Inelastic interactions of fast nucleons with nuclei and fission of nuclei

The cross section for the fission of actinide nuclei that is induced by fast neutrons is considered as a fraction of the cross section for inelastic nucleon interaction with nuclei. In turn, inelastic nucleon interaction with a nucleus is treated as scattering on intranuclear nucleons. It is shown that this interaction model describes satisfactorily the cross section for the inelastic interaction of 60- to 2200-MeV nucleons for a broad set of nuclei and that the energy dependence of the cross section for the fission of actinide nuclei that is induced by 400- to 1000–MeV protons replicates the energy dependence of the cross section for inelastic interactions with respective nuclei. From the model used, it follows that the cross sections for proton-nucleus interactions exceed cross sections for respective neutron-nucleus interactions in the energy range extending up to 550 MeV; at higher energies neutron cross sections are larger than proton cross sections.     

Multimode approach to 241Am and 237Np fission induced by 660-MeV protons

The results obtained by measuring cross sections for the formation of fragments originating from ²⁴¹Am and ²³⁷Np fission induced by 660-MeV protons are presented. The charge and mass distributions of fragments are analyzed within the multimode-fission model, symmetric and asymmetric fission channels being separated. The contributions of various fission components are estimated, and the fission cross sections for the ²⁴¹Am and ²³⁷Np nuclei are calculated along with the fissilities of these nuclei.     

Model of multiparticle preequilibrium decay

The possibility of calculating the spectra of several sequentially emitted nucleons was implemented on the basis of the exciton model of the preequilibriumdecay of a nucleus bymeans of a Monte Carlo simulation. A method for determining the instant of statistical equilibration in a composite system formed by intermediate- and high-energy nucleons was proposed. Calculations on the basis of the proposed model were combined with the results of calculations based on the statistical model of nuclear reactions and the intranuclear-cascade model. A systematic comparison of the results of these calculations with experimental data on the spectra of nucleons from (p, xn), (p, xp), (n, xn), and (n, xp) reactions in the projectile-energy range between 20 and 160 MeV was performed. The cross sections for the fission of heavy nuclei that was induced by protons and neutrons of energy in the range extending up to 3 GeV were calculated, and the results of those calculations were contrasted against available experimental data.     

Silicon fragmentation under the effect of high-energy cosmic-ray protons

The results obtained by calculating the cross sections for the elastic and inelastic scattering of 50- to 1000-MeV protons interacting with ²⁸Si, which is the main integrated-circuit element of onboard spacecraft electronics, are presented along with the calculated mass, charge, and energy distributions of heavy products of respective nuclear reactions. To compare the results of the calculations with experimental data, similar calculations were performed for the p + ²⁷Al reaction. This comparison shows that the elasticand inelastic-scattering cross sections calculated by using the EMPIRE-II-19 code are in satisfactory agreement with available experimental data. Considerably wider scatter of available data is observed in the isotope and isobar yields. A high sensitivity of the kinetic spectrum of the final nuclei to the incident-proton energy is demonstrated.     

New approximations to the energy dependences of the total cross sections for the proton-induced fission of <Superscript>197</Superscript>Au, <Superscript>203</Superscript>Tl, <Superscript>nat</Superscript>Pb,and <Superscript>209</Superscript>Bi nuclei

The total cross sections for ¹⁹⁷Au and ²⁰³Tl fission induced by protons of energy varied from about 200 to 1000 MeV with a step of about 100 MeV are measured. New approximations to the energy dependences of the cross sections for the proton-induced fission of ¹⁹⁷Au, ²⁰³Tl, natPb, and ²⁰⁹Bi nuclei are presented and discussed. For all of these nuclei, exponential functions are used as approximations.     

Deep processes in nuclei and in-medium dressing of the nucleons and mesons

K⁺ scattering and quasielastic electron scattering from nuclei are expected to provide information about the nucleons and mesons in the inner regions of nuclei. The K⁺- nucleus cross sections and the quasielastic electron-nucleus response functions have been calculated taking into account the same in-medium dressing of the nucleons and the same coupling of the σ and ω mesons to the polarization of nuclear matter. We obtain a good agreement with experimental data for the two processes.     

Formation of two pions on nuclei in A(γ, ππN)B reactions

A model is proposed for double pion photoproduction on nuclei that is accompanied by nucleon emission. Simple models that faithfully reproduce single-particle differential cross sections are used to describe photon interactions with intranuclear nucleons. The calculated cross sections for pion photoproduction on ¹²C nuclei are compared with inclusive pion spectra measured in the second resonance region of photon energies.     

