Isotopic distributions of Rb and Cs in the proton and neutron induced fission of 238U

The statistical model for fission is used to calculate the isotopic distribution of Rb and Cs in the fission of ²³⁸U induced by high-energy protons and reactor neutrons. The double-humped behaviour of the isotope yield curve as observed in high-energy proton-induced fission and the experimentally observed hump on the neutron-rich side in neutron-induced fission are semi-quantitatively reproduced.     

Low-lying states of the 16F nucleus

Low-lying proton-emitting states of ¹⁶F have been investigated through the sequential particle decay reactions ¹⁴N(³He, n)¹⁶F(p)¹⁵O. Excitation energies were determined by measuring outgoing proton energies. Estimations of proton decay widths and spin limitations were made from proton spectra and angular correlation data which were obtained by detecting the protons in time coincidence with the associated neutrons at θ_n = 0°. To date, the ground-state spin of ¹⁶F has been considered to be J = 0; however, the present work suggests J = 1 to be preferable.     

Multiparameter study of 1H, 3H and 4He in fast neutron induced fission of 235U

The emission probabilities per fission of α-particles, tritons and protons have been measured in fast neutron induced fission of ²³⁵U. The measurements were carried out at neutron energies of 120, 180, 230 and 550 keV. AΔE-E semiconductor detector telescope was used to identify different light charged particles and the fission fragments were detected with an ionization chamber. The three-parameter data corresponding to the pulse heights from the ΔE-E detectors and the ion-chamber were recorded event by event on magnetic tape and were analyzed off-line by computer. No significant variation in the most probable energy ($\text{E}$) and the standard deviation (σ_E) of the energy spectra of different light charged particles with incident neutron energy was observed, although $\text{E}{}_{\mathrm{\alpha }}$ was seen to have a slightly higher value beyond E_n = 230 keV. The yield of α-particles in fission induced by neutrons of E_n ～ 200 keV was found to be higher by about 20 % than that in thermal neutron induced fission. The yields of tritons and protons were found to increase significantly with neutron energy.     

Sequential and simultaneous transfer in the reactions 18O(p,t)16O, 48Ca(t,p)50Ca and 90Zr(t,p)92Zr

The effects of sequential transfer of a pair of neutrons in the reactions ¹⁸O(p, t)¹⁶O, ⁴⁸Ca(t, p)⁵⁰Ca and ⁹⁰Zr(t, p)⁹²Zr are found to be sizeable. Channel spin-orbit distortion is an important feature of the calculations of the ¹⁸O and the ⁴⁸Ca reactions.     

Intermediate structure of the giant dipole resonance in 54Fe and 56Fe

The cross sections for the (γ, n) reaction on ⁵⁴Fe and ⁵⁶Fe for the high-energy component of the neutron spectrum have been investigated using a neutron spectrometer and a synchrotron with a photon energy range from 5 to 26.3 MeV. Neutron energy spectra have been measured. It is shown that the intermediate structure in the (γ, n) reaction cross section is due to high-energy neutrons and correlates with the structure in the neutron spectrum.     

Measurement of neutron energy spectra and neutron-gamma angular correlations for the muon capture process 16O(μ−, νμxn)14, 15N

Neutron-gamma coincidence spectra have been measured for muon capture in ¹⁶O. The γ-spectrum is dominated by the ground state transitions from the $\text{3}\text{2}{}^{\mathrm{?}}\text{(6.32}\text{MeV}\text{)}\text{and}\text{1}\text{2}{}^{\mathrm{+}}\text{+}\text{5}\text{2}{}^{\mathrm{+}}\text{(5.3}\text{MeV}\text{)}$ states of ¹⁵N that are populated after the emission of one neutron. The neutron energy spectra and the neutron energy dependence of the ny angular correlation coefficient A₂ for these final states are presented. The observed transitions in ¹⁴N and the associated neutron spectra give direct evidence for the emission of two correlated neutrons. The data are discussed in terms of direct neutron emission plus emission via giant resonance intermediate states of ¹⁶N. The large yield for the emission of one and two fast neutrons is explained by a capture mechanism involving short-range nucleon-nucleon correlations.     

Cumulative fission yield measurements with 14.7 MeV neutrons on 238U

The fission yield data in the 14 MeV energy neutron induced fission of ²³⁸U play an important role in decay heat calculations and generation-IV reactor designs. In order to accurately measure fission product yields (FPYs) of ²³⁸U induced by 14 MeV neutrons, the cumulative yields of fission products ranging from ⁹²Sr to ¹⁴⁷Nd in the ²³⁸U(n, f) reaction with a 14.7 MeV neutron were determined using an off-line γ-ray spectrometric technique. The 14.7 MeV quasi-monoenergetic neutron beam was provided by the K-400 D-T neutron generator at China Academy of Engineering Physics (CAEP). Fission products were measured by a low background high purity germanium gamma spectrometer. The neutron flux was obtained from the ⁹³Nb (n, 2n)^92mNb reaction, and the mean neutron energy was calculated using the cross-section ratios for the ⁹⁰Zr(n, 2n)⁸⁹Zr and ⁹³Nb(n, 2n)^92mNb reactions. With a series of corrections, high precision cumulative yields of 20 fission products were obtained. Our FPYs for the ²³⁸U(n, f) reaction at 14.7 MeV were compared with the existing experimental nuclear reaction data and evaluated nuclear data, respectively. The results will be helpful in the design of a generation-IV reactor and the construction of evaluated fission yield databases.     

