In addition to these notes, a nice intro can be found here.

The Nucleus

• The nucleus consists of protons and neutrons.
• The number of protons is known as the atomic number and is generally designated by the letter Z.
• The total number of nucleons (protons or neutrons) is known as mass number and is generally designated by the letter A.
• Symbolically, A=Z+N, where N is the number of neutrons.

Radioactive decay

When an atomic nucleus is unstable, decay brings the nucleus to a more stable state.

There are 5 basic types of radioactive decay, although a given nucleus may decay through a combination of these:

• Alpha (α) emission--reduces mass number by 4 and atomic (proton) number by 2
  • alpha particle is actually a helium nucleus
  • most common type of decay.
  • least penetrating; can be stopped by a sheet of paper
  • smoke detectors use the alpha radiation from americium-241 to detect smoke particles in the air.
  • Example: 238/92 U --> 234/90 Th + 4/2 He  (note that 234+4=238 and 90+2=92)
• Beta (β) emission--increases atomic (proton) number by 1
  • beta particle is actually an electron which originates in the nucleus
  • can penetrate skin
• Gamma (γ) emission--does not change nuclear composition
  • gamma radiation is a form of electromagnetic radiation
  • most penetrating, will go through flesh and bone
• Electron Capture--reduces atomic (proton) number by 1
• Positron Emission--reduces atomic (proton) number by 1
  • positron is essentially an electron with a positive charge

Stability

• Of the 7000 or so nuclides that might possibly exist, about 2000 have either been found in nature or created in the laboratory, and of those only 256 are stable and do not undergo radioactive decay.
• Uranium-238 requires 8 alpha decays and 6 beta decays to eventually become Lead-206, a stable element.

Radiation dosage

• Radiation doses are measured in rads (short for radiation absorbed dose), where 1 rad corresponds to 0.01 joule of energy deposited per kilogram of tissue.
• Because alpha, beta, and gamma radiation differ in penetrating and ionizing ability, both the energy dose of the radiation and its effectiveness in causing human tissue damage must be considered.
• The rem (short for roentgen equivalent for man), which takes into account both the dosage and its relative biological effectiveness, is therefore the unit that we generally use when discussing the biological effects of radiation. The SI unit of radiation biological effectiveness is the sievert (Sv), where 1 Sv = 100 rem.
• The curie is a unit of activity of radioactive substances equivalent to 3.70 × 10¹⁰ disintegrations per second, or approximately the amount of activity produced by 1 g of radium-226.
• The average U.S. resident is exposed to about 0.2 rem of radiation each year, of which about 82% derives from natural sources and 18% is related to human activities.

Sources of radiation

• The largest single source of radiation exposure to the general public is naturally occurring radon gas, which comprises approximately 55% of the annual background dose.
  • Radon is a decay product of radium whose own origin traces back to the decay of Uranium.  Uranium is found in many common rocks, notably granite.
  • Radon is the second most common cause of lung cancer, after cigarette smoking, and radon-induced lung cancer is thought to be the 6th leading cause of cancer death overall. In the US, Radon claims about 20,000 lives annually.

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