XCIV.A determination of the Doppler Effect for gamma-rays of4·5and4·8mev

Abstract
The Doppler Effect has been observed for the gamma-rays of 4·5 and 4·8 Mev emitted in cascade when alpha-particles of 958 kev are captured in 7Li. The gamma-rays are detected in a Nal(Tl) crystal placed successively in forward and backward directions from the lithium target ; the observed shift in energy between the two directions is (1·15±0·12)% and the theoretical first-order Doppler shift is 1·30%. It is remarked that these observations show the possibility of investigating certain gamma-ray life-times in the range 10 -14 sec upwards.