Gamma-gamma angular correlation in nickel 60.

Abstract

A reinvestigation was conducted of an anomaly in the experimental angular correlation for the gamma-gamma cascade of Ni60 which was reported by Verser and Conway in 1960 and 1961, respectively. The measurement of this correlation was being used to test angular correlation equipment built at the US Naval Postgraduate School. Two new experimental determinations of the correlation function with the same equipment as used previously indicated good agreement with the theoretical function. Verser's and Conway's experimentally-determined angular correlation functions were found to deviate less significantly from the theoretical function than they had reported since their standard deviations had failed to take into account the variations of the characteristics of the electronic equipment due solely to electronic causes. It is concluded that the anomaly reported by previous experimenters was statistical in nature. Programs for the CDC 1604 computer have been developed in FORTRAN language for complete data reduction accepting as input the total counts in each channel, the total coincident counts, and other experimental parameters. The program provides for the calculation of the coefficients for a cosine series and a Legendre polynomial series expansion of the least squares fit to the experimental points. Other programs were developed to calculate the corrections for non-point detectors to be applied to the theoretical coefficients, and to calculate coincidence resolving times from data obtained during a large number of runs. Major improvements were made in the equipment to be used in future angular correlation experiments, including the construction and testing of both a slow and a fast coincidence unit. The author wishes to express his appreciation to Associate Professor H. E. Handler who has guided the development of angular correlation measuring equipment at the US Naval Postgraduate School for the last three academic years. His recommendations, particularly in the area of data analysis, and his perusal of the draft of this paper resulted in a still more thorough reinvestigation of the results of the angular correlation studies reported by previous experimenters at this School. It is a pleasure to acknowledge the guidance and aid received from Lt Cmdr P. A. Phelps (USN) in comprehending the theoretical aspects of the basic experiment, in becoming familiar with the electronic equipment, and in writing and debugging the computer programs. Appreciation is expressed to Mr. M. A. Brillhart for his construction of the coincidence units, and for his assistance in developing the mixer circuitry.