Nuclide | t1⁄2 | Yield | Q [a 1] | βγ |
---|---|---|---|---|
(Ma) | (%) [a 2] | (keV) | ||
99Tc | 0.211 | 6.1385 | 294 | β |
126Sn | 0.230 | 0.1084 | 4050 [a 3] | βγ |
79Se | 0.327 | 0.0447 | 151 | β |
135Cs | 1.33 | 6.9110 [a 4] | 269 | β |
93Zr | 1.53 | 5.4575 | 91 | βγ |
107Pd | 6.5 | 1.2499 | 33 | β |
129I | 15.7 | 0.8410 | 194 | βγ |
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 |
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.
Yield can be broken down by:
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%).
If a graph of the mass or mole yield of fission products against the atomic number of the fragments is drawn then it has two peaks, one in the area zirconium through to palladium and one at xenon through to neodymium. This is because the fission event causes the nucleus to split in an asymmetric manner, [1] as nuclei closer to magic numbers are more stable. [2]
Yield vs. Z - This is a typical distribution for the fission of uranium. Note that in the calculations used to make this graph the activation of fission products was ignored and the fission was assumed to occur in a single moment rather than a length of time. In this bar chart results are shown for different cooling times (time after fission).
Because of the stability of nuclei with even numbers of protons and/or neutrons the curve of yield against element is not a smooth curve. It tends to alternate.
In general, the higher the energy of the state that undergoes nuclear fission, the more likely a symmetric fission is, hence as the neutron energy increases and/or the energy of the fissile atom increases, the valley between the two peaks becomes more shallow; for instance, the curve of yield against mass for Pu-239 has a more shallow valley than that observed for U-235, when the neutrons are thermal neutrons. The curves for the fission of the later actinides tend to make even more shallow valleys. In extreme cases such as 259Fm, only one peak is seen.
Yield is usually expressed relative to number of fissioning nuclei, not the number of fission product nuclei, that is, yields should sum to 200%.
The table in the next section ("Ordered by yield") gives yields for notable radioactive (with half-lives greater than one year, plus iodine-131) fission products, and (the few most absorptive) neutron poison fission products, from thermal neutron fission of U-235 (typical of nuclear power reactors), computed from [ permanent dead link ].
The yields in the table sum to only 45.5522%, including 34.8401% which have half-lives greater than one year:
t½ in years | Yield |
---|---|
1 to 5 | 2.7252% |
10 to 100 | 12.5340% |
2 to 300,000 | 6.1251% |
1.5 to 16 million | 13.4494% |
The remainder and the unlisted 54.4478% decay with half-lives less than one year into nonradioactive nuclei.
This is before accounting for the effects of any subsequent neutron capture; e.g.:
Besides fission products, the other types of radioactive products are
Yield | Element | Isotope | Halflife | Comment |
---|---|---|---|---|
6.7896% | Caesium | 133Cs → 134Cs | 2.065 y | Neutron capture (29 barns) slowly converts stable 133Cs to 134Cs, which itself is low-yield because beta decay stops at 134Xe; can be further converted (140 barns) to 135Cs. |
6.3333% | Iodine, xenon | 135I → 135Xe | 6.57 h | Most important neutron poison; neutron capture converts 10–50% of 135Xe to 136Xe; remainder decays (9.14h) to 135Cs (2.3 My). |
6.2956% | Zirconium | 93Zr | 1.53 My | Long-lived fission product also produced by neutron activation in zircalloy cladding. |
6.1% | Molybdenum | 99Mo | 65.94 h | Its daughter nuclide 99mTc is important in medical diagnosing. |
6.0899% | Caesium | 137Cs | 30.17 y | Source of most of the decay heat from years to decades after irradiation, together with 90 Sr. |
6.0507% | Technetium | 99Tc | 211 ky | Candidate for disposal by nuclear transmutation. |
5.7518% | Strontium | 90Sr | 28.9 y | Source of much of the decay heat together with 137 Cs on the timespan of years to decades after irradiation. Formerly used in radioisotope thermoelectric generators. |
2.8336% | Iodine | 131I | 8.02 d | Reason for the use of potassium iodide tablets after nuclear accidents or nuclear bomb explosions. |
2.2713% | Promethium | 147Pm | 2.62 y | beta decays to very long lived Samarium-147 (half life>age of the universe); has seen some use in radioisotope thermoelectric generators |
1.0888% | Samarium | 149Sm | Observationally stable | 2nd most significant neutron poison. |
0.9% [3] | Iodine | 129I | 15.7 My | Long-lived fission product. Candidate for disposal by nuclear transmutation. |
0.4203% | Samarium | 151Sm | 90 y | Neutron poison; most will be converted to stable 152Sm. |
0.3912% | Ruthenium | 106Ru | 373.6 d | ruthenium tetroxide is volatile and chemically aggressive; daughter nuclide 106 Rh decays quickly to stable 106 Pd |
0.2717% | Krypton | 85Kr | 10.78 y | noble gas; has some uses in industry to detect fine cracks in materials via autoradiography |
0.1629% | Palladium | 107Pd | 6.5 My | Long-lived fission product; hampers extraction of stable isotopes of platinum group metals for use due to chemical similarity. |
0.0508% | Selenium | 79Se | 327 ky | |
0.0330% | Europium, gadolinium | 155Eu → 155Gd | 4.76 y | Both neutron poisons, most will be destroyed while fuel still in use. |
0.0297% | Antimony | 125Sb | 2.76 y | |
0.0236% | Tin | 126Sn | 230 ky | |
0.0065% | Gadolinium | 157Gd | stable | Neutron poison. |
0.0003% | Cadmium | 113mCd | 14.1 y | Neutron poison, most will be destroyed while fuel still in use. |
Cumulative fission yields give the amounts of nuclides produced either directly in the fission or by decay of other nuclides.
