It is a nice very idea for an experiment, but I don't think that radioactive decay would be an accurate enough 'clock' to use because generally with these types of measurements very small differences in time are detected - [generally atomic clocks are used to measure the time in these experiments][1]. With the radioactive decay process it is random decay and there will always be some uncetainty in the activity of the sample after the experiment.

I also wonder whether the centrifuge is equivalent to a gravitational field. According to [this reference][1] it is. The time dilation would be most noticeable if the sample was rotated at 'relativistic speeds'. If the speed is not so fast we would need more accurate time measurement.


  [1]: http://en.wikipedia.org/wiki/Gravitational_time_dilation