Nuclear Physics Flashcards
What is the Rutherford Scattering Experiment ?
It provides evidence for an atomic structure
- Scattering of alpha particles by thin metal foils
- alpha particles from a radioactive source fired at very thin gold foil
- strikes a fluorescent screen (circular) a tiny visible light if produced
What are the conclusions made from the Rutherford Scattering Experiment ?
1) ATOMS MUST BE MOSTLY EMPTY SPACE
- most of the alpha particles just pass straight through
2) NUCLEUS MUST HAVE A LARGE POSITIVE CHARGE
- as some alpha particles are repelled + deflected by large angle
3) NUCLEUS MUST BE TINY
- as very few particles are deflected by angle < 90
4) MOST MASS MUST BE IN THE NUCLEUS
- since fast alpha particles are deflected by the nucleus
How the structure of the nucleus has changed over time ?
- Matter was made of little lumps ‘atomos’
- Tiny spheres that couldn’t be broken down
- Plum pudding
- Rutherford scattering - protons and electrons
- Evidence for the neutron
What experiments can you measure the Nucleus radius ?
1) Close approach of a scattered particle
2) Electron diffraction
How to estimate the Radius of the nucleus using the Close approach of a scattered particle method ?
Initial Ek = E(electric potential energy)
E = Qq/4πEor
How to estimate the Radius of the nucleus using the electron diffraction method ?
- more accurate that ‘close approach’
- can be diffracted due to wave-article duality
- λ = hc/E
- FIRST MINIMUM (from diffraction pattern)
SinѲ = 1.22λ/2R
How does Intensity vary with diffraction angle ?
- central bright maximum containing the majority of the incident electrons
- intensity decrease as the angle of diffraction increases
- NEED TO KNOW GPAPH
How to calculate the Nuclear Density ?
R = RoA^1/3 -> R^3∝A -> V∝A
- p = m/v - assume nucleus is spherical
- p = A x M / 4/3πR^3
- p = A x M / 4/3π(RoA^1/3)^3
- p = 3M/4πRo^3 = constant
How to show the nuclear radius (R) is proportional to the cube root of the nucleon number (A)
As the nucleon (atomic mass) increase the nuclear radius increases - R/A graph
- linear relation between R and A^1/3
R = RoA^1/3
(Ro = 1.4x10^-15)
- show evidence that nuclear material have a CONSTANT DENSITY
What are the four types of Nuclear Radiation ?
1) Alpha
2) Beta-Minus
3) Beta-Plus
4) Gamma
What are the properties of Alpha Radiation (α) ?
CONSTITUENT - 2 Protons + 2 Neutrons (He) IONISING POWER - Strong SPEED - Slow PENETRATING POWER - Absorbed by paper/skin or few cm of air AFFECTED BY MAGNETIC FIELD - Yes
What are the properties of Beta-Minus Radiation (β-) ?
CONSTITUENT - Electron IONISING POWER - Weak SPEED - Fast PENETRATING POWER - Absorbed by 3mm of aluminium AFFECTED BY MAGNETIC FIELD - Yes
What are the properties of Gamma Radiation (γ) ?
CONSTITUENT IONISING POWER SPEED PENETRATING POWER AFFECTED BY MAGNETIC FIELD
What are the properties of Gamma Radiation (γ) ?
CONSTITUENT - Electromagnetic Wave IONISING POWER - Very Weak SPEED - Speed of Light PENETRATING POWER - Absorbed by thick lead or concrete AFFECTED BY MAGNETIC FIELD - No
What is Alpha Radiation used for ?
Is used for Smoke alarms because they allow current to flow but won’ travel far
- only need to amount of source
How to identify Radiation ?
Use a GM-tube ( GEIGER-MULLER )
- record count-rate/ mins^-1
- use different materials to receive count-rate
- repeat 3 times and average
- Corrected count-rate = CR - BCR
What is Gamma Radiation used for ?
- Radioactive tracers - help diagnose patients without the need of surgery
- radioactive source injected into body with short half-life to prevent prolonged radiation exposure
- PET scanner used to detect emitted gamma rays
- treat cancer by damaging cells (but all cells)
What is Beta Radiation used for ?
Is used for measuring the thickness of a material
- too little radiation being absorbed -> rollers move part so make material thicker
- too much radiation being absorbed -> rollers move closer so make material thinner
How to safely handle radioactive sources ?
- exposure time is minimum
- shielding during treatment
- inside lead box
- handle with long handling tongs
What is Background Radiation (BR) and type of sources of it ?
Is the low level of radiation always present
SOURCES
- Air (radon gas released from rocks)
- Ground and Buildings
- Cosmic radiation
- Living things e.g. plants/animals
- Man-made radiation e.g medical/nuclear power
What is the INVERSE SQUARE LAW ?
States the intensity of gamma radiation decreases with distance from a source
ɪ = K/x^2
- Intensity of radiation is the amount of radiation per unit area (Wm^-2)
- K - constant of proportionality (W)
- Graph of CCR/distance - ∝1/d^2
What is RADIOACTIVE DECAY ?
Is an unstable nucleus that breakdowns by releasing energy and/or particles to become more stable
- is random and can’t be predicted
What has the same rate of radioactive decay ?
ISOTOPES have the same rate of radioactive decay - constant decay probability
What is the ACTIVITY (A) of a sample ?
Is the number of nuclei that decay each seconds
- Measured in Bq
A = λN
- λ = decay contsant (s^-1)
- N = number of unstable nuclei in sample
What is the Decay constant (λ) ?
Is the probability of a specific nucleus decaying per unit time
- measure of how quickly an isotope will decay
- bigger λ - faster the rate of decay
How else can Activity be written as ?
A = -ΔN/Δt - Is the number of nuclei that decay each seconds - minus sign as always decreasing ΔN/Δt = -λN - model by using spreadsheet modelling
]What is the Decay Equation ?
N = Noe^-λt
A = Aoe^-λt
- Both N and A for a radioactive source both decrease exponentially
- can get Linear graph In(N) = -λt + In(No)
