Paper 1

Question 1

What is the radius of a typical atom?

Answer 1

1 × 10^-10

Question 2

Isotope:

Answer 2

Atoms of the same element, but with different masses that have the same amount of protons and electrons, but a different number of neutrons.

Question 3

Atoms and EM radiation:

Answer 3

• When electrons move to a higher orbit
  -The atom has absorbed EM radiation
• When the electrons falls to a lower orbit
  -The atoms has emitted EM radiation

If an electron gains enough energy, it can leave the atom to form a positive ion.

Question 4

Changes to the atomic model:

Answer 4

1. Dalton- Everything was made of atoms (tiny spheres) that could not be divided
   2.** JJ Thompson** - plum pudding model
2. Rutherford- Gold foil experiment: Most alpha particles went straight through, so most of the atom was empty space, some particles were slightly deflected, so the nucleus must have been positively charged, few particles were deflected at 90 degrees, so the nucleus contained most the atom’s mass. Negative electrons existed around the nucleus.
3. Bohr- discovered electron shells

Question 5

Radioactive decay:

Answer 5

Some atomic nuclei are unstable and give out radiation to become more stable.

Question 6

Activity:

Answer 6

Activity is the rate at which a source of unstable nuclei decays.
- So a sample with high activity has a fast rate of decay
- Measured in Becquerel, Bq

Question 7

Count-rate:

Answer 7

Count-rate is the number of decays recorded by a detector per second.
- E.g. a Geiger-Muller Tube

Question 8

Alpha decay:

Answer 8

E.g. a hellium nucleus
* Highly ionising
* Weakly penetrating
* Can travel through 5 cm of air

Question 9

Beta particle:

Answer 9

E.g. electron
* Medium ionising
* Medium penetration
* Can travel through 50 cm of air, a sheet of paper

Question 10

Gamma

Answer 10

A form of radiation
* Low ionising
* Highly penetrating
* Can travel very far, through a good few cm of lead

Question 11

Alpha particle equation:

Answer 11

4
He
2

This means that the mass of the nucleus will decrease by 4 and the charge by 2

Question 12

Beta

Answer 12

0
e
-1

Beta decay does not cause the mass of the nucleus to change, but the charge increases by 1.

Question 13

Gamma decay:

Answer 13

Does not cause the mass nor charge of the nucleus to change.

Question 14

Nuclear fission:

Answer 14

• Neutron absorbed by a uranium nucleus
• Nucleus splits into two parts
• And 2/3 neutrons are released
• And gamma rays are emmitted

Question 15

Nuclear fusion:

Answer 15

Two small nuclei fuse to form a heavier nucleus

• This releases lots of energy
• The sum of the masses of the two nuclei is heavier than the mass of the heavier nucleus
• Some of the mass is converted into energy

The sun is a natural fusion reactor. Nuclear fusion would be a much more efficient to produce energy than nuclear fission, however there has not been a design that could produce posisitve net energy on earth.

Question 16

Net decline:

Answer 16

Net decline= initial number-number of X half lives / initial number

Question 17

Irradiation:

Answer 17

• Lasts only for a short period of time
• The source emits radiation, which reaches the object
• Exposing an object to nuclear radiation, but does not make it radioactive
  o E.g. radioactive dust emitting beta radiation, which “irradiates” your skin
• Medical items are irradiated sometimes to kill bacteria on its surface, but not to make the medical tools themselves radioactive

Question 18

Contamination:

Answer 18

• Lasts for a long period of time
• The source of the radiation is transferred to an object
  o E.g. radioactive dust settling on your skin (your skin becomes contaminated)

Question 19

Radioactive contamination:

Answer 19

• Unwanted presence of radioactive atoms
  on other materials – the hazard is the decaying of the contaminated atoms, releasing radiation

Question 20

Background Radiation:

Answer 20

Weak radiation that can be detected from natural / external sources
* Cosmic rays
* Radiation from underground rocks
* Medical rays

The level of background radiation and radiation dose may be affected by occupation and/or location.

Measured in sieverts, sv.

Question 21

Tracers:

Answer 21

• Technetium is used as a medical tracer
• Half-life of 6hrs
• Decays into a safe isotope that can be excreted by the body
• It is injected/swallowed and there is enough time for it **flow ** through the body and be detected before it decays away but is only present for a short enough time to minimise any harm from radiation.
• It is a gamma emitter, so can pass through the body tissue without being
  absorbed (as it is the most penetrating)