Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

U-235 fission

  1. Feb 1, 2010 #1

    I know that there are a number of different ways that uranium-235 can decay when a slow neutron collides with it.

    I am trying to get a picture of all the possible reactions that can occur.

    One is U-235+n --> Ba-144 + Kr-90 +2n

    Another is: U-235 +n --> Xe-140 + Sr-94 +2n

    Can anyone give me any more examples of how it can decay? Can anyone give me an example where three neutrons are produced?

    What is the probability of each reaction occuring? The two I have here seem to be used pretty widely as examples, so I guess their probability would be higher than some others.

    Many thanks,


    EDIT: Just found U-235+n --> Xe-143 + Sr-90 + 3n... any others?
    Last edited: Feb 1, 2010
  2. jcsd
  3. Feb 1, 2010 #2


    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    It can decay into anything where the total number of neutrons and protons is conserved. You can make up literally thousands of examples.
  4. Feb 1, 2010 #3
    You'll find this data at the NNDC useful for answering part of your question:


    The colors show the relative frequency in which a given nuclide appears as a product of thermal fission of U-235. Notice that for thermal fission, the two most common regions are centered around about A = 90 and A = 135. That's why you'll see nuclides with those specific masses used as examples for products frequently. The region in the center around A = 115 isn't as frequent for thermal fission. If you click on one of the colored nuclides, you'll get some information at the bottom. The right column tells you how often that particular nuclide appears as a product of thermal fission. For example, click on Xe-135 and you'll see a fission yield of 0.00178. The fission yields won't tell you how often that particular decay happens since each one includes all possible numbers of neutrons (which can range from about 0 to 6 or more), but they'll at least give you an order of magnitude idea.

    If you assume 3 neutrons, the other product would be A = 235 - 3 - 135 = 97 and Z = 92 - 54 = 38, so Sr-97. You can go through the chart and pick out as many possibilities as you want.
    Last edited by a moderator: Apr 24, 2017
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook