The ABC's (or Alpha, Beta, Gamma) of Radioactivity Science Park HS -- Honors Chemistry

Agenda Definition of Radioactivity and emissions Discussion of the three most important types of emissions What do we mean by half-life? Where is Radioactivity encountered? Is Radioactivity dangerous? Science Park HS -- Honors Chemistry

Expectations SWBAT state what radioactivity is, where these rays come from, what each ray is made of and state why they are dangerous. SWBAT identify 4 pioneer scientists who made important contributions to understanding radioactivity SWABT to explain the meaning of “half-life”. Student will be asked to find any sources of Radioactivity in his/her environment Science Park HS -- Honors Chemistry

Early Pioneers in Radioactivity Rutherford: Discoverer Alpha and Beta rays 1897 Roentgen: Discoverer of X-rays 1895 The Curies: Discoverers of Radium and Polonium 1900-1908 Becquerel: Discoverer of Radioactivity 1896 Science Park HS -- Honors Chemistry

What do we mean by Radioactivity? Radioactive decay is the process in which an unstable atomic nucleus loses energy by emitting radiation in the form of particles or electromagnetic waves. There are numerous types of radioactive decay. The general idea: An unstable nucleus releases energy to become more stable Science Park HS -- Honors Chemistry

Some Key Definitions Before We Move on Z = The Atomic Number. It’s the Number of Protons in the nucleus of an Atom. Nucleus: It’s where the Protons and Neutrons are located in an Atom. Protons: Positively Charged Particles in the Nucleus of the atom. Mass = (approx) 1 AMU Neutrons: Neutrally charged particles in the nucleus of an atom Mass = (approx) 1 AMU Mass Number of an atom: Number of Protons + Number of Neutrons in the nucleus of an atom. Science Park HS -- Honors Chemistry

The Nuclear Stability Belt Science Park HS -- Honors Chemistry

Kinds of Radioactivity The three main decays are Alpha, Beta and Gamma Science Park HS -- Honors Chemistry

Three Common Types of Radioactive Emissions Alpha Beta Gamma Science Park HS -- Honors Chemistry

An alpha particle is identical to that of a helium nucleus. Alpha Decay An alpha particle is identical to that of a helium nucleus. It contains two protons and two neutrons.

X Y + He A Z A - 4 Z - 2 4 2 unstable atom alpha particle Alpha Decay X A Z Y A - 4 Z - 2 + He 4 2 unstable atom alpha particle more stable atom

Alpha Decay Rn 222 86 He 4 2 Ra 226 88

Alpha Decay X A Z Y A - 4 Z - 2 + He 4 2 Ra 226 88 Rn 222 86 + He 4 2

Alpha Decay Rn 222 86 + Y A Z He 4 2 Rn 222 86 He 4 2 + Po 218 84

Alpha Decay X A Z + Th 230 90 He 4 2 He 4 2 U 234 92 + Th 230 90

Alpha Decay Th 230 90 + Y A Z He 4 2 He 4 2 + Ra 226 88 Th 230 90

Alpha Decay X A Z + Pb 214 82 He 4 2 He 4 2 + Pb 214 82 Po 218 84

Beta Decay A beta particle is a fast moving electron which is emitted from the nucleus of an atom undergoing radioactive decay. Beta decay occurs when a neutron changes into a proton and an electron.

Beta Decay As a result of beta decay, the nucleus has one less neutron, but one extra proton. The atomic number, Z, increases by 1 and the mass number, A, stays the same.

Beta Decay b -1 At 218 85 Po 218 84

Beta Decay X A Z Y Z + 1 + b -1 Po 218 84 Rn 85 + b -1

Beta Decay Th 234 90 Y A Z + b -1 Th 234 90 Pa 91 + b -1

Beta Decay X A Z Pb 210 82 + b -1 Tl 210 81 Pb 82 + b -1

Beta Decay Bi 210 83 Y A Z + b -1 Bi 210 83 Po 84 + b -1

Beta Decay X A Z Bi 214 83 + b -1 Pb 214 82 Bi 83 + b -1

Three Common Types of Radioactive Emissions - Penetrability Alpha particles may be completely stopped by a sheet of paper, beta particles by aluminum shielding. Gamma rays, however, can only be reduced by much more substantial obstacles, such as a very thick piece of lead. Science Park HS -- Honors Chemistry

Another Contribution from Rutherford: Half-life of Radioactive Atoms The half-life of a radioactive substance, is the time required for one half of it to decay. Science Park HS -- Honors Chemistry

Sources of Radioactivity Primordial - from before the creation of the Earth Cosmogenic - formed as a result of cosmic ray interactions Human produced - enhanced or formed due to human actions (minor amounts compared to natural) Science Park HS -- Honors Chemistry

Where are the Sources of Radioactivity? Naturally Occurring Sources: Radon from the decay of Uranium and Thorium Potassium -40 – found in minerals and in plants Carbon 14 – Found in Plants and Animal tissue Manmade Sources: Medical use of Radioactive Isotopes Certain Consumer products –(eg Smoke detectors) Fallout from nuclear testing Emissions from Nuclear Power plants Science Park HS -- Honors Chemistry

Radioactivity – Is it a Health Problem? The Alpha, Beta and Gamma particles all add energy to the body’s tissues. The effect is called the Ionizing Energy. It can alter DNA. Even though Alpha particles are not very penetrative if the decaying atom is already in the body (inhalation, ingestion) they can cause trouble. The Time, Distance and Shielding principle Science Park HS -- Honors Chemistry

Radiation Exposure to Americans Science Park HS -- Honors Chemistry

Summary/Questions Name three of the science pioneers in the study of Radioactivity.? Why does a nucleus decay? Order these emissions from least to greatest penetrability: Gamma, Alpha, Beta. What is the greatest source of exposure to radioactivity in our everyday lives? If I tell you that that the half-life of Fellmanium-250 is 10 days, how much would be left after 30 days if I started with 1600 atoms? Science Park HS -- Honors Chemistry

Where to Get More Information http://www.physics.isu.edu/radinf/natural.htm EPA (Environmental Protection Agency) Dept of Energy Science Park HS -- Honors Chemistry