Product | Thermal fission yield | Fast fission yield | 14-MeV fission yield |
---|---|---|---|
1 1H | 0.00171 ± 0.00018 | 0.00269 ± 0.00044 | 0.00264 ± 0.00045 |
2 1H | 0.00084 ± 0.00015 | 0.00082 ± 0.00012 | 0.00081 ± 0.00012 |
3 1H | 0.0108 ± 0.0004 | 0.0108 ± 0.0004 | 0.0174 ± 0.0036 |
3 2He | 0.0108 ± 0.0004 | 0.0108 ± 0.0004 | 0.0174 ± 0.0036 |
4 2He | 0.1702 ± 0.0049 | 0.17 ± 0.0049 | 0.1667 ± 0.0088 |
85 35Br | 1.304 ± 0.012 | 1.309 ± 0.043 | 1.64 ± 0.31 |
82 36Kr | 0.000285 ± 0.000076 | 0.00044 ± 0.00016 | 0.038 ± 0.012 |
85 36Kr | 0.286 ± 0.021 | 0.286 ± 0.026 | 0.47 ± 0.1 |
85m 36Kr | 1.303 ± 0.012 | 1.307 ± 0.043 | 1.65 ± 0.31 |
90 38Sr | 5.73 ± 0.13 | 5.22 ± 0.18 | 4.41 ± 0.18 |
95 40Zr | 6.502 ± 0.072 | 6.349 ± 0.083 | 5.07 ± 0.19 |
94 41Nb | 0.00000042 ± 0.00000011 | 2.90±0.770 × 10−8 | 0.00004 ± 0.000015 |
95 41Nb | 6.498 ± 0.072 | 6.345 ± 0.083 | 5.07 ± 0.19 |
95m 41Nb | 0.0702 ± 0.0067 | 0.0686 ± 0.0071 | 0.0548 ± 0.0072 |
92 42Mo | 0 ± 0 | 0 ± 0 | 0 ± 0 |
94 42Mo | 8.70 × 10−10 ± 3.20 × 10−10 | 0 ± 0 | 6.20 × 10−8 ± 2.50 × 10−8 |
96 42Mo | 0.00042 ± 0.00015 | 0.000069 ± 0.000025 | 0.0033 ± 0.0015 |
99 42Mo | 6.132 ± 0.092 | 5.8 ± 0.13 | 5.02 ± 0.13 |
99 43Tc | 6.132 ± 0.092 | 5.8 ± 0.13 | 5.02 ± 0.13 |
103 44Ru | 3.103 ± 0.084 | 3.248 ± 0.042 | 3.14 ± 0.11 |
106 44Ru | 0.41 ± 0.011 | 0.469 ± 0.036 | 2.15 ± 0.59 |
106 45Rh | 0.41 ± 0.011 | 0.469 ± 0.036 | 2.15 ± 0.59 |
121m 50Sn | 0.00106 ± 0.00011 | 0.0039 ± 0.00091 | 0.142 ± 0.023 |
122 51Sb | 0.000000366 ± 0.000000098 | 0.0000004 ± 0.00000014 | 0.00193 ± 0.00068 |
124 51Sb | 0.000089 ± 0.000021 | 0.000112 ± 0.000034 | 0.027 ± 0.01 |
125 51Sb | 0.026 ± 0.0014 | 0.067 ± 0.011 | 1.42 ± 0.42 |
132 52Te | 4.276 ± 0.043 | 4.639 ± 0.065 | 3.85 ± 0.16 |
129 53I | 0.706 ± 0.032 | 1.03 ± 0.26 | 1.59 ± 0.18 |
131 53I | 2.878 ± 0.032 | 3.365 ± 0.054 | 4.11 ± 0.14 |
133 53I | 6.59 ± 0.11 | 6.61 ± 0.13 | 5.42 ± 0.4 |
135 53I | 6.39 ± 0.22 | 6.01 ± 0.18 | 4.8 ± 1.4 |
128 54Xe | 0 ± 0 | 0 ± 0 | 0.00108 ± 0.00048 |
130 54Xe | 0.000038 ± 0.0000098 | 0.000152 ± 0.000055 | 0.038 ± 0.014 |
131m 54Xe | 0.0313 ± 0.003 | 0.0365 ± 0.0031 | 0.047 ± 0.0049 |
133 54Xe | 6.6 ± 0.11 | 6.61 ± 0.13 | 5.57 ± 0.41 |
133m 54Xe | 0.189 ± 0.015 | 0.19 ± 0.015 | 0.281 ± 0.049 |
135 54Xe | 6.61 ± 0.22 | 6.32 ± 0.18 | 6.4 ± 1.8 |
135m 54Xe | 1.22 ± 0.12 | 1.23 ± 0.13 | 2.17 ± 0.66 |
134 55Cs | 0.0000121 ± 0.0000032 | 0.0000279 ± 0.0000073 | 0.0132 ± 0.0035 |
137 55Cs | 6.221 ± 0.069 | 5.889 ± 0.096 | 5.6 ± 1.3 |
140 56Ba | 6.314 ± 0.095 | 5.959 ± 0.048 | 4.474 ± 0.081 |
140 57La | 6.315 ± 0.095 | 5.96 ± 0.048 | 4.508 ± 0.081 |
141 58Ce | 5.86 ± 0.15 | 5.795 ± 0.081 | 4.44 ± 0.2 |
144 58Ce | 5.474 ± 0.055 | 5.094 ± 0.076 | 3.154 ± 0.038 |
144 59Pr | 5.474 ± 0.055 | 5.094 ± 0.076 | 3.155 ± 0.038 |
