# What is fission?

• I
What is defined as "fission"?
Isotopes that undergo "fission" under influence of fast neutrons, though not slow neutrons, are classified as "fissionable". Is Be-9 fissionable?
What is the dividing line between "fission" and "cluster decay"?

phyzguy
I have a group of nuclear engineering friends, and there is always rivalry between the fission folks and the fusion folks. The fission folks are fond of pointing out that the much studied aneutronic fusion reaction p+B11->3α should really be considered fission!

mathman
Speed of neutron does not define fissionable. Fissionable usually refers to a nuclide absorbing a neutron and splitting up in (usually) two smaller nuclides plus debris (neutrons, etc.). Be-9 is not fissionable.

https://en.wikipedia.org/wiki/Cluster_decay

Fissionable usually refers to a nuclide absorbing a neutron and splitting up in (usually) two smaller nuclides plus debris (neutrons, etc.). Be-9 is not fissionable.
Be-9+n=2α+2n
Common reaction. Is it fission?

mathman