A systematic study of the fission and evaporation residue excitation functions in complete fusion reactions with weakly bound stable nuclei

We carry out a systematic study on the fusion-fission and evaporation residue excitation functions for the reactions of ^6,7Li, ⁹Be, ^10,11B + ²⁰⁹Bi and ^6,9Li, ⁹Be + ²⁰⁸Pb, in which the projectiles are loosely bound and have low threshold energies against breakup. The fusion cross sections are calculated by the coupled-channel model. The compound nuclei decay are analyzed with the standard statistical model. The fission and evaporation residue excitation functions are well reproduced by our calculations, proving the validity of the standard statistical model in describing the compound nuclei decay in these characteristic reactions. For the compound nuclei with A=215-220 and Z=86-88, the liquid drop fission barriers need to be scaled by 0.80-1.02 to reproduce the experimental data. And a decreasing trend of the scaling factor with increasing fissionability parameter Z²/(50A) is found.     

Elastic and inelastic scattering of 800-MeV protons on <Superscript>16</Superscript>O and <Superscript>20</Superscript>Ne nuclei

Differential cross sections and polarization observables for the elastic and inelastic scattering of 800-MeV protons on ¹⁶O and ²⁰Ne nuclei are calculated on the basis of the theory of multiple diffractive scattering and the α-cluster model involving dispersion. The single-particle nucleon-density distributions obtained within the α-cluster model involving dispersion are used in the calculations. The differential cross sections and polarization calculated for elastic and inelastic p¹⁶O and p²⁰Ne scattering are compatible with available experimental data. The spin-rotation functions calculated for elastic p¹⁶O and p²⁰Ne scattering within the independent-nucleon model differ qualitatively from their counterparts calculated within the α-cluster model involving dispersion.     

Elastic deuteron scattering on 12C and 16O nuclei in the alpha-cluster model

On the basis of the dispersive alpha-cluster model for target nuclei and the theory of multiple diffractive scattering, differential cross sections and analyzing powers for the elastic scattering of 400 and 700-MeV deuterons on ¹²C and ¹⁶O target nuclei were calculated in the pointlike-deuteron approximation. In these calculations, the amplitude for incident-deuteron scattering on nuclei was constructed with the aid of amplitudes for dα scattering that were obtained from a fit to data on d ¹⁶O scattering. The same features were calculated on the basis of the diffraction approximation with allowance for the internal deuteron structure by using the amplitudes obtained earlier for nucleon scattering on ¹²C and ¹⁶O nuclei within the same dispersive alpha-clustermodel. The latter made it possible to perform calculations without employing adjustable parameters. The observables calculated on the basis of either approach agree with available experimental data.     

Experimental Cross Sections of Fission Fragments of Thorium-232 Irradiated with Medium-Energy Protons

This paper is focused on fission of Th-232 nuclei induced by protons with energies ranging from 20 to 140 MeV. This energy range is the most informative for studying the competition between asymmetric and symmetric fission modes. Experimental cross sections of production of radionuclides in thorium targets have been determined a year after irradiation. The corresponding theoretical values are calculated using the cascade–evaporation–fission model. The theoretical and experimental cross sections (literature data included) are compared.     

Total cross sections for fission of heavy nuclei by intermediate-energy protons

The results of measuring total cross sections for proton-induced fission of ^natPb, ²⁰⁹Bi, ²³²Th, ²³³U, ²³⁵U, ²³⁸U, ²³⁷Np, and ²³⁹Pu nuclei at proton energies from 200 to 1000 MeV are reported. The measurements were carried out in steps of ≈100 MeV. Complementary fission fragments were detected in coincidence by two parallel-plate avalanche gas counters placed in the beam line on both sides of the thin target close to it. Energy and isotope dependences of the fission cross sections are analyzed.     

Angular momentum dependence of 200Pb fission studied by comparison of 19F on 181Ta with 16O on 184W

The time development of fission in highly excited Pb nuclei has been studied by the crystal blocking technique. Thin Ta crystals were bombarded with ¹⁹F ions in the energy range 90–120 MeV and the yield of fission fragments was measured for emission directions close to a strong axis. The experimental blocking dips are compared with calculated dips containing a superposition of two components, corresponding to short- and long-lived compound nuclei. The information extracted is the energy dependence of the relative amount of fission which comes from compound nuclei with lifetimes of τ≳3 × 10⁻¹⁷s. The total fission cross section and angular distribution of fission fragments were also measured for ¹⁹F bombardment of ¹⁸¹Ta in the energy range 84.3–114.7 MeV and for ¹⁶O bombardment of ¹⁸⁴W in the energy range 83.4–107.9 MeV. The results of the three types of measurements have been interpreted through comparison with statistical model calculations that follow the spin and energy distribution of compound nuclei through the neutron evaporation cascade. The ¹⁹F + ¹⁸¹Ta measurements, when compared with the present ¹⁶O + ¹⁸⁴W cross section and angular distribution measurements and earlier lifetime measurements for ¹⁶O + W, yield information on the spin distribution for the compound nucleus and its influence on the fission process.     

