Neutrons don’t “see” metal

Neutrons pass through metal, but are absorbed by hydrogen. Metal is “invisible” to the radiation coming from the uranium, but organic material, such as carbon chains, absorbs the neutrons.

…but how do you image it?

The glowing uranium radiation casts a shadow of the objects that the neutrons don’t pass through. How do you capture that? Neutrons don’t expose photographic film the way photons do. Fortunately, they can be converted into photons by impacting a scintillator screen made of gallium nitride.

In a nut shell: you have this pile of uranium in a water jacket that emits a beam of neutrons through a dry pipe. That stream of neutrons passes through the objects you place in an aluminum cassette which is “invisible” to the neutrons. The cassette also has a thin film of gallium nitride behind the objects you want to photograph. The back side of the gallium film (aka scintillating screen) is sandwiched to the photographic film so the photons that are converted from the passing neutrons on the incoming side don’t have far to travel to make a latent image.

Simple, right? 🙂

The printing process

The cyanotype images were edited in photoshop to convert the tones into a range that prints in ultraviolet light. The emulsion is a standard 100+ year old mixture of green ferric ammonium citrate and potassium ferricyanide. The emulsion is brushed onto Fabriano Artistico watercolor blocks and let dry. A negative is printed onto clear acetate from the modified photoshop image that looks really pale and thin compared to a silver negative. The negative is laid on the dry emulsion of the watercolor paper and pressed under glass with a vacuum blanket. A mercury vapor lamp, a lot like a yellow city street light, is used to expose the image through the negative. The paper is separated from the negative and washed in running water.

Neutron Ray Seeds & Sea Creatures
(and other random things we put in a nuclear reactor)