Section 19.1 Radioactivity 1.Students will be able to describe the factors that lead to nuclear stability. 2.Students will be able to describe types of radioactive decay. 3.Students will be able to write equations to show radioactive decay. Objectives

Section 19.1 Radioactivity nucleons – particles found in the nucleus of an atom –neutrons –protons atomic number (Z) – number of protons in the nucleus mass number (A) – sum of the number of protons and neutrons isotopes – atoms with identical atomic numbers but different mass numbers nuclide – each unique atom A Review of Atomic Terms

Section 19.1 Radioactivity Nuclear Stability Small atoms tend to have neutron-proton ratios ~ 1:1 The ratio approaches 1.5:1 as the atomic number increases Explained by the relationship between strong nuclear forces and electrostatic repulsion

Section 19.1 Radioactivity Nuclear Stability Strong nuclear forces act over very short distances As the # of protons increases, the electrostatic force between protons increases More neutrons are needed to stabilize the nucleus

Section 19.1 Radioactivity A. Radioactive Decay radioactive – nucleus which spontaneously decomposes forming a different nucleus and producing one or more particles nuclear equation – shows the radioactive decomposition of an element

Section 19.1 Radioactivity A. Radioactive Decay Alpha-particle decay Alpha particle – helium nucleus –Examples Types of Radioactive Decay Common for heavy isotopes

Section 19.1 Radioactivity A. Radioactive Decay Beta-particle decay Types of Radioactive Decay Net effect is to change a neutron to a proton. Beta particle – electron –Examples

Section 19.1 Radioactivity A. Radioactive Decay Gamma ray release Types of Radioactive Decay Net effect is no change in mass number or atomic number. Gamma ray – high energy photon –Examples

Section 19.1 Radioactivity A. Radioactive Decay Positron production Types of Radioactive Decay Net effect is to change a proton to a neutron. Positron – particle with same mass as an electron but with a positive charge –Examples

Section 19.1 Radioactivity A. Radioactive Decay Electron capture Types of Radioactive Decay –Example

Section 19.1 Radioactivity A. Radioactive Decay

Section 19.1 Radioactivity A. Radioactive Decay Decay series

Section 19.1 Radioactivity Sample Problems 1.Silver-116 undergoes beta particle decay. 2.Bismuth-211 undergoes alpha particle decay 3.An isotope undergoes alpha particle decay and produces the isotope Polonium Silver 106 undergoes electron capture. 5.Potassium-38 undergoes positron emission.

Section 19.1 Radioactivity Detection of Radioactivity and the Concept of Half- life Objectives Students will be able to define the term half-life and explain how it relates to the stability of the nucleus. Students will determine the half-life of an isotope or the fraction of the isotope that remains given appropriate data.

Section 19.1 Radioactivity C. Detection of Radioactivity and the Concept of Half- life Half-life – time required for half of the original sample of radioactive nuclides to decay

Section 19.1 Radioactivity Half Life Problems: 1.Phosphorus-32 has a half-life of 14.3 days. How many days will it take for a radioactive sample to decay to one-eighth its original size. 2.Iodine-131 has a half life of 8.0 days. How many grams of an original 160 mg sample will remain in 40 days? 3.Carbon-14 has a half life of 5715 years. It is used to determine the age of ancient objects. If a sample today contains mg of carbon-14, how much carbon-14 must have been present in the sample 11,430 years ago>

Section 19.1 Radioactivity B. Nuclear Transformations Nuclear transformation – change of one element to another

Section 19.1 Radioactivity B. Nuclear Transformations Discovery of Protons: Rutherford performed the first artificial transmutation, by bombarding nitrogen gas with alpha particles (1919)

Section 19.1 Radioactivity B. Nuclear Transformations Discovery of Neutrons Chadwick discovered the neutron by bombarding Be with alpha particles. (1932)

Section 19.1 Radioactivity B. Nuclear Transformations

Section 19.1 Radioactivity B. Nuclear Transformations Production of Neptunium and Plutonium

Section 19.1 Radioactivity B. Nuclear Transformations Transuranium elements – elements with atomic numbers greater than 92 which have been synthesized

Section 19.1 Radioactivity C. Detection of Radioactivity and the Concept of Half- life Geiger-Muller counter – instrument which measures radioactive decay by registering the ions and electrons produced as a radioactive particle passes through a gas- filled chamber

Section 19.1 Radioactivity C. Detection of Radioactivity and the Concept of Half- life Scintillation counter – instrument which measures the rate of radioactive decay by sensing flashes of light that the radiation produces in the detector