Effect of the shell structure of nuclei on p 15C and p 15N scattering within diffraction theory

The differential cross sections for elastic proton scattering on ¹⁵C and ¹⁵N nuclei at energies of 150 and 800 MeV were calculated within the diffraction theory of Glauber multiple scattering. Shellmodel wave functions were used in these calculations, and particular attention was given to analyzing the sensitivity of the calculated features to distinctions between the shell structure of the ¹⁵C nucleus and the shell structure of the ¹⁵N nucleus. The calculations were performed in the approximation of double scattering. The multiple-scattering operator was written in a form that permits taking into account collisions with nucleons belonging to different shells. It is shown that the difference in structure between the two nuclei in question leads to substantial distinctions between the differential cross sections for scattering at an energy of 800 MeV and scattering angles larger than 25°.     

Interaction of intermediate-energy protons with <Superscript>20</Superscript>Ne and <Superscript>24</Superscript>Mg nuclei within the multiple-scattering model

Observables of the elastic and inelastic scattering of 800- and 250-MeV protons on ²⁰Ne and ²⁴Mg nuclei were calculated on the basis of the theory of multiple diffractive scattering and the dispersive α-cluster model. The ²⁰Ne and ²⁴Mg nuclei were assumed to consist of a core (¹⁶O nucleus) and additional alpha-particle clusters, which could be situated with the highest probability both in the vicinity of the center of mass of the core and outside the core. The multiparticle densities of these nuclei and single-particle nucleon-distribution densities as obtained from the dispersive α-cluster model were used in the calculations. The differential cross sections and polarizations for elastic and inelastic p ²⁰Ne and p ²⁴Mg scattering at the energy of 800 MeV are in better agreement with experimental data than the analogous calculations at the energy of 250 MeV. The spin-rotation functions calculated in the singleparticle approximation for elastic p ²⁰Ne and p ²⁴Mg scattering at these two energy values differ qualitatively from their counterparts calculated on the basis of the dispersive α-cluster model.     

Inclusive spectra of protons and α particles from reactions induced by protons with an energy of 30.0 MeV on the 209Bi nucleus

Inclusive spectra of protons and α particles resulting from the interaction between 30.0-MeV protons and the ²⁰⁹Bi nucleus are investigated. Double differential and integral cross sections for the (p,xp) and (p,xα) reactions are obtained and total partial cross sections for these reactions are subsequently determined. The experimental spectra are analyzed using a modified version of the exciton model of preequilibrium decay and the PRECO-2006 code. Contributions from the compound and direct mechanisms to the formation of integral cross sections are calculated.     

Separation of Coulomb fission from nuclear fission at medium energies

The cross sections for fission induced by one neutron transfer and by the electromagnetic field in the reaction 24.3 MeV/u ²³⁸U + ¹⁹⁷Au are calculated and compared to the experimental data. It turns up that the two calculated cross sections differ by five orders of magnitude at a distance of closest approach of 25 fm. It is shown that in the experiment in which one is able to select the events corresponding to a large distance of closest approach, a separation of Coulomb fission from nuclear fission events can be efficiently obtained.     

Fission in238U+238U collisions below the Coulomb barrier

Integral fission cross sections in the system²³⁸U+²³⁸U were measured at beam energies below the interaction barrierV _C. Scattering angle dependent probabilities and integral cross sections for Coulomb fission were calculated. It is concluded that earlier observed discrepancies between measured and calculated angular distributions for the one-neutron transfer product²³⁹U cannot be explained by sequential fission. Multi-nucleon transfer induced fission is observed down to energies (0.90±0.02)×V_C.     

Temperature effect of the integral flux of cosmic-ray muons at high energies

The temperature coefficients of the integral fluxes of cosmic-ray muons arriving at sea level vertically and horizontally with energies of 10², 10⁴, and 3 × 10⁶ GeV are calculated. Decays of pions, kaons, and charmed particles are considered as sources of muon generation in the atmosphere (according to current data on the generation cross sections of pions, kaons, and charmed particles in interactions between nucleons and the nuclei of atmospheric atoms, obtained in experiments on accelerators and in quantum chromodynamics models). The uncertainties in the generation cross sections of charmed particles are quite high.