Photoproton and photo-α cross sections of 19F to excited residual states

Cross sections and integrated cross sections for photodisintegration of ¹⁹F to excited residual states following emission of protons, neutrons and α-particles have been measured. The size of the photo-α cross sections appear to be too large to be explained by a semidirect reaction mechanism.     

In-beam γ -ray study of the neutron-rich nuclei 240U, 246Pu, and 250Cm produced by the (18O, 16O) reaction

We have measured deexcitation γ rays in the neutron-rich nuclei of ²⁴⁰U, ²⁴⁶Pu, and ²⁵⁰Cm produced by the (¹⁸O, ¹⁶O) two-neutron transfer reactions, in coincidence with the ¹⁶O particles using Si ΔE−E detectors. The γ rays in these nuclei were identified by selecting the kinetic energies of ¹⁶O particles, which correspond to the excitation energies in the residual nuclei below the neutron separation energies. The ground-state bands of ²⁴⁰U, ²⁴⁶Pu, and ²⁵⁰Cm were established up to 12⁺ states and the K ^π = 0⁻ octupole band of ²⁴⁰U was established up to 9⁻ states. The systematics of the moments of inertia of the ground-state bands for actinide nuclei shows that the deformed subshell closure at N = 152 is sustained for ₉₆Cm isotopes and that it disappears for ₉₄Pu isotopes. The text was submitted by the authors in English.     

Four-nucleon transfer with the 32S(16O, 12C)36Ar reaction

Angular distributions have been measured for the ³²S(¹⁶O,¹²C)³⁶Ar reaction at 45.5 MeV leading to excited states between E_x, = 0 and 8 MeV. Experimental cross sections are compared with exact finite-range DWBA calculations in combination with extensive shell-model calculations, which include sd- and fp-shell configurations. Transitions to low-energy positive-parity states and bound negative-parity states are well reproduced. The calculations, however, fail to describe some high-energy positive-parity states. Calculations with a complete cluster expansion for the four transferred nucleons give about 50% larger cross sections, but can not explain the observed discrepancies. Possible interference of reaction processes other than direct α-transfer and special structure effects are discussed.     

Inclusive neutron and proton energy spectra following the negative pion absorption at rest in 12C

The results of a measurement of the inclusive energy spectra of the neutrons and protons emitted following the absorption at rest of negative pions on ¹²C are presented. The spectra have been measured with the time-of-flight method with an overall resolution of 650 psec. From the neutron spectrum the rate of 1.7 × 10^?2 neutrons per stopped pion has been deduced for the single-neutron emission reaction ¹²C(π^?, n)¹¹ B. Comparisons are made with calculated spectra and other experimental spectra.     

Spectroscopy of intermediate 16F states with the reaction 14N(3He,np)15O

Excited states of ¹⁶F have been investigated with the reaction ¹⁴N(³He, np)¹⁵O at E = 10.5 and 12 MeV in kinematically complete experiments. Proton groups corresponding to the decays of intermediate ¹⁶F states were observed at various angles with counter telescopes in time coincidence with the associated neutrons detected at θ_n^lab = 0° with a time-of-flight spectrometer. Excitation energies and decay widths Γ_p0 of these states have been extracted from the proton spectra. Lower limits for the orbital angular momentum in the decay channel and for the spin of the states have been deduced from the obtained angular correlations. By comparison with the reaction ¹⁴N(³He, pp)¹⁵N measured at E = 13 MeV, pairs of $\text{T = 1}{}^{16}\text{F}$ parent/¹⁶O analog states have been identified. J^π assignments and shell-model configurations are discussed on the basis of the selectivity of the reactions measured.     

Photoinduced fission of the doubly even uranium isotopes 234U, 236U and 238U

A measurement of the angular distributions and yields of fission fragments in the photofission of ²³⁴U has been performed between 5.2 and 6.4 MeV. As γ-source, the bremsstrahlung from a microtron was used. For the detection of the fission fragments, solid-state track detectors were used. The present data for ²³⁴U have been analysed together with earlier obtained data for ²³⁶U and ²³⁸U. The values of the fission barrier parameters obtained are compared to results in theoretical macroscopic and microscopic fission potential energy calculations.     

Angular correlation of neutrons from thermal-neutron fission of 235U

The neutron-neutron angular correlation for neutrons with energies ? 1 MeV emitted in thermal-neutron-induced fission of ²³⁵U has been measured. The correlation could be adequately described by a simple model, assuming isotropic neutron emission in the fully accelerated fragment frames together with a 20% isotropic scission component and using binomial distributions to simulate the neutron multiplicity (instead of the usual gaussian form) for each fission fragment. The results give no indication of enhanced polar emission.     

