RADIOACTIVE+DECAY

IB PHYSICS > QUANTUM AND NUCLEAR PHYSICS
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RADIOACTIVE DECAY
Describe β+ decay, including the existence of the neutrino.

BETA DECAY: The emission from the nucleus of an electron or a positron (antiparticle of electron). The energies of the emitted particles form a continuous spectrum. NEUTRINO AND ANTINEUTRINO: To account for loss of energy (mass difference) and momentum, the neutrino and antineutrino were predicted. In β - decay, an antineutrino is emitted with the electron; in β + decay, a neutrino is emitted with a positron. Students should know that β energy spectra are continuous, and that the neutrino was postulated to account for these spectra.



State the radioactive decay law as an exponential function and define the decay constant.

Students should know that the decay constant is defined as the probability of decay of a nucleus per unit time.

λ = -( dN/dt)/N = rate of decay/ total number of nuclides in sample

EXPONENTIAL DECAY: The rate of decay is proportional to the number of nuclei. The more nuclei there are, the faster the sample decays (remember negative sign):

dN/dt α -N

DECAY CONSTANT (λ): The constant of proportionality between the rate of decay and the number of nuclei available to decay. The probability of decay of a nucleus in unit time. Units are s -1

ACTIVITY (A): The number of decays in a second. A=λN

Derive the relationship between decay constant and half-life.

Outline methods for measuring the half-life of an isotope.

Students should know the principles of measurement for both long and short half‑lives.

Solve problems involving radioactive half-life.