Radioactive Dating The principle: All living organisms contain carbon which they have absorbed from CO2 in the atmosphere. Most of this is the stable isotope But a small proportion is the radioactive isotope Which has a half life of 5570 years. When an organism dies, it stops absorbing CO2 , so the amount of in it remains the same, while the gradually decays to stable . This means the proportion of decreases, so the activity of a sample decreases. The activity of a sample therefore gives an indication of the length of time since a dead organism died, or how old it is. The method: 1. Find your dead dinosaur, viking boat, egyptian mummy etc, take a sample of known mass, and measure its activity. eg 0.28 Bq. 2. Find a sample of the same mass of similar living or recently dead material (bone, wood, bandage etc) and measure its activity. eg 1.3 Bq. 3. Calculate the decay constant of Carbon 14 .

4. Use the radioactive decay formula to find the time elapsed between the two activities: Limitations on use of radioactive dating. 1. It is only accurate for things whose age is a ‘sensible’ number of half lives. The activity of something whose age is less than about 0.5 half lives will not have changed enough. The activity of something whose age is more than about 5 half lives will have reduced to not much more than background. Older rocks can sometimes be dated using Argon decay. Argon has a half life of 1250 million years 2. Assumption that modern organic material will have the same activity as the old one did when new is only an estimate. NB Other uses of radioactivity. Thickness monitoring, Smoke alarms, medical etc as for GCSE.

Qu pg 171 1. a. Wood contains carbon and therefore it contains a small amount of the radioactive isotope Carbon 14.

Now need Decay Constant is seconds-1 2 a (i) (ii) (iii) Now need Decay Constant is seconds-1 This is number of Nuclei, but each nucleus contains 131 nucleons Book says 10-13 b. Second kidney is not passing substances through as quickly as first.

4 b. (i) (ii)

Radioactive Dating The principle: All living organisms contain carbon which they have absorbed from CO2 in the atmosphere. Most of this is the stable isotope But a small proportion is the radioactive isotope Which has a half life of 5570 years. When an organism dies, it stops absorbing CO2 , so the amount of in it remains the same, while the gradually decays to stable . This means the proportion of decreases, so the activity of a sample decreases. The activity of a sample therefore gives an indication of the length of time since a dead organism died, or how old it is. The method: 1. Find your dead dinosaur, viking boat, egyptian mummy etc, take a sample of known mass, and measure its activity. eg 0.28 Bq. 2. Find a sample of the same mass of similar living or recently dead material (bone, wood, bandage etc) and measure its activity. eg 1.3 Bq. 3. Calculate the decay constant of Carbon 14 .

4. Use the radioactive decay formula to find the time elapsed between the two activities: Limitations on use of radioactive dating. 1. It is only accurate for things whose age is a ‘sensible’ number of half lives. The activity of something whose age is less than about 0.5 half lives will not have changed enough. The activity of something whose age is more than about 5 half lives will have reduced to not much more than background. Older rocks can sometimes be dated using Argon decay. Argon has a half life of 1250 million years 2. Assumption that modern organic material will have the same activity as the old one did when new is only an estimate. NB Other uses of radioactivity. Thickness monitoring, Smoke alarms, medical etc as for GCSE.