View source for Fission product yield



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=== Mass vs. yield curve ===

[[Image:fission yield volatile.png|thumb|450px|From [[Fluoride volatility]]: Blue elements have volatile fluorides or are already volatile; green elements do not but have volatile chlorides; red elements have neither, but the elements themselves are volatile at very high temperatures. Yields at 10<sup>0,1,2,3</sup> years after [[fission]], not considering later [[neutron capture]], fraction of 100% not 200%. [[Beta decay]] [[Kr-85]]→[[Rubidium|Rb]], [[Sr-90]]→[[Zirconium|Zr]], [[Ru-106]]→[[Palladium|Pd]], [[Sb-125]]→[[Tellurium|Te]], [[Cs-137]]→[[Barium|Ba]], [[Ce-144]]→[[Neodymium|Nd]], [[Sm-151]]→[[Europium|Eu]], [[Eu-155]]→[[Gadolinium|Gd]] visible.]]
[[Image:ThermalFissionYield.svg |thumb|450px|Fission product yields by mass for thermal neutron fission of U-235, Pu-239, a combination of the two typical of current nuclear power reactors, and U-233 used in the thorium cycle]]

If a graph of the [[mass]] or [[Mole (unit)|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.[http://www.science.uwaterloo.ca/~cchieh/cact/nuctek/fissionyield.html]

'''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 [[proton]]s and/or [[neutron]]s 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 neutron]]s. The curves for the fission of the later [[actinides]] tend to make even more shallow valleys. In extreme cases such as <sup>259</sup>Fm, 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 gives yields for notable [[radioactive]] (with [[halflife]] greater than one year, plus [[iodine-131]]) [[fission product]]s, and (the few most absorptive) [[neutron poison]] fission products, from [[thermal neutron]] fission of [[U-235]] (typical of [[nuclear power]] reactors), computed from [http://books.elsevier.com/companions/075067136X/pdfs/Yield.bas?mscssid=HAX80JCKT7RB8LS6F675GU2LM83N1CL6].

The yields in the table sum to only 45.5522%, including 34.8401% which have halflife greater than one year:

{| class="wikitable" style="text-align:right;"
!t<sup>½</sup> 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 154.4478% decay with halflife less than one year into nonradioactive nuclei. 

This is before accounting for the effects of any subsequent neutron capture, e.g.:
*[[Xenon-135|<sup>135</sup>Xe]] capturing a neutron and becoming nonradioactive <sup>136</sup>Xe, rather than decaying to <sup>135</sup>Cs which is radioactive with a halflife of 2.3 million years
*Nonradioactive <sup>133</sup>Cs capturing a neutron and becoming <sup>134</sup>Cs which is radioactive with a halflife of 2 years
*Many of the fission products with mass 147 or greater such as [[Promethium-147]], [[Samarium-149]], [[Samarium-151]], [[Europium-155]] have significant cross sections for neutron capture, so that one heavy fission product atom can undergo multiple successive neutron captures.

Besides fission products, the other types of radioactive products are 

*[[plutonium]] containing [[Pu-238|<sup>238</sup>Pu]], [[Pu-239|<sup>239</sup>Pu]], [[Pu-240|<sup>240</sup>Pu]], [[Pu-241|<sup>241</sup>Pu]], and [[Pu-242|<sup>242</sup>Pu]], 
*[[minor actinides]] including [[Np-237|<sup>237</sup>Np]], [[Am-241|<sup>241</sup>Am]], [[Americium|<sup>243</sup>Am]], [[curium]] isotopes, and perhaps [[californium]]
*[[reprocessed uranium]] containing [[Uranium-236|<sup>236</sup>U]] and other isotopes
*[[tritium]]
*[[activation products]] of neutron capture by the reactor or bomb structure or the environment