142 60Nd | 6.30 × 10−9 ± 1.70 × 10−9 | 1.70 × 10−9 ± 4.80 × 10−10 | 0.0000137 ± 0.0000049 |
144 60Nd | 5.475 ± 0.055 | 5.094 ± 0.076 | 3.155 ± 0.038 |
147 60Nd | 2.232 ± 0.04 | 2.148 ± 0.028 | 1.657 ± 0.045 |
147 61Pm | 2.232 ± 0.04 | 2.148 ± 0.028 | 1.657 ± 0.045 |
148 61Pm | 5.00 × 10−8 ± 1.70 × 10−8 | 7.40 × 10−9 ± 2.50 × 10−9 | 0.0000013 ± 0.00000042 |
148m 61Pm | 0.000000104 ± 0.000000039 | 1.78 × 10−8 ± 6.60 × 10−9 | 0.0000048 ± 0.0000018 |
149 61Pm | 1.053 ± 0.021 | 1.064 ± 0.03 | 0.557 ± 0.09 |
151 61Pm | 0.4204 ± 0.0071 | 0.431 ± 0.015 | 0.388 ± 0.061 |
148 62Sm | 0.000000149 ± 0.000000041 | 2.43 × 10−8 ± 6.80 × 10−9 | 0.0000058 ± 0.0000018 |
150 62Sm | 0.000061 ± 0.000022 | 0.0000201 ± 0.0000077 | 0.00045 ± 0.00018 |
151 62Sm | 0.4204 ± 0.0071 | 0.431 ± 0.015 | 0.388 ± 0.061 |
153 62Sm | 0.1477 ± 0.0071 | 0.1512 ± 0.0097 | 0.23 ± 0.015 |
151 63Eu | 0.4204 ± 0.0071 | 0.431 ± 0.015 | 0.388 ± 0.061 |
152 63Eu | 3.24 × 10−10 ± 8.50 × 10−11 | 0 ± 0 | 3.30 × 10−8 ± 1.10 × 10−8 |
154 63Eu | 0.000000195 ± 0.000000064 | 4.00 × 10−8 ± 1.10 × 10−8 | 0.0000033 ± 0.0000011 |
155 63Eu | 0.0308 ± 0.0013 | 0.044 ± 0.01 | 0.088 ± 0.014 |
Product | Thermal fission yield | Fast fission yield | 14-MeV fission yield |
---|---|---|---|
1 1H | 0.00408 ± 0.00041 | 0.00346 ± 0.00057 | - |
2 1H | 0.00135 ± 0.00019 | 0.00106 ± 0.00016 | - |
3 1H | 0.0142 ± 0.0007 | 0.0142 ± 0.0007 | - |
3 2He | 0.0142 ± 0.0007 | 0.0142 ± 0.0007 | - |
4 2He | 0.2192 ± 0.009 | 0.219 ± 0.009 | - |
85 35Br | 0.574 ± 0.026 | 0.617 ± 0.049 | - |
82 36Kr | 0.00175 ± 0.0006 | 0.00055 ± 0.0002 | - |
85 36Kr | 0.136 ± 0.014 | 0.138 ± 0.017 | - |
85m 36Kr | 0.576 ± 0.026 | 0.617 ± 0.049 | - |
90 38Sr | 2.013 ± 0.054 | 2.031 ± 0.057 | - |
95 40Zr | 4.949 ± 0.099 | 4.682 ± 0.098 | - |
94 41Nb | 0.0000168 ± 0.0000045 | 0.00000255 ± 0.00000069 | - |
95 41Nb | 4.946 ± 0.099 | 4.68 ± 0.098 | - |
95m 41Nb | 0.0535 ± 0.0066 | 0.0506 ± 0.0062 | - |
92 42Mo | 0 ± 0 | 0 ± 0 | - |
94 42Mo | 3.60 × 10−8 ± 1.30 × 10−8 | 4.80 × 10−9 ± 1.70 × 10−9 | - |
96 42Mo | 0.0051 ± 0.0018 | 0.0017 ± 0.00062 | - |
99 42Mo | 6.185 ± 0.056 | 5.82 ± 0.13 | - |
99 43Tc | 6.184 ± 0.056 | 5.82 ± 0.13 | - |
103 44Ru | 6.948 ± 0.083 | 6.59 ± 0.16 | - |
106 44Ru | 4.188 ± 0.092 | 4.13 ± 0.24 | - |
106 45Rh | 4.188 ± 0.092 | 4.13 ± 0.24 | - |
121m 50Sn | 0.0052 ± 0.0011 | 0.0053 ± 0.0012 | - |
122 51Sb | 0.000024 ± 0.0000063 | 0.0000153 ± 0.000005 | - |
124 51Sb | 0.00228 ± 0.00049 | 0.00154 ± 0.00043 | - |
125 51Sb | 0.117 ± 0.015 | 0.138 ± 0.022 | - |
132 52Te | 5.095 ± 0.094 | 4.92 ± 0.32 | - |
129 53I | 1.407 ± 0.086 | 1.31 ± 0.13 | - |
131 53I | 3.724 ± 0.078 | 4.09 ± 0.12 | - |
133 53I | 6.97 ± 0.13 | 6.99 ± 0.33 | - |
135 53I | 6.33 ± 0.23 | 6.24 ± 0.22 | - |
128 54Xe | 0.00000234 ± 0.00000085 | 0.0000025 ± 0.0000012 | - |
