- Email: [email protected]
Neutron radiation damege in some birefringent crystals
Volume
SOA. number
PIIYSICS
5
NEUTRON
RADIATION
DAMAGE
Ll:TTE!
30 1)ccember
IN SOME BIREFRINGENT
1974
CRYSTALS”
C.F. WONG Department
of Phvsics, Queensland Institute of Technology,
Received
Natural quartz and natural calcite were irradiated in quartz and produced color centers in calcite
* Work supported partially by the Australian clear Science and Engineering.
346
Insitute
of Nu-
5 July 1974
with fast neutrons.
Quartz which is a covalent crystal receives serious damage when it is irradiated with fast neutrons (dose > 10lg n/cm2) [ 1 12 j Neutron radiation damage in calcite would be less important. Since calcite is an ionic covalent crystal, defects produced by irradiation are mobile. It is expected not to observe important structural changes in calcite. Specimen of natural quartz and natural calcite were used in this investigation. The samples in various shapes and sizes were irradiated in a reactor at Lucas Height. The integrated neutron flux was about 1020 n/cm2 The irradiation caused quartz samples to become slight brown in color. More important radiation effects came from internal mechanical stresses which were clearly demonstrated by the development of cracks in some of these samples. Further evidence which suggests the existence of these stresses is that the density of irradiated quartz decreased by about 4.1% and the optical properties were modified. The measurement of density was made on a perfect sample. The latter effect can be easily explained as a result of structural distortions. The experiment was performed by using a pair of crossed polaroids. The irradiated samples were examined with convergent beams. The conoscopes show characteristic patterns of a biaxial crystal similar to those obtained by Shtyrkova [3]. ‘These structural distortions have also been observed in the X-ray diffraction where a picture of low symmetry was obtained for an irradiated quartz sample. Irradiated calcites exhibit a dark brown color. The density decreased by about 0.3% which is insignificant.
Brisbane, Australia 4000
Radiation
effects
caused
structural
distortion
No visible crack or other mechanical damage was observed in these samples. The X-ray diffraction shows no observable change in structure. These results support our previous view. Calcites were damaged to a less degree by fast neutrons. The damage could be absorbed by the lattice because of the mobility of defects. Thermal spikes [4] similar to those created in irradiated quartz [5] do not exist a long enough period. An important radiation effect in calcite is the strong optical absorption in the visible region. We found that the absorption band of irradiated calcite starts from 700 nm while that of irradiated quartz starts from about 400 nm. This effect may be caused by the formation of color centers in the crystals. Further work is in progress on the determination of the detailed optical absorption spectrum and it is hoped to report this later. Generally, ionic bonding is difficult to break but it is possible to damage covalent bonding much more easily. In this experiment, serious structural damage in irradiated quartz was found. On the other hand, the damage in irradiated calcite is primarily by the production of ion vacancies.
References [l] (21 (31 [4]
J.S. Lukesh, Phys. Rev. 97 (1955) 345. W. Primak, Phys. Rev. 110 (1958) 1240. A.P. Shtyrkova, Sov. Phys. Crystal. 14 (1970) 624. G.J. Dienes and J.H. Vineyard, in Radiation effects in solids, (Wiley, 1957). [S] R. Comes, M. Lambert and A. Guinier, in interaction of radiation with solids, ed. A. Bishay (Plenum Press, 1967) p. 319.
SOA. number
PIIYSICS
5
NEUTRON
RADIATION
DAMAGE
Ll:TTE!
30 1)ccember
IN SOME BIREFRINGENT
1974
CRYSTALS”
C.F. WONG Department
of Phvsics, Queensland Institute of Technology,
Received
Natural quartz and natural calcite were irradiated in quartz and produced color centers in calcite
* Work supported partially by the Australian clear Science and Engineering.
346
Insitute
of Nu-
5 July 1974
with fast neutrons.
Quartz which is a covalent crystal receives serious damage when it is irradiated with fast neutrons (dose > 10lg n/cm2) [ 1 12 j Neutron radiation damage in calcite would be less important. Since calcite is an ionic covalent crystal, defects produced by irradiation are mobile. It is expected not to observe important structural changes in calcite. Specimen of natural quartz and natural calcite were used in this investigation. The samples in various shapes and sizes were irradiated in a reactor at Lucas Height. The integrated neutron flux was about 1020 n/cm2 The irradiation caused quartz samples to become slight brown in color. More important radiation effects came from internal mechanical stresses which were clearly demonstrated by the development of cracks in some of these samples. Further evidence which suggests the existence of these stresses is that the density of irradiated quartz decreased by about 4.1% and the optical properties were modified. The measurement of density was made on a perfect sample. The latter effect can be easily explained as a result of structural distortions. The experiment was performed by using a pair of crossed polaroids. The irradiated samples were examined with convergent beams. The conoscopes show characteristic patterns of a biaxial crystal similar to those obtained by Shtyrkova [3]. ‘These structural distortions have also been observed in the X-ray diffraction where a picture of low symmetry was obtained for an irradiated quartz sample. Irradiated calcites exhibit a dark brown color. The density decreased by about 0.3% which is insignificant.
Brisbane, Australia 4000
Radiation
effects
caused
structural
distortion
No visible crack or other mechanical damage was observed in these samples. The X-ray diffraction shows no observable change in structure. These results support our previous view. Calcites were damaged to a less degree by fast neutrons. The damage could be absorbed by the lattice because of the mobility of defects. Thermal spikes [4] similar to those created in irradiated quartz [5] do not exist a long enough period. An important radiation effect in calcite is the strong optical absorption in the visible region. We found that the absorption band of irradiated calcite starts from 700 nm while that of irradiated quartz starts from about 400 nm. This effect may be caused by the formation of color centers in the crystals. Further work is in progress on the determination of the detailed optical absorption spectrum and it is hoped to report this later. Generally, ionic bonding is difficult to break but it is possible to damage covalent bonding much more easily. In this experiment, serious structural damage in irradiated quartz was found. On the other hand, the damage in irradiated calcite is primarily by the production of ion vacancies.
References [l] (21 (31 [4]
J.S. Lukesh, Phys. Rev. 97 (1955) 345. W. Primak, Phys. Rev. 110 (1958) 1240. A.P. Shtyrkova, Sov. Phys. Crystal. 14 (1970) 624. G.J. Dienes and J.H. Vineyard, in Radiation effects in solids, (Wiley, 1957). [S] R. Comes, M. Lambert and A. Guinier, in interaction of radiation with solids, ed. A. Bishay (Plenum Press, 1967) p. 319.