Main Page/PHYS 3220/Radioactive Decays
Radioactive Decays
In this experiment a Geiger-Müller counter with a computer interface is used to detect the radiation coming from the natural background, as well as from some weak sources. The statistics of the decays is investigated to confirm the independence of the decay mechanism. The dependence of the count rate on the distance from the source is also investigated. Also, the Geiger-Müller method for detection of radioactivity will be investigated.
Introduction
Radioactive Decays
Radioactive nuclear decays can be classified according to their decay mechanism:
α-decay: heavy radionucleides often decay via the emission of a cluster composed of 2 protons and 2 neutrons, i.e., a 2He4 nucleus.
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β-decay: nuclei away from the line of stability N = Z, where N is the total number of neutrons, and Z the total number of protons, can lower their energy, and hence become more stable by emitting either an electron or a positron. In the case of neutron-rich nuclei a fast electron is emitted from the nucleus, thus converting a neutron into a proton (and an electron + antineutrino) - corresponding to the β- decay of free neutrons (half-life 10.6 min.). For proton-rich nuclei a fast positron emerges from the nucleus (β+ decay) whereby a proton is converted into a neutron and a neutrino. This latter process may seem counterintuitive as it cannot occur for free protons (why?). The rest of the nuclear system supplies the energy necessary for the reaction to take place.
γ-decay: the emission of photons with higher energies than hard X-rays (MeV-range) is the result of a nuclear transition from an excited to a lower state in complete analogy with photon emission from excited atoms (eV to keV-range). This decay almost always accompanies α- and β-decays, since these processes usually leave the daughter nucleus in an excited state.
(iv) spontaneous fission:the emission of nuclear clusters bigger than α-particles is a rare process that has been studied recently in a systematic way at heavy ion facilities. It represents an alternative but rare decay mechanism, which provides insight into the nature of nuclear forces.
