GB/T 11685-2003 Measurement methods for semiconductor X-ray detector systems and semiconductor X-ray spectrometers
Some standard content:
GB/T 11685—2003
This standard is a combination and revision of GB/T8992-1988 "Measurement methods for silicon (lithium) X-ray detector systems" and GB/T11685-1989 "Measurement methods for semiconductor X-ray spectrometers". Both GB/T8992-1988 and GB/T11685-1989 are non-equivalent versions of IEC60759:1983 (see reference [1]). This standard replaces GB/T8992-1988 and GB/T11685-1989. This standard covers the measurement methods for semiconductor X-ray detector systems and semiconductor X-ray spectrometers. Since the output of the detector system must be input into the multi-channel analyzer through the main amplifier, and then the X-ray energy spectrum is obtained on the multi-channel analyzer to observe and determine its performance characteristics, the detector system and the spectrometer basically use the same measurement method. This standard not only retains the integrity of GB/T11685--1989 and the operability of GB/T8992-1988, but also combines the two standards into a unified new version through organic integration. The main modifications of this standard to GB/T8992-1988 and GB/T11685-1989 are as follows: a)
The measurement of semiconductor X-ray detector systems is not limited to silicon (lithium) X-ray detector systems: for semiconductor X-ray spectrometers, the performance characteristics of the energy spectrum (full energy peak and peak position or spectrum line) on the multi-channel analyzer are measured; b)
The "Terms and Definitions" in Chapter 3 are arranged according to physical meanings and logical relationships, and the terms "semiconductor detector", "semiconductor X-ray detector system" and "main amplifier" are added, and the terms "window", "baseline" and "working distance" are modified, and the terms "gate" and "mode" are deleted. d)
Added Chapter 11 "Overload Effect" with reference to IEC60759; modified a small number of symbols, for example, the number of channels (channel address) of a multi-channel analyzer is represented by ㎡ instead of N or X; e)
f) Expanded and enriched the content of Chapter 5 "General Principles", and the measurement requirements (original basic requirements) are only one of them: - Standardized the concepts of "measured object", "measuring equipment" and "measurement system"; - Listed the main performance characteristics to be measured; - Specify the measurement conditions (including environmental conditions and radiation sources, etc.); Pointed out that the detector system and the spectrometer use the same measurement method and the differences in details. The content of "Calculating the approximate value of electrical noise from X-ray energy resolution" was adjusted from the main text to Appendix A; g)
h) The titles and contents of the chapters and clauses were standardized. For example, the title of Chapter 7 was changed directly from "Pulse Amplitude Linearity" to "Integral Nonlinearity", and the title of Chapter 9 was changed from "Pulse Amplitude Stability" to "Voltage Change Influence", "Temperature Effect" and "Long-term Instability"; i) In order to improve the operability of this standard and adapt to the development of new technologies, general methods are generally given in the measurement, and particularly specific methods are given in the form of examples;
The format is written in accordance with the requirements of GB/T1.1-2000 and other standards, and sub-clause titles are added to some clauses, and the figures and tables are concentrated at the end of the main text.
Appendix A of this standard is an informative appendix.
This standard is proposed by the National Technical Committee for Standardization of Nuclear Instruments. This standard is under the jurisdiction of the Nuclear Industry Standardization Institute. The drafting unit of this standard: Nuclear Industry Standardization Institute. The main drafter of this standard: Xiong Zhenglong.
