I have limited physics knowledge, but I have always been interested in the physics and I am an industrial radiation safety officer with an engineering background. Have there been any experiments in respect to measuring half life with large variance in gravitational fields? Although half life may be constant for a particular radioisotope, can I also assume this is only relative to a radioactive particle at rest? If a radioisotope was travelling away from me at 99.9% of the speed of light, would it not appear by measurement of alpha particles hitting a detector appear to have a different half life ? Where i also get confused is in respect to the relative gamma field. if the radioisotope was moving away, can I assume the gamma emission would remain the same, but that there would be a shift in the wavelength ? That is to say the gamma emission may end up being observed as visible light if the speed of the radioisotope was moving away fast enough? If this were true in respect to wavelength shift, how fast would a radioisotope like Cs137 need to be moving in order for its gamma emission to shift far enough down that it no longer poses a threat (no longer ionizing radiation)?