Summary of the international discussion meeting on radiation effects on superconductivity Page: 6 of 18
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Work involving a particle irradiation of A-15's has led to different
interpretation of the defect responsible for the degradation. T£ decreased
with dose and saturated i.a., showed no further decrease with dose, a
fact subsequently observed for neutron irradiation. Measurements of the
absolute structure factors in x-ray diffraction experiments in Nb^Sn
indicated large static displacements of both the Nb and Sn atoms from their
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equilibrium positions. The displacements of “vO.2 A result in bond-bending
distortions and can be viewed as resulting in a buckling of the chains of atoms.
Further work on channeling in a-damaged V^Si has supported this view. There
appeared, however, to be some disagreement on the procedure whereby the large
displacements of the atoms were unfolded from the original channeling data. It
is,also necessary to determine if these measurements are primarily probing the
surface as compared to the bulk neutron diffraction measurements.
A number of recent investigations were reported that support the dis-
ordering model. The drop in T£ was shown to occur simultaneously w? h an
increase in the normal state resistivity (p) during 20 K fast neutron irradia-
tion. An annealing or recovery stage was seen at room temperature for both
T£ and p, indicating defect motion, and presumably, reordering at this tempera-
ture. ^An extension of this work to large doses showed that both p and S varied
exponentially with dose, as predicted by earlier theoretical work. Neutron
irradiated Nb^Sn was viewed on superlattice reflections to reveal the presence
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of highly disordered regions ^35 A in size in a much less disordered matrix.
The observed T£ decreases in this highly inhomogeneous sample were explained
by the proximity effect.
The T decreases in the A-15’s were fit by a model that invoked a
smearing out of the anisotropy of the energy gap. In this and in other discussions,
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Brown, B. S. Summary of the international discussion meeting on radiation effects on superconductivity, article, January 1, 1977; Illinois. (https://digital.library.unt.edu/ark:/67531/metadc1074905/m1/6/: accessed July 16, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.