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Alpha radiation is strongly ionising radiation. Beta radiation is
Alpha(α) is radiation that is [] [] strongly ionising, travels a few centimeters in air and is stopped by a thin sheet of paper.
Beta(β) is [] radiation ionising radiation that penetrates [] or several sheets of [] card or several sheets of paper, but is stopped by a sheet of aluminium or other metal that's 3mm thick.
Gamma(γ) is [][] radiation weakly ionising radiation, it is reduced significantly by a thick sheet of lead or blocks of concrete.
The most penetrating type of radioactive emission is gamma radiation.
Alpha and beta radiation is deflected by both magnetic fields and electric fields, but gamma radiation is not affected.
Background radiation: radioactive materials occur n... natuarally, and can also be made a... artificially.
We recieve a low level of radiation called background radiation.
Building materials, rocks(e.g. granite) and soil; radioactive nuclei in all plants and animals; medical and industrial uses of radioactive materials and 'leaks' from radioactive waste and nuclear power station are whence comes background radiation.
Background radiation is radioactive emissions from nuclei in our surroundings.
In some parts of a country, the rocks may be more radioactive than the rocks in other parts and there is a higher level of background radiation.
Ionising radiation is radiation that has enough energy to break [] or [] molecules or atoms into [] called [] charged particles called ions.
"The molecules or atoms lose electrons in a process called ionisation. The ions can take part in chemical reactions. The is how ionising radiation damages living cells.
To damage living cells, ionising radiation either [] them kills them or damages the [] in the cell the DNA in the cell, so that the cell [] into a [] cel mutates into a cancer cell.
Ionising radiation includes alpha, beta and gamma radiation from the [] [] radioactive nuclei and also []-[] and []-[] radiation also x-rays and ultra-violet radiation.
Of all the radioactive emission, the most ionising are alpha particles, followed by beta, and the least ionising being gamma.
Gamma rays, X-rays and ultra-violet radiation are three types of [] radiation electromagnetic radiation with high enough frequency to cause ionisation.
"It is not possible" to predict which cells will be damaged by exposure to radiation, and "it is not possible" to say who will get c... cancer. Scientists have studied the survivors of incidents where people have been expose to ionising radiation. They measured the amount of exposure and recorded how many people later suffered from cancer. They introduce radiation dose, measured in sieverts, which is a measure of the possible harm done to the body. Radiation dose depends on the type of radiation, the time of exposure and how sensitive the tissue exposed to radiation. Scientists can then give a figure for the risk of cancer developing.
To reduce the risk to living cells, radioactive materials must be handled safely: wear protective clothing, make your distance away long, handle sources with tongs, keep the exposure time short, sources should be s... shielded and labelled with the radioactive symbol. "These precautions keep the dose as low as possible".
Radioactive materials are used, for example, in hospitals and nuclear power stations. "Employers must keep the dose for their employees As Low As Reasonably Achievable: this is known as the alara principle. Employees at places where nuclear sources are used, may wear a film badge to monitor the exposure to radiation. Hospital staff may move behind a screen or out of the room during X-ray photo graphs.
Uses of radioactivity.
For each use: the radiation is chosen depending on the r[] and the a[] on the range and the absorption, the source is chosen depending on how long it will remain radioactive. [Medical and health uses]. [Medical tracers]. Sources which emit gamma radiation (or sometimes beta radiation) are used in medical t... medical tracers. The patient drinks, inhales, or is injected with the tracer which is chosen to target the organ the doctor(s) want to examine. For example, radiactive iodine is taken up by the [] gland tyroid gland, which can then be viewed using a gamma camera that detects gamma radiation passing through the body.
A tracer must no decay before it has moved to the organ being investigated, but must not last so long that the patient, for weeks afterwards, stays radioactive. Sources which emit a higher dose of gamma radiation are used in the same way for treating cancer by, in the cell, building up and killing the cancer cells.
Treating cancer. Directed at a cancer is a b... beam of gamma rays to kill the cancer cells. One source of this is [c...]-[] cobalt-60. It emits [] rays gamma rays of high energy and remains radioactive for years.
