Charged particle scanners
A volume interrogation system can use an accelerated beam of charged particles to interrogate objects using charged-particle attenuation and scattering tomography to screen items such as portable electronic devices, packages, baggage, industrial products, or food products for the presence of materials of interest inside. The exemplary systems and methods in this patent document can be employed in checkpoint applications to scan items. Such checkpoint applications can include border crossings, mass transit terminals (subways, buses, railways, ferries, etc.), and government and private-sector facilities.
1. A method of operating a scanner for interrogating contents of a volume, the method comprising:
generating a collimated beam of charged particles;
creating a rastered fan beam by steering the generated beam of charged particles through a range of angles;
converting the rastered fan beam into a rastered parallel beam;
steering the rastered parallel beam through a range of illumination angles to scan an object;
detecting positions and directions of the charged particles that exit the object; and
generating an estimate of a spatial map of atomic number and density of the object based on at least the positions and the directions of the charged particles that exit the object.
2. The method of claim 1 , further comprising:
moving an object to be scanned through the range of illumination angles of the steered rastered parallel beam.
3. The method of claim 1 , further comprising:
determining scatter angles of the charged particles using at least the positions and the directions of the charged particles that exit the object, wherein the atomic number and the density of the object are proportional to the scatter angles.
4. The method of claim 3 , further comprising:
detecting positions and directions of the charged particles beam before the charged particles beam enter the object, wherein the scatter angles are determined based on the positions of the charged particles beam before the charged particles beam enter the object and based on the positions of the charged particles that exit the object.
5. The method of claim 1 , further comprising:
measuring energy of the charged particles that exit the object; and
determining energy loss of the charged particles based on the measured energy and an energy of the charged particles beam that enter the object.
6. The method of claim 5 , further comprising:
determining an estimate of the density of a part of the object along a path of the charged particles beam based on the energy loss, wherein the density of the part of the object is proportional to the energy loss.
7. The method of claim 1 , wherein the generated beam of charged particles is steered through the range of angles in one dimension.
8. The method of claim 1 , wherein the rastered fan beam having an angular deflection is converted into the rastered parallel beam by applying magnetic fields that causes the rastered fan beam to bend to the rastered parallel beam.
9. The method of claim 8 , wherein the magnetic fields have opposite polarities.
10. The method of claim 1 , wherein the rastered fan beam is created by sweeping a first magnetic field of a first magnet over a first range of magnetic fields.
11. The method of claim 1 , wherein the rastered parallel beam is steered by sweeping a second magnetic field of a second magnet over a second range of magnetic fields.
12. The method of claim 1 , wherein the steering of the rastered parallel beam adjusts entry angles of the charged particles.
13. The method of claim 1 , wherein the range of illumination angles to scan the object are selectable.
14. The method of claim 1 , wherein the creating the rastered fan beam, the converting the rastered fan beam into the rastered parallel beam, and the steering the rastered parallel beam is performed in an area where a vacuum is maintained or applied.
15. The method of claim 1 , wherein after the collimated charged particles beam is generated and before the rastered fan beam is created the method further comprises:
receiving the collimated charged particles beam in a first orientation; and
changing an orientation of the collimated charged particles beam from the first orientation to a second orientation, wherein the rastered fan beam is created after the orientation of the collimated charged particles beam is in the second orientation.
16. The method of claim 15 , wherein the first orientation is perpendicular to the second orientation.
17. The method of claim 1 , wherein the collimated charged particles beam is generated having a pre-determined energy.
18. The method of claim 1 , wherein the spatial map of the atomic number and the density of the object are displayed.