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280 lines
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<!-- #BeginEditable "Body" -->
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<h1 class="center">Radiation</h1>
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<p style="float:right; margin: 0 0 5px 10px;"><img src="../measure/images/sun-dog.jpg" width="156" height="255" alt="sun dog" /></p><p> </p>
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<p>Radiation is energy moving through space or matter.</p>
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<p>Radiation can be:</p>
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<ul>
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<li><a href="electromagnetic-spectrum.html">electromagnetic waves</a> like infrared, light, X-rays, etc</li>
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<li>mechanical waves like <a href="waves-sound.html">sound waves</a> and <a href="waves-seismic.html">seismic waves</a>, or</li>
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<li>particles like alpha particles and beta particles (more on those later)</li>
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</ul>
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<div style="clear:both">
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<h2>Words</h2>
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</div>
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<p>Radiation is <b>emitted</b> from a source, <b>transmitted</b> to a destination, where it can be <b>absorbed</b>.</p>
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<p class="center"><img src="images/radiation-names.svg" alt="radiation Sun emit, transmit, absorb at Earth" /><br>
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Here the Sun is the source<br>
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and the Earth is the destination</p>
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<p> </p>
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<p>Radiation can also be <b>scattered</b> when hitting particles along the way, as well as <a href="reflection.html">reflected</a>, <a href="refraction.html">refracted</a> and <a href="diffraction.html">diffracted</a> (read up on those topics to learn more).</p>
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<p class="center"><img src="images/light-beam.jpg" width="594" height="191" alt="light beam" /><br>
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Here we see light (a type of radiation) being <b>scattered</b> by the atmosphere.</p>
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<div class="example">
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<h3>Example: Microwave Oven</h3>
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<p class="center"><img src="images/microwave-works.svg" alt="microwave magnetron, stirrer, pie absorbs" /><br>
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the magnetron <b>emits</b> microwaves
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which get <b>reflected</b> off a stirrer and the sides<br>
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until <b>absorbed</b> by food.</p>
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</div>
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<h2>Intensity</h2>
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<p>We can measure radiation <b>intensity</b> at any location as <b>power per area</b>: usually Watts per square meter (W/m<sup>2</sup>).</p>
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<p>As it spreads out on its journey, the intensity gets less.</p>
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<p class="center"><img src="images/light-intensity.svg" alt="light intensity" /></p>
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<h2>Inverse Square</h2>
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<p>In fact the intensity changes as the Inverse Square of the distance.</p>
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<table style="border: 0; margin:auto;">
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<tr>
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<td><span class="larger"><img src="../algebra/images/proportion-inverse-square.svg" alt="brightness decreases by the square of the distance" /></span></td>
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<td class="larger"><span class="center"><b>Inverse Square</b></span>: when one value <b>decreases</b> as the square of the other value.</td>
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</tr>
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</table>
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<div class="example">
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<h3>Example: Light and distance</h3>
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<p>The further away we are from a light, the less bright it is.</p>
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<p class="center"><img src="images/inverse-square-law.svg" alt="inverse square law: distance=1 area=1 intensity=1, distance=2 area=4 intensity=0.25, distance=3 area=9 intensity=0.111..." /></p>
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<p>The brightness decreases as the <b>square</b> of the distance.</p>
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<p>Because:</p>
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<ul>
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<li>the energy twice as far away is spread over 4 times the area</li>
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<li>the energy 3 times as far away is spread over 9 times the area</li>
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<li>etc</li>
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</ul>
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</div>
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<h2>Absorbing!</h2>
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<p>As radiation gets <b>absorbed</b> it <b>loses intensity</b>.</p>
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<p>Materials <b>vary</b> in how much they absorb different types of radiation.</p>
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<p style="float:right; margin: 0 0 5px 10px;"><img src="images/feet-fire.jpg" width="220" height="141" alt="feet fire" /></p>
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<p>When energy is absorbed the material may:</p>
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<ul>
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<li>heat up</li>
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<li>produce electric currents (such as in aerials/antennas)</li>
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<li>help with chemical reactions (like photosynthesis)</li>
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<li>ionize atoms</li>
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</ul>
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<h2>Ionizing Radiation</h2>
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<p style="float:right; margin: 0 0 5px 10px;"><img src="images/ionizing-atom2.svg" alt="ionizing atom" /></p>
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<p><b>High energy </b> radiation is <b>ionizing</b>, meaning it can knock electrons out of atoms.</p>
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<p> </p>
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<p>Losing an electron makes the atom <b>charged</b> and more likely to form new chemical reactions which can be <b>harmful to our cells</b>.</p>
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<p>The cells can die or change so they grow out of control and form cancer.</p>
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<p> </p>
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<p>But medicine uses ionizing radiation to help us, such as with X-rays, or as a way to kill cancer cells.</p>
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<p>And we live with a small amount of ionizing radiation from the world around us every day.</p>
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<p>Ionizing radiation can come from</p>
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<ul>
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<li>Electromagnetic Radiation</li>
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<li>Radioactive atoms</li>
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</ul>
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<h2>Electromagnetic Radiation</h2>
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<p><a href="x-rays-gamma.html">Gamma rays and X-rays</a> and some <a href="ultraviolet.html">ultraviolet waves</a> have enough energy to be <b>ionizing</b>.</p>
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<div class="example">
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<p style="float:right; margin: 0 0 5px 10px;"> </p>
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<h3>Example: From The Sun</h3>
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<p>A lot of the the radiation from the Sun gets <b>reflected</b> or <b>absorbed</b> by the atmosphere.</p>
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<p>Only</p>
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<ul>
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<li>radio waves</li>
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<li>some infrared</li>
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<li>visible light, and</li>
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<li>some ultraviolet</li>
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</ul>
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<p>get all the way through:</p>
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<p><img src="images/electromagnetic-spectrum-block.svg" width="100%" alt="electromagnetic spectrum block vs absorb" /></p>
