Apparatus and method for temperature correction and expanded count rate of inorganic scintillation detectors

• US 20050269513A1
• Filed: 06/02/2004
• Published: 12/08/2005
• Est. Priority Date: 06/02/2004
• Status: Active Grant

• Current Assignee: Los Alamos National Security LLC (Government of the United States of America)
• Original Assignee: Los Alamos National Security LLC (Government of the United States of America)
• Inventors: Ianakiev, Kiril D., Hsue, Sin Tao, Browne, Michael C., Audia, Jeffrey M.
• Granted Patent: US 7,081,626 B2
• Time in Patent Office: Days
• US Class Current: 250/362
• CPC Class Codes: G01T 1/20 with scintillation detectors

Abstract

The present invention includes an apparatus and corresponding method for temperature correction and count rate expansion of inorganic scintillation detectors. A temperature sensor is attached to an inorganic scintillation detector. The inorganic scintillation detector, due to interaction with incident radiation, creates light pulse signals. A photoreceiver processes the light pulse signals to current signals. Temperature correction circuitry that uses a fast light component signal, a slow light component signal, and the temperature signal from the temperature sensor to corrected an inorganic scintillation detector signal output and expanded the count rate.

Claims

1. An inorganic scintillation detector having temperature correction and an extended count rate, comprising:

(a) an inorganic scintillator outputting a scintillator light pulse signal from incident radiation,

(b) a photoreceiver receiving said light pulse signal and outputting a current signal,

(c) a temperature sensor attached to said inorganic scintillator and outputting a temperature signal indicative of a temperature of said scintillator, and

(d) temperature correction circuitry receiving said current signal and said temperature signal, and configured to process a fast light component of said current signal, a slow light component of said current signal, and said temperature signal, and output a temperature corrected scintillator signal over an extended count rate.

2. The apparatus of claim 1 where said photoreceiver is selected from the group consisting of:

photomultiplier tubes, photodiodes, and avalanche photodiodes.

3. The apparatus of claim 1 where said temperature correction circuitry comprises:

(a) a preamplifier package for integrating said current signal,

(b) a gain control attenuator for compensating said current signal for total light yield temperature dependence and gain stabilization,

(c) a pulse shaper for shaping said current signal,

(d) a multi-channel analyzer outputting a pulse height spectrum from said current signal, and

(e) a microcontroller for outputting a control signal to said gain control attenuator and said pulse shaper.

4. The apparatus of claim 3 where said preamplifier package comprises:

(a) a capacitor for integrating said current signal and creating a voltage step proportional to said output from said photoreceiver,

(b) a resistor for preventing circuit saturation, and

(c) an amplifier for maintaining said current signal from said photoreceiver independent of voltage across said capacitor.

5. The apparatus of claim 3 where said preamplifier package comprises:

(a) a programmable fast light component attenuator configured for scaling an integral of said current signal proportional to said fast light component, and a fast light component RC network for outputting a voltage step as a first weighted sum of a first integrated current signal and a first voltage drop of a fast light component current signal across said fast light component RC network resistor,

(b) a programmable slow light component attenuator configured for scaling an integral of said current signal proportional to said slow light component, and a slow light component RC network to provide a second voltage step as a second weighted sum of a second integrated current signal and a second voltage drop of a slow light component current signal across said slow light component RC network resistor,

(c) a resistor for preventing circuit saturation, and

(d) an amplifier for maintaining said current signal from said photoreceiver independent of voltage across said fast component attenuator, said fast component RC network, said slow component attenuator, and said slow component RC network.

6. The apparatus of claim 3 where said pulse shaper is a gated integrator with offset compensation.

7. The apparatus of claim 6 where said gated integrator with offset compensation comprises:

(a) a pre-shaper module for shaping said current signal and providing a pre-shaper output signal,

(b) a gated integrator module providing a gated integrator output signal proportional to said pre-shaper output signal,

(c) an amplifier gain unit for scaling up said gated integrator output signal and providing an output voltage signal,

(d) a sample and hold module for sampling said output voltage signal and providing an offset error voltage signal,

(e) an attenuator module for scaling down said offset error voltage signal, and

(f) a subtractor module for subtracting said offset error voltage signal from said gated integrator output signal.

8. The apparatus of claim 3 where said temperature correction circuitry further comprises:

(f) a reference shape generator outputting a reference pulse shape signal proportional to said scintillator light pulse, and

(g) a reference light source outputting a reference light pulse with amplitude and a shape determined by said reference shape generator.

9. The apparatus of claim 8 where said reference shape generator comprises:

(a) a fast component generator outputting a fast reference pulse shape and a fast reference amplitude to said reference light source, and

(b) a slow component generator outputting a slow reference pulse shape and a slow reference amplitude to said reference light source.

10. The apparatus of claim 8 where said reference light source comprises:

(a) a light emitting diode (LED) and a photodiode, said LED outputting said reference light pulse to said inorganic scintillator and said photodiode, said photodiode converting said reference light pulse to a first reference electrical pulse,

(b) a reference pulse shaper module for outputting a second reference electrical pulse from said first reference electrical pulse with an amplitude proportional to the total light produced by said LED,

(c) a reference peak stabilizer module and an LED driver module, where said reference peak stabilizer module compares said second reference electrical pulse height to a reference signal from said microcontroller, and outputs an amplitude feedback signal to said LED driver module, said LED driver module outputting an electrical pulse to said LED with a shape provided by said reference shape generator and an amplitude provided by said reference peak stabilizer.

11. A method for temperature correction and extension of count rate of inorganic scintillation detectors due to a temperature effect, comprising:

(a) detecting incident radiation with an inorganic scintillator and outputting a light pulse,

(b) determining a temperature of said inorganic scintillator at a time of detecting said incident radiation and outputting a temperature signal,

(c) converting said light pulse into a current pulse with a photoreceiver, and

(d) compensating for amplitude and shape of said current pulse with temperature correction circuitry.

12. The method of claim 11 where compensating for amplitude and shape of said current pulse comprises:

(a) converting said temperature signal into a control signal, and

(b) adjusting a gain control attenuator with said control signal to compensate for said temperature effect on said current pulse output from said photoreceiver.

13. The method of claim 11 where compensating for amplitude and shape of said current pulse comprises:

(a) producing a reference light pulse that includes a fast light component and a slow light component with a reference shape generator,

(b) injecting said reference light pulse into said inorganic scintillator so that a reference peak appears in a multichannel analyzer (MCA), and

(c) compensating said scintillator pulse shape with a microcontroller by calculating a centroid of said reference peak, and adjusting a gain control attenuator to compensate for said inorganic scintillator temperature and provide gain stabilization.

14. The method of claim 13 where compensating amplitude and shape of said current pulse further includes:

(d) scaling an integral of said current pulse proportional to said slow light component and outputting a first voltage step as a first weighted sum from integrating said current pulse with a first voltage drop created by said current pulse across a first resistor, and

(e) scaling an integral of said current pulse proportional to said fast light component and outputting a second voltage step as a second weighted sum from integrating said current pulse with a second voltage drop created by said current pulse across a second resistor.