Several Technical Data of High Energy Radiography and radiation protection

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

Several Technical Data of High Energy Radiography

1. Inherent lack of clarity

The focus of high-energy X-ray equipment is small, and in high-energy radiography, in order to obtain a sufficiently large irradiation field, a larger focal length is usually used. Therefore, the geometric opacity is relatively small, while the inherent opacity is relatively large due to the high energy of the rays. Contrary to low-energy X-ray inspection, inherent lack of clarity becomes the main factor affecting the clarity of high-energy X-ray photography. Table 8-1 shows the inherent opacity values of high-energy radiography.

2. Sensitivity

In most material and thickness ranges, if the process is correct, the sensitivity of high-energy radiography can reach or be lower than 1%. Figure 8-3 shows the sensitivity curve of the linear image quality indicator for high-energy radiography of steel.

3. Enhanced screen

In high-energy radiography, the thickness of the front screen has a significant impact on both enhancement and filtering effects, while the thickness of the back screen is relatively unimportant for enhancement. Therefore, when using high-energy radiography, the back screen can be avoided.

Experiments have shown that under certain conditions, the sensitivity of high-energy radiography increases when the rear screen is not used, which is different from conventional radiography.

In actual photography, a lead intensifying screen with a thickness of about 0.25mm is usually selected for the front screen. If a rear screen is used, its thickness can be the same as the front screen.

The thickness of the intensifying screen for high-energy radiography can be selected based on the data in Table 8-2.

In addition to lead, materials such as copper, tantalum, and tungsten can also be used as intensifying screens according to actual needs to meet different testing requirements.

Radiation protection accelerated by high-energy rays

The high-energy rays generated by accelerators not only have high energy, but also have high intensity. Taking the Linatron400 model produced by Varian Company in the United States as an example, the device outputs a dose of 4Gy and an energy of 4MeV per minute of radiation at a distance of 1m from the target.

The half lethal dose of whole-body radiation in the human body is 4Gy. If personnel are mistakenly photographed by this equipment, it is very dangerous, therefore, safety protection measures must be taken.

1. The protection of accelerators mainly adopts shielding protection. The shielding room of accelerators must be specially designed for safety protection, and the outdoor dose rate must be lower than the national health standards.

2. Because the ozone and nitrogen oxides generated by high-energy X-rays ionizing the air are harmful to the human body, ventilation fans must be installed indoors for ventilation.

3. For linear accelerator, in addition to protection against accidental injury caused by high-energy X-ray, microwave radiation protection protection should also be carried out, and high voltage should also be prevented