1 Scope
Measurement methods for semiconductor X-ray detector systems
and semiconductor X-ray spectrometers GB/T11685--2003
This standard specifies the measurement methods for the main characteristics of semiconductor X-ray detector systems and semiconductor X-ray spectrometers. This standard applies to the measurement of the main performances of semiconductor X-ray detector systems and semiconductor X-ray spectrometers. 2 Normative references
The clauses in the following documents become clauses of this standard through reference in this standard. For any dated referenced document, all subsequent amendments (excluding errata) or revisions are not applicable to this standard. However, parties to an agreement based on this standard are encouraged to study whether the latest versions of these documents can be used. For any undated referenced document, the latest version shall apply to this standard. GB/T4079--1994 Test methods for amplifiers and charge-sensitive preamplifiers used with detectors of ionizing radiation (GB/T 4079-1994, neq IEC 61151:1992, Nuclear instrumentation--Amplifiers and preamplifiers usedwith detector of ionizing radiation-Test procedures) GB/T4960.6-1996 Nuclear science and technology terminology Nuclear instrumentation (GB/T4960.6-1996, neq IEC60050 (IEV50), International Electrotechnical Vocabulary, Chapter 391~394) 3 Terms and definitions
The terms and definitions established in GB/T4960.6 and the following terms and definitions apply to this standard. 3.1
Semiconductor detector semiconductor detector A detector that usually detects human radiation by using the movement of excess free charge carriers generated in a semiconductor by nuclear radiation. [2.4.1 of GB/T4960.6—1996]
Note: The term "detector" in this standard refers to semiconductor detectors unless otherwise specified. 3.2
Dead layer (of semiconductor detector) A layer in a semiconductor detector in which most of the energy lost by particles does not contribute to the signal formed. [2.4.26 of GB/T 4960.6—1996]
Window (of detector) Window (of detector) The part of the detector that allows the measured radiation to pass through. [2.1.26 of GB/T4960.6—1996]
Geometry of semiconductor detector The shape of the sensitive volume of a semiconductor detector under normal operating conditions. 3.5
Efficiency (of semiconductor detector for mono-energetic radiation source) efficiency (of semiconductor detector for mono-energetic radiation source)
GB/T11685—2003
The ratio of the number of particles in the spectrum distribution measured by the semiconductor detector to the number of such particles injected into the effective volume of the detector in the same time interval.
Energy resolution (of semiconductor detector) energyresolution (of semiconductor detector) The contribution of the semiconductor detector to the half-maximum width (FWHM) of the energy spectrum (including the leakage current noise of the detector), usually expressed in energy units.
Full width at half maximum (FWHM) The distance between the horizontal coordinates of two points on the curve at half the peak on a distribution curve composed of a single peak. Note: If the curve consists of several peaks, each peak has a half-maximum width. [3.2.20 of GB/T4960.6—1996]
Full width at tenth maximum (FWTM) On a distribution curve consisting of a single peak, at one tenth of the peak, the distance between the horizontal coordinates of two points on the curve. 3.9
Semiconductor X-ray detector system semiconductorX-raydetector system A system that measures X-rays using the principle that a semiconductor detector sensitive to X-rays produces an electrical signal (the number of electron-hole pairs) that is proportional to the energy of the X-rays. It usually consists of three parts: a semiconductor X-ray detector, a low-noise preamplifier, and a cryogenic vacuum device, hereinafter referred to as the detector system.
Semiconductor X-ray energy spectrometer semiconductorX-rayenergy spectrometer An instrument that consists of a detector system, a detector bias power supply, a main amplifier, and a multi-channel analyzer (including a computerized multi-channel analyzer) to measure the energy distribution of X-rays (hereinafter referred to as the spectrometer). 3.11
Main amplifier
Shaping amplifier
In an amplifier system, an amplifier following the preamplifier and including a pulse shaping network. [3.3 of GB/T 4079—1994]
Shaping network
A network consisting of a high-pass network (composed of one or several differentiators) and a low-pass network (composed of several integrators). It can reduce (change) the pulse width of the preamplifier output, thereby improving its time resolution and signal-to-noise ratio. LGB/T 4079-1994 3.1.10 13.13
Biased pulse amplifier A pulse amplifier that provides an amplified output only for the part of the input pulse signal that exceeds a predetermined threshold. 3.14
Multi-channel analyzer (MCA) An analyzer with more than one channel, usually containing a sufficient number of channels. The signal is classified and counted according to one or more characteristics of the input signal (amplitude, time, etc.), so as to determine its distribution function. [3.1.23 of [GB/T4960.6-1996] 2
spectrum line
indicates the peak part of the spectrum of a radiation characteristic, usually refers to the full-energy peak of monoenergetic radiation. 3.16
GB/T 11685--2003
background (associated with spectral peak from semiconductor detector)
non-ideal spectral response caused by radiation outside the spectral line of the monoenergetic radiation to be measured. 3.17
tail (of mono-energetic spectral peak) any peak shape distortion caused by the monoenergetic radiation to be measured that does not comply with the full-energy peak spectral shape (quasi-Gaussian shape) limit. 3.18
Peak positionpeak position
The energy or equivalent at the centroid of a peak (spectral line) in the pulse amplitude spectrum3.19
Baseline at pulse peakThe instantaneous value of the voltage at the corresponding pulse peak when there is no pulse. 3.20
Baseline restorationbaselinerestoration
Technique (linear or nonlinear) used to accelerate the voltage back to the baseline3.21
Integral non-linearity (INL)integral non-linearity (INL) (%)
The maximum deviation between the actual response curve and the ideal response straight line, expressed as a percentage of the maximum rated output pulse amplitude (or number of channels for a multichannel analyzer).
