Author Contributions
Conceptualization, M.K.; methodology, M.K. and P.T.; software, M.K.; validation, M.K. and P.T.; formal analysis, M.K., P.T. and M.M.; investigation, M.K.; resources, M.K.; data curation, M.K.; writing—original draft preparation, M.K.; writing—review and editing, M.K., P.T. and M.M.; visualization, M.K.; supervision, M.K.; project administration, P.T.; funding acquisition, M.K. and P.T. All authors have read and agreed to the published version of the manuscript.
Figure 1.
Comparison of the phenomenon of volume (left) and initial (right) recombination of ions in gas. The arrows represent the particle tracks. Initial recombination of ions occurs only between ions separated by the interaction of the same incident particle and does not depend on the number of particles incident on the detector (the clouds of ions formed as a result of the interaction of different incident particles do not overlap). Volumetric recombination also occurs between ions separated by the interaction of different particles and depends on the number of particles incident on the detector. The intensity of recombination occurrence, depending on its type, can be modified by the gas type and pressure inside the detector and the intensity of the electric field.
Figure 1.
Comparison of the phenomenon of volume (left) and initial (right) recombination of ions in gas. The arrows represent the particle tracks. Initial recombination of ions occurs only between ions separated by the interaction of the same incident particle and does not depend on the number of particles incident on the detector (the clouds of ions formed as a result of the interaction of different incident particles do not overlap). Volumetric recombination also occurs between ions separated by the interaction of different particles and depends on the number of particles incident on the detector. The intensity of recombination occurrence, depending on its type, can be modified by the gas type and pressure inside the detector and the intensity of the electric field.
Figure 2.
Simplified diagram of the measurement system built with a recombination chamber and a Keithley 6517B electrometer equipped with a high-voltage power supply and an electrometer circuit operating in current mode (top) or charge mode (bottom).
Figure 2.
Simplified diagram of the measurement system built with a recombination chamber and a Keithley 6517B electrometer equipped with a high-voltage power supply and an electrometer circuit operating in current mode (top) or charge mode (bottom).
Figure 3.
Diagram of the measurement system based on a recombination chamber and a Keithley 6517B type electrometer.
Figure 3.
Diagram of the measurement system based on a recombination chamber and a Keithley 6517B type electrometer.
Figure 4.
A flowchart of the existing (orange) and the new (green) measurement algorithms. The approximate measurement times for a current of about 100 pA (approximate calibration conditions of the REM-2 type detector in the NCBJ laboratory ) are for existing and new algorithms and are 220 s and 10 s, respectively. The existing measurement algorithm is based on the electrometer current mode and data acquisition by fetch command. The new algorithm uses a charge mode and data acquisition collected in an internal buffer using the trac:feed:cont next command.
Figure 4.
A flowchart of the existing (orange) and the new (green) measurement algorithms. The approximate measurement times for a current of about 100 pA (approximate calibration conditions of the REM-2 type detector in the NCBJ laboratory ) are for existing and new algorithms and are 220 s and 10 s, respectively. The existing measurement algorithm is based on the electrometer current mode and data acquisition by fetch command. The new algorithm uses a charge mode and data acquisition collected in an internal buffer using the trac:feed:cont next command.
Figure 5.
View of the software for performing measurements with SCPI-compliant instruments, in particular the Keithley 6517A and 6517B electrometers. The window is divided into five areas: (a) the area for setting the measurement mode, session parameters and measurement control; (b) the overall graph of the entire measurement; (c) the sub-graph for one measurement execution; (d) the communication flow window and (e) the measurement results window.
Figure 5.
View of the software for performing measurements with SCPI-compliant instruments, in particular the Keithley 6517A and 6517B electrometers. The window is divided into five areas: (a) the area for setting the measurement mode, session parameters and measurement control; (b) the overall graph of the entire measurement; (c) the sub-graph for one measurement execution; (d) the communication flow window and (e) the measurement results window.
Figure 6.