==Ordered by yield ([[thermal neutron]] fission of [[U-235]])==
{| class="wikitable sortable"
!Yield !!Isotope !!Halflife !!Comment
|-
| 6.7896% || [[cesium-133|<sup>133</sup>Cs]] [[neutron capture|→]] [[cesium-134|<sup>134</sup>Cs]] || 2.065y ||[[neutron capture]] (29 barns) slowly converts stable <sup>133</sup>Cs to <sup>134</sup>Cs, which itself is low-yield because [[beta decay]] stops at <sup>134</sup>Xe; can be further converted (140 barns) to [[Cs-135|<sup>135</sup>Cs]]
|-
|	6.3333%	|| [[iodine-135|<sup>135</sup>I]] [[beta decay|→]] [[xenon-135|<sup>135</sup>Xe]] || 6.57h ||most important [[neutron poison]]; [[neutron capture]] converts 10%-50% of <sup>135</sup>Xe to <sup>136</sup>Xe; remainder decays (9.14h) to [[Cs-135|<sup>135</sup>Cs]] (2.3my)
|-
|	6.2956%	|| [[Zr-93|<sup>93</sup>Zr]] || 1.53my
|-
|	6.0899%	|| [[Cs-137|<sup>137</sup>Cs]] || 30.17y
|-
|	6.0507%	|| [[Tc-99|<sup>99</sup>Tc]] || 211ky || Candidate for disposal by [[nuclear transmutation]]
|-
|	5.7518%	|| [[strontium-90|<sup>90</sup>Sr]] || 28.9y
|-
|	2.8336%	|| [[iodine-131|<sup>131</sup>I]] || 8.02d
|-
|	2.2713%	|| [[promethium-147|<sup>147</sup>Pm]] || 2.62y
|-
|	1.0888%	|| [[samarium-149|<sup>149</sup>Sm]] || nonradioactive || 2nd most significant [[neutron poison]]
|-
|	0.6576%	|| [[iodine-129|<sup>129</sup>I]] || 15.7my || Candidate for disposal by [[nuclear transmutation]]
|-
|	0.4203%	|| [[samarium-151|<sup>151</sup>Sm]] || 90y || [[neutron poison]]; most will be converted to stable <sup>152</sup>Sm
|-
|	0.3912%	|| [[ruthenium-106|<sup>106</sup>Ru]] || 373.6d
|-
|	0.2717%	|| [[krypton-85|<sup>85</sup>Kr]] || 10.78y
|-
|	0.1629%	|| [[palladium-107|<sup>107</sup>Pd]] || 6.5my
|-
|	0.0508%	|| [[selenium-79|<sup>79</sup>Se]] || 295ky
|-
|	0.0330%	|| [[europium-155|<sup>155</sup>Eu]] [[beta decay|→]] [[gadolinium-155|<sup>155</sup>Gd]] || 4.76y || both [[neutron poison]]s, most will be destroyed while fuel still in use
|-
|	0.0297%	|| [[antimony-125|<sup>125</sup>Sb]] || 2.76y
|-
|	0.0236%	|| [[tin-126|<sup>126</sup>Sn]] || 230ky
|-
|	0.0065%	|| [[gadolinium-157|<sup>157</sup>Gd]] || nonradioactive ||[[neutron poison]]
|-
|	0.0003%	|| [[cadmium-113m|<sup>113m</sup>Cd]] || 14.1y || [[neutron poison]], most will be destroyed while fuel still in use
|}

[[Image:fission yield.png|thumb|450px|Yields at 10<sup>0,1,2,3</sup> years after [[fission]], probably of [[Pu-239]] not [[U-235]] because left hump is shifted right, not considering later [[neutron capture]], fraction of 100% not 200%. [[Beta decay]] [[Kr-85]]→[[Rubidium|Rb]], [[Sr-90]]→[[Zirconium|Zr]], [[Ru-106]]→[[Palladium|Pd]], [[Sb-125]]→[[Tellurium|Te]], [[Cs-137]]→[[Barium|Ba]], [[Ce-144]]→[[Neodymium|Nd]], [[Sm-151]]→[[Europium|Eu]], [[Eu-155]]→[[Gadolinium|Gd]] visible.]]

