1. A system for improving the counting characteristic of an X-ray photon counting detector is characterized by comprising a constant temperature and constant voltage device (1), a sub-forbidden band light (2), a bias controller (4), a temperature test insulation board (6), a temperature controller (8) and a PC (personal computer); the detector is positioned in the inner cavity of the constant temperature and pressure device (1), one end of the electrode at the two ends of the detector is connected with the bias voltage controller (4), and the other end is grounded; an observation window (3) is arranged on one side of the constant temperature and pressure device (1), and the sub-forbidden band light (2) is positioned above the observation window (3) and corresponds to the detector; the temperature testing heat insulation plate (6) is positioned below the detector and is electrically connected with the temperature controller (8); the temperature controller (8) and the bias voltage controller (4) are electrically and electrically connected with the PC through signals.

2. A method for improving the counting characteristics of an X-ray photon counting detector using the system of claim 1, characterized by the steps of:

step 1: the counting rate test is carried out on the X-ray photon counting detector to be tested,

step 2: one end of the electrode at the two ends of the detector is connected with the bias voltage controller, and the other end is connected with the ground; a temperature test insulation board is placed under the probe, the temperature test insulation board is connected with a temperature controller, and the temperature controller and a bias voltage controller are in electrical signal connection with a PC;

and step 3: the sub-forbidden band light lamp is arranged above the observation window and can irradiate the detector with the sub-forbidden band light;

and 4, step 4: applying bias voltage to the detector at negative high voltage of-300V to-600V by a bias voltage controller, and finding out the bias voltage which can improve the counting rate of the detector best;

and 5: under the condition of selecting bias voltage in the step 4, counting and testing the detector within the temperature range of 25-35 ℃ to find out the most obvious working temperature for improving the counting rate;

step 6: keeping bias voltage and temperature unchanged, and performing sub-forbidden band light irradiation on the detector within the range of 1050 nm-1550 nm of the sub-forbidden band light wavelength to find out the most obvious sub-forbidden band light wavelength and intensity for improving the counting rate.

Background

With the development of science and technology, the requirements of people for the field of X-ray imaging are gradually increased, and people are shifting the photon counting technology direction to the detection of high dose and high count. The X-ray photon counting detector has great application value in the X-ray imaging fields of security inspection, medical treatment and the like due to excellent performance.

The application of the X-ray photon counting detector is limited by the fact that under the condition of high dose of X-rays, due to the accumulation of a large number of holes in the area near the cathode, a reverse electric field is established, so that the net electric field intensity is reduced, the drift speed of carriers is reduced, and meanwhile, a large number of carriers are subjected to recombination action, so that a polarization effect is generated, and the counting rate is reduced. In order to realize the application of the photon counting detector in the fields of medical imaging and the like, the polarization effect is reduced, and the counting rate of the detector under high dose is improved.

It has been investigated how to eliminate or reduce the effects of polarization effects by controlling the external conditions. Excitation under applied conditions such as bias voltage, temperature and sub-forbidden band light is a feasible method, but practical application of improving polarization effect and increasing counting rate of an X-ray photon counting detector by combining two or more of the above two is rarely reported. The counting characteristic is a main factor for realizing the function of the device and limiting the detection efficiency of the detector, and the improvement of the counting characteristic of the detector is a great trend for developing an X-ray photon counting detector.

Disclosure of Invention

Technical problem to be solved

In order to avoid the defects of the prior art, the invention provides a system and a method for improving the counting characteristic of an X-ray photon counting detector, which have good X-ray detection and imaging capabilities and higher detection efficiency compared with a detector without the method, and at least solve one of the technical problems in the prior art.

Technical scheme

A system for improving the counting characteristic of an X-ray photon counting detector is characterized by comprising a constant temperature and constant voltage device 1, a sub-forbidden band light 2, a bias controller 4, a temperature test insulation board 6, a temperature controller 8 and a PC (personal computer); the detector is positioned in the inner cavity of the constant temperature and pressure device 1, one end of the electrode at the two ends of the detector is connected with the bias voltage controller 4, and the other end is grounded; an observation window 3 is arranged on one side of the constant temperature and voltage regulator 1, and a sub-forbidden band light 2 is positioned above the observation window 3 and corresponds to the detector; the temperature test insulation board 6 is positioned below the detector and is electrically connected with the temperature controller 8; the temperature controller 8 and the bias controller 4 are electrically and signally connected to the PC.