Sterillisation. Sources which emit gamma radiation are used to produce a beam of gamma rays that will: [] equipment, such as surgical instruments, sterilise equipment by destroying microbes; extend the shelf-life of "perishable food", by destroying microbes. The food and equipment does not become radioactive, because it is only irradiated. It does not touch the [r...] [m...] radioactive material, so there is no contamination.
Other uses of radioactivity. Smoke detectors. Smoke detectors use sources that are radioactive and emit alpha radiation. The radiation from the sources [] the air ionise the air and ions cross a small gap and are picked up by a detector. If smoke is present, the alpha radiation is stopped by smoke particles. No ions reach the detector and and alarm is sounded. Beta and gamma radiation are unsuitable as they pass through the smoke.
Tracers. Souuces which emit beta radiation or gamma radiation are used as tracers. A detector can be used to track where it goes, because a tracer is radioactive. If a tracer is added to sewage at an ocean outlet, or as it enterrs a rive, then the movement can be traced. Leaks in power station heat exchangers can be tracked. The source used is carefully selected to be one with a radioactivity that can quickly fall to 0, after the test(is done).
Paper thickness detectors. Used in radioactive paper thickness detectors are radioactive sources that emit beta radiation. The sheet of paper is between rollers, there is a machine to adjust the rollers, there is a source of radiation above the paper, and the is a detector below the paper. Some of the beta radiation is, by the paper sheet, absorbed. If the sheet is too thick, less beta radiation is detected and the pressure of the rollers is increased. If the sheet is too thin: more beta radiation is detected and the pressure is reduced.
Non destructive testing. Another use of gamma radiation sources is non-destructive testing. An aircraft wing can be examined for minute cracks by placing, on one side, a strong [] source gamma source and on the other side a detector-in a similar way to using X-rays to check for broken bones.
Changes in the Nucleus
The nucleus and the isotopes. The atom is mostly empltyn space with almost all the mass concentrated in teh small positively charged nucleus at the centre. The nucleus of an atom contains two types of particle: neutrons, which have no charge; and protons, which each have a [s...] [p...] [c...] single positive charge. The nucleus is surrounded e orbiting electrons which have very little mass. Each electron has a charge that's negative. A neutral atom has an equal number of protons and electrons.
Different elements. "The number of protons in the nucleus decides which element the atom is, so for example, hydrogen always has one proton, helium has two, lithium has three and so on. Carbon always has six."
Isotopes. The number of neutrons in the nucleus can vary. An isotope is a [] of a [] nucleus of an element with the same number of protons but different number of neutrons. Some isotopes are stable, but others are unstable. Unstable isotopes are radioactive because they emit nuclear radiation in a process called radioactive decay.
Isotopes of the same element have exactly the same [] properties chemical properties, but they have different [d...] and nuclear [] density and nuclear stability. Different isotopes are referred to by the number of nucleons in the nucleus, fo rexample, carbon-12 has [] protons and [] neutrons 6 protons and 6 neutrons, whereas carbon-14 has [] protons and [] neutrons 6 protons and 8 neutrons.
Radioactive decay. A radioactive nucleus is un... unstable and emits nuclear radiation. This process is called radioactive decay. "It is not possible to predict when this will happen, nor is it possible to make it happen by a chemical or physical process, (for example by heating it.) The decay is random."
Radioactive emissions. Alpha emissions is when t two protons and two neutrons leave the nucleus as one particle. The alpha particle is identical to a [] nucleus helium nucleus. For example, the isotope of radon gas, radon- 220, decays by alpha emission. Beta emission occurs when a neutron decays to a [] and [] proton and an electron and the electron leaves the nucleus. The beta particle is a high energy electron.
The radioactive isotope of carbon, carbon-14 decays by beta emission. carbon-14 [arrow] nitrogen 14 + beta particle. A beta particle is an [] from the [] - not an orbital electron electron from the nucleus. An Alpha particle is two [] and two [] two - a [] nucleus a helium nucleus. A beta particle is a high energy particle from the nucleus. Gamma radiation is a high-[] and short [] high-frequency and short wavelength [] wave electromagnetic wave.
