Investigation of fast neutron interaction with235U

The angular distribution of neutrons emitted by elastic, inelastic and fission processes on²³⁵U were measured at the incident neutron energies of 1.5, 1.9, 2.3, 4.0, 4.5, 5.0 and 5.5 MeV using nanosecond time-of-flight technique. The differential elastic scattering cross sections and their angular distributions at all the seven energies are presented. The total elastic scattering cross sections, angle and energy integrated cross sections for the inelastically scattered neutrons in energy bands of 200 keV, fission cross sections and the angular distributions of fission neutrons were extracted at 1.5, 1.9 and 2.3 MeV incident neutron energies. The energy distributions of the prompt fission neutrons and of the inelastically scattered neutrons are given at the incoming neutron energies of 1.5, 1.9 and 2.3 MeV; and the average fission neutron energies and the inelastic neutron evaporation temperatures were also evaluated at these energies.     

Neutron scattering from elemental silver

Differential neutron elastic-scattering cross sections of elemental silver were measured from 1.5 → 10 MeV at scattering angles distributed between ≈17° and 160°. Cross sections for ten inelastically scattered neutron groups were determined, corresponding to observed excitations of 328 ± 13, 419 ± 50, 748 ± 25, 908 ± 26, 1150 ± 38, 1286 ± 25, 1507 ± 20, 1623 ± 30, 1835 ± 20, and 1944 ± 26 keV, all of which were composites of contributions from the two isotopes ¹⁰⁷Ag and ¹⁰⁹Ag. The experimental results were interpreted in terms of the spherical-optical and rotational and vibrational coupled-channels models.     

Messung der Neutronenpolarisation bei der Reaktion12C(d,n 0)13N mit Hilfe der Mott-Schwinger-Streuung

The polarization of neutrons produced in the reaction¹²C(d, n ⁰)¹³N was measured. Deuterons from the Karlsruhe isochronous cyclotron were used to induce this reaction at 51,5 MeV laboratory energy. The degree of polarization was determined by using the special features of Mott-Schwinger scattering. With an uranium scatterer analysing efficiencies of up to 0.92 can be obtained at very small angles (0.23°). The analysing efficiency can be calculated if the differential cross section at 0° and the total cross section is known. These quantities were experimentally determined. The differential cross section for 49.4 MeV neutrons, scattered by uranium, was measured between 0.88° and 2.10°. By an extrapolation the value 43.4±2.6 b/sr was found for the nuclear differential cross section at zero degree. A total cross section ofσ _t=4.80±0.22 b was obtained. The neutron polarization was measured at a reaction angle of 24.5° and the result isP=?0.45±0.07. This value is fairly above the semiclassical 1/3 limit and can be only explained, if spin orbit forces are taken into account. For (d, n) reactions this is the first neutron-polarization measurement above an energy of 20 MeV.     

Elastische und unelastische Streuung von Elektronen an Gasen

The theoretical differential cross section for the elastic scattering and for the excitation of optical transitions in helium by electron impact has been refined in Born approximation by use of the two parameter Eckart eigenfunction for the ground state and for the excited states. The angular distributions of 25 kev electrons scattered elastically and inelastically by helium were measured in the angular range 2·3·10^?4≦?≦4·10^?2. The intensity distribution of the elastically scattered electrons is in accordance with the theoretical curve for?>7·10^?3 and is disturbed at smaller angles by the primary beam. Normalization of the experimental values to the theoretical elastic differential cross section leads to agreement between the experimental differential cross section for the excitation of the 2¹ P and 3¹ P state and the scattering formulae given in this paper. There are small systematic deviations (<20%) for the 2¹ P differential cross section in the angular range 3·10^?3<?<1·10^?2 only. The oscillator strength of these two transitions has been determined from the scattering measurements:f ₂₁=0·312±0·04 andf ₃₁=0·0898±0·006.     

