10B. Nuclear Decay Electron Capture electron Gamma Emission Usually follows other types of decay.TransmutationAtom of one element changes into an atom of another element.
11B. Nuclear Decay Why nuclides decay… need stable ratio of neutrons to protonsDECAY SERIES TRANSPARENCY
12C. Half-life Half-life (t½) Time required for half the atoms of a radioactive nuclide to decay.Shorter half-life = less stable.
13C. Half-lifemf: final massmi: initial massn: # of half-lives
14C. Half-life t½ = 5.0 s mf = mi (1/2)n mi = 25 g mf = (25 g)(0.5)12 Fluorine-21 has a half-life of 5.0 seconds. If you start with 25 g of fluorine-21, how many grams would remain after 60.0 s?GIVEN:t½ = 5.0 smi = 25 gmf = ?total time = 60.0 sn = 60.0s ÷ 5.0s =12WORK:mf = mi (1/2)nmf = (25 g)(0.5)12mf = g
15C. Half-lifeNt: final massN0: initial masst: elapsed time
17C. Half-life t½ = 11.4 days k = 0.693 / t1/2 k = 0.693 / 11.4 days A sample of radium-223 has a half-life of 11.4 days. What is the rate constant for this isotope?GIVEN:t½ = 11.4 daysWORK:k = / t1/2k = / 11.4 daysk = days -1
18C. Half-life k = 0.035 yr -1 k = 0.693 / t 1/2 t ½ = 0.693 / k The rate constant for gold-200 is /year. What is the half-life of gold-200?GIVEN:k = yr -1WORK:k = / t 1/2t ½ = / kt ½ = / yr -1t ½ = yr ≈ 20. years
19C. Half-life t ½ = 1.7 x 107 yr ln (N0/Nt) = kt N0 = 3.75 g The half-life of iodine 129 is 1.7 x 107 years. If a nuclear bomb explosion resulted in 3.75 g of iodine-129, how much time would have to elapse for the amount of iodine-129 to be 0.75 g?GIVEN:t ½ = 1.7 x 107 yrN0 = 3.75 gNt = 0.75 gt = ?WORK:ln (N0/Nt) = ktln (3.75/0.75) = 0.693/1.7 x 107 tt = 3.9 x 107 years(39, 000, 000 years!)
20D. Radiocarbon DatingCarbon-14 is in all living things through the carbon cycle.Amount of carbon-14 stays constant until organism dies, then it begins to decay.
21D. Radiocarbon DatingAmount of carbon-14 can be expressed as either a percentage or as a decimal number.Example: amount of carbon-14 in a dead tree could be expressed as 38% or 0.38 of the original amount.
22Half-life of carbon-14 : 5730 years D. Radiocarbon DatingHalf-life of carbon-14 : years
23D. Radiocarbon DatingThe remnants of an ancient canoe are found in a cave in northern Australia. The amount of carbon-14 is 6.28 counts per minute, and the amount of carbon-14 in a tree today is 13.6 counts per minute. What is the approximate age of the canoe?
24D. Radiocarbon Dating t ½ = 5730 yr k = 0.693 / 5730 yr GIVEN:t ½ = 5730 yrN0 = 13.6 cts/minNt = 6.28 cts/mint = ?WORK:k = / 5730 yrk = x 10-4 yr -1ln (N0/Nt) = ktln (13.6/6.28) = x 10-4 tt = years2011 – 6390 = 4379 BC
25E. FissionOccurs when isotopes are bombarded with neutrons and split the nucleus into smaller fragments, accompanied by the release of neutrons and a large amount of energy. (Each atom can capture 1 neutron.)
26E. FissionChain reaction – occurs when atomic nuclei that have split release energetic neutrons that split more nuclei.
27E. Fission Two steps in controlling fission: Neutron moderation – water or carbon slows down the neutronsNeutron absorption – decreases the number of slow neutrons through the use of control rods made of neutron-absorbing materials (usually cadmium)
28F. FusionOccurs when two light nuclei combine to produce a nucleus of heavier mass, accompanied by the release of a large amount of energy.
29F. Fusion Occurs in all stars High temperatures are necessary to initiate fusion (no cold fusion yet)Possible future energy sourceHydrogen bomb is a fusion reaction (fusion of two deuterium nuclei).
30G. Methods of Detection Geiger Counters (primarily beta) Scintillation counter – coated screen detects radiation particles.Film badge – several layers of photographic film encased in a holder. Detects beta and gamma.
31H. Radioisotopes in Medicine X-rays: Useful in imaging soft-tissue organs.Tracers: Iodine-131 is used to check for thyroid problemsRadiation treatment: Some cobalt isotopes are used as radiation sources to treat cancer.