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Nuclear Reaction And Radioacticity

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In this ppt,following topics are discussed. content- nuclear reaction natural radioactivity nuclear reaction the nature of nucleus type of radioactive decay measurement of radiation radiation units radiation exposure nuclear energy nuclear fusion nuclear fission.

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    Nuclear reaction and Radioactivity. BY- TAMANG
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    @NucIear Reactions Decisions about nuclear energy require some understanding of nuclear reactions and the nature of radioactivity. This is one of the three units of Palo Verde Nuclear Generating Station in Arizona. With all three units running, enough power is generated to meet the electrical needs Of nearly 4 million people.
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    Natural Radioactivity — Henri Becquerel discovered radioactivity in 1896 Becquerel named the emission of invisible radiation from uranium ore radioactivity. Radioactive materials was the name given to materials that gave off this invisible radiation. ' Radioactivity was discovered by Henri Becquerel when he exposed a light-tight photographic plate to a radioactive mineral, then developed the plate. (A) A photographic film is exposed to an uranite ore sample. (B) The film, developed normally after a four-day exposure to uranite. Becquerel found an image like this one and deduced that the mineral gave off invisible radiation that he called radioactivity.
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    Ernest Rutherford later discovered that there were three kinds of radioactivity. Alpha particles (u) is a helium nucleus (2 protons and 2 neutrons) A beta particle (ß) is a high energy electron gamma ray (y) is electromagnetic radiation A with a very short wavelength. Radiation passing through a magnetic field shows that massive, positively charged alpha particles are deflected one way, and less massive beta particles with their negative charge are greatly deflected in the opposite direction. Gamma rays, like light, are not deflected.
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    — Radioactivity is the spontaneous emission of particles or energy from an atomic nucleus as it disintegrates. — Radioactive decay is the spontaneous disintegration of decomposition of a nucleus. container ray u particle Il particle South pole North pole Radioactive source
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    Nuclear Equations The two subatomic particles that occur in the nucleus, the proton and the neutron, are called nucleons. The number of protons is the atomic number O which determines the identity of the element. The number of protons and neutrons determines O the atomic mass of the element. Different isotopes Of an have the O atomic number (same number of protons) but different atomic masses (different number of neutrons)
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    The three isotopes of hydrogen have the same number of protons but different numbers of neutrons. Hydrogen-I is the most common isotope. Hydrogen-2, with an additional neutron, is named deuterium. Hydrogen-3 is called tritium. Neutrons and protons are called nucleons because they are in the nucleus. Hydrogen-I 31-1 (tritium) (deuterium) Mass number Atomic number
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    o Just like any other chemical reaction, we use symbols to show a nuclear reaction As an example, when uranium 238 emits O an alpha particle, it loses 2 protons and 2 neutrons. 238U - -93940Th+24He 92 Nuclear reactions must balance just like any other chemical reaction, but we must also be aware of balancing protons and neutrons
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    The Nature of the Nucleus. Protons and neutrons are held together by a nuclear force when they are very close together. The shell model of the nucleus visualizes the protons and neutrons moving on energy levels or shells, much like the electrons move in shells. We can predict the stability of a nucleus by using some simple rules All isotopes heavier than atomic number 83 have an unstable nucleus Isotopes with 2, 8, 20, 28, 50, 82, or 126 protons or neutrons in their nucleus occur in the most stable isotopes. Nuclei are the most stable with pairs of protons and neutrons, so those with all protons and all neutrons paired up are the most stable. Isotopes with an atomic number less that 83 are most stable when the ratio of protons to neutrons is 1 :1 .
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    The dots indicate stable nuclei, which group in a band of stability according to their neutron-to- proton ratio. As the size of nuclei increases, so does the neutron-to-proton ratio that represents stability. Nuclei outside this band of stability are radioactive. 150 140 130 120 110 100 90 80 Q) 70 50 40 30 20 10 1.5:1 ratio area Band of stability 1.25:1 ratio area 1:1 ratio area ratio line 10 20 30 40 50 60 70 80 90 100 Number of protons
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    Type of Radioactive Decay Alpha emission This is the expulsion of an alpha parti O Beta Emission Emission of a beta particle O a beta particle is an electron that is ejected form O the nucleus Gamma emission This is a high energy burst of electromagnetic O radiation Emission occurs as nuclei try to obtain a balance between nuclear attractions, electromagnetic repulsions, and a low quantum of nuclear shell energy.
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    Unstable nuclei undergo different types of radioactive decay to obtain a more stable nucleus. The type Of decay depends, in general, on the neutron-to-proton ratio, as shown. 0 150 140 130 120 110 100 90 80 70 60 50 40 30 20 10 Region of beta emission Alpha emissio Region of other decay processes 60 70 80 90 100 0 10 20 30 40 50 Number of protons
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    Radioactive Decay Series Radioactive decay produces a simpler and more stable nucleus. A radioactive decay series occurs as a nucleus disintegrates and achieves a more stable nuclei There are 3 naturally occurring radioactive decay series. O O O Thorium 232 ending in lead 208 Uranium 235 ending in lead 207 Uranium 238 ending in lead 206
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    238 92 92 91 87 86 85 83 82 238 pa 2 34 230 226 222 Mass nurnber 218 21 4 210 206 The radioactive decay series for uranium-238. This is one of three naturally occurring series. When there are a large number of nuclei the ration of the rate of nuclear decay per unit time to the total number of radioactive nuclei will be a constant k=rate O o n The radioactive decay constant is specific for each isotope