Noise line-widthnoise line-width
The contribution of noise to the width of the spectrum peak.
Pile-up (in counting assembly) A pulse superimposed on the trailing or leading edge of the previous pulse, causing an incorrect pulse amplitude reading. Pile-up can also make some pulses indistinguishable.
Pile-up rejection
Technique used to identify and reject piled-up pulses (signals). 3.25
Pole-zero cancellation A pulse shaping method used to eliminate long-duration undershoots. 3.26
Standard working axis (of semiconductor X-ray energy spectrometer)
standard working axis (of semiconductor X-ray energy spectrometer) A straight line passing through the center of the detector incident window and perpendicular to the incident window. 3
GB/T 11685--2003
working distance
Working distance
The distance between the X-ray radiation source and the outermost window of the detector (human radiation) along the standard working axis. 4 Symbols
This chapter lists the symbols related to the detector system and the spectrometer, but does not include the symbols defined in Chapter 3 and the symbols to be explained in the formulas of Chapters 6 to 10:
C. Calibration capacitor used for coupling the pulse generator and the circuit during measurement; Ca---detector capacitance;
Effective input capacitance of the preamplifier;
Feedback capacitance in the integral loop of the preamplifier; Energy corresponding to the maximum linear output of the spectrometer; Root mean square noise voltage:
Channel (channel address) of the energy spectrum measured by the multi-channel analyzer; Peak position channel (or highest count channel) of the energy spectrum measured by the multi-channel analyzer; Counts of channel m in the energy spectrum measured by the multi-channel analyzer; Counts of peak position channel mp in the energy spectrum measured by the multi-channel analyzer; R—-preamplifier The resistor used to release the charge on C in the amplifier to prevent the preamplifier operating point from exceeding the dynamic range; Rt. The load resistance of the detector; Vp-the voltage applied to C by the pulse generator; Z. ~-characteristic impedance; I--the characteristic wavelength corresponding to the X-ray photon; T-time constant. 5 General principles 5.1 Object to be measured and its performance characteristics The object to be measured is the detector system or spectrometer, and its performance characteristics are determined by the design and should meet the requirements of technical documents such as product standards. The performance characteristics to be measured in this standard refer to the main characteristics of the energy spectrum formed by X-rays on the multi-channel analyzer: energy resolution and energy spectrum distortion; b) integral nonlinearity; c) counting rate effect; d) voltage change effect, temperature effect and long-term instability; efficiency; f) overload effect.
Note: For the measurement of components in the detector system or spectrometer, see GB/T4079 and references [2], [3]. 5.2 Measuring equipment
Measuring equipment is a device used to measure the object being measured, such as a radiation source, a precision pulse generator, and an oscilloscope. The measuring equipment should comply with the relevant provisions of the standard (it is recommended to use standardized equipment), and its corresponding performance characteristics should be significantly better than the object being measured. For example, their influence on the characteristics of the object being measured should not exceed 10% of the measurement result to ensure the accuracy and validity of the measurement result. When the measuring equipment cannot meet the above requirements, measures should be taken to avoid their influence on the measurement results. For example, the final result should be corrected by deducting the error introduced by the measuring equipment (see 8.2.3.3). For example, when measuring the temperature effect and long-term instability of the detector system, the output amplitude of the precision pulse generator and the gain of the main amplifier are appropriately adjusted to make them unaffected by temperature and time (see 9.3 and 9.4 for details).
