RADIOACTIVITY

1. Alpha, Beta, Gamma particles are emitted from an unstable nucleus during decay of atoms. Radioactive decay is both a random and a spontaneous process. The rate of radioactive decay decreases exponentially with time.

2. Ionization - the radiation particles knock electrons out of atoms of gas. If the alpha, beta, and gamma particles pass through an electric or magnetic field the charges of the particles can be determined.

3. Alpha: +2e charge ; same as helium nucleus.

Beta:-e charge ; negative emission

Gamma: nuetral ; small wavelength

*Know summary table page 374

4. Absorption characterics of each. alpha - beta - gamma

5. Segre plots and stability. Generally, stable nuclei have more neutrons than protons in order to compensate for the repulsion of protons. Once nucleus starts to increase in size the strong nuclear force loses its effectiveness. Therefore more neutrons are necessary to hold the nucleus together.

6. Radioactive Decay.

Alpha Decay ... alpha partice emitted (A = 4, Z = 2). Energy of emitted particles is discrete.

Beta- Decay ... . This happens when there are too many neutrons (above stable band). Electron and antineutrino emitted. Continuous range of energy. The emitted electron is created within the nucleus ... one of the neutrons changes to a proton and in the process emits an electron in order to conserve energy. To distinguish from an orbital electron, these are often referred to as beta particles.

Beta+ Decay ... This happens when there are not enough neutrons (below stable band). Positron and neutrino emitted

Gamma Decay ... Gamma rays are photons having very high energy. Nucleus is in an excited state so when it drops to a lower state a photon is emitted. The energy of the photon is, of course, the difference in the energy states. In nuclear states this is a few million electronvolts. This yields a very small wavelength.

Remember that since E=hf and c=f(wavelength) that wavelength = (hc)/(change in Energy)

 

HW. PG 378: 1-6, 8-11, 13, 14, 16.

 

 

 

Segre Plot

 

7. Radioactive Decay Law: the number of nuclei that will decay per second is proportional to the number of atoms present that have not yet decayed

 

 

half-life