NIST PUBLISHES SPECIAL PUBLICATION 250-58: CALIBRATION OF X-RAY AND GAMMA-RAY MEASURING INSTRUMENTS.NIST (National Institute of Standards & Technology, Washington, DC, www.nist.gov) The standards-defining agency of the U.S. government, formerly the National Bureau of Standards. It is one of three agencies that fall under the Technology Administration (www.technology. has recently revised and published a key Measurement Services Guide, NIST Special Publication 250-58, which describes completely the x-ray and gamma-ray calibration services provided at NIST. This publication replaces the 1988 NBS (National Bureau of Standards) See NIST. NBS - National Bureau of Standards: part of the US Department of Commerce, now NIST. Special Publication 250-16 that has been widely distributed for the past decade to those interested in x-ray and gamma-ray measurements for medical applications. This revised edition now includes details of the NIST mammography mammography, diagnostic procedure that uses low-dose X rays to detect abnormalities in the breasts. The early diagnosis of breast cancer made possible by the routine use of mammography for screening women increases a woman's treatment alternatives and improves her calibration facility, results of recent international x-ray comparisons, new reference beam quality parameters, and documentation of current uncertainties associated with the calibration service. The calibration and irradiation of instruments that measure x rays and gamma rays Gamma rays Electromagnetic radiation emitted from excited atomic nuclei as an integral part of the process whereby the nucleus rearranges itself into a state of lower excitation (that is, energy content). are performed in terms of the physical quantity: air-kerma. The measurement of air-kerma and the calibration process involves a comparison of the test instrument to a NIST primary standard, which includes four free-air ionization ionization: see ion. ionization Process by which electrically neutral atoms or molecules are converted to electrically charged atoms or molecules (ions) by the removal or addition of negatively charged electrons. chambers for x rays and cavity ionization chambers for gamma rays. The document will be useful to those who use the NIST radiation calibration service and for others who are currently developing services similar to those provided at NIST. SP 250-58 will soon be available on the web. |
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