Fission producing Cs-137 This is I suppose quite a precise question about Nuclear fission. What produces, aside from U-235, via a fission process, Cs-137? 
Does any isotope of Actinium, for example, undergo a fission process and break into Cs-137 and something else?
Is there any way for me to easily figure this out for myself?
Many thanks.
 A: Fission reaction tend to produce a range of potential daughter nuclei, so the decay path is not just one single pair.
There is a broad literature on fission yields, much of it from the 1950's and 60's (not surprisingly).  For example, the 1965 IAEA symposium on Physics and Chemistry of Fission is available on-line at the IAEA. A search on Cs137 finds papers about the fission yields from Pu239 and Th232 presented at that conference. Interestingly, the paper on Ac227 fission does not report measurements of Cs137, but there is no reason to believe that it is not produced (with reasonable yields) given the curves of relative fission yield vs mass number. 
A: When an isotope of an element $A$ is fissioned, it breaks up in a number of pairs of daughter products, say $B$ and $C$, where $B$ and $C$ are isotopes of comparable atomic mass. Often 2 or 3 neutrons are also released (opening up the possibility of chain reactions).
However, the total number of nucleons, that is protons plus neutrons, is preserved during the nuclear reaction. The atomic number Z of the fissioned isotope is thus equal to the sum of the atomic numbers of the daughter nuclei:
$A_Z \to B_{Z1} + C_{Z2}$.
With $Z=Z_1+Z_2$.
Since as for Cs, $Z=55$, if the starting nucleus was $U_{92}^{235}$, then the second daughter product would be $Z_2=92-55=37$, which is Rb.
For an $Ac_{89}$ isotope and a Cs fission daughter, $Z_2=89-55=34$, which is Se, as the second daughter.
Other combinations of daughter products that could possibly arise from fissioning an Ac isotope  could be (Ba,As), (Xe,Br), (I,Kr) etc.