A block diagram of the RecCham measurement system. The nesting of the K6517 program within the RecCham system as a single session handling the measurement process of the Keithley 6517A/B device is presented. The concept of connecting an external system as a slave to RecCham is shown.
Figure 6.
A block diagram of the RecCham measurement system. The nesting of the K6517 program within the RecCham system as a single session handling the measurement process of the Keithley 6517A/B device is presented. The concept of connecting an external system as a slave to RecCham is shown.
Figure 7.
Measurements of the ionization current course of a REM-2 no. 8 chamber for step changes caused by exposure to the radiation source. Comparison of current waveform I(t) (left column of graphs) and autocorrelation functions (right column of graphs) of the ionization current for a Keithley 6517B-type electrometer operating in current mode with the damping function on (top row), with the damping function off (middle row) and in charge mode, for which the ionization current was determined as (bottom row). The gray shading indicates the area for which autocorrelation functions were determined.
Figure 7.
Measurements of the ionization current course of a REM-2 no. 8 chamber for step changes caused by exposure to the radiation source. Comparison of current waveform I(t) (left column of graphs) and autocorrelation functions (right column of graphs) of the ionization current for a Keithley 6517B-type electrometer operating in current mode with the damping function on (top row), with the damping function off (middle row) and in charge mode, for which the ionization current was determined as (bottom row). The gray shading indicates the area for which autocorrelation functions were determined.
Table 1.
Parameters of the REM-2 no. 8 recombination chamber, data from the detector information brochure and calibration of the detector performed in an accredited laboratory using a 137Cs radiation source, reference quantity .
Table 1.
Parameters of the REM-2 no. 8 recombination chamber, data from the detector information brochure and calibration of the detector performed in an accredited laboratory using a 137Cs radiation source, reference quantity .
Chamber Identification | REM-2 No. 8 |
---|
Chamber dimension | Ø 167 × 403 mm |
Mass | 6.5 kg |
Active volume | 1800 cm3 |
Gas type | 95% CH4 + 5% N2 |
Gas Pressure | approx. 8 bar |
Electrical capacity Cin | 550 ± 50 |
Ambient dose rate range D*(10) | 0.005 mGy/h ÷ 300 mGy/h |
Ambient dose rate accuracy D*(10) | 15% |
Saturation voltage US | 990 V |
Recombination voltage UR | 60 V |
Calibration factor A | (8.64 ± 0.43) × 10−11 |
Dark current | <1 × 10−13 (<100 fA) |
Calibration date | 19 September 2022 |
Relative neutron sensitivity | 1.03 |
Relative gamma sensitivity | 1.00 |
Table 2.
Keithley 6517B electrometer parameter settings to maximize measurement frequency.
Table 2.
Keithley 6517B electrometer parameter settings to maximize measurement frequency.
Function | SCPI Command |
---|
NPLC set to 0.01 | sense:function:mode:nplc 0.01 (mode: current or charge) |
Digital filters disabled | sense:mode:average:state 0; sense:mode:median:state 0 (mode: current or charge) |
Front panel of the device disabled | disp:enab 0 |
Relative humidity and temperature measurement disabled | system:tsc 0; system:hsc 0 |
Synchronization of measurement with mains power line disabled | system:lsync:state 0 |
Table 3.
The maximum continuous measurement time as a function of the measured current value IREF, the NPLC value and the charge measurement range of the Keithley 6517B electrometer. The maximum time is also limited by the fixed charge measurement range and the capacity of the electrometer’s internal buffer of 50,000 points.
Table 3.
The maximum continuous measurement time as a function of the measured current value IREF, the NPLC value and the charge measurement range of the Keithley 6517B electrometer. The maximum time is also limited by the fixed charge measurement range and the capacity of the electrometer’s internal buffer of 50,000 points.
