Why not use the "Fricke dosimeter" reaction? Fe2+ becomes Fe3+, which
is blue, and the reaction goes to completion in as little as 400 Gy.
One potential problem, however is the other component is ~ 1N sulfuric
acid, so this is probably not "compatible" with most proteins. Another
problem with this and most any liquid-based dosimeter reaction is that
the concentration of oxygen matters a lot. O2 converts many radical
species in aqueous solution into different kinds of radicals. Still, if
your dose is going to be really high, then the O2 concentration might
not matter, and you might not even need the acid.
Personally, I have not encountered too many things that become colored
in the x-ray beam. Quite the opposite, in fact. At room temperature,
pretty much any organic dye will eventually bleach in a strong x-ray
beam. One of the best studied is methylene blue, and one paper even
calibrated it as a dosimeter:
http://dx.doi.org/10.1016/S0969-806X(98)00091-7
Despite this, however, information on the "half dose" of different dyes
in aqueous solution is hard to come by. Mainly (I think) because it
depends so much on the solution conditions. For example, in the
above-linked paper, the sensitivity of methylene blue changes by two
orders of magnitude upon addition of 5% ethanol.
We once tried putting some off-the-shelf scintillation cocktail into a
Fluidigm chip to try and visualize the x-ray beam therein, but this was
unfortunately disappointing. It glows, but you can barely see it.
Nothing like a YAG or other solid-state phosphor. I think this is a
testament to how difficult it can be to get the one radiation chemistry
reaction you want to "go" in the liquid state.
If you want something that becomes colored upon irradiation, I would
start with pH-sensitive dyes. These obviously work by reacting with
protons, and I imagine the reaction with a radical hydrogen atom could
produce a similar result. The phrases you want to google are
"radiochromic dye" or maybe just "leuco dye". Very interesting review
is here:
http://www.aapm.org/pubs/reports/rpt_63.pdf
-James Holton
MAD Scientist
On 2/8/2011 3:32 AM, Richard Edward Gillilan wrote:
Does anyone know of a water soluble dye that changes color upon exposure to
x-rays?
Preferably from clear to a dark color. Must work in the liquid state
(non-frozen... so color centers are out).
Doesn't matter if it is organic or inorganic.
Thanks
Richard Gillilan
MacCHESS
Cornell University
Ithaca, NY
