Effect of material environment on a class of nuclear lifetimes

The connection between internal conversion of a nuclear transition and EXAFS is pointed out. A prediction is made of sizable variations of lifetimes of nuclear states depending on the surrounding material environment, provided that the transition energy is just above threshold and the internal conversion coefficient is appreciable. 12 refs., 2 figs

QUANTUM BEATS OF RECOIL-FREE γ-RADIATION

The radiation from a Mössbauer source of 57Co in a copper matrix is frequency-modulated by vibrating the source with a quartz piezo-crystal driven by an oscillator. If the radiation passes through a resonant absorber (a "filter"), a time structure containing the oscillator frequency and its harmonics appears in the resulting counting rate. It may be seen by sorting the time of each count with respect to the cross-over time of a subharmonic of the oscillator. These quantum beats are caused by interferences between the frequency components of the photon amplitude, and vanish unless there is some alteration of relative phase or amplitude of the original radiation by the filter. The harmonic constitution of the beats is a sensitive function of the relative shift of source and filter and may be used as a sensitive probe of small shifts. This is demonstrated by measuring the temperature shift in 57Fe-Be. If a velocity spectrum is made with counts collected during only a part of the vibration cycle, prominent dispersion effects are seen, with counting rates higher than background in some portions of the spectrum. A classical optical theory of the phenomenon is presented in summary. It explains the beats, the dispersion effects, and the sensitivity of the harmonic ratios to relative shifts

SERIAL STUDY OF LAKE MICHIGAN SEDIMENTS BY 57Fe MÖSSBAUER SPECTROSCOPY

Nous avons étudié par spectroscopie Mössbauer le fer contenu dans des sections horizontales d'une carotte extraite des sédiments du lac Michigan. Une composante due à des oxydes ferriques antiferromagnétiques diminue rapidement avec la profondeur, ce que l'on attribue à la pollution atmosphérique des aciéries situées au sud du lac.Mössbauer effect studies have been made of the 57Fe content of serial sections taken from a core of State Michigan bottom sediments. A component attributable to antiferromagnetic ferrioxides shows a rapid decrease with depth and is considered to a result of air pollution from the steel mills at the southern shores of the lake