Continuous Measurement [s] |
---|
Range [nC] | NPLC | Reference Current IREF [A] |
---|
1 × 10−13 | 5 × 10−13 | 1 × 10−12 | 5 × 10−12 | 1 × 10−11 | 5 × 10−11 | 1 × 10−10 | 5 × 10−10 | 1 × 10−9 |
---|
2 | 10 | 20,000 | 4000 | 2000 | 400 | 200 | 40 | 20 | 4 | |
| 1 | 3100 | 3100 | 2000 | 400 | 200 | 40 | 20 | 4 | 2 |
| 0.1 | 400 | 400 | 400 | 400 | 200 | 40 | 20 | 4 | 2 |
| 0.01 | 100 | 100 | 100 | 100 | 100 | 40 | 20 | 4 | 2 |
20 | 10 | 30,100 | 30,100 | 20,000 | 4000 | 2000 | 400 | 200 | 40 | 20 |
| 1 | 3100 | 3100 | 3100 | 3100 | 2000 | 400 | 200 | 40 | 20 |
| 0.1 | 400 | 400 | 400 | 400 | 400 | 400 | 200 | 40 | 20 |
| 0.01 | 100 | 100 | 100 | 100 | 100 | 100 | 100 | 40 | 20 |
200 | 10 | 30,100 | 30,100 | 30,100 | 30,100 | 20,000 | 4000 | 2000 | 400 | 200 |
| 1 | 3100 | 3100 | 3100 | 3100 | 3100 | 3100 | 2000 | 400 | 200 |
| 0.1 | 400 | 400 | 400 | 400 | 400 | 400 | 400 | 400 | 200 |
| 0.01 | 100 | 100 | 100 | 100 | 100 | 100 | 100 | 100 | 100 |
2000 | 10 | 30,100 | 30,100 | 30,100 | 30,100 | 30,100 | 30,100 | 20,000 | 4000 | 2000 |
| 1 | 3100 | 3100 | 3100 | 3100 | 3100 | 3100 | 3100 | 3100 | 2000 |
| 0.1 | 400 | 400 | 400 | 400 | 400 | 400 | 400 | 400 | 400 |
Table 4.
Description of the K6517 v. 3.0.1 software measurement modes.
Table 4.
Description of the K6517 v. 3.0.1 software measurement modes.
| Mode Description | Measured Quantity | Electrometer Mode |
---|
1 | Measurement of current-voltage characteristics by measuring the charge increase using the buffer | | Charge |
2 | Direct measurement of current-voltage characteristics | | Current |
3 | Measurement of current over time by measuring the charge increase using the buffer | | Charge |
4 | Direct measurement of current over time | | Current |
5 | Measurement of charge over time using the buffer | | Charge |
6 | Direct measurement of resistance versus voltage | | Resistance |
Table 5.
Settings for the measurement of the ionization current in a time-constant radiation field using Keithley 6517B electrometer, the number of measurement points for each measurement series and the measurement time step depending on the value of the NPLC parameter.
Table 5.
Settings for the measurement of the ionization current in a time-constant radiation field using Keithley 6517B electrometer, the number of measurement points for each measurement series and the measurement time step depending on the value of the NPLC parameter.
NPLC | [ms] | Buffer Points N |
---|
0.01 | 2.3 ± 0.1 | 1000 |
0.1 | 8.0 ± 0.1 | 1000 |
1 | 60.2 ± 0.1 | 500 |
10 | 602.0 ± 0.1 | 200 |
Table 6.
Minimum current values for which the charge increase in the measurement time step is at least one significant digit.
Table 6.
Minimum current values for which the charge increase in the measurement time step is at least one significant digit.
NPLC | [ms] | Resolution [N (1/2)] | Range r [nC] |
---|
2 | 20 | 200 | 2000 |
---|
0.01 | 2.3 | 3.5 | 4.35 × 10−10 | 4.35 × 10−9 | 4.35 × 10−8 | 4.35 × 10−7 |
0.1 | 8 | 4.5 | 1.25 × 10−10 | 1.25 × 10−9 | 1.25 × 10−8 | 1.25 × 10−7 |
1 | 60.2 | 5.5 | 1.66 × 10−11 | 1.66 × 10−10 | 1.66 × 10−9 | 1.66 × 10−8 |
10 | 602 | 6.5 | 1.66 × 10−12 | 1.66 × 10−11 | 1.66 × 10−10 | 1.66 × 10−9 |
Table 7.
