Nuclear Reactions: a, b, g Decay Chapter 4 Section 4.4 Nuclear Reactions: a, b, g Decay

Radiation and Radioactivity Radioactivity was discovered by Henri Becquerel in 1896. It is the spontaneous emission of particles or energy by unstable atomic nuclei. The emitted particles are called radiation, and the change in nucleus that results is called radioactive decay.

Radiation There are three types of radiation we will discuss, alpha (a), beta (b) and gamma (g) particles. Alpha particles have the least amount of energy, while gamma particles have the most.

1) Alpha Decay Alpha decay occurs when unstable isotopes try to stabilize by emitting an alpha particle. An alpha particle is made of two protons and two neutrons, and its symbol is a or He. Ra a 42 42 23688 42 23286 He + Rn

2) Beta Decay There are three types of beta decay; beta emission, positron emission and electron capture. A beta particle is the same thing as an electron with a symbol of b or e-. Beta emission looks like C a e- + N -1 -1 146 -1 147

Electron Capture and Positron Electron capture occurs when instead of emitting an electron, one is pulled into the nucleus. Au + e- a Pt A positron is an odd particle; it is an electron with a positive charge! Sb a e- + Sn 19579 -1 19578 11651 +1 11650

3) Gamma Radiation Frequently a or b decay produces energy, which is released as gamma rays (g). In most cases, it is only given off when other types of radiation occur, and since it has no particles, its symbol is just g.

Why does radioactive decay occur? All stable isotopes of an atom lay inside what is called the band of stability. This is a ratio of protons to neutrons that is inherently stable. Atoms not in this band will undergo radioactive decay to do so.

Predicting how an isotope will decay: An isotope is just too big: a decay An isotope has too many neutrons: b decay An isotope has too few neutrons: e- capture, positron emission

Write the Nuclear Reaction for: The a decay of Americum-245 The b decay of Thorium-236 The electron capture of Iodine-125 The positron emission of Potassium-40