HALF-LIFE. A radioactive source contains millions of n... nuclei. The number of nuclei decaying per unit time is called the [] of the source. activity of the source. "The activity depends on two things:" the type of isotope - some isotopes are more [] that others more stable than others; the number of undecayed nuclei in the sample - double he number of nuclei and, on average, there will be double the number of [] per [] decays per second. The half-life of an isotope is the average time taken for half of the active nuclei to decay.
Technetiun-99m (T -99m) decays by gamma emission to technetium-99 (Tc-99) with a half-life of six hours. After six hours, on average, only half of the Tc-99m nuclei remain active. After another six hours, on AVERAGE, the amount of nuclei active is one quarter. This pattern is the same for all isotopes but the value of the half-life is different.Carbon-14 has a half-life of 5730 years, but some isotopes have a half-life of less than a s... econd.
Tc99m is one of the most widely used radioactive isotopes in medicine. It is used to diagnose problems in many organs. The half-life of six hours means that the radiation last only long enough for the isotope to travel to the [] being investigated organ being investigated. Its activity decreases rapidly and "cannot" be [] after a few [] detected after a few days. Tc-99m does not occur n... "naturally" - it is made in "reactors".
DATING. The amount of carbon-14 in a living objct is fixed when it dies. The carbon-14 d... decays, so that a wooden spear that is 5730 years old has only half the carbon-14 left that it had when it was made. Objects that once lived can be [] dated carbon dated by the amount of [] that is left carbon-14 that is left.
Some rocks contain a radioactive isotope of uranium that decays to lead, so they can be dated by the [] - [] [] uranium - lead ratio, the more lead there is, the [] the rock is. the older the rock is. Because of small amounts of isotopes involved, and the long half-lifes, these methods "cannot" be used to find dates to find dates to within []s of years tens of years. They are "not" useful for objects that are less then a [] years old. hundred years old.
NUCLEAR REACTORS
NUCLEAR FISSION. If a nucleus of uranium-235 absorb a neutron, it becomes very unstable and can be split into two nuclei of about equal size, and two or three neutrons. This process is called nuclear fission. When this happens, there is a release of a lot of nuclear energy, about a million times more than the energy released in a chemical reaction.
The neutrons released in nuclear fission can strike more uranium nuclei and cause more [] reactions fission reactions - which in turn produce more neutrons, and so on. This is called a chain reaction. If the fission reaction runs out of control it is an atomic bomb, but if the process is controlled, the energy released can be used to generate electricity. This is how a [] in a power station works. nuclear reactor in a power station works.
The fuel rods contain uranium-235 and are put in the reactor. The reaction can be [] or [] controlled or stopped by using a material that [] [] absorbs neutrons. The neutron absorbing material is made into control rods. The control rods are moved into the reactor to absorb neutrons, and [] or [] the reactions. slow or stop the reactions, and out of the reactor to increase the reaction.
The energy heats up the [] [] and [] [] fuel rods and control rods. A coolant is circulated to remove the heat from the reactor. When the coolant has been heated, it is used to heat water to steam for the power station. When the coolant is cool, it, again, circulated through the reactor.
Another isotope, instead of uranium-239, nucleus, is plutonium- 239.
WASTE DISPOSAL. Radioactive waste is dangerous to living things and must be carefully disposed of. "The half-life of some isotopes is thousands, or millions, of years, so radioactive material must be disposed of in a way that will keep it safely contained for thousands of years". There are three types of radioactive waste: low-level waste(for example, used protective clothing), intermediate-level waste(for example, material and reactors) and high-level waste(for example, used fuel rods). Low level waste can be, into containers, sealed and put in [] sites landfill sites. Intermediate-level waste is mixed with concrete and stored in stainless-steel containers. "It must be stored for thousands of years".
High-level was is kept, at first, in cooling tanks, because it [] so fast decays so fast it gets hot. Eventually it becomes intermediate-level waste. High-level waste includes '[] grade plutonium' 'weapon grade plutonium', which is the radioactive element plutonium, "produced in nuclear reactors". It can be used to make [] weapons nuclear weapons.