5.3 Measurement system
When completing a characteristic measurement, the object to be measured and the measuring equipment (including the radiation source) are always connected (arranged) together to form a complete system, called a measurement system, such as the system shown in Figure 1. Oscilloscope
Precision pulse
Generator
Radiation source
Semiconductor
Detector
Bias voltage (bias)
Amplifier
Note: Using the detector capacitor instead of the test capacitor can reduce the distributed capacitance at the input end. Main amplifier
Figure 1 Basic measurement system of measured characteristics
GB/T11685---2003
Analyzer
Since the output of the detector system must be input into the multi-channel analyzer through the main amplifier and then the X-ray energy spectrum is obtained on the multi-channel analyzer to observe and determine its performance characteristics, the detector system and the energy spectrometer basically use the same measurement method. When measuring the detector system, the detector bias power supply, main amplifier and multi-channel analyzer are part of the measurement equipment. When measuring the energy spectrometer, all components of the energy spectrometer (including the multi-channel analyzer) are the objects to be measured. According to the actual situation, the measurement of the detector system and the measurement of the energy spectrometer are slightly different in details. 5.4 Measurement conditions
5.4.1 Environmental conditions
Measurements should be made under reference conditions or standard test conditions; if there is no objection to the environmental conditions, they can also be made under normal atmospheric conditions. When measuring the influence of power supply changes or temperature effects, only the influence quantity changes within a given range, and other conditions remain under reference conditions or standard test conditions. Reference conditions, standard test conditions and normal atmospheric conditions are shown in Table 1. Table 1 Reference conditions and standard test conditions
Influence quantity
Environmental temperature
Relative humidity
Atmospheric pressure
AC power supply voltage
AC power supply frequency
AC power supply waveform
Environmental radiation
(Air absorption dose rate)
External magnetic field interference
External magnetic induction
Radioactive contamination
Reference conditions
101.3 kPa
50 Hzh
Sine wave
0. 1 μGy/h
Negligible
Negligible
Negligible
Standard test conditions
18℃22℃
50% ~75%
86 kPa~106 kPa
(1±1%)Un
(1±1%)50 Hz
Total waveform distortion<5%
<0. 25 Gy/h
Less than the lowest value causing interference
Less than 2 times of the interference caused by the geomagnetic field
Negligible
Normal atmospheric conditions
15℃～35℃
45% ~75%
86 kPa~106 kPa
\U is a single-phase power supply of 220V or a three-phase power supply of 380V. When powered by a battery, the voltage change is ±1% of the rated value, ignoring the ripple. bAC power supply frequency, special cases shall be handled in accordance with product standards. 5
GB/T11685—2003
5.4.2 Radioactive source
Radioactive sources that are easily available, have simple energy spectra, and cover the entire energy range of interest as much as possible should be selected. The X-ray radiation sources in Table 2 are recommended, and other X-ray energy radiation sources can be supplemented when necessary. Impurities in the radioactive source should not have a significant impact on the measurement results. 5.4.3 Other conditions
Measurement conditions related to pulse shaping type and time constant, detector bias, count rate, etc. should be stated. 5.5 Measurement requirements
5.5.1 When measuring the performance characteristics of the object being measured, components such as semiconductor detectors and the first-stage field effect transistors (FETs) of preamplifiers should be kept at their respective specified low temperatures.