130 54Xe | 0.00166 ± 0.00056 | 0.00231 ± 0.00085 | - |
131m 54Xe | 0.0405 ± 0.004 | 0.0444 ± 0.0044 | - |
133 54Xe | 6.99 ± 0.13 | 7.03 ± 0.33 | - |
133m 54Xe | 0.216 ± 0.016 | 0.223 ± 0.021 | - |
135 54Xe | 7.36 ± 0.24 | 7.5 ± 0.23 | - |
135m 54Xe | 1.78 ± 0.21 | 1.97 ± 0.25 | - |
134 55Cs | 0.00067 ± 0.00018 | 0.00115 ± 0.0003 | - |
137 55Cs | 6.588 ± 0.08 | 6.35 ± 0.12 | - |
140 56Ba | 5.322 ± 0.059 | 5.303 ± 0.074 | - |
140 57La | 5.333 ± 0.059 | 5.324 ± 0.075 | - |
141 58Ce | 5.205 ± 0.073 | 5.01 ± 0.16 | - |
144 58Ce | 3.755 ± 0.03 | 3.504 ± 0.053 | - |
144 59Pr | 3.756 ± 0.03 | 3.505 ± 0.053 | - |
142 60Nd | 0.00000145 ± 0.0000004 | 0.00000251 ± 0.00000072 | - |
144 60Nd | 3.756 ± 0.03 | 3.505 ± 0.053 | - |
147 60Nd | 2.044 ± 0.039 | 1.929 ± 0.046 | - |
147 61Pm | 2.044 ± 0.039 | 1.929 ± 0.046 | - |
148 61Pm | 0.0000056 ± 0.0000019 | 0.000012 ± 0.000004 | - |
148m 61Pm | 0.0000118 ± 0.0000044 | 0.000029 ± 0.000011 | - |
149 61Pm | 1.263 ± 0.032 | 1.275 ± 0.056 | - |
151 61Pm | 0.776 ± 0.018 | 0.796 ± 0.037 | - |
148 62Sm | 0.0000168 ± 0.0000046 | 0.000039 ± 0.000011 | - |
150 62Sm | 0.00227 ± 0.00078 | 0.0051 ± 0.0019 | - |
151 62Sm | 0.776 ± 0.018 | 0.797 ± 0.037 | - |
153 62Sm | 0.38 ± 0.03 | 0.4 ± 0.18 | - |
151 63Eu | 0.776 ± 0.018 | 0.797 ± 0.037 | - |
152 63Eu | 0.000000195 ± 0.00000005 | 0.00000048 ± 0.00000014 | - |
154 63Eu | 0.000049 ± 0.000012 | 0.000127 ± 0.000043 | - |
155 63Eu | 0.174 ± 0.03 | 0.171 ± 0.054 | - |
JEFF-3.1 | Joint Evaluated Fission and Fusion File, Incident-neutron data, http://www-nds.iaea.org/exfor/endf00.htm, 2 October 2006; see also A. Koning, R. Forrest, M. Kellett, R. Mills, H. Henriksson, Y. Rugama, The JEFF-3.1 Nuclear Data Library, JEFF Report 21, OECD/NEA, Paris, France, 2006, ISBN 92-64-02314-3. |
Decays, even if lengthy, are given down to the stable nuclide.
Decays with half lives longer than a century are marked with a single asterisk (*), while decays with a half life longer than a hundred million years are marked with two asterisks (**).
Yield | Isotope | |||
---|---|---|---|---|
0.0508% | selenium-79 →* | bromine-79 | ||
0.2717% | krypton-85 → | rubidium-85 | ||
5.7518% | strontium-90 → | yttrium-90 → | zirconium-90 | |
6.2956% | zirconium-93 →* | niobium-93 | ||
6.0507% | technetium-99 →* | ruthenium-99 | ||
0.3912% | ruthenium-106 → | rhodium-106 → | palladium-106 | |
0.1629% | palladium-107 →* | silver-107 | ||
0.0003% | cadmium-113m → | cadmium-113 (essentially stable)→** | indium-113 | |
0.0297% | antimony-125 → | tellurium-125m → | tellurium-125 | |
0.0236% | tin-126 →* | antimony-126 → | tellurium-126 | |
0.9% | iodine-129 →* | xenon-129 | ||
2.8336% | iodine-131 → | xenon-131 | ||
6.7896% | caesium-133 → | caesium-134 → | barium-134 | |
6.3333% | iodine-135 → | xenon-135 → | caesium-135 →* | barium-135 |
