High-energy radiography: electron cyclotron and electron linac

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

Electron cyclotron

The electron cyclotron uses the magnetic induction effect of the transformer to accelerate the electron. The primary winding of the transformer is connected with the AC power supply, so that the voltage generated by the secondary winding on the iron core is equal to the product of the turns of the secondary winding and the time change rate of the magnetic flux, and the generated electron flow is composed of free electrons existing in the wire. The electron cyclotron is essentially a transformer.

The secondary winding is a circular tube that is evacuated, also known as a circular vacuum chamber. Circular tubes are usually made of porcelain, with a conductive target layer coated on the inside and grounded. In addition to replacing wires, circular tubes are also used to accommodate electrons that are accelerated to rotate at high speeds.

The annular vacuum tube is located between the two stages of an electromagnet that generates a pulsed magnetic field. The electrons injected into the tube will accelerate in the annular channel due to the magnetic field, and the force acting on the particles is proportional to the rate of magnetic flux change and the size of the magnetic field.

The accelerated electron needs to orbit several hundred thousand times before hitting the target to obtain sufficient energy.

The focus of electron cyclotron is very small, and its photographic geometric unsharpness is small, so it can obtain highly sensitive pictures. However, its application is affected by its complex equipment, high cost, large volume, and low radiation intensity. linear accelerator

The main body of a linear accelerator is an accelerating tube composed of a series of cavities, with holes at both ends of the cavity that allow electrons to pass through and enter from one cavity to the next.

Linear accelerators use radio frequency (RF) electromagnetic fields to accelerate electrons, and use magnetrons to generate self-excited oscillations and emit microwaves. The microwaves are input into the accelerator tube through a waveguide.

The cavity of the accelerating tube is designed as a resonant cavity, where electrons emitted by the electron gun are injected into the cavity at the appropriate time. Electrons passing through the resonant cavity reach a certain acceleration point in the magnetic field at the appropriate time and are accelerated, thereby increasing energy. The accelerated electrons exit the previous cavity and continue to accelerate into the next cavity until they obtain high energy.


The speed of electrons reaching the target can reach 99% of the speed of light, and high-speed electrons collide with the target to produce high-energy X-rays. There are currently two types of linear accelerators used for flaw detection, one using traveling wave acceleration and the other using standing wave acceleration.

Compared with the electron cyclotron, the linear accelerator has a slightly larger focus, but its size is small, the electron beam is large, and the X-ray intensity generated is large, so it is more suitable for industrial radiography.