A method for the determination of recoil ion ranges needed in DSA measurements

From the yield curve of the²⁷Al(p, γ)²⁸Si reaction obtained with implanted targets, the range distributions and mean ranges of 50 keV Al⁺-ions have been determined in C, Cu, Mo and Ta. The energy straggling of protons has been taken into account in the analysis. The DSA lifetime values in different backing materials are in good agreement when measured ranges are used for the determination of the stopping parameters.     

The influence of the fission barrier on the mass distribution in reactions with symmetric fragmentation

The mass distributions of reaction products with symmetric fragmentation resulting from the bombardment of¹⁴⁴Sm,¹⁶⁵Ho,¹⁷⁵Lu,¹⁷⁶Hf,¹⁸¹Ta, and²⁰⁸Pb with⁴⁰Ar projectiles have been studied. The incident energies were chosen to populate nearly the same angular momentum range of the composite system while the nuclear temperature varies only weakly. The reaction products were identified by their energy and time of flight using a solid state detector placed at 60°. The width of the mass distribution was found to increase by nearly a factor of two as the liquid drop fission barrier of the different compound nuclei decreases from 11 to 2.2 MeV. For all systems, the survival of evaporation residues proves that compound fission contributes to the observed symmetric reaction component.     

Determination of angular momenta in the incomplete-fusion channels of the reactions Ta+22Ne and Ir+12C

By using the γ-ray-multiplicity technique, experiments were carried out to determine the input angular momenta lⁱⁿ corresponding to the heavy-ion induced incomplete-fusion reactions involving the emission of fast charged particles. The α-particle and Li-nuclei emission channels were investigated in the reaction ¹⁸¹Ta + ²²Ne at the average Ne-ion energy of 155 MeV and for the α-particle emission channel in the reaction ^natIr+¹²C at E = 100 MeV. The separation of the reaction channels was carried out using an X-ray spectrometer. The angular distributions of the fission fragments were measured in the reaction ¹⁸¹Ta(²²Ne, αf). The data obtained indicate that input angular momenta are equal to about 60 ? and 50 ? for the channels of Li emission and α-emission, respectively, being practically independent of the particle energy. For the α-emission channel the lⁱⁿ values are the same for both reactions within experimental errors. The lifetime of the system of interacting target and projectile nuclei, prior to the emission of an α-particle, has been estimated to be equal to 10^?20s.     

Description of deep inelastic transfer reactions at the Fermi energy within transport models

The possibility of studying the dissipative processes near the Fermi energy using the transport equations arising within the Boltzmann-Nordheim-Vlasov approach is discussed. It is shown that this approach makes it possible to reproduce all the main features of deep inelastic collisions of heavy ions: specifically, the deviation curves for reaction fragments and their Coulomb and nuclear rainbows and the strong correlation between the fragment exit angle and kinetic energy loss. The theoretical results are compared with the experimentally obtained data on the isotopic and velocity distributions of light fragments escaping at small angles in the ¹⁸O + ¹⁸¹Ta and ¹⁸O + ⁹Be reactions at an energy of 35 MeV/nucleon. It is established that the experimental velocity distributions contain two components: dissipative (with a velocity smaller than that of the projectile ion) and direct (having a maximum at the particle beam velocity). It is shown that the transport equations describe well the dissipative part of the reaction, which is about 30% of the total output. The direct component arises during fission of the projectile ion nucleus and is described well within the Goldhaber model.     

A study of diffusion phenomena in the rare earth region: The reaction 159Tb + 620 MeV 86Kr

Kinetic energy spectra, charge and angular distributions have been measured with ΔE-E telescopes for over twenty-five identified elements from the reaction ${}^{159}\text{Tb}\text{+ 620}\text{MeV}{}^{86}\text{Kr}$. At all angles and for all observed atomic numbers, the energy spectra indicate the presence of energetically relaxed products in the vicinity of the Coulomb barrier. Elements near the projectile also show a sizable contribution from incompletely damped events at angles close to the grazing angle. The charge distributions are peaked near the projectile Z and demonstrate a strong shape dependence on the angle of observation. The angular distributions show a weakening of the side peaking with increasing proton transfer to or from the projectile. Angular distributions and angle-integrated charge distributions have been calculated with a diffusion model which assumes the formation of a rotating intermediate complex with an l-dependent lifetime. The mass exchange between the two segments of the intermediate complex is treated as a diffusive process which is described by the master equation. Values for the diffusion constant, the overlap of the two density distributions, the mean lifetime of the intermediate complex and the spread in the average lifetime were used which semiquantitatively reproduced data from the 620 MeV ⁸⁶Kr reaction on ¹⁸¹Ta and ¹⁹⁷Au targets. Satisfactory agreement was obtained between these calculations and the data from the ¹⁵⁹Tb target. In addition, by increasing the lifetime of the complex by 30 %, the previously measured data for the ^{107, 109}Ag + 620 MeV ⁸⁶Kr reaction was semiquantitatively reproduced.     

