Radioactivity

Menu Background Radiation Types of Radiation Dangers of Radiation Detecting Radiation Uses of Radiation Radioactive Decay & Half life

Background Radiation

What is Background Radiation? This is radiation that occurs NATURALLY ALL AROUND US. It only provides a very small dose altogether so there should be no danger to our health It comes from naturally occurring unstable isotopes in…. The air Food Building materials Rocks under our feet Space (Cosmic Rays), and Human activity (nuclear explosions, nuclear waste)

The Proportion of Sources of Background Radiation

The Level of background radiation changes depending on where you are… At high altitudes (e.g. On a jumbo jet) it increases because of more exposure to cosmic rays ……. LESS ATMOSPHERE TO PROTECT US!

This is a major problem for astronauts that ‘fly’ above the Earth’s atmosphere (on the International Space Station for example) A number of astronauts have suffered from cancer as a result.

The astronauts that will be chosen to go to Mars will be OLDER than usual. This is because they are more experienced and also because they will be exposed to far more radiation than their bodies can be protected from They know that they are likely to die of cancer within 10 years of their return to Earth

People who work in underground mines will receive more radiation as a result of the rocks giving off radiation all around them. It is the natural decay of radioactive isotopes that makes the earth hotter as you go deeper down a coal mine.

The coloured areas indicate where there is more radiation given off by the rocks. These are usually associated with igneous rocks

Background Radiation Count Must Always Be Taken Away I f You Want to Measure the Radioactivity of a Sample Radioactivity is measured in Becquerel (Bq) One Becquerel is one nucleus decaying per second Return to menu

This is Madame Curie and her husband. They both died of cancer because of the radioactive materials. The books they used are SO radioactive that they have to be kept in lead containers. If a scientist wants to read them they have to wear full lead protection!

Nuclear Processes Release More Energy Than Chemical Processes When a nucleus splits it gives out a lot more energy than a chemical bond. This is why nuclear bombs release a lot more energy than other bombs

What Are the Types of Radiation?

What are the 3 types of radiation? ALPHA PARTICLES BETA PARTICLES GAMMA RAYS

A radioactive substance can emit one of the following types of radiation. A simple way to distinguish between them is their ability to be absorbed by different types of material. Alpha – absorbed by thin sheet of paper (or few cm’s of air) Beta – Absorbed by a few mm’s of aluminium Gamma – VERY penetrating needs several cm’s of lead

What are ALPHA PARTICLES? They are relatively big, heavy & slow moving and cause a large amount of ionisation They therefore don’t travel far into materials but are stopped quickly They are made up of 2 protons and 2 neutrons and are actually helium nuclei

What are BETA Particles? These can penetrate quite well They are fast moving electrons with small mass They cause a small amount of ionisation

What are GAMMA Rays? These are the opposite of alpha particles in a way! They penetrate a long way into materials without being stopped They cause little ionisation They are high energy Electromagnetic waves with a very short wavelength

TypeAlpha Particles Beta Particles Gamma Rays Description2 protons & 2 neutrons electrone.m. wave Charge + - No charge MassHeavy in comparison Very light … Speed1/10 th speed of light 9/10 th speed of light Speed of light Ionizing EffectstrongweakVery weak Penetrating Effect Not very (stopped by paper) Penetrating (stopped by 5mm of aluminium) Highly penetrating Effect of Electric & Magnetic Fields Bent by electric & magnetic fields Bent strongly by electric & magnetic fields Not bent by electric & magnetic fields

These are the tracks left by radiation in a bubble chamber How many different types of tracks can you see? Return to Menu

Dangers of Radiation

Alpha, Beta and Gamma Radiation will harm living cells. When they enter the cells they collide with the molecules and cause ionisation. Lower doses usually cause minor damage to the cell and can result in mutant cells that divide uncontrollably. This is CANCER. Higher doses tend to kill the cells completely, which causes radiation sickness.

What is IONISATION? This is when radiation collides with neutral atoms or molecules, altering their structure by knocking out electrons. This leaves them as IONS or CHARGED PARTICLES. Neutral atom or molecule Ion Electron Alpha Particle

The extent to which your cells are damaged depends on How long you are exposed to the source and How strong the radiation source is.

Dangers of Radioactivity OUTSIDE the body Beta & Gamma radiation are more dangerous as Alpha radiation is blocked by the skin. INSIDE the body an Alpha source causes the most damage because it is the most ionising. Radiation ionises atoms in living cells – this can damage them and cause life threatening cancer or leukaemia.

The Safety Precautions In The Laboratory Are:- Never allow skin contact Keep the source pointing away from you ( and others!) always keep the source in the lead box It is assumed that you would not be eating, drinking or smoking at the same time as this would take the radiation inside your body!

You will often see people in hospitals wearing these This Dosage Monitor contains photographic film & shows how much radiation the wearer has been exposed to We Can Detect Radiation Using Photographic Film

We can also detect radiation with a ‘Geiger Counter’

Extra precautions for Nuclear Radiation workers…. Wear full protective suits to stop tiny particles getting into your lungs or underneath your nails Use remotely controlled robot arms Return to Menu

Uses of Radiation

How can radioactivity be used for thickness control? Rollers Beta Detector Paper Beta Emitter If paper thickness becomes too great less radiation passes through to detector which sends a signal to the rollers to move closer.

Radiation can be used as a ‘TRACER’ to see how the body is functioning For example the Thyroid Gland absorbs Iodine If radioactive Iodine is injected into the patient, we can see how much iodine is absorbed To avoid it getting out of hand like this ‘Overactive’ Thyroid Gland

Tracers Can Also Be Used in Industry To:- Detect leaks in pipes to show flow rates to show uptake of fertilizers in plants

Radiation can be used to Kill mould and bacteria on your strawberries …..and to date an Egyptian mummy Return to Menu

Radioactive Decay & Half Life

This is the TURIN SHROUD. It has been radiocarbon dated to find out its age.

Half Life The Radioactivity of a sample always decreases over time HALF LIFE is the TIME TAKEN for HALF of the radioactive atoms now present to DECAY How quickly the activity of a radioactive sample drops varies from one sample to another. It may take hours or millions of years

How do we measure Half Life? You can use a graph to work out Half Life Or you can calculate it step by step

A Radioactive Decay Graph Time 1 half life Count Rate Time in Hours One Half Life Radioactivity of Sample

Half Life Calculations The radioactivity of a simple isotope is 640 counts per minute. Two hours later it has fallen to 40 counts per minute. Calculate the half Life of the sample. Initial count 640 After one Half Life 320 After two Half Lives 160 After three Half Lives 80 After four Half Lives 40 : 2 :2:2 Two Hours for 4 Half Lives. Therefore half Life is 30 Minutes Return to Menu