A method for improving the counting characteristics of an X-ray photon counting detector using the system of claim 1, characterized by the steps of:

step 1: the counting rate test is carried out on the X-ray photon counting detector to be tested,

step 2: one end of the electrode at the two ends of the detector is connected with the bias voltage controller, and the other end is connected with the ground; a temperature test insulation board is arranged below the probe, the temperature test insulation board is connected with a temperature controller, and the temperature controller 8 and the bias voltage controller 4 are in electrical signal connection with a PC;

and step 3: the sub-forbidden band light lamp is arranged above the observation window and can irradiate the detector with the sub-forbidden band light;

and 4, step 4: applying bias voltage to the detector at negative high voltage of-300V to-600V by a bias voltage controller, and finding out the bias voltage which can improve the counting rate of the detector best;

and 5: under the condition of selecting bias voltage in the step 4, counting and testing the detector within the temperature range of 25-35 ℃ to find out the most obvious working temperature for improving the counting rate;

step 6: keeping bias voltage and temperature unchanged, and performing sub-forbidden band light irradiation on the detector within the range of 1050 nm-1550 nm of the sub-forbidden band light wavelength to find out the most obvious sub-forbidden band light wavelength and intensity for improving the counting rate.

Advantageous effects

The system and the method for improving the counting characteristic of the X-ray photon counting detector comprise three parts, namely bias voltage regulation, temperature control and sub-forbidden band light selection, and the purpose of improving the counting characteristic of the X-ray detector for the bone densitometer is achieved by combining the three parts. The bias voltage is adjusted to find the most appropriate polarization correction bias voltage for different detectors by adjusting the magnitude of the bias voltage under the polarization condition of the detectors, so that reverse built-in electric fields of the detectors are weakened or even eliminated, carrier collection efficiency is obviously improved, and the spectrum of the detector is shifted towards the direction of a high-energy threshold. The temperature control is that under the polarization condition of the detector, the working temperature of the detector is controlled, when the X-ray dosage is higher, the distortion of the electric field of the detector is weakened along with the temperature rise, the carrier collection efficiency is improved, and the optical spectrum is shifted to the right. The optical selection of the sub-forbidden band is to select the most appropriate optical wavelength and intensity of the sub-forbidden band under the polarization condition of the detector, excite the recombination of valence band electrons and holes captured on the defect energy level, reduce the accumulation of the holes, weaken the built-in electric field, shift the energy spectrum of the detector to the right, and improve the collection efficiency. The bias voltage regulation, temperature control and sub-forbidden band light selection method provided by the invention can obviously improve the response of the detector to X-rays and the photon counting capacity under the polarization condition, and the whole method has high detection efficiency and excellent counting performance. Can meet the application requirements of high precision and high imaging quality of the X-ray bone densitometer detector.

The invention has the beneficial effects that:

firstly, the built-in electric field of the detector is weakened by bias voltage, temperature and external excitation of forbidden band light, the collection efficiency is increased, and the counting rate is improved.

Secondly, different parameter setting schemes for detectors with different counting characteristics can be realized (flexibly controllable). Different bias voltages, temperatures and sub-forbidden wavelengths and intensities are used for the unique counting characteristics of different detectors.

And thirdly, the whole method is easy to implement and control, is not limited to a specific detector, can be realized for the X-ray detector with poor counting performance under large dose, improves the counting performance and accurately detects the counting rate.

Drawings

FIG. 1 is a schematic diagram of the system architecture of the present invention;

FIG. 2 is a plot of count rate versus X-ray dose without applied excitation to the detector;

FIG. 3 is a graph of count rate versus X-ray dose at different operating biases;

FIG. 4 is a graph of count rate versus X-ray dose for various operating temperatures at a bias of-600V;

FIG. 5 is a graph of the change in the count rate of a detector under different wavelengths of sub-forbidden band illumination at 33.3 ℃ under a bias of-600V;

FIG. 6 is a flow chart of a method test of the present invention.

Description of the main symbols: 1-constant temperature and constant voltage device, 2-sub forbidden band lamp, 3-observation window, 4-bias controller, 5-electrode, 6-temperature test heat preservation board, 7-PC, 8-temperature controller, and 9-detector.

Detailed Description

The invention will now be further described with reference to the following examples and drawings:

for an X-ray photon counting detector with poorer detection performance due to polarization effect, the essence of the polarization effect is electric field distortion and space charge region formation in the crystal, and electric field distribution and space charge in the crystal are calculated due to electric field distortion caused by carrier trapping. And (4) estimating and finding: the detector with poor counting performance has high electric field linear change coefficient, high space charge density and large electric field distortion. The bias controller, the temperature controller and the external excitation of the sub-forbidden band light irradiation are beneficial to weakening of a built-in electric field, the front-end amplification rising edge time is reduced, the carrier collection efficiency is improved, and the counting rate is increased. And for different crystals with different internal defects, the most suitable bias voltage, temperature and forbidden band light are selected by carrying out counting rate test on the detector.

One end of the two end electrodes of the detector is connected with the bias voltage controller, and the other end is connected with the ground.

A temperature test insulation board is placed below the probe and connected with a temperature controller.

The detector is directly above and irradiated by sub-forbidden band light, and an observable window is arranged between the detector and the detector.

The detector is placed in the constant temperature and pressure device.

The temperature controller and the bias controller directly carry out data transmission with the PC.

