Who is this?

Marie Curie

Born 1867 Poland1893 degree in physics, 1894 degree in mathematics.1894 Denied a place in Krakow University because she was a womanThen became first female professor at the Sorbonne1896 Becquerel discovers that radioactive substances affect photographic plates1898 After working on Becquerel’s discovery, she discovers new element

“polonium”Established that radioactivity was a result of something in the atom. 1903 first woman to be awarded the Nobel prize for physics.1906 Pierre Curie dies in road accident.1911 first (and only so far) person to be awarded a Nobel Prize for Chemistry (and

Physics).1934 After years of working with radioactive substances, whose dander was not

recognised at the time, with no safety procedures, she dies of a blood disorder linked to radiation exposure.

All her research documents and even her cook book are too dangerous to handle and are kept in a lead lined box.

Photographic film

1. What happens to film when radiation is incident upon it?

It darkens.

2. Can photographic film tell you the type of radiation incident upon it?

No, just the amount of radiation received.

3. What can this be used for?

Can be used in radiation badges, that record the exposure of workers to radiation. Different windows detect different types of radiation.

mica window

Argon gas

Geiger-Muller Tube

counter

collision & ionisation

radiation

124125

The detector is a metal tube filled with gas. The tube has a thin wire down the middle and a voltage between the wire and the casing.

When the radioactivity enters the tube, it ionises the gas in the tube. This produces a pulse of current which is amplified and passed to a counter.

The Argon contains a little

bromine to act as a quenching agent and prevent

continuous discharge.

Good at detecting alpha and beta, not as good at detecting gamma (why?).

Argon gas

Cloud chamber

Cloud chambers show the actual paths of the ionising particles. They rely on ionisation. The cloud chamber is cooled and then is super-saturated with alcohol. If an ion is formed a droplet of condensation appears. Best for alpha radiation as alpha most ionising; then Beta which shows faint traces, but cloud chambers are not as good for gamma as gamma is only weakly ionising.

Solid carbon dioxide

Radioactive source Cooled alcohol vapour

Detection of radiation

• Photographic film• The amount of darkening of the film shows the amount of

radiation. This was the early method of detection. Qualitative only – tells us radiation is present but not which type. Used in modern monitors in conjunction with metallic shielding, which can stop alpha and beta particles but not the more penetrating gamma rays.

• Cloud chamber• The instrument contains a super saturated vapour of an alcohol.

When radiation passes through it, it ionises some of the air particles, which causes them to act like nuclei onto which alcohol droplets form. In this way the radiation is made visible: alpha particles form dense white tracks, beta particles form less dense zig-zag tracks, gamma rays form even fainter tracks.

Detection of radiation• Geiger-Muller counter• Uses the ionising power of particles, esp good for beta. The beta

particle is passed into a chamber where it hits a gas molecule – usually argon. The argon is ionised and loses an electron. The electron accelerates towards an electrode and as it does so hits another argon atom causing it to ionise and lose an electron. This results in a stream of electrons from lots of ionised argon atoms reaching the electrode. This constitutes and electrical impulse which is measured by either a digital counter or by generating clicks. It allows us to determining amount but not type of radiation present.

• Scintillation counter • Certain substances will emit a flash of light when irradiated by

different types of radiation. Especially good for gamma rays. The more energy the gamma rays have the brighter the flash of light, which is detected by a photo-multiplier. This generates an electrical signal, which can be counted. It is able to detect low intensities of radiation and magnify them so they can be recorded electronically.