Flashcards in P2 6 Nuclear Radiation Deck (18):
What is a radioactive substance?
A radioactive substance contains unstable nuclei that become stable by emitting radiation.
What are the three main types of radioactive substances?
Alpha, beta and gamma radiation.
When does radioactive decay happen?
Radioactive decay is a random event, we cannot predict when it will happen.
Where is background radiation from?
Background radiation is from radioactive substances in the environment or from space or from devices such as x-ray machines.
What did Rutherford's experiment show?
Most alpha particles passed straight through the metal foil.
The no. of alpha particles deflected per minute decreased as the angle of deflection increased.
About 1 in 10000 alpha particles were deflected by more than 90 degrees.
What was the previous model called?
Plum pudding model
What is an isotope?
Isotopes of an element are atoms with the same number of protons but different numbers of neutrons.
What is released in alpha decay?
In alpha emission, the atomic number goes down by 2 and the mass number goes down by 4.
Eg: 228 Th ---> 224 Ra + 4 a
90 88 2
What is released in beta decay?
A beta particle is an electron. The relative mass of a beta particle is effectively zero and the relative charge is -1 . The atomic number increases by 1.
Eg: 40 K ---> 40 Ca + 0 beta
19 20 -1
What is released in gamma decay?
Gamma is uncharged and has no mass. So it does not change the number of protons or the number of neutrons in a nucleus.
Give characteristics of alpha radiation
Alpha radiation is stopped by paper and it has a range of a few centimetres in air. It consists of particles, each composed of two protons and two neutrons.
Give characteristics of beta radiation
Beta radiation is stopped by thin metal usually aluminium, it has a a range of about a metre in air and it consists of fast moving electrons emitted from the nucleus.
Give characteristics of gamma radiation
Gamma radiation is stopped by thick lead and it has an unlimited range in air. It consists of electromagnetic radiation.
Deflection by a magnetic field
Beta radiation is deflected in the opposite direction to alpha radiation. Beta radiation is deflected more than alpha radiation as the mass of an alpha particle is 8000 x greater than the mass of a beta
particle. Alpha radiation is deflected less. Gamma is undeflected by the magnetic field as it is uncharged.
Deflection by an electric field
Alpha particles are attracted towards the negative plate because they are positively charged. The beta particles are attracted towards the positive plate as they are negatively charged. The same theory about the mass and the amount of deflection occurs here.
Radiation from a radioactive substance can knock electrons out of atoms. The atoms become charged as they lose electrons.This is called IONISATION. Alpha is the most ionising but least penetrative. Beta is in the middle and gamma is the least ionising and the most penetrative.
What is half life?
The half life of a radioactive isotope is the average time taken for the number of nuclei of the isotope in a sample to halve.