Secondary Standard Sources Research Articles

Comparison of calibration results for an extrapolation chamber obtained with different 90Sr+90Y secondary standard sources

Two secondary standard systems of beta radiation were used to calibrate a PTW extrapolation chamber Model 23391. Three (90)Sr+(90)Y sources of different activities were used in this calibration procedure. Medium-term stability of the response of the chamber was also studied. The calibration was performed with and without field-flattening filters. The relative standard deviation of the obtained calibration factors was 8.3% for the aluminum collecting electrode and 4.1% for the graphite collecting electrode.

Characteristics of an extrapolation chamber for β-ray protection level measurements

An absolute determination of the absorbed dose rates to tissue from a Sr90Sr+90Y β-ray secondary standard source was attempted using an extrapolation chamber developed at the Calibration Laboratory of São Paulo. The performance of this chamber and its main characteristics are presented in this work. A comparison of the results obtained with those of the calibration certificate indicates an absorbed dose rate agreement within 1.0%.

The Suitability of Tungsten Strip Lamps as Secondary Standard Sources below 1064°C

High-stability tungsten strip lamps are assessed as a means of maintaining the International Practical Temperature Scale below 1064.43°C. The variation of spectral radiance temperature with changes in the lamps and their environment is discussed. Factors necessary to correct the spectral radiance temperature for changes in the resistance and pin temperature of two lamps are given. It is shown that applying corrections for changes in lamp resistance reduces the uncertainty in the use of lamps by an order of magnitude. The uncertainties which are to be associated with the use of tungsten strip lamps under practical conditions are 0.015°C at 1064°C and 0.045°C at 770°C (99% confidence limits). These results indicate that the platinum resistance thermometer appears to be a better alternative means of maintaining temperature scales in the range considered.

The High Frequency Radio Spectra of Secondary Standard Sources

Eight sources commonly used as standards were compared at 3.24, 6.63 and 10.63 GHz with 3C 274, a source that has been established recently on an absolute scale. As a result, accurate high frequency spectra for these eight sources have been obtained.

Transition Radiation as a Secondary Standard Source in the VUV

The optical radiation caused by electron bombardment of metallic surfaces was tested for its use as a secondary standard source in the VUV. Aluminum of high purity was found to be a suitable target material. The reproducibility of the radiation is of the order of 4% to 2% for 0.11 < lambda < 0.15 microm and 0.15 < lambda < 0.27 microm, respectively. In the spectral region 0.17 microm to 0.27 microm, the source was calibrated absolutely by comparison with a deuterium lamp of known absolute intensity.

The Suitability of Vacuum Tungsten Blackbody Lamps as Secondary Standard Sources in Photoelectric Pyrometry

The suitability of vacuum tungsten blackbody lamps as secondary standard sources in photoelectric pyrometry has been investigated. It has been found that although the sources are stable when operated for long periods at temperatures up to 1625 °C they will not maintain calibration when physical strain is introduced into the tungsten tube or supports, for example, by vibration of the lamp. All changes detected in calibration of lamps have been accompanied by changes in their electrical resistances, and therefore this parameter can be used as a monitor of calibration stability. Variations in resistance at the gold point of 0.1% produce significant changes in calibration. The effect of pin temperature on the lamp resistance and spectral radiance temperature are given. When precautions are taken in handling, mounting and storage to minimise the introduction of strain in the lamps the uncertainty in their calibration at the gold point is less than ±0.1°C.

The suitability of tungsten strip lamps as secondary standard sources in photoelectric pyrometry

It is shown that the tungsten strip lamp is satisfactory for use as a secondary standard of temperature measurement in realizing the International Practical Temperature Scale above 1063° C with a photoelectric pyrometer. The errors of calculation due to uncertainties in the tungsten emissivity and transmittance of the lamp window are 0.01 degC at 1063° C and 0.03 degC at 2000° C. Typical curves are given for the variation of luminance temperature with position along the strip and with angle of view. The reproducibility of tungsten strip lamps is ±0.05 degC for vacuum lamps at 1063° C and ±0.10 degC for gas-filled lamps at 1400° C. The long term stability of the best lamps tested was a decrease in luminance temperature of 0.2 degC per 100 hours for a vacuum lamp at 1400° C and 0.3 degC per 100 hours for a gas-filled lamp at 2000° C.

Noise measurements in the 3-cm waveband using a hot source

The method discussed uses the noise power produced in a waveguide termination at temperatures up to 600°C as a standard source of low-level power. A suitable type of hot source and associated waveguide and detecting circuits are described. Some experimental results are given of measurements on the effective temperature of a gas-discharge tube used as a secondary standard source.