Method and system for obtaining x-ray single photon spectroscopic data using room-temperature solid state detectors by measuring the induced electron current

• US 5,936,249 A
• Filed: 10/16/1997
• Issued: 08/10/1999
• Est. Priority Date: 10/23/1996
• Status: Expired due to Term

• Current Assignee: The State of Israel Atomic Energy Commission Soreq Nuclear Research/Center
• Original Assignee: State of Israel Atomic Energy Commission Soreg Nuclear Research Center
• Inventors: Eisen, Yosef, Engler, Gideon, Pollak, Eli, Shor, Asher
• Primary Examiner(s): Hannaher, Constantine
• Assistant Examiner(s): Israel, Andrew
• Application Number:
  US08/951,510
• Time in Patent Office: 663 Days
• Field of Search: 250/370.06, 250/370.07, 250/370.01, 250/370.04, 250/370.03
• US Class Current: 250/370.06
• CPC Class Codes: G01T 1/247 Detector read-out circuitry for processing gain or off-set correction H04N

Abstract

A method and a system for obtaining spectroscopic data of a single photon of a given energy that undergoes an interaction, beginning at a given point in time, with a room-temperature solid state detector of a given thickness and fitted with two electrodes, which detection is held at a given bias by a voltage applied to the electrodes. In the course of the interaction, pairs of electrons and holes are created within the solid state detector which induce charge on the electrodes; the method and system enable for determination of a current induced by the electrons, being a measurable and quite accurate parameter for deducing spectroscopic data. The electron induced current is defined as the charge induced on the electrodes due to the electrons only, divided by the time it takes the electrons to induce this charge. The mentioned time is considered equal to that of a particular portion of a signal of the complete induced charge, and both the time and the charge are determined by the method and the system.

Claims

1. A method for obtaining spectroscopic data of a single photon of a given energy that undergoes an interaction, beginning at a given point in time, with a room-temperature solid state detector of a given thickness and fitted with two electrodes, which detection is held at a given bias by a voltage applied to the electrodes;

said interaction creating pairs of electrons and holes within the solid state detector which induce charge on said electrodes, the method comprising the steps of;

taking sequential measurements in time of said induced charge whereby induced charge signal samples are obtained;

obtaining a slope signal by deriving time rate of change values of said induced charge signal samples at given points in time;

identifying a point in time at which a significant decrease in said slope signal samples occurs;

deriving an electron transit time value from the point in time at which a significant decrease in said slope occurs and the point in time at which the interaction begins;

determining an electron induced charge value from the induced charge signal samples at the point in time at which a significant decrease in said slope signal occurs as compared to the induced charge signal samples at the point in time at which the interaction begins;

deriving an electron induced current value from the electron induced charge value and the electron transit time value; and

converting into single photon spectroscopic data said electron induced current value.

2. The method according to claim 1, wherein said applied voltage is low.

3. The method according to claim 1, wherein the thickness of the solid state detector is greater than 5 millimeters.

4. The method according to claim 1, wherein the induced charge, measured before the point in time at which a significant decrease in said slope signal samples occurs, is multiplied by a linearizing projection function.

5. The method according to claim 1, wherein said sequential measurements of the induced charge are performed digitally by sequentially sampling the induced charge.

6. The method according to claim 5, wherein said slope signal is obtained by performing a statistical best fit on said induced charge signal samples.

7. The method according to claim 5, wherein a statistical best fit is a least χ

² fit.

8. The method according to claim 6, wherein the electron induced charge and the electron transit time are derived from said statistical best fit.

9. The method according to claim 1, wherein said photon is a gamma-ray photon.

10. The method according to claim 1, wherein said photon is an x-ray photon.

11. A system for obtaining spectroscopic data of a single photon of a given energy that undergoes an interaction, beginning at a given point in time, with a room-temperature solid state detector of a given thickness fitted with electrodes and held at a given bias by an applied voltage applied to the electrodes, an interaction creating pairs of electrons and holes within the solid state detector which induce charge on said electrodes, the system comprising:

measuring means for taking sequential measurements of said induced charge whereby induced charge signal samples are obtained;

slope determination means for determining a slope signal of said induced charge signal samples at given points in time;

first processor means for identifying a point in time at which a significant decrease in said slope signal samples occurs;

means for deriving an electron transit time value from the point in time at which a significant decrease in said slope occurs and the point in time at which the interaction begins;

means for determining an electron induced charge value from the induced charge signal samples at the point in time at which a significant decrease in said slope signal occurs as compared to the induced charge signal samples at the point in time at which the interaction begins;

second processor means for deriving an electron induced current value from the electron induced charge value and the electron transit time value; and

third processor means for converting into single photon spectroscopic data from said electron induced current value.

12. The system according to claim 11, including digital components whereby said sequential measurements of said induced charge signal are performed digitally by sequentially sampling the induced charge signal by means of an analog to digital converter thereby yielding induced charge signal samples.

13. The system according to claim 12, further including memory means for storing said induced charge signal samples.

14. The system according to claim 11, wherein said first, second and third processor means are combined in one processor means.

15. The system according to claim 14, wherein said one processor means is a microprocessor.

16. The system according to claim 11, including analog components to determine the electron induced charge and the electron transit time.

17. The system according to claim 16, further provided with an electronic Zero Time Level Discriminator which identifies a single photon interaction event whereupon a recording of the induced charge signal is initiated.

18. The system according to claim 16, wherein said slope determination means comprises a Change of Slope Discriminator.

19. The system according to claim 16, wherein said measuring means is a Sample/Hold circuit for determining the electron induced charge at the point in time at which a significant decrease in said slope signal occurs.

20. The system according to claim 16, wherein the electron transit time is determined by a Zero Time Level Discriminator and a Change in Slope Discriminator.

21. The system according to claim 16, wherein the electron induced current is derived from a Pulse Divider Analyzer.

22. The system according to claim 11, wherein said photon is a gamma-ray photon.

23. The system according to claim 11, wherein said photon is an x-ray photon.