Tag: atomic physics

P7 Atomic and Nuclear Physics

Posted on by a web

Nucleus

Nucleus is composed of protons and neutrons.

Isotopes are multiple forms of the same element containing different numbers of neutrons.

Isotopes can be used to treat cancer, in radiation, etc.

 

Radioactivity

 

  • Background radiation is ionizing radiation at an environment that doesn’t come from deliberately introduced radiation materials. Could be naturally occuring radioactive elements, cosmic radiation and fallout. It is always there and measured.
  • Radioactive emissions occur randomly over space and time as particles decay.
  • Radioactive decay is the process by which an unstable atomic nucleus loses energy and emits radiation to become another element.
  • Half-life is the the time taken for the radioactivity of a specified isotope to fall to half its original value. Equation: n*(½)^t
  • Detecting radioactivity: Geiger-muller tube and ratemeter counts number of pulses per second. Scaler keeps running total of number of counts

 

 

Alpha, beta, gamma rays

 

α particles β particles Y rays
Charge +2 -1 Not charged
Mass 4 amu negligible none
Nature Helium nucleus (2 protons, 2 neutrons) Electron (e-1) Electromagnetic radiation, short wavelength
Stopping it A sheet of paper, or 10 cm of air. Few mm of aluminum Thick lead or concrete
Range in air Within centimeters A meter High
Ionizing ability Very strong Weaker than a, but still ionizing Weak

 

  • Alpha decay equation: AZX → A-4Z-2Y + 42He
  • Beta decay equation: AZX → AZ+1Y + 0-1e(β)
  • Gamma decay is simply loss of energy.   

 

Electric and Magnetic Field effects

Positive attracts negative beta particles and negative attracts positive alpha particles, while gamma rays pass uneffected. The same goes on in magnetic fields.

 

Beta deflects more than alpha because it has a larger mass.

 

Safety

    • Hazards of ionizing radiation:
      • Damagement of living cells causing cancer
      • Affecting DNA and causing mutation

 

  • Minimizing hazards:

 

    • Handling: Using tongs used to pick up sources
    • Protective clothing worn by those who work with radioactivity
    • Storage: Sources are kept in lead-lined containers
    • Usage: Sources are never pointed at people
    • Exposure times are limited

 

P7 Equations

  • Alpha decay equation: AZX → A-4Z-2Y + 42He
  • Beta decay equation: AZX → AZ+1Y + 0-1e(β)
  • Half life equation: n*(½)^t