High speed x-ray beam chopper

• US 6,418,194 B1
• Filed: 03/29/2000
• Issued: 07/09/2002
• Est. Priority Date: 03/29/2000
• Status: Expired due to Fees

• Current Assignee: US Department of Energy (Government of the United States of America)
• Original Assignee: United States Department of Energy (Government of the United States of America)
• Inventors: McPherson, Armon, Mills, Dennis M.
• Primary Examiner(s): Porta, David P.
• Assistant Examiner(s): Barber, Therese
• Application Number:
  US09/537,992
• Time in Patent Office: 832 Days
• Field of Search: 378/86, 378/89, 378/145, 378/146, 378/147, 378/160, 378/16
• US Class Current: 378/160
• CPC Class Codes: G21K 1/04 using variable diaphragms, shutters, choppers
• CPC Class Codes: G21K 1/043 changing time structure of beams by mechanical means, e.g. choppers, spinning filter wheels

Abstract

A fast, economical, and compact x-ray beam chopper with a small mass and a small moment of inertia whose rotation can be synchronized and phase locked to an electronic signal from an x-ray source and be monitored by a light beam is disclosed. X-ray bursts shorter than 2.5 microseconds have been produced with a jitter time of less than 3 ns.

Claims

1. A device for chopping x-ray beams emanating from a source, the device comprising a rotating disk, said disk defining a channel extending along a diameter of said disk wherein the source is pulsating, wherein the angular position of said channel on said rotating disk can be phase locked to said pulsating source, and wherein the variation in the time required for each revolution in the rotational speed of the channel is less than 5 ppm.

2. The device as recited in claim 1 wherein said channel allows traversal by the x-ray beam for a time span shorter than 2500 nanoseconds.

3. The device as recited in claim 1 wherein said rotation allows traversal by the x-ray beam at a frequency of greater than 2600 Hz.

4. The device as recited in claim 1 wherein said disk rotates at a rate as high as 1335 Hz.

5. The device as recited in claim 1 wherein the disk is confined to a controlled atmosphere.

6. The device as recited in claim 5 wherein the controlled atmosphere provides a low-friction environment.

7. The device as recited in claim 1 wherein the source is continuous.

8. A device for chopping x-ray beams comprising a rotating disk having a first side and a second side, said disk defining a passage extending along the entire diameter of the disk.

9. The device as recited in claim 8 wherein the passage is a channel formed on the first side of said disk.

10. The device as recited in claim 8 wherein the passage is a tunnel formed between the first side and second side.

11. A device for chopping x-ray beams comprising:

a disk having a channel extending along a diameter of said disk and positioned at a specific height relative to a base face of said disk;

a shaft connecting said disk to a motor;

an first electrical means for powering said motor and a second electrical means for controlling said motor'"'"'s speed;

an optical means for determining a speed associated with said disk and for communicating said speed to said second electrical means;

an x-ray beam incident on said disk where said x-ray beam strikes said disk at a specific incident frequency and at a position on said disk coincident with said position of said channel relative to said base of said disk.

12. The device as recited in claim 11 wherein the device is enclosed in a housing having a first pair of ports and a second pair of ports where said first and said second pair of ports are positioned such that when each pair of ports is independently aligned with said channel that a beam will transverse from one port through said channel to the next port of said pair, and where in a plane constructed through said first pair of ports and said second pair of ports, a line joining the first pair of ports is offset from a line joining said second pair of ports by a specified angular separation.

13. The device as recited in claim 11 wherein said first electrical means is in communication with said second electrical means and wherein said second electrical means has a timing device which acts as a master clock for said chopping device.

14. The device as recited in claim 12 wherein said optical means comprises an optical beam which is focused on an outer circumferential surface of said disk, on which, a plurality of equally spaced polished facets exist and where a plurality of reflections from said facets is optically coupled to an optical encoder which transmits a frequency associated with said disk to said second electrical means for comparison to said master clock.

15. The device of claim 14 wherein said second electrical means contains a delay generator to control a phase difference between said master clock and said disk frequency.

16. The device of claim 15 wherein said second electrical means operates to phase-lock said rotational frequency of said disk to said master clock.

17. The device of claim 13 wherein master clock of said timing device is coupled to said specific incident frequency of said x-ray.