Really radioactive - igcse physics
- 1. presents a production Really Radioactive 1
- 2. The nucleus The tiny core of the atom is very dense. It consists of protons and neutrons and is orbited by electrons. A proton is about the same mass as a neutron but about 2000 times larger than an electron. Images: PHET build an atom sim Proton (aka atomic) number: 6 = 6 protons Nucleon (aka mass) number:213 = 6 protons + 7 neutrons
- 3. Isotopes Isotopes of an element are atoms which have the same number of protons but different numbers of neutrons. Images: PHET build an atom sim 3
- 4. Unstable nuclei Certain nuclei are unstable. They decay spontaneously and emit a particle (either alpha or beta) and the nucleus forms an isotope of a new element. Unstable = Radioactive Decay = Disintegrate An unstable nucleus Random = Spontaneous decays spontaneously A radioactive nucleus disintegrates randomly 4
- 5. Alpha, beta, gamma An alpha particle consists of 2 protons and 2 neutrons (charge = +2). It is the same as a helium nucleus. It leaves the Image: ionactive parent nucleus at a speed of 15 000 km/s. A beta particle consists of one electron (charge =-1; mass 1/8000 th of alpha). It leaves the nucleus at speeds of up to nearly 300 000 km/s. A gamma ray is NOT a particle. It is the most energetic electromagnetic radiation which is emitted by the nucleus at 300 thousand km/s,5the speed of light.
- 6. Penetration Passes through ... Stopped by ... few cm of air paper, skin air, paper, skin few mm aluminium few mm aluminium, thick lead most things 6
- 7. Ionisation of atoms in the Nuclear radiation can knock electrons out air or in your body.You can think of this as damage. Image: remnet causes a lot of ionisation in a short distance causes some ionisation and travels further When ionised, an atom becomes an causes very little ionisation ion pair and is difficult to stop 7
- 8. Detecting radioactivity The Geiger-Muller tube is one of many ways to do this. One alpha or beta particle entering the detector ionises the gas within which creates a voltage which is counted as a ‘click’ by the ratemeter. A photographic film will darken when exposed to radiation 8 Image: darvill.clara.net
- 9. Background radiation Medical 12% The Earth We are constantly Cosmic rays 10% 14% exposed to low- Other level radiation in Food 2% our environment. 12% Most of these sources are Radon gas naturally occurring. 50% 9
- 10. Uses of radioactivity Thickness control Radiotherapy Find Leak out tracer about them Medical tracers The smoke detector too 10
- 11. Carbon things After death, no All living dating There is a fixed contain the same more C-14 is proportion of fraction of C-14 as absorbed and it carbon 14 in the the atmosphere due decays with a atmosphere. to the food chain. half-life of 5730 years. The fraction of C-14 remaining in old organic material can be used to calculate its age. Images: Answersingenesis NN takes no responsibility for the 11 views expressed by its sources
- 12. Hazards of radioactivity Find out about them 12
- 13. Radioactive decay Unstable nuclei decay randomly. They change into other elements. The decay is exponential which means that the number of nuclei always reduces by half in a given time. The rate of decay falls as well, but it never gets mathematically to zero. 13
- 14. Half-life The activity of a sample is measured in Bq (Bequerels = decays per second). The activity decays exponentially with time, just like the number of nuclei. A sample of 24 million nuclei has a half-life of 3 Solutions years. After how many over the years will there be 3 page million nuclei left? What is the half-life of a sample whose activity falls from 640 Bq to 40Bq in 30 minutes? 14
- 15. Nuclear equations 9 years 7.5 min Parent Daughter nucleus nucleus A X−4 4 Alpha can be XZ ⇒ Y Z−2 + α 2 also written as He A X 0 Beta can be XZ ⇒ Y Z+1 + β also written −1 as e The particles in the nucleus are not changed by gamma decay. 15
- 16. Nuclear transformations The daughter nucleus is 2 elements lower than the parent on the Periodic table. The daughter nucleus is one element higher than the parent on the Periodic table. The daughter nucleus is identical to the parent nucleus.