P3-Radioactive Materials

ENERGY CONSUMER- Every day you use energy sources. For example heating and the television; the heating system may use natural gas and the TV uses electricity. Natural gas is a primary energy source. Electricity is called a secondary energy source because it is generated from primary sources

IS ELECTRICITY EFFICIENT- Electricity is convenient. But it is also wasteful- especially when used fro heating. A gas-fired power station wastes nearly half of the primary energy source. More energy is wasted in the cables and transformers of the National Grid. By contrast, a domestic gas water boiler is about 80% efficient

ENERGY USE AROUND THE WORLD- As countries become industrialized, living standards rise and energy use increases. Energy use in India and China is now growing especially fast. Global energy demands are expected to grow by 60% between 2005 and 2030. This has the potential to cause a significant increase in greenhouse gas emissions associated with climate change. In 1997, government ministers from around the world met in Kyoto, Japan. They produced targets to reduce CO2 emissions. This is difficult when global demand is increasing.

BACKGROUND RADIATION- If you switch on a Geiger counter, you will hear it click. It is picking up BACKGROUND RADIATION which is all around you. Most background radiation comes from natural sources, like radon gas from the ground and medical treatment.

RADON- Radon is a hazardous gas. It is produced naturally in some rocks. We know that radon gas is harmful because it is RADIOACTIVE. It produces IONIZING RADIATION that can damage cells. Ir can damage cells and cause lung cancer.

DOSE- The risk from radon gas is high because- Radon can build up in enclosed spaces. In the atmosphere, the radon gas can spread out. In mine, rocks keep producing the gas and can't escape.Radon concentration is high in enclosed spaces. Radon is breathed in can damages the delicate lung tissue. Radiation does is measured in millisieverts (mSv)- the average UK dose is 2,6 mSv. Ionizing radiation from outer space is called cosmic radiation. Radiation dose is affected by the amount and type of radiation.

IRRIDATION AND CONTAMINATION- Radon in the air exposes you to ALPHA radiation. Exposure to a radiation source outside your body is called IRRIDATION. Radon irradiationprevents a very low risk because alpha radiation only travels a few cm's in air and it is easily absorbed. Also, your clothes and skin stop alpha radiation. But if a radiation source enters your body or gets on your clothes or skin, it is called CONTAMIINATION- you become contaminated. If you swallow or breathe in any radioactive material, your vital organs will have no protection. They will absorb this radiation

RADON AND RISK- About 2500 people die each year from the effects or radon, or about 1 in 20 000 people. But many risky activities have a benefit, you need to decide whether the rick is worth taking or not.

USES OF RADIATION - Radioactive materials can cause cancer. But they can also be used to diagnose and cure many health problems. It can be used for sterilising surgical instruments and herbs and spices.

TYPES OF RADIATION - There are 3 main types of radiation 1. Alpha, 2 Beta and 3. Gamma. Alpha is the most ionizing of the 3 radiation's. Therefore it can cause the most damage to a cell. The same amount of alpha radiation gives a bigger dose than Beta or Gamma radiation.

BENEFITS & RISKS - A Gamma scan is used to locate parts of the body that are cancerous. Some of the benefits of a gamma scan is that it can put your mind at rest over the risk of cancer and can treat the problem. But exposure to Gamma is a risk.

REGULATING RADIATON DOSE - The Health Protection Agency studies radiation hazards and gives advise to protect against them. It also keeps a close eye on the many people who regularly work with radioactive materials. They are called radiation workers.

THA ALARA PRINCIPLE - Employers must ensure that radiation workers receive a radiation dose As Low As Reasonably Achievable (ALARA). The ALARA principle applies when better equipment or procedures can reduce the risks of an activity. Any extra cost this involves must be balanced against the amount by which the risk is reduced. To reduce their dose, medical staff take a number of precautions:-

• Use protective clothing and screens
• Wear gloves and aprons
• Wear special badges to monitor their dose

The ALARA principle applies equally to hospital patients who receive radiation treatment. If the HPA finds that 1 hospital uses smaller doses and is effective, all hospitals are encouraged to copy them.

Many elements have more than 1 type of atom. EG. There are carbon 12 and carbon 11 atoms. They are both different isotopes of carbon.

