Folio Radioactivity Ting 5

Radioactivity - Introduction All substances are made of atoms. These have electrons (e) around the outside, and a nucleus in the middle.

The nucleus consists of protons (p) and neutrons (n), and is extremely small. (Atoms are almost entirely made of empty space!)

In some types of atom, the nucleus is unstable, and will decay into a more stable atom. This radioactive decay is completely spontaneous.

This form of Lithium is not radioactive - it's just an example of a simple atom. Most radioactive substances have many more particles in their nucleus.

You can heat the substance up, or subject it to high pressure or strong magnetic fields - in fact, do whatever you like to it - and you won't affect the rate of decay in the slightest.

When an unstable nucleus decays, there are three ways that it can do so. It may give out:•

an alpha particle (we use the symbol á)

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a beta particle (symbol â)

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a gamma ray (symbol )

Many radioactive substances emit á particles and â particles as well as rays. In fact, you won't find a pure source; anything that gives off rays will also give off á and/or â too.

Types of Radioactive Rays Alpha Alpha radiation is a heavy, very short-range particle and is actually an ejected helium nucleus. Some characteristics of alpha radiation are: •

Most alpha radiation is not able to penetrate human skin.

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Alpha-emitting materials can be harmful to humans if the materials are inhaled, swallowed, or absorbed through open wounds.

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A variety of instruments has been designed to measure alpha radiation. Special training in the use of these instruments is essential for making accurate measurements.

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A thin-window Geiger-Mueller (GM) probe can detect the presence of alpha radiation.

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Instruments cannot detect alpha radiation through even a thin layer of water, dust, paper, or other material, because alpha radiation is not penetrating.

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Alpha radiation travels only a short distance (a few inches) in air, but is not an external hazard.

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Alpha radiation is not able to penetrate clothing.

Examples of some alpha emitters: radium, radon, uranium, thorium.

Alpha Particles Alpha particles are made of 2 protons and 2 neutrons. This means that they have a charge of +2, and a mass of 4 (the mass is measured in "atomic mass units", where each proton & neutron=1) Alpha particles are relatively slow and heavy. They have a low penetrating power - you can stop them with just a sheet of paper. Because they have a large charge, alpha particles ionise other atoms strongly.

Beta Beta radiation is a light, short-range particle and is actually an ejected electron. Some characteristics of beta radiation are: •

Beta radiation may travel several feet in air and is moderately penetrating.

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Beta radiation can penetrate human skin to the "germinal layer," where new skin cells are produced. If high levels of beta-emitting contaminants are allowed to remain on the skin for a prolonged period of time, they may cause skin injury.

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Beta-emitting contaminants may be harmful if deposited internally.

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Most beta emitters can be detected with a survey instrument and a thin-window GM probe (e.g., "pancake" type). Some beta emitters, however, produce very low-energy, poorly penetrating radiation that may be difficult or impossible to detect. Examples of these difficult-todetect beta emitters are hydrogen-3 (tritium), carbon-14, and sulfur35.

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Clothing provides some protection against beta radiation.

Examples of some pure beta emitters: strontium-90, carbon-14, tritium, and sulfur-35. Beta Particles Beta particles have a charge of minus 1, and a mass of about 1/2000th of a proton. This means that beta particles are the same as an electron. They are fast, and light. Beta particles have a medium penetrating power - they are stopped by a sheet of aluminium or plastics such as Perspex. Beta particles ionise atoms that they pass, but not as strongly as Alpha particles do.

Gamma Gamma radiation and x rays are highly penetrating electromagnetic radiation. Some characteristics of these radiations are: •

Gamma radiation or x rays are able to travel many feet in air and many inches in human tissue. They readily penetrate most materials and are sometimes called "penetrating" radiation.

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X rays are like gamma rays. X rays, too, are penetrating radiation. Sealed radioactive sources and machines that emit gamma radiation and x rays respectively constitute mainly an external hazard to humans.

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Gamma radiation and x rays are electromagnetic radiation like visible light, radio waves, and ultraviolet light. These electromagnetic radiations differ only in the amount of energy they have. Gamma rays and x rays are the most energetic of these.

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Dense materials are needed for shielding from gamma radiation. Clothing provides little shielding from penetrating radiation, but will prevent contamination of the skin by gamma-emitting radioactive materials.

