Evaluation of monthly variations in electrometer calibration coefficients using a charge generator for radiation therapy.

Electrometers are important devices that are part of the standard dosimetry system. Therefore, we evaluated the variation of electrometer calibration coefficients (kelec) over 1 year in this study. We investigated two types of electrometers: a rate mode and an integrate mode. Each electrometer was connected to a charge generator, a constant charge was applied, and kelec was determined by measuring the current. The current measurements were repeated once a month. For electrometers with multiple ranges, measurements were taken at low and medium ranges. Almost all kelec measurements agreed within 0.2% of the initial measurements. However, the low range of the electrometer with an integrate mode showed seasonal variation, with a variation greater than 0.2%. This study shows that electrometers may exhibit errors that cannot be detected through annual inspections. The importance of quality assurance using a charge generator at one's own institution was demonstrated.

[Verification of Response Uncertainty in Electrometers through Cross-Comparison with a Novel Current Source: A Comparative Study with Guidelines for Electrometers Used in Radiation Therapy Dosimeters].

BACKGROUND: A new quality assurance and control method for electrometers using a new current source, different from the method published in the guidelines for electrometers, has been reported. This current source uses dry batteries and exhibits excellent performance in terms of voltage, temperature, and time characteristics. The electrometer sensitivity coefficient can be calculated by comparing the sensitivity of one electrometer with that of another on the electrometer calibration coefficient that has been calibrated by a calibration laboratory in advance in both methods. The guideline method requires two or more sets of ionization chambers and electrometers in the facility. In contrast, our method does not use ionization chambers; therefore, the sensitivity ratio of the electrometer can be measured in any facility. This study compared the uncertainty of the electrometer sensitivity factor calculated using the new current source method (current method) with that calculated using a linear accelerator (LINAC) and ionization chambers (LINAC method) described in the electrometer guidelines. METHOD: In this study, we used a current source that we invented previously by Kawaguchi Electric Works in Japan. The sensitivity ratios of the electrometers were measured with three manufacture's electrometers. The electrometer sensitivity factor was calculated by multiplying the electrometer calibration coefficient. The ionization chamber was 30013 (PTW), and the current source was the current obtained from 10 MV TrueBeam X-rays under calibration conditions. The mean value, standard deviation, and coefficient of variation were calculated. The time required to set up the ionization chamber for calculating the sensitivity ratio of the electrometer was also measured. The accuracy was confirmed by calculating the expanded uncertainty of the electrometer sensitivity coefficients. RESULTS: The LINAC method had a maximum coefficient of variation of 0.072%. The gross time of the LINAC method was approximately 110 min. The current method had a maximum coefficient of variation of 0.0055% and took less than half the time taken by the LINAC method (35 min) because there was no waiting time for the ionization chamber to be set up and the applied voltage to stabilize under calibration conditions. The expanded uncertainties of the electrometer calibration coefficients were 0.36% and 0.36%, respectively. CONCLUSION: The new cross-comparison method for electrometer sensitivity factors using a current source is more efficient and useful than the linear accelerator method described in the guidelines; furthermore, this method ensured accuracy for quality assurance and control of electrometers.

Assessment of a self-inspection method and reporting measured electrometer correction factors for reference-class electrometers in radiotherapy.

BACKGROUND AND PURPOSE: The standard dosimetry system of medical accelerators in radiotherapy consists of an ionization chamber, an electrometer, and cables. Guidance for TG-51 reference dosimetry reported that the electrometer correction factor (Pelec ) should be checked every few years. Therefore, continuous Pelec measurements have not been reported. The purpose of this study is to measure the Pelec with a charge generator at our institution and to evaluate variations over time. The measurements are compared with calibration data given by an Accredited Dosimetry Calibration Laboratory (ADCL). MATERIALS AND METHODS: We used four reference-class electrometers: RT521R (RTQM system/EMF Japan), Model 35040 (FLUKE), RAMTEC Duo (Toyo medic), and UNIDOS-E (PTW). Each electrometer was connected to the charge generator, and the required charge was applied. The measurement points used were the same as those used for calibration by the ADCL. From the measured charges at each point, the Pelec was obtained from the slope of the linear regression function. The measurements were repeated over a 3-month period to evaluate variations over time for each electrometer. Additionally, error budgets for the Pelec measurements were estimated, and the overall uncertainty was determined. RESULTS: The measured Pelec values were 1.0000, 0.9995, 1.0009/0.9999, and 0.9995/0.9998 for RT521R, Model 35040, the low/medium (L/M) ranges of RAMTEC Duo, and the L/M ranges of UNIDOS-E, respectively. The measured Pelec values agreed within 0.1% with those given by the ADCL. We found a small drift in the measurements for one electrometer. Additionally, the uncertainty considered was 0.26% for k = 2 (k, coverage factor). CONCLUSION: In this study, stable Pelec values were obtained for four electrometers using a charge generator over a three-month period. The measured Pelec values were within the overall uncertainty stated in the electrometer guidelines. However, performing periodic measurements for the Pelec was able to help in detecting small errors.

