1. IB Physics Power Points
Topic 07 and 13
Atomic and Nuclear Physics
www.pedagogics.ca
Nuclear
Reactions

2. Nuclear Transmutations
Definition: A nuclear reaction where one nuclide is
changed into another. Examples of nuclear
reactions include fission, fusion, and radioactive
decay

3. Artificial (induced) Transmutations
• target nucleus is bombarded with another particle
such as a nucleon, an alpha particle or another small
nucleus
• if the target nucleus „captures‟ an incoming particle a
transmutation reaction occurs

4. Artificial (induced) Transmutations
This reaction was first observed by Rutherford in 1919.
4 2+ 14 17 1 +
2 He 7 N 8 O+ p 1
This nuclear reaction equation is balanced. The sums
of the mass and atomic numbers are equal for both
sides of the reaction arrow (don‟t worry about the
electrons ie the ionic charges).

5. Practice
A neutron is observed to strike a 16O nucleus and a
deuteron (2H) is given off. What is the nuclide that
results?
1 16 2
0 n 8 O 1 H ?
1 16 2 15
0 n 8 O 1 H 7 N

6. Nuclear Reactions – common notations
4
alpha particle 2 He or
1
neutron 0 n or n
electron 0
1 e or
1
proton p or p
1

7. Unified atomic mass unit
1.660538782(83)×10−27 kg
/12
1 amu = 931.46 MeV/c2 = 0.93146 GeV/c2

8. Einstein’s mass – energy equivalence
E=mc2
Big Idea
mass and energy are interconvertible
Einstein‟s equation relates rest mass to an equivalent energy
1 kg = c2 J of energy (a lot!)
1 amu = 931.46 MeV = 0.93146 GeV of energy

9. Now convert the energy value (in Joules) to electron volts
10 19
1.494 10 1.6 10 934 MeV

11. mass defect
Consider a helium nucleus: 2 protons and 2 neutrons
Total mass of mass 4.001504 u
protons and
neutrons?
4.031882 u
mass defect = 4.031882 – 4.001504 = 0.030378 u
(Δm or σ)

12. Practice
1.The mass of an atom of Ne-20 is 19.992435 u.
Determine the mass defect for this nuclide.
m 10 (0.000549 1.007276 1.008665) 19.992435
m 0.172465 u

13. binding energy – explaining the missing mass
“assembling” a nucleus
binding energy
Individual
protons and
neutrons

14. Practice
1. Determine the binding energy in O-16 (MeV and J).
The mass of an O-16 atom is 15.994915 u.
m 8 (0.000549 1.007276 1.008665) 15.994915
m 0.137005 u
E 0.137005 u 931.5 127.6 MeV

15. binding energy per nucleon
depends on nuclide
iron has highest value – mental note

16. Practice
Use the graph to estimate the binding energy per nucleon for Fe-
56. Verify your estimate mathematically. Mass of Fe-56 ATOM
is 55.934940 u
m (26 0.000549) (26 1.007276) (30 1.008665) 55.934940
m 0.52846 amu
0.52846 amu 931.5 MeV c 2 492.26049 MeV
492.26049 MeV
8.79 MeV / nucleon
56

17. How much energy is required to remove a neutron from a C-13
nucleus? Write a balanced nuclear equation for this reaction.
C-13 atom mass = 13.003355 amu, and of course C-12 has a
mass of ? 13 12 1
6 C 6 C 0 n
m (12.000 1.008665) 13.003355
m 0.00531 amu
2
0.00531 amu 931.5 MeV c 4.946 MeV

18. STOP HERE and Complete Worksheet 1

19. fusion and fission reactions
where does the energy come from?

20. fusion and fission reactions
Fusion
2 light nuclides (low binding energy per nucleon) combine
to make one heavy nuclide (higher binding energy per
nucleon)
Fission
One heavy nuclide (lower binding energy per nucleon) splits
to form lighter nuclides (higher binding energy per nucleon)

21. (235.043924 1.008665) (90.910187 141.929630 3 1.008665)
0.186777
931.5 173.99MeV

24. 1
H + 1H
1 1
2
H+
1
0
+1 e + ν + 0.4 MeV
1 2 3
H+ H
1 1 2 He + 5.5 MeV
3 3 4 1
2 He + He2 2 He + 2 H + 12.9 MeV
1

25. Big Fusion Problem Number 1: Confinement of plasma
Possibility 1 – inertial confinement: beams of laser
light or ions compress a fuel pellet from all sides while
heating it.
Possibility 2 – magnetic confinement: using a magnetic
field to cause plasma (charged gas particles) to
circulate endlessly within a confined space.
.

26. Big Fusion Problem Number 2: Extracting energy
Once a fusion reaction is initiated and confined, the
energy must be extracted in order to be any use (and
to stop the whole thing melting down).
One possibility is to use a molten lithium blanket
surrounding the fusion reaction to transfer the heat to
a water based heat transport system.