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Gamma radiation is easily detected by survey meters with a sodium iodide detector probe.

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Gamma radiation and/or characteristic x rays frequently accompany the emission of alpha and beta radiation during radioactive decay. Examples of some gamma emitters: iodine-131, cesium-137, cobalt-60, radium-226, and technetium-99m.

Gamma Rays

Gamma rays are waves, not particles. This means that they have no mass and no charge. Gamma rays have a high penetrating power - it takes a thick sheet of metal such as lead, or concrete to reduce them significantly. Gamma rays do not directly ionise other atoms, although they may cause atoms to emit other particles which will then cause ionisation. We don't find pure gamma sources - gamma rays are emitted alongside alpha or beta particles. Strictly speaking, gamma emission isn't 'radioactive decay' because it doesn't change the state of the nucleus, it just carries away some energy.

Radioactive decay Radioactive decay is the process in which an unstable atomic nucleus spontaneously loses energy by emitting ionizing particles and radiation. This decay, or loss of energy, results in an atom of one type, called the parent nuclide transforming to an atom of a different type, called the daughter nuclide. For example: a carbon-14 atom (the "parent") emits radiation and

transforms to a nitrogen-14 atom (the "daughter"). This is a random process on the atomic level, in that it is impossible to predict when a given atom will decay, but given a large number of similar atoms the decay rate, on average, is predictable. Alpha Decay In alpha decay, the nucleus emits an alpha particle; an alpha particle is essentially a helium nucleus, so it's a group of two protons and two neutrons. A helium nucleus is very stable. An example of an alpha decay involves uranium-238:

The process of transforming one element to another is known as transmutation. Alpha particles do not travel far in air before being absorbed; this makes them very safe for use in smoke detectors, a common household item.

Beta decay A beta particle is often an electron, but can also be a positron, a positively-charged particle that is the anti-matter equivalent of the electron. If an electron is involved, the number of neutrons in the nucleus decreases by one and the number of protons increases by one. An example of such a process is:

In terms of safety, beta particles are much more penetrating than alpha particles, but much less than gamma particles.

Gamma decay The third class of radioactive decay is gamma decay, in which the nucleus changes from a higher-level energy state to a lower level. Similar to the energy levels for electrons in the atom, the nucleus has energy levels. The concepts of shells, and more stable nuclei having filled shells, apply to the nucleus as well. When an electron changes levels, the energy involved is usually a few eV, so a visible or ultraviolet photon is emitted. In the nucleus, energy differences between levels are much larger, typically a few hundred keV, so the photon emitted is a gamma ray. Gamma rays are very penetrating; they can be most efficiently absorbed by a relatively thick layer of high-density material such as lead. A list of known nuclei and their properties can be found in the chart of the nuclides at the Brookhaven National Laboratory.

Radioactive Decay Seiries A radioactive decay series is the chain of decays that occur starting with a radioactive isotope. An example of this is the uranium-radium series: Uranium-238

decays

Thorium-234 decays

thorium-234

protactinium-234

Protactinium-234 ß decays to form uranium-234 Uranium-234 Thorium

decays decays

thorium-230 radium-226

Radium-226 goes through five more decays and four more ß decays to yield the non-radioactive isotope 206Pb, or lead. This series is also called the 4n+2 series, because the mass numbers of each of the isotopes in the series can be represented by 4n+2, where n is an integer. The thorium series is a 4n series; it starts at thorium-232 and the end result is 208>Pb. The actinium series, or 4n+3 series, begins with uranium-235 and ends at Pb-207.

Half life of radioactive elements The half-life of a radioactive element is the time that it takes for one half of the atoms of that substance to disintegrate into another nuclear form. These can range from mere fractions of a second, to many billions of years. In addition, the half-life of a particular radionuclide is unique to that radionuclide, meaning that knowledge of the half-life leads to the identity of the radionuclide.

 The Half-Life From A Decay Curve

256 →128 T1/2 T1/2= radioactive decay

T1/2 = 3 hours

Define Isotope Isotopes (Greek isos = "equal", tópos = "site, place") are any of the different types of atoms (nuclides) of the same chemical element, each having a different atomic mass (mass number). Isotopes of an element have nuclei with the same number of protons (the same atomic number) but different numbers of neutrons. Therefore, isotopes of the same element have different mass numbers (number of nucleons).

