In many fields such as nuclear energy utilization, medical radiotherapy, industrial non-destructive testing, and scientific research experiments, radiation is ubiquitous. Accurately measuring the radiation dose received by the human body and ensuring personal radiation safety has become a crucial issue. The thermoluminescent dosimeter, as a classic and reliable radiation detection tool, plays a vital role in this regard. This article will take you on a deep dive into thermoluminescent dosimeters, from their core principle of "crystal luminescence" to their key position in personal radiation safety protection systems.
I. Thermoluminescence Phenomenon and Crystal Materials
The working principle of thermoluminescent dosimeters is based on the thermoluminescent properties of certain specific crystalline materials. These crystals, such as lithium fluoride (LiF) and calcium sulfate (CaSO₄), have unique crystal lattice structures. When irradiated by ionizing radiation, the radiation energy causes electrons in the crystal to gain enough energy to break free from the atomic nucleus and jump to the conduction band, forming free electrons. At the same time, holes are left in the valence band. In this process, some electrons are captured by "traps" formed by impurities or defects in the crystal, remaining in a metastable state. At this point, although the crystal has absorbed radiation energy, there is no obvious change in appearance, essentially storing the radiation information in the form of a "latent image."
II. Measurement Process: Heating Excitation, Releasing Light
To read the radiation dose information stored in the crystal, heating is required. When the irradiated crystal is slowly heated, the electrons captured by the "traps" will return to the conduction band due to the sufficient thermal energy. Subsequently, these electrons will recombine with the holes, and during the recombination process, the excess energy is released in the form of photons—this is the thermoluminescence we observe. Furthermore, the intensity of the released light is directly proportional to the radiation dose previously received by the crystal. By measuring this light signal with a highly sensitive photomultiplier tube or other photodetector, and then performing complex calibration and conversion, the corresponding radiation dose value can be obtained. The entire process is like telling the radiation story "remembered" by the crystal using the language of light. III. Advantages in Personal Radiation Safety Applications
1. Wide Measurement Range and High Accuracy: It can cover a wide range of environments, from low-dose rate environments such as background radiation monitoring in ordinary public areas to high-dose scenarios such as radiotherapy rooms. Within its applicable range, it provides highly accurate measurement results with a small margin of error, meeting the needs of different occupational groups, such as nuclear power plant workers and interventional radiology medical personnel, for precise control of personal cumulative dose.
2. Good Tissue Equivalence: Because the commonly used thermoluminescent crystal materials have physical properties similar to human soft tissue, this means that its response to radiation is closer to the actual exposure situation of the human body. Compared with some devices that only measure indirect parameters such as air kerma, it can more accurately reflect the true absorbed dose of the human body, providing a reliable basis for evaluating the potential harm of radiation to human health.
3. Reusability and Long-Term Stability: After appropriate annealing treatment, the thermoluminescent elements can be reused multiple times. After a measurement is completed, the previous "memory" is eliminated through high-temperature annealing, and it can be used again for the next radiation dose monitoring task. At the same time, high-quality crystal materials and mature manufacturing processes ensure that the instrument remains stable even after being stored for a long time, eliminating the need for frequent calibration, reducing operation and maintenance costs, and ensuring the continuity and reliability of continuous monitoring data.
4. Small, Portable, and Suitable for Individual Wear: Modern devices are designed to be compact and lightweight, and can be easily made into card-like forms, allowing personnel to easily wear them on their chests, in their pockets, or other locations. Without affecting normal work activities, it can monitor the radiation level in the surrounding environment in real time. In case of accidental overexposure, it can promptly issue an alarm to remind personnel to evacuate the dangerous area, effectively avoiding unnecessary health damage.
In short, thermoluminescent dosimeters, with their unique principles, play an important role in safeguarding personal radiation safety. Whether for daily occupational protection or emergency monitoring in response to sudden radiation incidents, it silently yet faithfully safeguards the health and rights of everyone exposed to radiation, serving as a vital bridge connecting the microscopic world of radiation with macroscopic safety protection.
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