Waste can be dispersed (for example when sewage is discharged in the sea), or contained (for example when rubbish is put in a [] site landfill site). Some radioactive waste is too dangerous to be dispersed.
Where to store the waste? At the bottom of the sea - but containers may leak; under-[] underground - but containers may lead, and [] or other changes to the rocks may occur. earthquakes or other changes to the rocks; on the surface - but "needs guarding" (for example, from terrorists) for thousands of years."
|ENERGY|
THE EFFECT OF HEATING
Temperature and heat. Temperature is a measure of how [] an object is how hot an object is. The temperature scale we use measures temperature in degrees Celsius. On this scale 0 degrees is defined as the temperature at which [] [] [] pure ice melts - but temperatures can be much lower than this. Different temperatures can be shown on a [] - each colour represents a different temperature thermogram - each colour represents a different temperature. Heat is a form of energy. If an object is cooled until all the particles stop moving then they cannot lose any more [] energy kinetic energy. The amount of heat in the object is a minimum.
Specifice hear capacity. If the temperature of a solid, liquid or gas changes, then it has gained, or lost, energy. The amount of energy depends on: the temperature change, the object's mass, the object's material.
The specific heat capacity of a material is a measure of the material's energy. For different materials, it is different and tells us how much energy (in joules) you need to [] the [] raise the temperature of one kilogram of the material by one degree Celsius.
The specific heat capacity ('specific' means 'for each kilogram') heat capacity of a material is the [] needed energy needed to increase the temperature of 1kg of the material by 1 degree celsius: Energy = [] x [] x [] mass x specific heat capacity x temperature change. Specific heat capacity is measured in J / kg °C.
Latent heat. Heating an object raises its temperature except at the [] [] and [] [] melting point and boiling point. At these temperatures, the energy is being used to change the state, from solid to liquid, or liquid to gas. Because the temperature does not change, the heat given to the substance is called latent heat('latent' means hidden).
Solid objects are held together by forces between the particles([] or []) heated, [] more (atoms or molecules), and have a regular shape. The particles, as the object is vibrate more. Liquid particles have enough energy to break the inter-[] [] inter-molecular bonds and [] over each other. slide over each other.
At the melting point, heating the solid does not increase the vibrations, but gives the particles enough energy to [] the [] break the bonds. When a liquid freezes, it loses this energy to its surroundings.
Here is the equation relating energy to specific heat capacity: E = m × c × θ m × c × θ. E is the [] [] in [], [] E is the energy transferred in joules, J; m is the[...] in [] m is the mass of the substance in kg; c is the [] in [] c is the specific heat capacity in J / kg °C; θ (‘theta’) is the [...] in [...], [] θ (‘theta’) is the temperature change in degrees Celsius, °C.
Gas particles have enough energy to completely seperate. Heating the liquid completely breaks the []-[] [] inter-molecular bonds and the particles form a gas.
When an object changes from solid to liquid, there is a small increase in [] energy kinetic energy; when a liquid changes to gas, there is an [] that's [] increase that's bigger.
The specific latent heat of melting of a material is the [] in [] energy in joules "needed" to melt 1kg of the material without changing its temperature.
ALLEDGEDLY POSSIBLY
A radioactive nucleus is un stable and will emit radiation. The three main types or radioactive emissions are (with symbols) Alpha(α), Beta(β) and Gamma(γ).
Contamination or irradiation? If a person has a radioactive material on their skin or clothes, or has swallowed or inhaled it, this is called radioactive contamination. Over a period of time, the radioactive material will decay. This results in a higher dose of radiation than being exposed to a source that's external, because when a person moves away from the source they are no longer irradiated. This is especially true of the type of radiation that's alpha radiation. Unlike beta and gamma radiation, alpha radiation cannot penetrate the skin, so outside the body - a few centimetres away - it is not dangerous. But if a person inhales, or swallows, material that emits alpha particles, inside the body, the source will continue to emit until all the radioactive nuclei have decayed. This increases the risk of cancer.
Created by: Toluo