Gamma-ray spectrometer

1. An apparatus comprising a calibration source and a gamma-ray spectrometer arranged to receive gamma-rays from the calibration source,

the gamma-ray spectrometer comprising:

a scintillator material optically coupled to two or more photomultipliers, the two or more photomultipliers being arranged to detect photons generated in the scintillator material associated with gamma-ray interactions between the scintillator material and gamma-rays received from the calibration source, wherein the two or more photomultipliers are operable to output respective detection signals associated with the gamma-ray interactions;

the calibration source comprising:

a radioactive material having a decay transition associated with emission of a radiation particle and a gamma-ray, a detector arranged to receive radiation particles emitted from the radioactive material, and a gating circuit coupled to the detector and arranged to output a gating signal in response to a detection of a radiation particle by the detector:

the apparatus further comprising:

a switch coupled to receive the respective detection signals from the two or more photomultipliers and operable to select detection signals from one of the two or more photomultipliers; and

a stabilization circuit coupled to the switch and the gating circuit, wherein the stabilization circuit is operable to receive the selected detection signal of the respective photomultiplier and to stabilize the gain of the photomultiplier that output the selected detection signals based on the detection signals measured in association with gating signals from the gating circuit.

2. The apparatus according to claim 1 , wherein the stabilization circuit is operable to generate and output a control signal to the switch for selecting the detection signals of one of the two or more photomultipliers.

3. The apparatus according to claim 1 , wherein the stabilization circuit is operable to generate a gain-change signal for the photomultiplier associated with the selected detection signals based on a comparison of an observed energy spectrum calculated from the selected detection signals and a reference energy spectrum of the calibration source.

4. The apparatus according to claim 3 , wherein the control circuit is operable to output the gain-change signal to the photomultiplier associated with the selected detection signals.

5. The apparatus according to claim 3 , wherein the stabilization circuit is operable to compare Compton-edges of the observed energy spectrum and the reference energy spectrum of the radioactive material in the calibration source.

6. The apparatus according to claim 3 , wherein the stabilization circuit is operable to compare the median channel of the reference energy spectrum and the median channel of the observed energy spectrum.

7. The apparatus according to claim 3 , wherein the stabilization circuit is operable to compare the median channel of the reference energy spectrum and the median channel of the observed energy spectrum, rescale the energy axis of the observed energy spectrum and measure the difference between the rescaled energy spectrum and the reference energy spectrum, and determine if a gain-change estimated from the medians is consistent with a gain change estimated by rescaling the energy spectrums.

8. The apparatus according to claim 3 , wherein the stabilization unit is operable to compare the count-rate in the observed energy spectrum with the count-rate observed in the reference energy spectrum.

9. The apparatus according to claim 1 , comprising: a data acquisition circuit operable to process the selected detection signals associated with a radioactive material in the calibration source and output an energy spectrum associated with the radioactive material in the calibration source.

10. The apparatus according to claim 1 , wherein the stabilization circuit is operable to rescale the energy axis of the observed energy spectrum and measure the difference between the rescaled energy spectrum and the reference energy spectrum.

11. The apparatus according to claim 10 , wherein the stabilization unit is operable to rescale the calibration spectrum with reference to the reference spectrum and compare the shape of the rescaled calibration spectrum with the shape of the reference spectrum.

12. The apparatus according to claim 1 , wherein each of the two or more photomultipliers comprises an amplifier.

13. A method for calibrating a gamma-ray spectrometer, comprising the steps of:

providing a calibration source and a gamma-ray spectrometer arranged to receive gamma-rays from the calibration source; the gamma-ray spectrometer comprising: a scintillator material optically coupled to two or more photomultipliers, the two or more photomultipliers being arranged to detect photons generated in the scintillator material associated with gamma-ray interactions between the scintillator material and gamma-rays received from the calibration source, wherein the two or more photomultipliers are operable to output respective detection signals associated with the gamma-ray interactions, and the calibration source comprising: a radioactive material having a decay transition associated with emission of a radiation particle and a gamma-ray, a detector arranged to receive radiation particles emitted from the radioactive material, and a gating circuit coupled to the detector and arranged to output a gating signal in response to a detection of a radiation particle by the detector;

detecting photons generated in the scintillator material associated with gamma-ray interactions between the scintillator material and gamma-rays received from the calibration source;

selecting detection signals from one of the two or more photomultipliers; and

stabilizing the gain of the photomultiplier associated with the selected detection signal based on the detection signals measured in association with gating signals from the gating circuit.