Polarization of preequilibrium proton emission in the 93Nb + 14N reaction

Spin polarization of protons emitted at 20° and 40° in the ⁹³Nb + ¹⁴N reaction at 95 MeV has been measured by the double scattering method using a polarimeter particularly designed for protons having a continuous energy distribution.The result shows that the polarization is small for low-energy protons, but increases smoothly with the increase of proton energy, reaching around + 20 % at about 20 MeV in the center-of-mass system. Energy and angular distributions of protons measured in the same reaction indicate coexistence of equilibrium and preequilibrium components in the proton emission of interest, the fraction of the preequilibrium component increasing with the increasing proton energy. If we assume that protons emitted in equilibrium are completely unpolarized, and that the value of polarization (P) for the preequilibrium component is independent of proton energy, the present result is consistent with $\text{P ? + 22 \%}$ for the emission at 20° and $\text{P ? + 38 \%}$ for the emission at 40°.The result is discussed in terms of the hot-spot model for precompound decay.     

Neutron emission and fragment yield in high-energy fission

The KRIS special library of spectra and emission probabilities in the decays of 1500 nuclei excited up to energies between 150 and 250 MeV was developed for correctly taking into account the decay of highly excited nuclei appearing as fission fragments. The emission of neutrons, protons, and photons was taken into account. Neutron emission fromprimary fragments was found to have a substantial effect on the formation of yields of postneutron nuclei. The library was tested by comparing the calculated and measured yields of products originating from the fission of nuclei that was induced by high-energy protons. The method for calculating these yields was tested on the basis of experimental data on the thermal-neutroninduced fission of ²³⁵U nuclei.     

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

Inclusive energy spectra and angular distributions for heavy ions $\text{(Z ≧ 3)}$ produced in the reactions of 227 MeV and 310 MeV ¹⁶O 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.     

Recherche de l'isotope 19N par la réaction 10Be(11B, 2p)19N

The ¹⁰Be(¹¹B, 2p)¹⁹N reaction has been used to search for the ¹⁹N isotope. No evidence was found for delayed γ-rays from ¹⁹N(β^?)¹⁹O. Delayed neutrons were observed with a half-life of 0.42 ± 0.04 s, which are tentatively assigned to the neutron emitting states in ¹⁹O fed by the β-decay of ¹⁹N. Analysis of the data implies allowed β-transitions to neutron emitting ¹⁹O states, and makes probable an assignment of even parity for the 3.945 MeV ¹⁹O state.     

The influence of the nature of soil and plant and pollution on the 238U, 232Th, 222Rn and 220Rn concentrations in various natural honey samples using nuclear track detectors: Impact on the adult consumers

²³⁸U and ²³²Th concentrations as well as ²²²Rn and ²²⁰Rn α-activities per unit volume were measured in various natural honey samples collected from different regions in Morocco using CR-39 and LR-115 type II solid state nuclear track detectors (SSNTDs). These radionuclides were also measured in soils, plant flowers and nectar solutions corresponding to the honey samples studied. In addition, these radionuclides were measured in different imported honey samples. The measured ²³⁸U, ²³²Th, ²²²Rn and ²²⁰Rn concentrations ranged from (1.5±0.1) mBq kg⁻¹ to (10.6±0.6) mBq kg⁻¹, (1.1±0.1) mBq kg⁻¹ to (4.2±0.2) mBq kg⁻¹, (1.5±0.1) Bq kg⁻¹ to (10.6±0.6) Bq kg⁻¹ and (1.1±0.1) Bq kg⁻¹ to (4.2±0.2) Bq kg⁻¹ for the honey samples studied, respectively. Annual ²³⁸U, ²³²Th and ²²²Rn intakes by Moroccan adults from the consumption of honey were assessed. The influence of the nature of soil and plant on the ²³⁸U and ²³²Th contents of the studied honey samples was investigated. These measurements were completed by an investigation of the ²³⁸U and ²³²Th transfer between soils and plant flowers and that between plant flowers and honey, and also by the investigation of the influence of pollution due to different material dusts on ²³⁸U, ²³²Th and ²²²Rn in the honey samples studied. Committed equivalent doses due to the annual intake of ²³⁸U, ²³²Th and ²²²Rn were evaluated in the organs of adult members of the Moroccan rural population from the ingestion of the honey samples. The maximum total committed effective dose due to ²³⁸U, ²³²Th and ²²²Rn from the ingestion of natural honey by the Moroccan rural population was found to be equal to 0.64 μ Sv y⁻¹.     

12C(7Li,t)16O和20Ne(d,6Li)16O反应的研究

本文把用于处理重离子引起的单粒子转移反应的Goldfarb-Buttle方法推广到多粒子转移反应。计算了¹²C(⁷Li,t)¹⁶O和²⁰Ne(d,⁶Li)¹⁶O反应,用了¹⁶O的全相干波函数,考虑了某些反冲因素,并将结果与实验作了比较。