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

3. Irradiation Facility 45Figure 3.9: Flux of fast neutrons (E > 0.1 MeV) divided by reactor power versus the reactorpower. The constant value of this ratio conrms the validity of the assumption that the neutronux scales linearly with the reactor power. The scattering of measurements (RMS=3%) is withinthe error of the ux measurements.after April 1998 are less reliable since the reactor core was going through a set of changesthat mayhave aected the spectrum. For that reason a new measurement of the spectrumis planned after the new core conguration is set.The homogeneity of the neutron eld was determined by a separate measurement[43]. At the irradiation spot F19, the radial gradient was measured to be about 4%/cmand the vertical gradient about 1%/cm. Since the dosimetry foil was attached to the wallof the cylinder with rotational freedom, it induced an additional error of about 5% to theuence measurement 22 .As already mentioned irradiations at the F19 channel were performed at dierentreactor powers, thus varying the neutron ux. It is expected that the neutron ux scaleslinearly with power. As can be seen in gure 3.9, measurements agree well with thisexpectation with 7:5 10 9 n/kWcm 2 s of fast neutrons (6:8 10 9 n/kWcm 2 s of 1 MeVneutron equivalent).22The radius of the irradiation cylinder was 1.3 cm.