The cross-sections for the binary and ternary fission of platinum induced by 14, 18 and 23 GeV protons

The cross-sections for the binary and ternary fission of platinum have been determined using a polycarbonate as the detector of fission fragments. The incident proton energies were 14, 18 and 23 GeV.     

The binary and ternary fission of thorium,lead and platinum induced by 12.2 GeV protons

We have investigated the decay of^123g+mIn to excited states of¹²³Sn.¹²³In was produced by the¹²⁴Sn(y,p)¹²³In reaction on an enriched SnO₂ target. The isomeric transition to the¹²³In ground state was not observed. In the beta decay of^123m In excited states at 24, 150.9, 920.5, 1194, 2621, 3151, 3256 and 3306 keV in¹²³Sn withJπ values 3/2⁺, 1/2⁺, (5/2⁺), 5/2⁺, 1/2⁺, (1/2⁺, 3/2⁺), 3/2⁺ and (l/2⁺, 3/2⁺), are fed. In the β decay of the¹²¹In ground state only the 7/2⁺ level at 1154 keV in¹²³Sn is observed.     

An analysis of the binary and ternary fission of uranium induced by 12.2 GeV protons

In this work the binary and ternary fission of uranium induced by 12.2 GeV protons has been investigated with a polycarbonate detector registering the tracks of particles with mass numbersA>16. The basic characteristics of binary and ternary fission are discussed and the corresponding cross-sections are given. The values of the cross-sections for binary and ternary fission are calculated to be σ _b =(915 ± 120) mb and σ _t -(12.8 ± 2.5) mb, respectively.     

Fission cross sections of medium-weight and heavy nuclei induced by 1 GeV protons

Coincidence studies performed in 4π geometry with silicon detectors and parallel plate avalanche counters have been used to measure total fission cross sections of²³⁸U,²³²Th,²⁰⁹Bi,²⁰⁸Pb,¹⁹⁷Au,^natYb,^natHo,^natTb,^natSm,^natTe,^natAg and^natNi nuclei induced by 1 GeV protons. The experimental results agree qualitatively with cascade-evaporation calculations.     

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.     

Possible mass instability of binary fission in Ag by 1 GeV protons

Using an improved time-of-flight technique we obtained directly the mass distribution of the correlated fragments of binary fission in Ag by 1 GeV protons. We have found the FWHM and the shape of the distribution in agreement with the LDM-predictions.     

Differential cross sections for the photoproduction of eta mesons from protons near 2 GeV

Differential cross sections for the process γp → pη have been measuredd at c.m. angles of 28°, 35° and 42° at incident energies between 2 GeV and 2.8 GeV. Data from an earlier experiment below 2 GeV have been re-analysed and corrected. The whole set of data is compared with the form (s?M²)² dσ/dt, which fits data at higher energies. There is good agreement above 2 GeV, particularly at the largest angle, but strong departures below.     

Parity nonconservation in binary and ternary nuclear fission induced by polarized neutrons

Within the quantum-mechanical theory of the nuclear-fission process, the conditions of the emergence of coherent effects in the angular distributions of fragments originating from the binary and ternary fission of polarized nuclei are analyzed with allowance for the properties of transition fission states. In the case of ternary fission, the coefficients of P-odd asymmetry in the angular distributions of a light particle and a third particle, which is taken here to be an alpha particle, are calculated under the assumption that the third particle and two fragments are produced through a one-step mechanism. In order to confirm the ideas developed here, it is proposed to repeat, at a higher level of statistical accuracy, experiments devoted to seeking P-odd asymmetries for alpha particles in the ternary fission of nuclei.     

Differential cross sections for excitation of atomic hydrogen by protons

Calculations are presented for the differential cross section for the excitation of atomic hydrogen to the (2s + 2p) level by protons at 50, 100 and 150 keV, employing a close-coupling pseudo-state model. Good agreement is obtained with the recently published data.     

Isobaric production cross sections from 0.6 GeV proton irradiation of neptunium and thorium using mass spectrometry

A high-fluence proton irradiation of neptunium was the last experiment in PSIs programme ATHENA related to accelerator-based transmutation. The principal aim of the programme has been to provide experimental data for the validation of theoretical models in nucleon–meson transport codes, with emphasis on the mass yield distribution of fission and spallation products. An improved mass spectrometry method has allowed the direct derivation of isobaric production cross sections with only minor corrections and an estimate of the fission cross section by integration in the fission hump. In a second sample position of the irradiation head, a repetition of the previous ATHENA experiment with thorium was possible, profiting from the improved mass spectrometry technique. The experimental results are better predicted by the code FUSSPOT than by HETC/RAL, both used at PSI.     

