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Absolute and Reference Dosimetry
Published in Harald Paganetti, Proton Therapy Physics, 2018
The first codes of practice for heavy charged particle dosimetry emerged in the 1980s and early 1990s in AAPM Report 16 produced by the Task Group 20 of the AAPM [41] and ECHED [37,38]. They all had in common that the first recommendation was to use a calorimeter for reference dosimetry. If not available, a Faraday cup could be used as reference instrument or calibrated against a calorimeter or an ionization chamber calibrated in terms of exposure in air or air kerma in a 60Co calibration beam. In AAPM Report 16, the quantity of interest was defined as dose to tissue, and ionization chambers filled with other gasses than air were considered. The third factor of Equation 10.11 thus contained a tissue-to-gas rather than a water-to-air mass stopping power ratio. Also in the original ECHED code of practice, the quantity of interest was defined as dose to tissue, but only air-filled ionization chambers were considered and thus there appeared a tissue-to-air mass stopping power ratio. For both of those two protocols, the second factor in Equation 10.11 was, apart from a few details, similar as what was used in AAPM TG-21 [47] for photon and electron dosimetry, although no consideration was given to the fact that, in the 60Co calibration beam, part of the electron spectrum in the air cavity is not generated in the wall. Both used the stopping power tables of Janni [48]. In the Supplement to the ECHED protocol [38], dose to water was defined as the quantity of interest, and in addition, the stopping powers of ICRU Report 49 [33] were recommended, which was a step in bringing proton dosimetry in better harmony with high-energy photon and electron dosimetry. One of the more substantial differences between the recommendations of the AAPM and the ECHED was, as discussed earlier, the substantial discrepancy of about 2.6% in the Wair value for proton beams.
Emerging Biomedical Analysis
Published in Lawrence S. Chan, William C. Tang, Engineering-Medicine, 2019
The detection of an ion in a modern mass spectrometer is achieved by creating an electric signal. The basic ion detector is the Faraday cup. The principle of the Faraday cup is that a current is induced when a packet of ions hits the dynode surface. The number and charge of ions are determined by measuring the current.
Repeatability and intermediate precision of a mass concentration calibration system
Published in Aerosol Science and Technology, 2019
Jordan Titosky, Ali Momenimovahed, Joel Corbin, Kevin Thomson, Greg Smallwood, Jason S. Olfert
A Faraday cup is a device which captures particles; where the charge induced by the charged particles is measured with an electrometer. The combination of the Faraday-cup, electrometer, and flow controller is often called an aerosol electrometer. Particle capture inefficiencies or leakage current caused by the Faraday cup may result in erroneous currents measured by the electrometer. A method to determine the instrumental bias of the Faraday cup by measuring an accepted standard is not known. The repeatability and intermediate precision of the two aerosol electrometer systems were determined by comparing the simultaneous measurement of a stable charged particle source.