Bulk Radiation Research Articles

Radiation-induced bulk polymerization of N-vinylpyrrolidone in aqueous solutions and investigation of the molecular characteristics of polyvinylpyrrolidone

The bulk radiation polymerization of N-vinylpyrrolidone in water is studied. The molecular mass characteristics of this compound are studied as a function of process conditons by viscometry, GPC, and light scattering methods. A relation is obtained between the intrinsic viscosity and the molecular mass in ethanol, which is described over the whole of the molecular mass range by the Mark-Kuhn-Howink equation [ η] = 1.05 × 10 −2 M 0.75, and values of the conformational parameters are obtained.

Improved operating modes and the evaluation of confinement improvement

Various improved confinement modes of tokamaks are surveyed and their characteristics reviewed. In search of optimal plasma performance for a fusion reactor, the core performance has been examined. The fusion product near ignition, where Q is large, is used for the evaluation. The dilution of the fuel ions and the profile effect are examined in combination with the effect of increased τE.Because of the fuel dilution and of the bulk radiation, optimal performance does not always correspond to modes with the longest τE. We confirm that tokamak research should, at present, proceed to the discharge mode with the highest fusion product rather than that with the longest τE. If the time evolution is taken into account, the problem becomes more severe. Control of the fuel purity is surely needed to ensure long pulse operation,which certainly requires further extensive research.

Improved modes and the evaluation of confinement improvement.

Various improved confinement modes in tokamak are surveyed and their characteristics are reviewed. To search for the potentiality as a fusion core plasma in reactor, an examination to evaluate the core performance has been made. The fusion product near the ignition condition, where Q is large, is used for the evaluation. The dilution of the fuel ion and the profile effect are simultaneously examined together with the obtained τE. Because of the fuel dilution and of the bulk radiation, the good performance does not always correspond to the mode with long r E. If their time evolution is taken into account the problem becomes more serious. Further extensive research to control the fuel purity is surely needed to ensure the long pulse operation.

Optical characterization of radiative semiconductors

This paper describes a direct photoluminescent method of characterizing high quantum efficiency semiconductors in terms of an “effective absorption coefficient” which is a function of the absorption coefficient and of the diffusion length of excess minority carriers injected optically. The results obtained by this method indicate that the diffusion lengths in unintentionally doped (pure) and n and p-type GaAs can be in excess of 0.03 cm at room temperature, and that surface and bulk radiation processes in these materials can be separated.

Tunnel recombination of surface and bulk radiation defects in finely dispersed CaO at 4.2 and 77 K

Recombination of radiation defects in CaO is shown to occur through electron tunneling from surface Fs+ to V−-center stabilized in the bulk.

Bulk Radiation by Surface Acoustic Waves Propagating Under a Grating

Attenuation d'une onde de Rayleigh due a la diffusion dans le volume par un reseau periodique sur la surface d'un milieu elastique. Cas d'une onde de Rayleigh tombant sous incidence normale et oblique sur des reseaux a sillons dans LiNbO 3 a coupe Y a direction de propagation Z

Induced swelling in radiation damaged ZrSiO 4

A hydrothermal gelation method was used to prepare phase pure polycrystalline ZrSiO 4 which was sintered to 95% theoretical density. Actinide doped samples containing 10 wt% 238Pu were prepared by an analogous procedure and incurred bulk radiation damage through internal alpha-decay processes. Undoped samples were subjected to external irradiation from 5.5 MeV alpha sources, and from a 60Co gamma source. Actinide doped ZrSiO 4 exhibits dose dependent swelling caused by displacement processes leading to ingrowth of amorphous regions. Bulk density and XRD measurements, as a function of dose, showed first order exponential ingrowth behavior similar to that observed in other actinide doped materials. Results are compared with reported data for naturally damaged crystals subjected to significantly lower alpha decay rates. No significant dose rate dependence on damage ingrowth has been observed. Kinetic models for the observed dose dependent swelling are proposed and rate constants for damage ingrowth in synthetic and natural crystals are compared. To study localized damage induced by both external alpha and gamma irradiation, vibrational Raman measurements were obtained for several accumulated doses. Results indicate that the initial stage of damage ingrowth is confined to the silicate sublattice. Vibrational results will be discussed in terms of microstructural changes which result from irradiation.

Radiation dosimetry for quality control of food preservation and disinfestation

In the use of x and gamma rays and scanned electron beams to extend the shelf life of food by delay of sprouting and ripening, killing of microbes, and control of insect population, quality assurance is provided by standardized radiation dosimetry. By strategic placement of calibrated dosimeters that are sufficiently stable and reproducible, it is possible to monitor minimum and maximum radiation absorbed dose levels and dose uniformity for a given processed foodstuff. The dosimetry procedure is especially important in the commisioning of a process and in making adjustments of process parameters (e.g. conveyor speed) to meet changes that occur in product and source parameters (e.g. bulk density and radiation spectrum). Routine dosimetry methods and certain corrections of dosimetry data may be selected for the radiations used in typical food processes.

Thin film on metal: Resonance effects in light diffraction at the edge

The theory of light diffraction at the impedance step is developed which allows for an additional surface wave. Reflection and transmission coefficients for a surface wave are determined as well as radiative losses at the diffraction of the surface polaritons (SP). Coefficients of transformation of the incident bulk radiation energy to the SP energy are calculated. Resonance effects in the mirror reflection of bulk radiation are investigated. Possible application of the predicted effects for the study of optical properties of thin films and transition layers are discussed.

