Key words: extrinsic optical fiber sensor, X-ray detector, X-ray radioluminescence

Transcription

1 Title: Evlution of n extrinsic X-ry opticl fier sensor Key words: extrinsic opticl fier sensor, X-ry detector, X-ry rdioluminescence Technique: Visile emission spectroscopy Appliction: chrcteriztion of X-ry detector operting prmeters 1. Introduction Opticl fiers nd opticl fier sensors were investigted quite extensively in reltion to the possile use in rdition monitoring nd dosimetry. Vrious opticl fier intrinsic nd extrinsic dosimeters sed on rdition induced ttenution, rdition induced rdio-luminescence, thermo-luminescence, Cerenkov rdition, or opticlly stimulted luminescence were proposed [1]. One novel extrinsic opticl fier dosimeter, pproch pioneered y tem t University of Limerick, ws uilt y encpsulting the end of PMMA opticl fier, to which the outer jcket ws removed, into tip of scintillting mteril. This end of the opticl fier constitutes the detector hed nd is exposed to X-ry rdition (Fig. 1). The other end of the opticl fier is coupled either to the QE65000 Ocen Optics spectrometer or to the Hmmtsu C U Multi-Pixel Photon Counter. When exposed to ionizing rdition the sensor tip emits visile rdition ecuse of the fluorescence effect. Prt of the opticl rdition, hving wvelength dependent on the type of phosphor used to prepre the tip, is coupled to the core of the plstic opticl fier nd guided towrds the detecting unit (mini spectrometer/ MPPC) [2]. In some cses the emitted opticl spectrum hs severl emission nds (Fig. 2). Such sensor is of interest to e used for in-situ, in vivo rdition dosimetry during ptient rdiologic tretment. The mjor dvntge of this type of rdition sensor is its low cost. Fig. 1. The picture of the tip for two of the sensors (); Cu wires were wrpped on the tips to identify different zones when X-ry fluorescence is used. The tomogrphic view of one sensor tip (). The chllenge of our investigtion ws to evlute the response of these sensors (for different phosphor mterils nd technologies used) under X-ry exposure nd to chrcterize them. The investigtions were complex involving X-ry

2 rdioluminescence, X-ry fluorescence nd X-ry tomogrphy. In this Appliction Note we shll refer only to those tests where the Ocen Optics QE65000 cted s detecting system. Fig. 2. The spectr detected y QE65000 when different scintillting mterils were used to fricte the sensors tips, s the detector ws exposed to X-rys generted for the source voltge of 45 kv nd the driving current of 850 μa. 2. Experiment nd results Depending on the technology employed in the preprtion nd fixing of scintillting tip X-ry tomogrphy highlighted some non-uniformities concerning the distriution of the phosphor in the glue mteril (Fig. 1) [3]. The first step of our reserch tried to ssocite these non-uniformities with the locliztion of the phosphor grins in the tip volume. For this purpose, the tip of ech sensor ws scnned long its xis nd the X-ry induced rdioluminescence ws recorded. The X-ry excittion ws done with 2 mm spot produced y miniture AMPTEK Inc. X-ry tue system, operting with n Ag trget, while the X-ry fluorescence ws detected y AMPTEK Inc. Silicon Drift Detector [4]. The rdioluminescence signl produced during the X-ry exposure, coupled in the plstic opticl fier ws recorded y the QE65000 spectrometer. Cu wires were plced long the sensor tip to identify different zones during X-ry fluorescence investigtions. For our investigtions the mplitude of the pek emitted y the opticl signl ws monitored s the X-ry em scnned the sensor tip. In order to hve 3D mesurement fter full scn of the tip this ws rotted y 90 O for nother longitudinl scn. In this wy we mpped the genertion nd coupling of the opticl rdition in the opticl fier (Fig. 3).

3 Fig. 3. The 3 D mp of the opticl rdition coupled to the plstic fier core [4]. By using the sme scnning nd detection technique we evluted the effect of two reflecting mterils on the coupling efficiency of the rdioluminescent signl towrds the spectrometer (Fig. 4).

4 Fig. 4. The effect of the externl reflector on the efficiency of generted opticl signl coupling to the opticl fier core: () sensor without reflector; () the sme sensor with n Al foil reflector [4]. The detection of the rdioluminescence signl ws lso used to estimte the dosimeter response s function of the X-ry source high voltge or current. In this sitution, the opticl signl recorded y the spectrometer ws correlted with the operting prmeters of the X-ry emitter (Fig. 5). The sensitivity nd the linerity of the sensor response were evluted. Fig. 5. The responsivity of sensors t λ = 542 nm, s function of the X-ry source driving current, for the driving voltge V = 40 kvp (); the responsivity of sensors t λ = 542 nm, s function of the X-ry source driving voltge, for the driving current I = 80 μa (). 1-4 designte sensors sed on different technologies or scintillting mterils. 3. Conclusions

5 The visile emission spectroscopy proved to e vlule tool in the evlution of severl chrcteristics of new type of extrinsic opticl fier dosimeter: the dependence of sensor response on the driving condition of the X-ry source; the effect of different reflector mterils pplied to the sensor tip; the coupling efficiency of the rdioluminescence signl to the core of the connecting plstic opticl fier. These results mke possile the optimiztion of the sensor design nd its clirtion for specific operting conditions. By comining spectrl mesurements with X-ry fluorescence investigtions, the contriution of different scintillting mterils to the generted opticl signl cn e estimted. The extreme sensitivity of the QE65000 spectrometer mde possile the detection of very wek signls ssocited with the rdioluminescence emission. Acknowledgments This work ws finncilly supported y the contrct Sensor Systems for Secure Opertion of Criticl Instlltions, Grnt 8/2012 of the Romnin Executive Agency for Higher Eduction, Reserch, Development nd Innovtion Funding (UEFISCDI). The contriution of uthors from University of Limerick ws prt of the ilterl coopertion etween Romni nd Irelnd in the frme of the Europen Union COST Action TD1001 Novel nd Relile Opticl Fire Sensor Systems for Future Security nd Sfety Applictions (OFSeS). The Irish uthors cknowledge the support of the Europen Commission under the 7th Frmework Progrmme through the Mrie Curie Re-integrtion ction of the Peoples Progrmme (PERG ). References 1. Spore, D.; Spore, A.; O Keeffe, S.; McCrthy, D.; Lewis, E. Opticl Fiers nd Opticl Fier Sensors Used in Rdition Monitoring. In Selected Topics on Opticl Fier Technology; Ysin, M., Hrun, S.W., Arof, H., Eds.; InTech: Vienn, Austri, 2012; pp McCrthy, D., O'Keeffe, S., Lewis, E., Spore, D., Spore A. nd Tisenu, I., Rdition dosimeter using n extrinsic fire optic sensor, IEEE Sensors Journl, Vol. 14, Issue 3, 2013, pp , doi: /JSEN Spore, D., Mihi, L., Tisenu, I., Vât, I., McCrthy, D., O'Keeffe, S., nd Lewis, E., Multidisciplinry evlution of X-ry opticl fier sensors, Sensors nd Actutors A: Physicl, Vol. 213, 2014, pp , doi: /j.sn Spore, D., Mihi, L., Vât, I., McCrthy, D., O'Keeffe, S. nd Lewis, E., Chrcteriztion of Scintillting X-ry Opticl Fier Sensors, Sensors, Vol. 14, No. 2, 2014, pp ; doi: /s