Study of radiation damage in silicon detectors for high ... - F9

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38 3. Irradiation FacilityHP 4263BLCR meterWENTZELHV power supply-KEITHLEY 617as µ A-meterR=4.7kΩC=100nFcca. 10mBPPADGRFigure 3.3: Schematic view of the measurement setup at the irradiation site. BP, TOP andGR are connections to sample back plane, pad and guard ring, respectively.supply, computer controlled via a DAC converter, a KEITHLEY 617 source-measure unitused as a precise ampermeter and a HP4263B LCR-meter (gure 3.3). Decoupling capacitorswere used to shield LCR meter from the high bias voltage. Four dierent frequenciesof measuring voltage (100 Hz, 1 kHz, 10 kHz and 100 kHz) were used in C/V measurements.The sample temperature during and after the irradiation was measured by aPT100 sensor. The measurement method used in this work is discussed in more detail insection 3.5.A careful study of the activation had to be performed on all materials used in thehighly radiative environment close to the reactor core. The selection was mostly reducedto pure aluminium and a certain type of plastic (Novilon Oilon, produced by Akripol,Slovenia). After irradiations, few days had to pass before activity of the sample andcooling system decreased suciently to safely remove the sample and transfer it to thelaboratory. The conditions were even harsher in channel F19 due to much higher neutronuxes, leading to higher saturation activities.3.3.3 Neutron Spectrum and DosimetryThe low ux of fast neutrons (up to few times 10 8 n/cm 2 s) at this irradiation site anddesired total uences around 10 14 n/cm 2 demanded for irradiation times of over 100 hours.The long irradiation time prohibited direct use of In foil activation ( 115 In + n ! 115In + n 0 , 115 In ! 115 In + , = 4:4 h) to monitor the fast neutron ux because ofthe short lifetime of the excited state. Thus an indirect way was established consisting
3. Irradiation Facility 39Fission platerRzza)Figure 3.4: Dependence of the fast neutron ux on the distance from the ssion plate. a)Schematical presentation of the setup. b) Comparison of measurements [36] and calculations.of a calibration and an irradiation measurement. During short calibration measurementsan In foil in a Cd shield 18 was placed at the sample position and a Zn foil was putin the middle of the box. After the irradiation, the activation of Zn (thermal neutroncapture, decay time 244 days) was measured and compared to the uence of fast neutronsas determined from the activation of In with a well known activation cross-section. In theirradiation run only the Zn foil was placed at the same position as in the calibration run.By comparison of Zn activations in both runs, the irradiation uence was determined.The error of this method was estimated to be about 15%.Due to the limited size of the ssion plate, the fast neutron ux depends on thedistance from the plate. Dependance on the distance can be determined by geometricalconsiderations (g. 3.4) 19 . The following relation is obtained(z 1 )(z 2 )R2ln(1 + )z= 2 1ln(1 + )R2z 2 2(3.1)where R is the radius of the ssion plate and z the on-axis distance from it (g. 3.4a).Measurements were performed at three dierent distances from the ssion plate: 3.5cm(218Cd shield was used to reduce In activation due to thermal neutrons.19From the collision probability P 1 = 4rwhere is a reaction cross-section and r distance from2the neutron source one obtains reaction probability as its integral over the surface of the ssion plateP = R dNf:pl: dS P 1dS. From this ux dependence can be determined by (z) = P = R dN 1f:pl: dS 4rdS =2dN 1dSln z2 +R24 z 2:
Page 1: UNIVERSITY OF LJUBLJANAFACULTY OF M
Page 5: Najprej gre moja zahvala delovnima
Page 8 and 9: PovzetekSevalne poskodbe v siliciju
Page 10 and 11: 3.5 Measurement Setup, Methods and
Page 13 and 14: 1IntroductionSilicon detectors play
Page 15 and 16: 1. Introduction 7Figure 1.2: Schema
Page 17 and 18: 1. Introduction 9R(cm)Z(cm)Figure 1
Page 19 and 20: 2Operation and Radiation Damage of
Page 21 and 22: 2. Operation and Radiation Damage o
Page 43 and 44: 3Irradiation Facility3.1 The Reacto
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Page 51 and 52: 3. Irradiation Facility 43Figure 3.
Page 53 and 54: 3. Irradiation Facility 45Figure 3.
Page 55 and 56: 3. Irradiation Facility 47the inuen
Page 57 and 58: 3. Irradiation Facility 49width of
Page 59 and 60: 3. Irradiation Facility 51The full
Page 61 and 62: 3. Irradiation Facility 53percent.
Page 63 and 64: 4Time Development of DefectsIn this
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Page 69 and 70: 4. Time Development ofDefects 61for
Page 71 and 72: 4. Time Development ofDefects 63Fig
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Page 89 and 90: 5Dose Rate Dependence5.1 Motivation
Page 91 and 92: 5. Dose Rate Dependence 83Figure 5.
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6Inuence of Bias VoltageIt was a ge
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6. Inuence of Bias Voltage 91energy
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6. Inuence of Bias Voltage 93Figure
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6. Inuence of Bias Voltage 99that t
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6. Inuence of Bias Voltage 101(abou
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6. Inuence of Bias Voltage 103Figur
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7Comparison with Other GroupsWhile
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7. Comparison with Other Groups 107
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8ConclusionsA systematic study of r
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8. Conclusions 111Implications for
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9Povzetek doktorskega dela9.1 UvodS
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9. Povzetek doktorskega dela 115Ski
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9. Povzetek doktorskega dela 117sre
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9. Povzetek doktorskega dela 1199.2
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9. Povzetek doktorskega dela 121Sli
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9. Povzetek doktorskega dela 123Ce
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9. Povzetek doktorskega dela 127Cep
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9. Povzetek doktorskega dela 129Mer
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9. Povzetek doktorskega dela 131Sam
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9. Povzetek doktorskega dela 1379.6
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10Appendix: List of Symbols and Abb
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10. Appendix: List of Symbols and A
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References[1] J. Straver et al., Nu
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[27] A.M. Ougang et al.: Dierential
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[57] M. Huhtinen et al, HU-SEFT-R-1
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