Even?odd effects in prompt emission in fission

Compared to the extensively studied proton even?odd effects in fission fragment distributions, the even?odd effects in prompt emission received less attention. In this context the present paper is focusing on the even?odd effects (in both Zand N) appearing in prompt neutron and gamma ray emission. The study of even?odd effects in the prompt emission of four fissioning nuclei with even Zand even N, 233,235U(nth, f), 239Pu(nth, f) and 252Cf(SF), shows that these effects are mainly due to the Zeven?odd effects in fragment distributions and charge deviations and the Neven?odd effect in average neutron separation energies.
The most pronounced even?odd effect in prompt emission is for the prompt neutron multiplicity. The average multiplicity as a function of Z, ?(Z), has a sawtoothshape and exhibits a visible staggering for asymmetric fragmentations. The size of the global even?odd effect in prompt neutron multiplicity shows a decrease with increasing fissility. The Neven?odd effect in average neutron separation energy influences the global even?odd effect in prompt neutron multiplicity often in an opposite way compared to the Zeven?odd effect. The average prompt neutron multiplicity as a function of TKE shows an increase of the Zeven?odd effect with increasing TKE and this effect is decreasing for heavier fissioning systems.
The Zeven?odd effects in the average prompt ?-ray energy and the average prompt neutron energy have comparable sizes and are lower than the even?odd effects in prompt neutron multiplicity.
Different average prompt emission quantities (as a function of A, of Z, of TKE and total average ones)?being dependent on fragment distributions?are affected by the even?odd effects in Y(A, Z, TKE). The Neven?odd effect in neutron separation energy and the Zeven?odd effect in the charge deviation enter the primary multi-parametric matrices of prompt emission quantities (e.g. ?(A, Z, TKE)) which are not depending on fragment distributions.

Authors:

VISAN I., GIUBEGA G., TUDORA A., HAMBSCH Franz-Josef

Publisher:

ELSEVIER SCIENCE BV

Format medium:

Online