One thermal fission of releases energy in the following channels: fragment kinetic…

PHYSICS · Multi-part · Fermi University Physics · Nuclear Physics · Fission, fusion and nuclear energy · Fission, fusion and nuclear energy

The Nucleus Resolved, Ch Fission: the double-humped barrier and the shells the drop cannot see

Problem

One thermal fission of

{}^{239}\mathrm{Pu}

releases energy in the following channels: fragment kinetic energy

175.8\,\mathrm{MeV}

; prompt neutrons (mean number

\bar\nu = 2.87

) carrying

5.8\,\mathrm{MeV}

in all; prompt gammas

7.3\,\mathrm{MeV}

; delayed betas

5.4\,\mathrm{MeV}

; delayed gammas

5.2\,\mathrm{MeV}

; antineutrinos

6.9\,\mathrm{MeV}

. A chain

Q

value computed from mass excesses for

{}^{239}\mathrm{Pu} + n \to

(a particular fragment pair)

+\,3n

gives

207.8\,\mathrm{MeV}

, for exactly three emitted neutrons. Each extra neutron beyond two carries with it about

6\,\mathrm{MeV}

of binding energy that would otherwise appear as release. ((a)) Add the six channels to give the total energy released per fission. ((b)) Give the energy deposited locally (all channels except the antineutrinos, which escape any absorber). ((c)) Adjust the chain

Q

value from three emitted neutrons to the actual mean

\bar\nu = 2.87

, and check that it agrees with the total from part (a) to within about one per cent.

Related theory

Nuclear Physics

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