γ-ray Level Radiometric Measurement System

1. Introduction to equipment technology

The γ-ray  Level Radiometric Measurement System is composed of three parts: a radiation source, a detector, and a secondary display instrument. The radioactive source and the detector are respectively installed at opposite positions on the outer wall of the container to be tested, and the secondary meter can be installed on site or in the main control room according to specific requirements. After the γ-ray emitted by the radioactive source passes through the container wall, it is partially or completely shielded by the measured medium in the container. The scintillation detector installed on the other side of the container receives more, less, or presence or absence of ray pulses than the inside of the container. Measure the low, high or empty or full of the material level of the medium. After the pulse signal is processed by the detector and the host, the low, high, empty, or full signal representing the medium level in the measured container is input to the customer's PLC or DCS in data or analog mode for display or tracking control.

2. Schematic diagram of the system scheme

2.1 Schematic diagram of material level detection system

(1)Level switch detection

(2)Schematic diagram of continuous level detection

3. System composition description

The material level detection system is mainly composed of radioactive source parts, detectors, transmitter and communication cables.

3.1. Radioactive source part

3.1.1 Introduction to radioactive sources

The radioactive source part consists of a radioactive source and a ray output device.

Radioactive level gauge and density meter can choose Cs-137γ or Co-60 radioactive source according to the characteristics of the equipment under test. Co-60 radioactive source has high energy, strong penetrating power, but short half-life. It is generally used for continuous level and level switch detection of equipment with large diameter and thick container wall. The penetration power of Cs-137 radioactive source is relatively weak, but the half-life is longer. It is generally used for continuous level, level switch and density detection of equipment with smaller diameter and thinner wall thickness.

The external form of the radioactive source is a stainless steel cylinder, and the size is generally φ6×10, φ8×10, etc. It has been directly loaded into the storage container or ray output device by a dedicated person in a specific environment when it leaves the factory. The ray output device generally uses lead or depleted uranium as the protective layer, and uses carbon steel or stainless steel as the lining and shell. The shape is divided into two types: horizontal and vertical. One side of the output device is provided with a certain angle hole or collimation hole according to different measurement requirements, so that the ray beam can be emitted according to a certain angle or straight line. The ray output hole is designed with switches and locks, and the key is kept by a dedicated person. Usually the ray switch is closed and locked, and can only be opened by a special person in charge when it is in use. The output device is installed on the mounting bracket on the side of the tested container. The mounting bracket is generally welded to a certain position in advance when the tested container is manufactured. If the equipment does not have welding conditions, it can also be directly built from the ground or on the construction platform. Build a stand, and then fix the source on the built-up stand.

When selecting a radioactive source, first determine how large and what kind of radioactive source to use according to the diameter, wall thickness, and thickness of the insulation layer or water-cooled jacket of the tested equipment, and then according to the range, the diameter of the tested equipment, etc. The parameters determine the number of radioactive sources used and the opening angle of the ray output device. The measurement of the material level switch generally opens a collimating hole, and the continuous material level measurement opens a certain angle fan-shaped hole according to the detection requirement.

3.1.2、Some technical indicators of radioactive sources



Technical index






Radioactive source activity

Calculate according to the specific parameters of the device under test


Radioactive source half-life

Co-60:5.3 years

Cs-137:31 years

Ray exporter

Surface dose rate:≤25μsv/h

Comply with relevant national standards


Shielding materia

Lead or depleted uranium

Use depleted uranium protection when the source activity is large

3.2, Detector

3.2.1 Introduction to the detector part

The detector consists of a ray pulse counter, a photomultiplier tube, a signal processing circuit and a high-voltage power supply module.

The isotope detection instrument produced by our company uses a scintillation crystal counter. The specific working principle is as follows:

When the ray particles irradiate the scintillation crystal, the scintillation crystal emits a certain number of photons. The photons hit the photocathode of the photomultiplier tube to produce a photoelectric effect and release electrons. The electrons are amplified by the photomultiplier tube to form an electric pulse and After amplifying and shaping, the amplified electrons are collected by the anode as a signal output. The number of electrons generated by the photocathode is proportional to the number of photons irradiated on it, that is, the more gamma rays the detector receives, the more photons are generated on the scintillator, and the more pulses the instrument records. The number of pulses characterizes the state of the material in the container under test, and is converted by the host into the current or voltage signal required by the DCS system.

Our company mainly chooses PVT (plastic scintillator) or NaI scintillation crystal as the counter. PVT (plastic scintillator) is mainly used for continuous level measurement, and the maximum effective detection range of a single probe can reach 3 meters; NaI crystal detector is mainly used for level switch measurement and density measurement, and it can also be made according to site requirements Continuous material level gauge with smaller measuring range. The photomultiplier tube is made of Hamamatsu, Japan, which has the characteristics of strong light sensitivity, high photoelectric conversion efficiency, good anti-interference performance, and long service life.

Compared with similar products, the signal receiving efficiency of the crystal counter detector is 10%-30% higher than that of other types of detectors, and the service life of the crystal is 2 to 3 times that of other types of detector crystals. With this type of detector, the performance is more stable, the quality is more reliable, and the accuracy is higher. It can meet the needs of customers for various measurement ranges (using a single crystal to meet continuous level measurement in the range of 0 to 3 meters), and the activity of using radioactive sources under the same measurement conditions is small, which more effectively guarantees the equipment The normal use and personal safety of operators.


3.2.2 Technical indicators of the detector



Technical index




NaI  detector

Level switch

PVT scintillator detector

Continuous level measurement


Detection accuracy


Level measurement accuracy


Shell material

304 stainless steel

Can be used for anti-corrosion and acid-proof treatment in special occasions


power supply

+15V D


Explosion-proof grade



Protection level


Signal transmission capacity


Operating temperature


Optional heating or water cooling


10Storage temperature-40~+70℃

Working humidity


Relative humidity

3.3、Transmitter (secondary instrument)

3.3.1  Introduction to transmitter function

The transmitter is the latest development of our company for the *** series of isotope detection instruments, adopts a modular design, the key modules and data chips are imported industrial-grade products. The CPU frequency is up to 400MHz, with embedded operating system, powerful data processing function; industrial-grade color LCD screen, graphical display, rich information. The system has stable performance, simple operation and good maintainability.

On the one hand, the transmitter computer processes the pulse signal sent by the detector through the relevant algorithm, and converts it into information corresponding to the material status, such as the presence or absence of the material level, high and low, etc. The information is displayed on the color LCD screen in digital and graphical manner. Finally, the low, high, empty, or full signals representing the medium level in the measured container are input to the customer's PLC or DCS in data or analog mode for display or tracking control.

The transmitter software has powerful functions, simple operation and stable work. The algorithm combines the latest nuclear technology application theory and years of practical experience in nuclear instrument engineering, and the reliability and accuracy of the measurement have reached a high level.

       3.3.2 Technical indicators of transmitter






Signal output type

Switch output

Load Resistance MAX:500Ω


Transmitter protection level



Transmitteroperating temperature


No condensation

Transmitterstorage temperature

-40~+70℃No condensation

Working power requirements



Host working power consumption

About 15VA(AC)

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