Relative standard error of the mean ionization current of the REM-2 no. 8 recombination chamber in the gamma radiation field for different radiation dose rate power values and different electrometer settings (NPLC and measurement range). The error is calculated relative to the sample average of the measured values. Measurements were performed in LPD using isotope radiation fields of 137Cs and 60Co.
Table 7.
Relative standard error of the mean ionization current of the REM-2 no. 8 recombination chamber in the gamma radiation field for different radiation dose rate power values and different electrometer settings (NPLC and measurement range). The error is calculated relative to the sample average of the measured values. Measurements were performed in LPD using isotope radiation fields of 137Cs and 60Co.
Range [nC] | NPLC | Reference Current IREF [A] |
---|
1.00 × 10−13 | 5.00 × 10−13 | 1.00 × 10−12 | 5.00 × 10−12 | 1.00 × 10−11 | 5.00 × 10−11 | 1.00 × 10−10 | 5.00 × 10−10 | 1.00 × 10−9 |
---|
Reference Ambient Dose Equivalent D*(10) [μGy/h] |
---|
0.93 | 4.67 | 9.35 | 46.73 | 93.46 | 467.29 | 934.58 | 4672.90 | 9345.79 |
---|
2 | 10 | 13.24% | 2.34% | 1.08% | 0.26% | 0.13% | 0.03% | 0.02% | 0.02% | |
| 1 | 83.57% | 9.06% | 4.65% | 0.93% | 0.50% | 0.11% | 0.06% | 0.02% | 0.03% |
| 0.1 | 164.35% | 23.44% | 11.40% | 2.35% | 1.16% | 0.23% | 0.12% | 0.03% | 0.04% |
| 0.01 | | 52.99% | 28.25% | 6.30% | 3.14% | 0.64% | 0.32% | 0.09% | 0.09% |
20 | 10 | 12.16% | 2.27% | 1.21% | 0.22% | 0.13% | 0.03% | 0.02% | 0.01% | 0.01% |
| 1 | 179.42% | 10.67% | 4.61% | 1.05% | 0.49% | 0.11% | 0.05% | 0.02% | 0.01% |
| 0.1 | 232.37% | 52.98% | 19.75% | 5.38% | 2.95% | 0.46% | 0.24% | 0.05% | 0.03% |
| 0.01 | | | | | | 5.43% | 2.90% | 0.24% | 0.12% |
200 | 10 | 7.12% | 2.19% | 1.11% | 0.26% | 0.13% | 0.04% | 0.02% | 0.01% | |
| 1 | 72.78% | 19.73% | 13.20% | 3.86% | 1.71% | 0.28% | 0.16% | 0.04% | 0.02% |
| 0.1 | | | | | | 5.43% | 2.87% | | 0.10% |
| 0.01 | | | | | | | | 5.29% | 2.87% |
2000 | 10 | 38.89% | 8.45% | 4.75% | 1.11% | 0.57% | 0.12% | 0.06% | 0.01% | 0.01% |
| 1 | | | | | 13.89% | 4.28% | 1.66% | 0.18% | 0.09% |
| 0.1 | | | | | | | | 5.28% | 2.87% |
Table 8.
Relative standard error of the mean current measured with a Keithley 261 current source for different electrometer settings (NPLC and measuring range) The error is calculated relative to an average of the measured values.
Table 8.
Relative standard error of the mean current measured with a Keithley 261 current source for different electrometer settings (NPLC and measuring range) The error is calculated relative to an average of the measured values.
