AutoradiographyandIntensifyingScreens

Autoradiography and Intensifying Screens

From time to time, someone asks a question about intensfying screens, both in my lab and in these web forums (like why do you put them in the deep freeze?). Recently, John Attwood of Kodak submitted the following explanation about how they work, and gave permission to post it here as a general "protocol".

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Intensifying screens are used to reduce the exposure time or increase the sensitivity in the detection of radiolabeled samples. Intensifying screens diminish the resolution of an image compared to a direct (no intensifying screen) exposure. The decrease in resolution is due to the increased distance from the origin (sample) and the emulsion, where the image is formed. To get the best resolution possible you should use a sensitive single emulsion film like BioMax MR film available from Kodak.

Intensifying screens work by generating photons through the interaction of the radiolabeled particles energy and the phosphor in the intensifying screen. The energy from the beta particles interacts with the phosphor to generate a large number of photons (optimal sensitivity in such a system is reached when the photons (generated by the screen) wavelength match the peak spectral response of the film). Keep in mind the photons are less energetic than the beta particles used to create them.

All intensifying screens perform optimally at -60 to -80 degrees Celsius. The reason for this simplistically is, the activation energy required to form a stable latent image (chemicals are required to create a permanent image) on the film is lowered. At room temperature a larger activation energy is required to form the stable latent image. Therefore more energy is required to achieve an image at room temperature using an intensifying screen compared to using a screen at -60 Celsius. The activation energy needs to be reduced because the photons (though more numerous) are less energetic than the radioisotope particles

Conventional intensifying screens work by placing a radiolabeled sample on a sheet of autoradiography film with the intensifying screen laying under the film (i.e. the film is sandwiched between the screen and the sample). To make use of the intensifying screen, the radioisotope particles must have enough energy to pass through the film. 32P and 125I have sufficient energies to penetrate through the film. Radioisotopes such as 3H, 14C, 35S, & 33P lack sufficient energy to penetrate the estar component of the film. The estar is the solid matrix the emulsion is coated onto. Therefore, intensifying screens used in this way offer no benefit to weak and medium energy radioisotopes such as 3H, 33P, 35S and 14C.

Scientific Imaging Systems (Kodak) has recently introduced an innovative intensifying screen system called the BioMax TranScreen system. This system solves the problem of the film attenuating the beta particle before it reaches the intensifying screen. This system is described in detail on the Kodak Scientific Imaging Systems web site - www.kodak.com/go/scientific .

Disclaimer: Links to Kodak's web pages are provided as a courtesy and do not imply endorsement by the National Marine Fisheries Service or the Northwest Fisheries Science Center.