I looked and looked and looked and could really only find this.. and I'm not even sure if this is describing what you are asking:
"
Transuranics:
[FONT=Arial, Helvetica] In previous texts we talked about how the 238U in a fuel rod is not fissile and is a neutron absorber. We made the point that because it absorbs neutrons, it stops the chain reaction in a nuclear power plant from running away (and producing a nuclear bomb effect). This is a good thing. However, think about what it means when we say "238U is a neutron absorber". The following reaction expresses that statement:
[/FONT] [FONT=Arial, Helvetica]1 neutron + 238U
239U
[/FONT]
[FONT=Arial, Helvetica]
[/FONT]
[FONT=Arial, Helvetica]When 238U "captures" a neutron, it is added to the original uranium nucleus, producing the radioactive isotope of uranium, 239U. This isotope has a half-life of 23.45 months. It decays, through ß-, into 239Np. 239Np is also radioactive and decays into 239Pu. 239Np has a short half-life of about 2 days. This sequence of decays can be expressed like this:
[/FONT]
[FONT=Arial, Helvetica]
[/FONT]
[FONT=Arial, Helvetica]1 neutron + 238U
239U
239U
(ß- decay) 239Np
239Np
(ß- decay) 239Pu"[/FONT]