**7. Radiophotoluminescent dosimeters (RPLDs)**

The physical phenomenon of photoluminescence is the basis for the detection of ionizing radiation with radiophotoluminescent dosimeters. Radiophotoluminescence as a phenomenon shows that some materials, after irradiation with sources of ionizing radiation, begin to luminesce under illumination with ultraviolet (UV) light and the luminescent light is proportional to the dose they were irradiated [21] (See **Figures 3** and **4**).

This effect was used to create radiophotoluminescent (RFL) dosimeters, which are alumina-phosphate glasses, activated with silver and synthesized by a special technology that used the effect of photoluminescence.

In 1949, the RPL phenomenon was first discovered and applied for measuring the dose in the event of a radiation accident. The magnitude of the radiation dose ranged from 0.1 to 1 Gy [22]. At that time, there were still some problems with glass surface contamination and measuring the RPL signal became a technical challenge. Later, the ability to register ionizing radiation was drastically improved by changing the chemical composition of the glass used. Thus, the measurement range is from 0.1 mGy to 10 Gy [23].

Radiophotoluminescent dosimeters are an accumulative type of dosimeter. They work on the principle of the phenomenon of radiophotoluminescence, which is

#### **Figure 3.**

*Schematic representation of the RPL process in phosphate glass doped with silver Ag+ ions [21].*

#### **Figure 4.**

*The amount of luminescent light is proportional to the radiation dose [21].*

observed in some solids. RPLDs are made of silver-activated phosphate glass and are shaped like small glass rods (See **Figure 5**).

The glass rods are 12 mm long and 1.5 mm in diameter. Each glass rod has an identification number engraved on one end. The sensitive area of the dosimeter is 6 mm long. When irradiated with ionizing radiation, stable luminescent centers are formed in the silver ions - positive and negative. The measurement of the absorbed dose is performed by optical excitation of the dosimeter with a laser emitting ultraviolet light [21]. The first RPLD was produced in 1949 [22]. Significant technological improvements have been made over time, including the accuracy and reliability of their measurement [23]. They are currently one of the best solid state dosimeters [21].

**Figure 5.** *General type of radiophotoluminescent dosimeters (RPLDs) – glass rods.*

#### *Dosimetry Audit in Modern Radiotherapy DOI: http://dx.doi.org/10.5772/intechopen.100941*

Today, the production of RPL dosimetry is advancing remarkably thanks to modern electronics and is well accepted as a solid-state, passive dosimeter operating in the range of 10μGy to 10 Gy, using a pulsed laser beam of UV light. Radiophotoluminescence dosimeters (RPLD) as a new type of solid state dosimeters are used in radiation dosimetry for radiotherapy in the last two decades.