Measurement of the proton total reaction cross section for 159Tb, 181Ta and 197Au between 20 and 48 MeV

Proton total reaction cross sections have been measured for the nuclei ¹⁵⁹Tb, ¹⁸¹Ta and ¹⁹⁷Au at seven proton energies between 20 and 48 MeV using an attenuation technique. The experimentally determined energy dependence of the total reaction cross sections is compared with results obtained for black nucleus and optical model calculations.     

Angular and energy dependences of emission probability for light particles in 22Ne-induced reactions at 8 MeV/nucleon

Inclusive energy spectra and angular distributions have been measured for light charged particles with Z = 1–4 emitted in the interaction of ²²Ne ions with a ¹⁸¹Ta target. The reaction products were analysed and detected by means of a system of ΔE-E telescopes placed in the focal plane of a magnetic spectrometer. The end-point energies of the light particles correspond to the calculated kinematic limits taking into account the rotational energy of the residual nucleus. The angular distributions of the high-energy particles are strongly forward peaked. The data obtained are analysed on the basis of the moving source, rotating hot spot, massive transfer and breakup fusion models. The relative yields of the different isotopes and their most probable energies are described by the massive transfer model. The qualitative behaviour of the spectra in the vicinity of the kinematic limits can be explained in terms of the breakup fusion model.     

Transfer reactions of B with Ta

Excitation functions and mean recoil ranges are reported for the formation of ¹⁸²Os, ¹⁸³Re, ¹⁸²Re, ¹⁸¹Re and ¹⁸²Ta in ^{10, 11}B interactions with ¹⁸¹Ta. The stacked foil technique was used. The results are indicative of formation through a transfer reaction. We have considered a nucleon group transfer mechanism in a surface interaction followed by de-excitation via nucleon emission from the excited intermediate. Thus the energy dependence of recoils and cross sections of single nucleon and multinucleon transfer products have been calculated and found in good agreement with experimental results.     

Étude de la dissipation d'énergie dans la fission de 234u à l'aide de la réaction 233U(d,pf)

The energy balance in the fission of ²³⁴U has been investigated on the basis of experimental results from the ²³³U(d, pf) reaction. Taking into account the neutron evaporation we have deduced the total kinetic energy and excitation energy distributions of the primary fragments as functions of the excitation energy of the fissioning nucleus. The neutron evaporation temperatures have been adjusted so as to reproduce the average value and width of the measured kinetic energy distributions for each fragmentation. Excitation energy distributions of the fragments have been deduced. The data are discussed in the framework of the liquid-drop model with shell corrections. Evidence for energy dissipation in the fission of ²³⁴U, involving drastic changes in the scission configuration, is shown for some fragmentation modes.     

Photodisintegration of tantalum

The yields of photonucleon reactions on the isotope ¹⁸¹Ta that are induced by bremsstrahlung photons whose endpoint energy is 67.7 MeV are measured by the residual-activity method. The cross sections for photonucleon reactions on the isotope ¹⁸¹Ta are calculated on the basis of the TALYS code and a combined model. The measured reaction yields are compared with their counterparts rescaled from cross sections obtained in experiments that employed beams of quasimonochromatic and bremsstrahlung photons. The spectra of neutrons emitted from ¹⁸¹Ta nuclei after the absorption of photons having various energies are calculated within the TALYS code and the combined model in question.     

Preequilibrium α-particle emission in heavy-ion reactions

The α-particle emission following ¹⁴N-induced reactions on various heavy targets at 85–115 MeV has been studied. Cross sections of heavy residual nuclei produced after α-emission were measured in the case of the ²⁰⁹Bi target and were found to be close to the angle-integrated cross sections of α-particles, indicating that the α-emission mainly takes place in a binary process. The measured angular distributions of α-particles are pronouncedly forward-peaked, while the energy spectra are always characterized by the Maxwellian distribution even at forward angles and reproduced excellently by the statistical evaporation formula when nuclear temperature is treated as a free parameter. The resultant value of the temperature is high (4–6 MeV) at forward angles and decreases monotonically with increasing emission angles.The energy and angular distributions of protons, deuterons and tritons were also measured in the ¹⁸¹Ta + ¹⁴N reaction at 115 MeV. The results are similar to those of α-particles. In particular, nuclear temperatures turned out nearly equal to each other, being consistent with the hot-spot interpretation for the relevant preequilibrium light-particle emission.     

Investigation of 16O excited states via the 14N(3He,p) reaction

The reaction ¹⁴N(³He, p)¹⁶O has been investigated at a bombarding energy of 15.0 MeV, using a differentially pumped gas target. Angular distributions were measured for 30 levels below 16.5 MeV in excitation. Data were compared with shell-model calculations of Zuker, Buck and McGrory for states whose correspondence with theory is established. Many states are found to possess a large compound-nucleus reaction component. Several previously unreported levels are observed at high excitation. Angular distributions for all except the weakest levels have been compared with DWBA calculations.     