6.3333% | iodine-135 → | xenon-135 → | xenon-136 (essentially stable)→** | barium-136 |
6.0899% | caesium-137 → | barium-137 | ||
2.2713% | promethium-147 → | samarium-147 →* | neodymium-143 | |
1.0888% | samarium-149 | |||
0.4203% | samarium-151 | |||
0.0330% | europium-155 → | gadolinium-155 | ||
0.0065% | gadolinium-157 |
Nuclide | Half-life | Decay mode | Branching fraction | Source | Notes |
---|---|---|---|---|---|
85 35Br | 2.9 ± 0.06 m | β− | 1.0 | [6] | [lower-alpha 1] |
85 36Kr | 10.752 ± 0.023 y | β− | 1.0 | [7] | |
85m 36Kr | 4.48 ± 0.008 h | IT | 0.214 ± 0.005 | [6] | |
β− | 0.786 ± 0.005 | ||||
90 38Sr | 28.8 ± 0.07 y | β− | 1.0 | [8] | |
95 40Zr | 64.032 ± 0.006 d | β− | 1.0 | [8] | |
94 41Nb | (7.3 ± 0.9) × 106 d | β− | 1.0 | [9] | |
95m 41Nb | 3.61 ± 0.03 d | β− | 0.025 ± 0.001 | [8] | [lower-alpha 2] |
IT | 0.975 ± 0.001 | ||||
95 41Nb | 34.985 ± 0.012 d | β− | 1.0 | [9] | |
99 43Tc | (2.111 ± 0.012) × 105 y | β− | 1.0 | [6] | |
103 44Ru | 39.247 ± 0.013 d | β− | 1.0 | [9] | |
106 44Ru | 1.018 ± 0.005 y | β− | 1.0 | [9] | |
106 45Rh | 30.1 ± 0.3 s | β− | 1.0 | [9] | |
121m 50Sn | 55 ± 5 y | β− | 0.224 ± 0.02 | [6] | |
IT | 0.776 ± 0.02 | ||||
122 51Sb | 2.7238 ± 0.0002 d | EC | 0.0241 ± 0.0012 | [6] | |
β− | 0.9759 ± 0.0012 | ||||
124 51Sb | 60.2 ± 0.03 d | β− | 1.0 | [6] | |
125 51Sb | 2.7584 ± 0.0006 y | β− | 1.0 | [9] | |
129 53I | (5.89 ± 0.23) × 109 d | β− | 1.0 | [9] | |
131 53I | 8.0233 ± 0.0019 d | β− | 1.0 | [7] | |
133 53I | 20.87 ± 0.08 h | β− | 1.0 | [8] | [lower-alpha 3] |
135 53I | 6.57 ± 0.02 h | β− | 1.0 | [6] | |
131m 54Xe | 11.930 ± 0.016 d | IT | 1.0 | [7] | |
133 54Xe | 5.243 ± 0.001 d | β− | 1.0 | [6] | |
133m 54Xe | 2.19 ± 0.01 d | IT | 1.0 | [6] | |
135 54Xe | 9.14 ± 0.02 h | β− | 1.0 | [6] | |
135m 54Xe | 15.29 ± 0.05 m | β− | 0.003 ± 0.003 | [6] | [lower-alpha 4] |
IT | 0.997 ± 0.003 | ||||
134 55Cs | 2.063 ± 0.003 y | EC | 0.000003 ± 0.000001 | [9] | [lower-alpha 5] |
β− | 0.999997 ± 0.000001 | ||||
137 55Cs | 30.05 ± 0.08 y | β− | 1.0 | [9] | |
140 56Ba | 12.753 ± 0.004 d | β− | 1.0 | [7] | |
140 57La | 1.67850 ± 0.00017 d | β− | 1.0 | [7] | |
141 58Ce | 32.508 ± 0.010 d | β− | 1.0 | [8] | |
144 58Ce | 285.1 ± 0.6 d | β− | 1.0 | [9] | |
144 59Pr | 17.28 ± 0.05 m | β− | 1.0 | [6] | |
147 60Nd | 10.98 ± 0.01 d | β− | 1.0 | [6] | |
147 61Pm | 2.6234 ± 0.0002 y | β− | 1.0 | [6] | |
148m 61Pm | 41.29 ± 0.11 d | IT | 0.042 ± 0.007 | [6] | |
β− | 0.958 ± 0.007 | ||||
148 61Pm | 5.368 ± 0.002 d | β− | 1.0 | [6] | |
149 61Pm | 2.2117 ± 0.0021 d | β− | 1.0 | [6] | |
151 61Pm | 1.1833 ± 0.0017 d | β− | 1.0 | [6] | |
151 62Sm | 90 ± 6 y | β− | 1.0 | [6] | |
153 62Sm | 1.938 ± 0.010 d | β− | 1.0 | [9] | |
152 63Eu | (4.941 ± 0.007) × 103 d | β− | 0.279 ± 0.003 | [9] | [lower-alpha 6] |
EC | 0.721 ± 0.003 | ||||