Spin-flip probability for 7.6 MeV neutrons scattered inelastically (Q = −2.23 MeV) by a sulfur target

The spin-flip probability for 7.6 MeV (ΔE = 0.250 MeV) neutrons scattered inelastically (Q = ?2.23 MeV) from naturally occuring sulfur has been measured at scattering angles between 40° and 160° using a γ-correlated neutron time-of-flight method. The scattering by the natural sulfur target was assumed to be characteristic of ³²S. The results of the measurement were compared with an incoherent sum of statistical compound-nucleus (CN) and direct-interaction (DI) contributions. The DI contributions were obtained using either a DWBA calculation or the coupled-channel (CC) formalism. Neither combination of CN plus DI contributions reproduced the experimental spin-flip probability angular distribution which was peaked near 110° with a maximum value of 0.33 ± 0.08.     

Neutron total,scattering and inelastic Gamma-ray cross sections of yttrium at few MeV energies

Neutron total, scattering and (n; n′,γ) cross sections of elemental yttrium (⁸⁹Y) were measured in the few-MeV region. The neutron total-cross-section measurements were made with broad resolutions from ≈0.5 to 4.2MeV in steps of ?0.1 MeV. Neutron elastic- and inelastic-scattering cross sections were measured from ≈1.5 to 4.0 MeV, at incident-neutron energy intervals of ≈50keV and at ten or more scattering angles distributed between 20 and 160 degrees using neutron detection. Inelastic-scattering cross sections were also determined using the (n; n′,γ) reaction at incident energies from 1.6 to 3.8 MeV at intervals of 0.1 MeV. Gamma-rays and/or inelastically-scattered neutrons were observed corresponding to the excitation of levels at: 909.0±0.5, 1,507.4 ±0.3, 1,744.5±0.3, 2,222.6±0.5, 2,530±0.8, 2,566.4±1.0, 2,622.5±1.0, 2,871.9 ±1.5, 2,880.6±2.0, 3,067.0±2.0, 3,107.0±2.0, 3,140.0±2.0, 3,410.0±2.0, 3,450.0±2.0, 3,504.0 ±1.5, 3,514.0±2.0, 3,556.0±2.0, 3,619.0±3.0, 3,629.0±3.0 and 3,715.0±3.0 keV. The experimental results are discussed in terms of the spherical-optical-statistical, coupledchannels, and core-coupling models, and in the context of previously reported excitedlevel structure.     

Eine Anordnung für Experimente zur Elektronenstreuung unterhalb 60 MeV

The facilities for electron scattering experiments at the Darmstadt electron linear accelerator (60 MeV at zero current) are described. They include an energy analyzing system with three 40° magnets and a 120° double focussing (n=0.5) magnetic spectrometer. Spectra of electrons scattered inelastically from carbon are presented up to 20 MeV excitation energy. For the scattering peaks, total half widths down to about 100 keV are obtainable at 52 MeV. Energies of excited levels can be measured with an accuracy of ±10 keV in favourable cases.     

Neutron-helium scattering

Relative differential cross sections of neutrons elastically scattered from ⁴He were measured at neutron energies of 0.55, 0.84, 1.16 and 1.33 MeV. The scattered neutrons were detected in a time-of-flight spectrometer for c.m. angles ranging from 25° to 161°. The relative differential cross sections are compared to curves generated from phase shifts published elsewhere.     

Streuung von 25 keV-Elektronen an Gasen

The angular distribution of 25 kev electrons scattered elastically and inelastically by molecular hydrogen has been measured in the angular range 7·10^?4≦?≦4,3·10^?2. By the separation of the inelastically scattered electrons observation of deviations from the Debye Ehrenfest theory of the electron diffraction by molecules at small angles is possible. These deviations are due to the alteration of the electron density distribution of the hydrogen atoms induced by the bonding. The energy loss spectra at different scattering angles (energy resolution ≈1 ev) shows a strong peak atΔE=12,6 ev. At larger angles forΔE>15 ev a continuum appears. That part of the inelastic processes which leads to ionization of the molecule is raising with increasing scattering angle. Normalization of the experimental values to the theoretical elastic differential cross section enables comparison of the angular distribution of the 12,6 ev energy loss with the distribution calculated byRoscoe. The shape of the experimental curve is in fairly good agreement with the calculated one but the experimental values at small angles are 20–30% higher. For zero angle the energy loss spectrum is taken with better resolution (≈0,04 ev). It shows vibrational states of the Lyman and Werner band and higher terms. The probability of the excitation of some vibrational states of the Werner band (square of the overlapp integral) calculated here is inspite of the required approximations in excellent agreement with the measurement, while Hutchisson's result fails for the Lyman band.     

