Carriers for radiochemical seperation

[marc]

I just started working as a chemist (grad in may09) and am having to do a lot of on the job training. I learned a lot of theory in school but not much practical knowledge.  I am currently working on a writing up a separation procedure and am coming across something we never talked about in any of my classes and that is adding carriers to samples. I have flipped through a couple of books but haven't been able to find anything that gives a reason for adding them.


 ex when we analyze for 226Radium we use a Barium Carrier.

[Borek]

I suppose Mitch will be much better at answering this question, but my bet would be on coprecipitation - whatever you want to separate is in small quantities, but it will coprecipitate with some other substance - one that can be prepared in much larger quantities and as such will be much easier to oeprate with. That means carrier must be similar enough. But that's just a guess.

[marc]

After some searching I found my answer.

When using radioactive tracers in small concentration (ex. 1E-10M) the properties of the chemical might be very different then it is at higher concentrations. So if you add a macroscopic amount of isotopic nonradioactive sample along with the tracer it ensures normal chemical behavior.