The only thing I need is an appropriate scintillator block to finish construction of a neutron generating fusor.
The question is: Just how hard is it to make a BC-720 scintillator? Can one cast a solid block of ZnS doped resin or do I need the more complex configuration of concentric cylinders of doped resin, shown in Richerd Hull's tapes?
Tom Dressel
Sintillator Questions?
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Re: Sintillator Questions?
A solid block of resin with incorporated phosphor is a close cousin of the Hornyak button, named after its creator. The resin should be one with a fairly high hydrogen content, but little or no fluorescence or energy storage of its own. Hornyak used a mixture of ZnS and lucite granules. What ever the base resin used, the result is a white translucent chunk of plastic. Neutons passing through the material transfer energy to the hydrogen nuclei via collision. These recoil protons spend all their energy in a few hundreths to a tenth of a millimeter, and excite the phosphor. A hornyak button should not be more than about an inch thick, otherwise the scintillation light has difficulty escaping from the translucent plastic. Hornyak buttons have fair gamma rejection, as gammas and their attendent electrons via Compton scattering, pair production, and photoelectric effect are not as efficient at exciting the ZnS phosphor as are the recoil protons. Gammas can be discriminated against by setting the discriminator level to reject low level events. This also throws out the low energy portion of the recoil protons. The resulting detector can be somewhere between a few tenths of a percent to one percent efficient. depending on the setup and the level of amplitude rejection.
The BC-720 is a variant of the Hornyak button that increases the gamma rejection with an arrangement of coencentric rings of ZnS loaded plastic in a clear matrix. The result looks like a bull's eye. The relatively thin rings of phosphor loaded material alternating with inactive material help to reduce gamma sensitivity, while still retaining enough neutron sensitivity to make the effort worthwhile.
The BC-720 is a variant of the Hornyak button that increases the gamma rejection with an arrangement of coencentric rings of ZnS loaded plastic in a clear matrix. The result looks like a bull's eye. The relatively thin rings of phosphor loaded material alternating with inactive material help to reduce gamma sensitivity, while still retaining enough neutron sensitivity to make the effort worthwhile.