Differential cross section and polarization for 2.63 MeV neutrons scattered from 12C

The differential cross section and polarization of 2.63 MeV neutrons scattered from ¹²C have been measured at eight angles between 17° and 118° in the laboratory system. By simultaneously fitting the cross section and polarization data, a set of scattering phase shifts was obtained. The values of the resulting d-wave phase shifts were larger than those of other existing sets of phase shifts in the energy region. A subsequent R-function analysis, reflecting these larger d-wave phase shifts, gave excellent fits to other experimental data below 3 MeV neutron energy region. The influence of narrow states at 7.50 and 7.55 MeV excitation energy in ¹³C is discussed.     

Study of Compton scattering of gamma rays from atomic electrons

In the present work, measurements are made on the intensity and angular distribution of Compton scattered gamma rays of energy 279 keV from K-shell electrons of tin at scattering angles ranging from 30° to 150° and also determined the K-shell to free electron differential collision, absorption and scattering cross section ratio. For this purpose, two NaI(Tl) scintillation detectors working in coincidence with 30 nsec resolving time are used to record the events. The experimental results are compared with the available experimental and theoretical data.     

Measurement of the Neutron-Proton Differential Cross Section at 14.1 MeV

A new measurement of the differential cross section for neutron-proton scattering was performed at a neutron energy of 14.1 MeV. The neutrons were scattered from a polyethylene foil and the associated recoil protons were observed. Data were taken at 6 angles between 89.7° and 155.7° in the centre-of-mass system. Extensive Monte-Carlo simulations were performed in order to optimize the experimental setup and to reduce the influence of systematical errors. The data were normalized to the well-known neutron-proton total cross section. The overall uncertainty is about ±2%. The data are in excellent agreement with the prediction of the multi-energy phase shift analysis SM94 of Arndt and coworkers. Received December 21, 1995; revised November 20, 1996; accepted for publication December 23, 1996     

Fast-neutron total and scattering cross sections of58Ni

Neutron total cross sections of⁵⁸Ni were measured at 25 keV intervals from 0.9 to 4.5 MeV with 50–100 keV resolutions. Attention was given to self-shielding corrections to the observed total cross sections. Differential elastic- and inelastic-scattering cross sections were measured at 50 keV intervals from 1.35 to 4.0 MeV with 50–100 keV resolutions. Inelastic excitation of levels at 1.458±0.009, 2.462+-0.010, 2.791±0.015, 2.927+-0.012 and 3.059+-0.025 MeV was observed. The experimental results were interpreted in terms of optical-statistical and coupled-channels models.     

Small-angle neutron scattering from Pb and 238U between 0.6 and 2.2 MeV

Differential cross sections for neutrons scattered from natural Pb and 99.9 % isotopically pure ²³⁸U have been measured at 0.5°, 1.0°, and 1.5°. A neutron energy continuum was produced by bombarding a thick natural lithium target with a 4 MeV, nanosecond-pulsed proton beam. Neutron energies were determined by time-of-flight techniques. Flight paths from the neutron source to the scatterer and from the scatterer to the detector were each about 5 m. For the 0.5° measurements an annular detector geometry with an angular resolution of ± 0.1° was developed to maximize detection solid angle. Data were averaged over 100 keV intervals from 0.6 to 2.2 MeV and were corrected for backgrounds, multiple scattering and inelastic scattering. Measured cross sections were compared to optical-model calculations which included electromagnetic interactions of neutrons with the nuclear Coulomb field. Inclusion of an induced neutron electric dipole moment interaction was not warranted by the data. The angular dependence of the cross section was fitted with a function $\text{A + B}\text{cot}{}^2\text{case1}\text{2}$θ at each energy. Mean values of B for ²³⁸U are in agreement with theoretical predictions. Values of B for Pb are apparently 15 % too low.     

Study of the Three-Nucleon Force Effects in the 2H(p, n) Breakup Reaction at 170 MeV

For the study of three nucleon force (3NF) effects in the intermediate energy region, the differential cross sections and the vector analyzing power A _y were measured for the ²H(p, n) inclusive breakup reaction at 170 MeV. The polarized proton beam of 170 MeV was injected to the deuterated polyethylene (CD₂) target and the energy of scattered neutrons were deduce by TOF method. The data was compared with the results of the Faddeev calculations with and without 3NFs. Concerning about the differential cross sections, we can see large discrepancies between the data and the calculations in the region where the energies of scattered neutrons are low, which are similar to the results of the ²H(p, p) inclusive breakup reaction at 250 MeV.     

