Chapter 7: Radioactivity Flashcards
What is a radioactive substance?
It contains unstable nuclei that become stable by emitting radiation.
What are the three types of radiation?
Beta, gamma and alpha
What do radioactive sources emit?
Either alpha, gamma or beta particles
What is an alpha particle made up of?
An alpha particle is made up of 2 protons and 2 neutrons
Its relative mass is +2
It is usually represented by the symbol 4_2a
What happens to the nucleus of a nucleus that has just emitted an alpha particle?
It atomic number goes down by 2
Its mass number goes down by 4
The mass and charge of the nucleus are both reduced
For example 228_90Th decays by emitting an alpha particle so it form an isotope 224_88Ra
What will the equation look like for alpha decay?
228_90Th > 224_88Ra + 4_2a
The top number shows the increase in the mass number 224+4
The number along the bottom show the protons after the change 90-2
What is a beta particle made up of?
A beta particle is an electron created and emitted by a nucleus that has too many neurones compared with its protons.
- It is created when a neutron in the nucleus changes into a proton and an electron is emitted. The beta particle has no mass and a charge of -1
- So a beta particle can be represented by the symbol 0_-1B
What happens when an unstable nucleus emits a beta particle?
- The atomic number of the nucleus goes up by 1 and its mass number is unchanged(because a neutron changes into a proton)
- The charge of the nucleus is increased and the mass of the nucleus is unchanged.
e. g. 40_19K decays by emitting a beta particle so it forms an isotope 40_20Ca
What is an example of the equation?
40_19K > 4020Ca + 0-1B
The number on the top shows that the neutrons and protons after the change is equal after the change.
The bottom number shows the change from 20 to 19
Describe gamma radiation.
A gamma ray is an electromagnetic radiation from te nucleus of the atom. It is uncharged and has no mass. Its emission does not change the number of protons or neutrons in the nucleus. So the mass and the charge of the nucleus are both unchanged
Why isn’t every nucleus unstable?
Because the protons and neutrons inside a nucleus are held together by a strong attractive force called the nuclear force. The force in normal nucleus is strong enough to overcome the electrostatic repulsion of the protons and to stop the neutrons moving away from the nucleus
Describe the penetrating power of alpha radiation.
Alpha radiation is stopped by paper and has a range of few centimetres in air
Describe the penetrating power of beta radiation.
Beta radiation is stopped by a thin sheet of metal and has a range of about 1 meter in the air
Describe the penetrating power of gamma radiation
It is stopped by thick lead and has an unlimited range in air.
Describe the order of ionising power that the three radiations have.
Alpha is the most ionising
Beta is the second most
Gamma is the least ionising
