Nuclear physics. Flashcards
Revision (21 cards)
Alpha scattering experiment
to prove that the central part of an atom is the nucleus with +ve charge.
Apparatus: Very thin sheet of gold, Alpha particles
Process: To strike alpha particles on the sheet of gold.
3 scenarios were observed
1. Passing straight through means most of the space is empty.
2. Deflecting( changing the angle)- Means there is some charge in some space.
3. Bounced back- Means there is a +ve charged object at the center containing most mass and causing particles to repel.
Structure of an atom
Center has a positive charger nucleus containing protons and neutrons.
The electrons orbit the nucleus in energy levels/ orbitals/ shells.
Protons and neutrons have mass 1 and electrons has mass 1/2000.
Protons- +1
Electrons- -1
Neutrons- 0 (combination of proton and electron)
Isotopes
The atom of same element with same proton number but different mass number and basically have different number of neutrons.
2 TYPES:
Stable isotopes
Unstable isotopes- Give out radiation until they become stable.
Hydrogen 1- protium
Hydrogen 2- Deuterium
Hydrogen 3- Tritium
Alpha (α), Beta (β), and Gamma (γ) radiations (3-4 points each)
Alpha:
A helium nucleus (helium atom with double +ve charge)
It is heavy as it has the mass of a nucleus this is why it can not penetrate much.
It looses energy in ionizing as it has high charge. Can be stopped by a thin sheet of paper.
Beta:
A single electron
-1 charge.
They are fine at penetrating and ionizing.
They have no mass.
Gamma :
These are electromagnetic radiations and only carry energy, no mass.
Very good at penetrating due to no mass.
Few cm of lead is required to stop these.
Brings particles from excited to non-excited state.
No charge
Alpha (α), Beta (β), and Gamma (γ) Decay
Alpha:
The proton no decreases by 2 and mass no by 4.
Element shifts 2 places behind in the table.
Beta:
A neutron turns into a proton and electron.
There is no change in the neutron number as when the neutrons turns into proton the proton increases and adds up to the mass number.
Gamma:
Only brings the particle from excited to non excited state as it re-arranges the subatomic particles.
Background radiation
We are exposed to background radiation all the time.
Cosmic rays
Potassium-40 in food and water.
Radon gas
Radioisotopes use in medicine industry.
Measure radiation
Alongside argon, a small amount of a quenching gas (like halogen or alcohol vapor) is added. This stops continuous discharges by absorbing the energy from positive ions and preventing false signals.
Geiger muller tube
1. The radiation enters through the mica window and if penetrating enough it can penetrate through.
2. The cathode/ anode attract the radiation.
3. Inside a gas is filled (argon gas).
4. When they reach electrodes, current is produced and fed into the ratemeter/ scale.
Scale- shows the count of pulse received in the time.
Ratemeter- gives the no of radiations per second.
Geiger muller can detect background radiations and to fix this count rate correction is used.
The background radiation is subtracted from the total radiations.
To test penetrating power
A radium source is kept on one side and a Geiger muller on the other side of an aluminum foil.
It can be determined if the radium passes through aluminum foil if it is detected by the Geiger counter.
Nuclear stability
If above stability line ( beta -ve decay)
If below stability line (beta +ve decay)
If proton no higher than 82 (alpha decay)
(An atom is unstable when neutrons are more than protons)
Nature of decay
It is spontaneous
It is random.
The longer the decay happens the more stable the isotope becomes.
Half life
The time taken for the isotope to reduce to half its atoms.
Magnetic and electric deflection
Beta bends before alpha as alpha is heavier.
Gamma doesn’t bend at all.
Uses of radiation- Diagnoses using tracer
Radioactive tracer contains chemical compounds that emit radiations. This is put in patient’s body.
The tracer circulates through the body making it easy to detect any tumor.
The tracer with a half life appropriate to the treatment is chosen.
This is also used in agriculture to detect fertilizers taken by plants.
Uses of radiation- Smoke detector
An alpha source gives out alpha particles.
The particles ionize the air.
The charged plate attracts the charged ir particles and so the current flows.
When there is presence of smoke, the alpha particles are blocked and the current can not flow. This is detected by sensors and an alarm starts to ring.
Uses of radiation- Measuring thickness gauge
There is a source of beta particles at the top of the gauge and on the bottom is a detector.
If there is a change in the number of beta particles detected then the thickness is adjusted.
Gamma is not used as it will go through even if the material is thicker.
Uses of radiations- Radiotherapy
Treatment of cancer using radiations.
Gamma rays is showered at the tumor and penetrates through to damage the cell. The beams are rotated so that they don’t harm healthier cells. A source with short half life is taken.
Uses of radiations- Sterilizing
Irradiation- Killing organisms from instruments to sterilize them.
The item is placed in safe bags to stop contamination.
Food can also be sterilize.
Contamination- accidental exposure to radiation.
Uses of radiations-Archeology
Plants take in carbon 12 and carbon 14 which is radioactive.
After dying they don’t take in any carbon but the decay still continues.
Carbon-14 with half life 5700 years can be used to find the age of the wood used.
It can be compared to carbon- 12 to see how much is decayed and how much is left.
Dangers of radiations
Can destroy living cells.
Mutate DNA- If radiation gets in healthy cells, it can ionize the DNA and damage it.
It this damaged DNA replicated itself then tumor can be formed causing cancer.
Disrupt food chain, skin burns, Reduce the white blood cells.
Safety precautions
While transporting radioactive material use lead boxes.
Minimize exposure.
Use gloves and lead aprons.
Maintain distance.
Wear a badge which measures radioactivity and check if the image is too dark that means high exposure.
Concrete walls should be built for workers’ safety.
Radioactive waste is buried underground.
Kinetic energy in alpha beta and gamma
Alpha particles are very heavy and have low speed, but they carry high kinetic energy due to their mass.
This high kinetic energy helps them collide strongly with atoms, causing lots of ionisation in a short distance.
