Directional radiation detectors

1. A method of determining a location of a radioactive source, the method comprising:

scanning a volume with one or more directional radiation detectors, the respective directional radiation detectors comprising:

a radiation sensor capable of sensing slow neutrons;

a first radiation attenuator partially surrounding the radiation sensor, the first radiation attenuator defining a first aperture and composed at least in part of a first material selected to slow neutrons;

a second radiation attenuator positioned between the first radiation attenuator and the radiation sensor, the second radiation attenuator defining a second aperture at least partially overlapping the first aperture, the second radiation attenuator composed at least in part of a second material selected to absorb neutrons slowed by the first radiation attenuator, where the second material is different from the first material; and

a third radiation attenuator positioned between the second radiation attenuator and the radiation sensor, the third radiation attenuator composed at least in part of a third material selected to slow neutrons, the third radiation attenuator being further positioned such that incident radiation that passes through the first aperture of the first radiation attenuator and the second aperture of the second radiation attenuator passes through the third radiation attenuator prior to reaching the radiation sensor,

wherein the scanning comprises automatically moving the one or more radiation detectors to a plurality of predetermined positions, and for the respective positions, taking a reading of radiation magnitude;

receiving detector data from the one or more directional radiation detectors, the detector data obtained from the scanning of the volume,

wherein the detector data comprises, for each of the one or more directional radiation detectors, a plurality of readings of a radiation magnitude and a corresponding detector orientation; and

for each of the one or more directional radiation detectors:

determining, based on the received detector data, that a radiation magnitude represents radiation emitted by the radioactive source and received through the first and second apertures;

identifying the corresponding detector orientation; and

based on the detector orientation, calculating a solid angle within which the radioactive source is located.

2. The method of claim 1 , wherein for given radiation emitted by the radioactive source, if the radiation is received through the first and second apertures, the radiation magnitude is higher than if the radiation were received through the first and second radiation attenuators of the detector.

3. The method of claim 1 , wherein automatically moving the one or more radiation detectors to a plurality of predetermined positions comprises rotating through the plurality of predetermined positions over a time period.

4. The method of claim 1 , wherein scanning the volume further comprises:

varying the size of the first or second aperture of the one or more directional radiation detectors and taking a reading of radiation magnitude for a plurality of detector aperture sizes.

5. The method of claim 1 , wherein scanning the volume is a first scan performed while the one or more directional radiation detectors are at a first location, and further comprising:

performing a second scan of the volume while the one or more directional radiation detectors are at a second location; and

for each of the one or more directional radiation detectors:

determining, based on received detector data from the second scan, that a radiation magnitude represents radiation emitted by the radioactive source and received through the first and second apertures;

identifying the corresponding detector orientation; and

based on the detector orientation, calculating a solid angle within which the radioactive source is located; and

determining a location of the radioactive source based on the solid angles calculated using the detector data from the first and second scans.

6. The method of claim 1 , wherein detector data is received for at least three directional radiation detectors, and the method further comprising:

determining a location of the radioactive source based on the solid angles calculated for the at least three directional radiation detectors.

7. The method of claim 6 , wherein the determining comprises identifying an intersection of the solid angles calculated for the at least three directional radiation detectors.

8. A directional radiation detector, comprising:

a radiation sensor capable of sensing slow neutrons;

a first radiation attenuator partially surrounding the radiation sensor, the first radiation attenuator defining a first aperture, the first radiation attenuator composed at least in part of a first material, the first material selected to slow neutrons;

a second radiation attenuator positioned between the first radiation attenuator and the radiation sensor, the second radiation attenuator defining a second aperture at least partially overlapping the first aperture, the second radiation attenuator composed at least in part of a second material, the second material selected to absorb neutrons slowed by the first radiation attenuator, where the second material is different from the first material; and

a third radiation attenuator positioned between the second radiation attenuator and the radiation sensor, the third radiation attenuator composed at least in part of a third material, the third material selected to slow neutrons, the third radiation attenuator being further positioned such that incident radiation that passes through the first aperture of the first radiation attenuator and the second aperture of the second radiation attenuator passes through the third radiation attenuator prior to reaching the radiation sensor, wherein the first and second radiation attenuators are shaped such that a source of the incident radiation can be located using a plurality of readings obtained at different detector orientations and corresponding different times.

9. The directional radiation detector of claim 8 , wherein the first material is at least one of water or polyethylene, and wherein the second material is at least one of boron carbide or cadmium.

10. The directional radiation detector of claim 8 , wherein the radiation sensor comprises a scintillator crystal, and further comprising:

an optical sensor that detects an optical output from the scintillator crystal and provides an electrical output signal proportional to the optical output.

11. The directional radiation detector of claim 8 , wherein at least one of the first aperture or the second aperture is adjustable.

12. The directional radiation detector of claim 8 , wherein a distance between the radiation sensor and at least one of the first aperture or the second aperture is adjustable.

13. The directional radiation detector of claim 8 , wherein a solid angle defined by the first and second aperture is greater than or equal to 2π steradians.

14. The directional radiation detector of claim 8 , wherein the radiation sensor comprises a gas-filled tube.

15. A system, comprising:

at least two radiation detectors, the respective radiation detectors comprising:

a radiation sensor capable of sensing slow neutrons;

a first radiation attenuator partially surrounding the radiation sensor, the first radiation attenuator defining a first aperture, the first radiation attenuator composed at least in part of a first material, the first material selected to slow neutrons;

a second radiation attenuator positioned between the first radiation attenuator and the radiation sensor, the second radiation attenuator defining a second aperture at least partially overlapping the first aperture, the second radiation attenuator composed at least in part of a second material, the second material selected to absorb neutrons slowed by the first radiation attenuator, where the second material is different from the first material; and

a third radiation attenuator positioned between the second radiation attenuator and the radiation sensor, the third radiation attenuator composed at least in part of a third material, the third material selected to slow neutrons, the third radiation attenuator being further positioned such that incident radiation that passes through the first aperture of the first radiation attenuator and the second aperture of the second radiation attenuator passes through the third radiation attenuator prior to reaching the radiation sensor, wherein the first and second radiation attenuators are shaped such that a source of the incident radiation can be located using a plurality of readings obtained at different detector orientations and corresponding different times.

16. The system of claim 15 , wherein the first material is at least one of water or polyethylene, and wherein the second material is at least one of boron carbide or cadmium.

17. The system of claim 15 , wherein the radiation sensor comprises a scintillator crystal, the system further comprising an optical sensor configured to detect an optical output from the scintillator crystal and provide an electrical output signal proportional to the optical output.

18. The system of claim 15 , wherein the radiation sensor comprises a gas-filled tube.

19. The system of claim 15 , wherein at least one of i) at least one of the first aperture or the second aperture is adjustable or ii) a distance between the radiation sensor and at least one of the first aperture or the second aperture is adjustable.

20. The system of claim 15 , wherein the system comprises at least three radiation detectors.