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Hardening of KBr by heavy gamma irradiation at LNT
Volume 43A, number 2
PHYSICS LETTERS
26 February 1973
HARDENING OF KBr BY HEAVY GAMMA IRRADIATION AT LNT H. NARAMOTO* and K. OZAWA Japan Atomic Energy Research Institute, Tokai-mura, Japan
and
T. OKADA and T. SUITA Faculty of Engineering, Osaka University, Suita, Japan Received 4 January 1973 The anomalous enhancement of the flow stress was observed in KBr heavily irradiated at LNT by gamma ray. The enhancement is closely related to the growth of the intrinsic component in the V 4.envelope.
The radiation hardening of alkali halides by ionizing radiation has been by a model of Fleischer 21 based upon the described elastic interaction between disloca-[1, tions and the tetragonal strain field of induced defects [3, 41. It is very important to appreciate the role of the interstitial type defects produced together with the Vacancy type defects as the Frenkel pair in radiation hard. ening study. The interstitial type absorption band termed as the “V 4-envelope” by Comins [51in KBr grows predominantly in 275 nm region at low temperatures. It is the purpose of this paper to correlate the growth of the V4-envelope with the radiation induced hardening at LNT by simultaneous measurements of the flow stress and the optical absorption. KBr crystals were purchased from Harschaw Chemical Company as pure crystal so as to minimize the influences to the hardening by the V1 and Vk.centres. The flow 2 at LNT. stress of annealed samples was 241 ±30 g/mm These samples were irradiated at LNT by gamma rays with a dose rate of 5.2 X iO~nh. Mechanical samples were compressed using an Instron testing machine, operating with a crosshead speed of 0.05 cm/mm. The increase in the flow stress ~T at LNT is shown in fig. 1 as a function of gamma dose. The feature is the anomalous enhancement of ~r in the higher dose region than ~ 2 X IO~r. The ~r growth curve may be aporoximated by the exponential saturation hardening and the additional hardening in the higher dose. The value of ~r corresponding to the dosage (~2 X I o7 r) *
JAERI research student from the postgraduate course of Osaka University, 1968—1969.
above which 2. theInanomalous enhancement appears is order to examine the effect of sample
~ 450 g/mm sources on the anomalous hardening, KBr, (Harshaw) from another blocks and KBr (Horiba Ltd., Kyoto) doped with the divalent cations were also measured. These three kinds of crystals showed almost the same amount of the additional hardening independent of sample sources. From the optical measurement over the entire region of gamma dose in this experiment, it was obtained that the growth curve of the V4-en. velope consisted of two stages, keeping a linear rela. tion with the F-band in spite of the complexity of the V4-envelope. In the inset of fig. I, ~r is plotted logarithmically versus absorption coefficient of the V4-envelope peak at LNT. The growth of L~rmay be divided into the two different regions as the function of the V4-envelope Each region corresponds to each stagecolouration. in the growth curve of the V 4. envelope and the value of ~i- at the deflection point in the inset is approximately equal to the value from which the anomalous enhancement emerges in IXT versus gamma-dose curve. The results mentioned above reveal that the momalous growth of I~Tis closely related to the two stage colourations in the V4 -envelope having a composite structure. The enhancement of ~i in the higher dose region is likely to be caused by the intrinsic defects in the sense that the enhancement is structure insensitive and is closely related to the second stage of the V4-envelope growth. In the lower dose region, the hardening is likely to be caused by the colour centres 95
Volume 43A, number 2
PHYSICS LETTERS
26 February 1973
revealed that annealing to 220°Kreduced the values 1.0
of ~.r and the absorption coefficient at the peak of
~
the V4-envelope to the ones of the deflection point
KBr (Horshaw) 0.8
~
/
V
—
__________
0.4
-
-
~
—
0.2
—
in the inset. Thus it can be excluded that the hardening in the higher dose region is caused by the aggregates of the defects produced in the lower dose region. The discussions about the changes of i~i-accompanied with the thermal destruction of the V4envelope will be done elsewhere. As to the V1. and Vk-centres, their absorptions were not observed. Furhtermore, the thermo-glow and the change of i~rby isochronal annealing of KBr (Harshaw) irradiated at LNT were not obtained at the annihilation temperatures of these centres. These
—
a~~o’ M — _______ ~
—
~° — ~° ~Zv4.twSIQ~SI~’)
~
results imply that the defects composing the V4-en-
velope are the dominant hardening agents in KBr irTr) Fig. 1. The induced flow 1-dose stress ~r(lOat LNT as a function of the dosage in KBr irradiated at LNT by gamma ray. The inset shows the growth of ~r logarithmically versus the absorption coeffecient of the V 4-envelope peak.
