Photon-counting in a spectral radiation detector

1. A radiation detector for registering incident photons, comprising:

detection circuitry configured to provide an electric output signal in response to incident photons, the output signal, being a voltage signal, comprising pulses having an amplitude indicative of energies deposited in the radiation detector by the incident photons;

an energy estimating circuit configured to detect that the output signal is larger than at least one threshold corresponding to an energy value in order to determine energies of incident photons; and

a registration circuit configured to detect incident photons independent of a comparison of the output signal with the at least one threshold, wherein the registration circuit comprises a maximum detector configured to detect and/or count local maxima of the output signal, the maximum detector comprising:

a peak detector circuit which includes a capacitor charged substantially to the value of the output signal when a voltage of the signal increases and which holds a charge when the value of the output signal decreases, and

a comparator circuit configured to detect a local maximum of the output signal when the value of the output signal falls below the voltage across the capacitor.

2. The radiation detector according to claim 1 , wherein the detection circuitry comprises:

a conversion element producing a pulse-like current signal in response to a photon incident onto the conversion element;

an integrating amplifier coupled to the conversion element and producing a step-like signal portions in response to the pulse-like current signal; and

a shaper circuit configured to process the step-like signal portions to generate the output signal.

3. The radiation detector according to claim 2 , wherein the registration circuit is configured to detect and/or count step-like portions of the signal produced by the integrating amplifier as the incident photons.

4. The radiation detector according to claim 1 , wherein a number and/or rate of incident photons with respect to each of a plurality of predetermined photon energy ranges is output, the photon energy ranges being defined based on the at least one threshold.

5. The radiation detector according to claim 4 , wherein the number and/or rate of photons detected in the registration circuit is output.

6. The radiation detector according to claim 4 , wherein the number and/or rate of incident photons with respect to each of the plurality of predetermined photon energy ranges is determined based on detections of photons in the registration circuit.

7. The radiation detector according to claim 6 , wherein the number and/or rate of incident photons with respect to one predetermined energy range is determined based on number of photons detected in the registration circuit while the output signal is larger than a threshold corresponding to a lower boundary of the energy range.

8. A method for detecting photons, comprising:

providing, by detection circuitry, an electric output signal in response to incident photons, the output signal, being a voltage signal, comprising pulses having an amplitude indicative of energies deposited in the radiation detector by the incident photons;

detecting, by an energy estimating circuit, the output signal being larger than at least one threshold corresponding to an energy value in order to determine energies of incident photons; and

detecting, by a registration circuit, incident photons independent of a comparison of the output signal with the at least one threshold, wherein the registration circuit comprises a maximum detector configured to detect and/or count local maxima of the output signal, the maximum detector comprising:

a peak detector circuit which includes a capacitor charged substantially to the value of the output signal when a voltage of the signal increases and which holds a charge when the value of the output signal decreases, and

a comparator circuit configured to detect a local maximum of the output signal when the value of the output signal falls below the voltage across the capacitor.

9. The radiation detector according to claim 1 , wherein the capacitor is discharged when the value of the output signal falls below the voltage across the capacitor.

10. The radiation detector according to claim 9 , wherein a detected local maximum is assigned to an energy range pertaining to the highest threshold crossed by the output signal at the time of the detection of the local maximum, and a photon having an energy in said range is detected based on the detection of the local maximum.