==Ordered by [[mass number]]==
{| class="wikitable sortable"
!Yield !!Isotope
|- 
|	0.0508%	|| style="background:{{Element color/Nonmetals}}" | [[selenium-79]]
|-
|	0.2717%	|| style="background:{{Element color/Noble gases}}" | [[krypton-85]]
|-
|	5.7518%	|| style="background:{{Element color/Alkaline earth metals}}" | [[strontium-90]]
|-
|	6.2956%	|| style="background:{{Element color/Transition metals}}" | [[zirconium-93]]
|-
|	6.0507%	|| style="background:{{Element color/Transition metals}}" | [[technetium-99]]
|-
|	0.3912%	|| style="background:{{Element color/Transition metals}}" | [[ruthenium-106]]
|-
|	0.1629%	|| style="background:{{Element color/Transition metals}}" | [[palladium-107]]
|-
|	0.0003%	|| style="background:{{Element color/Transition metals}}" | [[cadmium-113m]]
|-
|	0.0297%	|| style="background:{{Element color/Metalloids}}" | [[antimony-125]]
|-
|	0.0236%	|| style="background:{{Element color/Poor metals}}" | [[tin-126]]
|-
|	0.6576%	|| style="background:{{Element color/Halogens}}" | [[iodine-129]]
|-
|	2.8336%	|| style="background:{{Element color/Halogens}}" | [[iodine-131]]
|-
|	6.7896%	|| style="background:{{Element color/Alkali metals}}" | [[caesium-133]] [[neutron capture|→]]||style="background:{{Element color/Alkali metals}}" | [[caesium-134]]
|-
|	6.3333%	|| style="background:{{Element color/Halogens}}" | [[iodine-135]] [[beta decay|→]]||style="background:{{Element color/Noble gases}}" | [[xenon-135]] [[beta decay|→]]||style="background:{{Element color/Alkali metals}}" | [[caesium-135]]
|-
|	6.0899%	|| style="background:{{Element color/Alkali metals}}" | [[caesium-137]]
|-
|	2.2713%	|| style="background:{{Element color/Lanthanides}}" | [[promethium-147]]
|-
|	1.0888%	|| style="background:{{Element color/Lanthanides}}" | [[samarium-149]]
|-
|	0.4203%	|| style="background:{{Element color/Lanthanides}}" | [[samarium-151]]
|-
|	0.0330%	|| style="background:{{Element color/Lanthanides}}" | [[europium-155]] [[beta decay|→]]||style="background:{{Element color/Lanthanides}}" | [[gadolinium-155]]
|-
|	0.0065%	|| style="background:{{Element color/Lanthanides}}" | [[gadolinium-157]]
|}

==Ordered by [[halflife]]==
{| class="wikitable sortable"
!Yield !!Isotope !!Halflife !!Comment
|-
|	2.8336%	|| [[iodine-131|<sup>131</sup>I]] || 8.02d ||Important in nuclear explosions and accidents but not in cooled [[spent nuclear fuel]]
|-
|	0.3912%	|| [[ruthenium-106|<sup>106</sup>Ru]] || 373.6d
|-
| 6.7896% || [[cesium-133|<sup>133</sup>Cs]] [[neutron capture|→]] [[cesium-134|<sup>134</sup>Cs]] || 2.065y ||[[neutron capture]] converts a few percent of nonradioactive <sup>133</sup>Cs to <sup>134</sup>Cs, which has low direct yield because [[beta decay]] stops at <sup>134</sup>Xe
|-
|	2.2713%	|| [[promethium-147|<sup>147</sup>Pm]] || 2.62y
|-
|	0.0297%	|| [[antimony-125|<sup>125</sup>Sb]] || 2.76y
|-
|	<0.0330%	|| [[europium-155|<sup>155</sup>Eu]] [[beta decay|→]] [[gadolinium-155|<sup>155</sup>Gd]] || 4.76y ||both [[neutron poison]]s, most will be destroyed by [[neutron capture]] while still in reactor
|-
|	0.2717%	|| [[krypton-85|<sup>85</sup>Kr]] || 10.78y ||Current [[nuclear reprocessing]] releases it to atmosphere
|-
|	<0.0003%	|| [[cadmium-113m|<sup>113m</sup>Cd]] || 14.1y || most will be destroyed by [[neutron capture]] while still in reactor
|-
|	5.7518%	|| [[strontium-90|<sup>90</sup>Sr]] || 28.9y || One of two principal medium-term radiation and heat sources
|-
|	6.0899%	|| [[Cs-137|<sup>137</sup>Cs]] || 30.17y || One of two principal medium-term radiation and heat sources
|-
|	<0.4203%	|| [[samarium-151|<sup>151</sup>Sm]] || 90y || Most will be destroyed by [[neutron capture]] while still in reactor
|-
|	6.0507%	|| [[Tc-99|<sup>99</sup>Tc]] || 211ky || Dominant radiation source among FP in period about {{e|4}} to {{e|6}} years; mobile in environment; candidate for disposal by [[nuclear transmutation]]
|-
|	0.0236%	|| [[tin-126|<sup>126</sup>Sn]] || 230ky
|-
|	0.0508%	|| [[selenium-79|<sup>79</sup>Se]] || 295ky
|-
|	6.2956%	|| [[Zr-93|<sup>93</sup>Zr]] || 1.53my
|-
|	<6.3333%	|| [[Cs-135|<sup>135</sup>Cs]]|| 2.3my
|-
|	0.1629%	|| [[palladium-107|<sup>107</sup>Pd]] || 6.5my
|-
|	0.6576%	|| [[iodine-129|<sup>129</sup>I]] || 15.7my || Mobile in environment; candidate for disposal by [[nuclear transmutation]]
|-
|	<1.0888%	|| [[samarium-149|<sup>149</sup>Sm]] || nonradioactive || [[neutron poison]]
|-
|	<0.0065%	|| [[gadolinium-157|<sup>157</sup>Gd]] || nonradioactive || [[neutron poison]]
|}

