In each Fission event 3 neutrons are released.

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    Fission Neutrons
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SUMMARY

In nuclear fission, the number of neutrons released varies by isotope and reaction type. Specifically, U-235 typically releases an average of 2.42 neutrons per fission event, while Pu-239 releases approximately 2.87 neutrons. The emission of neutrons can be categorized into prompt neutrons and delayed neutrons, with the latter allowing for better control in nuclear reactors. Additionally, neutron emission rates can increase with neutron energy, although the likelihood of causing further fission decreases.

PREREQUISITES
  • Understanding of nuclear fission processes
  • Familiarity with isotopes such as U-235, U-233, Pu-239, and Pu-241
  • Knowledge of neutron behavior in nuclear reactions
  • Basic principles of nuclear reactor control mechanisms
NEXT STEPS
  • Research the differences between prompt and delayed neutrons in nuclear fission
  • Study the fission characteristics of U-233 and Pu-241
  • Explore neutron capture theory and its implications for reactor design
  • Examine the role of fission products like Kr-87* in neutron emission
USEFUL FOR

Nuclear physicists, reactor engineers, and anyone involved in nuclear safety and reactor design will benefit from this discussion.

satrohraj
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In each fission event of nuclear 3 neutrons are released.
Is that for all nuclear reactions or just U-235?
 
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This is NOT true. For all fission reactions, the number of neutrons can change. U-235 can fission and, besides the fission products, result in only two other neutrons or even more than three, but rarely. There are also differences in when neutrons are emitted - the different cases are called prompt neutrons and delayed neutrons.
 
As theCandyman already mentioned, the main fissile isotopes of U and Pu release either 2 or 3 neutrons from each fission.

The average number of neutrons released by each thermal fission is:

2.49 for U-233
2.42 for U-235
2.87 for Pu-239, and
2.93 for Pu-241.

As the neutron energy increases, the average number of neutrons emitted per fission increases, but the probability that a neutron will cause fission, rather than simply being captured, decreases with increasing energy.

These and other heavier nuclei can also undergo spontaeous fission but at very low rates.

Some fission products, e.g. Kr-87*, a decay product of Br-87. Kr-87* is an excited state of Kr-87 and emits a single neutron. The delay is based on the half-life of the precursor Br-87. There are several groups of delayed neutron precursors and this delay allows for control of nuclear reactors.

This might be of interest -
http://hss.energy.gov/NuclearSafety/techstds/standard/hdbk1019/h1019v1.pdf
 
Last edited by a moderator:
Thanks, the pdf file helped me a lot..
 

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