154 63Eu | (3.1381 ± 0.0014) × 103 d | EC | 0.00018 ± 0.00013 | [9] | [lower-alpha 6] |
β− | 0.99982 ± 0.00013 | ||||
155 63Eu | 4.753 ± 0.016 y | β− | 1.0 | [9] |
Barns | Yield | Isotope | t½ | Comment |
---|---|---|---|---|
2,650,000 | 6.3333% | 135I → 135Xe | 6.57 h | Most important neutron poison; neutron capture rapidly converts 135Xe to 136Xe; remainder decays (9.14 h) to 135Cs (2.3 My). |
254,000 | 0.0065% | 157Gd | ∞ | Neutron poison, but low yield. |
40,140 | 1.0888% | 149Sm | ∞ | 2nd most important neutron poison. |
20,600 | 0.0003% | 113mCd | 14.1 y | Most will be destroyed by neutron capture. |
15,200 | 0.4203% | 151Sm | 90 y | Most will be destroyed by neutron capture. |
3,950 60,900 | 0.0330% | 155Eu → 155Gd | 4.76 y | Both neutron poisons. |
96 | 2.2713% | 147Pm | 2.62 y | Suitable for radioisotope thermoelectric generators with annual or semi-annual refueling. |
80 | 2.8336% | 131I | 8.02 d | |
29 140 | 6.7896% | 133Cs → 134Cs | ∞ 2.065 y | Neutron capture converts a few percent of nonradioactive 133Cs to 134Cs, which has very low direct yield because beta decay stops at 134Xe; further capture will add to long-lived 135Cs. |
20 | 6.0507% | 99Tc | 211 ky | Candidate for disposal by nuclear transmutation. |
18 | 0.6576% | 129I | 15.7 My | Candidate for disposal by nuclear transmutation. |
2.7 | 6.2956% | 93Zr | 1.53 My | Transmutation impractical. |
1.8 | 0.1629% | 107Pd | 6.5 My | |
1.66 | 0.2717% | 85Kr | 10.78 y | |
0.90 | 5.7518% | 90Sr | 28.9 y | |
0.15 | 0.3912% | 106Ru | 373.6 d | |
0.11 | 6.0899% | 137Cs | 30.17 y | |
0.0297% | 125Sb | 2.76 y | ||
0.0236% | 126Sn | 230 ky | ||
0.0508% | 79Se | 327 ky | ||
Nuclear fission is a reaction in which the nucleus of an atom splits into two or more smaller nuclei. The fission process often produces gamma photons, and releases a very large amount of energy even by the energetic standards of radioactive decay.
Stable nuclides are nuclides that are not radioactive and so do not spontaneously undergo radioactive decay. When such nuclides are referred to in relation to specific elements, they are usually termed stable isotopes.
A nuclide is a class of atoms characterized by their number of protons, Z, their number of neutrons, N, and their nuclear energy state.
In nuclear engineering, fissile material is material that can undergo nuclear fission when struck by a neutron of low energy. A self-sustaining thermal chain reaction can only be achieved with fissile material. The predominant neutron energy in a system may be typified by either slow neutrons or fast neutrons. Fissile material can be used to fuel thermal-neutron reactors, fast-neutron reactors and nuclear explosives.
