Fission product yield

Nuclear fission splits a heavy nucleus such as uranium or plutonium into two lighter nuclei, which are called fission products. Yield refers to the fraction of a fission product produced per fission.

Long-lived fission products
Nuclide t1⁄2 Yield Q βγ
(Ma) (%) (keV)
99Tc 0.2116.1385294 β
126Sn 0.2300.10844050 βγ
79Se 0.3270.0447151 β
135Cs 1.33 6.9110269 β
93Zr 1.53 5.457591 βγ
107Pd 6.5  1.249933 β
129I 15.7  0.8410194 βγ
  1. Decay energy is split among β, neutrino, and γ if any.
  2. Per 65 thermal neutron fissions of 235U and 35 of 239Pu.
  3. Has decay energy 380 keV, but its decay product 126Sb has decay energy 3.67 MeV.
  4. Lower in thermal reactors because 135Xe, its predecessor, readily absorbs neutrons.
Medium-lived
fission products
t½
(year)		 Yield
(%)		 Q
(keV)		 βγ
155Eu  4.76 0.0803  252 βγ
85Kr 10.76 0.2180  687 βγ
113mCd 14.1  0.0008  316 β
90Sr 28.9  4.505   2826 β
137Cs 30.23 6.337   1176 βγ
121mSn 43.9  0.00005 390 βγ
151Sm 88.8  0.5314  77 β

Yield can be broken down by:

  1. Individual isotope
  2. Chemical element spanning several isotopes of different mass number but same atomic number.
  3. Nuclei of a given mass number regardless of atomic number. Known as "chain yield" because it represents a decay chain of beta decay.

Isotope and element yields will change as the fission products undergo beta decay, while chain yields do not change after completion of neutron emission by a few neutron-rich initial fission products (delayed neutrons), with half-life measured in seconds.

A few isotopes can be produced directly by fission, but not by beta decay because the would-be precursor with atomic number one greater is stable and does not decay. Chain yields do not account for these "shadowed" isotopes; however, they have very low yields (less than a millionth as much as common fission products) because they are far less neutron-rich than the original heavy nuclei.

Yield is usually stated as percentage per fission, so that the total yield percentages sum to 200%. Less often, it is stated as percentage of all fission products, so that the percentages sum to 100%. Ternary fission, about 0.2–0.4% of fissions, also produces a third light nucleus such as helium-4 (90%) or tritium (7%).

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