RADIOACTIVE DECAY - The main difference is that carbon 12 atoms do not change. They are stable. Carbon 11 atoms are radioactive. Randomly, these atoms give out energetic radiation. Each carbon 11 atom does it only once. What is left afterwards is not carbon, but a different element, BORON. This process is called RADIOACTIVE DECAY. It is not a chemical change, it is a change inside the atom.

WHAT MAKES AN ATOM RADIOACTIVE - Some atoms, with particular combinations of protons and neutrons in the nucleus are unstable. The atom decays to become more stable. It emits energetic radiation and the nucleus changes.

RADIOACTIVE CHANGES - The emission of either an alpha or beta particle from any neucleus produces an atom of a different element, called a DAUGHTER OR DECAY PRODUCT. The daughter product may itself be unstable. There may be a series of changes, but eventually the stable end element is formed.

NUCLEAR FISSION - Radioactive atoms have an unstable nucleus. Other nuclei can be made so unstable that they split in two. This process is called NUCLEAR FISSION. The products of NF have kinetic energy. The fission of 1 atom can set of several more, because each fission reaction releases a few neutrons. If there are enough atoms close together, there will be a chain reaction, involving more and more atoms.

NUCLEAR POWER STATIONS - The nucleus of an Uranium 235 atom is used for NUCLEAR FUSION in nuclear power stations. At the heart of the nuclear power station is a reactor. It is designed to release the energy of Uranium at a slow and steady rate, by controlling a chain reaction.

• The fission takes place in fuel rods that contain uranium 235. This makes them extremely hot.
• Control rods, which contain the elements boron, absorb neutrons. Moving control rods in or out of the reactor decreases or increases the reaction rate.

GENERATING ELECTRICITY - A fluid, called a coolant, is pumped through the reactor. The hot fuel rods heat the coolant to around 500 degreeC. It then flows through a heat exchanger in the boiler, turning water to steam. The steam drives turbines that, in turn, drives generators. The electricity is transferred to a transformer, which is used to change the voltage up or down to the level required.

THE UK'S NUCLEAR LEGACY - The government set up the Nuclear Decommissioning Authority (NDA) to clean up hazardous nuclear waste sites around the UK. More than 95% of the radioactive waste comes form nuclear power stations. The rest comes form medical uses, industry and scientific research. Nuclear waste is a cocktail made of different radioisotopes. They call it the UK Nuclear Legacy. Before the NDA can start of disposing of Nuclear waste, it must find a method that is acceptable to the public. It must be safe and secure for many generations.

HALF LIFE - The amount of radiation from a radioactive material is called its activity. This decreases with time.

• At first there are alot of radioactive atoms.
• Each atom gives out radiation as it decays to become stable.
• The activity falls, fewer radioactive atoms remain.

A graph (showing radon 220) shows that the amount of radiation halves every minute, the half life of radon 220. The half life is the time it takes for activity to drop by half. All radioactive materials follow the same pattern of decay, but have different half lives.

RADIO ACTIVE DECAY CONTINUED - There is no way of slowing down or spreading up the rate at which radioactive materials decay. The shorter the half life, the greater the activity for the same amount of material.

METHODS OF DISPOSAL - Years ago the UK dumped nuclear waste at sea, to be dispersed. Later, people suggested burying it the Arctic ice or firing it into space. But these options are to risky. Current possibilities include:-

• Keeping it on the surface, in storage containers
• Burying it deep in rock

The UK first investigated deep disposal for nuclear waste in the late 1980's. In secrete, a short list of 12 possible sites was decided.

WAYS OF GENERATING ELECTRICITY - Primary sources of energy:-

• Fossil fuels like coal, oil and gas are finite. One day they will run out. Power stations burn fossil fuels and release waste, including carbon dioxide, into the atmosphere.
• Nuclear fuel comes from Uranium mines. They are large but finite reserves. It produces solid radioactive waste that has to be handled carefully. But it could reduce the amount of CO2.
• Renewable energy sources like wind, geothermal and solar power produce very little waste. They are sustainable primary sources, because they should last forever. They also produce less CO2 than fossil fuels.

Fossil and nuclear fuels are used to boil water and make steam. The high pressure steam passes through a steam turbine. Power stations burning natural gas have an extra turbine that harnesses the flow of hot exhaust gasses. This makes them the most efficient type of power station, reducing the amount of CO2 produced. Another way is through reducing the total electricity consumption.