Nuclear

Question 1

Describe the Rutherford scattering experiment.

Answer 1

● A beam of alpha particles was directed at a thin gold foil.
● Occurs in a vacuum so that no collisions between air particles and alpha particles can occur.
● The experiment was done in order to determine structure of an atom.

Question 2

In the Rutherford scattering experiment it was observed that most of the alpha particles passed straight through. What can we infer from that?

Answer 2

That most of the atom is made from empty space.

Question 3

What evidence was there that suggested that the nucleus had a positive charge?

Answer 3

Because the the nucleus repels the alpha particles and caused it to deflect from its original path, some of them even bounced back.

Question 4

Describe Electron Capture

Answer 4

causes a proton to change into a neutron and emits a neutrino and gamma photon.

Question 5

Why is ionising radiation seen as dangerous?

Answer 5

Because it can kill or mutate cells, which could
lead to mutations and lead to things such as cancer.

Question 6

Give an example of a real life use of Beta decay and explain why Beta is chosen for this

Answer 6

Beta radiation can be used to measure the thickness of paper or aluminium foil. Alpha isn’t used as it is less penetrative and wouldn’t reach the detector on the other side of the sheet. Gamma radiation is too penetrative and would pass through everything

Question 7

Which type of radiation follows the inverse square law?

Answer 7

Gamma radiation.

The intensity is inversely proportional to the square of the distance from the source.

Question 8

What is intensity measured in?

Answer 8

watts per square meter (W/m2).

Question 9

What is background radiation?

Answer 9

Radiation that is constantly in the surrounding from sources such as rocks and food.

Question 10

What is the decay constant?

Answer 10

The probability of a nucleus decaying per second.(s-1)

Question 11

What is half life?

Answer 11

The time it takes for half of the unstable nuclei in a substance to decay.

Question 12

What is activity measured in ?

Answer 12

Bq (decays per second).

Question 13

Why is Technetium 99m useful in medicine?

Answer 13

● Because it releases gamma radiation
● It has a short half life therefore it doesn’t stay highly radioactive for long
● Half life of 6 hours: long enough for it to be detected
● It can also be made near to the hospital
● Easy to detect outside the patient
● ‘Clears away’ after a few days

Question 14

What does the graph of N against Z show?

Answer 14

IT shows the relationship between proton number and neutron number. The graph shows a stability curve which starts as N=Z until N value of 20. After that the graph curves upward and becomes steeper.

Question 15

How does the heavier nuclei often decay?

Answer 15

Through alpha decay. This is because alpha decay emits a helium nucleus (2 protons and two neutrons) therefore causing the nuclei to become less heavy and more stable.

Question 16

What is the mass defect?

Answer 16

The difference between the total mass of all the
nucleons separately compared to the mass of the nucleus.

Question 17

Why is there a mass defect?

Answer 17

Because energy is needed to bring the constituent parts of a nucleus together, therefore the mass equivalent of the energy is lost and the total mass decreases.

Question 18

What is binding energy?

Answer 18

The energy required to separate a nucleus into its constituent parts.

Question 19

What is nuclear fission?

Answer 19

● Where a unstable nucleus splits into 2 smaller nuclei.
● Often occurs with the larger nuclei.
● The binding energy per nucleon increases when fission occurs therefore the overall process releases energy.

Question 20

What is fusion?

Answer 20

When two small nuclei fuse together to create a larger nuclei. The new nucleus has a larger binding energy per nucleon than the old nuclei therefore energy is released in the process.

Question 21

Why is it difficult to make fusion occur on earth?

Answer 21

There is a large repulsion between the two positively charged nuclei, therefore a lot of energy is required to overcome the repulsion and fuse them together.
It is hard to get a material that can withstand the heat and be cost effective.

Question 22

How is fission used in nuclear reactors?

Answer 22

Rods of uranium-235 absorb neutrons and
become unstable and then split into two daughter nuclei. It also releases 2/3 more neutrons. These then go on to be reabsorbed by another uranium-235.

Question 23

What is the purpose of a moderator?

Answer 23

To slow down the neutrons so they travel slow enough to be absorbed by the uranium.
They do this through elastic collisions between the moderator and the nucleus.

Question 24

Why is control rods essential for a nuclear power station?

Answer 24

They stop the chain reaction from being out of control.
They absorb neutrons so that only 1 of the neutrons released in each reaction can go on to be absorbed by another uranium.
If not then the nuclear reactor would overheat as too many reactions would happen at once.

Question 25

What is the critical mass?

Answer 25

The minimum mass of fuel needed for a chain reaction to occur.