Review and Radioactivity Put together by THE Coach Hyde

Radioactivity Nucleus contains almost all the mass of an atom (p/n have all mass)…electrons are negligible (little mass) EX. Marble sitting in middle of football field When a nucleus decays (loses particles) matter and energy is given off (lots of energy) This happens spontaneously (naturally) Occurs mostly in large elements because attraction forces aren’t as strong to hold particles within nucleus Large nuclei are unstable and decay more than small nuclei

Nuclear Decay When unstable nuclei decay…particles and energy (called nuclear radiation) are emitted (given off) 3 types of nuclear radiation A. Alpha-particles B. beta-particles C. gamma-electromagnetic wave

Alpha Very massive particle (made of p/n) Most electric charge Lose energy quickly Least penetrating power-stopped by paper Charge =+2…….mass + 4 Transmutation occurs=changing one element to another through nuclear decay

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Alpha Particle in Depth 1) The nucleus of an atom splits into two parts. 2) One of these parts (the alpha particle) goes zooming off into space. 3) The nucleus left behind has its atomic number reduced by 2 and its mass number reduced by 4 (that is, by 2 protons and 2 neutrons).

OK, write the alpha decay equations for these five nuclides OK, write the alpha decay equations for these five nuclides. The answers are on the next slide

Beta particle An electron is emitted (given off) from nucleus decay Much faster and penetrate more than alpha Go thru paper….stopped by foil Undergoes transmutation like alpha Charge is -1………mass .0005 (small)

131 131 I + e- = Xe 53 54

3) The atomic number goes UP by one and mass number remains unchanged. Beta Decay Beta decay is somewhat more complex than alpha decay is. These points present a simplified view of what beta decay actually is: A neutron inside the nucleus of an atom breaks down, changing into a proton. 2) It emits an electron and an anti-neutrino (the anti-particle of a neutron) 3) The atomic number goes UP by one and mass number remains unchanged. Here is an example of a beta decay equation:

Beta Decay Continued The nuclide that decays is the one on the left-hand side of the equation. 2) The order of the nuclides on the right-hand side can be in any order. 3) The way it is written below is the usual way. 4) The mass number and atomic number of the antineutrino are zero and the bar above the symbol indicates it is an anti-particle. 5) The neutrino symbol is the Greek letter "nu.“ 6) Notice that all the atomic numbers on both sides ADD UP TO THE SAME VALUE and the same for the mass numbers.

Here's your first set of exercises Here's your first set of exercises. Write out the full beta decay equation. Then click the link to see the answer

Gamma Rays Most powerful and penetrating of all No mass and no charge Given off by nucleus during alpha/beta decay Lead and concrete can only stop gamma rays

Gamma-rays A nucleus which is in an excited state may emit one or more photons (packets of electromagnetic radiation) of discrete energies. The emission of gamma rays does not alter the number of protons or neutrons in the nucleus but instead has the effect of moving the nucleus from a higher to a lower energy state (unstable to stable). Gamma ray emission frequently follows beta decay, alpha decay, and other nuclear decay processes.

Half-life The amount of time a radioactive isotope takes for half the nuclei of a sample to decay Very hard stuff so pay attention Used in science to date rocks, fossils, bones..etc

Half Life Table

Problems examples The half life of calcium is 10 days. How much of a 100 g sample will remain after A. 20 days B. 30 days C. 40 Days D. 50 days

Another look A sample of Phosphorous-18 originally has 30g. Phosphorous-18 has a half life of 2,000 years. In _______________ years, how many grams would remain undecayed? A. 2,000 yrs B. 4,000 yrs C. 8,000 yrs

Another look At the end of 45 days, 100 g of Carbon-14 has decayed to 12.5 g. What is the ½ life of Carbon 14?

The Geiger–Müller counter, also called a Geiger counter, is an instrument used for measuring ionizing radiation used widely in such applications as radiation dosimetry, radiological protection, experimental physics and the nuclear industry