Study of Internal Indium Oxidation in Silver by TDPAC
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Nuclear and Electron Des''ance Spectroscooies -nDplinto -uterials Science
415 STUDY OF INTERNAL INDIUM OXIDATION IN SILVER BY TDPAC A. F. PASQUEVICH, F. H. SANCHEZ*, A. G. BIBILONI*, C. P. MASSOLO= and A. LOPEZ-GARCIA*# Departamento de Fisica, Facultad de Ciencias Exactas, Universidad Nacional de La Plata, C.C. 67, 1900 La Plata, Argentina ABSTRACT Internal oxidation of indium in a silver matrix is studied by time-differential perturbed angular correlations. The oxidizer treatments were performed in air at 1 atm. Our results are consistent with the formation of different In-O complexes. The time-differential perturbed angular correlation (TDPAC) technique permits the study, through the hyperfine-electric quadrupole interaction, of defects and impurities effects on probe nuclei in cubic metals. Here we report first results on internal oxidation of indium in silver obtained by this technique. The indium activity was obtained by means of the 1 1'"Ag(,,2n)'' In nuclear reaction on 99.99 at % purity and 500 pm thick silver foil targets. The irradiated foils were encapsulated in quartz tubes at about 10-3 Torr and melted in order to procure an homogeneous distribution of the radioactive impurities and to get rid of interactions associated with radiation damage. Finally, the samples were rolled to a thickness of about 600 L.m. The radioactive impurity concentration in all cases remained below 5 ppm. Before each sequence of oxidation treatments the absence of any quadrupole interaction was verified. See Fig. la for a typical result. Treatments done in air and in 02 atmosphere led to equivalent results. Hereafter we present only those results obtained in air at p = 1 atm. For the TDPAC measurements, all done on the " cascade 171 keV - 243 keV in ...Cd, a conventional two NaI(Tl)-detector setup with standard electronics was used. The movable detector chanqed its position every 1800s ano from the measurer: ](90 0 ,t), N(130 0 ,t) coincidence counting rates the asymmetry ratios 0 A~t) = 2 N(180 N(180 0 ,t) ,t)
0 -+ N(90 ,t) 2N(900,t)
AexpG 22 22 (t)
were calculated after corrections for random coincidences. typical result is shown in fig. lb.
*Member of CONICET, Argentina. =Member of CIC Prov. Buenos Aires, Argentina. #Present address: Rutgers University, Nuclear Physics Laboratory, New Brunswick, N. J. 08903, U.S.A.
(1) A
416
A(t)
(a) -. 150 -
-. 100 -
(b) 1-r1. 1
-. 050-
I
I
100
200
t(ns) Fig. 1. Typical TDPAC spectra at room temperature. (a) after a treatment of 90 min at 450'C and 0.5 atm N2 . (b) after a similar treatment on 02. The full line shows the fitted curve to the data. The calculated A(t)-value has been fitted A(t) = A2exp {f + 22 0
3 s
X2n n=0
0n)
f cos(W t) n
to the function: exp(-6wt) } n
(2) )
417 and
f
+f=l
0
folded with the measured time resolution curve (2T = 3.44 ns). Here f 0 is the fraction of nuclei at unperturbed lattice sites and f the fraction of nuclei subject to the interaction characterized by the quadrupole frequency wn = Fn(f)wQ where 'Q-
eQVzz 40
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