INFLUENCE OF EVEN NUCLEON NUMBERS AND CLOSED SHELLS ON MASS AND CHARGE-DISTRIBUTION IN LOW-ENERGY FISSION

Extensive experimental and evaluated yield data are now available for the fragments in low energy nuclear fission. Using these data we re-ex amined the influence of even nuclear numbers and closed shells on the mass and charge distribution in low energy fission. We used WAHL's Zp model and Ap model. We also examined the effects of Z = 50, N = 82 and possibly N = 88 shells. A new method was developed based on two Gauss ian curves for the even and odd products. The EOZ and EON values calcu lated are based on these different methods and are seen to be consiste nt with each other in spite of the somewhat different definitions of t he even-odd effect. The even-odd effect decreases with an increasing f issility parameter. The EON values are substantially lower than the co rresponding EOZ values, probably due to the effect of washing out the neutron pairing effect by prompt neutron emission. The magnitude of th e even-odd effect varies with different mass regions. The EOZ and EON values decrease as they go from asymmetric to symmetric regions in mas s distributions.