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Transcript
Unit 4 Chapter 16 Atomic Energy Radioactivity • 1896 • Henri Becquerel • Hypothesized that fluorescent minerals gave off X-rays • Placed a fluorescent mineral on top of a photographic plate wrapped in paper • Put it in sunlight and got an image of mineral Radioactivity • Next day was cloudy, so no sun • Put experiment in desk drawer, where there was no light • Image still showed up on paper, due to energy from minerals • This energy is nuclear radiation Radioactivity • Nuclear radiation – High energy particles emitted by the nucleus of some atoms • Marie Curie named the process by which nuclei give off energy radioactivity • Radioactivity is also called radioactive decay Radioactivity • There are three types of radioactive decay – Alpha – Beta – Gamma Radioactivity • Alpha decay - α – Release of alpha particle (2 protons and 2 neutrons, no electrons) – Alpha particle is same as Helium nucleus – Many large radioactive nuclei give off alpha particles and become different elements – Radium-226 does this – Mass number and total charge of starting materials is same as ending materials – Can be stopped by paper Radioactivity • Beta decay – β – Release of beta particle – Beta particle is an electron – Has no mass – With beta decay, a neutron breaks into a proton and electron, element becomes a different element – Mass number and total charge remain the same – Beta radiation can be stopped with few mm of aluminum Radioactivity • Gamma decay – γ – Is basically pure energy – Has no mass or charge – Cannot cause change into different element – VERY high energy = VERY dangerous! – Cannot be stopped by clothes or aluminum foil – Needs lots of lead or uranium to stop gamma rays Power of radiation • Exposure to radiation can lead to radiation sickness (fatigue, hair loss, loss of appetite) • Can cause damage to living and non-living matter, such as burns and even death • Atoms get destroyed, so cells get destroyed • Chemoradiation kills cancer cells Radiation • You can find how old something is by its rate of nuclear decay – Iceman in Italian Alps, found to be 5300 years old – Some carbon atoms (C-14) are radioactive and break down over time – C-14 atoms will break down after an organism dies – Half of the atoms will decay after a certain amount of time, this is called half-life Half-life • Half-life is amount of time it takes for half of the nuclei of a radioactive isotope to decay • Carbon-14 = 5730 years • Uranium-238 = 4.5 billion years • Hydrogen-3 = 12.3 years • Calcium-36 = .1 seconds • Nitrogen-13 = 10 minutes Half-life • We can use half-life to figure out how old things are, based on how much of a radioactive element is left in the object • With Iceman, scientists found that almost one half of C-14 had changed, so Iceman was almost 5730 years old. • Fossils can be dated this way Half-life • The half life of Nitrogen-13 is 10 minutes • A 20 gram N-13 sample is prepared for an experiment. If a scientist is late and starts the experiment 20 minutes later, how many grams of N-13 are left? • If only 2.5 grams of N-13 are left at the end of the experiment, how much time has gone by? Uses of radioactivity • Radioactive materials are used in everyday things • Smoke alarms have very small amounts of radioactive material to detect fires • Doctors use tracers (radioactive elements used to follow a path) in patients to find things inside the body • Microwaves cook using radiation • X-rays/MRIs/CT scans all use radiation Energy from the nucleus • Nuclei from some atoms decay into smaller, more stable nuclei • Nuclear fission: process by which a nucleus splits into two smaller nuclei and releases energy • Uranium can undergo this naturally • Humans can throw neutrons at other atoms to force them to split (Large Hadron Collider) Energy from the Nucleus • Nuclear fission in fuel pellet of U can release as much energy as burning 1000 kg of coal • This is due to the chain reaction • When one nucleus splits, the neutrons released hit another nucleus and split that one, causing a domino effect Chain reaction • Domino demo Chain reaction • Uncontrolled – Large amounts of energy released very quickly – Atomic bombs • Controlled – Energy released over longer periods of time – Nuclear power plants Nuclear Power (Fission) • Advantages – Very clean compared to coal – Relatively inexpensive – No greenhouse gases released – More electricity produced Nuclear Power (Fission) • Disadvantages – Accidents release dangerous radiation (Chernobyl, Fukushima, Three Mile Island*) – Nuclear waste that is still radioactive – Limited amount of nuclear material to start with Nuclear Power (Fusion) • Fusion – Two or more single nuclei combine to form one larger nucleus – Hydrogens join to form helium – Must overcome the repelling charges (remember, positive repels positive) – Need VERY high temperatures to do this – Temperature of 100,000,000 °C (like the middle of the sun) Nuclear Power (Fusion) • Can make virtually unlimited amounts of energy • Very little radiation produced • However, we simply do not have the technology yet to make fusion reactors capable of powering nations (remember, need to have VERY high temperatures, and materials strong enough to withstand those temperatures)