Fiesta Ware 2009, Prentice-Hall, Inc.
Measuring Radioactivity One can use a device like this Geiger counter to measure the amount of activity present in a radioactive sample. The ionizing radiation creates ions, which conduct a current that is detected by the instrument. 2009, Prentice-Hall, Inc.
Definition is the study of reactions involving the nucleus of the atom. 3
Types of Change 1. Natural Radioactivity: nuclei naturally losing particles or energy to become new elements 2. Transmutation- scientists bombarding nuclei with particles to make new nuclei 3. Fusion. The combination of small, light nuclei into a larger one. (Sun & H-Bombs) 4. Fission. A heavy nucleus is split into lighter nuclei. (Power Plants & A-Bombs) 4
Historical Background In 1896, Henri Becquerel - discovered that uranium emitted radiation. Wrapped a U compound in black paper on photo film plate foggy. 5
Historical Background In 1898, Marie & Pierre Curie found that impure uranium was even more radioactive than pure uranium. From a large amount of pitchblende (U 3 O 8 ), they succeeded in isolating two new radioactive elements: radium & polonium (1876-1934) 6
In 1919, Ernest Rutherford performed the first conversion of one nucleus into another: N-14 to O-17 by alpha particle bombardment 14 N + 4 α 17 O + 1 p 7 2 8 1 2009, Prentice-Hall, Inc.
Transuranium Elements Elements beyond 92 (transuranium) were made starting with neutron bombardment 238 92 U + 1 0n ---> 239 92U + γ 239 92 U ---> 239 93Np + 0-1β 239 93 Np ---> 239 94Pu + 0-1β
Fusion Fusion light nuclei are fused into a heavier nucleus. Energy is released. This is the energy producing reaction in the Sun: H-3 + H-2 yields a helium nucleus + a neutron + energy
THE SUN
Fission Fission- the process in which a heavy nucleus (mass number > 200) divides to form smaller nuclei and neutrons. Energy is released. Uranium-235 was the first element discovered to go through nuclear fission.
Fission 235 U + 1 n 90 Sr + 143 Xe + 3 1 n + Energy 92 0 38 54 0
Fission Bombardment of the radioactive nuclide with a neutron starts the process. Neutrons released in the transmutation strike other nuclei, causing their decay and the production of more neutrons. 2009, Prentice-Hall, Inc.
Fission This process continues in what we call a nuclear chain reaction. 2009, Prentice-Hall, Inc.
Fission If there are not enough radioactive nuclides in the path of the ejected neutrons, the chain reaction will die out. 2009, Prentice-Hall, Inc.
Fission Therefore, there must be a certain minimum amount of fissionable material present for the chain reaction to be sustained: critical mass. 2009, Prentice-Hall, Inc.
in Your Life
Medicine: Imaging Thyroid imaging using Tc-99
Food Irradiation Food can be irradiated with γ rays from 60 Co or 137 Cs. Irradiated milk has a shelf life of 3 mo. without refrigeration. USDA has approved irradiation of meats, eggs, and produce.
Effects of Radiation
Penetrating Ability
Types of Radioactive Decay 2009, Prentice-Hall, Inc.
Particles involved in Decay Reactions alpha α 4 2 He positron β + 0 +1 e beta β 0 1 e proton P 1 1 H gamma γ 0 0 γ deuteron D 2 1 H neutron η 1 0 η triton T 3 1 H 24
Alpha Decay Alpha decay is the loss of an α-particle (a helium nucleus). 4 He 2 238 U 92 234 Th 4 He 90 + 2 2009, Prentice-Hall, Inc.
Beta Decay Beta decay is the loss of a β-particle (a high energy electron). 0 1 β or 0 e 1 131 I 131 Xe 53 54 0 1 + e 1 n 1 p + 0 e 0 1-1 2009, Prentice-Hall, Inc.
Positron Emission 0 e 1 Some nuclei decay by emitting a positron, a particle that has the same mass as but an opposite charge to that of an electron. 11 C 6 11 B 0 5 + e 1 1 p 1 n + 0 e 1 0 +1 2009, Prentice-Hall, Inc.
Gamma Emission This is the loss of a γ-ray, which is highenergy radiation that almost always accompanies the loss of a nuclear particle. 0 0 γ 0 e + 0 e 2 0 γ +1-1 0 2009, Prentice-Hall, Inc.
Radioactive Series Large radioactive nuclei cannot stabilize by undergoing only one nuclear transformation. They undergo a series of decays until they form a stable nuclide (often a nuclide of lead). 2009, Prentice-Hall, Inc.
Write Equations! Write the nuclear equation for the beta emitter Co-60.
Write Equations! What product is formed when radium-226 undergoes alpha decay?
Learning Check What radioactive isotope is produced in the following bombardment of boron? 10 B + 4 He? + 1 n 5 2 0
Balancing Reactions Atomic numbers must balance and Mass numbers must balance Use a particle or isotope to fill in the missing protons and neutrons
Complete the Reaction 239 93 239 92 99 44 99 43 260 105 15 7 249 98 17 8 4 2 14 7 4 2 56 25 59 27 + + + + + + + + Np U Ru Tc Ha N Cf O He N He Mn Co 34
Half-Life HALF-LIFE is the time that it takes for 1/2 a sample to decay into a new element.