Patent Number: 047633441
Section: claims

1. A source for producing X-rays at an energy greater than 2 keV corresponding to a peak frequency .omega., comprising: a number of foils, M, arranged as a succession of parallel elements to form a stack, the foils being constructed of a material having an atomic weight A, atomic number 15.ltoreq.Z.ltoreq.79, and a density .rho..gtoreq.3 gm/cm.sup.3, with each foil having a minimum thickness l.sub.2 ;  holding means for holding the foils in the stack and for maintaining a spacing l.sub.1 between adjacent foils in the stack;  electron accelerating means for directing an electron beam toward the stack to create transition radiation, the electron beam having an energy ##EQU16## but less than 500 MeV, where E.sub.o is the electron rest energy, A is the atomic weight of the foil material, Z is the atomic number of the foil material, m.sub.e is the mass of the electron, N.sub.o is Avogadro's number, .rho. is the density of the foils, and e is the electron charge, all units in the cgs system;  housing means for providing a controlled environment for the electron beam and the foil stack;  where M.gtoreq.(0.5)2/.mu.l.sub.2, where .mu. is the absorption coefficient of the foil material at the frequency .omega.;  where ##EQU17## where .lambda. is the wavelength of the X-rays at the peak frequency .omega., and where .gamma.=(1-.beta..sup.2).sup.1/2 where .beta. is the velocity of the electrons in the electron beam relative to the speed of light, and .omega..sub.p is the plasma frequency of the foil material;  where ##EQU18## if the housing means provides a vacuum environment; and where ##EQU19## if the housing means provides a gas environment, where .omega..sub.pg is the plasma frequency of the gas.  a number of foils M arranged as a succession of parallel elements to form a stack, the foils being constructed of a material of atomic weight A, atomic number 15.ltoreq.Z.ltoreq.79) and a density .rho..gtoreq.3 gm/cm.sup.3, with each foil having a minimum thickness l.sub.2 ;  holding means for holding the foils in the stack and for maitaining a spacing l.sub.1 between adjacent foils in the stack;  the number of foils M is M.ltoreq.2/.mu.l.sub.2 where .mu. is the absorption coefficient of the foil material at frequency .omega.;  the thickness ##EQU21## where .lambda. is the wavelength of the X-rays at the peak frequency .omega., and where .gamma.=(1-.beta..sup.2).sup.1/2 where .beta. is the velocity of the electrons in the electron beam relative to the speed of light, and .omega..sub.p is the plasma frequency of the foil material;  where ##EQU22## if the stack is used in a vacuum, and where ##EQU23## if the stack is used in a gas, and .omega..sub.pg is the plasma frequency of the gas.  a number of foils, M, arranged as a succession of parallel elements to form a stack, the foils being constructed of a material having an atomic weight A, a atomic number 15.ltoreq.Z.ltoreq.79, and a density .rho., with each foil having a minimum thickness l.sub.2 ;  holding means for holding the foils in the stack and for maintaining a spacing l.sub.1 between adjacent foils in the stack;  electron accelerating means for directing an electron beam toward the stack to create transition radiation, the electron beam having an energy ##EQU29## but less than 500 MeV, where E.sub.o is the electron rest energy, A is the atomic weight of the foil material, Z is the atomic number of the foil material, m.sub.e is the mass of the electron, N.sub.o is Avogadro's number, .rho. is the density of the foils, and e is the electron charge, all units in the cgs system;  housing means for providing a controlled environment for the electron beam and the foil stack;  M.gtoreq.(0.5)2/.mu.l.sub.2, and .mu. is the absorption coefficient of the foil material at the frequency .omega.;  where ##EQU30## and .omega..sub.k is the k-shell photoabsorption-edge frequency of the foil material, .lambda. is the wavelength of the X-rays at the peak frequency .omega., and where .gamma.=(1-.beta..sup.2).sup.1/2 and .beta. is the velocity of the electrons in the electron beam relative to the speed of light, and .omega..sub.p is the plasma frequency of the foil material; and ##EQU31## if the housing means provides a vacuum environment; and ##EQU32## if the housing means provides a gas environment, and .omega..sub.pg is the plasma frequency of the gas. 2. A source as in claim 1 wherein the foil thickness l.sub.2 satisfies the equation ##EQU20## where .omega..sub.k is the k-shell photoabsorption-edge frequency of the foil material. 3. A source as in claim 2 wherein the number of foils M is EQU M.gtoreq.(0.5)2/.mu..sub.k l.sub.2 4. A source as in claim 3 wherein 15.ltoreq.Z.ltoreq.60. 5. A source as in claim 2 wherein 15.ltoreq.Z.ltoreq.60. 6. A source as in claim 1 wherein 15.ltoreq.Z.ltoreq.60. 7. A source as in claim 6 wherein .rho..gtoreq.8.95 gm/cm.sup.3. 8. A source as in claim 6 wherein .rho..gtoreq.7.9 gm/cm.sup.3. 9. A target for use with an electron beam for producing transition radiation at a peak frequency .omega., comprising: 10. A target as in claim 9 wherein the foil thickness l.sub.2 satisfies the equation ##EQU24## where .omega..sub.k is the k-shell photoabsorption-edge frequency of foil material. 11. A target as in claim 10 wherein the number of foils M is EQU M.gtoreq.(0.5)2/.mu..sub.k l.sub.2 12. A target as in claim 11 wherein 15.ltoreq.Z.ltoreq.60. 13. A target as in claim 10 wherein 15.ltoreq.Z.ltoreq.60. 14. A target as in claim 9 wherein 15.ltoreq.Z.ltoreq.60. 15. A target as in claim 14 wherein .rho..gtoreq.8.95 gm/cm.sup.3. 16. A target as in claim 14 wherein .rho..gtoreq.7.9 gm/cm.sup.3. 17. A source as in claim 1 wherein ##EQU25## and ##EQU26## if the housing means provides a vacuum environment; and ##EQU27## if the housing provides a gas environment. 18. A source as in claim 17 wherein the foil thickness ##EQU28## where .omega..sub.k is the k-shell photoabsorption-edge frequency of the foil material. 19. A source as in claim 18 wherein the number of foils M is M=2/.mu..sub.k l.sub.2 where .mu..sub.k is the absorption coefficient of the foil material at a photon frequency .omega.=.omega..sub.o where .omega..sub.k -.epsilon.&lt;.omega..sub.o &lt;.omega..sub.k where .epsilon.=0.35 .omega..sub.k. 20. A source for producing X-rays at an energy greater than 2 keV corresponding to a peak frequency .omega., comprising: