Key Knowledge and Skills

1. Types of Radioactive Decay Key Knowledge and Skills • apply a simple particle model of the atomic nucleus to the origin of α, β and γ radiation, including changes to the number of nucleons; • describe the detection and penetrating properties of α, β and γ radiation; • describe the effects of α, β and γ radiation on humans, including short- and long term effects from low and high doses, external and internal sources, including absorbed dose (Gray), dose equivalence (Sieverts) and effective dose (Sieverts); • describe the effects of ionising radiation on living things and the environment; • explain nuclear transformations using decay equations involving α, β and γ radiation; • analyse decay series diagrams in terms of type of decay and stability of isotopes;

2. Rutherford discovered that there were three types of emissions from radioactive substances: alpha, beta and gamma radiation. Alpha Radiation ()

3. Beta Radiation () Note that this happens in the nucleus, not the electron cloud. Beta decay occurs in nuclei where there is an imbalance of neutrons toprotons. Typically, if a light nucleus has too many neutrons to be stable, aneutron will spontaneously change into a proton, and an electron and anuncharged massless particle called an antineutrino,  , are ejected to restorethe nucleus to a more stable state.

4. Gamma Radiation ()

10. Penetrating Ability Gamma rays can pass through human tissue and sheets of aluminium quite readily. A 5 cm thick sheet of lead is needed to stop 97% of the gamma rays in a beam. By comparison, alpha particles are not capable of penetrating through a sheet of paper or beyond the skin of a person.

11. The ionising abilities of radiation Alpha: slow speed an double charge – interacts with just about every atom in its path and dislodges electrons turning them into ions. Eventually it slows down, picks up some loose electrons and becomes a helium atom (within a cm or two of air). The air becomes ionised and alpha is said to be highly ionising. Beta: negative charge means it glances off the electron cloud of atoms it interacts with. Doesn’t lose as much energy as alpha and is therefore not as ionising. Gamma: no charge and moving at the speed of light – interact with matter infrequently, so they a poor ionisers.

12. What is ionisation?At treating products with ionising rays, e.g. electron beams or gamma rays and/or X–ray photons, orbital electrons can be driven out from the atom's electron shell (ionisation).

13. As a positively charged alpha particle moves through matter, it attracts many orbital electrons leaving a wake of ion pairs.  When the speed is slowed enough, the alpha particle will capture electrons to produce elemental helium.

14. Radiation Energy One ELECTRONVOLT is an extremely small quantity of energy equal to 1.6 X 10−19 J, i.e. 1 eV = 1.6 X 10−19 J, An electron volt is the energy that an electron would gain if it were accelerated by 1 volt.

16. Activity Measuring Radiation Becquerel[Bq] - SI unit of activity. 1 Bq = 1disintegration per second. Curie [Ci] - Historical unit of activity, corresponding to the activity of 1 gram of pure 226Ra. 1 Ci = 3.7x1010Bq. A Geiger counter measures activity http://www.digitalvideo.com/misc/html/geiger.htm

17. The disintegration of each nucleus of radium-226 release 4.6 MeV of energy. What is the energy which will be produced by 1 gram of radium in 1 hour (the activity of 1 g of radium-226 equals 3.7x1010 Bq and 1 eV = 1.6 x 10-19J)? 1 hour = 60 x 60 = 3600 seconds 3.7x1010radium-226 nuclei disintegrate every second. That’s equal to 3600 x 3.7x1010= 1.3 x 1014 disintegrations every hour. Each disintegration releases 4.6 x 106 eV of energy. That’s equal to 4.6 x 106 x 1.6 x 10-19= 7.4 x 10-13Joules. So, in an hour 1.3 x 1014 x 7.4 x 10-13= 98 Joules of energy are released. (That’s equivalent to lifting an 80 kg person 12 cm. Not bad for only 1 gram of radium!)

18. Homework: Questions 1.2 and 1.3