In nuclear science, the decay chain refers to a series of radioactive decays of different radioactive decay products as a sequential series of transformations. It is also known as a "radioactive cascade". The typical radioisotope does not decay directly to a stable state, but rather it decays to another radioisotope. Thus there is usually a series of decays until the atom has become a stable isotope, meaning that the nucleus of the atom has reached a stable state.
Neutron emission is a mode of radioactive decay in which one or more neutrons are ejected from a nucleus. It occurs in the most neutron-rich/proton-deficient nuclides, and also from excited states of other nuclides as in photoneutron emission and beta-delayed neutron emission. As only a neutron is lost by this process the number of protons remains unchanged, and an atom does not become an atom of a different element, but a different isotope of the same element.
Nuclear fission products are the atomic fragments left after a large atomic nucleus undergoes nuclear fission. Typically, a large nucleus like that of uranium fissions by splitting into two smaller nuclei, along with a few neutrons, the release of heat energy, and gamma rays. The two smaller nuclei are the fission products..
Uranium (92U) is a naturally occurring radioactive element that has no stable isotope. It has two primordial isotopes, uranium-238 and uranium-235, that have long half-lives and are found in appreciable quantity in the Earth's crust. The decay product uranium-234 is also found. Other isotopes such as uranium-233 have been produced in breeder reactors. In addition to isotopes found in nature or nuclear reactors, many isotopes with far shorter half-lives have been produced, ranging from 214U to 242U. The standard atomic weight of natural uranium is 238.02891(3).
Naturally occurring samarium (62Sm) is composed of five stable isotopes, 144Sm, 149Sm, 150Sm, 152Sm and 154Sm, and two extremely long-lived radioisotopes, 147Sm (half life: 1.06×1011 y) and 148Sm (6.3×1015 y), with 152Sm being the most abundant (26.75% natural abundance). 146Sm is also fairly long-lived, but is not long-lived enough to have survived in significant quantities from the formation of the Solar System on Earth, although it remains useful in radiometric dating in the Solar System as an extinct radionuclide. A 2012 paper revising the estimated half-life of 146Sm from 10.3(5)×107 y to 6.8(7)×107 y was retracted in 2023. It is the longest-lived nuclide that has not yet been confirmed to be primordial.
Caesium (55Cs) has 41 known isotopes, the atomic masses of these isotopes range from 112 to 152. Only one isotope, 133Cs, is stable. The longest-lived radioisotopes are 135Cs with a half-life of 1.33 million years, 137
Cs
with a half-life of 30.1671 years and 134Cs with a half-life of 2.0652 years. All other isotopes have half-lives less than 2 weeks, most under an hour.
