Isochronal recovery of high-energy d-Be neutron damage in Cu,Nb, and Pt from 8 to 400 K

The isochronal recovery of high-energy d-Be neutron damage has been measured in Cu, Nb, and Pt from 8 to 400 K, using changes in the electrical resistivity. High-purity wire specimens were irradiated at 4.2 K with neutrons produced at the Oak Ridge Isochronous Cyclotron by the reaction of 40-MeV deuterons on a thick Be target. The resulting neutron energy spectrum was broadly peaked near 15 MeV. When compared with recent fission neutron results the recovery of d-Be neutron damage is slightly suppressed through stage II for Cu and Nb, but significantly reduced (about a factor of two) in stage I in Pt. This suggests that the primary damage state remains essentially unaltered in lighter elements as the mean neutron energy increases from 2 to 15 MeV, but that substantial configurational changes may occur over the same energy range for heavier elements. The results of recent damage-production measurements and room-temperature irradiations using d-Be neutrons are discussed in terms of the recovery spectra.     

Spectra of neutrons produced by 14-Mev neutrons in fissile materials

Measurements have been made of the energy distribution of neutrons produced in the passage of 14-Mev neutrons through layers of Th²³², U²³³, U²³⁵, U²³⁸ and Pu²³⁹. It is shown for all nuclides which were investigated that the secondary-neutron spectrum consists of two components; fission neutrons and evaporation neutrons. The dependence of the coefficients in the secondary neutron spectrum on the nuclear constants of the corresponding nuclides are determined, thus making it possible to find these coefficients without an experimental investigation of the neutron spectra.The authors wish to express their thanks to V. A. Davidenko for his interest in the work and discussion of the results, to A. G. Shlygin for taking part in the initial stages in the work, to Iu. A. Vasil'ev, G. S. Malkiel' and E. I. Sirotinin for exposing the plates in the accelerator, and to L. S. Andreev, L. V. Evseev, N. F. Nikolaev and V. A. Chernyshov for scanning the plates.     

Analysis of surface damage produced by pulsed laser ablation on metal Al and semiconductor Si

The suraface morphological changesd produced by Nd:YAG pulsed laser ablation of metal Al and semiconductor Si were carefully examined and analyzed by using scanning elkectron microscope.The formation mechanism of the droplets was discussed.and the reasons for formation of the microcracks on the laser irradiated area of the target surface were analyzed by calculating the thermal stress,the vapor pressure and the shock pressure induced by the laser supported detonation.     

Flux of secondary neutrons produced by 660 MeV protons in shielding

With the help of a set of threshold and resonance detectors, measurements were made of the spatial and energy distribution of secondary neutrons in graphite and nickel blocks. Absolute values of the neutron flux as a function of depth in an infinite slab were obtained for a plane, monodireetionat proton source. The energy distribution of the secondary neutrons in the energy range 2.5·10^–8 to 6.6·10² Mev was represented by seven groups. The magnitude of the dose behind plane nickel and graphite shielding as a function of thickness was also determined. The results are discussed.Translated from Atomnaya Énergiya, Vol. 18, No. 6, pp. 573–578, June, 1965     

Angle and energy characteristics of neutrons produced by a high-energy ion beam

Translated from Atomnaya Énergiya, Vol. 66, No. 3, pp. 213–215, March, 1989.     

Investigation of inelastic scattering of slow neutrons by polyethylene

Inelastic scattering of slow neutrons by polyethylene was studied in one of the horizontal channels of the VVR-M reactor at the Institute of Physics of the Academy of Sciences of the Ukainian SSR by the time of flight method. Energy spectra of neutrons scattered by polyethylene at 15°, 30°, 60°, 90° and 120° were measured for seven values of incident-neutron energy (15.4, 25.5, 49.4, 98,8, 136.1, 193.2, and 317 MeV). Doubly differential cross sections for neutron scattering by polyethylene were obtained, the scattering law S(, ) was found, and the frequency spectrum P() was generalized for polyethylene. Averaged characteristics for neutron scattering by polyethylene were computed (average energy release, logarithmic loss, etc.).Translated from Atomnaya Énergiya, Vol. 20, No. 1, pp. 30–35, January, 1966     

Energy spectra of neutrons produced by α-particles in thick targets of light elements

Energy spectra of neutrons produced by 4–5.5 MeV α-particles in thick targets of C, Mg, Al, Si, BN, CaF₂, Al₂O₃, SiO₂ and UO₂ have been determined. A Van de Graaff accelerator has been used as a pulsed α-particle source and neutrons were detected at 0, 30, 60, 100 and 140° by a calibrated NE 213 scintillator used as a time-of-flight spectrometer. Angle-integrated spectra were derived not only for the above materials but also for B, F and O. Energy integration delivers yields in good agreement with recent results from 4π moderator detector measurements.     

用缓发中子探测核弹头的技术探索

根据缓发中子的时间特征行为分析了缓发中子的中子输运过程,讨论了缓发中子探测核弹头的技术与方法。研究表明,测量缓发中子可以有效地探测到核弹头。但在不知道核弹头的内部设计信息的情况下,需用其他方法加以配合才能甄别真假核弹头。     

Observation and analysis of defect structure evolution from radiation damage by D-T fusion neutrons

A previous report on the defect structure evolution in metals, alloys and other materials by D-T fusion neutron irradiation (J. Nucl. Mater. 133&134 (1985) 85) was not accompanied with figures and illustrations, and they are all presented in this paper. More than half of the figures consists of electron micrographs, including the following: disordered zones to show the flight distances of interstitial atoms, amorphous zones in a semiconductor, grouped defect clusters developed from sub-cascade damage, stereo-micrographs of three dimensional configurations of defect clusters in sub-cascade groups, variation of defect structures with irradiation temperature, comparison of defect structures developed in thin foil and bulk specimens to demonstrate the role of free interstitials, homogeneous and localized formation of interstitial clustered defects, detection of invisible defects by the aid of electron illumination, and dislocation structures introduced by the deformation of irradiated materials. The other figures contain numerical results of micrograph analysis, which can be used for the estimation of neutron collision cross-section and primary knock-on energy. Point defect processes occurring during the damage structure evolution, including the dynamical effect of collisions, are discussed on the basis of experimental observations.     

Irradiation damage in Zircaloy-2 produced by high-dose ion bombardment

Damage produced in Zircaloy-2 by 5 MeV Ni ion bombardment was examined by transmission electron microscopy. Nickel ion bombardment was done over an integrated flux ranging from about $\text{5.6 × 10}{}^{15}$ to $\text{7 × 10}{}^{16}\text{Ni}{}^{\mathrm{++}}$ ions/cm² and over the temperatures from 300 to 600°C. The gross damage which occurred at low temperature consisted of dark unresolved areas and uniformly distributed ‘black dots’, somewhat similar to those observed in neutron-irradiated Zircaloy. With increasing irradiation temperature and dose, two features have appeared in the microstructures. One of the features was randomly oriented dislocation loops and the other well-defined alignment of defects with the projection of aligned defects oriented in the «101̄0å> directions. Detailed examination of these aligned defects revealed that they exhibit two kinds of images; one is associated with precipitation of second-phase material and the other with lattice displacement of matrix material. With further increase in irradiation temperature, the damage structure changed markedly to that of random dislocation network.