Effects of recent knowledge of atomic constants and of humidity on the calibrations of the National Bureau of Standards thermal-radiation standards

Abstract

Th e National Bureau of Standards the rm a l-rad iation standards, as established and maintained since 1913, are based prim a ril y upon t he emission of a blackbody, using the Stefan-Bo ltzmann consta nt of total radiation u = 5. 70 X 10-12 watt/ ( cm2 deg·) .The present status of t his constant is rev iewed in relat ion to the recent ex perim ental ev idence for more accurate values of the velocity of light and for the other atomic co nstan ts effecti ng the valu e of u . It is conclud ed that an y c hange in t he Stefan-Bol tz mann constant is unimpor ta nt at t his t im e.An investigation is r eported on the effect of the atmospheric water vapor on t h e transmitted radiant intensities of these lamps at the wor kin g distance of 2 meters. T he usua l vari ations in la borator y hum idities will affect the cert ified calibrations of t hese s tandard lamps less t han 0.3 p ercent a nd hence may be n eglected in aU radiom etric work wherein they are e mployed .One section of t he paper is given to gen eral instru ctions for the use of these standards in precision work.

Absolute Spectral Sensitivity of Phototubes and the Application to the Measurement of the Absolute Quantum Yields of Chemiluminescence and Bioluminescence*

“…It starts to absorb in the infrared at about 3 p making it necessary to correct the calibration value for this amount. This correction has been closely studied (15) and found, for a 1.5 mm thick crystal quartz window, to amount to an absorption of about 8.5 per cent of the light from an NBS Radiant Energy Standard Lamp operated at 0.35-0.40A. The reflection from the two sides of the window, amounting approximately to a further 8 per cent, must be added to this absorption to obtain a total radiant energy attenuation, but as the fractional change in reflection property is much less than in absorption when going from the infrared to the visible, it can safely be ignored.…”

Standard of spectral radiance for the region of 0.25 to 2.6 microns

“…Fifty years ago the principal need in the evaluation of radiant energy was a convenient standard against which a radiometer might be calibrated. Although several crude standards of total radiance in the form of oil lamps or candles existed about 1900, the establishment of the carbon filament lamp [ 1 , 2 , 3 ] 1 provided a convenient working standard for a limited range of total radiance. Then, as today, the blackbody was considered the reference standard, but its use was relegated only to the few primary scientific laboratories.…”