Review and Radioactivity

Review Atomic # = # P = # e Isotope…same p/e…different # of neutrons form electrically neutral atom If # P does not equal #e then it is called an ION Isotope…same p/e…different # of neutrons ex - C12 or C14 as is mass # You can determine valence e- by the group number on Periodic Table Properties of Metals vs. Nonmetals Elements with full valence electron shells are STABLE

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 Nuclear decay/Radioactive decay – When unstable nuclei decay particles and energy (called nuclear radiation) are emitted (given off) This happens spontaneously (naturally) Occurs mostly in large elements because large nuclei are unstable and decay more than small nuclei attraction forces aren’t as strong to hold particles within nucleus

Nuclear Decay 3 types of nuclear radiation A. Alpha-particles B. beta-particles C. gamma-electromagnetic wave

Alpha Particle Helium nucleus is emitted (2 p/2 n) Charge =+2 Mass = 4 LARGEST Least energy Least penetrating power - stopped by paper Dangerous if swallowed or inhaled (Radon gas) Transmutation occurs

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Beta particle Particle An electron is emitted (given off) Charge is -1 mass is .0005 (very small) More energy than alpha Goes thru paper….stopped by foil Penetrates skin and nerve cells Transmutation occurs

131 131 I + e- = Xe 53 54

Gamma Rays Waves No mass and no charge Most powerful and penetrating of all Lead and concrete can stop gamma rays Passes through body – can cause or cure cancer Transmutation does NOT occur

Half-life Half-life - The amount of time a radioactive isotope takes for half the nuclei of a sample to decay Steps: Set up your chart (EVERYTIME)! Fill in your ZEROS. Fill in what you already know. Calculate what you don’t know. a) Amount – divide by 2 b) Time – add another half life Use the chart to answer the question.

Half Life Table

Problems examples The half life of calcium is 10 days. How much of a 100 g sample will remain after 1) 20 days? 2) 30 days? 3) 40 days? 4) 50 days?

Another look A sample of Phosphorous-18 originally has 30g. Phosphorous-18 has a half life of 2,000 years. In 2000 years, how many grams would remain undecayed? 1) 4,000 yrs 2) 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?

What is the half life of the radioisotope? Gieger counter data Time in days 0.0 5.0 10.0 15.0 Counts per second 1000 2000 3000 4000 What is the half life of the radioisotope?

Type? Transmutation?

FUSION AND FISSION

THE SUN Every second, the sun converts 500 million metric tons of hydrogen to helium. Due to the process of fusion, 5 million metric tons of excess material is converted into energy in each second. This means that every year, 157,680,000,000,000 metric tons are converted into energy.

Nuclear Fusion Nuclear fusion is the process by which multiple nuclei join together to form a heavier nucleus. It is accompanied by the release of energy

FUSION DEUTERIUM NEUTRON HELIUM TRITIUM http://fusioned.gat.com

Fusion Changes Mass to Energy E=mc2 .993 kg Helium He H 1kg Hydrogen

NUCLEAR FISSION A reaction in which a nucleus of a radioactive element splits by bombardment from an external source, with simultaneous release of large amounts of energy, used for electric power generation

Nuclear Fission Neutron induced in U235 Fission is Exothermic The sum of the masses of the resulting nuclei is less than the original mass (about 0.1% less) The “missing mass” is converted to energy according to E=mc2

Review Nuclear fission: A large nucleus splits into several small nuclei when impacted by a neutron, and energy is released in this process ENERGY GENERATION Nuclear fusion: Several small nuclei fuse together and release energy. THE SUN