lecture_4_F11 - Physics 433 Lecture 4 This weeks...

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October 20, 2011 Henry Lubatti Physics 433 – Lecture 4 This week’s laboratory, PMT Energy Measurements, explores measuring the energy of gamma rays ( γ ) energy with a scintillation counter Light output of a scintillating material is approximately proportional to the energy deposited by the particle we are detecting If in addition, the response of the phototube is proportional to the light input we can easily use a scintillation counter to make energy measurements For the first part of this lab a light pulser (source of short duration light pulses) is used to study the response of the phototube as a function of light intensity For the second part you will observe the pulse height spectrum (PHS) of the output of plastic and NaI scintillation counters for several radioactive sources A Multi-channel Analyzer (MCA) is used to record the PHS 1
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October 20, 2011 Henry Lubatti Physics 433 – Lecture 4 Radioactive sources are used in this and subsequent labs Certain nuclei are unstable resulting in Radioactive Decay The three different radiations produced by radioactive decay: Alpha ( ) particles are He nuclei (two protons and two neutrons) » Alpha particles do not travel far in air before being absorbed; used, for example, in smoke detectors » Example Beta decay occurs when an electron (e - ) or positron (e + ) and an antineutrino ( -bar) are spontaneously emitted from the nucleus » Beta particles are much more penetrating than alpha particles, but much less than gamma particles » Example gamma decay ( ) occurs when a nucleus in an excited state drops to a lower energy and emits a -ray of a few hundred KeV » Example with E = 1.17 and 1.32 MeV » Gamma rays are very penetrating; they can be most efficiently absorbed by a relatively high density material The half-life of a radioactive isotope is the time for half of
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lecture_4_F11 - Physics 433 Lecture 4 This weeks...

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