The Atomic Model

Who gave the name to the smallest particle of matter (atom)?

Demotricus

Who revived Demotricus’ atomic theory?

John Dalton

Who invented the Plum Pudding model in 1904?

J.J. Thompson

What did the Plum Pudding model suggest?

An atom is a sphere of positive charge, with negatively charged electrons embedded in it

What is the evidence behind the Plum Pudding model?

• worked with CRTs

• noticed particles were deflected by magnetic electric fields

  • these were very small and negatively charged - called electrons

Who conducted the Gold Foil experiment or the alpha particle scattering experiment in 1909?

Ernest Rutherford

What did Ernest Rutherford discover?

• nuclear model

  • the nucleus is small and positive

• the atom has negative electrons moving around it but it is mostly empty space

What is the evidence behind Rutherford’s model of the atom?

• particles passing through the foil meant it was mostly made of empty space

• particles being deflected at large angles suggested concentration of positive charge in atom (like charges repel)

• particles coming back meant positive charge + mass are concentrated in nucleus

The way electrons are arranged can be changed if…

they are hit with light energy

If an electron is hit by a photon…

then it moves to a higher energy state - it is now in an excited state

When an electron moves to a lower energy state,…

it releases out the energy

What is radioactivity measured in?

Becquerels (Bq)

What does 1Bq equal to?

1 decay per second

What piece of equipment displays the amount of radioactivity in Bq?

Geiger-Müller tube

count rate

number of decays per second

How does a Geiger counter detect ionising radiation?

• uses Geiger-Müller tube with low pressure gas

  • radiation enters tube, ionizes gas then creates charged particles

  • particles attracted to oppositely charged electrodes cause short electrical impulses - no. of pulses/ clicks indicates level of radiation

isotope

An element that has the same number of protons but different number of electrons

radioactive

used to describe a substance with an unstable nucleus that emits energy or particles

Who discovered the concept of shells in 1913?

Niels Bohr

How did Bohr discover the shells?

used Max Planch’s quantum theory to show that electrons exist in different energy levels

Who discovered neutrons in 1932?

James Chadwick

What are the types of radiation?

alpha (α), beta (β), gamma (γ)

What does alpha radiation consist of?

2 neutrons and protons (helium nuclei)

What is the charge and atomic mass of alpha radiation?

+2, 4

What is the ionizing and penetration power of alpha radiation?

strongly ionizing, stopped by paper or a few cm of air

What does beta radiation consist of?

a high energy electron

What is the charge and atomic mass of beta radiation?

-1, 1/1860th of proton

What is the ionizing and penetration power of beta radiation?

weakly ionising, stopped by few mm of aluminium

What does gamma radiaiton consist of?

high energy electromagnetic radiation

What is the charge and atomic mass of gamma radiation?

0, 0

What is the ionizing and penetration power of gamma radiation?

very weakly ionising, reduced by several cm of lead or several m of concrete

Order the types of radiation by deflection, first one being strongly deflection

beta, alpha, gamma

How can alpha radiation be represented?

as a helium atom

How can beta radiation be represented?

e or beta symbol with 0 at top and -1 at bottom

How can gamma radiation be represented?

γ

nuclear equation for alpha decay

memorised

nuclear equation for beta decay

memorised

contamination

• unwanted presence of materials containing radioactive atoms

  • occurs when people swallow, breathe in, or absorb through the skin or radioactive materials

irradiation

• when an object is exposed to nuclear radiation

  • means that the atoms absorb energy and become ionised but do not become radioative

characteristics of contamination

• once object contaminated, radiation can not be blocked

• can be very difficult to remove all contamination

• contaminated object will be radioactive for as long source is on or in it

• occurs if radioactive source is on or in object

characteristics of irradiation

• doesn’t cause object to become radioactive

• occurs when object exposed to source of radiation outside the object

• can be blocked from object with suitable shielding

• stops as soon as source is removed

Sievert (Sv)

• unit of radiation exposure dose that a person requires

  • assosciated with radiation effects

uses of irradiation

• sterilize medical equipment without boiling it

• beams of gamma rays to destroy cancer cells in body

uses of contamination

• tracers inside body

  • isotope emits gamma rays that easily pass through body to a detector outside body

• find leaks in pipes

natural sources of background radiation

• radon gas from ground and rocks

• living things and food

• cosmic rays

human sources of background radiation

• medical applications + waste

• fallout from nuclear bomb testing

• nuclear accident

How do you measure background radiation?

1. Remove any extra radioactive sources from the room.

2. Use a Geiger-Müller tube and count how many clicks there are in a minute.

3. Number of clicks / 60 seconds to get the count rate in Becquerels (Bq).

4. Repeat and find an average count rate.

half life

• time it takes for half the number of radioactive particles in a sample to decay

• time it takes the activity (in Bq) to be half of its previous value

background radiation

natural radiation that is always present in the environment