Nuclear Physics Flashcards
What were scientists thoughts on the Plum Pudding model
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
How is rutherford scattering done
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
What is the results of the Rutherford scattering experiment
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
Why is electron diffraction accurate to estimate nuclear radius
Electron is type of lecpton
Lepton don’t interact with strong nuclear force
So electron diff is accurate
WHat type of wavelength is needed to investigate the nuclear radius
Wavelength should be tiny so electrons will have very high energy
What is the equation for the first minima when a beam of high-energy electrons is directed onto a film
sin0 = 1.22λ / 2R
Describe the relation between intensity and diffraction angle
Intensity of maxima Decreases as the angle of diffraction increases
Compare the size of a nucleus radius to the atomic radius
Nuclear radius is smaller than atomic radius as the nucleus contains the nucleons within the atom.
What is the relation between Nuclear radius and Nucleon Number
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
How do you work out the density of a nuclear matter
Proton and neutron = m-nucleon
Density = mass / vol
so
Density = A(nucleons no.) x m-nucleon / 4/3πR^3
What does the huge density of the nuclear matter suggest
Contain lots of empty space , with most of mass being in the centre of the small nucleus
What happens when a nuclei is unstable
Break down to become stable
Having too many nucleons or not enough or too much energy
What is radioactive decay
Nucleus decays by releasing energy and particles until it is stable
What is ioinising radiation
When radioactive particle hits an atom and knocks of electrons , creating ions
Describe the ionising properties of Alpha Particles
Strongly Positive - pull electrons off atoms
QUicklt ionise atoms and lose ites energy .
Cannot penetrate skin but when ingested can ionise body tissue
Describe the ionising properties of Beta minus particles
Less mass and charge compared to alpha particles
Not as ionising as alpha particles but can still damage body cells.
Describe the uses of Gamma rays in medicine
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
Give examples of background Radiation
Air
Ground and buildings
Cosmic Radiation
Living things
Man-made radiation
What is the relation of the intensity of gamma radiation
an inverse square law
I= k / x^2
What is the rate of decay
The nuber of nuclei that decay each second is proportional to the siize of the sample
Measured in becquerels.
1Bq = 1 decay per sec
What is the equation for activity
Activity = decay constant x no.of nuclei
A = λN
∆N / ∆T = - λN
Define Half- Life
The average time it takes for the number of unstable nuclei to halve
What is the equation for half life/Decay
T1/2 = Ln2 / λ
N = ne^- λt
What is the uses of Half-lives
Radioactive dating of objects
Medical diagnosis