Example: Components such as semiconductor detectors and the first-stage field effect transistors (FETs) of preamplifiers should be encapsulated in cold fingers. When measuring various performance characteristics, the cold fingers should be kept at the low temperature of liquid nitrogen. There should be more than 24 hours between the first injection of liquid nitrogen and the start of measurement (equilibrium from room temperature to low temperature). Each subsequent injection of liquid nitrogen generally requires 2 hours before measurement. 5.5.2 During measurement, the detector should be biased according to the specified polarity, and the maximum bias and the rate of change of the bias should not be exceeded. In addition, the rated values of the irradiation and irradiation rate, the maximum temperature of the detector and the limits of other specified technical conditions should not be exceeded. 5.5.3 Before measuring any characteristic, preheating should be carried out according to technical documents such as product standards. After measuring any or all characteristics, the measurement results should be repeatable within the measurement precision range. 5.5.4 It should be ensured that power supply noise, ground loop noise and mechanical vibration have no significant effect on the measurement results. 5.5.5 Characteristics measured under different operating conditions or forms are not allowed to appear in the same curve or the same table. When expressing, the operating conditions or forms should be used as parameters and expressed by a family of curves. When the same system is measured under different operating conditions or forms, the results can be used for comparison.
6 Energy resolution and energy spectrum distortion
6.1 Overview
The measurement system is shown in Figure 1. The precision pulse generator is mainly used for noise measurement. Avoid using 50Hz mains as the generator power supply. If the precision pulse generator simulates the detector signal pulse, the output pulse of the pulse generator should be sent to the input of the preamplifier when in use. When measuring X-ray resolution, especially when measuring at high counting rate and (or) long pulse shaping time, the pulse generator should be turned off.
The main amplifier for measurement should have a "quasi-Gaussian" shaper, and the differential and integral time constants should be adjustable; the pole-zero compensation of the amplifier should be adjusted to the optimal state. If the circuit system is equipped with a baseline restorer, it should be explained. 6.2 Measurement of electrical noise
6.2.1 Pulse amplitude distribution method to measure electrical noise
6.2.1.1 Measurement system
The measurement system for measuring noise by the pulse amplitude distribution method is shown in Figure 1. The coupling capacitor C in the figure. The detector's own capacitance Ca can be used instead to reduce the distributed capacitance at the input of the preamplifier. During the measurement, all components of the system should work within the linear range. 6.2.1.2 Measurement Procedure
Apply the specified bias voltage to the detector and place it under the irradiation of a suitable X-ray radiation source (such as 5'Fe 5.9keV manganese K line). Adjust the measurement system gain and pulse amplitude so that the half-height width (FWHM) of the X-ray peak is at least 8 channels, and accumulate a spectrum on the multi-channel analyzer. Remove the radiation source and replace the X-ray radiation source with the output pulse of the pulse generator. Adjust the output amplitude of the pulse generator so that the peak position obtained by the multi-channel analyzer coincides with the original measured X-ray peak position and the half-height width is at least 5 channels. Calibrate the energy of the pulse generator output amplitude and then fix the output of the pulse generator. When the half-height width of the spectrum peak of the pulse generator output pulse is less than 5 channels, the number of channels of the multi-channel analyzer should be increased until the requirement is met, and then repeat the above measurement and calibrate the energy of the pulse generator output amplitude again. Under the above measurement conditions, when the equivalent output energy of the pulse generator is E and E2, the corresponding two peaks are accumulated in the multi-channel analyzer, and their peak position channels are mpi and mp2, as shown in Figure 2. 6
The count of the peak position channel should be greater than 4000.
Count/channel
6.2.1.3 Data processing
Figure 2 Typical noise measurement pulse amplitude spectrum
—Number of channels
GB/T11685—2003
The electrical noise line width is the contribution of electronic circuits and detectors to the energy resolution, that is, the half-height width or one-tenth of the height width in units of energy.
First, calculate the equivalent energy S (energy unit/channel) of each channel of the multi-channel analyzer according to formula (1): S = E,-E
mp2 -- mp
The electrical noise linewidth △ (half-height width expressed in energy units) is defined according to formula (2): A = SXaT -
Where:
(E2-EL)AT
The half-height width FWHM of the energy spectrum peak expressed in the number of channels is obtained by the interpolation method given by the manufacturer (see Figure 2). The electrical noise linewidth % (one-tenth of the height width expressed in energy units) is defined according to formula (3): (Ez-EL)or
(mp2mpI
Where:
——FWTM, the one-tenth width of the energy spectrum peak expressed in the number of channels, obtained by the interpolation method given by the manufacturer (see Figure 2). When the background is large, the background should be deducted before calculating the half-height width and one-tenth width of the energy spectrum peak. 1
（2）
（3）
When stating the total noise linewidth, all data of pulse shaping (including full pulse width) should be given (for example, a 2μs CR-RC shaping circuit, or a quasi-Gaussian circuit with four 2μs CR integrals and one 2usRC differential). If baseline recovery and/or gate techniques are used, their performance should be described.
