A parameter R(v), relevant to velocity-sensitive Mössbauer spectroscopy, has been computed for the case where the orientation of 57Co nuclei is produced dynamically by the Overhauser effect. This particular pumping scheme for producing nuclear orientation brings out two features. (1) It allows the determination of η, the ratio of flip-flop to flip-flip thermal relaxations, by an experimental measurement of R(v), since the theoretical expressions for R(v) are found to be quite sensitive to the value of η. A numerical evaluation for three cases of overlap between absorber and emitter lines indicates wide variation in R(v) for increasing values of η from 10−7 to 107: for case (a), R(v) increases monotonically from 8.5 × 10−7 to 1.07 × 106 when emission line 3/2 → 1/2 overlaps absorption line −1/2 → −3/2; for case (b), R(v) decreases monotonically from 1.34 × 1014 to 8.91 × 10−5 when emission line −1/2 → 1/2 overlaps absorption line −1/2 → 1/2; and for case (c), R(v) decreases monotonically from 1.62 × 102 to 6.14 × 10−3 when source lines −1/2 → −1/2, 1/2 → −1/2, 1/2 → 1/2, and 3/2 → 1/2 overlap absorber lines −1/2 → −3/2, −1/2 → 1/2, 1/2 → −1/2, and 1/2 → 1/2 respectively. (2) Since these R(v)'s are found to be much different from those that would be achieved through a pumping scheme using the Jeffries–Abragam effect, the possibility of using the Mössbauer effect to distinguish between the various ways of producing the nuclear orientation is suggested.
Gaia-assisted discovery of a detached low-ionisation BAL quasar with very large ejection velocities