PSI - Issue 26

George Saatsakis et al. / Procedia Structural Integrity 26 (2020) 3–10 Saatsakis et al. / Structural Integrity Procedia 00 (2019) 000 – 000

7

5

Table 2. X-ray Tube output measurements with the Piranha (RTI) dosimeter. kVp nominal kVp measured msec mGy mGy/sec HVL

Total filtration (mm)

50 60 70 80 90

49.59 60.59 69.92 80.68 91.68

999.2 999.2 999.2 999.2 999.7 999.2 999.2 999.2 999.7

0.03586 0.1146 0.2481 0.4522 0.7323

0.03583 0.1144 0.2478 0.4514 0.7314

4.41 5.58 6.65 7.53 8.36 9.05 9.68 10.3 10.4

23 22 24 22 22 23 23 24 24

100 110 120 130

101.64

1.086 1.512 2.016 2.275

1.083 1.507 2.011 2.269

111.9

122.98 126.02

25

20

LE = 31.545e-0.016 o C R² = 0.9918

15

10

5

Luminescence Efficiency (E.U.)

0

0

20

40

60

80

100

120

140

Temperature ( o C)

Fig. 2. Absolute luminescence efficiency of the heated CaF 2 :Eu single crystal (90 kVp).

This is important, especially in applications requiring crystals of large dimensions. The luminescence efficiency was found maximum at the lowest examined temperature (22.01 efficiency units- E.U. at 22 °C -environmental). With increasing temperature, the luminescence efficiency decreased almost exponentially due to thermal quenching (4.43 efficiency units- E.U. at 128 °C). These results are indicative of the performance of the crystals in applications in harsh environments, such as in space exploration. For example, spacecraft which approach the Sun should be extremely resource limited in both mass and power since they will face harsh environments (radiation levels and increased temperature) regarding the onboard instrumentation. In this case, detectors that need little or no cooling, lasting on high radiation fluxes, will be able to succeed in the mission goals. 4. Conclusion In this research, an initial investigation of the effect of temperature on the luminescence efficiency properties of Calcium Fluoride (Eu) single crystal scintillators, for applications in harsh environments, was performed. From the measured luminescence efficiency values, a decrease of the order of almost 80% was observed when the crystal surface was heated to the maximum temperature value of this experiment. Thus, it is crucial to use crystals showing