Gamma-spectrometric uranium age-dating using intrinsic efficiency   calibration
  A non-destructive, gamma-spectrometric method for uranium age-dating is presented which is applicable to material of any physical form and geometrical shape. It relies on measuring the daughter/parent activity ratio 214Bi/234U by low-background, high-resolution gamma-spectrometry using intrinsic efficiency calibration. The method does not require the use of any reference materials nor the use of an efficiency calibrated geometry. 
Cong Tam Nguyen and Jozsef Zsigrai