Characteristics of high-energy radiography

High-energy radiography

X-rays with energy above 1MeV are called high-energy rays. Most of the high-energy rays used in industrial testing are obtained through electron accelerators. Industrial radiography usually uses two kinds of accelerators, namely, cyclotron and linear accelerator.

1、 Electron cyclotron and electron linac

2、 Characteristics of high-energy radiography

3、 Several Technical Data of High Energy Radiography

4、 The structure, principle, and operation of linear accelerators

5、 Radiation protection of high-energy accelerating rays

Characteristics of high-energy radiography

In terms of application, high-energy radiography has the following five characteristics

1. Strong ray penetration ability and large transparency thickness

At present, the penetration thickness of X-ray machines on steel is usually less than 100mm, with Co60 γ The maximum penetration thickness of radiation on steel is about 200mm, while the energy range of high-energy radiation in industrial applications is 1-24MeV, and the penetration thickness of steel can reach over 400mm. Therefore, high-energy radiation is almost the only choice for radiographic testing of workpieces with a thickness of over 200mm.

2. Small focus, large focal length, and high photographic clarity

The volume of high-energy X-ray equipment is much larger than that of general X-ray inspection machines, and the heat dissipation problem is relatively easy to solve, so the focus can be made very small. For example, the electron cyclotron is only 0.3~0.5mm, and the linear accelerator focus is only 1~3mm. In addition, in order to ensure a sufficiently large irradiation field, high-energy radiography requires the use of large focal lengths. Both small and large focal lengths are beneficial for improving photographic clarity.

3. Less heat dissipation lines and high photographic sensitivity

In the high-energy range, the interaction between ray photons and matter is mainly due to Compton scattering and electron pair effect, and the trend of scattering ratio change is that the scattering ratio continuously decreases with the increase of ray energy.; On the other hand, due to the high energy of the secondary particles generated by the interaction process, further scattering is mainly concentrated in the direction of the primary ray, and the total amount of large angle scattering is small. Therefore, high-energy radiography has a low scattering ratio and high photographic sensitivity 


                                                                                               

4. High radiation intensity, short exposure time, continuous operation, and high work efficiency

The measurement of the linear accelerator at a distance of 1m from the target can reach 4-100Gy/min, which is much higher than various industrial detection applications γ The dose rate of the radiation source. The ratio of working to intermittent for ordinary industrial X-ray machines is generally 1:1, while accelerators can operate continuously without intermission. Therefore, the exposure time of using a linear accelerator to take photos of workpieces is very short, especially for large thickness workpieces. The exposure time of taking photos of 100mm thick steel workpieces is about 1 minute, which is incomparable to other equipment.

5. Large tolerance for photographic thickness

The absorption law of matter for high-energy rays is significantly different from that of low-energy rays, and its absorption coefficient changes slowly with energy. In the range of approximately 1-10 MeV, the ray absorption coefficient of a substance decreases with increasing energy, while in the range of 10-100 MeV, the ray absorption system of a substance