Resonant photon absorption The Mossbauer effect Photon attenuation

Resonant photon absorption The Mossbauer effect

Photon attenuation Source x Detector Absorber Radiation attenuation by: -- photoelectric effect -- compton scattering (E << 1. 02 Me. V) Atomic interactions

Photon attenuation Source x Detector Absorber E* E* 0. 0 Consider nuclear resonant absorption Assume source and absorber are identical

Kinematics emission absorption Source x Detector Absorber E* E* 0. 0 for resonant absorption Assume source and absorber are identical

Ignore energy scale Source Absorber

Estimates Consider an 57 Fe source 57 Co E* E* 0. 0 57 Co Fe Natural width of the state

Enter -- Mr. Mossbauer Place 57 Fe source bound in a metal matrix Resonant Absorption! Place 57 Fe absorber bound in a metal matrix

move source +v Source Doppler shift frequency: h ’- h = ED Kinematics -v x Absorber E* E* 0. 0 Detector move source Assume source and absorber are identical

-v no resonant absorption Source Absorber

-v small resonant absorption Source Absorber

-v more resonant absorption Source Absorber

v = 0. 0 maximum resonant absorption Source Absorber

-v less resonant absorption Source Absorber

-v small resonant absorption Source Absorber

-v no resonant absorption Source Absorber

Resulting transmission curve

Kinematics Source x Detector Absorber E s* 0. 0 E a* 0. 0 Assume source and absorber are NOT identical

Doppler kinematics +v move absorber! -v Source x Detector Absorber E s* when - 0. 0 E a* 0. 0 Resonant absorption Assume source and absorber are NOT identical

-v no resonant absorption Source Absorber transition energy shifted

-v small resonant absorption Source Absorber transition energy shifted

-v more resonant absorption Source Absorber transition energy shifted

v = 0. 0 less resonant absorption Source Absorber transition energy shifted

-v small resonant absorption Source Absorber transition energy shifted

-v no resonant absorption Source Absorber transition energy shifted

“Isomer shift” Doppler energy shifted

Isomer shift +v -v Source x Absorber E s* when - 0. 0 E a* 0. 0 Resonant absorption move absorber! Detector Isomer shift: Level shifts due to atomic electronic charge distribution in the nucleus. Constant velocity data

-0. 33 mm/sec

57 Fe What is the J for the ground state and the 14. 4 Kev state? ENSDF/NNDS What is the multipolarity of the transition? What is the degeneracy for the -- ground state and the -- 14. 4 Kev state? If there is a B field, then we can have a nuclear Zeeman effect that will remove the degeneracies

move source with constant acceleration -v +v 57 Fe Source x Absorber E s* 0. 0 Detector m-sublevels

Dipole transition selection rules

Mossbauer resonant absorption with constant acceleration time t -v v Use MCS/MCA 0 +v = dwell time = one channel Source velocity curve v=0 maximum +v v=0 data maximum -v v=0 Source displacement curve

Possible absorption transitions Source x Absorber E s* 0. 0 Detector m-sublevels

Possible absorption transitions m-sublevels 6 4 2 5 3 1

Possible absorption transitions Compare these predictions with the measurements… …follow guidelines in Problem. 10. C. and eventually determine

The Pound-Rebka Experiment Be prepared to explain what the experiment discovered and how the Mossbauer resonant photon absorption was essential to the measurement. Phys. Rev. Lett. 4, 337 (1960)