/total solid angle) the Bragg curve spectrometer gives ΔZZ ⋍ 5% at Z = 12 and ΔEE ⋍ 6% for silicon ions depositing 100 MeV in the detector. Mixed mode operation has 70% geometric efficiency with a measured ΔZZ ⋍ 5% for Z = 8. Phoswich mode operation also has 70% geometric efficiency and gives ΔZZ ⋍ 6% for Z = 2; isotopic identification of light ions is unambiguous.

Application of radioanalytical techniques in the study of the products of heavy-ion reactions

The use of heavy ions to induce nuclear reactions was reported as early as 1950. Since then it has been one of the most active areas of nuclear research. Intense beams of ions as heavy as uranium with energies high enough to overcome the Coulomb barriers of even the heaviest elements are available. The large variety of possible reactions gives rise to a multitude of products, which have been studied by many chemical and physical techniques. Chemical techniques have been of special value for the separation and unequivocal identification of low-yield species from the plethora of other nuclides present. Heavy-ion reactions have been essential for the production of the transmendelevium elements and a host of new isotopes. The systematics of compound nucleus reactions, transfer reactions and deeply inelastic reactions have been elucidated using chemical techniques. The variety of chemical procedures and techniques which have been developed for the study of heavy-ion reactions and their products has been examined. The determination of the chemical properties of the transmendelevium elements, which are very short-lived and can only be produced an “atom at a time” via heavy-ion reactions, is discussed.

Tests of a magnetic emulsion spectrometer by high energy heavy ions

A good momentum resolution (approximately 12% for a 2 GeV/ e pion beam) has been successfully obtained at KEK using a magnetic emulsion spectrometer (MES) developed by the authors. An investigation on the usefulness of the MES in the study of intermediate heavy ion reactions (0.8 GeV/ c per nucleon nitrogen ions on a tungsten nucleus) has been conducted at Saclay, and the results are reported in this paper.

A study of heavy-ion reactions in the algebraic scattering theory

Applications of algebraic scattering theory (AST) to heavy-ion collisions are presented. It is shown that the algebraic approach provides a simple and yet detailed description of complex coupled channel problems.

Heavy-ion reaction studies of 35,36P

The spectroscopy of the T z⩾ 3 2 nuclei 35P and 36P has been studied using a variety of multi-nucleon heavy-ion transfer reactions. This has led to the observation of a number of new levels in both nuclei. The probable structure of these and previously reported levels are deduced through comparison with DWBA and shell-model calculations.

Nuclear structure information derived from the study of heavy ion reactions using SSNTD

Abstract The use of SSNTD for the study of heavy ion reactions has opened a new vista for nuclear physics. The most interesting aspects of this method are its off-line nature and the possibility of exclusive measurements. Although the accuracies of measurements are limited, however a reliable estimation of the kinematically relevant quantities can be made by using the statistically significant number of individual events observed directly. It is shown that the nuclear structure information can also be extracted from the data. Particularly, the elastic scattering process and its analysis leading to nuclear size information has been discussed. The measurements of the ‘out-of-plane’ angles of fission fragments and the derivation of pre-fission nuclear spins and excitation energies is also elucidated.

Peripheral Like Interaction Model of Spectator Residue with Central Fireball in High Energy Heavy Ion Collisions

The experimental data of differential cross sections of 80 productions in P+ Au, He+ Au and Ne + Au collisions at high energies are analyzed in terms of the peripheral like interaction model of spectator residue with central fireball. The results show that the interaction between the central fireball and the spectator residue gradually becomes peripheral or diffractive as the projectile energy increases. The study of high energy heavy ion reactions has been pursued for both peripher­ al and central collisions of projectile and target. In central collision there are two parts 1H ) of the interaction region, in one of which the overlapping part of the projectile and the target becomes hot and thermalized at a high temperature (called the central fireball) and subsequently decays by emitting fast nucleons and possibly light fragments. The non-overlapping region (called the spectator residue) being formed simultaneously along with the formation of the central fireball remains cold and promptly decays into relatively large and slow fragments. 3 ),4) In this paper we study the nature of the interaction between the central fireball and the spectator residue and also the fragmentation mechanisms of the spectator residue based on a nova mode1. 5

SOLUTIONS OF THE LANDAU-VLASOV EQUATION IN NUCLEAR PHYSICS

The properties of Vlasov equation solutions obtained by projection on coherent state basis are discussed. Such solutions satisfy stationarity conditions and satisfactorily describe the average diffusivity of nuclear phase space and reproduce the bulk properties of nuclei. Sampling methods and their effects on dynamics are discussed for the study of heavy ion reactions at intermediate energies. The non-local Gogny force is easily computable on this basis which allows to use it for dynamical nuclear studies.

