Nuclear Physics

Question 1

What were scientists thoughts on the Plum Pudding model

Answer 1

Democritus though the identical lumps were atoms

Dalgon agreed and thought each element was made up of different atoms

jj Thomson discovered electron can be removed

’’ Suggest atoms were spheres of positive charge

Rutherford suggest atoms do not have uniform charge and density

Question 2

How is rutherford scattering done

Answer 2

Fire beam of alpha particles at thin gold foil

Circular detector used to detect alpha particles deflected at any angle

Expect alpha particles to deflect by electrons by small amount

Mot particles went straight through foil

Question 3

What is the results of the Rutherford scattering experiment

Answer 3

Atoms must have a small positive charged nucleus at centre

Large +ve charge = a particle were repelled and deflected by large angle

Nucleus is small and very few particles deflected back

So mass is in the centre as fast particles are deflected by nucleus

Question 4

Why is electron diffraction accurate to estimate nuclear radius

Answer 4

Electron is type of lecpton
Lepton don’t interact with strong nuclear force
So electron diff is accurate

Question 5

WHat type of wavelength is needed to investigate the nuclear radius

Answer 5

Wavelength should be tiny so electrons will have very high energy

Question 6

What is the equation for the first minima when a beam of high-energy electrons is directed onto a film

Answer 6

sin0 = 1.22λ / 2R

Question 7

Describe the relation between intensity and diffraction angle

Answer 7

Intensity of maxima Decreases as the angle of diffraction increases

Question 8

Compare the size of a nucleus radius to the atomic radius

Answer 8

Nuclear radius is smaller than atomic radius as the nucleus contains the nucleons within the atom.

Question 9

What is the relation between Nuclear radius and Nucleon Number

Answer 9

Proportional to the cube root of the nucleon number

Linear relationship - as nucleon number inc , radius inc proportional to the cube root of A

so R ∝ A^1/3

so R =rA^1/3

Question 10

How do you work out the density of a nuclear matter

Answer 10

Proton and neutron = m-nucleon

Density = mass / vol
so
Density = A(nucleons no.) x m-nucleon / 4/3πR^3

Question 11

What does the huge density of the nuclear matter suggest

Answer 11

Contain lots of empty space , with most of mass being in the centre of the small nucleus

Question 12

What happens when a nuclei is unstable

Answer 12

Break down to become stable
Having too many nucleons or not enough or too much energy

Question 13

What is radioactive decay

Answer 13

Nucleus decays by releasing energy and particles until it is stable

Question 14

What is ioinising radiation

Answer 14

When radioactive particle hits an atom and knocks of electrons , creating ions

Question 15

Describe the ionising properties of Alpha Particles

Answer 15

Strongly Positive - pull electrons off atoms

QUicklt ionise atoms and lose ites energy .

Cannot penetrate skin but when ingested can ionise body tissue

Question 16

Describe the ionising properties of Beta minus particles

Answer 16

Less mass and charge compared to alpha particles

Not as ionising as alpha particles but can still damage body cells.

Question 17

Describe the uses of Gamma rays in medicine

Answer 17

Weakly ionising , less damage to body tissue.

Radioacctive tracers - short half life
Treatment for cancerous tumours

Long term - infertility , risk to medical staff for long exposure time

Question 18

Give examples of background Radiation

Answer 18

Air
Ground and buildings
Cosmic Radiation
Living things
Man-made radiation

Question 19

What is the relation of the intensity of gamma radiation

Answer 19

an inverse square law

I= k / x^2

Question 20

What is the rate of decay

Answer 20

The nuber of nuclei that decay each second is proportional to the siize of the sample

Measured in becquerels.
1Bq = 1 decay per sec

Question 21

What is the equation for activity

Answer 21

Activity = decay constant x no.of nuclei

A = λN

∆N / ∆T = - λN

Question 22

Define Half- Life

Answer 22

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

Question 23

What is the equation for half life/Decay

Answer 23

T1/2 = Ln2 / λ

N = ne^- λt

Question 24

What is the uses of Half-lives

Answer 24

Radioactive dating of objects

Medical diagnosis

Question 25

How can a nucleus be unstable

Answer 25

has :
Too many neutrons
too few neutrons
too many nucleons altogether
too much energy

Question 26

When does alpha emission happens

Answer 26

Happens in heavy atomes
eg . uranium and radium
Nuclei are too massive to be stable

Question 27

When does beta minus emission happens

Answer 27

Happens in Neutron rich nuclei , neutron changed into proton

Question 28

Wheen does gamma radiation emission happens

Answer 28

Emitted from nuclei with too much energy.
Often comes with alpha or beta decy in the form of lost energy/

Question 29

What is another way gamma radiation is produced

Answer 29

Electron capture -
proton to change into neutron ,makes a nucleus unstable and it emits gamma radiation

Question 30

What is conserved in nuclear reactions

Answer 30

Energy , momentum , charge nucleon number

Question 31

Describe fission

Answer 31

Large nuclei split into smaller nuclei

Spontaneous annd induced.

Question 32

Why is energy released during fissions

Answer 32

The new smaller nuclei have a higher binding energy per nucleon

Question 33

What is the nature of a large nucleus

Answer 33

More unstable , more likely to spontaneously fission , limits the number of nuleons , limits number of possible elements.

Question 34

What does a fission nuclear reaction contains.

Answer 34

Rods of uranium
Control rods
Cool water
moderator
concrete case