Unit 6, Lesson 1

the process by which nuclei emit particles & rays

the penetrating rays & particles emitted by a radioactive source

an isotope that has an unstable nucleus & undergoes radioactive decay

a positively charged particle emitted from certain radioactive nuclei; consists of 2 protons & 2 neutrons & is identical to nucleus of a helium atom

an electron resulting from the breaking apart of a neutron in an atom

a high-energy photon emitted by a radioisotope

In 1896, French chemist Antoine Henri Becquerel (1852-1908) made accidental discovery He was studying ability of uranium salts that had been exposed to sunlight to fog photographic film plates During bad weather, he couldn't expose the sample to sunlight, but happened to leave it on top of photographic plate; when he developed plate, he discovered that uranium salt still fogged the plate At that time, 2 of Becquerel's associates were Marie Curie (1867-1934) & Pierre Curie (1859-1906); they were able to show that rays emitted by uranium atoms caused fogging of the plates

Account for radioactivity & differ from chemical reactions in a number of important ways In chemical reactions, atoms tend to attain stable electron configurations by losing electrons or sharing electrons; in nuclear reactions, nuclei of unstable isotopes (radioisotopes) gain stability by undergoing changes These changes are always accompanied by emission of large amounts of energy Unlike chemical reactions, nuclear reactions aren't affected by changes in temperature, pressure, or presence of catalysts & are also unaffected by compounds in which unstable isotopes are present Nuclear reactions of a given radioisotope cannot be sped up, slowed down, or turned off

by emitting radiation during process of radioactive decay

Discovery disproved Dalton's assumption that atoms are indivisible Radioactive atom (radioisotope) undergoes drastic changes as it emits radiation; these radioisotopes have unstable nuclei Stability of nucleus depends on ratio of neutrons to protons in nucleus & on overall size of nucleus Too many or too few neutrons relative to number of protons makes a nucleus unstable Unstable radioisotopes of one element are transformed into stable (nonradioactive) isotopes of a different element Radioactive decay is spontaneous & doesn't require any input of energy

radiation

alpha radiation, beta radiation, & gamma radiation

Composed of Alpha particle (helium nucleus) Symbol is a or 4/2He Charge is 2+ Mass (amu) is 4 Common source is Radium-226 Penetrating power is low (0.05 mm body tissue) Shielding is paper, clothing

Composed of Beta particle (electron) Symbol is b or 0/-1e Charge is 1- Mass (amu) is 1/1837 Common source is Carbon-14 Penetrating power is moderate (4 mm body tissue) Shielding is metal foil

Composition is high-energy electromagnetic radiation Symbol is y Charge is 0 Mass (amu) is 0 Common source is Cobalt-60 Penetrating power is very high (penetrates body easily) Shielding is lead, concrete (incompletely shields)

Type of radiation that consists of helium nuclei that have been emitted from a radioactive source Each of these emitted particles (an alpha particle), contains 2 protons & 2 neutrons & has a double positive charge In nuclear equations, alpha particle is written 4/2He or a (electric charge symbol is generally omitted) Radioisotope uranium-238 releases alpha radiation & is transformed into another radioisotope, thorium-234 Due to large mass & charge, alpha particles don't tend to travel very far & aren't very penetrating; sheet of paper or surface of your skin easily stops them Radioisotopes that emit alpha particles are dangerous when ingested; the particles don't have to travel far to penetrate soft tissue & cause damage

the atomic number of the product atom is lower by 2 & its mass number is lower by 4

Beta particle is an electron resulting from the breaking apart of a neutron in an atom Neutron breaks apart into a proton, which remains in the nucleus, & a fast-moving electron, which is released Symbol for electron has subscript of -1 where atomic number would be written; this represents electron's negative charge; superscript 0 where mass number would be written represents extremely small mass of electron compared to that of a proton Carbon-14 emits beta particle as it undergoes radioactive decay to form nitrogen-14 Beta particle has less charge than alpha particle & much less mass than alpha particle Consequently, beta particles are more penetrating; they can pass through paper but are stopped by aluminum foil or thin pieces of wood

the atomic number of the product atom increases by 1 & the atom contains an additional proton & 1 fewer neutron

Gamma ray is a high-energy photon emitted by a radioisotope; high-energy photons are electromagnetic radiation Nuclei often emit gamma rays along with alpha or beta particles during radioactive decay Because gamma rays have no mass & no electrical charge, emission of gamma radiation doesn't alter atomic number or mass number of an atom Gamma rays are extremely penetrating & can be very dangerous; pass easily through paper, wood, & human body; can be stopped, although not completely, by several meters of concrete or several centimeters of lead