Nuclear Physics

Question 1

What experiment proved the existence of the nucleus?
What did the apparutus contain and what was it observed by?

Answer 1

Rutherford Scattering Experiment.

A chamber coated with fluorescent, containing an alpha source emitting towards a gold foil.
Observed by movable microscope.

Question 2

Rutherford Scattering hypothesis vs results:

Answer 2

Hypothesis: Plum pudding model&raquo_space; positive alpha particles wiuld deflect slightly.

Results:
1. Most alpha particles passed straight through (0 deflection)
» Meaning most of atom is empty space & density isn’t uniform.
2. Small amount of alpha p’s deflected at a large angle.
» Meaning centre (of atom) is positively charged since pos. p’s deflected.
3. Very few deflected by more than 90°.
» ∴ centre of atom must be very dense

Question 3

Practical uses of gamma radiation in medicine:

Answer 3

1. As a detector - can be injected to diagnose patients.
2. Sterilising medical equipment - kills any bacteria present.
3. In radiation therapy - kills cancerous cells. However can also kill healthy cells.

Question 4

2 Uses of radioactive decay:

Answer 4

1. Dating of objects - measuring current amount of carbon-14 and comparing it to initial amount. (Uses nuclei of long half-lives)
2. Medical Diagnosis - nuclei of short half-lives used as radioactive tracers.

Question 5

4 reasons a nucleus may get unstable and which emission causes each:

Answer 5

1. Too many neutrons. (Decays by beta-minus emission)
2. Too many protons. (Decays by beta-plus emission or electron capture)
3. Too many nucleons. (Decays by alpha emission)
4. Too much energy. (Decays through gamma emission.

Question 6

At which point is a particle at distance of closest approach, how can you find the distance, and how can this be used to find electric potential energy?

Answer 6

When Kinetic Energy = 0
At this point electric potential (V) = initial Ek, so you use the V equation.
Multiply this equation by the charge (Q) of the particle and you get electric potential energy.

Question 7

Differences between nuclear fission and fusion:

Answer 7

Fission is the splitting of a large nucleus into 2 daughter nuclei; Fusion is two smaller nuclei joining together to form on larger nucleus.

Energy is released during: Fission due to the 2 smaller nuclei having a higher binding energy per nucleon; Fusion due to the larger nucleus having a much higher binding E /nucleon.

Fission can be induced; Fusion can only occur at extremely high temperatures. (Because of the amount needed to overcome the electrostatic force of repulsion between nuclei)

Question 8

Graph of no. nucleons x avg.bE per nucleon (MeV):

Answer 8

Iron has the highest binding energy per nucleon.

Nuclei smaller than iron can undergo fusion;
Nuclei larger than iron can undergo fission.