# Where do 35S and 32P come from?

1. May 13, 2008

### Mr.V.

Hi all,

I remember a long time ago in highschool our bio teacher mentioned that radiotracers used in biology back in the 40s-50s came out of the Manhattan project.

But searching through google, i haven't really been able to find which radiotracers that we commonly use in biology come from decaying uranium/plutonium etc.

2 of the big radiotracers we use are $$^{35}S$$ and $$^{32}P$$. Normally sulfur is used to label proteins and phosphorus is used to label DNA (although $$^{32}P$$ is useful for phosphorylation states of proteins too)

There are also others used such as $$^{123}I$$ and $$^{125}I$$.

Many of these (particularly $$^{32}P$$) have incredibly short half-lives so I'd imagine if they weren't being made from something with a much longer 1/2 life they'd have burned out of the universe long ago. So where do they come from and how are they made?

Last edited: May 13, 2008
2. May 13, 2008

### mgb_phys

They aren't made from heavy metal decay but from neutron irradiation of smaller atoms -
for which you need a reactor.
Today they are generally made in small specialised reactors or as a side product in a few powerstations.
Very short lived isotopes you have to make on-site in an accelarator and then inject them directly into the patient - often involving a frantic sprint accross the hospital.