Nuclear Reactions

IB Physics Power Points

Topic 07 and 13

Atomic and Nuclear Physics

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

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

   

Artificial (induced) Transmutations

This reaction was first observed by Rutherford in 1919.

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).

4 2+ 14 17 1 +2 7 8 1He N O + p

PracticeA neutron is observed to strike a 16O nucleus and a deuteron (2H) is given off. What is the nuclide that results?

1 16 20 8 1 ?n O H

1 16 2 150 8 1 7n O H N

Nuclear Reactions – common notations  

01

42

10

11

alpha particle He or

neutron n or n

electron e or

proton p or p

Unified atomic mass unit  

/121 amu = 931.46 MeV/c2 = 0.93146 GeV/c2

1.660538782(83)×10−27 kg

Einstein’s mass – energy equivalence  

E=mc2

1 amu = 931.46 MeV = 0.93146 GeV of energy

Big Ideamass and energy are

interconvertible

Einstein’s equation relates rest mass to an equivalent energy1 kg = c2 J of energy (a lot!)

Now convert the energy value (in Joules) to electron volts

10 191.494 10 1.6 10 934 MeV

mass defect

Consider a helium nucleus: 2 protons and 2 neutrons

mass 4.001504 u

Total mass of protons and neutrons?

4.031882 u

mass defect = 4.031882 – 4.001504 = 0.030378 u (Δm or σ)

Practice1.The mass of an atom of Ne-20 is 19.992435 u. Determine the mass defect for this nuclide.

10 (0.000549 1.007276 1.008665) 19.992435

0.172465

m

m u

binding energy – explaining the missing mass

“assembling” a nucleus

binding energy

Individual protons and neutrons

Practice1. Determine the binding energy in O-16 (MeV and J). The mass of an O-16 atom is 15.994915 u.

8 (0.000549 1.007276 1.008665) 15.994915

0.137005

m

m u

0.137005 931.5 127.6 MeVE u

binding energy per nucleon

depends on nuclide

iron has highest value – mental note

PracticeUse 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

2

(26 0.000549) (26 1.007276) (30 1.008665) 55.934940

0.52846

0.52846 931.5 492.26049

492.26049 8.79 /

56

m

m amu

amu MeV c MeV

MeVMeV nucleon

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 6 0C C n

2

(12.000 1.008665) 13.003355

0.00531

0.00531 931.5 4.946

m

m amu

amu MeV c MeV

STOP HERE and Complete Worksheet 1

fusion and fission reactions

where does the energy come from?

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)

(235.043924 1.008665) (90.910187 141.929630 3 1.008665)

0.186777

931.5 173.99MeV

1 1 2 01 1 1 +1

1 2 31 1 2

3 3 4 12 2 2 1

H + H H + e + ν + 0.4 MeV

H + H He + 5.5 MeV

He + He He + 2 H + 12.9 MeV

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. 

 .

Big Fusion Problem Number 1: Confinement of plasmaPossibility 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. 

 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.