Unit 5 - Nuclear physics Flashcards
Mass and charge of a proton
- 1
- +1
Mass and charge of a neutron
- 1
- 0
Mass and charge of an electron
- 1/2000
- -1
Ernest Rutherford’s alpha particle experiment setup
- Beam of alpha particles directed through a slit in a circular fluorescent screen towards a piece of thin gold foil
- Carried out in a vacuum so alpha particles wouldn’t collide with anything else
- A flash would be produced when the alpha particles hit the screen showing their position
- Most particles travelled through the foil but some were deflected
Rutherford’s findings from his experiment & proof
- Number of protons and electrons are equal - atoms don’t have an overall charge
- Most of the atom is empty space or nucleus is incredibly small - Most particles went straight through the foil and only 1/8000 were deflected
- The nucleus is positively charged - Alpha particles are positive some were repelled
- The nucleus accounts for nearly all the mass - some particles deflected back in the opposite direction, hence the tiny nucleus contains most of the mass to cause that change in momentum
Subatomic particles
- Proton
- Electron
- Neutron
Nuclide
An atom of nucleus characterized by a specific number of protons and neutrons
Nuclide notation
- Symbol of the element from the periodic table with the nucleon number on the top left and the proton number on the bottom left
Isotopes
Atoms of the same element with the same number of protons and electrons but with a different number of neutrons
Nuclear fusion
The process by which lighter nuclei collide with high energy and join to form a larger nucleus and energy is released
Nuclear fission
Due to the instability of a nuclei with a large nucleon number, it breaks apart either completely independently or if a neutron is fired into the large nucleus making is break and energy is released
Source of released energy in nuclear fission and fusion
A decrease in mass (usually -0.1%)
Equipment used to measure radiation
- Geiger-Müller tube - can detect alpha and beta particles and gamma radiation
- Spark counter - can detect alpha, beta, and gamma radiation
- Cloud chamber - shows the path of alpha and beta particles by producing a vapor in the trail
Unit of measurement for radioactive decay
- Count rate - number of emissions of radiation in a certain time - (count/s) or (count/min)
Count rate equation
Count rate (count/s) = measured count rate (count/s) - background radiation (count/s)
Largest source of background radiation on earth
Radon gas
Radioactivity
The process by which an unstable nucleus becomes more stable by emitting radiation
Properties of alpha particles
- Made of two protons and two neutrons
- Mass of 4
- Charge of +2
- Highly ionizing
- Least penetrating radiation
- Can only travel 5cm through air and can be stopped by thin paper or skin
- Attracted by negative and is deflected by a small amount
- Direction of the particle is equal to the direction of the current
Properties of beta particles
- High-energy electron
- Mass of 1/2000
- Charge of -1
- Mildly ionizing
- Can travel through skin but are stopped by a few mm of aluminum foil
- Attracted to positive and if deflected by a large amount
- Direction of the particle is opposite to the direction of the current
Properties of gamma emissions
- Electromagnetic waves
- Very high frequency and very high energy
- No mass and no charge
- Weakly ionizing
- Most penetrating, can only be stopped by thick lead or concrete
- Path is not altered by an electric field
Ionizing radiation
Able to strip away the electrons of a material that it comes into contact with
Radioactive decay
When a nucleus emits alpha or beta particles of gamma radiation in order to become more stable - the decay is spontaneous and in a random direction - nucleus changes to a different element after emission
Effect of an emitted alpha particle on a nucleus
Loses two protons and hence reduces atomic number by 2
Effect of an emitted beta particle on a nucleus
Neutron transforms into a proton raising the atomic number
Effect of emitted gamma radiation on a nucleus
No effect / nucleus remains unchanged
Rule of nuclear decay equations
Total mass if conserved
Half-life
- The time taken for the count rate of a radioactive source to decrease by half / for the number of radioactive nuclei to decrease by half
Uses of alpha, beta and gamma radiation
- Food is irradiated with beta or gamma radiation to kill bacteria - increases shelf life
- Alpha particles are used in smoke detectors - smoke collides with alpha particles so less current flows between positive and negative plates causing an alarm to sound
- Beta particles are used to test and control thickness of materials
- Gamma radiation is used in medical tracers
- Gamma radiation is used on a single point in the body for cancer treatment - can kill cancer cells
- Gamma rays can be used to sterilize equipment by killing viruses
Safety equipment when dealing with radiation
- Lead shield
- Gloves
- Glasses or goggles
- Tongs when moving materials
Storing alpha particles
- Thin package
- Protective clothing must be worn when handling
Storing beta particles
- Stored in lead or a similarly dense metal container
Storing gamma radiation
- Buried deep underground
Safety strategies with radioactivity
- Exposure time - reduce exposure time
- Shielding - placing a barrier between the person and the radiation
- Distance - increasing the distance from the source reduces intensity
