X-ray tube

The principles of gamma-ray radiography are the same as X-ray radiography except that a radioisotope is used as the radiation source rather than an X-ray tube. 

Due to the possibility of selecting the radiation energy of X-ray tubes in accordance with the material thickness under investigation there is another increase in wire sensitivity at low steel thicknesses. Starting from approx. 20 - 25 mm steel thickness the differences between X-rays and Selenium decrease and merge at about 40 mm. 

It is easy to notice, that the protection against a short-circuit failure in the X-ray tube circuit implements due to the "soft" outer characteristic of the apparatus main circuit. The overvoltage protection at emergencies in the control system happens due to the redistribution of the magnetie flow, created by power winding I, between the 3,6 control yokes. Therefore the voltage on the X-ray apparatus anode drops approximately two times. 

The magnetic regulators allow to synthesize in one module of the X-ray apparatus main cir-euit commutator, form converter, noncontact smooth ac voltage amplitude regulator, para-metrie stabilizer, ac supply filter, fimetional protection against the short-circuit in the X-ray tube and protection against emergencies in the control circuits. 

The X-ray tube generates an X-ray image of the workpiece via central projection. 

The inspection class SA is based on the requirements of real-time serial inspection that are covered by standard minifocus X-ray tubes. 

Application of experimental devices allows to perform NDT of products, made out of materials of low density (Al-Mg - alloys, Be, plastics) with high defectoscopic sensitivity up to 0,5 %. Inch-size X-ray vidicons used complete with microfocal X-ray tubes and X-ray image enlargement method allow to obtain resolution up to SO pairs of lines per mm. 

Figure 3 A blade on the rotation table in front of the image intensifier Technical data of the X-Ray tubes are given in table 1.

The lead time for making a image by film X-Ray is 10 to 15 minutes. Where about 2 minute are needed in inspection by Real-Time X-Ray. Another advantage of Real-Time X-Ray is the feature that the effect of manipulating the part or changing the setting of the X-Ray tube can be observed directly. This is often used in investigating quality problems. 

The volume of defects is calculated using intensity evaluation. Considering the polychromatic radiation of microfocus X-ray tubes the X-ray beam is represented by an energy dependent intensity distribution Io(E). The intensity Ip behind a sample of thickness s is given by integrating the absorption law over all energies ... 

In traditional Fan-Beam CT the radiation emitted from the X-ray tube is collimated to a planar fan, and so most of the intensity is wasted in the collimator blades (Fig. 2a). Cone-Beam CT, where the X-rays not only diverge in the horizontal, but also in the vertical direction, allows to use nearly the whole emitted beam-profile and so makes best use of the available LINAC photon flux (Fig. 2b). So fast scanning of the samples three-dimensional structure is possible. For Cone-Beam 3D-reconstruction special algorithms, taking in consideration the vertical beam divergence of the rays, were developed. 

A New Series of Metal-Ceramie X-Ray Tubes for Low Power Applications. 

Sealed metal-ceramic X-ray tubes are in use since the sixties. Whereas glass tubes still are the most common known form of X-ray tubes in the public, and are certainly the most used technology firom point of view of sold tubes per year, metal-ceramic X-ray tubes in lots of applications are state-of-the-art. 

The actual goal of the development was not to replace glass tubes in their main markets, but to open new markets for X-ray tubes in general. 

When we look at a very simple sketch of an X-ray tube, we can outline some aspects of the applied technique of construction ... 

X-ray tubes are used in a broad variety of technical applications the classical application certainly is the radiographic inspection. For the penetration of high-Z materials, relatively high power is required. This lead to the development of X-ray tubes for laboratory and field use of voltages up to 450 kV and cp power up to 4,5 kW. Because of design, performance and reliability reasons, most of these maximum power stationary anode tubes are today made in metal-ceramic technology. 

An advantage of the use of ceramics over the use of glass as an insulator in X-ray tubes is the larger freedom in design due to better stability and more reliable quality of the ceramics. Therefore, typical markets for metal-ceramic tubes are applications where only a relatively low amount of tubes, but in special designs, are used. 

Our company is dedicated solely to metal-ceramic X-ray tubes since 25 years over this time, we have made lots of different tube models especially for tyre inspection systems. The major reasons for the use of metal-ceramic tubes in this inspection technology are robustness, their small and individual shapes, and the frequent need for modifications of their design due to custom designed systems. 

All these specific needs in this market lead to the metal-ceramic technology as the most economic solution for X-ray tubes. 

Metal-ceramic technology would be -if price problems were neglected- the better choice for a variety of small-power X-ray applications. The problem is that an universal X-ray tube is not (and probably will never be) available. 

Flence, the aims of the new series of metal-ceramic X-ray tubes for lower applications were ... 

At present time, our company is running a development project on the production technology of the MCB type X-ray tubes. The goals of this project are the improvement of the existing technology and making available new tube designs in the near future. 

Specific features of the new cathode-grounded X-ray tubes shall be ... 

Most of the advantages of MCB technology can be used to make small anode-grounded metal-ceramic X-ray tubes as well. These could be water- or air-cooled and reach power ranges up to 1 kW at voltages up to lOOkV. 

The metal-ceramic X-ray tubes described here provide new possibilities to the developer of X-ray equipment ... 

The well-known properties of metal-ceramic X-ray tubes are now available for applications in the low budget range. 

For the radiographic testing of the samples a microfocus X-ray tube, manufactured by Feinfokus, Garbsen was used. The X-ray tube has a focal spot, depending on the power, with a diameter from 5 pm to 50 pm. 

This focal spot diameter is very much smaller than the spots of conventional X-ray tubes. The goodness of a X-ray image is influenced by contrast and sharpness. Caused by the almost punctual point of origin of the X-rays, a low geometrical unsharpness according to equation 1 is reached. 

Modem NDT film systems (with Pb screens) are very linear X-ray detectors. This is shown in fig.l for different NDT film systems and a X-ray tube at 160 kV. Note that for histoncal reasons the film response curve is often plotted as film density versus log (radiation dose), which hides this linear relationship. The film density is the difference between the measured optical film density and the fog density Db of the film base. 

Fig.l Film response curves of several NDT film systems (160 kV X-ray tube)... 

Fig. 2 shows the response of a C2 film system on a step wedge (wall thickness range 2. .. 18 mm) exposed with a X-ray tube at 160 kV. For the exposure withy-rays (Irl92 or Co60) corresponding linear relationships are obtained. From this linear relationship it is followed, that the influence of the scattered radiation and the energy dependence of the absorption coefficient can be considered by an effective absorption coefficientPcff in equation (1). 

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