Measurements of covariance for cascading gamma rays

An apparatus has been developed to measure covariance and delayed covariance of the counting rates of detectors of the separate members of gamma ray cascades. This method offers advantages over conventional time coincidence measurements, particularly for long lived intermediate nuclear states. The method has been used to measure the half-life of the 304 keV level (16.9±0.6 ms) and anisotropy (0.543±0.002) of the 121-280 keV gamma cascade in ⁷⁵As produced by the radioactive decay of ⁷⁵Se. Other applications are discussed.