1. Physics 362 – week 13 Modern Physics Seminars

2. How to measure the Lifetime of an Isotope Several measurements over a period of time Single measurement of radioactivity and mass

3. Dating with radioactive nuclei Dating of fossils Dating of rocks

4. Carbon Nuclear Data ZA Atomic Mass (u) Nuclear Mass(GeV/c 2 ) Binding Energy(MeV) Spin Natural Abund. Half-lifeDecay Q MeV 61111.01143310.254173.443/2...20.3mb+1.98 61212.00000011.175092.1600.989stable... 61313.00335512.109697.111/20.011stable... 61414.00324113.0410105.290...5715yb-0.016 Three principal isotopes of carbon occur naturally 12 C - 98.89% 13 C - 1.11% 14 C - (radioactive) 0.00000000010%.

5. Carbon-14 Decay 14 C  14 N + e - + e  1/2 =5715 yr M C14 =14.003242 u M N14 =14.003074 u Q=0.016 MeV

6. Carbon Dating Libby, Anderson and Arnold (1949)   has been measured in the laboratory  We can measure N in the sample  If we know N 0 we can derive t

7. Carbon Dating

8. Measuring Carbon-14 activity  1/2 =5715 yr  Only good up to about 50,000 yr The sample is disintegrated and the activity is measured using a radiation detector

9. Dating of rocks and meteorites Potassium-Argon: 40 K  40 Ar + e + + e ;  1/2 =1.28 10 9 yr Rubidium-Strontium: 87 Rb  87 Sr + e - + e ;  1/2 =4.8 10 10 yr Samarium-Neodymium: 147 Sm  143 Nd +  ;  1/2 =10.5 10 10 yr Lutetium-Hafnium: 176 Lu  176 Hf + e - + e ;  1/2 =3.8 10 10 yr Rhenium-Olmium: 187 Re  187 Ol + e - + e ;  1/2 =4.2 10 10 yr

10. Determining N and N 0 We measure the ratio between parent and daughter abundances: How do we evaluate N 0 -N?

11. Potassium-Argon Argon is a gas. Whenever rock is melted to become magma or lava, the argon tends to escape. Once the molten material hardens, it begins to trap the new argon produced since the hardening took place. In this way the potassium-argon clock is clearly reset when an igneous rock is formed. In nearly all of the dating methods, except potassium- argon and the associated argon-argon method, there is always some amount of the daughter product already in the rock when it cools.

12. Rubidium-strontium

13. Rubidium-Strontium