The Atomic Nucleus & Radioactive Decay (Chapter 10) Creative Commons Images

Student Learning Objectives Describe the structure of the atom and the resultant changes through fission, fusion, and radioactive decay. Analyze radioactive decay processes Differentiate between nuclear Fission & Fusion

How do we know the number of neutrons? Atomic number = number of protons Atomic Mass = mass in amu or grams Mass number = protons + neutrons 178O−2

Classify each atom. Is it an ion? Is it an isotope? Practice Classify each atom. Is it an ion? Is it an isotope? 32He 136C 3417Cl−1 5226Fe 63Li+1

What is the limit for the Strong Nuclear Force? The protons and neutrons in the core of an atom are held together by the strong nuclear force. Diameter < 10-15 m The strong nuclear force balances the electric force in a stable atom. FN FE

Nuclear Force vs. Electric Force Strong Nuclear Force Electric Force Attraction Repulsion Protons & Neutrons Protons Range < 10-15 m Range > 10-15 m

Practice Would a helium (He) atom or a bismuth (Bi) atom tend to be more unstable? Analyze the possible stability of a 32He atom.

What does radioactivity mean? Radioactivity is the transformation of an unstable atom into a different type of atom. Over 60 radioactive elements can be found in nature. There are 3 general sources of radioactivity. Earth Cosmic Rays Human Produced

How do we determine the new isotope? Atoms radioactively decay by emitting high energy particles. X  Y + a (alpha decay) X  Y + b (beta decay) X  X + g (gamma decay)

Can cause damage on the surface of matter Alpha Decay Alpha radiation: particle (He+) is a positively charged particle that leaves the nucleus. Can cause damage on the surface of matter Image Credit: JAHSCHem - Wikispaces

Can penetrate through several millimeters of matter Beta Decay Beta radiation: (e−) is a negatively charged particle that leaves the nucleus. Beta Particle 83Li 84Be Can penetrate through several millimeters of matter Creative Commons Image

Can pass through all types of matter Gamma Rays: (g) are high energy photons. High Energy Gamma Ray released High Energy Atom No change to nucleus Can pass through all types of matter Creative Commons Image

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The Rules Unstable Condition Name Symbol The Rules 83+ Protons Alpha +2 a D(Mass #) = – 4 D(Atomic #) = – 2 Neutron/Proton Ratio Beta e– –1 b D(Mass #) = – 0 D(Atomic #) = + 1 Excited Nucleus Gamma photon g No Change

Is the atom an isotope? What makes it unstable? What is the new atom? Practice Is the atom an isotope? What makes it unstable? What is the new atom? 22688Ra  X + e− 22688Ra  X + a 22286Rn  X + 42He 146C  X + b 3618Ar  X + g

What does the half-life of an element indicate? Half-life is the time it takes for one half of an unstable substance to decay into a different substance. Isotope Half Life 156C 2.449 seconds 146C 5,730 years

Practice An isotope of radium (Ra) has a half-life of 1620 years. If 1000 grams were placed in a barrel, how much of the material in the barrel would be radium after 6480 years? 22589Ac (Actinium) has a half-life of 10.0 days. How many days would it take to decrease the original amount placed in a barrel to 1/64th of the original amount?

More Practice Caffeine has a half-life of 6 hours. If you drink an 8 oz (95 mg) cup of coffee, how long will it take for there be less than 3 milligrams remaining in your body? A can of Mountain Dew has 56 mg of caffeine. How long would it take to have less than 3 milligrams of caffeine in your body after finishing this drink?

What is carbon dating? Carbon dating is the process of using the known half-life of carbon to determine age of a sample. Living plants and animals take in CO2 (Carbon-14) Carbon-14 is a radioactive isotope The half life of carbon 14 is 5,730 years 146C  147N + b

Practice If a piece of wood has 1/2 as much carbon-14 as compared to a living tree, how old is the wood? If a piece of wood has 1/32nd as much carbon-14 as compared to a living tree, how old is the wood? It is assumed the relative abundance of carbon-14 in our atmosphere has remained constant for the last 50,000 years. How do you think this assumption could affect carbon dating?

What is Nuclear Fission? Nuclear fission is splitting apart a nucleus. Electric force wins Nucleus flies apart Huge amounts of energy released Nuclear fission is used in atomic bombs & nuclear reactors. Atomic bombs produce a chain reaction. Nuclear reactors control the rate of fission.

Uranium Uranium fusion yields 2.5 Million times more energy per gram than coal burning. Creative Commons Image

Diablo Canyons Nuclear Power Plant Question Nuclear energy is a clean fuel. It does not pollute the atmosphere. What reasons may people have for not wanting to utilize nuclear energy? Diablo Canyons Nuclear Power Plant California

What is Nuclear Fusion? Nuclear fusion is the process of forcing atoms together into a new type of atom. Requires very high temperatures and pressures Nuclei must overcome Coulomb Barrier Some mass is converted into energy

Proton-Proton Chain E = mc2 Hydrogen nuclei are forced together into helium. Mass becomes energy. E = mc2

Nuclear Fusion & Stars Nuclear Fusion occurs naturally in stars. Our Sun releases 4x1026 Joules per second Image Credit: NASA

1 Second In The Sun 1038 Reactions 600 Billion kg H  He 4 Billion kg Mass  Energy 4 x 1026 Watts

How is radiation measured? Radiation is energy. The rem is defined as the dosage in rads that will cause the same amount of biological injury as one rad of x-rays. Lethal doses begin at about 400 – 500 rems Human exposure is about 0.2 rems/year Food 39 mrems Electronics 11 mrems Tobacco 1,300 – 9,000 mrems

Practice Compare and contrast nuclear fission and fusion. How many hydrogen atoms are consumed in the process of fusion? Use the atomic mass to determine the amount of mass lost from the Sun in each PPC reaction. How much energy would result from a 5 gram grape, under the right conditions?