Interaction mechanisms

1. Mechanisms for gamma rays
   1. Photoelectric effect
   2. Compton scattering
   3. Pair production
2. Mechanisms for alphas
   1. Low-energy alpha particles - cannot enter nucleus due to electrostatic repulsion
   2. Alpha particle interacts strongly with electrons, gives off energy quickly
   3. Range very short
3. Mechanisms for betas
   1. Betas are either positive or negative electrons - low energy: do not enter nucleus
   2. Interact with other electrons
   3. Elastic collisions between equal masses produce greater range
4. Mechanism for neutrons
   1. Neutrons only interact with nuclei
   2. Nuclei very small
   3. Collision probability (cross section) very small
   4. Range of neutrons very long
   5. Nuclear collisions dangerous
      1. May change nucleus to new type
      2. May create radioactive nucleus
      3. Only neutrons cause radioactivity

Half-intensity thickness

1. Half-intensity thickness
   1. Interaction with material where dN proportional to N
   2. Result is exponential absorption, similar to half-life
2. Energy deposited
   1. Gamma
   2. Beta
   3. Alpha
   4. Protons
   5. Neutrons
3. DEMO P4-01: GEIGER COUNTER
   1. Typical nuclear alpha, beta, and gamma properties
   2. Alpha stops in sheet of paper
   3. Beta stops in 2mm aluminum sheet
   4. Gamma requires two-inch lead brick

Radiation Detector Applications

1. Types of radiation detectors
   1. Cloud chamber
   2. Geiger tube
   3. Scintillator (eg, NaI)
   4. Film (eg, film badge)
   5. Solid state silicon or germanium detectors
2. Demonstrations of radiation counters
   1. DEMO P4-01: GEIGER COUNTER
   2. DEMO P4-31: CLOUD CHAMBER – INDIVIDUAL VIEWNG
   3. DEMO P4-33: BUBBLE CHAMBER TRACKS: 3 DIMENSIONAL VIEWMASTER

Radiation exposure to people

1. Sources of exposure
   1. Article: Radioactivity in Nature
   2. Radiation exposure pie graph
   3. Natural exposure
      1. Total dose of about 360 millirem (3600 microsieverts)
      2. Over half (~200 millirem or 2600 microsieverts) from radon and its progeny
      3. Other sources are discussed in the article above
   4. Man-made exposure
      1. Primarily medical and dental diagnostic x-rays
      2. Also nuclear medicine treatment, if any
      3. Nuclear weapons testing, nuclear power very small
2. Biological effects of radiation exposure
   1. Effects of radiation exposure

      Source	Exposure (rems)
      Average yearly dose	0.4
      Suggested maximum additional	0.2
      Maximum for radiation worker	5.0
      Minimum for any observed problems	50.0
      Possible blood changes, no disability	100.0
      Injury with possible disability	200.0
      Injury and disability, possible death	400.0
      Fatal to 50% within 30 days	450.0
      Fatal to 100% within 30 days	800.0

   2. Sensitivity of human organs
      1. Most sensitive: lymphatic cells, blood, gastro-intestinal, reproductive, growing fetus
      2. Least sensitive: muscle, bone

Useful applications of radiation