radiated at LNT.
of extrinsic interstitial type defects produced at the primary stage of the V4 -envelope growth considering the saturating character of ~r. These conclusions are consistent with the results obtained by Treacy and Royce [6] in the point that the V4-envelope has the extrinsically saturating component (the D3-band at 268 nm associated with the divalent cation impurity) and the intrinsically growing component (the band at 280 nm). Pulse annealing experiment of 7 r)KBr at LNT (Harshaw) heavily irradiated (~5.7 X i0
References
96
Authors are very indebted to Dr. K. Kubo in JAERI for encouragement and helpful remarks.
[11 R.L. Fleischer, Acta Met. 10 (1962) 835. [21 R.L. Fleiseher, J. Appl. Phys. 33(1962) 3504. [3] J.S. Nadeau, I. App!. 2248; 35 (1964) 1248.Phys. 33 (1962) 3480; 34 (1963) [4] W.A. Sibley and E. Sonder, J. Appi. Phys. 34 (1963) 2366. [5] J.D. Comins, Solid State Commun. 5 (1967) 709. [6] D.J. Treacy and B.S.H. Royce, J. Phys. Chem. Solids 33 (1972) 853.
PHYSICS LETTERS
26 February 1973
HARDENING OF KBr BY HEAVY GAMMA IRRADIATION AT LNT H. NARAMOTO* and K. OZAWA Japan Atomic Energy Research Institute, Tokai-mura, Japan
and
T. OKADA and T. SUITA Faculty of Engineering, Osaka University, Suita, Japan Received 4 January 1973 The anomalous enhancement of the flow stress was observed in KBr heavily irradiated at LNT by gamma ray. The enhancement is closely related to the growth of the intrinsic component in the V 4.envelope.
The radiation hardening of alkali halides by ionizing radiation has been by a model of Fleischer 21 based upon the described elastic interaction between disloca-[1, tions and the tetragonal strain field of induced defects [3, 41. It is very important to appreciate the role of the interstitial type defects produced together with the Vacancy type defects as the Frenkel pair in radiation hard. ening study. The interstitial type absorption band termed as the “V 4-envelope” by Comins [51in KBr grows predominantly in 275 nm region at low temperatures. It is the purpose of this paper to correlate the growth of the V4-envelope with the radiation induced hardening at LNT by simultaneous measurements of the flow stress and the optical absorption. KBr crystals were purchased from Harschaw Chemical Company as pure crystal so as to minimize the influences to the hardening by the V1 and Vk.centres. The flow 2 at LNT. stress of annealed samples was 241 ±30 g/mm These samples were irradiated at LNT by gamma rays with a dose rate of 5.2 X iO~nh. Mechanical samples were compressed using an Instron testing machine, operating with a crosshead speed of 0.05 cm/mm. The increase in the flow stress ~T at LNT is shown in fig. 1 as a function of gamma dose. The feature is the anomalous enhancement of ~r in the higher dose region than ~ 2 X IO~r. The ~r growth curve may be aporoximated by the exponential saturation hardening and the additional hardening in the higher dose. The value of ~r corresponding to the dosage (~2 X I o7 r) *
JAERI research student from the postgraduate course of Osaka University, 1968—1969.
