ATOMIC AND NUCLEAR PHYSICS ATOMIC AND NUCLEAR PHYSICS Scintillation detector for 518000 This detector is the ideal companion for the 518000 multichannel analyser. It is powered directly by the MCA unit. The caesium iodide scintillation crystal used measures 6 x 6 x 15 mm, which provides an exceptional angular resolution, e.g. for Compton scattering experiments. This crystal size will obviously be less sensitive than the huge NaI crystals commonly used with photomultiplier tubes, but with our standard gamma source from Risø Educational Sources, a total count rate of 1,800 per second can still be achieved. Energy resolution (full width at half maximum) is approx. 7% at 662 keV (Cs-137) and 5% at 1333 keV (Co-60). The detector's bias voltage is software-controlled (through the MCA) in order to keep the gain independent of temperature. Item no. 518500 Compton scattering, kit The Compton effect illustrates the particle nature of gamma radiation. When a gamma quantum bounces off an electron, its energy loss depends on the scattering angle. This kit comprises two pairs of shell-shaped targets and a central holder with adjustment screws and lead absorber. These rotationally symmetrical aluminium targets give a high count rate for the two fixed scattering angles of approx. 60° and 90°. With our gamma spectrometer and a standard Cs-137 source, viable difference spectra for both angles can be obtained within an hour. A lead absorber blocks the direct radiation from the source to the detector. Correction for background radiation (including scattered radiation from the table top etc.) is handled by the 518000 software. The principle behind this device is the old geometric truth that the size of a peripheral angle is defined by the arc it spans. We can thus obtain the same scattering angle over a very large solid angle. In addition to the Cs-137 Risø source (item no. 510030), the following are required: 514102 Rail for mounting bench 294610 Saddle with Ø 10 mm hole (2 of) 514180 Source holder for mounting bench, simple 518500 Scintillation detector 518000 Multichannel analyser Item no. 519000 155 155
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