Background Radiation: A small amount of radiation is around us all the time because of radioactive materials in the environment. It mainly comes from natural sources such as soil, rocks, air, building materials, foods and drink — and even space
Geiger-Müller (GM) Tube
This detects α, β, and γ
The ‘window’ is thin enough for alpha particles to pass through
If an alpha particle enters the tube, it ionizes the gas inside
This sets off a high-voltage spark across the gas and a pulse of current in the circuit
A beta particle or gamma radiation has the same effect
It can be connected to a rate meter (tells the counts per seconds) or a scaler (tells the total number of particles or bursts of gamma radiation)
Characteristics of the 3 Kinds of Emissions
Radioactive emissions occur randomly over space and time
Radioactive Decay
Radioactive Decay: A radioisotope (unstable arrangement of neutrons and protons) is altered to make a more stab;e arrangement.
The parent nucleus becomes a daughter nucleus and a particle (decay products)
Alpha Decay:
An element with a proton number 2 lower than that of the parent and nucleon number 4 lower than that of the parent and an alpha particle are made
For example: Radium-226 nucleus → Radon-222 + helium-4 nucleus
Beta Decay:
A neutron changes into a proton, an electron and an antineutrino. So an element with the same nucleon number but with a proton number 1 higher.
For example: iodine-131 → xenon-131 + beta particle + antineutrino
Gamma Emission:
Gamma emission by itself causes no change in mass number or atomic number; they just emit energy
Some isotopes do not change in mass or atomic number, however they emit energy as their particles rearrange themselves to become more stable
Half Life
Half-life of a radioisotope is the time taken for half the nuclei present in any given sample to decay
Some nuclei are more stable than others
Safety Precautions
Radioactive material is stored in a lead container
It is picked up with tongs, not bare hands
It is kept away from the body and not pointed at people
It is left out of its container for as short a time as possible
Atomic Model
Atoms consist of:
Nucleus: The central part of the atom made of protons (positively charged) and neutrons. These two types of particles are nucleons. They are bound together by the strong nuclear force
Electrons: They are almost mass-less particles which orbit the nucleus in shells
Rutherford’s Experiment
A thin gold foil is bombarded with alpha particles, which are positively charged
Most pass straight through, but few are repelled so strongly that they bounced back or deflected at large angles
Rutherford concluded that the atom must be largely empty space, with its positive charge and most of its mass concentrated in a tiny nucleus.
Properties of Magnets
The nucleus is composed of protons and neutrons
Proton number is the number of protons in an atom
Nucleon number is the number of nucleons (protons + neutrons) in an atom
Isotopes
Isotopes are atoms of the same element that have different numbers of neutrons. E.g. Carbon-12 and Carbon-14
There are non-radioactive isotopes and radioisotopes
Radioisotopes are unstable atoms which break down, giving radiation
Medical use: Cancer treatment (radiotherapy) — rays kill cancerous cells using cobalt-60
Industrial use: To check for leaks — radioisotopes (tracers) added to oil/gas. At leaks, radiation is detected using a Geiger counter
Archaeological use: Carbon-14 is used for carbon dating
