Unit 17 Radioactivity
Atomic mass is the average number of p+ and n found in the nucleus. All elements have Isotopes. Atoms of the same element with a different number of neutrons found in the nucleus, therefore they have different masses. Carbon 12.0111 Chemical symbol: 1 or 2 letters used to represent an element. The 1st letter is always capital. If there is a 2nd letter, it is lower case. C 6 Atomic number is the number of p+ found in the nucleus.
Structure of the Atom Protons & Neutrons
Radioactivity • All naturally occurring elements with atomic numbers greater than 83 are radioactive. Uranium is the largest naturally occurring element. Every element above 92 is man-made. • Radioactivity is the uncontrollable decay of an atomic nucleus with the emission of particles and rays, with a lighter element formed. • Radioactive elements can affect photographic plates, ionize gases, and cause physical effects (mutations).
Half-life is the TIME it takes for ½ of the radioactive atoms to decay. Different elements take a different amount of time for a half-life to occur. U Th half-life takes 4.5 billion years Po Pb half-life takes 1.6 x 10-4 seconds
1 line = 5 atoms Go from 0 to 120 atoms Radioactive Decay curve U Th Po Pb Atoms remaining 1 line = (depends of class data) Go from 0 rolls to ____ rolls Time (rolls)
Remember that half-life is the period of time required for half of the atoms to go through decay. For a single element, each half – life is the same amount of time. So, if it takes 2 minutes for element X to go through one half – life, it takes 4 minutes to go through 2 half – lives. During each half – life, half of the atoms go through decay. remaining 1 g 1st half-life 2nd 3rd decayed ½ g ¼ g 1/8 g ½ g ¾ g 7/8 g
Radioactive Emissions • Alpha particle a = Helium nucleus 4 He easily stopped • Beta particle b = electron e- moderately difficult to stop • Gamma ray g = pure energy very difficult to stop 2
Radioactive emission a or b causes ionization of Ar gas, completing circuit, clicks! How a Geiger Counter works
Radioactivity verses Distance Radioactivity (clicks/min) 1 line = 1 inch Go from 0 to 12 inches Distance (in) 1 line = depends on class data Go from 0 to ____
Effectiveness of Various Barriers to Radioactivity Card board Al Pb Radioactivity clicks/min 1 line = depends on class data Go from 0 to ? 1 line = 1 barrier Go from 0 to 10 barriers Number of barriers
New structure that will enclose the destroyed reactor at Chernobyl. 500 feet long, 840 feet wide, and taller than the Statue of Liberty.
Nuclear Notation AX Kinds of Decay Alpha decay aA XA-4N + 4 He N = new element Beta decay bAX A N + e- N p+ + e- Atomic mass Element symbol z Atomic number a Z Z-2 2 b Z Z+1
b a 241Pu 94 a b a a b
Calculating half-life of 137Ba 56 To calculate the half-life from data, determine the time when exactly half of the radioactive atoms remain. Radioactivity (clicks/min) Time (sec)
g 137 Ba 137 BaRadioactive Decay of Ba to determine the half - life 56 56 Time (s) (clicks/min) 0 25,000 30 23,000 60 20,500 90 18,500 120 16,800 150 15,200 180 13,800 210 12,750 240 11,500 270 10,300 Time (s) (clicks/min) 300 9,400 330 8,700 360 7,800 390 7,000 420 6,200 450 5,600 480 5,050 510 4,650 540 4,200
Review a a 1. a. 226Ra 222Rn 218Po 88 86 84 b b • b. 214Bi 214Po 214At Top # = proton + neutron (atomic mass) • 83 84 85 Bottom # = protons (atomic number) 2. Protons and neutrons are located in the nucleus, with the electrons located in energy levels around the nucleus. 3. Alpha a particle is a helium nucleus Beta b particleis an electron Gamma g ray is pure energy 4. 1/8 pound remaining • 7/8 pound decayed 5. A device used to detect radiation by counting the number of emissions per unit of time
Down 27. Cyclotron 28. Spectrograph 39. Meson Across 16. Emanations 18. Crystallization 34. Becquerel 40. Rutherford 45. Electroscope Nuclear chemistry Crossword
Bikini Atoll is a circle of island with a deep central lagoon.From 1946 to 1958 the US exploded 23 nuclear bombs to analyze what happens. All of the local people were relocated to another atoll before the explosions
Light Bright Assignment 1H 2H 3H . ..... . . .