6.2.2 Using an oscilloscope 6.2.2.1 Measurement system
The measurement system for measuring electrical noise using an oscilloscope and an RMS voltmeter is shown in Figure 3. The RMS electrical noise voltage is displayed on the RMS voltmeter.
The frequency response of the RMS voltmeter is required to be flat, and the bandwidth should be extended to at least 10 times the center frequency of the amplifier pulse shaping network band; in addition, no matter how much its noise level is reduced, the gain of the amplifier should remain constant. This measurement method is only applicable to general energy spectrometers, not to energy spectrometers with bias amplifiers, baseline recovery or gating amplifier circuits, nor to measuring the electrical noise of the detector system. 7
GB/T 11685--2003
6.2.2.2 Measurement procedure
Preamplifier
Precision pulse generator
Attenuated output
Main amplifier
Direct output
Precision RMS voltmeter
Oscilloscope
Figure 3 Measurement system for noise measurement using oscilloscope and RMS voltmeter Multichannel analyzer
The measurement shall be carried out in accordance with the operating conditions and technical requirements specified in 6.2.1. The normalization control of the pulse generator is the same as in 6.2.1, except that the pulse amplitude of the radiation source and the pulse generator are compared by an oscilloscope. A pulse equivalent to energy Ep is added from the pulse generator, and the output pulse amplitude of the amplifier is measured by an oscilloscope as V. Then turn off the pulse generator and read the RMS noise voltage en from the voltmeter. (Units are the same as V).
6.2.2.3 Data Processing
The electrical noise linewidth A (half-maximum width in energy units) is calculated from equation (4): EE
=2.35Xa×em(
where:
a-- is 1.11 for an average reading voltmeter on a sine wave scale and 1 for a true RMS voltmeter. 6.2.3 Approximate calculation of electrical noise from X energy resolution The method for calculating the approximate value of electrical noise from X energy resolution is given in Appendix A. 6.3 Noise linewidth as a function of amplifier time constant (4))
Data on the noise contribution can be obtained from a plot of the noise linewidth versus the amplifier time constant. This plot will give important information regarding both count rate and energy resolution. This measurement can be made using an amplifier with an adjustable shaping time constant as described in 6.2.1. The results are plotted as a plot of the noise linewidth versus the pulse shaping time constant (with other possible variables such as baseline recovery as parameters). 6.4 Energy Resolution
6.4.1 X-ray Sources
The energy resolution is measured using one of the sources listed in Table 2. If the resolution is to be determined at only one energy, it is best to use an Fe source. The 5.9 keV manganese X-rays will present a reasonable compromise between amplifier noise broadening and other resolution broadening effects of the detector. Spectral lines greater than 30 keV are mainly used for germanium detectors. To prevent spectral distortion from backscattered radiation, the thickness and atomic number of the source backing material should be as small as possible. 8
Radioactive source
1o9 Cd
57 Coh
Table 2 Commonly used radioactive sources for measurement
11. 25 keVbZxz.net
13.94 keV-
21.99kev.
Mn K.(5. 894 keV)
MnK.(6.489keV)
14.4 keV-..
122.0keV-
a55Fe source should be accurate to 3 decimal places when measuring energy width and resolution. b When measuring count rate effect, 57Co source is not used. 6.4.2 Measurement system
GB/T11685—2003
Energy resolution measurement is to measure the total width of the X-ray energy spectrum by the pulse amplitude distribution method. The measurement system is shown in Figure 1. Turn off the pulse generator during measurement. The radiation source should be placed on the standard working axis, and the distance from the radiation source to the detector system window should not be less than the working distance specified by the manufacturer. The effective diameter of the source should not significantly exceed the standard source diameter. The amplifier time constant should be selected to be the value with the minimum total noise.
