Nuclear Physics and Radioactivity - Exam Study Notes

Nuclear physics concerns the nucleus of the atom.
An atom consists of a nucleus containing protons and neutrons, with electrons orbiting outside.
Protons and neutrons have approximately the same mass (1 U), while electrons have negligible mass.
Protons have a +1 charge, electrons have a -1 charge, and neutrons have no charge.
Neutrons are composed of a proton and an electron.
Nuclide notation: $^{A}_{Z}X$ , where A is the mass number (protons + neutrons) and Z is the proton number.
Number of neutrons = mass number - proton number.
Isotopes are atoms of the same element with the same number of protons but different numbers of neutrons.

Rutherford's experiment involved firing alpha particles at a thin gold foil.
Observations:
- Most alpha particles passed through undeflected.
- Some alpha particles were deflected.
- A few alpha particles were deflected backward.
Conclusions:
- Most of the atom is empty space.
- The nucleus is positively charged.
- The nucleus is small and contains most of the atom's mass.

Nuclear fission is the splitting of a large nucleus into smaller nuclei, often initiated by neutron absorption.
Nuclear fusion is the joining of two small nuclei, typically hydrogen isotopes, to form a larger nucleus like helium.
In nuclear reactions, mass number and proton number must be balanced on both sides of the equation.
Example of nuclear fission: $\^{235}{92}U + \^{1}{0}n \rightarrow Ba + Kr + neutrons$
Example of nuclear fusion: $H + H \rightarrow He$

Property	Alpha ($\alpha$)	Beta ($\beta$)	Gamma ($\gamma$)
Mass	4 U	~1/2000 U	0
Charge	+2	-1	0
Ionizing Power	Strongly ionizing	Strongly ionizing	Weakly ionizing
Range in Air	~10 cm	~10 m	~10 km
Penetration	Stopped by paper	Stopped by aluminum	Stopped by thick lead
Nulide Notation	$\begin{matrix} 4 \ 2 \end{matrix}He$	$\begin{matrix} 0 \ -1 \end{matrix}e$	N/A

Alpha and beta particles are deflected by electric fields due to their charge.
Beta particles deflect more than alpha particles due to their smaller mass.
Magnetic fields deflect charged particles; the direction can be determined using Fleming's left-hand rule.

Alpha decay: A nucleus emits an alpha particle, losing 4 in mass number and 2 in proton number.
Beta decay: A neutron in the nucleus converts into a proton and emits a beta particle (electron); mass number remains the same, and the proton number increases by 1.
Example alpha decay: $\^{235}{92}U \rightarrow \^{4}{2}He + \^{231}_{90}X$
Example beta decay: $\^{14}{6}C \rightarrow \^{0}{-1}e + \^{14}_{7}N$

Background radiation is always present due to natural sources.
Measurements must be corrected for background radiation to determine the radiation from a specific source.
Corrected reading = Detector reading - Background reading.

Half-life is the time taken for half of the nuclei in a radioactive sample to decay.
The decay process is random and spontaneous.
After each half-life, the amount of radioactive material is reduced by half.
$Remaining Activity = Initial Activity * (\frac{1}{2})^n$ where n = number of half-lives
The time it took to decrease by half is called the half-life, and it's constant.
Half life Example: iodine-131 is a radioactive isotope that has a half-life of 8 days

Smoke alarms: Use alpha particles to ionize air; smoke blocks ionization, triggering the alarm.
Irradiating food: Gamma radiation kills bacteria to preserve food.
Sterilizing equipment: Gamma radiation sterilizes medical tools.
Measuring thickness: Beta particles measure the thickness of materials during manufacturing.
Diagnosing and treating cancer: Radioactive isotopes help locate and kill cancer cells.