Development of fibre based radioluminescence-probes with europium doped Yttriumoxide (Y2O3:Eu)

F KATTNER; T TEICHMANN; P MOLINA; M SOMMER; J HENNIGER

Halle

Congreso; 8th International Conference on Luminescent Detectors and Transformers of Ionizing Radiation - LUMDETR 2012; 2012

Centre for Innovation Competence SiLi-nano

In medicine and the dismantling of nuclear facilities, dosimetry has to face two challenges. The possibility of measuring high dose rates without influencing the electronics and to get into complex geometries with limited access. These tasks can be complied by fibre-based dosimetry. Small sensitive detector dimensions and a spatial separation of the sensor and the electronic evaluation unit are achievable. Spontaneous emission of light caused by irradiation, Radioluminescence (RL), is used to detect radiation fields. In the presentation europium doped Yttriumoxide (Y2O3:Eu) probes are introduced. One problem of fibre-based RL-dosimetry is, that when irradiated the fibre emits light itself. The signal of the phosphor is impaired by CHERENKOV and luminescence light inside the fibre (stem effect) and leads to an interference, mainly in the blue/UV region depending on the length of fibre inside the radiation field. Therefore a good discrimination for a proper signal-to-noise ratio is desired. A solution are probes of Y2O3:Eu, because of its emission line in the orange spectrum (around 612 nm). Besides, this material is already used in cathodoluminescence applications and therefore a well known phosphor [1]. The advantage of the irradiated Y2O3:Eu is its narrow emission spectrum. The excited Eu3+ ions inside the doped material cause a 5D0 - 7F0 transition known as materials like YVO4:Eu and Y2O2S:Eu. The emitted fluorescent light can be detected and well selected from the stem effect by suitable bandpass filtering. This simple method minimises and discriminates the stem effect in an easy way. Besides the appropriate emission line, Y2O3:Eu shows a short after-glow behaviour decay within microseconds [2]. This physical property distinguishes the material from others already established. Because of their properties, PMMA and High-OH silica fibre were taken into account for the light transfer. The transmission characteristics in the visible spectrum are excellent for High-OH silica which are therefore preferred. Even with long lightguides, low signals of the phosphor can be measured. One of the main achievements in the presented work is the connection of the powdery luminescent material with the silica fibre for a high signal level and therefore a lower detection limit. Polymers like Epoxy, Paraffin and PMMA were mixed with Y2O3:Eu and afterwards attached to the lightguide. The luminescent material is covered from humidity and the measuring head is characterised by mechanical and thermal stability. Finally, the units were combined in one portable reliable construction. The comparison of the three polymers, the different fibre and the covering of the material from outside are part of the presentation. [1] T. Igarashi, J.Appl.Phys. Letters Vol. 76, Nr. 12 (2000) [2] D.R. Tallant, J.Appl.Phys. Letters Vol. 91. Nr. 7 (2002)