6.4.3 Measurement procedure
Adjust the distance between the radiation source and the detector so that the count rate of the K. spectrum line is 1000s\1. The half-height width should not be less than 10 channels, and the counts in the peak channel or the highest count channel should not be less than 40,000. When the radiation source emits true characteristic X-rays, K. and K peak can be used to calibrate the equivalent energy S of each channel of the multi-channel analyzer. The specific calculation is shown in formula (1). In other cases, or when K. and K. When it is impossible to distinguish, the pulse amplitude distribution method of 6.2.1 can be used for calibration.
6.4.4 Data processing
The measurement results of energy resolution are expressed in half-height width and (or) one-tenth of the height width (energy unit). The half-height width A is calculated by formula (5):
Where:
(mP2-mP1
A%—the half-height width FWHM of the energy spectrum peak expressed in channel numbers (within the interpolated fractional channels, the interpolation method is given by the manufacturer). One-tenth of the height width % is calculated by formula (6): (5)
GB/T 11685-2003
Where:
%= S×%-(E-EL)%
Imp2-mpi
——One tenth of the height width of the energy peak expressed in the number of channels (within the interpolated fractional channels, the interpolation method is given by the manufacturer). For Gaussian energy peaks, 0%=1.78(△%), so =1.78(4). The report of energy resolution measurement should state: a) the source of human X-ray radiation and its energy; b) the counting rate used for measurement; c) the geometric conditions of the radiation source-detector (working distance and diameter of the radiation source); (6) the detailed parameters of the detector (such as silicon or germanium semiconductor, working bias of the detector, shape, area, thickness of the depletion layer, etc.); e) the use and parameters of the collimator; f) the system noise linewidth under the same working conditions; g) the amplifier pulse shaping parameters (including full pulse width and baseline recovery parameters). 6.4.5 Data Verification
Except for electrical noise, the line broadening caused by all other factors (statistical fluctuations and charge collection problems), the half-height width and one-tenth of the height width expressed in energy units can be obtained by deducting the electrical noise (line width) from the energy resolution by the orthogonal method (square root of the square difference), and calculated by formulas (7) and (8):
= V()2-()2
% ()-()2
The limit of energy resolution (half-height width △° expressed in energy units) contributed only by statistical fluctuations is calculated by formula (9):lim(A) = 2.25 FeE
where:
E—X-ray energy;
E—average energy required to form an electron-hole pair in the detector; F—Fano factor. The Fano factor F value for silicon and germanium has not yet been accurately determined, and the commonly used estimated value is 0.1. 6.5 Peak-to-valley ratio and peak-to-tail ratio
6.5.1 Overview
(7)
The peak-to-valley ratio (6.5.2) and peak-to-tail ratio (6.5.3) of two closely spaced peaks (e.g., Mn K and K from a 55Fe source) can very sensitively reflect spectral distortions caused by various factors, ranging from charge collection problems in the detector (or its partial dead layer window) to baseline instability in the electronic instrument and other related counting rate effects. The peak-to-tail ratio can also sensitively indicate the line-to-background ratio performance of the object being measured. When quoting the peak-to-valley ratio or the peak-to-tail ratio, the measurement conditions should be fully described, including the source-detector geometry (working distance and source diameter), the setting of the amplifier time constant, the input count rate, and other major variables that can significantly affect the measurement. When measuring the peak-to-valley ratio or the peak-to-tail ratio, the parameters of the measuring equipment should be the same as those when measuring characteristics such as the half-height width. 6.5.2 Peak-to-valley ratio
The peak-to-valley ratio between two given spectral peaks is the ratio of the height of the larger peak to the minimum height of the valley between the two peaks. The peak-to-valley ratio should be described based on sufficient statistical information (such as the counts per channel in the peak and valley) to ensure that its maximum statistical error is less than 5%. When the minimum count between the K. line and the K: line of manganese in the measured energy spectrum is greater than 400, first record the energy spectrum curve, and then calculate the counts Np of the highest count channel of the K. line and the average Cv of the counts of the 5 adjacent channels with the lowest count between the K. and K: lines, and the peak-to-valley ratio P of the system. Calculated by formula (10):
.....-+( 10 )
6.5.3 Peak-to-tail ratio
GB/T 11685—2003
Place the active surface of the 5Fe standard source vertically and centered on the standard working axis, and the working distance is the distance specified by the manufacturer. Adjust the system gain so that the half-height width is at least 10 channels, accumulate counts in the peak channel or the highest count channel corresponding to the 5.9keV energy, and record the energy spectrum curve when Np exceeds 20,000. Take 5 consecutive channels centered around 5.4keV, 4.5keV and 1keV energy as a group, and take the average value CI, C2 and C3 of each group of counts, then the peak-to-tail ratio P1, P2 and P: can be calculated by formula (11): P = Np/C
P2 Np/C2
P3 = Np/C.