Annual Heat Gain of the Tropical Atlantic Computed from Subsurface Ocean Data

Abstract Charts are presented which show the seasonal and annual rates of heat gain of the tropical North Atlantic Ocean. These rates have been computed using subsurface oceanographic data and wind-stress data. In these computations the interseasonal rates of heat gain are determined primarily by the rate of local heating, and their magnitude, in general, is several times larger than the annual rate. The annual mean rate implies a net heat loss over much of the tropical ocean. The probable mechanism for this heat loss is an annual excess in cooling due to evaporation over heating due to the net incoming radiation. The present results show similarities to some results of previous authors who have based their calculations on bulk aerodynamical formulas and radiation estimates.

The European programme on fusion materials

After an assessment of the irradiation methods for simulating bulk radiation damage in candidate fusion materials, a survey is given of the present experimental and theoretical investigations performed by the European Communities in the field of the microstructural evolution and the mechanical behaviour of materials under irradiation. Some attention is also paid to the efforts pertaining to corrosion effects. Finally an outline is presented of the main trends of the future five-year programme and of the prospects for an increased international co-operation.

Radiation Patterns of Bulk Modes from a Finite Interdigital Transducer on Y-Z LiNbO3

Radiation patterns of bulk acoustic modes from a finite in- terdigital transducer on Y-Z LiNb03 were found using moment method and then compared with the experimental results. The power density radiation patterns of shear and longitudinal bulk modes were computed as functionsof the radiation angle, the electrode metallization ratio, and the frequency. It was shown that a SAW transducer can be very effi- ciently used for shear bulk wave excitation. For instance, at the sec- ond harmonic of the Rayleigh wave the percentage power of the shear, longitudinal, and SAW is 67.2,26.4, and 6.4 percent, respectively. The bulk power density distribution versus radiation angle does not change in form with a change in the metallization ratio. The SAW power density increases with increasing values of the metallization ratio.

Radiation enhanced diffusion in F.C.C. metals

Abstract Near surface and bulk radiation enhanced self-diffusion of Ni0.3 in nickel was measured after irradiations with 2 MeV electrons. In the temperature range between 550 and 800°K the bulk diffusion coefficient is DRad = 1.347 × 10−12 exp (-0.41/kT cm2/s) for a flux of 20 μA/cm2. The measured diffusion coefficients are at least two orders of magnitude larger than those predicted by theories based either on the one- or the two- interstitial model. This discrepancy between experiment and theory is resolved for the two-interstitial model by considering the interactions between sell-interstitials and vacancies during their life times. These interactions led to an effective migration energy of self-interstitials of EM eff , = 0.82 eV. which is smaller than EM = 1.0 eV. The experimental data can be described by DRad α2 n f(Kvell 1)1 2. Radiation enhanced diffusion data obtained in other laboratories for gold in gold. silver in silver, for copper and for gold in aluminium arc analysed and results analogous ...

The depth resolution of sputter profiling

It is shown that the bulk radiation damage accompanying sputtering events sets ultimate limits to the depth resolution attainable in sputter profiling. These limits have been reached in a few cases but most published experimental resolutions are dominated either by instrumental effects or deterioration of depth resolution caused by surface-topography changes. The radiation-damage induced mixing is called “cascade mixing”. Guidelines for selection of projectile species and energies to minimize such mixing are given and numerical estimates for attainable depth resolutions are presented. Finally, the influence of cascade mixing is assessed relative to that of recoil implantation.

Effecis of Electron Irradiation on Operational Amplifiers

Second generation operational amplifiers, which are widely used in space applications, show considerable sensitivity to electron irradiation at fluences corresponding to unshielded long term operation in the earth synchronous orbit. Surface and bulk radiation effects are described for different device types. It is shown that the surface effects are very process dependent. Guidelines are given for the selection of reasonably radiation resistant components.

High-Energy Radiation Damage in Silicon Transistors

An experimental investigation of electron and gamma ray damage in silicon transistors is presented. At low values of fluence (?e < 1014 electrons/cm2), loss in common-emitter dc current gain of medium frequency n-p-n planar transistors at collector currents of one to 10 milliamperes is attributed to changes in the surface recombination velocity. Displacement-induced recombination centers in the base region cause a reduction in gain when ?e is greater than 1014 electrons/cm2. A technique of saturating the surface damage with low energy electrons (E = 125 kev) so as to permit a separation of surface and bulk damage is demonstrated. The minority-carrier lifetime-damage constant, K?, has been estimated from the separated bulk-damage curve. It agrees with the value determined from electron irradiation of a low frequency (f?b = 1.25 Mc/sec) mesa n-p-n transistor which is shown to suffer degradation in gain only from bulk recombination current losses within the base region. Surface damage from both electrons and gamma rays is annealed at 250°C or by injecting emitter currents of 200 milliamperes which generate a high internal temperature. In contrast to this behavior, electron irradiation of p-n-p transistors caused loss in gain which is attributed to bulk damage. Damage constants, K?, determined from the data show that p-n-p transistors suffer bulk radiation damage about five times greater than n-p-n transistors.