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<p>So ultraviolet is the only ionizing radiation that reaches us at ground level.</p>
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</div>
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<h2>Radioactive Materials</h2>
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<p style="float:left; margin: 0 10px 5px 0;"><img src="images/nucleus-unstable.gif" width="142" height="130" alt="nucleus unstable" /></p>
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<p> </p>
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<p>Some atoms have <b>too much</b> energy.</p>
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<p>They will randomly <b>decay</b> to a more stable state by sending out radiation.</p>
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<p>We say those atoms are <b>radioactive</b> (they can <i>actively</i> emit <i>radiation</i>!)</p><div style="clear:both"></div>
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<p>The radiation emitted has <b>high energy</b>, is <b>ionizing</b> and can be of 3 types (<span class="times">α</span>, <span class="times">β</span> and <span class="times">γ</span>):</p>
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<p class="center"><img src="images/alpha-beta-gamma.gif" width="400" height="131" alt="alpha beta gamma from nucleus" /></p>
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<h3>Alpha Particles (<span class="times">α</span>)</h3>
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<p>Alpha particles have two protons and two neutrons in the form of an atomic nucleus.</p>
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<p>They are highly charged, fairly heavy and slow. So they are easily stopped by a sheet of paper or even a few centimeters of air.</p>
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<h3>Beta Particles (<span class="times">β</span>)</h3>
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<p>Beta particles are high energy electrons.</p>
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<p>They have 100 times more penetrating power than alpha particles, but can be stopped by a few millimeters of aluminium or a centimeter or so of water.</p>
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<h3>Gamma rays (<span class="times">γ</span>)</h3>
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<p>Gamma rays are high frequency electromagnetic waves.</p>
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<p>They need thick lead or lots of water to stop them.</p>
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<p>Most will go straight through our bodies. But when they hit atoms in our body they can harm us.</p>
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<p style="float:right; margin: 0 0 5px 10px;"><img src="images/nuclear-power-station.jpg" width="320" height="148" alt="nuclear power station" /></p>
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<h2>Neutron Radiation</h2>
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<p>There is also neutron radiation, which occurs in nuclear reactions such as thermonuclear explosions or inside nuclear reactors.</p>
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<h2>Sources</h2>
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<p>Typical sources of radiation are</p>
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<ul>
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<li>the Sun (many types of radiation, some of which are ionizing)</li>
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<li>X-ray machines</li>
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<li>radioactive materials like uranium and thorium (which are in tiny amounts in the ground, in bricks, stones, soil and concrete, and even in bananas!)</li>
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<li>microwave ovens (non-ionizing)</li>
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<li>and more</li>
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</ul>
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<h2>Irradiation and Contamination</h2>
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<div class="words">
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<p><b>Irradiation</b> is when we are exposed to radiation (usually meaning <b>ionizing</b> radiation)</p>
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</div>
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<div class="words">
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<p><b>Contamination</b> is when we breath in or swallow radioactive material</p>
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</div>
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<p>Irradiation may happen for only a short time, but contamination is inside our body and keeps us irradiated for a long time.</p>
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<h2>Radiation Doses</h2>
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<p>We get small amounts of radiation all the time from the world around us. And sometimes a little extra when we have an X-ray.</p>
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<p>The health effect of ionizing radiation is measured in <b>Sieverts</b> (Sv).</p>
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<p>1 Sv is a <b>very large and dangerous dose</b>, so we tend to talk about:</p>
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<ul>
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<li>microSieverts (µSv), which are one-millionth of a Sv, or</li>
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<li>milliSieverts (mSv) which are one thousand of a Sv</li>
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</ul>
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<p>Some typical values:</p>
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<div class="simple">
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<table border="0" align="center" cellpadding="2">
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<tr>
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<th>Source</th>
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<th>Typical Dose</th>
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<th>As Sieverts</th>
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</tr>
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<tr>
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<td>Dental X-Ray</td>
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<td>10 µSv</td>
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<td>0.000 01</td>
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</tr>
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<tr>
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<td>Chest X-ray</td>
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<td>20 µSv</td>
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<td>0.000 02</td>
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</tr>
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<tr>
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<td>Mammogram</td>
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<td>400 µSv</td>
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<td>0.000 4</td>
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</tr>
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<tr>
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<td>Typical yearly background</td>
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<td>2 mSv</td>
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<td>0.002</td>
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</tr>
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<tr>
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<td>Head CT Scan</td>
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<td>3 mSv</td>
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<td>0.003</td>
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</tr>
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<tr>
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<td>Full CT Scan</td>
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<td>30 mSv</td>
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<td>0.03</td>
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</tr>
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<tr>
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<td>Severe radiation poisoning</td>
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<td>2 Sv</td>
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<td>2</td>
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</tr>
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<tr>
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<td>Fatal acute dose</td>
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<td>5 Sv</td>
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<td>5</td>
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</tr>
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</table>
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</div>
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<p class="center"><img src="images/x-ray-hand.jpg" width="300" height="170" alt="x ray hand" /><br>
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X-ray of a hand on a computer mouse</p>
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<p>Stay safe!</p>
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<p> </p>
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<div class="related">
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<a href="electromagnetic-spectrum.html">Electromagnetic Spectrum</a>
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<a href="index.html">Physics Index</a>
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Copyright © 2020 MathsIsFun.com
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