Spontaneous Decay, Fission, & Fusion Nuclear Reactions Spontaneous Decay, Fission, & Fusion

The N-Z Graph Why do nuclei decay at all? Provides a survey of nuclear stability For light nuclei (Z<20) N=Z for stable isotopes As Z increases, stable nuclei have increasing proportion of neutrons providing strong force “glue” Away from the stability curve, unstable nuclei decay to move closer to the stability curve

Nuclear Decay Occurs when an unstable nucleus breaks apart in some fashion and releases radiation. This decay occurs at a steady, measurable rate and is described with the following formula: ln (At/A0) = - kt A0 = initial amount of substance At = amount of substance after a certain time k = rate constant t = time

Nuclear Decay Half-life (t1/2) is the time required for half the amount of a radioactive sample to decay, so we can also estimate how much of a radioactive sample remains after a given amount of time if we know the half-life k * t1/2 = 0.693

Alpha Decay

Beta Decay

Decay Series An unstable isotope will decay in a series of steps until it reaches a stable state. Releases alpha, beta, and/or gamma radiation

Nuclear Reactions Transmutation is the process of converting one element into another (using bombardment with high energy particles). The target nucleus is the isotope which is bombarded The projectile is the particle fired at the nucleus The product is the new nucleus produced by the reaction The ejected particle is the light nucleus or particle emitted in the reaction.

Nuclear Reactions For Example: 79 197 Au + 2 4 He ----> 81 200 Tl + 0 1 n + γ Target Projectile Product Ejected Particle

Nuclear Reactions This bombardment takes place in a particle accelerator (cyclotron, synchrotron, linac, etc.). Many of the radioactive products of nuclear bombardment are useful in medicine and industry as tracers, radiation sources, etc.

Fission The splitting apart of an atomic nucleus into two smaller nuclei accompanied by a release of energy. Occurs in nuclear power plants and nuclear bombs

Fission in War August 6 and 9, 1945

Fission in Peace

Fusion The joining of two nuclei to form a larger nucleus accompanied by a release of energy. Occurs in stars and certain nuclear bombs