The application of a multiple gas counter spectrometer to the study of heavy ion reactions

A large solid angle particle spectrometer, consisting of two avalanche counters separated by an ionisation counter in the same gas volume, has been calibrated using elastic scattering of 58Ni from 208Pb. The spectrometer has been applied to a study of inelastic scattering and transfer reactions following the bombardment of 163Dy with 280–304 MeV 58Ni ions, in which gamma rays observed simultaneously in a GeNaI spectrometer have been classified in terms of the Z and angular distribution of the scattered projectile, and the Q of the reaction.

A compact gridless channel plate detector for time-of-flight measurements

A compact channel plate detector used as a start detector in heavy ion reaction studies is described. In order to avoid spurious structures in the energy spectra of the detected ions the usual electron accelerating grid is replaced by five electrodes which provide a uniform electric field. The start detector has an intrinsic resolution of 85 ps and efficiency of 90% for medium mass nuclei. The overall time resolution with a solid state detector as stop is 105 ps.

An energy resolving scintillator telescope for multiparticle detection of light charged particles

A modular plastic scintillator telescope was developed which can be used in vacuum to investigate light charged particle production in heavy ion reaction studies at a time-focused accelerator beam. Light signals from NE 111A plastic scintillators are amplified by photomultiplier tubes (RCA 4516). Remarkable features of the plastic scintillator telescope are: good time resolution (127 ps for 20 MeV α-particles), high counting rate stability ( f = 125 kHz). Particle energies derived from time-of-flight measurements (resolution typically 4%) show good reproducibility and are easy to calibrate. Pulse heights are used for particle identification only. Experience in recent accelerator experiments (using 11 modules) is reported on.

Transition-State Theory for Fission Angular Distributions: A Flexible-Rotor Model

Current studies of heavy-ion reactions make extensive use of fission-fragment angular distributions to prove the limits of statistical equilibrium. The "standard" theory was derived for a rigid-rotor, transition-state nucleus. Here a more complete theory is developed by inclusion of the dependence of transition-state shape on orientation of the symmetry axis. It is concluded that even this improved application of the liquid-drop model cannot give an adequate prediction of the $\frac{{Z}^{2}}{A}$ dependence of fission-fragment anisotropies.

Magnetic field measurement of the Jaeri heavy-ion spectrograph “ENMA”

A new magnetic spectrograph, named ENMA, for heavy-ion reaction studies was constructed. Magnetic field measurements for two dipoles, one quadrupole and three multipoles, of which the spectrograph consisted in the QMDMDM form, were performed. Almost perfect field distributions were obtained over a full range of the field strength in accordance with the two-dimensional calculation by the programs TRIM and LINDA. The fringing field distribution and the location of the effective field boundaries of the dipole magnets were quite stable against a change of the excitation current. The multipole magnets of the current sheet type were successfully constructed. The field strength of the quadrupole component of the multipole magnet M2 was enough for making the kinematic correction from k = −0.7 to 2.0.

Neutron Multiplicity Distributions and the Role of Transfer and Breakup in Quasielastic Heavy-Ion Reactions at 15 MeV/Nucleon

A new tool for the study of heavy-ion reactions is obtained by adapting a $4\ensuremath{\pi}$-neutron-multiplicity counter to accelerator experiments. The instrument registers almost all neutrons emitted in each single reaction event. For quasielastic reactions of 290-MeV $^{20}\mathrm{Ne}$+$^{197}\mathrm{Au}$ the measured neutron multiplicity distributions allow a quantitative decompsotion of the cross section into two contributions: one with higher $Q$ value from transfer reactions, one with lower $Q$ value due to the decay of the decay of the projectilelike fragments.

High mass resolution in reactions induced by medium-heavy ions ( A

The study of heavy-ion reactions requires the measurement of the kinetic energy, nuclear charge, and mass of the reaction products over a wide range. For medium-heavy ions ( A<60) the energy and the charge number can be measured by surface barrier detectors ( E− ΔE) telescope) with appropriate accuracy. The mass is usually derived from a time-of-flight measurement. An attractive method to determine the time of flight and consequently the mass with good resolution is the use of very-short heavy-ion pulses (start signal) together with a fast signal derived from a surface barrier detector (stop signal). The production of such short pulses with a pulsing-rebuncher system is described. The time resolution of the system installed at Heidelberg which is routinely obtained is about 70 ps. This allows for mass resolutions of ΔA/ A⩽1% for A≲60 and a flight path of 30 cm. The conditions for fast timing with surface barrier detectors are discussed. Finally an example of an application of the method for the reaction 32S+ 27Al is presented.

A multi-angle detector for heavy ion reaction studies

A gas-filled detector, using gas ΔE and surface-barrier residual energy determination for ion identification capable of simultaneous measurement at 8 discrete angles, is described. Examples of reaction studies, including fission, fusion and transfer reactions, illustrate the characteristics of the detector.