above which 2. theInanomalous enhancement appears is order to examine the effect of sample
~ 450 g/mm sources on the anomalous hardening, KBr, (Harshaw) from another blocks and KBr (Horiba Ltd., Kyoto) doped with the divalent cations were also measured. These three kinds of crystals showed almost the same amount of the additional hardening independent of sample sources. From the optical measurement over the entire region of gamma dose in this experiment, it was obtained that the growth curve of the V4-en. velope consisted of two stages, keeping a linear rela. tion with the F-band in spite of the complexity of the V4-envelope. In the inset of fig. I, ~r is plotted logarithmically versus absorption coefficient of the V4-envelope peak at LNT. The growth of L~rmay be divided into the two different regions as the function of the V4-envelope Each region corresponds to each stagecolouration. in the growth curve of the V 4. envelope and the value of ~i- at the deflection point in the inset is approximately equal to the value from which the anomalous enhancement emerges in IXT versus gamma-dose curve. The results mentioned above reveal that the momalous growth of I~Tis closely related to the two stage colourations in the V4 -envelope having a composite structure. The enhancement of ~i in the higher dose region is likely to be caused by the intrinsic defects in the sense that the enhancement is structure insensitive and is closely related to the second stage of the V4-envelope growth. In the lower dose region, the hardening is likely to be caused by the colour centres 95
Volume 43A, number 2
PHYSICS LETTERS
26 February 1973
revealed that annealing to 220°Kreduced the values 1.0
of ~.r and the absorption coefficient at the peak of
~
the V4-envelope to the ones of the deflection point
KBr (Horshaw) 0.8
~
/
V
—
__________
0.4
-
-
~
—
0.2
—
in the inset. Thus it can be excluded that the hardening in the higher dose region is caused by the aggregates of the defects produced in the lower dose region. The discussions about the changes of i~i-accompanied with the thermal destruction of the V4envelope will be done elsewhere. As to the V1. and Vk-centres, their absorptions were not observed. Furhtermore, the thermo-glow and the change of i~rby isochronal annealing of KBr (Harshaw) irradiated at LNT were not obtained at the annihilation temperatures of these centres. These
—
a~~o’ M — _______ ~
—
~° — ~° ~Zv4.twSIQ~SI~’)
~
results imply that the defects composing the V4-en-
velope are the dominant hardening agents in KBr irTr) Fig. 1. The induced flow 1-dose stress ~r(lOat LNT as a function of the dosage in KBr irradiated at LNT by gamma ray. The inset shows the growth of ~r logarithmically versus the absorption coeffecient of the V 4-envelope peak.
radiated at LNT.
of extrinsic interstitial type defects produced at the primary stage of the V4 -envelope growth considering the saturating character of ~r. These conclusions are consistent with the results obtained by Treacy and Royce [6] in the point that the V4-envelope has the extrinsically saturating component (the D3-band at 268 nm associated with the divalent cation impurity) and the intrinsically growing component (the band at 280 nm). Pulse annealing experiment of 7 r)KBr at LNT (Harshaw) heavily irradiated (~5.7 X i0
References
96
Authors are very indebted to Dr. K. Kubo in JAERI for encouragement and helpful remarks.
[11 R.L. Fleischer, Acta Met. 10 (1962) 835. [21 R.L. Fleiseher, J. Appl. Phys. 33(1962) 3504. [3] J.S. Nadeau, I. App!. 2248; 35 (1964) 1248.Phys. 33 (1962) 3480; 34 (1963) [4] W.A. Sibley and E. Sonder, J. Appi. Phys. 34 (1963) 2366. [5] J.D. Comins, Solid State Commun. 5 (1967) 709. [6] D.J. Treacy and B.S.H. Royce, J. Phys. Chem. Solids 33 (1972) 853.