Electromagnetic spectrum Mini-book – Due 17th September

• One type of EM wave for each page• Each page should contain the wavelength• Each page should contain uses and other

interesting information (including dangers)• Attractive to look at (and funny?)-

Last year June 2012

• describe the structure of an atom in terms of protons, neutrons and electrons and use symbols to describe particular nuclei

• Rutherford’s alpha scattering experiment • understand the terms atomic (proton) number,

mass (nucleon) number and isotope

Radioactivity

The atom

orbiting electrons

Nucleus (protons and neutrons)

Nuclide notation

Li3

7

Atomic number (proton number) = number of protons

Atomic mass (mass number) = number of protons and neutrons

Isotopes

Li3

7

It is possible for the nuclei of the same element to have different numbers of neutrons in the nucleus (but it must have the same number of protons)

Li3

6

Isotopes

Li3

7

For example, Lithium atoms occur in two forms, Lithium-6 and Lithium-7

Li3

6

4 neutrons3 neutrons

Relative atomic mass

On average, lithium atoms have a mass of 6.941 (relative to Carbon 12)

Li3

6.941

Let’s try some questions.

Do Now!1.Date &

Title – Properties of Radiation

2. Do exam question 11 and stick in your book

Unstable nuclei

Some nuclei are unstable, for example Uranium 235

Hi! I’m uranium-235 and I’m unstable. I really need to

lose some particles from my nucleus to become more

stable.

Unstable nuclei

To become stable, an unstable nuclei emits a particle

Weeeeeeeeeeeeee!

Unstable nuclei

We say the atom has decayed

Weeeeeeeeeeeeee!

Unstable nuclei

The decay of an unstable nucleus is random. We know it’s going to happen, but we can’t say when! It cannot be affected by temperature/pressure etc.

Weeeeeeeeeeeeee!

Today’s lesson

• 7.4 understand that alpha and beta particles and gamma rays are ionising radiations emitted from unstable nuclei in a random process

• 7.5 describe the nature of alpha and beta particles and gamma rays and recall that they may be distinguished in terms of penetrating power

• 7.6 Begin to describe the effects on the atomic and mass numbers of a nucleus of the emission of each of the three main types of radiation

3 types of particle

There are 3 (at least in IGCSE!) types of particles that can be ejected from an unstable nuclei.

Please fill in the table with the information in the Powerpoint

You’ll learn about some really weird

ones in year 12!

Ionisation – Please copy

Ionisation occurs when an atom loses or gains one or more electrons.

When an atom loses electrons it becomes a positive ion.

When an atom gains electrons it becomes a negative ion.

Lithium atom (uncharged)

Lithium ion (positively charged)

Alpha particles

α

Alpha particles

• 2 protons and 2 neutrons joined together

• The same as the nucleus of a helium atom

• Stopped by paper or a few cm of air

• Highly ionising

• Deflected by electric and strong magnetic fields

He2

4 2+

Alpha Decay

U92

235

Th90

231

+ αAtomic number goes down by 2

Atomic mass goes down by 4

Beta particles

β

Beta particles

• Fast moving electrons from the nucleus

• Stopped by about 3 mm of aluminium

• Weakly ionising

• Deflected by electric and magnetic fields

e-1

0

Beta decay

• In the nucleus a neutron changes into an electron (the beta particle which is ejected) and a proton (which stays in the nucleus)

• During beta decay the mass number stays the same but the proton number goes up by 1.

e-1

0Th90

231

Pa91

231

+

Gamma rays

Gamma rays

• High frequency electromagnetic radiation

• several cm of lead or thick concrete will reduce the intensity.

• Very weakly ionising

• NOT affected by electric or magnetic fields

Gamma rays

Associated with alpha decay

U92

235

Th90

231

+ α

Deflection by electric fields

Alpha and beta particles are deflected in opposite directions due to their opposite charges.

Due to their much larger mass alpha particles are deflected far less than beta.

Gamma rays are not deflected because they are not charged.Electric field produced by

positively and negatively charged plates

+ + +

- - -

S

Deflection by magnetic fields

Alpha and beta particles are deflected in opposite directions due to their opposite charges.

Due to their much larger mass alpha particles are deflected far less than beta.

Gamma rays are not deflected because they are not charged.

Magnetic south pole placed behind the rays

Stick your table in your books

• please complete information about speed and mass from the text book

The penetrating power of alpha, beta and gamma radiation – Please copy

Paper or a few cm of air stops alpha particles

1cm or 1m of air of aluminium

stops beta particles

Several cm of lead or 1m of concrete

reduces the intensity of gamma rays

Alpha, beta and gamma radiationAn alpha particle consists of two protons and two neutrons.It is strongly ionising.

A beta particle is a high speed electron.It is produced when a neutron has decays into an electron and proton.It is moderately ionising.

Gamma rays are very high frequency electromagnetic waves.They are produced when an unstable nucleus loses energy..They are weakly ionising.

Let’s try some questions.

Do L15.1 ionizing

radiation and question 2 page 253

Rayneritis!