Quadrupole splitting on57Fe nuclei and local structure of the amorphous alloys Ni−Zr,Ni−Ta

Quadrupole splittings on⁵⁷Fe nuclei were studied by Mössbauer spectroscopy in amorphous and crystalline Ni-based alloys with 37 at .% Zr and 25–50 at .% Ta with 0.5 at .%⁵⁷Fe addition. Quadrupole splitting distributions and then the topological short range in Ni?Ta alloys were found to be similar to that of the Ni₃Ta intermetallic compound. The distribution of splittigs for Ni?Zr alloy is similar to that of its crystalline counterpart.     

Development of a Method for Measurement of Photonuclear-Reaction Cross Sections with the Aid of Simulated Quasimonoenergetic-Photon Spectra

A procedure for measuring photonuclear-reaction cross sections by employing the method of quasimonochromatization of the bremsstrahlung photon spectrum is developed. This procedure permits determining reaction cross sections via measuring the reaction yield at three fixed values of the electron energy. The procedure is equivalent to measuring the cross section in question for quasimonochromatic photons. Bremsstrahlung-photon spectra are obtained using state-of-the-art simulation means involving the GEANT4 code as applied to a specific experiment with allowance for its geometry, target thicknesses, electron-beam parameters, etc. The results obtained by simulating quasimonochromatic distributions of bremsstrahlung photons are presented for experiments at the LUE-8-5 linear electron accelerator of Institute for Nuclear Research (Moscow, Russian Academy of Sciences). These results are found to be in good agreement with the experimental energy distribution of the cross section for the reaction ¹¹¹Cd(γ, γ') in the energy range between 5 and 8 MeV.     

Projectile fragmentation of <Superscript>40,48</Superscript>Ca and isotopic scaling in a transport approach

We investigate theoretically projectile fragmentation in reactions of ^40,48Ca on ⁹Be and ¹⁸¹Ta targets using a Boltzmann-type transport approach, which is supplemented by a statistical decay code to describe the de-excitation of the hot primary fragments. We determine the thermodynamical properties of the primary fragments and calculate the isotope distributions of the cold final fragments. These describe the data reasonably well. For the pairs of projectiles with different isotopic content we analyze the isotopic scaling (or isoscaling) of the final fragment distributions, which has been used to extract the symmetry energy of the primary source. The calculation exhibits isoscaling behavior for the total yields as do the experiments. We also perform an impact-parameter-dependent isoscaling analysis in view of the fact that the primary systems at different impact parameters have very different properties. Then the isoscaling behavior is less stringent, which we can attribute to specific structure effects of the ^40,48Ca pair. The symmetry energy determined in this way depends on these structure effects.     

Angular distributions and cross-sections of projectile-like fragments in the 19F + 159Tb reaction

The angular distribution of projectile-like fragments (PLFs) in the ¹⁹F + ¹⁵⁹Tb reaction have been measured at beam energy equal to 98MeV. Angular distributions of PLFs showed a systematic change with increasing mass transfer, starting from the peaking at grazing angle for heavier PLFs to very forward peaked angular distributions for lighter PLFs. Cross-sections of the different PLFs were obtained by integrating their centre-of-mass angular distributions. The PLF cross-sections have been compared with the incomplete fusion cross-sections obtained from the earlier measurement of the evaporation residue cross-section. Reduced cross-sections for lighter PLFs were observed to be higher compared to those observed in ¹⁹F + ⁶⁶Zn reaction at similar values of E _cm/V _b. Also, elastic scattering measurements were carried out to get information about the grazing angle and total reaction cross-section.     

Mass distribution of fission fragments in the19F+197Au reaction

Mass distributions of fission fragments have been measured for the reaction of¹⁹F on¹⁹⁷Au as a function of scattering angle. The mean fragment mass is dependent on the scattering angle, the asymmetry increasing with increasing projectile energy.     

Experimental signature of entrance channel effect in heavy mass region via evaporation residue cross section and spin distribution measurements

Evaporation residue (ER) cross sections and gamma multiplicity distributions have been measured for ¹⁶O + ¹⁸⁴W and ¹⁹F + ¹⁸¹Ta systems in the excitation energy range of 50–90 MeV, leading to the same compound nucleus ²⁰⁰Pb^∗. Comparison of experimental results of both the systems shows that ER cross sections and moments of gamma multiplicity distribution of ¹⁶O + ¹⁸⁴W system are significantly higher than those of ¹⁹F + ¹⁸¹Ta system at higher excitation energies. Present measurements directly shows the experimental signature of entrance channel effect even with the systems which are not very different with respect to their entrance channel mass asymmetry. It is further demonstrated that the reduction in the ER cross section and moments of spin distribution for ¹⁹F + ¹⁸¹Ta system is mainly due to the suppression of fusion of higher l values.     

Evidence for energy dependence in the isospin dependent part of the nuclear optical model potential

Angular distributions and the excitation function of the total cross section for the ²⁰⁸Pb(p, n) charge exchange reaction are fitted with DWBA calculations. Isospin potentials which have the relative real volume and surface imaginary strengths found in the optical model studies of Becchetti and Greenlees provide adequate fits to the angular distributions. The excitation function indicates a strong energy dependence in the strength of the isospin potential.