In the process of detecting X-rays, the detector applies a certain bias voltage to the detector through a bias voltage controller connected with the detector, and the main function of the working bias voltage is to weaken or even eliminate the function of a reverse built-in electric field in an electric field distortion region. And the front-discharge rising edge time is obviously reduced along with the increase of the bias voltage within a certain range, the carrier collection efficiency is improved, the optical spectrum is shifted to the right, and the counting rate above the threshold value is increased.

Secondly, the working temperature of the detector is controlled at the same time, thermal excitation of impurities and defects is influenced, and de-trapping is increased. The detector crystals tend to accumulate to form built-in electric fields at lower temperatures. The temperature rise is beneficial to weakening of a built-in electric field, the front-end amplification rising edge time is reduced, the carrier collection efficiency is improved, and the counting rate is increased.

Finally, the detector is irradiated by the sub-forbidden band light, and the accumulation of holes is reduced because the electrons of the excited valence band are combined with the holes captured on the defect energy level, so that the electric field distortion of the detector is weakened, the collection efficiency is increased, the counting rate is improved, and the performance is improved more obviously when the light intensity is larger in a certain range.

Preferably, the bias voltage controller is biased at negative high voltage, and the bias voltage is-300 to-600V.

Preferably, the temperature controller controls the temperature to be 25-35 ℃.

Preferably, the wavelength of the sub-forbidden band light is 1050 nm-1550 nm.

Preferably, the distance between the X-ray tube and the detector is 40-50 cm.

Reference will now be made in detail to embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like or similar designations denote like or similar elements or elements having like or similar functionality throughout. The embodiments described below with reference to the drawings are illustrative and intended to be illustrative of the invention and are not to be construed as limiting the invention.

In the description of the present invention, the terms "first", "second", "third", etc. are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or implying any number of technical features referred to. Thus, features defined as "first," "second," "third," etc. may explicitly or implicitly include one or more of the features.

The invention is a method for improving the counting characteristic of an X-ray photon counting detector, so that the selection of bias voltage, temperature and forbidden band light is corresponding to the performance of the X-ray photon counting detector in practical application. The design idea of the invention is as follows:

firstly, carrying out counting rate test on an X-ray photon counting detector which does not use the method, then applying-300 to-600V to the detector to find out a bias voltage which can improve the counting rate of the detector best, secondly, selecting the bias voltage to carry out counting test on the detector within the temperature range of 25 to 35 ℃, finding out the most obvious working temperature for improving the counting rate under the bias voltage, keeping the bias voltage and the temperature unchanged, applying sub-forbidden band light irradiation to the detector, and finding out the most obvious sub-forbidden band light wavelength and intensity for improving the counting rate under the bias voltage and the temperature. And finally, the counting rate of the X-ray photon counting detector is improved by controlling the three through respective controllers.

The invention is further illustrated by the following figures and examples:

example 1: and selecting different bias voltage, temperature and sub-forbidden band light for the CdZnTeX ray photon counting detector to carry out counting rate test.

The method structure is schematically shown in fig. 1, and the method test flow chart is shown in fig. 6. The CdZnTe photon counting type detector adopted in the method is a 16-pixel linear array detector, and the crystal size of the detector is 16.7 multiplied by 4.4 multiplied by 2mm³The size of the pixel electrode is 1.8 multiplied by 0.9mm². Connecting the packaged linear array photon counting type CdZnTe detector with a reading circuit system, then placing a counting rate testing system into a shielding lead chamber, adjusting the position to enable the counting rate testing system to be positioned under an X-ray source, enabling the distance between the detector and the X-ray source to be about 45cm, and applying negative high voltage to enable X-rays to be incident from a cathode of the detector. The voltage of the optical mechanical tube is set to be 80KV, and the tube current range is set to be 0.01-0.6 mA. The test results are shown in fig. 2.

Other conditions are unchanged, the counting rates of the two CdZnTe detectors are tested to be changed along with the X-ray dose under different working biases, the working bias range is-300V to-600V, and the test result is shown in figure 3. The best detector count rate characteristic is obtained from the graph at-600V bias. Under the bias voltage, other conditions are unchanged, the counting rates of the two CdZnTe detectors are tested to be changed along with the X-ray dose under different working temperatures, the working temperature range is 25-35 ℃, and the test result is shown in figure 4. The graph shows that the counting rate characteristic of the detector at 33.3 ℃ is the best. The bias voltage of-600V is kept, other conditions are unchanged at 33.3 ℃, the counting rates of two CdZnTe detectors with different working wavelengths and intensities are tested to change along with the X-ray dose, the test result is shown in figure 5, the counting rates have no obvious influence on the sub-forbidden band light above 1550nm and the sub-forbidden band light below 1050nm, the sub-forbidden band light of 1200nm and the sub-forbidden band light of 1300nm are selected, different light intensities are obtained according to actual conditions, and the light intensity is improved more obviously when the light intensity is larger.