A.N. Goland

Calculation of radiation effects as a function of incident neutron spectrum

Abstract A method for calculating radiation effects parameters as a function of neutron energy is described. The computer code DON is used to generate damage parameters from ENDF/B nuclear data. Both integral data such as neutron spectrum averaged cross-sections and recoil energy spectra are generated. These data were used to characterize initial defect production in Al, Cu, Nb and Au in selected fission reactor, fusion reactor and fusion simulation neutron spectra. The principal differences between fission and fusion damage are the spatial characteristics of defect production and the importance of non-elastic scattering (e.g. He production). The comparison of the damage produced in one spectrum with that produced in another is dependent on the model or parameter chosen to represent the damage. This dependency is important in analyzing simulation spectra for fission and fusion reactor radiation damage problems.

Radiation damage parameters in multicomponent nonmetals

Abstract Evaluations of contributions to radiation damage parameters in nonmetals are made for several neutron and gamma-ray interactions. Damage parameters for C, Al 2 O 3 , Si 3 N 4 , and MgAl 2 O 4 are evaluated for neutron spectra from the EBR-II, ORR, and LPTR reactors, for a hypothetical first-wall fusion spectrum, for a 14-MeV neutron spectrum, and for a neutron spectrum from the Fusion Materials Irradiation Test Facility being built at HEDL. Included in these evaluations are calculations of recoil atom damage initiated by neutrons and gamma-rays, gas production rates, energy absorbed through electronic processes, and displacement damage initiated by repulsion between a recoil atom and atoms it ionizes (ionization-assisted displacements). Evaluations were performed using the damage program DON with either the Robinson form of the Lindhard damage energy function or with special damage energy or displacement functions generated specifically for Al 2 O 3 , Si 3 N 4 , and MgAl 2 O 4 by Coulter and Parkin.

The effects of irradiation at cryogenic temperatures and electron irradiation on Tc and the transport properties of A-15 superconductors☆

The electrical resistivity ρ and Tc have been measured on vapor deposited films of Nb3Ge and Nb3Sn subjected to α-particle and electron irradiation. Both Nb3Sn and Nb3Ge films held at 30 K were irradiated with 2.5 MeV α particles. Tc and ρ0, the electrical resistivity at 25 K, were measured in situ as a function of fluence without warming up the samples. In addition, Nb3Sn films held at 50°C were irradiated with 2.0 MeV electrons. Tc was found to correlate with ρ0, which implies that Tc is affected by the total defect concentration. Of particular interest is the shape of the Tc vs. ρ0 curve for low fluences. A discussion will be given of why this low fluence region is important in distinguishing between different models of Tc depressions. We believe that the strong depression in Tc with increasing ρ0 (until saturation of Tc) is due to smearing of the density of states. The density of states in the damaged films was estimated from critical field data, along with measurement of ρ0.

Integrating low-temperature methanol synthesis and CO2 sequestration technologies: application to IGCC plants

Abstract Coupling a low-temperature once-through methanol synthesis process with CO 2 separation technology would provide an option for integrated gasification combined cycle (IGCC) power plants to address the CO 2 mitigation issue and also create the capability to utilize methanol as a peak-shaving fuel. Data are presented that show that several nickel complexes activated by alkoxide bases catalyze facile synthesis of methanol from synthesis gas (primarily a mixture of CO and H 2 ) in homogeneous liquid phase under mild conditions of temperature ( 2 mitigation. The potential of this low-temperature methanol synthesis approach is considered in light of the recent advances in CO 2 sequestration technologies. A successful development of this technology may also provide an atom-economical pathway to transport remote natural gas in the form of methanol, a liquid energy-carrier.

Tracing the evolution of bubbles in helium-injected aluminum by means of positron annihilation

Abstract Pure aluminum was injected with 0.6 appm of helium. Positron lifetime measurements were performed following isochronal annealing between 25 and 600° C. Transmission electron micrographs were taken after several of these anneals. The results are consistent with a model in which the injected helium quickly becomes substitutional. This substitutional helium is a trapping site for positrons. By monitoring the concentration and size of this trapping site through the measurement of the positron lifetimes it is concluded that migration of the helium begins at ~ 100°C and that helium continually agglomerates up to ~250°C. Above this temperature the increasing size of the trapping site indicates bubble growth. Bubble growth proceeds up to 600° C, but whether by continued arrival of helium at nucleation sites or by bubble migration and coalescence (or both) being indeterminable. The major stage of bubble growth is between 300 and 600° C. The electron microscopy verified the presence of bubbles both in grain boundaries and matrix after annealing to 625°C, but only cavities in grain boundaries were observed in annealing to 500° C. Positron-lifetime measurements are a useful complement to electron microscopy in the study of bubbles in metals, especially in the early stages of the nucleation and growth of small cavities.

Use of Li(d,n) Neutrons for Simulation of Radiation Effects in Fusion Reactors

In this paper we show that the neutron spectrum from high-energy deuteron bombardment of a thick Li target is suitable for simulation of radiation effects in a fusion reactor. Neutron spectra from 15, 20, 25, 30 and 35-MeV deuterons incident, respectively, on a 2-cm thick Li target are reported. For these spectra, a recently-developed computer code was used to evaluate damage-energy cross sections, primary recoil energy distributions, and spectrum-averaged reaction cross sections in several metals. The results indicate that a (d,n) source can simulate the energy dependence of the recoil spectra, and the rate of helium production anticipated in a real fusion reactor

Experimental evaluation of the primary damage process — neutron energy effects☆

Abstract Experimental evaluation of the neutron energy dependence of the primary damage state depends upon a number of theoretical concepts. This state can only be observed after low- or perhaps ambient-temperature, low-fluence irradiations. The primary recoil energy spectrum, which determines the character of the displacement cascades, can be calculated if dosimetry has provided an accurate neutron spectrum. A review of experimental results relating neutron-energy effects shows that damage energy or damage energy cross section has often been a reliable correlation parameter for primary damage state experiments. However, the forthcoming emphasis on higher irradiation temperatures, more complex alloys and microstructural evolution has fostered a search for additional meaningful correlation parameters.

Defect production in thorium by low-temperature electron irradiation

The increase in the electrical resistivity of 99.98% pure thorium per unit electron flux was measured as a function of incident electron energy from 1.6 to 2.8 MeV. During irradiation, the temperature of foil samples was held below the temperature of the first major recovery peak at 10 deg K. For unit displacement probability, the theoretical displacement cross section best reproduces the experimental damage rates at an effective threshold displacement energy of 35 eV and a Frenkel resistivity of 15 x 10/sup -4/ ohm-cm per unit fractional concentration of Frenkel pairs. (auth)

Calculation of radiation damage in insulators for fusion reactors

The MORSE neutron transport code has been used to characterize the neutron and gamma ray fluxes in a typical irradiation cave from a Li(d,n) neutron source. Recoil-atom damage and gas generation have been evaluated for Al/sub 2/O/sub 3/ and Si/sub 3/N/sub 4/ using the damage program DON.

Studies of the Transition Temperature and Normal State Resistivity of Nb3Ge and Nb Films

Correlations between Tc and specific features of the normal state resistance vs temperature curves are discussed for both Nb3Ge and ion damaged Nb films. Of particular interest is the correlation between Tc and ρo in Nb3Ge films.