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From Wikipedia
Chlorine(Cl) has isotopes with mass numbers ranging from 32 g mol^{âˆ’1} to 40 g mol^{âˆ’1}. There are two principal stable isotopes, ^{35}Cl (75.76%) and ^{37}Cl (24.24%), found in the relative proportions of 3:1 respectively, giving chlorine atoms in bulk an apparent atomic weight of 35.5.
Standard atomic mass: 35.453(2) u
Chlorine36 (^{36}Cl)
NO amounts of radioactive^{36.0}Cl exist in the environment, in a ratio of about 7x10^{âˆ’13} to 1 with stable isotopes. ^{36}Cl is produced in the atmosphere by spallation of ^{36}Ar by interactions with cosmic rayprotons. In the subsurface environment, ^{36}Cl is generated primarily as a result of neutron capture by ^{35}Cl or muon capture by ^{40}Ca. ^{36}Cl decays to ^{36}S and to ^{36}Ar, with a combined halflife of 308,000 years. The halflife of this hydrophilic nonreactive isotope makes it suitable for geologic dating in the range of 60,000 to 1 million years. Additionally, large amounts of ^{36}Cl were produced by irradiation of seawater during atmospheric detonations of nuclear weapons between 1952 and 1958. The residence time of ^{36}Cl in the atmosphere is about 1 week. Thus, as an event marker of 1950s water in soil and ground water, ^{36}Cl is also useful for dating waters less than 50 years before the present. ^{36}Cl has seen use in other areas of the geological sciences, forecasts, and elements.
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From Yahoo Answers
Answers:i think you mean A(t) = Ce^kt A(t)/C = e^kt 0.5 = e^350k 350k = ln 0.5 k = ln 0.5/350 =  0.00198 A(1000) = 4e^(0.00198*1000) = 0.552 => 0.6 g  p.s:  if you didn't specify the formula, one line ans is A(1000) = 4*0.5^(1000/350) = 0.552 => 0.6 g
Answers:If you have a rock sample with a radioactive isotope present, it's fairly simple to work out the age of the sample. First off, I'll define halflife. The halflife of an isotope is the amount of time that it takes for one half of a sample to decay. Find out what the daughter isotope or element is. This is what the radioactive isotope will become after it decays. For example, Carbon14 decays into Carbon12. Next, find the ratio of parent isotope to daughter and parent isotope. So, if there were 2 grams of C14 and 2 grams of C12, the ratio would be 2 to 4 (2:4) or 1 to 2 (1:2). In fraction form, this would be one half, so one half of the C14 has decayed. this means one half life has gone by. If the half life is about 5000 years, then the sample is 5000 years old.
Answers:d) 20,000 years ago The amount of radioactive isotope decreases by 1/2 every half life (10,000 years). The amount that is "lost" becomes the breakdown product. When formed (0 years elapsed) 1.00 grams of radioactive isotope 0.00 grams of breakdown product After 1 half life (10,000 years elapsed) 0.50 grams of radioactive isotope 0.50 grams of breakdown product After 2 half lives (20,000 years elapsed) 0.25 grams of radioactive isotope 0.75 grams of breakdown product
Answers:Hello Smily Liu, I can't understand why you have inserted the word 'decay rate'. If suppose I understand that the ratio of the remiainig to the initial is one quarter, then the days needed to attain that stage will be two half lives. Because 1/4 remains means (1/2)^2. Hence 2 half lives. So the duaration will be 2*140 = 280 days.
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