Increasing Energy Decreasing Energy Increasing Frequency Decreasing Frequency Decreasing Wavelength Increasing Wavelength

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Caroline Cannon
7 years ago
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1 Chapter 7 Radiation and Nuclear Energy radiation - energy given off by a body electromagnetic radiation - energy which is made up of a varying electrical field and a varying magnetic field. The fields travel as waves which are N Sync with each other and travel at right angles to each other. (Eg. Sun energy) Increasing Energy Decreasing Energy Increasing Frequency Decreasing Frequency Decreasing Wavelength Increasing Wavelength Rules - - high frequency = high energy = short wave length - low frequency = low energy = long wave length 1

2 wave length - ( λ )the distance between two peaks or two valleys or two 0 values frequency - ( f ) how many waves pass by a certain point in 1 second 7.2 Radiation from Atoms Normal proton-proton repulsion in the nucleus of an atom nuclear force - the neutrons help serve as a weak atomic glue * or a buffer between (+) protons. (keeps nucleus together) 2

3 So most nuclei of atoms are stable. However, some nuclei will give off particles (will slowly break apar isotopes - means same type. variations of atoms of the same element which have: a) the same number of protons (same atomic number) b) the same number of electrons (to balance charge) c) different number of neutrons (different atomic mass) atomic number = number of protons = number of e- atomic mass = number of protons + number of n Eg Hydrogen-1 Hydrogen-2 Hydrogen-3 Deuterium Tritium Eg. Carbon -12 Carbon -13 Carbon -14 Types of Radiation alpha decay (α decay) occurswhen an atom loses an alpha particle. Alpha particle are really just Helium nuclei (a.k.a 4 2 He ++ ) just two protons and two neutrons (2n / 2p) in one little packet. You can also write an alpha particle like this: 4 2α 3

4 Whenever α-decay happens the atomic mass of the atom goes down 4 amu and 2 protons are lost; so a NEW ELEMENT is formed. This change to a new element is called transmutation. beta decay (β-decay) under special circumstances a neutron can change into a proton and an electron. n p(+) + e- You can also write beta decay like this 0-1e. The proton stays in the nucleus but the new electron shoots out! So - atomic mass stays the same but atomic number increases by one. Therefore, new element is formed and transmutation has occurred 4

5 gamma decay ( γ decay ) sometimes in α-decay or β decay the resulting nucleus has extra energy making it unstable. Gamma decay happens when that energy is given off! (NO loss of particles - just energy) 5

6 Type Electrical Description Charge alpha 2+ (+2n) He nucleus. Low energy. Low penetrating power beta -1 Hi energy electron Moderate energy Moderate penetrating power gamma 0 Electromagnetic radiation High energy High penetrating power * Effects of electrical magnetic force radioactivity the number of decays/second measured in becquerels (Bq) Eg. Unknown A has 125 decays (or emission) in 5 seconds 125 decays = 5 seconds = 25 Bq the activity of unknown A half life - the time it takes for a sample of an element to lose half its mass by decay 6

7 7.3 Radiation on Living Organisms natural background radiation - radioactive substances in earth and water cosmic radiation (from space) hazardous radiation - α, β, γ from nuclear decay UV, X-ray (sun and nuclear decay) ionizing radiation - causes damage when radiation knocks out an element in atoms in the cell DNA causes cancer (cell division gone crazy) causes mutations (changes in DNA) *N.B.radiation that goes right through is not dangerous...absorbed radiation is! Radiation doses for living things is measured in Sieverts (Sv). 7

8 Some common values: Sv = 1 (1 micro sievert) Sv = 100 X-ray - teeth or chest = recommended maximum yearly 0.25 = no visible change 1.0 = damage to blood forming cells 5.0 = death in a few days or weeks Protection against harmful radiation- - lead so dense that it stops most radiation - sun screen against UV radiation - distance - stay back from a source (microwaves for example) - time - avoid long periods of exposure (sun burn) Uses of radiation - medical X ray radiographs Technetium 99 (radioactive dye). γ- radiation for detecting tumors. Iodine magic bullet. β-decay finds and destroys hyper active thyroid gland Strontium - 89 magic bullet. β-decay finds and destroys bone cancer (It is similar to calcium so body thinks it is taking up calcium instead.) X-ray/γ-ray bombardment of cancers Uses of radiation - Nuclear Energy By splitting uranium atoms it is possible to produce huge amounts of energy which can be used to produce electricity. 8

9 In a nuclear reaction a neutron entering the nucleus of the parent fuel atom causes it to split apart. This releases a HUGE amount of energy PLUS three more neutrons to continue the chain reaction. nuclear reactor - a device to a) control the speed of a chain reaction b) harness the energy released from nuclear fission. Control is by The gas pedal - a moderator such as graphite on heavy water. These slow the speed of neutrons so too fast neutrons don t just go right through. Instead they are slowed enough to react with more uranium atoms. The brakes - cadmium or boron control rods which absorb excess neutrons. These are retractable such that more or less neutrons can be made available to slow or speed up reactions. critical mass - the minimum amount of fuel needed for nuclear fission to continue - usually a few kilograms of U-235 Harnessing is via using the heat energy to produce steam from circulating water. Steam then turns electric turbo-generators. 9

10 Nuclear Fusion The idea - to produce large amounts of energy by joining two smaller nuclei into a larger one (Eg. hydrogen) The problem - need 1000,000,000 degrees C in order for nuclei to move fast enough. SO no workie yet! Fusion bombs - Hydrogen bombs - produce huge heat and very devastating 10

1. In the general symbol cleus, which of the three letters. 2. What is the mass number of an alpha particle?

1. In the general symbol cleus, which of the three letters Z A X for a nu represents the atomic number? 2. What is the mass number of an alpha particle? 3. What is the mass number of a beta particle? 4.