..........(l1)
Because of the backscattering of the surrounding or source substrate, high counting rate, system noise (ground loop, AC noise, etc.), improper equipment adjustment (improper adjustment of the pole-zero cancellation network, non-optimal forming time, etc.) or other radiation sources nearby, the performance of the measured object will deteriorate, resulting in a decrease in the peak-to-tail ratio. In order to make the above measurement meaningful, the background caused by other reasons except the 5Fe radiation source should be small enough to be negligible.
If there are other radioactive nuclides (impurities) in the radiation source that contribute to the tail event, the above method of measuring the peak-to-tail ratio may produce erroneous results. After inserting an absorber between the 5Fe radiation source and the detector and then measuring the peak-to-tail ratio, the error caused by impurities in the radiation source can be measured.
7 Integral nonlinearity
7.1 Pulse amplitude analysis method
7. 1. 1 Measurement system
The measurement system for measuring integral nonlinearity by the pulse amplitude analysis method is shown in Figure 1. A set of characteristic X-rays with an appropriate energy range are used to irradiate the detector. Usually, in order to better measure the integral nonlinearity, at least 10 spectral lines are used, and these 10 spectral lines should be as evenly distributed as possible in the energy range of interest. The lowest energy of the spectral line should be less than 110% of the lower limit of the energy range of interest, and the highest energy of the spectral line should be greater than 90% of the upper limit of the energy range of interest. If the radiation sources in Table 2 cannot fully meet the requirements, they can be produced by secondary fluorescence excited by X-rays, gamma rays or charged particles.
The measurement of integral nonlinearity should be carried out under the same conditions as the measurement energy resolution. Spectra with accurately calibrated characteristic energies should be used, and those multiple spectral lines that cannot be resolved should be avoided as much as possible, which will cause obvious broadening of the spectral lines. In addition, in order to avoid the gain offset or drift of the measuring equipment caused by the counting rate being mistaken for the nonlinearity of the object being measured, the most appropriate way is to acquire all spectral lines at the same time at a low counting rate. If these spectral lines are not acquired simultaneously but acquired one by one or in groups, the measurement should ensure that the counting rate is low and the counts of each spectral line should be accumulated to a level that can be compared with each other. 7.1.2 Data Processing
From the previously measured X-ray spectrum, draw a curve of the peak position channel of each peak versus the X-ray energy of the peak on a rectangular coordinate with energy as the horizontal axis and the number of channels of the multi-channel analyzer as the vertical axis, and then use the least square method (or plotting method) to fit the ideal straight line of the curve, as shown in Figure 4.
Integral nonlinearity INI expressed as a percentage is calculated by formula (12): INL = LAEmxl × 100%
Where:
1△Emx! —The absolute value of the maximum deviation between the actual value of an energy and the ideal response value, expressed in energy units; E corresponds to the full scale of the energy range of interest, expressed in the same energy unit as △Emax. (12)
When a single non-directly measured value is used to characterize the integral nonlinearity, this value should not be exceeded over the entire working range specified for the object being measured.
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