Patent Number: 
Section: claims

1. A modular photon emitter, comprising:a spring;a disk including a Beta source;a plastic scintillator disk adjacent said Beta source;a neutral density filter over said scintillator disk; anda bottom cap and a capsule securable together to define a cylindrical chamber with an opening in said capsule on one end;wherein said spring, Beta source disk, plastic scintillator disk, and filter are encapsulated in said cylindrical chamber with said filter adjacent said opening on one end of said capsule and said spring biasing said Beta source disk and said scintillator disk toward said opening. 2. The photon emitter of claim 1, wherein the surface of said scintillator disk adjacent said Beta source disk is roughened. 3. The photon emitter of claim 1, wherein said Beta source is C14. 4. The photon emitter of claim 1, wherein said capsule includes an annular face surrounding said opening, and said filter is secured against said face.