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Michigan State UniversityPHY 431 Optics at MSU

Nuclear Physics

About the experiment

Poisson Statistics

Distributions in numbers of counts for random events at fixed mean counts of approximately 1, 10, and 100 are measured with a scintillation counter exposed to a weak source of gamma rays. The results can be compared to the theoretical Poisson distributions for the measuredmeans, and with the results of Monte Carlo simulations of Poisson distributions based on the use of a random number generator on a PC.

Gamma Ray Spectroscopy

Gamma rays are MeV photons. They are typically emitted in the  electronic transitions radioactive nuclei, and carry information on nuclear binding and energy levels. They are recently of increased astrophysical interest, as "gamma-ray bursters" seem to be telling us something about the mechanics of stellar collapse. In this experiment, you will establish the function of a NaI crystal + photomultiplier system to detect gamma-rays, and use the system to study some interesting nuceli. Co-60, used for medical radiation treatment, is a standard gamma ray reference source. Na-22 undergoes beta decay to positrons, and you can see the gammas rays that result when they annihilate with electrons. The  gamma ray energy spectra also contain information about how gamma rays interact with matter.

Muon Lifetime

The muon is a heavy unstable version of the electron, with mass mm= 105.6 MeV/c2 and lifetime tm ~ 2.1 msec. The decay m g e ne nm, or "muon beta decay"  is one of the simplest manifestations of the weak interaction. Particle production from the rain of cosmic rays on the upper atmosphere creates a muon flux of approx. 100/m2-s at sea level.

Several cosmic ray muons are stopped each minute in a large volume of scintillator. By studying the spectrum of time delays between muon entry into the scintillator and muon decay, the mean lifetime can be measured.

In this experiment we use a photomultiplier in a tank of liquid scintillator to detect cosmic ray muons, and to time the delay between stoppage of a cosmic ray muon and appearance of its decay electron. The distribution of muon lifetimes has an exponential form characteristic of radioactive decay; the lifetime is extracted and compared to expectations for the universal weak interaction.

Victor Hess discovered cosmic rays in 1912, and Carl Anderson discovered the muon in 1936 while studying cosmic rays. Anderson and Hess received the 1936 Nobel Prize in Physics.

What you will learn

Gamma Ray Spectroscopy

  • Detection and measurement of gamma rays
  • NaI crystal photomultiplier, NIM electronics, computer controlled ADC and histogramming with the Amptek "Pocket MCA"
  • Interactions of photons with matter: Compton effect, photoelectric effect
  • Mass of the electron via photon energy when electron annihilates with positron

Muon Lifetime

  • Cosmic Rays
  • Muons and the Weak Interaction
  • Scintillators, photomultipliers, NIM electronics for fast timing measurments, computer controlled ADC and histogramming with the Amptek "Pocket MCA"

Preparation

Poisson Statistics

Gamma Ray Spectroscopy

Required reading:

Recommended reading: 

    • Detecting Nuclear Radiation
    • G. Gilmore and J. Hemingway, Practical Gamma-ray Spectrometry (A great book crammed with useful information.)
    • W.R. Leo, Techniques for Nuclear and Particle Physics Experiments
    • G.F. Knoll, Radiation Detection and Measurement, Chapter

Muon Lifetime

If you are completely unfamiliar with the tools of scintillator detection, you may want to do the Gamma-Ray Spectroscopy experiment before trying Muon Lifetime.

Required reading:

Recommended reading: 

    • http://pdg.lbl.gov/2001/cosmicrayrpp.pdf (Particle Data Book entry on cosmic rays)
    • Fraunfelder and Henly, Subatomic Physics, Chap 11 (Weak Interaction), Chapter 19 (Cosmic Rays)
    • G.F.Knoll, Radiation Detection and Measurement, Chap 2,8,9,16, 17

Supplementary materials

Videos:

  • Gamma Ray Spectroscopy (GMA) [from UC Berkeley]
  • Muon Lifetime (MUO) [from UC Berkeley]

References:

Instruments:

 

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