Radioactivity

Radioisotopes The discovery of radioactivity by Becquerel and the Curies showed that one of Dalton’s ideas, that matter is indestructible and indivisible, is not always true. Certain isotopes, because of their size and/or ratio of protons and neutrons are not stable. Radioisotopes have unstable, high energy nuclei Radioisotopes lose energy by emitting radiation and matter

Radioactive Decay Radioisotopes decay from one element to another until they are transformed into stable, non-radioactive isotopes. For example, 238 U decays 11 times, shedding mass and energy each time, eventually becoming 206 Pb, a stable isotope. Radioactive decay is spontaneous – it does not require an input of energy. Another term for radioactive decay is transmutation.

Three Types of Radiation alpha radiationα beta radiationβ -, β + gamma radiationϒ

Alpha Radation In alpha radiation, helium nuclei are ejected from the nucleus. The process studied by Curie involved uranium-238, among other radioisotopes: In alpha decay, the atomic number decreases by 2, the mass number decreases by 4.

The helium nucleus is known as an alpha particle. This process is known as  emission. In this case, an atom of uranium changes into an atom of thorium. The general process of atoms changing into different elements is known as transmutation. These alpha particles are less dangerous than other forms of radiation. Their large mass insures that they do not penetrate very far into materials. This is a good thing because they steal two electrons from other atoms they encounter. Because of their positive charge, alpha particles are easily detected in electric and magnetic fields.

Penetrating Power of Radiation

Beta Radiation Beta radiation is composed of high energy electrons, known as beta particles. A neutron breaks down to form a proton and an beta particle (  ):

Alpha Decay Equations Nuclide +1 1 p o1n o1nDecay Equation 215 At 217 Rn 218 Fr 228 U 236 Pu 241 Am 217 Po

Beta Particles and Neutrinos The v particle is a neutrino, a very tiny particle of negligible mass. Note that this equation can also be written Table O:

Neutrinos are virtually undetectable and are often left out of nuclear equations. The proton remains in the nucleus and is not ejected. Thus in beta decay, the atomic number increases by one! The most famous example is carbon-14.

Carbon-14 is radioactive. By decaying to nitrogen-14, it attains stability. Beta particles are less massive, and therefore more penetrating. They represent a greater health risk than alpha particles.

Beta Minus Decay Equations Nuclide +1 1 p o1n o1nDecay Equation 16 C 19 O 25 Na 10 Be 66 Cu 71 Zn 213 Bi

Positron Emission There is another interesting form of beta emission. A proton will transform itself into a neutron, releasing a positron, a positively charged electron-like particle. Positrons are a form of antimatter.

Positron Emission Artificially created radioactive nuclei of the lighter elements often undergo positron emission: Many artificial radionuclides are have too many protons, so a proton changes into a neutron. In positron emission, the atomic number goes down by 1, and the mass number remains unchanged.

Positron Emission Equations Nuclide +1 1 p o1n o1nDecay Equation 10 C 14 O 22 Na 7 Be 58 Cu 63 Zn 203 Bi

Gamma Radiation Gamma rays are high frequency radiation – they have no mass or charge. Gamma emission does not change the atomic number or mass number of the atom, and often accompanies  or  emission

Gamma Radiation Often Accompanies Other Forms of Decay Gamma rays are extremely dangerous and will pass completely through the body, damaging cells as they go. Several cm of lead is necessary to contain gamma rays.

Which type of emission has the highest penetrating power? alpha beta positron gamma

Natural Transmutation Alpha decay: Mass number ↓4, atomic number ↓2 Beta minus decay: mass number unchanged, atomic number↑1 Beta plus decay: mass number unchanged, atomic number ↓1

Deflection by Magnetic/Electric Fields

The diagram represents radiation passing through an electric field. Which type of emanation is represented by the arrow labeled 2? alpha particle beta particle positron gamma radiation

Which type of radiation would be attracted to the positive electrode in an electric field?

Which type of radiation has neither mass nor charge? gamma neutron alpha beta

Which radioactive emanations have a charge of 2+? alpha particles beta particles gamma rays neutrons

Famous Radioisotopes The type of decay is indicicated by the decay mode. Homework: Write decay equations for each nuclide on Table N

Which radioisotope is a beta emitter? 90 Sr 220 Fr 37 K 238 U

Which isotope will spontaneously decay and emit particles with a charge of +2? 53 Fe 137 Cs 198 Au 220 Fr

Positrons are spontaneously emitted from the nuclei of potassium-37 radium-226 nitrogen-16 thorium-232

In the equation: Which particle is represented by X?

The fossilized remains of a plant were found at a construction site. The fossilized remains contain the amount of carbon-14 that is present in a living plant. Which answer choice correctly completes the nuclear equation for the decay of C-14?