Fast-neutron total and scattering cross sections of elemental titanium

Energy-averaged total neutron cross sections of elemental titanium are measured from ? 1.0 to 4.5 MeV with statistical accuracies of ? 1%. Differential elastic neutron-scattering angular distributions are measured from 1.5 to 4.0 MeV at incident energy intervals of ≦ 0.2 MeV. Differential cross sections for the inelastic neutron excitation of “states” in titanium at 158 ± 26, 891 ± 8, 984 ± 15, 1428 ± 39, 1541 ± 30, 1670 ± 80, 2007 ± 8, 2304 ± 22, 2424 ± 16 and 2615 ± 10 keV are measured in the incident-neutron energy range 1.5 to 4.0 MeV. Neutrons corresponding to additional states at approximately 2845 and 3010 keV were qualitatively observed. The experimental results are interpreted in terms of an energy-averaged optical-statistical and coupled-channels models including consideration of collective vibrations. The implications of these models and their use in the context of strong fluctuating structure are discussed.     

Elastische und unelastische Streuung von Deuteronen an Sr,Zr, Nb,Pd und Ag bei 11,8 MeV

Continuing previous experiments on the elastic and inelastic scattering of 11·8MeV deuterons on medium weight nuclei, Sr, Zr, Nb, Pd, and Ag targets have been studied. In addition to elastically scattered deuterons, angular distributions of inelastically scattered deuterons have been obtained for one group in Sr, and three groups in Zr and Nb, respectively, between 20° and 165°. The correlation between the diffraction maxima is discussed in terms ofBlair's phase rule. As in our previous results, this rule works poorly in the comparison between elastic and inelastic angular distributions. However the strongly excited inelastic groups which are interpreted as collective vibrational states do follow this rule. In the case of Pd and Ag, energy spectra at several scattering angles have been measured. The integrated differential cross sections of the inelastically scattered deuterons atΘ=90° of all investigated elements are compared with those of previous measurements. They show the influence of closed shells but no systematic decrease or increase with increasing atomic weight.     

Charge exchange cross sections for He+ incident on Cs

The total charge-exchange cross section, σ₊₀, for He⁺ incident on Cs vapor has been measured in the energy range 0.5 to 41 keV. The cross section falls from (1664 ± 100) × 10^?17 cm² at 1.4 keV to (224 ± 20) × 10^-17 cm² at 41 keV. These measurements are compared with previous measurements and with theoretical calculations of this cross section.     

Wirkungsquerschnitte für elastische und unelastische Elektronenstreuung an amorphen Kohlenstoff- und Germaniumschichten

Absolute intensities of electrons scattered by amorphous carbon and germanium foils were measured for various energies (20–60 keV) and foil thicknesses (200–800 Å). Electrons scattered elastically were separated from those scattered inelastically by means of a retarding field. Thus total cross sectionsσ _e for elastic scattering andσ _u for inelastic scattering were obtained. Agreement of observed and theoretical values is satisfactory, especially regarding the dependence on electron energy.     

Scattering of fast neutrons on238U,average energy and angular distributions of fission neutrons

Angular distributions of neutrons elastically and inelastically scattered from²³⁸U have been measured with a time-of-flight spectrometer at seven incident neutron energies between 1.5 and 5.5 MeV. Inelastic angular distributions for groups of unresolved levels are given for incoming neutron energies of 1.5, 1.9 and 2.3 MeV. The corresponding neutron cross-sections were obtained relative to then-p scattering cross-sections. The average energies and angular distributions of the fission neutrons were extracted from the measured fission neutron spectra at 1.5,1.9 and 2.3 MeV. Cross-section calculations based on a spherical optical model have shown to be inadequate to describe the neutron-nucleus interaction in case of strong nuclear deformation. The experimental reality may be better approached, instead, if the calculations are made using a potential which takes into account the deformation of the target nucleus. Some of the present measurements are interpreted in this theoretical perspective.