Range [nC] | NPLC | Reference Current IREF [A] |
---|
5.00 × 10−13 | 1.00 × 10−12 | 5.00 × 10−12 | 1.00 × 10−11 | 5.00 × 10−11 | 1.00 × 10−10 | 5.00 × 10−10 | 1.00 × 10−9 |
---|
2 | 10 | 0.01% | 0.01% | 0.01% | 0.05% | 0.01% | 0.01% | 0.04% | |
| 1 | 0.24% | 0.22% | 0.05% | 0.02% | 0.01% | 0.01% | 0.00% | 0.02% |
| 0.1 | 28.39% | 13.85% | 2.49% | 1.28% | 0.28% | 0.13% | 0.03% | 0.03% |
| 0.01 | | 107.53% | 33.23% | 14.63% | 2.85% | 3.55% | 0.60% | 0.51% |
20 | 10 | 0.04% | 0.02% | 0.01% | 0.01% | 0.01% | 0.01% | 0.01% | 0.01% |
| 1 | 4.94% | 2.52% | 0.28% | 0.22% | 0.04% | 0.03% | 0.01% | 0.01% |
| 0.1 | 185.66% | 106.75% | 20.30% | 10.25% | 2.90% | 1.03% | 0.21% | 0.11% |
| 0.01 | | | | 172.77% | 20.94% | 15.84% | 5.53% | 4.59% |
200 | 10 | 0.65% | 0.35% | 0.11% | 0.05% | 0.01% | 0.01% | 0.00% | 0.00% |
| 1 | 17.03% | 11.79% | 4.80% | 2.52% | 0.46% | 0.23% | 0.02% | 0.03% |
| 0.1 | | 657.51% | 186.72% | 110.41% | 26.35% | 10.46% | 2.35% | 1.03% |
| 0.01 | | | | | | | 29.39% | 22.51% |
2000 | 10 | 6.20% | 3.38% | 0.87% | 0.50% | 0.09% | 0.06% | 0.01% | 0.01% |
| 1 | | 70.66% | 18.59% | 12.95% | 4.80% | 2.50% | 0.31% | 0.34% |
| 0.1 | | | | | 235.31% | 105.10% | 20.83% | 9.90% |
Table 9.
REM-2 no. 8 recombination chamber ionization current as a function of the X-ray exposure time. The detector was placed at a distance of 0.5 m from the beam axis. A PMMA phantom measuring 24 cm × 24 cm × 15 cm was placed in the beam. Comparison of the ionization current, calculated from the total charge accumulated during the exposure Icalc, and the measured current, determined as the average of the points of the derivative of the charge during the exposure Imeas.
Table 9.
REM-2 no. 8 recombination chamber ionization current as a function of the X-ray exposure time. The detector was placed at a distance of 0.5 m from the beam axis. A PMMA phantom measuring 24 cm × 24 cm × 15 cm was placed in the beam. Comparison of the ionization current, calculated from the total charge accumulated during the exposure Icalc, and the measured current, determined as the average of the points of the derivative of the charge during the exposure Imeas.
NPLC | Ionization Current [nA] | Exposure Time [ms] |
---|
10 | 20 | 32 | 50 | 63 | 71 | 80 | 90 | 100 | 125 | 160 | 200 | 250 |
---|
0.01 | Icalc | 2.63 | 2.70 | 2.74 | 2.76 | 2.77 | 2.77 | 2.77 | 2.78 | 2.78 | | | | |
| Imeas | 2.54 | 2.73 | 2.76 | 2.76 | 2.78 | 2.77 | 2.78 | 2.78 | 2.78 | | | | |
| | −3.3% | 1.3% | 0.8% | 0.1% | 0.2% | 0.0% | 0.3% | −0.1% | 0.0% | | | | |
0.1 | Icalc | | 2.73 | 2.76 | 2.77 | 2.78 | 2.78 | 2.78 | 2.78 | 2.79 | | | | |
| Imeas | | 2.71 | 2.75 | 2.78 | 2.79 | 2.79 | 2.79 | 2.79 | 2.79 | | | | |
| | | −0.9% | −0.1% | 0.4% | 0.3% | 0.2% | 0.2% | 0.1% | 0.1% | | | | |
1 | Icalc | | | | | | | | | | 2.79 | 2.78 | 2.79 | 2.79 |
| Imeas | | | | | | | | | | 2.71 | 2.74 | 2.77 | 2.79 |
| | | | | | | | | | | −2.8% | −1.6% | −0.5% | −0.1% |