Brightness enhancement of positron sources

Claim 2

Method for producing a substantially monoenergetic low-energy beam of positrons comprising (a) accelerating at least part of the low-energy beam to an energy substantially greater than the initial low energy of the beam, (b) causing at least part of the accelerated beam to enter into an interaction region adapted to subject the beam to non-conservative forces, characterized in that the method further comprises (c) arranging the interaction region such that at least part of the beam that enters the region is again emitted from the region, the positrons in the emitted beam having substantially less energy after being emitted from the region than before entering it, and (d) accelerating at least part of the beam emitted from the interaction region to an energy substantially greater than the energy of the beam after emission from the interaction region.

Claim 3

Method of claim 1 wherein the interaction region is the surface and volume of a positron moderator.

Claim 4

Method of claim 2 wherein the positron moderator is an activated monocrystalline moderator.

Claim 5

Method of claim 3 wherein the moderator is a Cu(111)+S moderator.

Claim 6

Method of claim 1 wherein the positron source comprises radioactive atoms having a positron-emitting decay mode, the atoms being contained in a matrix material.

Claim 7

Method of claim 5 wherein the radioactive atoms are 58 Co.

Claim 8

Method of claim 1 wherein the positron source comprises neutron-activated atoms having an excited state that has a positron-emitting decay mode, the atoms being contained in a thin layer of matrix material.

Claim 9

Method of claim 7 wherein the atoms are 64 Cu.

Claim 10

Method of claim 7 wherein the positron source consists of at least one segment having spherical curvature.

Claim 11

Method of claim 7 wherein the positron source consists of at least one segment having cylindrical curvature.

Claim 12

Method of claim 1 wherein at least part of the moderated positron beam is subjected to time-varying electric potentials adapted to result in the transformation of the essentially continuous positron beam into a succession of positron pulses.

Claim 13

Method of claim 11 wherein the time-varying electric potential consists of potential pulses V(t)=(1/2)m l 2 t -2 , where m is the positron mass, t is the time, with t max ≦t≦0 for each pulse, and V(t) is applied along an acceleration path of length l, at the end of the acceleration path being a target, whereby the positrons present within l at t=t max will arrive substantially simultaneously at the target at t=0.

Claim 14

Method of claim 11 wherein the time-varying electric potential consists of potential pulses of constant amplitude for 0≦t≦t max , and duration greater than (π/2) √m/k, where m is the positron mass and k an arbitrary constant, the potential varying spatially according to V(z)=kz 2 along an acceleration path of length l, at the end of the acceleration path being a target at z=0, where z is the distance along the beam axis, whereby the positrons present within l at t=0 will arrive substantially simultaneously at the target.

Claim 15

Apparatus for producing a substantially monoenergetic low-energy beam of positrons comprising (a) means for accelerating at least part of the low-energy beam to an energy substantially greater than the initial low energy of the beam, (b) means for subjecting in an interaction region the accelerated beam to nonconservative forces, characterized in that (c) the means in (b) are adapted to emit from the interaction region at least part of the accelerated beam that enters the interaction region, the emitted beam having substantially lower energy than the accelerated beam, and the apparatus further comprises (d) means for accelerating at least part of the beam emitted from the interaction region to an energy substantially greater than the energy of the beam after emission from the interaction region.

Claim 16

Apparatus for producing a substantially monoenergetic low-energy beam of positrons comprising (a) means for accelerating at least part of the low-energy beam to an energy substantially greater than the initial low energy of the beam, (b) means for subjecting in an interaction region the accelerated beam to nonconservative forces, characterized in that (c) the means in (b) are adapted to emit from the interaction region at least part of the accelerated beam that enters the interaction region, the emitted beam having substantially lower energy than the accelerated beam, and the apparatus further comprises (d) means for accelerating at least part of the beam emitted from the interaction region to an energy substantially greater than the energy of the beam after emission from the interaction region.

Claim 17

Apparatus of claim 14, wherein the means for subjecting in an interaction region the accelerated beam to nonconservative forces are positron moderating means.

Claim 18

Apparatus of claim 15, wherein the positron moderating means is an activated monocrystalline moderator.

Claim 19

Apparatus of claim 16, wherein the activated monocrystalline moderator is a Cu(111)+S moderator.

Claim 20

Apparatus for producing quasi-monoenergetic positron pulses, the apparatus being adapted to being traversed by the positrons in a longitudinal direction from an entrance side to an exit side, the apparatus comprising (a) means for maintaining a substantially uniform constant longitudinal magnetic field B o in a region of the apparatus comprising a drift region, (b) means for maintaining a constant longitudinal magnetic field B m >B o throughout a part of the drift region, thereby maintaining a magnetic mirror, (c) an RF cavity, driven at the positron cyclotron resonance frequency, the cavity being located in the drift region at the exit side of the magnetic mirror, the cavity being adapted to impart only transverse energy to the positrons that pass through the cavity, (d) electrical means for repelling positrons of longitudinal energy less than a predetermined energy ε l , the means being located in the drift region at the exit side of the RF cavity, (e) means for applying a time-varying potential along an acceleration region, the acceleration region being located at the exit side of the electrical means for repelling charged particles, characterized in that the apparatus further comprises (f) means for subjecting positrons in an interaction region to nonconservative forces.

Claim 21

Apparatus for producing quasi-monoenergetic positron pulses, the apparatus being adapted to being traversed by the positrons in a longitudinal direction from an entrance side to an exit side, the apparatus comprising (a) means for maintaining a substantially uniform constant longitudinal magnetic field B o in a region of the apparatus comprising a drift region, (b) means for maintaining a constant longitudinal magnetic field B m >B o throughout a part of the drift region, thereby maintaining a magnetic mirror, (c) an RF cavity, driven at the positron cyclotron resonance frequency, the cavity being located in the drift region at the exit side of the magnetic mirror, the cavity being adapted to impart only transverse energy to the positrons that pass through the cavity, (d) electrical means for repelling positrons of longitudinal energy less than a predetermined energy ε l , the means being located in the drift region at the exit side of the RF cavity, (e) means for applying a time-varying potential along an acceleration region, the acceleration region being located at the exit side of the electrical means for repelling charged particles, characterized in that the apparatus further comprises (f) means for subjecting positrons in an interaction region to nonconservative forces.