Tin (50Sn) is the element with the greatest number of stable isotopes. This is probably related to the fact that 50 is a "magic number" of protons. In addition, twenty-nine unstable tin isotopes are known, including tin-100 (100Sn) and tin-132 (132Sn), which are both "doubly magic". The longest-lived tin radioisotope is tin-126 (126Sn), with a half-life of 230,000 years. The other 28 radioisotopes have half-lives of less than a year.
Technetium (43Tc) is one of the two elements with Z < 83 that have no stable isotopes; the other such element is promethium. It is primarily artificial, with only trace quantities existing in nature produced by spontaneous fission or neutron capture by molybdenum. The first isotopes to be synthesized were 97Tc and 99Tc in 1936, the first artificial element to be produced. The most stable radioisotopes are 97Tc, 98Tc, and 99Tc.
Naturally occurring zirconium (40Zr) is composed of four stable isotopes (of which one may in the future be found radioactive), and one very long-lived radioisotope (96Zr), a primordial nuclide that decays via double beta decay with an observed half-life of 2.0×1019 years; it can also undergo single beta decay, which is not yet observed, but the theoretically predicted value of t1/2 is 2.4×1020 years. The second most stable radioisotope is 93Zr, which has a half-life of 1.53 million years. Thirty other radioisotopes have been observed. All have half-lives less than a day except for 95Zr (64.02 days), 88Zr (83.4 days), and 89Zr (78.41 hours). The primary decay mode is electron capture for isotopes lighter than 92Zr, and the primary mode for heavier isotopes is beta decay.
Plutonium (94Pu) is an artificial element, except for trace quantities resulting from neutron capture by uranium, and thus a standard atomic weight cannot be given. Like all artificial elements, it has no stable isotopes. It was synthesized long before being found in nature, the first isotope synthesized being plutonium-238 in 1940. Twenty plutonium radioisotopes have been characterized. The most stable are plutonium-244 with a half-life of 80.8 million years; plutonium-242 with a half-life of 373,300 years; and plutonium-239 with a half-life of 24,110 years; and plutonium-240 with a half-life of 6,560 years. This element also has eight meta states; all have half-lives of less than one second.
Nuclear binding energy in experimental physics is the minimum energy that is required to disassemble the nucleus of an atom into its constituent protons and neutrons, known collectively as nucleons. The binding energy for stable nuclei is always a positive number, as the nucleus must gain energy for the nucleons to move apart from each other. Nucleons are attracted to each other by the strong nuclear force. In theoretical nuclear physics, the nuclear binding energy is considered a negative number. In this context it represents the energy of the nucleus relative to the energy of the constituent nucleons when they are infinitely far apart. Both the experimental and theoretical views are equivalent, with slightly different emphasis on what the binding energy means.
This page discusses each of the main elements in the mixture of fission products produced by nuclear fission of the common nuclear fuels uranium and plutonium. The isotopes are listed by element, in order by atomic number.
In nuclear physics, the valley of stability is a characterization of the stability of nuclides to radioactivity based on their binding energy. Nuclides are composed of protons and neutrons. The shape of the valley refers to the profile of binding energy as a function of the numbers of neutrons and protons, with the lowest part of the valley corresponding to the region of most stable nuclei. The line of stable nuclides down the center of the valley of stability is known as the line of beta stability. The sides of the valley correspond to increasing instability to beta decay. The decay of a nuclide becomes more energetically favorable the further it is from the line of beta stability. The boundaries of the valley correspond to the nuclear drip lines, where nuclides become so unstable they emit single protons or single neutrons. Regions of instability within the valley at high atomic number also include radioactive decay by alpha radiation or spontaneous fission. The shape of the valley is roughly an elongated paraboloid corresponding to the nuclide binding energies as a function of neutron and atomic numbers.
An activation product is a material that has been made radioactive by the process of neutron activation.
Long-lived fission products (LLFPs) are radioactive materials with a long half-life produced by nuclear fission of uranium and plutonium. Because of their persistent radiotoxicity, it is necessary to isolate them from humans and the biosphere and to confine them in nuclear waste repositories for geological periods of time. The focus of this article is radioisotopes (radionuclides) generated by fission reactors.
Isotopes are distinct nuclear species of the same chemical element. They have the same atomic number and position in the periodic table, but differ in nucleon numbers due to different numbers of neutrons in their nuclei. While all isotopes of a given element have similar chemical properties, they have different atomic masses and physical properties.