Radioisotope A radioactive form of an element. A radioisotope consists of unstable atoms that undergo radioactive decay emitting alpha, beta or gamma radiation. Radioisotopes occur naturally, as in the cases of radium and uranium, or may be created artificially. Applications of Radioactivity and Radioisotopes  Radioisotopes find numerous uses in different areas such as medicine, chemistry, biology, archaeology, agriculture, industry and engineering.  Tracer Techniques Radioisotopes are frequently used as tracers or tagged atoms in various fields. In tracer technique, a radioactive isotope is added to the reactants and its movement is studied by measuring radioactivity in different parts. In medicine  In order to find if blood is circulating to a wound or not, a radioactive isotope is injected into the blood stream. After a time period, blood from the wound is examines for its radioactivity. If no radioactive isotope is detected, it means that passage of blood is hindered. The rate of circulation can also be detected by this method.  Tracer technique is also used for the detection of thyroid disorder and brain tumours.

 Cancer therapy g - rays emitted by the radioisotopes can be used in the treatment of cancer. These radiations tend to destroy cancerous cells and the way can arrest the spreading of the cancerous cells. 60CO is used in the treatment of tumours and cancers.

In Agriculture  The uptake of phosphorous by plants is studied by mixing radioactive phosphorous with phosphatic fertilisers. In Chemistry  Tracer technique is used To find the solubility of sparingly soluble salt like lead sulphate. A lead salt containing known amount of radioactive lead is dissolved in water. Sulphuric acid is added to the aqueous solution to precipitate lead as lead sulphate.  Tracer technique is also used to study the path or mechanism of the reaction.  Consider the reaction The question is how does the elimination of water take place - does the oxygen atom in water come from the alcohol or acid. This is studied by labelling or tagging the oxygen in the alcohol molecule. In other words, the alcohol is prepared with O18. Results show that the ester formed has the radioactive oxygen. This shows that the starred oxygen comes from the alcohol. Thus the -OH group of the acid and the H atom of the alcohol are eliminated in the form of water.

Dangers of Radioactive Rays The main danger from radioactivity is the damage it does to the cells in your body. Most of this damage is due to ionisation when the radiation passes, although if levels of radiation are high there can be damage due to heating effects as your body absorbs the energy from the radiation, rather like heating food in a microwave oven. This is particularly true of gamma rays.

Alpha Particles ( ) Alpha particles are slow, have a short range in air, and can be stopped by a sheet of paper. You might therefore assume that alpha particles are the least dangerous of the three types of radiation.

Whilst they cannot penetrate your skin, you could easily eat or drink something contaminated with an source. This would put a source of particles inside your body, wreaking havoc by ionising atoms in nearby cells. If this happens to part of the DNA in one of your cells, then that cell's instructions about how to live and grow have been scrambled. The cell is then likely to do something very different to what it's supposed to do, for example, it may turn cancerous and start multiplying uncontrollably. Thus alpha particles, whilst they have a low penetrating power, can be the most dangerous because they ionise so strongly.

Beta Particles ( ) -particles have a longer range than 's, but ionise much less strongly, with the result that they do around 1/20th of the damage done by the same dose of alpha particles. However, they do have more penetrating power, which means that they can get through your skin and affect cells inside you.

Gamma Rays ( ) Gamma rays hardly ionise atoms at all, so they do not cause damage directly in this way. However, gamma rays are very difficult to stop; you require lead or concrete shielding to keep you safe from them. When they are absorbed by an atom, those atom gains quite a bit of energy, and may then emit other particles. If that atom is in one of your cells, this is not good!

Nuclear Energy Nuclear energy is released by the splitting (fission) or merging together (fusion) of the nuclei of atom(s). The conversion of nuclear mass to energy is consistent with the mass-energy equivalence formula ΔE = Δm.c², in which ΔE = energy release, Δm = mass defect, and c = the speed of light in a

vacuum (a physical constant). Nuclear energy was first discovered by French physicist Henri Becquerel in 1896, when he found that photographic plates stored in the dark near uranium were blackened like X-ray plates, which had been just recently discovered at the time 1895.  Atomic Mass Unit

