372595896

JPRS-UMS-92-003 16 March 1992

TREATMENTS

39

three to four orders of magnitude greater than the sputtering coefficient as a result of scattering of the accelerated ions on the atoms of the lattice. When a quartz surface is irradiated in a close-to-optimal modę, it is possible to achieve a minimal P-phase layer thickness (i.e., a thickness not exceeding several lengths of the projective run of the accelerated ions). The optimal ion energy values were found to rangę from 0.5 to 2 MeV, the optimal current density was found to lie between 100 and 1,000 A/cm², and the optimal pulse duration was determined to be between 100 and 200 ns. Irradiation of polished quartz surfaces by a high-power nanosecónd ion beam was found to have no detrimental effects on surface relief and, in some cases, even improved it. The researchers proposed a thermal erosion model that ade-quately describes the vaporization of Silicon dioxide molecules and phase transformation kinetics occurring in irradiated quartz. Figures 5; references 9: 5 Russian, 4 Western.

Sets of Radiation EfTect Functions in the Problem of Predicting the Stability of Materials and Instruments in Ionizing Radiation Fields *

927D0089D Moscow FIZIKA IKHIM1YA OBRABOTKI MATERIALOV in Russian No 6,

Nov-Dec 91 (manuscript received 14 May 90) pp 33-38

[Article by V.I. Ostroumov, G.G. Solovyev, and A.I. Trufanov, Irkutsk, Moscow, and Leningrad]

UDC 539.1.043    “    •

[Abstract] Several approaches have been taken to the problem of predicting the damage inflicted on different materials and equipment subjected to ionizing radiation fields such as those existing in outer space. One such approach is based on the concept of the radiation effect function. The concept of the radiation effect function is in tum based on the assumption that in a materiał whose primary damage mechanism is one of shock damage, the first atoms knocked off by bombarding particles that possess an identical energy contribute identically to the ensuing changes in the given substance’s properties. Although the approach does have its limitations, it has been used as a framework for examining all types of ionizing radiation (including electron, positrón, gamma-quantum, proton, neutron, etc.) with an arbitrary energy distribution. The authors of the study examined the possibility of expanding the set of problems that may be solved by using a previously developed method of predicting the degradation of the electrophysical parameters of materials and equipment based on the concept of a radiation effect function. They focused their analysis on the problems of giving adequate consideration to the effect of fluence and the intensity of irradiation. Their analysis led them to conclude that the radiation effect function approach to predicting radiation stability may be extended to the solution of most problems concemed with damage sustained by materials and equipment in ionizing radiation fields. Specifically, they concluded that the approach is valid in such practically important problems as problems in which materials are subjected to extensive variations in fluence and bombarding particie flux density or else to simultaneous irradiation by several types of particles. The analysis presented further demonstrated that radiation effect functions may be reconstructed on the basis of data from independent ground experiments on readily accessible and econom-ical testing units. Figurę 1; references 11 (Russian). .

The Effect of y- and Electron Irradiation on the Optical Properties of Barium-Sodium-Niobate (Ba₂NaNb₅0₁₅) Crystals

927D0089E Moscow FIZIKA IKHIMIYA OBRABOTKI MATERIALOV in Russian No 6,

Nov-Dec 91 (manuscript recei\ed 15 May 90) pp 39-42

[Article by S.A. Baryshev, G.A. Yermakov, V.N. Kara-sev, V.P. Nosov, and S.V. Protasova, Moscow]

UDC 535/34:621.

[Abstract] The authors of the study examined the effect of electron and y-irradiation on the process of the twinning of Ba₂NaNb₅0_I5 crystals and on the magnitude of the optical loss coefficient (K) in crystals at the wavelength of a neodymium laser (1,064 nm). Ba₂NaNb₅0₁₅ crystals in the form of parallelepipeds measuring 12 x 5.0 x 3.5 mm along the X, Y, and Z axes were grown by the Czochralski method. They were irradiated with a y-quantum in the amount of 1.25 MeV. During the irradiation, the specimens’ temperaturę did not exceed 30°C. The irradiated specimens then under-went a twinning process that included heating to a temperaturę of 260-300°C, holding at the said temperaturę under a load applied perpendicular to the (100) piane of a tetragonal crystal celi, and cooling (also under a load) to room temperaturę. Nonirradiated control specimens were subjected to the same twinning regimen. Both before and after the twinning, the researchers measured the test and control specimens’ refractivity gradient (An) along the direction (010) at X * 632.8 nm and the transmission coefficients at the wavelengths \ = 532 and 1,064 nm. Preliminary y-irradiation of the Ba₂NaNb₅0₁s crystals was found to have a significant effect on their twinning process. The refractivity gradient of the irradiated crystals after twinning did not exceed 10*⁵, whereas that of the nonirradiated crystals was between 10*⁴ and 10‘⁵. Notably, the period for which the irradiated crystals were held under a load was much shorter (by a factor of 3 to 5). The measurements of the transmission coefficient at X » 532.8 nm revealed that preliminary y-irradiation followed by thermomechanical treatment resulted in a 10% reduction in the Ba₂NaNb₅O_l5 crystals’ optical sensitivity to irradiation in the dose rangę from 10² to 10⁶ Gy. The same effect was achieved by heat treatment in air at 650°C for 5 to 15 hours. The transmission coefficients of both the test and control specimens measured at X = 1,064 nm remained virtually unchanged from their starting values.