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New concepts for the measurement of focal spot parameters of nano- and microfocus X-ray tubes
(2019)
Accurate measurement of focal spot sizes of X-ray tubes, betatrons and linear accelerators is still an open problem. Several standards are currently active, which provide different results depending on the focal spot shape. CEN published the standard series EN 12543 (five parts) in 1999, which describes the measurement of focal spot sizes of X-ray tubes for NDT applications. The measurement procedure and its tolerances deviate from the measurement standards for medical X-ray tubes, e.g. EN 60336:2006 / IEC 60336:2005. EN 12543 describes different measurement methods for X-ray tubes with focal spots in several size ranges, defined as macrofocus, minifocus and microfocus. CEN TC 138 WG 1 und ASTM E 07.01 are revising (CEN) or have just revised (ASTM) the standards for focal spot size measurements, basing them on pin hole or edge measurements only. Slit cameras are applied for medical tube evaluation only. Tomographic methods for focal spot size shape reconstruction were proposed and will be discussed, but have not yet been used for standardization. The currently available standards cover the range of spot sizes from 5 µm up to several millimetres. During the last years, more and more nanofocus tubes have been developed for high-resolution applications and microscopy. Manufacturers and users apply different methods for measurement of nanofocus spot sizes and image resolution, which differ by a factor of up to two. These well-known methods and new alternative methods for the measurement of nanofocus spots (size and shape) will be evaluated and improved in the EMPIR project “NanoXSpot” in order to develop a related measurement standard.
EMPIR Project NanoXSpot
(2019)
The overall objective of project NanoXSpot (Nanometre X-ray Focal Spot Measurement) is to develop traceable measurement methods for determining the focal spot size, shape, and position of nanometre resolution X-ray tubes. The impact of the technical results will be ensured by preparing prenormative documents for submission to CEN TC 138 (Non-destructive testing) WG 1 (Radiographic testing), which directly addresses the research needs of CEN, currently revising standards in the series 12543 for focal spot measurements below 5 µm spot size to harmonise standards and measurement method between ASTM and CEN.
Im Rahmen des EMPIR-Projektes NanoXSpot (Nanometre X-Ray Focal Spot Measurement) werden rückführbare Messverfahren zur Bestimmung der Brennfleckgröße und -form von Röntgenröhren mit Submikrometerauflösung (100 nm – 20 µm) entwickelt, die die Grundlage für die Erarbeitung eines Standardentwurfes bilden. Der Standardentwurf wird bei CEN TC 138 (Non-destructive testing) WG 1 (Radiographic testing) eingereicht und mit ISO und ASTM harmonisiert. Zur Untersuchung der entwickelten Methoden (Brennfleck-CT, Fit-Prozedur für Strichgruppenkörper) und des im Projekt NanoXSpot neu entworfenen Testkörpers, NxS, wurde ein Ringversuch durchgeführt. Dabei wurde sowohl der angestrebte Überlappungsbereich mit EN 12543 Teil 5 (Messung der effektiven Brennfleckgröße von Mini- und Mikrofokus-Röntgenröhren) und ASTM E 2903 (Standard Test Method for Measurement of the Effective Focal Spot Size of Mini and Micro Focus X-ray Tubes) für Brennflecke >5 µm als auch Brennflecke <5 µm untersucht. Im Mittelpunkt standen dabei Stabilität und Wiederholbarkeit der entwickelten Methoden zur Bestimmung der Brennfleckgröße. In diesem Beitrag werden die Ergebnisse des durchgeführten Ringversuches vorgestellt und diskutiert, um Schlussfolgerungen und Empfehlungen für die Vorbereitung eines erweiterten Ringversuchs mit Partnern und Stakeholdern abzuleiten.