Nuclear+Physics

Contents

 * Radioactivity
 * Stable and Unstable Nuclei

Radioactivity
Radioactivity, or radioactive decay, is the spontaneous breakdown of unstable nuclei as they attempt to become more stable by emitting either (or both) of energy and particles.

It is perhaps worth making clear that the all-encompassing term used to refer to these emissions is "radiation", specifically ionising radiation. However this use of the term radiation is separate and distinct from the term "radiation" commonly used when talking about the electromagnetic spectrum (although both can be dangerous, and there is some overlap, as should become clear).

Three types of nuclear radiation have been identified:

Charge +2e (3.2 x 10 -19 ) "Slow", typically 1/20c
 * ~ Characteristic ||~ ALPHA DECAY, a ||~ BETA DECAY, b ||~ GAMMA DECAY, g ||~  ||
 * Description of radiation || Like a Helium nucleus. 2n + 2p

Mass: 4.0015u || Nuclear electron (i.e. source is nucleus, not electron shell). Charge -e Fast, up to .98c Mass: u/1822 || Very short wavelength EM radiation ||  || Although the a -particle has a lot of energy when emitted it is relatively massive, so moves relatively slowly. As it has a high charge it interacts readily (e.g. with air), so loses energy rapidly.
 * Penetration || Few cm in air. Blocked by skin.

Ingested alpha (and beta) sources are much more dangerous than external sources (particularly for alpha) || Few mm in Aluminium; Perhaps a metre in air.

Increased penetration as much smaller than alpha's, and less charged. Will penetrate and burn skin. || Several cm lead; couple of metres of concrete ||  || knocking electrons off atoms as you pass) || Intense; about 1x10 4 ion pairs per mm.
 * Ionisation (generally:

Ionisation is dangerous, as it can ionise atoms in the body (in the cells or DNA) which makes them highly chemically reactive, resulting in changes in the cells or DNA. || Less intense than alpha, about 1x102 ion pairs per mm.

High doses of ionising radiation can cause radiation burns or even acute radiation syndrome. || Weak interaction, about one ion pair per mm.

Note: gamma rays are not charged, but are EM radiation, therefore will interact with atoms, e.g. photoelectric effect, where gamma ray photon is absorbed, exciting an electron enough so that it is emitted, ionising the atom. ||  || Magnetic (B) field || Deflection in either as positively charged, but only slight deflection as relatively massive || Strong deflection (less charge but much less massive) and in opposite direction to alpha. || No effect. ||  || eliminator in industry (ionisation generates a current; smoke stops it) || * Iodine-131 is used to treat certain cancers and for luminous dials, gauges and wrist watches. old. thickness gauges || * Cesium-137: cancer treatment; measure and control the flow of liquids in industrial processes; measure soil density at construction sites; ensure the proper fill level for packages of food (see below); pasteurise food; gauge the thickness of metals. radioactive isotope for diagnostic studies. ||  || 1899 while working with uranium ([|US EPA Link])
 * Effect of Electric (E) or
 * Common sources and uses || * Radium-226 - treat cancer
 * Polonium-210 - serves as a static
 * Americium-241 - smoke detectors
 * Strontium-90 is used as a radioactive tracer
 * Tritium is used for drug metabolism studies
 * Carbon-14 dating matter up to 30,000 years
 * Beta emitters are used for industrial
 * Cobalt-60: sterilise medical equipment
 * Technetium-99m: the most widely used
 * Notes || First discovered by Rutherford in

Alpha particles themselves are not radioactive, so once they have lost much of their energy, they pick up electrons from the environment and become helium atoms. || Henri Becquerel is credited with the discovery. In 1900 he showed that they were identical to the electron (which had been discovered by JJ Thompson in 1987). ([|US EPA])

Once they have lost their energy, they will be picked up by a positive ion. || Henri Becquerel is credited with discovery, in 1896. He noticed that uranium could expose photographic paper through intervening layers of paper. ([|US EPA]). Marie Curie did much to advance understanding in this area, and shared the Nobel Prize in 1903 with Becquerel and her husband, Pierre.

Eventually lose energy and disappear.

Sterilisation of medical equipment and food: Place the item in a bag; place bag in path of gamma radiation. The Gamma rays either directly damage DNA, by breaking it apart, or ionise atoms in cells, and these "free radicals" damage the DNA. In this way cells are killed. ||  ||

Stable and Unstable Nuclei
Within, or near, the nucleus of an atom, the two dominant forces are the strong nuclear force (which effects all hadrons, i.e. particles made of quarks) and the electrostatic force (between the protons). For the lighter elements the number of neutrons and protons is roughly equal, as the uncharged neutrons provide enough extra strong nuclear force to overcome the electrostatic repulsion of the protons. However, for heavier elements proportionately more neutrons are required to provide enough nuclear attraction and to dilute the electrical repulsion.

Radioactivity

 * Spontaneous break up of an unstable nucleus to acquire a more stable state.
 * Rate of emission of radiation independent of chemical composition - as property of the nucleus and nothing to do with the outer electrons that determine the chemical properties.
 * Process is completely random. Depends only on the number of unstable atoms present.

Nuclear Power - Fission and Fusion


The above slides include notes on the generation of nuclear power, fusion and fission reactors, safety issues and relative advantages.