1. Radioactivity – Outcomes  Describe the experimental evidence for there being three types of radiation.  Discuss the nature and properties of each type.  Solve problems about mass and atomic numbers in radioactive decay.  Demonstrate ionisation and penetration of each type.  Give uses of radioisotopes.  Describe the principle of operation of a radiation detector.  Demonstrate a radiation detector. 1

2. Radioactivity – Outcomes  Define the becquerel (Bq).  Interpret nuclear reactions.  HL: State the law of radioactive decay.  Discuss the concept of half-life.  HL: Discuss the decay constant.  Solve problems about rates of decay and half-lives. 2

3. Radiation  Radioactivity is the decay of unstable nuclei with the emission of one or more types of radiation.  There are three types of radiation, evidenced by the effect of an electric field. 3

4. 4

5. 5

6. 6

7. Radioactive Decay  e.g. Write the nuclear reaction for potassium-40 undergoing beta decay.  e.g. If actinium-225 decays to francium-221, what type of radiation was emitted?  e.g. bismuth-214 has a decay chain (i.e. multiple decays in a row) ending at stable lead-206. If lead, bismuth, and polonium are the only elements in the chain, write out each reaction in the decay chain. 7

8. Ionisation and Penetration  Radiation can knock electrons out of matter, ionising it.  Alpha is the best ioniser, beta is the second best, and gamma is the worst at this. 8  The opposite is true for penetration:  gamma requires thick lead or concrete to block it  beta will be blocked by a thin sheet of aluminium  alpha will be blocked by a sheet of paper, or a few cm of air. by stannered, ehamberg – CC-BY-SA-3.0

9. Demonstrate the Ionising Ability of Radiation 1.Charge an electroscope. 2.Bring a radioactive source near the electroscope. 3.Note that the leaves collapse. 4.The radiation ionises the air around the electroscope and the new charges neutralise the electroscope. 9

10. Demonstrate the Penetrating Power of Radiation 1.Turn on a GM tube and note the number of counts over two minutes. 2.Aim a source of alpha radiation at the GM tube and record the number of counts over two minutes. 3.Place a sheet of paper between the source and GM tube. Record the number of counts over two minutes. 4.Repeat for sources of beta and gamma radiation, using a thin sheet of aluminium and a thick sheet of lead respectively. 10

11. Demonstrate the Penetrating Power of Radiation 1.Alpha radiation will be blocked by a sheet of paper. 2.Beta radiation will pass through paper, but be blocked by a thin sheet of aluminium. 3.Gamma radiation will pass through paper and aluminium, but be blocked by a thick sheet of lead. 11

12. Radiation NatureChargeIonising Ability Penetrating Power Range helium nucleus +2greatestleasta few cm of air, a piece of paper electronmedium a few cm of aluminium photons0leastgreatesta few cm of lead, thick concrete 12

13. Uses of Radioisotopes 13

14. GM Tube  A Geiger-Müller tube consists of an inert gas with a high voltage across it.  Normally the inert gas does not conduct, but ionising radiation will create ions and electrons. 14  The high voltage accelerates these charges, which bump into neutral molecules, creating more charges.  Thus, a single ionisation can produce many charges.  Each electron hitting the anode will cause a small current, which is counted. by svjo-2 – CC-BY-SA-3.0

15. Solid State Detector  Solid state detectors consist of a reverse biasedp-n junction which is sensitive to ionising radiation. 15  Radiation creates electron-hole pairs in the depletion layer.  These charges move due to the voltage across the diode, creating a small pulse of current which can be counted.

16. Activity  The activity, A of a radioactive isotope is the number of decays it undergoes per unit time.  Activity depends on the type and number of nuclei present.  The Becquerel (Bq) is the unit of activity. Activity is 1 Bq if one nucleus decays in one second. 16 Higher Level

17. Activity 17 Higher Level

18. Half-Life 18

19. Half-Life 19 Higher Level

20. Half-Life  e.g. What is the half- life of the isotope depicted in the graph if the t-axis shows N? 20 Higher Level