a passive l O - c m - t h i c k l e a d shield in a l a b o r a t o r y on the ground during a medium m e a s u r e m e n t time (2 h) and in the case of a small sample volume (50 ml) is not above the a d m i s s i b l e concentration of the nuclides in water and is for some of the nuclides even much lower to a degree which suffices for many t a s k s of environmental protection~ If it is n e c e s s a r y to determine a much lower activity, the background of the c o s m i c radiation can be reduced by t r a n s f e r r i n g the s p e c t r o m e t e r into an underground laboratory, as indicated in [4-6], or by e m ploying an active detector shield. LITERATURE !o

2. 3. 4.

5o

6,

THE

CITED

Yu. V. Khol'nov, V. P. Chechev, V. G. Nedovesov, et al., C h a r a c t e r i s t i c s of the Radiations of Radioactive Nuclides Employed in the National Economy [in Russian], Atomizdat, Moscow (1980). V. A. Dement'ev, The Measurement of Low Activities of Radioactive Samples [in Russian], Atomizdat, Moscow (1967}. Radiation Safety Standards NRB-76 and Basic Health Regulations OSP-72/80 [in Russian], t~nergoizdat, Moscow (1981}. L. I. Shekherov, Yao D. Prodanov, G. V. Stefanov, et al., nComparative m e a s u r e m e n t s of the radioactive background of g a m m a radiation in v a r i o u s shielding c h a m b e r s with the aid of a g e r m a n i u m - l i t h i u m detector, ~ in: Radiation Safety in the Operation of Atomic P o w e r Stations [in Russian], Book 4, ~ n e r g o atomizdat, Moscow (1984), pp. 3-10. L. I. Shekherov, Ya. D. Prodanov, G. I. Stefanov, et al~ "A low-background Ge(Li} s p e c t r o m e t e r under various conditions of shielding, ~ in: Radiation Safety in the Operation of Atomic Power Stations [in Russian], Book 5, l~nergoatomizdat, Moscow (1984}, pp. 160-176. O. S~ Tsvetkov and N. G. Triumfov, ~The m e a s u r e m e n t of low concentrations of radionuclides under the conditions of an underground l a b o r a t o r y shielded f r o m c o s m i c radiation, ~ in: Radiation Safety in the Operation of Atomic Power Stations [in Russian], Book 5, t~nergoatomizdat, Moscow (1984), pp. 177-185~

KINETICS

FROM

A 20-45

OF

LIBERATING

NICKEL

ALLOY

IMPLANTED

HELIUM

IN H I G H - T E M P E R A T U R E

DEFORMATIONS B. A. Kalin, A. V. M a r k i n , A . A . V o l k o v , S. No K o r s h u n o v , D. M. S k o r o v , V. T . F e d o t o v , I. I. C h e r n o v , a n d A . N. M a n s u r o v a

UDC 669.018.8 : 621.039.531

Cold helium, desorbed f r o m the f i r s t wall by heating and radiation-induced e r o s i o n will significantly contribute to the energy balance of the plasma in a t h e r m o n u c l e a r r e a c t o r . M e c h a n i c a l s t r e s s and deformations a r i s e in the f i r s t wall during the operation of the r e a c t o r and substantially affect the s u r f a c e destruction by erosion. The goal of the present work is to develop a method of recording the desorption of helium during a h i g h - t e m p e r a t u r e deformation. The experiment setup comprised a unit for mechanical testing in vacuum and a P T I - 1 0 m a s s s p e c t r o meter. The sample was heated by passing through it an electric c u r r e n t so that good vacuum and low t h e r m a l inertia w e r e guaranteed. In o r d e r to obtain t e m p e r a t u r e levelling over the useful length, a sample of special construction [1] was used. The method was tested with Kh20N45 alloy s a m p l e s which had been previously i r radiated with 40-keV helium ions at 370~ and up to a flux of 3 "1021 m -2 (Fig. 1). The desorption rate decreased uniformly during a 2-h exposure at 1000~ (see Fig. 2). After applying a load, an incubation period of 100 sec was observed within which the desorption rate was constant. Then the desorption r a t e increased sharply. A s t r e s s reduction reduced the desorption rate. When the s t r e s s was increased again, the incubation period did not show up. The activation energy H of p r o c e s s e s accounting for the creep and the helium desorption was determined with the technique of small t e m p e r a t u r e jumps based on a formula of [2] T r a n s l a t e d f r o m Atomnaya l~nergiya, Vol. 59, No. 2, p. 150, August, 1985. Original a r t i c l e submitted J a n u a r y 3, 1984.

712

0038-531X/85/5902-0712509.50 9 1986 Plenum Publishing C o r p o r a t i o n

~,

o

2t zUOF. . . . . . . . .

zao

800

soo

~" a"

T,K

Fig. I

}

2

3 t,h

Fig~ 2

Fig. 1. Helium liberation Q f r o m the Kh20N45 alloy in the case of 1000"K heating at a r a t e of 0.5 K / s e c . Fig. 2o Dependence of the r a t e of helium liberation upon the mechanical s t r e s s 0".

ll--:kT ~--~ln q (T+AT) ~!(T)

'

where k denotes the Boltzmann constant; T, absolute t e m p e r a t u r e ; and q, rate of creep or desorption. The calculated activation e n e r g i e s coincided within the e r r o r limits and amounted to 3 eV. This means that t h e r e exists a vacancy m e c h a n i s m of helium migration in the p a r t i c u l a r alloy at 1000~ The dependence which we obtained f o r the r a t e of helium liberation upon the mechanical s t r e s s s e e m s to be associated with an i n c r e a s e in the mobility of the helium atoms by diffusion because the v a c a n c y c o n c e n t r a tion r i s e s in deformations, Besides that, s t r u c t u r e studies of the alloy, which were made with an electron m i c r o s c o p e , have shown that slip along boundaries and sliding inside g r a i n s o c c u r after a deformation. This leads to the development of 1 0 - 1 0 0 - n m - h i g h steps on the sample s u r f a c e and implies the breakup of the implanted l a y e r (the a s s u m e d range of the 40-keV helium ions in the alloy is 200 nm). Accordingly, the d e s o r p tion rate must depend upon the deformation rate, and the incubation period must obviously be a s s o c i a t e d with a delayed deformation of the s u r f a c e l a y e r of the sample. Thus, our r e s u l t s indicated that deformations substantially affect the liberation of helium. This must be taken into account in the energy balance of the p l a s m a . LITERATURE 1.

2.

CITED

"A sample for studying the strength of m a t e r i a l s under high t e m p e r a t u r e s , " I n v e n t o r ' s Certificate No. 974,208, Byull. Izobret., No. 42, 196 (1982)o F. Garofalo, The Laws of Creep and of L o n g - T e r m Strength of Metals [in Russian], Metallurgiya, Moscow (1978).

E RRATU M The article by E. P. Veretenkin et al. "Use of m e t a l l i c lithium f o r detecting s o l a r n e u t r i n o s " (Vol. 58, 1, pp. 82-83 (1985)) contains a misprint. Line 13 of the f i r s t p a r a g r a p h should r e a d : "and this is 1000 t i m e s lower than the usual contamination of the surrounding m a t e r i a l s . "

No.

713