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    The rate of radioactive decay is expressed in terms of half-life Of an element is the required The half-life o from one-half of its unstable nuclei to decay The half-life of an element is related to the ration o of 0.693 to its radioactive decay constant = 0.6931k for IJ238 is 4.87 X 10-18/s The decay constant O The half life is therefore O = 0.693/4.87 X 10-18/s = 1.42 X 1017s = 4.5 X 1 09 years The half-life of U238 is 4.5 billion years. O
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    ,ooo 900 800 700 600 500 400 300 200 .ocn gra rns 500 g rarns 250 _gr._ryms 1 25 grarns Radioactive decay of a hypothetical isotope with a half-life of one day. The sample decays each day by one-half to some other element. Actual half-lives may be in seconds, minutes, or any time unit up to billions Of years.
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    4.5 X 109 yr 238 234 24.1 days 234 1.1 min 234 920 230 90 218 84 214 84 90 2.7 X yr 8.3 X yr 226 1.62 X 103 yr 222 88 Ra 86 Rn 3.83 days 3.05 min 214 26.8 min 214 82 83 13.1 min 1.5 X 104 sec 210 82 140 days 206 210 22 yr 210 83 Bl 5 days 82 o 82 The half-life of each step in the uranium-238 radioactive decay series.
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    Measurement of Radiation @ Measurement Methods Film badges Workers who are exposed to radioactivity carry film badges The film is exposed and the optical density of the film shows the workers exposure levels during the time the film badge was worn. Ionization counter. Measure ions that are produced by radiation Scintillation counter. Measures the flashes of light that occur when radiation strikes a phosphor. Geiger counter Measures pulses of electrons released from the ionization of gas molecules in a metal cylinder Each pulse of electrons is heard as a pop or click
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    This is a beta-gamma probe, which can measure beta and gamma radiation in millirems per unit of time.
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    Radiation Units , Curie (Ci) Measurement of the activity of a radioactive source. o Measured as the number of nuclear disintegrations per unit of time o A curie is 3.70 X 1010 nuclear disintegrations per second. o , Rad Measures the amount of energy released by radiation striking living o tissue Short for radiation absorbed dose O One rad releases 1 X 10-2 J/kg , Rem Short for roetgen equivalent man This takes into account the possible biological damage to humans o O certain types of radiation.
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    Radiation Exposure Background radiation is constantly present in our environment. Most people are exposed to between 100 to 500 millirems per year. This background radiation comes from many natural source. The harm that radiation does to living organisms is due to the fact that it produces ionization which can: Disrupt chemical bonds in biological macromolecules such as DNA Produce molecular fragments which can interfere with enzyme action O and essential cell functions. The linear model of exposure proposes that any exposure above zero is damaging and can produce cancer and genetic damage, mostly through its effect on DNA The threshold model proposes that there is a threshold limit of exposure up to which the human body can repair damage caused by the exposure It is not until we reach and exceed this threshold that we begin to see irreversible damage.
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    Nuclear Energ @ Introduction. Albert Einstein showed us that energy and matter are the same thing, both are inter-convertible. E-=mc2 Using mass losses during nuclear reactions, one can calculate the energy change of a system. AE=Amc2 There is a difference between the mass of the individual nucleons that make up a nucleus and the actual mass of the nucleus. This is called the mass defect of the nucleus. The mass defect occurs as energy is released when nucleons join to form a nUCIeUS.
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    The energy that is released is called the binding energy This is also the energy that is required to break the nucleus into its individual protons and neutrons. The ratio of the binding energy to the nucleon number is a measure of O a nucleus' stability 0 Massive nuclei can gain stability by breaking into smaller nuclei with a release of energy. 0 Smaller nuclei can gain stability by joining together with the release of energy. I ron —5 6 2-0 0.0 8-0 6.0 2-0 50 Fission a 50 mnass nurnber 200 2 50 The maximum binding energy per nucleon occurs around mass number 56, then decreases in both directions. As one result, fission of massive nuclei and fusion of less massive nuclei both release energy.
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    Splitting massive nuclei apart with the release of energy is called nuclear fission. The joining together of less massive nuclei with the release of energy is called nuclear fusion. @ Nuclear Fission As a nuclear reaction occurs, it has the ability to produce a chain reaction 0 A chain reaction is a reaction where the products are able to produce more products in a self-sustaining reaction series. In order to achieve a chain reaction there must be: A sufficient mass. O A large concentration of fissionable nuclei The critical mass is when the mass and concentration are high enough to sustain a chain reaction. A sub-critical mass is one that is too small to achieve a chain reaction.
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    236 92 235 92 The fission reaction occurring when a neutron is 92 36 141 56 absorbed by a uranium-235 nucleus. The deformed nucleus splits any number of ways into lighter nuclei, releasing neutrons in the process.
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    A schematic representatiOn Of a chain reaction. Each fissioned nucleus releases neutrons, which move out to fission other nuclei. The number of neutrons can increase quickly With each series. eoi 000 235 92 Noutrons Frssion prod'*ts
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    Nuclear fusion If light nuclei are forced together, they will fuse with a yield of energy because the mass of the combination will be less than the sum of the masses of the individual nuclei. If the combined nuclear mass is less than that of iron at the peak of the binding energy curve, then the nuclear particles will be more tightly bound than they were in the lighter nuclei, and that decrease in mass comes off in the form of energy according to the Einstein relationship. For elements heavier than iron, fission will yield energy. For potential nuclear energy sources for the Earth, the deuterium-tritium fusion reaction contained by some kind of magnetic confinement seems the most likely path. However, for the fueling of the stars, other fusion reactions will dominate.
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    Nuclear Fusion Deuterium cc Tritium Fusion Helium Energy , Neutron
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    ΤΗΑΝΚ γου


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