Nuclear

Question 1

Binding energy

Answer 1

The amount of energy required to split a nucleus into all its separate constituent nucleons. It is equivalent to the mass defect.
(Or the energy required to bind together the nucleons, where nuclei with higher binding energy per nucleon are more stable as more energy needed for separation)

Question 2

Closest approach

Answer 2

A method of estimating a nuclear radius by firing an alpha particle at it. It involves calculating the distance at which all the alpha particle’s kinetic energy is converted to electric potential energy.

Question 3

Contamination

Answer 3

The introduction of radioactive material to another object. The object is consequently radioactive.

Question 4

Control rods

Answer 4

Rods found in nuclear reactors to absorb neutrons and control the rate of reaction. They can be raised or lowered depending on the rate required.

Question 5

Critical mass

Answer 5

The smallest mass of fissile material required in a fission reactor for a chain reaction to be sustained.

Question 6

Electron capture

Answer 6

A process that occurs in proton-heavy nuclei, in which an electron is drawn into the nucleus, causing a proton to transition into a neutron. An electron neutrino is also produced.

Z= 82. Z= 81
²⁰⁵Pb + e– → ²⁰⁵Tl + v(e)

Question 7

Irridation

Answer 7

The exposure of an object to radiation. The exposed object does not become radioactive

Question 8

Mass defect

Answer 8

The difference in mass between a nucleus and the sum of the masses of its constituent nucleons

Question 9

Decay constant

Answer 9

The probability that a particular nucleus will decay per time (s^-1)
The fraction of the total number of nuclei that decay per second.

Question 10

Rutherford conclusions

Answer 10

1) most alpha particles passed through undeflected → most atoms must be empty space.
2) many were deflected → must be part of an atom that’s positively charged.
3) very few were deflected backwards → the charged nucleus must be very small compared to the size of the atom.

Question 11

Electron diffraction

Answer 11

• High speed electrons are fired at a thin sheet of material
• as they pass through the atoms they diffract, concentric circles is formed on a screen behind the material.
(More accurate)
Sintheta = (1.22lambda)/2R

Question 12

1Bq

Answer 12

1 decay per second

Question 13

Intensity unit

Answer 13

Wm^-2

Question 14

Radioactive decay equations

Answer 14

N = Noe^-(lambda)t
Nuclei number
Activity
Mass
Count rate

Question 15

Nuclear waste treatment

Answer 15

1) should be cooled in cooling ponds to reduce temps to safe levels
2) stored in thick (several metres) concrete containers deep underground for hundreds of years/vitrified
3) all handling should be done remotely

95% spent fuel rods (3% vol)
4% sludges and resins (7% vol)
1% clothes worn etc (90% vol)

Question 16

Below iron
Above iron

Answer 16

Fusion
Fission

Question 17

Why does fusion release more energy

Answer 17

Due to the larger nucleus having a larger binding energy per nucleon.

Question 18

Density of a nucleus

Answer 18

P =m/v
m = 3Au (mass number x atomic unit)
V=4/3πr
R=RoA^⅓

Therefore density = 3Au/4π(RoA^⅓)³
=3u/4πRo³

Therefore density is independent of radius and a constant. As Ro = 1.05x10^-15. should always be x10^17 magnitude.

Question 19

Why is inverse square law not always accurate

Answer 19

1) dead time
2) may not be pure gamma, could have beta in it

Question 20

Explain why there is an imbalance in the number of neutrons and protons in a larger nucleus

Answer 20

More neutrons are needed to hold the nucleus together to add to binding force, to reduce repulsion between protons and therefore reduce instability

Question 21

Why are gamma rays useful for medical diagnosis

Answer 21

Low half life therefore doesn’t remain in body too long after medical diagnosis
High penetration therefore can leave body
Weakly ionising therefore less damage to body

Question 22

What provides evidence for the existence of:
Electrons
Energy levels in nuclei

Answer 22

1) existence of X-ray line spectra
2) existence of gamma radiation

Question 23

How to use R = RoA⅓

Answer 23

Ro is a constant and therefore can be worked out.
Or proportionality (R1/A⅓) = (R2/A⅓)
Therefore R1 = (A1/A2)⅓ x R2

Question 24

Benefits of nuclear power?

Answer 24

1) less pollution
2) little Co2 produced (not pollution)
3) high energy density

Question 25

Purpose of a moderator

Answer 25

To slow down fast neutrons produced during nuclear reactions. By slowing down these neutrons, the probability of their interaction with fissile material (like uranium-235 or plutonium-239) increases. This enhanced interaction improves the efficiency of the nuclear reaction, allowing sustained and controlled energy production. .

Question 26

Why does the number of collisions needed depend on the nucleon number of the moderator atoms?

Answer 26

Collisions are elastic
More nucleons = larger mass
Therefore less KE transferred to nucleus therefore more collisions are needed