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1. Nuclear Physics & Particles
Students are expected to:
New vocabulary
1. Explain the equation governing radioactive decay.
2. Calculate the rate of disintegrations, number of disintegrated
nuclei as a function of time.
3. Explain how nuclear reactions can be induced and provide
examples of such reactions.
4. List elementary and composite particles.
5. Differentiate between elementary and composite particles.
Radioactive Decay
Half life
Decay constant
Activity
Artificial radioactivity
Elementary particles
Composite particles

2. Nuclear Structure
Most of the atom is empty space. The rest consists of a
positively charged nucleus of protons and neutrons
surrounded by a cloud of negatively charged electrons.
The nucleus is the positively charged center of an atom
and contains most of its mass. It is composed of
protons, which have a positive charge, and neutrons,
which have no charge.
Nuclear force is responsible to attract all nucleons of
nuclei, the nuclear force acts on neutron-neutron,
neutron-proton, and proton-proton pairs. The nuclear
force is much greater than electric force and it is charge
independent.
Nuclear Stability
It depends on number of protons and neutrons in a nucleus.
Light nuclei (A < 30): protons = neutrons
Heavy nuclei (A > 30): protons < neutrons
Z: number of protons
N: number of neutrons
A: number of nucleons
A = Z + N

3. Nuclear Structure
The mass of atoms is measured in terms of the atomic
mass unit (amu), which is defined to be 1/12 of the mass
of an atom of carbon-12,
amu = 1.66 x 10–27 kg
Mass of proton almost equals to the mass of neutron
𝑋𝑍
𝐴
Atomic mass number (A)
number of protons and neutrons, number of nucleons,
that determines the mass of atom.
Isotopes
nuclei of the same number of protons but different numbers
of neutrons.
Atomic number (Z)
number of protons in the nucleus that determines the
chemical properties of an atom
𝑍
𝐴
𝑋

4. Nuclear Structure
Ex: For cobalt nucleus Co27
60
find:
Number of protons
Number of neurons
Atomic number
Mass number
The mass in amu
The mass in kg
amu = 1.66 x 10–27 kg

5. Radioactive Decay
Radioactive Decay (Radioactivity): emission of radiation or particles caused by spontaneous (natural)
disintegration of radioactive nucleus to become stable.
Nuclear decay occurs when the nucleus is unstable and spontaneously emits energy in the form of radiation.
The result is that the nucleus changes into the nucleus of one or more other elements.
These daughter nuclei have a lower mass and are more stable (lower in energy) than the parent nucleus.
The stability of nuclei depends on number of nucleons and nuclear force connects the nucleons.
Nuclear decay gave the first indication of the connection between mass and energy.
Radioactivity is spontaneous nuclear emission.
Nuclear reaction is induced nuclear emission.

6. Radioactive Decay
Types of decay:

7. Radioactive Decay
Types of decay:
Alpha (α) Beta (β) Gamma (γ)
Common name helium electron em radiation
Charge +2 - 1 0
Penetration low medium high
Radiation or
Particle
particle particle radiation
Ex: Write the nuclear equation for the radioactive lead isotope 82
214
𝑃𝑏 can change
to the radioactive bismuth isotope Bi 83
214
𝐵𝑖 by the emission of a β particle.

8. Radioactive Decay
Complete the nuclear reactions, and write the type of each reaction:

9. Radioactive Decay
Half-life: the time in which half of the original number of nuclei decay
There is a tremendous range in the half-lives of various nuclides, from
as short as 10−23 s for the most unstable, to more than 1016 y for the
least unstable.
Decay constant: is its probability of decay per unit time.
It depends only on nuclear force among nucleons
𝑁 = 𝑁𝑜𝑒−𝜆𝑡 N: number of remaining atoms
No: number of original atoms
λ: decay constant
t: time
𝜆 =
ln 2
𝑡1/2
=
0.693
𝑡1/2
To calculate the number of undecayed nuclei:

10. Radioactive Decay
Ex: Calculate the age of the Shroud of Turin given that the amount of 14C found in it is 92% of that in living tissue.
half-life of Carbon-14 is 5730 y.
Ex: The isotope Po-209 has a half-life of 103 years. How long would it take for a 100-g sample to decay so that
only 3.1 g of Po-209 was left?

11. Radioactive Decay
Activity: rate of decay expressed in decays per unit time for a radioactive substance
𝑅 = 𝑅𝑜𝑒−𝜆𝑡 R: present activity (Bq)
Ro: initial activity (Bq)
λ: decay constant
t: time
𝑅 =
Δ𝑁
Δ𝑡
1 Bq = 1 decay/s 1 Ci = 3.70 ×
1010 Bq
Ex: A sample of 210-Po is purchased 9 months ago. Its activity is 2 × 106 Bq. The sample is used in an experiment
these days. What activity can be expected if it has a half-life of 138 days?

12. Nuclear Reactions

13. Nuclear Reactions
Ex: Identify the unknown isotope in this reaction:
𝑛 + 7
14
𝑁 → 6
14
𝐶 + _______
A. 1
1
𝐻 B. 1
2
𝐻
C. 1
3
𝐻 D. 2
4
𝐻𝑒

14. Nuclear Reactions/Fission
Nuclear Fission: division of large nucleus into two or more fragments.

15. Nuclear Reactions/Fission

16. Nuclear Reactions/Fusion
Nuclear Fusion: combination of small nuclei to form a larger nucleus.
Fusion happens with presence of high thermal energy to overcome
repulsion between nuclei, in that process the nuclei in plasma state.
The amount of energy required for fusion is available inside core of stars
or by nuclear fission.

17. Particles
Hundreds of subatomic particles exist, and new ones keep on
being discovered.
elementary particles are indivisible
composite particles are built from other particles
Three types:
• Fermions: matter particles spin = 1/2
• Bosons: force carriers (“exchange particles”) spin = 1
• Higgs: special particle spin = 0
Spin is an intrinsic form of angular momentum carried by
elementary particles, composite particles (hadrons), and
atomic nuclei.

18. Particles