A new laboratory dedicated to establishing a national primary air-kerma rate standard for Xoft's AXXENT™ miniature x-ray source has been fabricated
The Xoft source was designed to provide low-energy x-rays (<50 keV) for use in brachytherapy. The air-kerma rate is being directly realized through use of the Lamperti free-air chamber, which was compared with another national x-ray standard with these sources. A high-purity germanium (HPGe) x-ray spectrometer is used to monitor the energy spectrum of the beam in real time, as well as provide necessary input data for Monte Carlo calculations of correction factors for the free-air chamber. To account for spatial anisotropy of emissions, the free-air chamber and spectrometer are rotated about the long axis of the x-ray tube during measurements. The response of well-ionization chambers to the x-ray sources is being studied in preparation for the development of a measurement assurance program for the dissemination of the new NIST standard to Accredited Dosimetry Calibration Laboratories (ADCLs). The ADCLs are accredited by the American Association of Physicists in Medicine (AAPM), and calibrate radiation measuring instruments for use in therapy clinics.