SCH 3U1 Unit 1: Assignment RADIOISOTOPES and HALF LIFE
1)The following data shows the decay rate (number of disintegrations /min/gram) of carbon-14.
Graph the data with time on the "x" and decay rate on the "y" using "KALEIDAGRAPH"
Time (years) / Decay Rate(dis/min/g) / Time (years) / Decay Rate(dis/min/g) / Time (years) / Decay Rate(dis/min/g)0 / 15.30 / 6500 / 6.97 / 13 000 / 3.17
500 / 14.40 / 7 000 / 6.56 / 13 500 / 2.99
1000 / 13.56 / 7 500 / 6.18 / 14 000 / 2.81
1 500 / 12.76 / 8 000 / 5.81 / 14 500 / 2.65
2 000 / 12.01 / 8 500 / 5.47 / 15 000 / 2.49
2 500 / 11.31 / 9 000 / 5.15 / 15 500 / 2.35
3 000 / 10.64 / 9 500 / 4.85 / 16 000 / 2.21
3 500 / 10.02 / 10 000 / 4.56 / 16 500 / 2.08
4 000 / 9.43 / 10 500 / 4.30 / 17 000 / 1.96
5 000 / 8.36 / 11 500 / 3.81 / 18 000 / 1.73
5 500 / 7.87 / 12 000 / 3.58
6 000 / 7.40 / 12 500 / 3.37
**From your graph answer questions 2 - 5
2) Estimate the time it takes for a sample of carbon-14 to reach half of its original level of radioactivity. (the half-life of the isotope). – Show your calculation(work) on your graph
3) Two fossils containing carbon-14 produced decay rates of a) 8.62 disintegrations /min/g
b) 4.15 disintegrations /min/g
From your graph, how old would you estimate these fossils to be ?
4) The dead sea scrolls were analyzed and carbon dated when discovered. The disintegration rate was found to be 12.1 /min/g. Approximatey how old are these scrolls.
5. An old piece of wood was recently unearthed in a region of the Middle East and thought to be part of Noah's Ark. It was carbon dated at 13.4 disintegrations/min/g. Could it be from Noah's Ark ?? (explain)
6. a) The half life of Fm-253 is 4.5 days. What fraction of 10 g of Fm would remain after 13.5 days ?
b) A 50 g sample of Cs-137 was left for 40 days when only 3.125 g remained. What is the half life of Cs-137 ?
7. Detail an example of a radioactive isotope and its use in a) medical diagnosis / therapy or b) industrial manufacturing.
8. The uranium-238 decay series begins with 238U and ends with the stable 206Pb. The particles given off are, in succession. Write the nuclear equations for each step in the process.