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 is Radioactivity and Radiation? • Radioactive decay is the process in which an unstable atomic nucleus loses energy by emitting radiation in the form of particles or electromagnetic waves. • In some instances, a new element is formed and in other cases, a new form of the original element, called an isotope, appears. • this process of change is often referred to as the decay of atoms. • The rate of Radioactive decay is described in half-lives.
Why? • the nucleus of an atom attempts to become more stable
The Nuclear Stability Belt Science Park HS -- Honors Chemistry
Geiger Counter • Used to measure radiation. • The more intense the radiation the more “clicks”.
Kinds of Radioactivity The three main decays are Alpha, Beta and Gamma Science Park HS -- Honors Chemistry
Alpha Particles and Alpha Decay Alpha particles consist of two protons and two neutrons, identical to the nucleus of a helium atom. A sheet of paper or a person’s surface layer of skin will stop them. Alpha particles are only considered hazardous to a person’s health if they are ingested or inhaled and thus come into contact with sensitive cells such as in the lungs, liver and bones.
Beta Particles and Beta Decay • They can travel a few feet in air but can usually be stopped by clothing or a few centimeters of wood. • They are considered hazardous mainly if ingested or inhaled, but can cause radiation damage to the skin if the exposure is large enough. • Unstable Neutron decays into a proton.
Gamma Rays and Gamma Radiation • Gamma rays are a form of electromagnetic radiation that come from the nucleus of a radioactive atom. • Occurs when an unstable nucleus emits electromagnetic radiation. The radiation has no mass, and so its emission does not change the element. • They penetrate matter easily and are best stopped by water or thick layers of lead or concrete. • Gamma radiation is hazardous to people inside and outside of the body.
Three Common Types of Decay Alpha Beta Gamma Science Park HS -- Honors Chemistry
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
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. 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
Radiation is used positively in a variety of ways • Medicine • For example, radiation and radioactive tracers are used to diagnose and treat medical problems. • A radioactive tracer is a radioactive isotope that is added to a substance so that the substance can be detected later. • Radioactive tracers are used to locate tumors, to study the functioning of a particular organ, or to monitor the flow of blood. • For example, radioactive iodine-131 is used to diagnose thyroid problems. • Radiation therapy used to treat cancer may involve the use of implanted radioactive isotopes such as gold-198 or iridium-192.
Industry • Manufacturers can also use radiation to check the thickness of metal containers by measuring the amount of radiation that passes through. • Small amounts of radioactive isotopes, like magnesium-28, can be introduced in a water source to determine the flow of underground water or to determine if an underground water system is leaking. • Radioactive isotopes are even used in smoke alarms.
Radiation Exposure to Americans Science Park HS -- Honors Chemistry
Your Personal Annual Radiation Dose Environmental Protection Agency Radiation has existed everywhere in the environment since the Earth's formation in rocks, soil, water, and plants. The mining and processing of naturally occurring radioactive materials for use in medicine, power generation, consumer products, and industry inevitably generate emissions and waste. Recognizing the potential hazards of these activities, Congress designated EPA as the primary federal agency charged with protecting people and the environment from harmful and avoidable exposure to radiation. http://www.epa.gov/rpdweb00/understand/calculate.html
Half-Life The half-life of a radioactive substance, is the time required for one half of it to decay. Science Park HS -- Honors Chemistry
14C • Radioactive 14C acts chemically just like 12C, so it becomes incorporated into plants an animals. • When the animal/plant dies the 14C begins to decay into 14N at a know rate, so we can determine how long ago the organism died. • This is called Carbon Dating. • It’s only good for about 50,000 years.
The half life of 14C is 5,730 years. If a sample originally contained 100 g, how much would be left after 11,460 years? 50g 25g
Older Dating Methods • The isotopes 235U and 238U can be used to date objects billions of years old. • 235U has a half life of 704 million years. • 238U has a half life of 4.5 billion years. • Mainly used for rocks.
Nuclear Decay Equations mass #Reactant mass #Products + … atomic # atomic # 2 H 1
Alpha Decay 210 Po A X + 4 He 84 Z 2
Beta Decay 140Ba A X + 0e- 56 Z -1