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The atomic mass unit it the unit of mass for atoms and subatomic particles such as the proton, neutron an electron • 1 atomic mass unit or 1 u is 121 of the mass of the carbon-12 atom. • The mass of one carbon-12 atom is 1.99265 x 10-26 kg ∴ 1 u = 261099265.1121−×× kg 1 u = 1.66 x 10-27 kg  Mass defect Definition: The distance between theoretical calculated mass and experimentally measured mass of nucleus is called mass defect. It is denoted by Δm. It can be calculated as follows: Mass defect = (Theoretical calculated mass) - (measured mass of nucleus) i.e, (sum of masses of protons and neutrons) - (measured mass of nucleus) - In nuclear reactions, the energy that must be radiated or otherwise removed as binding energy may be in the form of electromagnetic waves, such as gamma radiation, or as heat. Again, however, no mass deficit can in theory appear until this radiation has been emitted and is no longer part of the system. - The energy given off during either nuclear fusion or nuclear fission is the difference between the binding energies of the fuel and the fusion or fission products. In practice, this energy may also be calculated from the substantial mass differences between the fuel and products, once evolved heat and radiation have been removed. - When the nucleons are grouped together to form a nucleus, they lose a small amount of mass i.e. There is mass defect. This mass defect is released as (often radiant) energy according to the relation E = mc2; thus binding energy = mass defect * c2 . This energy holds the nucleons together and is known as binding energy. In fact, mass defect is a measure of the binding energy of the nucleus. The greater the mass defect, the greater is the

binding energy of the nucleus.  Nuclear Fussions • Nuclear fission is the splitting of a heavy nucleus into two lighter nuclei • Fission occurs when the nucleus of an atom is bombarded with a neutron. • The energy of the neutron causes the target nucleus to split into two (or more) nuclei that are lighter than the parent nucleus, releasing a large amount of energy during the process. Problem Solving Involving Nuclear Fussion The relationship between the mass and the energy: E = mc2 Where E = energy released, in joules, J m = loss of mass or mass defect, in kg c = speed of light = 3.0 x 108 m/s

Example of nuclear power plant

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A nuclear reactor -

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It produces tremendous amount of energy through nuclear fission. Uranium fuel rods

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The nuclei are split by neutrons in a controlled chain reaction, releasing a large amount of energy. The energy released heats up the cold gas that passes through the reactor core. Graphite moderator

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Acts as a moderator to slow down the fast neutrons produced by the fission. Slower neutrons are more readily captured by the uranium nuclei.] Boron or cadmium control rod

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The boron control rods absorb neutrons. It can control the rate of fission reaction. When rods are lowered into the reactor core to absorb some of the neutrons, the rate of the fission reaction reduced. Concrete shield

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Prevents leakage of radiation from the reactor core.

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Coolant -

Take away the heat from the nuclear reactor. Substances with high specific heat capacity such as water and carbon dioxide are used.

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Heat exchanger -

Heat energy from the very hot gas is used to boil the water into steam

Importance Of Propermanagment Of Radioactive Substance The negative effects of radioactive substance Somatic effects

Genetic effects

Radiation burns

Cancer

Leukemia

Birth defects

Organ failure

Down Syndrome

Vomitting

Turner Syndrome

Hair loss

Klinefelter Syndrome

Fatigue Skin burn Safety precautions needed in handling of radioactive substances - Radioactive material is sealed in special designed containers - Radioactive contamination may exist on surfaces or in volume of air - Workers should work behind shields - Weak radioactive sources are to be handled with forceps - Food and drinks are prohibited in the laboratory

The management of radioactive waste  High-level radioactive waste Spent fuel is highly radioactive and needs to be handled with great care and forethought. However, spent nuclear fuel becomes less radioactive over the course of thousands of years of time. After about 5 percent of the rod has reacted the rod is no longer able to be used. Today, scientists are experimenting on how to recycle these rods to reduce waste. In the meantime, after 40 years, the radiation flux is 99.9% lower than it was the moment the spent fuel was removed, although still dangerously radioactive.

 Low-level radioactive wast The nuclear industry also produces a huge volume of low-level radioactive waste in the form of contaminated items like clothing, hand tools, water purifier resins, and (upon decommissioning) the materials of which the reactor itself is built. In the United States, the Nuclear Regulatory Commission has repeatedly attempted to allow low-level materials to be handled as normal waste: landfilled, recycled into consumer items, et cetera.[citation needed] Most low-level waste releases very low levels of radioactivity and is only considered radioactive waste because of its history.