==Ordered by [[thermal neutron]] [[neutron absorption]] [[cross section]]==
{| class="wikitable sortable"
!Barns !!Yield !!Isotope !!t<sub>½</sub> !!Comment
|-
|2650000||	6.3333%	|| [[iodine-135|<sup>135</sup>I]] [[beta decay|→]] [[xenon-135|<sup>135</sup>Xe]] || 6.57h ||Most important [[neutron poison]]; [[neutron capture]] rapidly converts <sup>135</sup>Xe to <sup>136</sup>Xe; remainder decays (9.14h) to [[Cs-135|<sup>135</sup>Cs]] (2.3my)
|-
|254000||	0.0065%	|| [[gadolinium-157|<sup>157</sup>Gd]] || ∞ || [[neutron poison]], but low yield
|-
|40140||	1.0888%	|| [[samarium-149|<sup>149</sup>Sm]] || ∞ || 2nd most important [[neutron poison]]
|-
|20600||	0.0003%	|| [[cadmium-113m|<sup>113m</sup>Cd]] || 14.1y || most will be destroyed by neutron capture
|-
|15200 ||	0.4203%	|| [[samarium-151|<sup>151</sup>Sm]] || 90y || most will be destroyed by neutron capture
|-
|3950||	0.0330%	|| [[europium-155|<sup>155</sup>Eu]] [[beta decay|→]] [[gadolinium-155|<sup>155</sup>Gd]] || 4.76y ||both [[neutron poison]]s
|-
|96||	2.2713%	|| [[promethium-147|<sup>147</sup>Pm]] || 2.62y
|-
|80||	2.8336%	|| [[iodine-131|<sup>131</sup>I]] || 8.02d
|-
|29<br>140|| 6.7896% || [[cesium-133|<sup>133</sup>Cs]] [[neutron capture|→]] [[cesium-134|<sup>134</sup>Cs]] || ∞<br>2.065y ||[[neutron capture]] converts a few percent of nonradioactive <sup>133</sup>Cs to <sup>134</sup>Cs, which has very low direct yield because [[beta decay]] stops at <sup>134</sup>Xe; further capture will add to long-lived <sup>135</sup>Cs
|-
|20||	6.0507%	|| [[Tc-99|<sup>99</sup>Tc]] || 211ky || candidate for disposal by [[nuclear transmutation]]
|-
|18||	0.6576%	|| [[iodine-129|<sup>129</sup>I]] || 15.7my || candidate for disposal by [[nuclear transmutation]]
|-
|2.7||	6.2956%	|| [[Zr-93|<sup>93</sup>Zr]] || 1.53my || transmutation impractical
|-
|1.8||	0.1629%	|| [[palladium-107|<sup>107</sup>Pd]] || 6.5my
|-
|1.66||	0.2717%	|| [[krypton-85|<sup>85</sup>Kr]] || 10.78y
|-
|0.90||	5.7518%	|| [[strontium-90|<sup>90</sup>Sr]] || 28.9y
|-
|0.15||	0.3912%	|| [[ruthenium-106|<sup>106</sup>Ru]] || 373.6d
|-
|0.11||	6.0899%	|| [[Cs-137|<sup>137</sup>Cs]] || 30.17y
|-
| ||	0.0297%	|| [[antimony-125|<sup>125</sup>Sb]] || 2.76y
|-
| ||	0.0236%	|| [[tin-126|<sup>126</sup>Sn]] || 230ky
|-
| ||	0.0508%	|| [[selenium-79|<sup>79</sup>Se]] || 295ky
|-
|}

==References==
*[http://www-nds.iaea.org/sgnucdat/c1.htm Chain Fission Yields] For 90-Th-232 92-U-233 92-U-235 92-U-238 94-Pu-239 94-Pu-241, and Thermal, Fast, 14MeV.
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