Air Density Correction Factor Research Articles

Evaluation of influential correction factors applicable for absolute beta dosimetry of 85Kr, 90Sr–90Y and 106Ru–106Rh beta emitters

Extrapolation ionization chamber is normally used for absolute measurement of absorbed dose to tissue and in standardization of beta particle emitting sources in particular. However, in this technique, several correction factors are applied to the measured ionization current to evaluate the true value of the dose to the tissue from beta radiation. These correction factors are described in ISO 6980–2:2004. Out of these, ion recombination correction factor (ksat) and ambient air density correction factor (kad) are evaluated experimentally during measurement of ionization current. Other significant correction factors are backscatter correction factor (kba), correction factor for perturbation in electron spectrum due to ionization chamber side wall scatter (kpe), correction factor for difference in attenuation of beta spectrum due to change in ambience condition (kabs) and correction factor for radial non-uniformity of dose inside detector volume (kra). Experimental evaluation of correction factors kba, kpe and kabs are not easily achievable. In the present work four significant correction factors kba, kpe, kabs and kra are derived theoretically by Monte Carlo particle transport simulation. These correction factors are evaluated for beta emission spectrum of 85Kr, 90Sr–90Y and 106Ru–106Rh radioactive sources.

TDC-based horizontal leakage area estimation in multiunit residential buildings: Three correction factors

Infiltration and interzonal airflow driven by wind and stack interactions in a multi-unit residential building (MURB) are crucial factors affecting indoor air and environmental qualities. To analyze the weather-driven airflow in MURBs, it is essential to define accurately the horizontal leakage areas for serial airflow paths on typical and basement floors in the multizone airflow modeling. Considering the challenges in measuring numerous leakage areas, a horizontal leakage estimation method based on the thermal draft coefficient (TDC) is proposed, in which the leakage areas are calculated by the stack-driven pressure differences relatively easy to measure. Moreover, three correction coefficients are theoretically suggested to minimize the TDC uncertainties from (1) different household envelope areas, (2) horizontal temperature distributions on each floor, and (3) multiple shafts in real MURBs. Two validation studies were conducted in a real MURB. First, the TDC-based models were validated by CONTAMW, and the effectiveness of the three correction factors was shown in the simulation-based case. The envelope area ratio correction factor was most effective for leakage areas in dwelling units. The shaft ratio correction factor was necessary for elevator doors on typical floors and all leakage areas on basement floors. The air density correction factor could improve all leakage areas under the horizontal temperature distributions on each floor. Then, based on field measurements, the proposed method was applied to leakage estimation in the building. Compared with the existing method, the field-measurement-based validation case demonstrated a significant improvement in the leakage estimation under measurement uncertainties.

Impulse breakdown voltages of air gaps: a new approach to atmospheric correction factors applicable to international standards

In the design of high-altitude high-voltage transmission systems and in the optimization of the reliability of power sources in aeronautical environments, it is important to have reliable data concerning the effect of air density and humidity on reducing air insulation performance under local conditions. This is helpful also in the modeling of discharges and lightning in mountainous regions. This paper describes a systematic laboratory investigation of the combined effects of humidity and gas density on the breakdown strength of a 0.2 m rod/plane air gap that is subjected to positive-polarity lightning impulses, using a test chamber to reproduce the conditions commonly found in such regions. The results show that there are appreciable deviations between the measured humidity and air density correction factors and those of the 1973 and 1989 IEC Standards when extended to low air density. The paper proposes the adoption of a radically different correction procedure, based upon the influence of density and humidity on streamer propagation field, and including the effect of the high gradient in the anode region.

Air density correction in ionization dosimetry

Air density must be taken into account when ionization dosimetry is performed with unsealed ionization chambers. The German dosimetry protocol DIN 6800-2 states an air density correction factor for which current barometric pressure and temperature and their reference values must be known. It also states that differences between air density and the attendant reference value, as well as changes in ionization chamber sensitivity, can be determined using a radioactive check source. Both methods have advantages and drawbacks which the paper discusses in detail. Barometric pressure at a given height above sea level can be determined by using a suitable barometer, or data downloaded from airport or weather service internet sites. The main focus of the paper is to show how barometric data from measurement or from the internet are correctly processed. Therefore the paper also provides all the requisite equations and terminological explanations. Computed and measured barometric pressure readings are compared, and long-term experience with air density correction factors obtained using both methods is described.

Critical switching impulse strength of long air gaps: modelling of air density effects

A physical modeling approach to investigate the effect of reduced air density on leader inception and sparkover of long air gaps under positive switching impulses with critical front time is presented. The model accounts for the effect of air density on continuous leader inception voltage, leader length, and sparkover voltage. The results of the model provides critical positive switching impulse air density correction factors for rod-plane, rod-rod, conductor-plane, conductor-rod, and conductor-tower window gaps over a wide range of gap distances and relative air densities. The model findings were extensively checked against previous experimental results with quite satisfactory agreement.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Malfunction of linear accelerator dose monitoring systems.

Malfunctions of the dose monitoring systems of two linear accelerators were studied. A variation of plus or minus 2.5% over an air density correction factor range from 1.02 to 1.07 was measured, suggesting that the ionization-type monitor chambers were open to the atmosphere. An average variation of minus 2.0% was present between early morning calibrations and those performed later in the day. Any variation caused by changes in control console temperature was within experimental error. This type of malfunction can lead to errors in delivered doses of 5%.

Simple Device for Measurement of Air Density Correction Factors

First Page

Radio-Frequency Spark-over in Air

Measurements of spark-over voltage were made at 700 and 1800 kilocycles using needle points, blunt electrodes, and spheres. By impressing the voltage across a shielded capacitance of known value, then measuring the current which flows and the frequency, the voltage was calculated. Ultraviolet irradiation of the spark gap was required for consistent results. When spheres were used, the radio-frequency spark-over voltage was 17 to 20 per cent below the 60-cycle voltage. The air-density correction factor at 700 kilocycles was found to be nearly proportional to the air density. Measurements of radio-frequency spark-over voltage were made on a number of air condensers and a plate thickness of one half to one third the air gap was found to be the most satisfactory.

A new correlation of sphere-gap data

The similarity principle for electrical discharges is used to correlate the most recent AIEE sphere-gap data for both positive and negative impulses. Empirical formulas are developed from which the entire range of data can be calculated to within about 1.5 per cent. Some practical results of this study are: 1. Spark-over curves for each value of spacing to diameter ratio are straight lines when plotted to logarithmic scales, at least to within the certainty of the present data. 2. A spark-over voltage chart covering the entire useful range of sphere sizes, spacings, and air densities can be constructed easily. 3. New air-density correction factors are derived which differ appreciably from those previously published.

A New Correlation of Sphere-Gap Data

The similarity principle for electrical discharges is used to correlate the most recent AIEE sphere-gap data for both positive and negative impulses. Empirical formulas are developed from which the entire range of data can be calculated to within about 1.5 per cent. Some practical results of this study are: 1. Spark-over curves for each value of spacing to diameter ratio are straight lines when plotted to logarithmic scales, at least to within the certainty of the present data. 2. A spark-over voltage chart covering the entire useful range of sphere sizes, spacings, and air densities can be constructed easily. 3. New air-density correction factors are derived which differ appreciably from those previously published.