Single-Electron Transport and Detection of Graphene Quantum Dots.

The integrated structure of graphene single-electron transistor and nanostrip electrometer was prepared using the semiconductor fabrication process. Through the electrical performance test of the large sample number, qualified devices were selected from low-yield samples, which exhibited an obvious Coulomb blockade effect. The results show that the device can deplete the electrons in the quantum dot structure at low temperatures, thus, accurately controlling the number of electrons captured by the quantum dot. At the same time, the nanostrip electrometer coupled with the quantum dot can be used to detect the quantum dot signal, that is, the change in the number of electrons in the quantum dot, because of its quantized conductivity characteristics.

[Evaluation on the Availability of the Electrometer Inspection by Users Using a Newly Developed Current Source].

BACKGROUND: If we try to perform the inspection for an electrometer, two types of electronic signals energized to the electrometer can be used. One is the signal that occurs in the ionization chamber irradiated by radiation. The other is the signal that is derived from a current source. The former signal is changed by radiation output, so we need to use two or more sets of the chambers and the electrometers in the inspection. In addition, the high-performance current source is relatively expensive. Therefore, it is difficult for users to inspect the electrometer simply. To deal with these, we have developed a new current source that allows users to perform highly accurate electrometer inspections at their own facilities. AIM: The purpose of this study was to verify that users can perform electrometer inspections with high accuracy in their own facilities by using a new current source. MATERIALS AND METHODS: A newly current source equips a dry cell battery as a charge generator. Current, polarity, and energized time can be changed by the source setting. We conducted an inspection by energizing the electrometer using the developed current source. RESULTS: The coefficient of variation of the charge amount in the measurement using the new current source was within 0.05%. The electrometer calibration coefficients measured by sensitivity comparison using this current source could be obtained based on electrometers calibrated at a certified facility of the Japan Calibration Service System. CONCLUSION: We have shown that the new current source can be used as a relative current value by using a calibrated electrometer as a reference, indicating that the user can check the electrometer.

Examining electrometer performance checks with direct-current generator in a clinic: Assessment of generated charges and implementation of electrometer checks.

PURPOSE: Medical physicists use a suitable detector connected to an electrometer to measure radiotherapy beams. Each detector and electrometer has a lifetime (due to physical deterioration of detector components and electrical characteristic deterioration in electronic electrometer components), long-term stability [according to IEC 60731:2011, ≤0.5% (reference-class dosimeter)], and calibration frequency [according to Muir et al. (J Appl Clin Med Phys. 2017; 18:182-190), generally 2 years]; thus, physicists should check the electrometer and detector separately. However, to the best of our knowledge, only one study (Blad et al., Phys Med Biol. 1998; 43:2385-2391) has reported checking the electrometer independently from the detector. The present study conducts performance checks on electrometers separately from the detector in clinical settings, using an electrometer equipped with a direct current (DC) generator (EMF 521R) capable of injecting DC (effective range: ±20 pA to ±20 nA) into itself or another electrometer. METHODS: First, to check the nonlinearity of the generated currents from ±20 pA to ±20 nA, charges generated from the DC generator were measured with the EMF 521R electrometer. Next, six reference-class electrometers classified according to IEC 60731:2011 were checked for repeatability at a current of ±20 pA or a minimum effective indicated value meeting IEC 60731:2011, as well as for nonlinearity within the current range from ±20 pA to ±20 nA. RESULTS: The nonlinearities for the measured currents were less than ±0.05%. The repeatability for the six electrometers was < 0.1%. While the nonlinearity of one electrometer reached up to 0.22% at a current of -20 pA, all six electrometers displayed nonlinearities of less than ±0.1% at currents of ±100 pA or higher. CONCLUSIONS: This work suggests that it is possible to check the nonlinearity and repeatability of clinical electrometers with DCs above the ±30 pA level using a DC generator in a clinic.

Dead or "undead"? The curious and untidy history of Volta's concept of "contact potential".

Much of the long controversy concerning the workings of electric batteries revolved around the concept of the contact potential (especially between different types of metals), originated by Alessandro Volta in the late eighteenth century. Although Volta's original theory of batteries has been thoroughly rejected and most discussions in today's electrochemistry hardly ever mention the contact potential, the concept has made repeated comebacks through the years, and has by no means completely disappeared. In this paper, I describe four salient foci of its revivals: dry piles, thermocouples, quadrant electrometers, and vacuum phenomena. I also show how the contact potential has maintained its presence in some cogent modern scientific literature. Why has the death of the Voltaic contact potential been such an untidy affair? I suggest that this is because the concept has displayed significant meaning and utility in various experimental and theoretical contexts, but has never been successfully given a simple, unified account. Considering that situation, I also suggest that it would make sense to preserve and develop it as a multifarious concept.

On the Performance of an Aerosol Electrometer with Enhanced Detection Limit.

