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

42 3. Irradiation FacilityPt100 sensorCooling liquid outletCooling liquid inletDiodeAluminaCooling cylinderKaptonBias/Pt100 connectorFigure 3.7: Schematic view of the cooling cylinder for sample cooling in the F19 irradiationchannel. A sample mounted on Al 2 O 3 ceramics and a Pt100 temperature sensor is displayedtogether with the connector for bias/measurement lines.be obtained in pulsed mode. To pulse the reactor one of the control rods is pneumaticallyred to a preset upper position, driving the reactor highly over-critical. This results ina fast increase of the neutron ux and heating of the reactor core. Temperature raisehowever causes an increase of neutron absorption in 238 U and hardens the thermal partof the spectrum thus decreasing the reaction rate in 235 U. Thus the pulse is stopped andthe reactor is shut down. In the pulsed mode a total uence of about 10 14 n/cm 2 can beobtained in around 20 ms (approximate pulse width).3.4.2 Neutron Spectrum and DosimetryThe neutron spectrum in the irradiation channel F19 (g. 3.8) was determined by simulation[38] and measurement [36].The simulated spectrum was obtained using the MCNP4B Monte Carlo simulationcode [39]. Since the reliability of the results depend crucially on the source description,a detailed description of the real TRIGA geometry [40] was used in the simulation. Itincluded the exact conguration of all 91 locations in the core and a detailed descriptionof fuel elements as well as control rods. It was tested with experimental results of a criticalexperiment [41]. Very good agreement with experimental results conrms the reliabilityof the model developed.