The ABCs or Alpha Beta Gamma of Radioactivity

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

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

Expectations l l 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: Roentgen: Discoverer Alpha and Beta rays 1897 Discoverer of Xrays 1895 The Curies: Discoverers of Radium and Polonium 19001908 Science Park HS -- Honors Chemistry Becquerel: Discoverer of Radioactivity 1896

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 l l l 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

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

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

Alpha Decay 222 226 Ra 88 Rn 86 4 He 2

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

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

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

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

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

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 218 Po 84 At 85 0 b -1

Beta Decay A X Z 218 Po 84 A Y + Z+1 218 Rn + 85 0 b -1

Beta Decay 234 A 234 Th 90 Y + Z Pa + 91 0 b -1

Beta Decay A 210 b -1 210 0 X Z Tl 81 Pb + 82 0 b -1

Beta Decay 210 A 210 Bi 83 Y + Z Po + 84 0 b -1

Beta Decay A 214 b -1 214 0 X Z Pb 82 Bi + 83 0 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 l l l 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? l l 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? l l l 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 l l l 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 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. h tm l EPA (Environmental Protection Agency) l Dept of Energy l Science Park HS -- Honors Chemistry