5.1.1- Radioactivity And Nuclear Energy

Question 1

What principle can you use when calculating the closest approach of a scattered particle deflected by 180°

Answer 1

That the initial kinetic energy equals the final electric potential energy

Question 2

Why is electron diffraction more accurate than alpha particle scattering

Answer 2

As electrons are leptons they do not interact with the strong nuclear force where as neutrons and alpha particles do

Question 3

How is this electron diffraction different to the AS level syllabus

Answer 3

At AS-level the electrons defected through the gaps between the atoms however hear the electrons diffract around an individual nucleus. This is why Lambda must be near the diameter of the nucleus for maximum diffraction.

Question 4

How do you convert electron volts (eV) to Joules

Answer 4

Multiply by the charge of an electron (1.6x10^-19)

Question 5

What is the equation for where the first minimum appears with electron diffraction which can be used to work out the diameter of the nucleus.

Answer 5

Sinø= 1.22 x wavelength/diameter

Question 6

What is the typical radius of an atom

Answer 6

1x10^-10 m

Question 7

What is the typical radius of a nucleus

Answer 7

1x10^-15 m

Question 8

What is the constituent part of Gamma radiation

Answer 8

Sort-wavelength, high-frequency electromagnetic wave

Question 9

Why is u (atomic mass units) used when referring to masses

Answer 9

To simplify things, one atomic mass unit is equal to 1.661×10^-27 kg, about the mass of a proton or neutron.

Question 10

What is the penetrating power of alpha particles

Answer 10

Absorbed by paper or a few centimetres of air

Question 11

What is the penetrating power of beta minus radiation

Answer 11

Absorbed by around 3 mm of aluminium

Question 12

What is the penetrating power of beta plus radiation

Answer 12

Annihilated by electron so virtually zero range

Question 13

What is the penetrating power of gamma radiation

Answer 13

Absorbed by many centimetres of lead, or several metres of concrete

Question 14

What are the conclusions from Rutherford scattering

Answer 14

The nuclei must be positive to repel alpha particles, they must be very small as very few are deflected by big angles, and most of the mass and positive charge must be contained within a small nucleus as most just pass straight through. (TL:DR- small, positive nucleus with lots of empty space)

Question 15

Name five sources of background radiation

Answer 15

1. The air- Radon gas released from rocks (largest contributor)
2. Ground and buildings- the rocks they contain
3. Cosmic radiations- cosmic rays are high energy particles from space that collide with particles in the upper atmosphere producing nuclear radiation
4. Living things- radioactive Carbon-14
5. Man made- medical and industrial sources

Question 16

What is the decay constant

Answer 16

The probability of an atom decaying per unit time

Question 17

What is the activity of a sample

Answer 17

The number of atoms that decay each second, measured in Becquerels (Bq)
Is also equivalent to the the rate of change of unstable nuclei.

Question 18

What is the half life of a substance

Answer 18

The average time it takes the number of unstable nuclei to halve

Question 19

Name two uses of radioactive isotopes

Answer 19

1. Radiocarbon dating using Carbon-14

2. Medical radioactive tracers- show tissue/organ functions

Question 20

State 4 problems with radiocarbon dating

Answer 20

1. Can only find age of material, not the object
2. Uncertainty in the amount of C-14 that existed thousands of years ago
3. Small sample size so statistically unreliable
4. May have had contamination with other radioactive sources.

Question 21

In what type of nuclei does Alpha mission

Answer 21

V.heavy nuclei

Question 22

In which type of nuclei does beta minus decay occur

Answer 22

Neutron rich

Question 23

In which type of nuclei does beta plus decay occur

Answer 23

Proton rich

Question 24

In which type of nuclei does gamma emission occur

Answer 24

Too much energy/excited

Also caused by electron capture

Question 25

What is the mass defect of a nucleus

Answer 25

The difference between the mass of a nucleus and the sum of the masses of its constituent nucleons
The energy released when forming the nucleus is equivalent to the mass defect using e=mc^2

Question 26

What is the binding energy of a nucleus

Answer 26

The energy that needs to be overcome to pull the nucleons apart in the nucleus, measured in MeV

(This amount of energy needed to pull the nucleons apart is equivalent to the mass defect, using e= mc^2)

Question 27

How many MeV of energy is 1 atomic mass unit (u)

Answer 27

931.5 MeV

(The mass of nucleons is often given in the form of u for simplicity, you can use this figure to convert the mass defect in u into MeV (energy).)

Question 28

What is the max value for the binding energy per nucleon?

Answer 28

8.7 MeV (Iron)

Question 29

Define the atomic mass unit

Answer 29

1/12 the mass of a C-12 atom