Alpha beta and gamma radiation

What was the Rutherford scattering experiment?

beams of alpha particles passed through thin sheet of gold foil to investigate angle of deflection of alpha particles and number of alpha particles deflected at each angle. Included a source of alpha particles in a lead container, a thin sheet of gold foil, a moveable detector and an evacuated chamber.

What was the purpose of the lead container in Rutherfords scattering experiment?

alpha particles are emitted in all directions so container with narrow hole produced a beam of them since lead absorbs alpha particles.

What was the purpose of the thin sheet of gold foil in Rutherfords scattering experiment?

A thicker foil would stop the alpha particles completely, gold was malleable and easy to hammer into thin sheets.

What was the purpose of the evacuated chamber in Rutherfords scattering experiment?

alpha particles are highly ionising so it ensured the alpha particles didn’t collides with any other particles.

What were the findings from Rutherfords scattering experiment?

The majority of alpha particles passed through foil undetected, suggesting the atom is mostly empty space.

Some alpha particles deflected through small angles of <10 degrees, this suggests there is a positive nucleus at the centre, since alpha particles are positive and two positives repel.

Only a small number of alpha particles deflected straight back at angles <90 degrees, this suggests nucleus is very small and most of mass and charge of the atom are concentrated.

What is an alpha particles?

2 protons, 2 neutrons. the most ionising type of radiation ( most damage to cells), the least penetrating radiation (travel shortest distance in air before being absorbed).

What are beta particles?

Beta minus- high energy electron, beta plus- high energy positron. moderately ionising and moderately penetrating.

What are gamma rays?

High energy electromagnetic radiation., least ionising type of radiation, most penetrating type of radiation, has an infinite range.

What is ionising?

When a type of radiation collides with an atom and knocks out electrons.

What happens to radiation when it enters a field?

Electric: Alpha particles are directed to negative plate, beta particles deflected to positive plate, gamma radiation is not deflected. The deflection of a particle depends on their speed, mass and charge. in strong electric and magnetic fields alpha particles can be deflected slightly since they have the highest charge but also the greatest mass, beta particles can be deflected through large angles since they travel at greater speeds and have less mass, gamma rays aren’t deflected at all.

What is an application of alpha and beta?

alpha- smoke detectors, smoke enters alarm, absorbs alpha particles, reduces current causing alarm sound.

beta- thickness control, measure how thick somethingis by seeing how much beta radiation passes through

What is the equation for intensity of gamma radiation?

I=k/x²

I= intensity of gamma radiation ( Wm -² )

k= constant of proportionality

x= distance from source (m)

What is the equation for intensity of gamma radiation at two different points?

I₁/I₂= (x₂/x₁)²

What is background radiation?

The ionisng radiation present in the environment, it can be separated into natural sources and artificial sources.

What are some natural sources of background radiation?

Radon gas from rocks and buildings- radioactive elements which occur naturally in rocks and soil that then decay into radon gas, can only be by Geiger counter.

Cosmic rays from space- protons from sun collide with molecules in air in earth’s atmosphere and produce gamma radiation.

Carbon-14 in biological material.

What are some artificial sources of background radiation?

Nuclear medicine- X-rays, radiation therapy

Nuclear waste- dangerous for people handling it

Nuclear fallout from nuclear weapons- residue radioactive material thrown into air from nuclear bomb

Nucleur accidents sich as Chernobyl, extremely rare but catastrophic.

What is corrected count-rate?

When readings with no radioactive source present are taken and then subtracted from readings with a source present.

What is count rate?

The number of radioactive decays detected by a Geiger muller tube per unit time.

How can damage done by exposure to radiation be described?

By dose equivalent, measured in sieverts, which depends on amount of energy absorbed per kg of a body and type of radiation absorbed.

What are some precautions that must be taken to reduce harm when using radioactive sources?

Keeping sources shielded when not in use, wearing protective clothing, limiting exposure time, handling materials with long tongs, monitoring exposure of workers.

What is the required practical for inverse square law for gamma radiation?

aim- to verify the inverse square law for gamma radiation.

method- measure background radiation using Geiger muller tube, take several readings and find an average

put gamma source a set starting distance (5 cm) from Geiger muller tube and measure number of counts in 60 seconds

record 3 measurements for each distance and take an average

What do you do with the results from the inverse square law for gamma radiation practical?

subtract background radiation from each count rate, plot graph of 1/√C against distance x, if it’s straight line graph this confirms the relationship.