The cubic spline has been used as the efficiency curve model of Ge (Li) gamma-ray spectrometric instrument and improved the algorithm of stepwise regression. Methods such as AIC test etc have also been employed to majorize the model. Thus the problems of the numbers of the partition points

the locations of the best points and the continuity of fitting function at these points are solved. This model contains fewer parameters and better precision than those old ones.

We have used this method to do efficiency calibration for our 185 cm

3

Ge (Li) coaxial detector. The every model obtained contains only three parameters and the precision is about 2.5% in the region from 59 keV to 1408 keV. The deviation of

152

Eu emissionrate measured by our calibrated system from the international comparision at 1978 is equal to or less than 3%.