lecture_3_F11 - Physics 433 Lecture 3 In this weeks lab...

Info iconThis preview shows pages 1–5. Sign up to view the full content.

View Full Document Right Arrow Icon
October 13, 2011 Henry Lubatti Physics 433 – Lecture 3 In this week’s lab (Time Measurements and Counting) you will observe the output PM output when a 22 Na source is directed on a plastic scintillator connected to a Photomultiplier (PM) This lab give’s you an opportunity to understand how a scintillating detector is prepared, connected optically to the phototube and used to detect signals Beginning with a plastic scintillator we will mount it on a phototube-see lab instructions for details Next you will apply high voltage to the tube Establish that there are no light leaks You are now ready to observe signals from a 22 Na source, which emits two back-to-back rays – use external trigger on scope Discriminate and scale/count the emissions per fixed time Observe the pulse height spectrum of the emitted ray using the pulse height analyzer available in the lab - print out the spectrum for insertion into your lab report Set up a second PM and observe coincidences between the pulses
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
October 13, 2011 Henry Lubatti Physics 433 - Lecture 3 Detecting gamma rays Gamma rays ( ) are photons, the quanta of electromagnetic radiation, that have energies of KeV or greater In this laboratory the gamma rays we will use come from the decay of radioactive nuclei that emit gamma rays as they undergo transitions from a higher to a lower energy state Gamma rays have no charge consequently do not directly excite scintillating atoms or molecules – need charged particles such as electrons Fortunately gamma rays interact with matter to produce charged particles which then excite the scintillating material that in turn emits light that can be funneled to the photomultiplier tube Measuring the energy of gamma rays therefore requires transferring their energy to charged particles
Background image of page 2
October 13, 2011 Henry Lubatti Physics 433 - Lecture 3 Basic interactions of gamma rays with mater Photoelectric absorption In this case the photon interacts with an atom, completely disappears, and a photoelectron is ejected from one of the atoms shells The ejected photoelectron has energy E e = h –E b , where E b is the binding energy of the photoelectron in its atomic state before the interaction that leaves the atom in an ionized state The atom then captures a free electron and/or undergoes a rearrangement of electrons from other atomic states In general one or more x-rays are emitted in this process The photoelectric effect is the predominant energy interaction mechanism for gamma rays of energies less than a few MeV The photoelectron has essentially the entire energy of the gamma ray, the scintillation light emitted because of the interactions of the electron provides a good estimate of the total energy of the of the gamma ray – it results in the “photopeak” that is observed from scintillating detectors
Background image of page 3

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
October 13, 2011 Henry Lubatti Physics 433 - Lecture 3 Compton scattering
Background image of page 4
Image of page 5
This is the end of the preview. Sign up to access the rest of the document.

Page1 / 20

lecture_3_F11 - Physics 433 Lecture 3 In this weeks lab...

This preview shows document pages 1 - 5. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online