An aerosol electrometer with enhanced detection limit was developed for measuring the collected particles electrical current ranging from -50 pA to 50 pA with no range switching necessary. The detection limit was enhanced by suppressing the electric current measurement noise and improving the detection efficiency. A theoretical model for the aerosol electrometer has been established to investigate the noise effect factors and verified experimentally. The model showed that the noise was a function of ambient temperature, and it was affected by the characteristics of feedback resistor and operational amplifier simultaneously. The Faraday cup structure of the aerosol electrometer was optimized by adopting a newly designed cup-shaped metal filter which increased the surface area of the cup; thus the particle interception efficiency was improved. The aerosol electrometer performance-linearity, noise and the particle detection efficiency, were evaluated experimentally. When compared with TSI-3068B, a 99.4% ( R 2 ) statistical correlation was achieved. The results also showed that the root mean square noise and the peak-to-peak noise were 0.31 fA and 1.55 fA, respectively. The particle detection efficiency was greater than 99.3% when measuring particle diameter larger than 7.0 nm.

Electrometer offset current due to scattered radiation.

Relative dose measurements with small ionization chambers in combination with an electrometer placed in the treatment room ("internal electrometer") show a large dependence on the polarity used. While this was observed previously for percent depth dose curves (PDDs), the effect has not been understood or preventable. To investigate the polarity dependence of internal electrometers used in conjunction with a small-volume ionization chamber, we placed an internal electrometer at a distance of 1 m from the isocenter and exposed it to different amounts of scattered radiation by varying the field size. We identified irradiation of the electrometer to cause a current of approximately -1 pA, regardless of the sign of the biasing voltage. For low-sensitivity detectors, such a current noticeably distorts relative dose measurements. To demonstrate how the current systematically changes PDDs, we collected measurements with nine ionization chambers of different volumes. As the chamber volume decreased, signal ratios at 20 and 10 cm depth (M20/M10) became smaller for positive bias voltage and larger for negative bias voltage. At the size of the iba CC04 (40 mm³) the difference of M20/M10 was around 1% and for the smallest studied chamber, the iba CC003 chamber (3 mm³), around 7% for a 10 × 10 cm² field. When the electrometer was moved further from the source or shielded, the additional current decreased. Consequently, PDDs at both polarities were brought into alignment at depth even for the 3 mm³ ionization chamber. The apparent polarity effect on PDDs and lateral beam profiles was reduced considerably by shielding the electrometer. Due to normalization the effect on output values was low. When measurements with a low-sensitivity probe are carried out in conjunction with an internal electrometer, we recommend careful monitoring of the particular setup by testing both polarities, and if deemed necessary, we suggest shielding the electrometer.

Design and Evaluation of an Aerosol Electrometer with Low Noise and a Wide Dynamic Range.

A low-noise aerosol electrometer with a wide dynamic range has been designed for measuring the total net charge on high concentration aerosol particles within the range of -500 pA to +500 pA. The performance of the aerosol electrometer was evaluated by a series of experiments to determine linearity, sensitivity and noise. The relative errors were controlled within 5.0%, 1.0% and 0.3% at the range of -40 pA to +40 pA, ±40 pA to ±100 pA, and ±100 pA to ±500 pA respectively. The stability of the designed aerosol electrometer was found to be highly sensitive to temperature variations, but under temperature control, the root mean square noise and the peak-to-peak noise were 1.040 fA and 5.2 fA respectively, which are very close to the calculated theoretical limit of the current noise. The excellent correlation and the advantage of a wide dynamic range have been demonstrated by comparing with the designed aerosol electrometer to a commercial aerosol electrometer. A 99.7% (R²) statistical correlation was obtained; meanwhile, the designed aerosol electrometer operated well even when an overrange phenomenon appeared in the commercial aerosol electrometer.

The effect of additional enamel etching on microleakage of the adhesion of self-etching primer system / 대한치과보존학회지

The purpose of this study is to evaluate the effect of additional enamel etching with phosphoric acid on the microleakage of the adhesion of self-etching primer system. Class V cavity(4 mmx3 mmx1.5 mm) preparations with all margins in enamel were prepared on buccal surface of 42 extracted human upper central incisor teeth. Prepared teeth were randomly divided into 3 groups. Group 1 : no additional pretreatment with 37% phosphoric acid (NE). Group 2 : additional pretreatment with 37% phosphoric acid for 10 seconds (E10s). Group 3 : additional pretreatment with 37% phosphoric acid for 20 seconds (E20s). The adhesives(Clearfil SE Bond(R), Kuraray, Osaka, Japan) and composite resins(Clearfil AP-X(R), Osaka, Kuraray, Japan) were applied following the manufacturer's instructions. All the specimens were finished with the polishing disc(3M dental product, St Paul, MN, USA), thermocycled for 500 cycles between 5degrees C and 55degrees C and resected apical 3-mm root. 0.028 stainless steel wire was inserted apically into the pulp chamber of each tooth and sealed into position with sticky wax. Surrounding tooth surface was covered with a nail varnish 2 times except areas 1 mm far from all the margins. After drying for one day, soaked the samples in the distilled water. Microleakage was assessed by electrochemical method(System 6514, Electrometer(R), Keithley, USA) in the distilled water. In this study, the microleakage was the lowest in group 1(NE) and the highest in group 3(E20s)(NE