1. What is going on in there?
Nuclear Physics
What is going on in there?

2. Nuclear structure A – atomic mass number
Z – atomic number (number of protons)
N – number of neutrons (N = A – Z)
X – element symbol (ex. He for helium)

3. example What element is this? How many protons does it have?
How many neutrons does it have?

4. Strong nuclear force Fundamental force
Strong enough to overcome the electrostatic repulsion of the protons – binds nucleus together
Short range (< m) – (this will explain why large nuclei can be unstable)

5. Binding Energy
The nucleus has slightly smaller mass than the sum of its parts…
Call this “missing mass” the Mass defect (Dm)
1 u is equivalent to MeV

6. example
Use the mass table to calculate the mass of 8 protons (same as atomic mass of hydrogen)
Use the mass table to calculate the mass of 8 neutrons
Total these two results. Compare this total to the mass of the oxygen nucleus:
( u)
Difference is mass defect = binding energy

7. Binding energy curve

8. Stability

9. Radioactivity
As nuclei get larger, the neutrons help provide stability because they contribute to the strong force, but do not have charge to push the nucleus apart
BUT – strong force has limited range (< m), so as nucleus gets beyond this size adding more nucleons makes it unstable
10-15 m

10. Notice that Fe is most stable

11. Modes of decay a decay – a 42He is ejected from the nucleus
b decay – an electron (0-1e) is ejected from the nucleus
g decay – a high-energy photon is emitted as a nucleon changes nuclear energy levels
a - GIRL
b - BOY
g - MAN

12. In the fission of 238U energy is released as KE and gamma ray (g)
Example
In the fission of 238U energy is released as KE and gamma ray (g)
Use the mass tables to determine the energy released in this reaction

13. example

14. example

15. Radioactive Decay
The rate of decay is proportional to the number of nuclei
The half-life is the time for ½ of the sample to decay

16. When N/N0 = ½, we get t½ = ln(2)/l ln(AB) = ln(A) + ln(B)

17. example
The half-life of 14C is 5730 yr (1.81 x 1011 s).
What is the decay constant for 14C?
Bones of a woolly mammoth have 30% of what would be present in a live animal. How long ago did the animal live?