M. Kaminsky

Radiation blistering of polycrystalline niobium by helium‐ion implantation

The radiation blistering of polycrystalline niobium surfaces at room temperature has been investigated for different doses of helium ions implanted at 0.5 MeV and for different amounts of initial defect structure in the samples. The cold‐worked samples show large blisters (up to 500 μm in diameter), many of which are ruptured. In samples annealed before irradiation, the blistering at low doses (0.1 C/cm2) was lower than in the cold‐worked sample, but at a higher dose (1.0 C/cm2) the blistering was even greater. The observation of interconnecting bubbles offers a possible explanation for the formation of such large blisters at low temperatures.

Energy Distribution and Fragmentation Processes Resulting from Electron Impact on Propane and n‐Butane

The internal energy distribution has been determined for propane and n‐butane ions produced by electron impact. The method involves the use of differential ionization efficiency curves and depends on the validity of the linear threshold law for simple ionization. The experimental distributions are in fair agreement with theoretical calculations of Lennard‐Jones and Hall and indicate that the major fraction of the parent ions are formed by simple removal of a valence electron. Only a minor fraction of the parent ions are apparently formed by removal of one valence electron together with excitation of one or more remaining electrons. Breakdown curves for propane and n‐butane have been determined experimentally and, except for the energy scales, are in fair qualitative agreement with the predictions of the statistical theory of mass spectra. The discrepancy between theoretical and experimental energy scales is ascribed at least in part to inadequacy of the theoretical rate equations used in the statistical t...

Radiation blistering of structural materials for fusion devices and reactors

Abstract Radiation blistering can be an important erosion process when the structural components of controlled thermonuclear fusion devices or reactors are exposed to the impact of energetic particles leaving the plasma region. A brief review of some of the important parameters governing the radiation blistering process is given. Erosion rates associated with helium blistering in V, Nb and Type 304 stainless steel are reported for different irradiation temperatures and different projectile energies.

The significance of a correlation of blister diameter with skin thickness for Ni and Be for blistering models

It has been suggested that large lateral stresses introduced in an ion implanted surface layer may cause elastic instability and buckling of the implant layer (blister formation), and result in a relationship D/sub mp/ varies as t/sup 3///sup 2/ between the most probable blister diameter D/sub mp/ and the blister skin thickness, t, for metals such as Be, V, stainless steel, Nb and Mo. To test this relationship a systematic study of the correlation between blister diameter and skin thickness for helium blistering of annealed polycrystalline Ni and Be has been conducted for helium ion energies in the range of 15-300 keV. For beryllium the relationship between D/sub mp/ (..mu..m) and t(..mu..m) can be fitted by the expression D/sub mp/ = 24.6t/sup 1/./sup 25/ whereas for nickel a best fit is obtained for the expression D/sub mp/ = 1.24t/sup 1/./sup 15/. These results, together with our earlier results for Nb and V, show that the relationship between D/sub mp/ and t is strongly dependent on the type of metal studied and do not support the lateral stress model for blister formation.

On the correlation of blister diameter and blister skin thickness in helium‐ion‐irradiated Nb

A systematic study of the correlation between blister diameter and blister skin thickness has been performed for helium‐ion irradiation of monocrystalline and polycrystalline Nb for ion energies ranging from 20 to 500 keV. The results indicate that a relationship Dmp∝t1.50 between the most probable blister diameter, Dmp, and blister skin thickness, t, which has been suggested by other authors, does not exist for the various types of Nb targets studied. For example, for room‐temperature irradiation of annealed polycrystalline Nb the experimentally determined relationship is Dmp=10.3t1.22. Furthermore, the D‐t relationship was found to depend on the irradiation temperature in contrast to theoretical predictions by the lateral stress model of blister formation. These results do not appear to support the lateral stress model which predicts the relationship D∝t1.5. However, the experimentally determined relationships can be explained in part by the gas pressure model of blister formation.

Particle emission from solids under 14 MeV neutron impact

Abstract The recent studies of particle emission from cold-rolled niobium under 14 MeV neutron impact were extended to annealed polycrystalline niobium surfaces with various surface finishes. The type and amount of material released and deposited on a substrate surface were determined independently by four analytical techniques. Again, two types of deposits were discovered, - one in the form of large chunks, the other a more even layer covering the surface. The chunk deposites are not uniformly distributed over the collector area but are clustered along certain streaks or appear in certain patches. The direction of the streaks appears to be parallel to the direction of cold-rolling of the niobium sample and is not related to any microstructure of the collector surface. The number of deposited chunks decreases by about a factor of 25 if one irradiates an annealed polycrystalline biobium surface with a microfinish of ≅0.5 μ M instead of a cold-rolled niobium surface with a microfinish of only ≈ 5 μ m .

Magnesium interaction with the surface of calcite in seawater.

Magnesian calcite overgrowth containing 4 (� 2) mole percent magnesium carbonate forms on calcite exposed to natural seawater near the ocean surface. This magnesian calcite is approximately 30 percent less soluble in seawater than pure calcite. The formation of the magnesian calcite of reduced solubility may have a major influence on calcite accumulation in deep sea sediments.

Radiation blistering of Nb implanted sequentially with helium ions of different energies (3-500 keV)

Cold rolled, polycrystalline niobium samples were irradiated at room temperature with

The effect of dose on the evolution of cavities in 500-keV 4He+-ion irradiated nickel

sup 4

Correlation of blister diameter and blister skin thickness for helium‐bombarded V

He