Section 8 - Nuclear Physics

Question 1

What are the three types of radiation?

Answer 1

Alpha,beta, gamma

Question 2

What is the plum pudding model?

Answer 2

a sphere of positive charge, with small areas of negative charge evenly distributed throughout

Question 3

What set up did rutherofrd use to do the scattering experiment?

Answer 3

• alpha source ,gold foil in an evacuated chamber which was covered in a fluorescent coating,
• Microscope on the outside of the chamber to view the screen

Question 4

What was observed in the rutherford scattering experiment?

Answer 4

Most alpha particles passed straight through the foil with no deflection ; the atom is mostly empty space
● A small amount of particles were deflected by a large angle ; the
centre of the atom is positively charged, as positively charged alpha particles were
repelled from the centre and deflected.
● Very few particles were deflected back by more than 90° ; centre of the atom was very dense as it could deflect fast moving alpha particles, but
also that is was very small as a very small amount of particles were deflected by this
amount.
it was concluded that the atom has a small, dense, positively charged
nucleus at its centre.

Question 5

How many particles are deflected by an angle greater than 90 degrees for a given foil that has n layers of atoms

Answer 5

1/10000n

Question 6

What order is nuclear radius in?

Answer 6

10^-15 (femtometers)

Question 7

What is the ratio of nuclear diameter to atomic diameter?

Answer 7

d^2 = D^2/10000n

Question 8

In what sort of elements does alpha decay occur?

Answer 8

Generally heavier elements such as uranium

Question 9

What is alpha radiation stopped by?

Answer 9

Paper or a few centimeters of air(2-10cm)

Question 10

Is alpha radiation highly, medium or weakly ionising?

Answer 10

Highly

Question 11

name a use for alpha radiation

Answer 11

Smoke detectors

Question 12

What sort of elements decay due to beta decay?

Answer 12

Generally lighter elements

Question 13

what happens inside the nucleus during beta - decay?

Answer 13

Neutron turns into proton

Question 14

is beta decay highly,medium or weakly ionsing?

Answer 14

medium

Question 15

What is beta decay stopped by?

Answer 15

3mm of aluminimm foil, 1m in air

Question 16

What are beta particles use for?

Answer 16

Measuring the thickness of paper

Question 17

What is gamma decay?

Answer 17

High frequency em wave

Question 18

How ionising is gamma decay?

Answer 18

Weakly

Question 19

what is gamma radiation stopped by?

Answer 19

Several inches of lead or several meters of concrete

Question 20

Uses pf gamma radiation

Answer 20

Medical tracers, radiotherapy

Question 21

What is the decay constant for an isotope?

Answer 21

It is the probability that an isotope will decay per unit time

Question 22

Formula for finding the deacy constant?

Answer 22

ΔN/Δt = -λN

Question 23

what is radioactivty measured in?

Answer 23

Counts per second or bq

Question 24

What is half life?

Answer 24

Time taken for activity of a radioactive material to half

Question 25

What is halved when a material decays by a half-life?

Answer 25

Undecayed nuclei
Mass of undecayed material
Activity

Question 26

What is the relationship between Activity and Number of un deacyed nucleons?

Answer 26

A α N
A = -λN
dN/dt = -λN

Question 27

What is the relationship between activity, mass and undecayed nuclei?

Answer 27

A/A0 = N/N0= M/m0 = e^-λt

Question 28

Half life equation

Answer 28

λ = ln2/t

Question 29

what do A Z and N represent?

Answer 29

A: atomic mass number
Z: proton number
N: neutron number

Question 30

What is the definition of 1u?

Answer 30

1/12 the mass of a carbon-12 atom

Question 31

What sort of nuclei does fission happen to?

Answer 31

Heavy nuclei

Question 32

What is nuclear fission?

Answer 32

The process of splitting up a large nucleus into two daughter nuclei (and two or 3 neutrons)

Question 33

What is the mass defect?

Answer 33

Difference between the mass of a nucleus and the mass of its equivalent constituents

Question 34

What is the definition for binding energy?

Answer 34

The energy required to split a nucleus/atom into its constituents

Question 35

Where does the mass defect come from?

Answer 35

Mass is lost when some of the mass from the constituents is converted into energy so that they can form an atom

Question 36

what is 1u in Mev?

Answer 36

931.3 Mev

Question 37

Where does the energy come from in nuclear fission?

Answer 37

Binding energy increases as the daughter nuclei are more stable so it becomes harder to separate them

Question 38

Explain what is binding energy per nucleon and how they relate to fission and fusion

Answer 38

The higher the bepn is the better it is to fission as it will be more unstable and less energy is required to induce fission so there are better enrgy returns
For fusion a lower bepn is better as to fuse lighter elements requires less energy so the energy returns ar better.

Question 39

What are the 4 reasons nuclei might decay?

Answer 39

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

Question 40

Why does the number of neutrons and protons in a stable nucleus does not increase uniformly beyond around 20?

Answer 40

more neutrons are needed to increase the distance between protons in order to decrease
the magnitude of the electromagnetic force

Question 41

Where are beta+ - and alpha decay on the NZ curve?

Answer 41

beta- above N=z towards the bottom
beta+ below N=Z towards the bottom
Alpha towards top of curve

Question 42

Diameteter of an atom

Answer 42

10^-10

Question 43

Diamter of a nucleus