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
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
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
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
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
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
7.3 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
Some common values: 0.00 001 Sv = 1 (1 micro sievert) 0.00 01 Sv = 100 X-ray - teeth or chest 0.005 = 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 - 131 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
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
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