Cluster aspects of binary and ternary fission

On the basis of the statistical approach and calculation of the potential energy of the scission configurations, binary and ternary fissions are described. The text was submitted by the authors in English     

Phenomenological analysis of fission induced by high-energy protons

High-energy proton induced fission is studied in the framework of a two-step model. In the first step, the projectile penetrates the target nucleus, knocks out few nucleons and leaves the residual nucleus with a spectrum of excitation energies depending upon the number of projectile-nucleon collisions. This stage is described in terms of a simplified version of Glauber's multiple-scattering theory. The second stage in which the residual nucleus fissions, is treated by assuming phenomenological expressions for the dependence of the fission probability on excitation energy which take into account the onset of fragmentation at a certain “crack” energy. Comparison with experimental data suggests that high energy fission of heavy nuclei proceeds in a way similar to low-energy fission. Light nuclei, however, require a more violent fission mechanism.     

Bimodal fission in binary and ternary spontaneous fission of 252Cf

The hot bimodal fission of ²⁵²Cf is reexamined with new high-statistics data. We constructed a γ-γ-γ coincidence cube for binary fission and LCP-gated γ-γ matrix for ternary fission. By identifying the secondary fission fragments from their γ-ray transitions, we measured the yields for various fission splits. The normal neutron yield distribution is found to be Gaussian for Xe-Ru. However, the binary fission split of Ba-Mo is found to exhibit a bimodal neutron distribution with the “hot mode” corresponding to ≈3.1% of the total yield. In α ternary fission, the first measurements of yields for specific fission splits are presented. The Te-α-Ru and Xe-α-Mo neutron yields fit well with a single mode, but the Ba-α-Zr split shows evidence for an enhanced hot mode with an intensity of ≈13.8% of the normal mode. The text was submitted by the authors in English.     

Cross sections for 209Bi, 232Th, 235U, 238U, and 237Np fission induced by intermediate-energy protons and deuterons

The cross sections for ²⁰⁹Bi, ²³²Th, ²³⁵U, ²³⁸U, and ²³⁷Np fission induced by protons of energy in the range 1.0–3.7 GeV and by deuterons of energy 1.0 GeV were measured. The results are compared with data from other experiments, with available estimates, and with the predictions of theoretical models.     

Measuring the cross sections of heavy-metal spallation induced by deuterons with energies of 2, 2.94, and 3.5 GeV per nucleon

The cross sections for the spallation of the heavy-metal nuclei ¹⁸¹Ta, ¹⁹⁷Au, ²⁰⁷Pb, ²⁰⁹Bi, ²³²Th, and ²³⁸U induced by relativistic deuterons with energies of 2, 2.94, and 3.5 GeV per nucleon are measured using the deuteron beam from the Nuclotron accelerator of the JINR Laboratory of High Energy Physics in Dubna, Russia. The cross-section measurements employ a combined experimental technique involving the solidstate nuclear-track detectors and the activation gamma spectrometry. Adding our measurements to the database of experimental nuclear data will make it possible to test the computer codes used for selecting the parameters of the ADS-type facilities.     

Langevin analysis of fission excitation functions induced by protons

The stochastic Langevin approach to fission is applied to analyze fission excitation functions measured in p+²06Pb and p+²09Bi systems. A presaddle friction strength of（3–5）×10²¹s^-1is extracted by comparing theoretical predictions with experimental data. Furthermore, the small distortion of the formed compound nuclei with respect to the spherical shape under the condition of low angular momentum suggests that experimentally, populating an excited compound system via light-ion induced reactions favors a more accurate determination of presaddle friction with a fission cross section.     

Isotopic production cross sections of residues in reactions induced by relativistic heavy ions with protons and deuterons

The isotopic production cross sections of heavy residues in relativistic heavy-ion collisions have been investigated in inverse kinematics. The primary reaction products were fully identified in mass and atomic number prior to beta decay using the fragment separator FRS. The huge collection of data obtained helps in the understanding of the two main reaction mechanisms involved: fragmentation and fission. These data provide basic information for future radioactive ion beam facilities and for technical applications like intense neutron sources by means of spallation targets.     

Systematization of cross sections for the production of residual nuclei on separated tin isotopes in reactions induced by various-energy protons

Cross sections for the production of residual nuclei on the isotopes ^{112,118,120,124}Sn irradiated with 0.66-, 1.0-, 3.65-, and 8.1-GeV proton beams were investigated. A ten-parameter semiempirical formula was used to systematize the cross sections in question. A comparative analysis of parameter values obtained at different proton energies was performed.