Flashcards
PHYSICS UNIT 2- CHAPTER 6
Flashcards do conjunto (20)
- 1What is a radioactive substance?A substance the contains unstable nuclei that become stable by emitting radiation.
- 2What types of radiation are given out from a radioactive substance?Either; gamma, alpha or beta. (these are the main types of radiation)
- 3When does a radioactive source give out radiation (radioactive decay)?Radioactive decay is a random event- we cannot predict or influence when it will happen
- 4Where does background radiation come from?Background radiation comes from substances in the environment or from space or from devices such as X-ray machines.
- 5How was the nuclear model of the atom established?Rutherford used the measurements from alpha scattering experiments to prove that an atoms has a small positively charged nucleus where most of the mass is located. Because of this it abolished the plum pudding model.
- 6Why was the plum pudding model rejected?The plum pudding model could not explain why some alpha particles were scattered through large angles. The plum pudding model thought that the positively matter was evenly spread out. And that the electrons were buried throughout.
- 7Why was the nuclear model accepted?The nuclear model of the atom correctly explained why the alpha particles are scattered and why some are scattered through large angles.
- 8What is an isotope?It is a version of the element with the same number of protons but different numbers of neutrons.
- 9How does the nucleus of an atom change when it emits an alpha or a beta particle?alpha: nucleus loses 2 protons and 2 neutrons
beta: an electron changes into a proton - 10How can we represent the emission of an alpha particle from a nucleus?
- 11How do we represent the emission of a beta particle from a nucleus?
- 12Describe alpha radiation.It is a helium nucleus. It has a 2+ charge
It is absorbed by paper, air, metal and it is highly ionising. It has a slow speed. - 13Describe beta radiation.It is a fast moving electron. It has a charge of -1. It can be absorbed by aluminium, it is fairly ionising and is 90% the speed of light.
- 14Describe gamma radiation.It is an electromagnetic wave. It has no charge, and can be reduced by lead. It is highly penetrating but weakly ionising. It is the speed of light.
- 15How can we separate a beam of alpha, beta and gamma radiation?A magnetic or an electric field can be used to separate a beam of radiation.
- 16What do we mean by the half life of a radioactive source?The half life of a radioactive isotope is the average time it takes for the number of nuclei of the isotope in a sample to halve.
- 17What do we mean by the activity of a radioactive source?The activity is the number of nuclei that decay each second.
- 18What happens to the activity of a radioactive isotope as it decays?The number of atoms of a radioactive isotope and the activity both decreases by half every half life.
- 19How can we use radioactivity for monitoring?the isotope should have a long half life
- 20What is radioactive dating?Tests used to find out the age of an ancient material. For this we need a radioactive isotope that is present in the sample which has a half life about the same as the age of the sample.