Kinetic energy and fragment mass distributions for ${}^{240}{Pu}$ (s.f.), ${}^{239}{Pu} (n_{th}, f)$ , and ${}^{240}{Pu} (γ, f)$

Energy correlation measurements were performed for

{}^{240}{Pu}

(s.f.),

{}^{239}{Pu} (n_{th}, f)

, and the photofission of

{}^{240}{Pu}

with 12-, 15-, 20-, and 30-MeV bremsstrahlung. The photofission cross section for

{}^{240}{Pu}

was determined up to 30 MeV, which permitted the calculation of the average excitation energy

〈 E_{exc} 〉

of the compound nucleus. The average total kinetic energy

〈 E_{k} 〉

of the fragments for

{}^{240}{Pu}

(s.f.) was found to be 1.2±0.5 MeV higher than for

{}^{239}{Pu} (n_{th}, f)

. A decrease of

〈 E_{k} 〉

, with

〈 E_{exc} 〉

\frac{d 〈 E_{k} 〉}{d 〈 E_{exc} 〉} = - 0.37 \pm 0.08

, is observed in the photofission of

{}^{240}{Pu}

. Fragment shell effects are present in the kinetic energy and mass distributions for

{}^{240}{Pu}

(s.f.). Changes in the measured distributions with increasing excitation energy of the compound nucleus

{}^{240}{Pu}

are discussed in the framework of the scission point model of Wilkins et al.

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Kinetic energy and fragment mass distributions forPu240(s.f.),Pu239(nth,f), andPu240(γ,f)