Radioactivity

What is it?

Radioactivity is the spontaneous breaking up of unstable nuclei with the emission of one or more types of radiation

                            

Radioactivity was discovered by Henri Becquerel

Becquerel In 1896, Becquerel accidentally discovered radioactivity while investigating phosphorescence in uranium salts

Becquerel’s Discovery

Image of Becquerel's photographic plate which has been fogged by exposure to radiation from uranium salts. The shadow of a metal Maltese Cross placed between the plate and the uranium salts is clearly visible.

Discovery of Radioactivity

                         

      

                         

      

                         

      Antoine Henri Becquerel

Pierre Curie Marie Curie, née Sklodowska

The Curies discovered Polonium and Radium

The Curies

Marie Sklodowska CuriePhysicist 1867-1934

The Curies

Madame Curie shared with her husband, Pierre Curie, the honours for discovering two radioactive elements, radium and polonium.

The discovery of these elements laid the foundation for future discoveries in nuclear physics and chemistry.

Marie Curie was the first woman to win two Nobel prizes

Types of RadiationAlpha, Beta, and Gamma

Historically the products of radiation were called ALPHA, BETA and GAMA when it was found that they could be analyzed into three

distinct species by either a magnetic field or an electric field.

                                                                       

Types of Radiation

In an electric field: Beta particles go to positive side

Alpha particles go to negative side

Alpha Emission

-Particle emission:

This occurs when a positive -particle leaves the nucleus. Since the -particle is simply the nucleus of a helium atom with mass number 4, the daughter nuclide which results from this type of decay has a mass number 4 atomic mass units and an atomic number 2 less than the parent nuclide

Beta-Emission

-Particle emission:This occurs when one neutron in the nucleus is converted to a proton and a high-energy electron, called a -particle. Since the mass of the -particle is negligibly small compared to nucleons, this type of decay does not change the mass number, but as the number of protons increases by 1, the daughter nuclide will have an atomic number 1 larger than the parent nuclide.

Many isotopes of light elements are subject to this type of decay.

What is the atomic number, Z, of the daughter nuclide produced by the nuclear reaction shown below?

Beta - emission

• What is the atomic number, Z, of the daughter nuclide produced by the nuclear reaction shown below?

Alpha Emission

What is the mass of the daughter nuclide produced by the nuclear reaction shown below?

Alpha DecayPu239 U235 + particle (He-4 nucleus)

                                                                        

   

                                                                 

   

Alpha and Beta Emission

.e.

                                

Alpha Emission .

                            

Beta Decay

Beta - decay                                                                               

   

                                                                        

   

                                                                               

Alpha and Beta emission

Alpha

Beta

Penetrating Distances

Half-Life

Geiger-Muller Tube

               

The Geiger-Müller Tube•widely used for detecting ionising particles or radiation

•ionising radiation ionises atoms of gases. (an electron is 'knocked off' a gas molecule leaving a charged particle) •this phenomena is used in all methods of detection

Detects radiation

Geiger Muller Tube

•widely used for detecting ionising particles or radiation •ionising radiation ionises atoms of gases. (an electron is 'knocked off' a gas molecule leaving a charged particle) •this phenomena is used in all methods of detection

                

                                              

                                                      

                     

•contains a central thin wire, the anode, insulated from a surrounding cylinder, the cathode, (metal or graphite-coated). the tube may have a very thin mica end window, this allows alpha and beta particles to enter. The anode is kept at a positive potential (~ +400 V) relative to the cathode, which may be earthed.

Uses of Radioactivity

• As Tracers• Cancer Treatment• Carbon Dating• Killing Germs – Irradiation of food• Measuring Thickness of films• In smoke detectors

Radioactive Tracers

• As tracers: Radioactive isotopes can be detected in extremely small amounts. If a drug is labelled with a radioisotope, its passage through the body can be mapped, and valuable medical information gathered about the functioning of organs. For example, 123I (iodine-123) is used in determining the state of health of the thyroid gland.

Treatment of Cancer

• In treatment of cancer: The radiological damage caused by g-rays is exploited in the treatment of cancer. If the radioactive element (60Co, 137Cs or 99Tc) can be introduced into a tumour, its radiation will kill tumour cells, hopefully without causing too much damage to healthy cells

Carbon Dating• Radioactive dating• Radioactivity can also be used to work out how old

something is. When an unstable nucleus splits up (disintegrates) it emits radiation and turns into a different atom. As something radioactive gets older, it emits less radiation. Scientists measure radioactivity to check the age of fossils and rocks - they call this radioactive dating

Carbon Dating

•Carbon dating: 14C (carbon-14) is present in small amounts in the atmosphere (as CO2), where it is produced by the irradiation of 14N by neutrons from cosmic rays:

Living organisms pick up this isotope, which "labels" all tissues. When the organism (a tree, for example) dies, the uptake of 14C ceases, and the radioactive carbon atoms undergo -decay at a known rate:

The residual radioactivity of a sample of wood from that tree can be measured and an estimated age for the specimen determined. This method is limited to ages not exceeding 70000 years. For longer periods of time, other isotopes are used.

Sterilisation

Radiation is also used to sterilize medical instruments and food.

Because they kill cells radioactive materials are used to kill germs. We use them to irradiate food

Measurements

Radiation is used by nondestructive testing personnel to inspect materials and make measurements.

Radioactive materials are used to measure the thickness of films in, for example, a canning factory.

Smoke Detectors

Radioactive materials are used in smoke detectors and to check welds in pipes.