(unit8:terms)=
## Unit 8 : Equations & Terms

Review material will be added for this part of the course in later weeks.

### Equations 
To aid with exam revision below is a list of all equations that you should learn for this unit in the course.

#### Breit Wigner Form
```{math}
:label: cross_section_compound
\begin{equation}
 \sigma_{(a,b)}B = \sigma_{a+A→C*} \times BR(C* → B + b), 
\end{equation}
```

#### Breit Wigner Form
```{math}
:label: breit-wigner
\begin{equation}
 \sigma_{BW}(E) = \frac{\pi}{(k)^2} \frac{(2J + 1)}{(2I_a + 1)(2I_A + 1)} \frac{\Gamma_a(E)\Gamma_b(E)}{(E - E_R)^2 + \Gamma(E)^2/4}, 
\end{equation}
```

#### Compound Branching Ratio 
```{math}
:label: branching_ratio
\begin{equation} BR(C* \rightarrow b + B) = \frac{\Gamma_b}{\Gamma}.
\end{equation}
```

#### Difference in timescales
- Direct reactions are fast $(\sim10^{-22}~\textnormal{s})$ 
- Compound-nucleus reactions are slower ($~10^{-18} - 10^{-16} s$) 


### Terms
In addition you should make sure you understand the following key terms in this unit.
- Direct Reactions
- Compound Reactions
- Independence Hypothesis
- Characteristics of compound-nucleus reactions
- Resonances
- Breit-Wigner distribution
- Photo-nuclear reactions
- Photodisintegration
- Nuclear resonance fluorescence 
- Giant dipole resonance