M.N. Namboodiri

Light-particle emission in the reactions of 16O with Ti

Abstract Inclusive energy spectra and angular distributions for heavy ions (Z ≧ 3) produced in the reactions of 227 MeV and 310 MeV 16 O with Ti were measured. Also measured at the projectile energy of 310 MeV were energy and angular correlations between light charged particles ( Z ≦ 2) and heavy ions. From comparisons with statistical model calculations upper limits to the complete fusion cross sections of 647 mb and 265 mb were derived for projectile energies of 227 MeV and 310 MeV, respectively. At 310 MeV the cross section of incomplete fusion processes was estimated to be over 505 mb. Emission of fast, high-energy α-particles and protons was observed to be a characteristic feature of quasi-elastic, deep-inelastic and fusion-like reactions. Average multiplicities of fast light particles in coincidence with heavy ions at +20° and +40° were estimated to be of the order of 1. The prompt emission of light appears to be the principal mechanism which limits complete fusion. A second component of α-particles observed in coincidence with deep-inelastic projectile-like fragments and having an energy comparable to Coulomb energies of particles emitted from target-like and projectile-like fragments appears as an excess yield in the direction of the recoiling target-like fragments. This component cannot be accounted for in terms of sequential emission processes and may result from a mechanism other than the one which leads to fast particle emission.

Evidence for large angular momentum induced deformations of 59Cu

Abstract The α -particle spectra observed in coincidence with evaporation residues of 59 Cu nuclei produced in the fusion of 214 MeV 32 S with 27 Al deviate at both high and low particle energies from the spectra calculated for spherical nuclei. The observed differences suggest large angular momentum induced deformations comparable to those predicted by rotating liquid drop model calculations.

The strongly damped collisions of 120 MeV 20Ne with 27Al

Abstract The reactions of 120 MeV 20 Ne with 27 Al have been studied using detector telescopes. Energy distributions and angular distributions of the products of quasielastic, deep inelastic and fusion reactions were measured. The limiting angular momentum for evaporation residue formation was found to be 33.6±1.7 h . Products of atomic number≦12 are found to result predominantly from quasi-two-body breakup of the composite system with increased damping of the initial kinetic energy as the mass transfer and the angle of detectiion increase. The elongation of the symmetric scission configuration of a fissioning 47 V nucleus is derived from the kinetic energies obtained for completely damped collisions. The contribution to the fragment kinetic energy from rapid rotation of the fissioning system is found to be comparable to the kinetic energy from Coulomb repulsion. The evolution of molecule-like composite nuclei and the similarities between deep inelastic reactions of relatively light nuclei and those observed for much heavier projectiles are discussed.

Non-equilibrium α-particle emission at 20 MeVnucleon☆

Abstract Energy and angular correlations between α particles and heavier products of the reactions of 310 MeV 16 O with Ti reveal two non-equilibrium components in the particle emission observed in coincidence with heavy products.

The fusion of 12C with 12C at projectile energies from 45 to 197 MeV

Abstract Evaporation residues arising from the deexcitation of 24 Mg produced in the reactions of 12 C with 12 C have been identified on the basis of energy and angular distributions measured with a semiconductor detector telescope. Excitation functions for the individual product elements have been obtained over the projectile energy range from 45 to 197 MeV. Evaporation residue cross sections for B and C were not directly measured because of interferences from other reaction mechanisms, but were determined from the systematics of the residue yields as a function of projectile energy and atomic number. Limiting angular momenta have been calculated from the summed yields of the evaporation residue cross sections. These limiting angular momenta are compared to limits predicted by several models.

Emission of light charged particles in the reactions of 120 MeV 20Ne with 27Al

Abstract The emission of H and He isotopes in the reactions of 120 MeV 20 Ne with 27 A1 has been studied using light particle-heavy ion coincidence measurements. The energy spectra and angular correlations of the light particles emitted in coincidence with products of Z ≧ 14 agree well with the predictions of the statistical model applied to the decay of the compound nucleus 47 V. Results on α-particle emission associated with deep inelastic reactions leading to carbon and oxygen products are also reported.

Total kinetic energies in the fission of 101Rh, 110Cd, 119I and 138Ba nuclei

Abstract Singles and coincidence experiments with solid state detector telescopes have been used to determine the total fragment kinetic energies in the symmetric fission of 101Rh, 110Cd, 119I and 128Ba nuclei produced in reactions induced by 197 MeV 12C projectiles. These kinetic energies are found to be in excellent agreement with the predictions of Davies et al. based upon a dynamic liquid drop model calculation. For the reactions of 12C with Ag, the dependence of the kinetic energy release on angular momentum has been explored. The increase in kinetic energy with increasing angular momentum is found to be ≦ 0.7 keV h 2 .

Prompt γ-ray emission in the reactions of 120 MeV 20Ne with 27A1☆

The emission of prompt γ-radiation in the de-excitation of the products of the reactions of 120 MeV 20Ne with 27Al has been studied. Three NaI detectors placed at angles of 35°, 90° and 145° to the direction of the 20Ne beam were used to detect γ-rays in coincidence with reaction products having 6 ≦ Z ≦ 20, detected in a counter telescope. Data were obtained with the counter telescope in the same plane, as well as in a plane perpendicular to the plane defined by the beam and the NaI detectors. The average multiplicities 〈Mγ〉, average energies 〈Eγ〉, primary γ-ray energy spectra and the variation of 〈Mγ〉 and 〈Eγ〉 with angle of observation and kinetic energy of the detected products are presented and discussed in terms of the dominant reaction mechanisms.

The prompt γ-ray de-excitation of evaporation residues of 39K and Se☆

Abstract Average multiplicities 〈 M γ 〉 and average energies 〈 E γ 〉 have been measured for evaporation residues of the compound nuclei 39 K and Se produced in reactions of 107, 155 and 197 MeV 12 C projectiles with 27 Al and nat Ni target nuclei. Both quantities are found to be essentially independent of the projectile energy. For the reaction 197 MeV 12 C + 27 A1, 〈 M γ 〉 increases as a function of product atomic number. The results are interpreted in terms of the angular momentum dissipation which occurs during the particle evaporation cascade.

The reactions of 12C with 12C AT 293 MeV

Abstract Energy spectra, angular distributions, and elemental yield distributions have been measured for products Z = 1−9 produced in the reactions of 12 C on 12 C. A total reaction cross section 1170 −100 +170 mb was determined from the measured elemental cross sections and the principle of charge conservation. This total reaction cross section is about 250 mb less than the geometric cross section and agrees with the Glauber-model calculations of DeVries and Peng. The experimental energy spectra, angular distributions, and yield distributions were compared with those from model calculations for the statistical decay of the products of fusion and of incomplete fusion reactions. For both types of calculations, a modified version of the code LILITA was used. By comparing the data to model calculations, an upper limit of 75 mb for the fusion cross section was determined. That limit corresponds to an upper limit of L crit for fusion of 10ħ in the sharp-cutoff approximation. The dominant reaction mechanisms appear to be incomplete fusion processes.