Download Radiometric Dating Principles

Radiometric Dating Principles
Note 4
- Radiometric dating uses the half-life of
unstable isotopes to estimate the age of the
rock
- method can only be used if rock was in a
closed system (no way for addition or loss of
parent or daughter isotopes)
* Unstable isotopes (like Uranium 238) decay
into more stable daughter products by
emitting particles
* Some isotopes will produce many unstable
daughter products before becoming stable
Radioactive decay – unstable atom (too
many neutrons compared to protons)
emits particle to become more stable
Steps in Uranium 238
decay to lead 206
Types of Radioactive decay
A. Alpha emission– parent emits an alpha
particle (2 protons + 2 neutrons)
- mass # reduced by 4,
- atomic # reduced by 2
B. Beta emission: parent emits an electron
- mass # stays same,
- atomic # increases by 1
Alpha emission – Note the mass number is
decreased by 4 (how has the atomic #
changed?
Beta emission – note mass # stays the
same, how has the atomic # changed?
If a radioactive isotope of Uranium (atomic
number 92, mass number 238) emits 4 alpha
particles and 2 beta particles during the course of
radioactive decay, what are the atomic number
and mass number of the daughter product?
Answer:
U 92 - [ 4 (2α ) – 2 ( -1β)]
238
4
0
92 – 8 + 2 = 86(atomic #) (Radon)
238 – 16 222 (mass # )