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Nuclei that have unstable n:p ratios undergo spontaneous radioactive decay. The most common types of radioactivity are α decay, β decay, γ emission, positron emission, and electron capture. Nuclear reactions also often involve γ rays, and some nuclei decay by electron capture. Each of these modes of decay leads to the formation of a new nucleus with a more stable n:p ratio. Some substances undergo radioactive decay series, proceeding through multiple decays before ending in a stable isotope. All nuclear decay processes follow first-order kinetics, and each radioisotope has its own characteristic half-life, the time that is required for half of its atoms to decay. Because of the large differences in stability among nuclides, there is a very wide range of half-lives of radioactive substances. Many of these substances have found useful applications in medical diagnosis and treatment, determining the age of archaeological and geological objects, and more.
What are the types of radiation emitted by the nuclei of radioactive elements?
α (helium nuclei), β (electrons), β + (positrons), and η (neutrons) may be emitted from a radioactive element, all of which are particles; γ rays also may be emitted.
What changes occur to the atomic number and mass of a nucleus during each of the following decay scenarios?
(a) an α particle is emitted
(b) a β particle is emitted
(c) γ radiation is emitted
(d) a positron is emitted
(e) an electron is captured
What is the change in the nucleus that results from the following decay scenarios?
(a) emission of a β particle
(b) emission of a β + particle
(c) capture of an electron
(a) conversion of a neutron to a proton: (b) conversion of a proton to a neutron; the positron has the same mass as an electron and the same magnitude of positive charge as the electron has negative charge; when the n:p ratio of a nucleus is too low, a proton is converted into a neutron with the emission of a positron: (c) In a proton-rich nucleus, an inner atomic electron can be absorbed. In simplest form, this changes a proton into a neutron:
Many nuclides with atomic numbers greater than 83 decay by processes such as electron emission. Explain the observation that the emissions from these unstable nuclides also normally include α particles.
Why is electron capture accompanied by the emission of an X-ray?
The electron pulled into the nucleus was most likely found in the 1 s orbital. As an electron falls from a higher energy level to replace it, the difference in the energy of the replacement electron in its two energy levels is given off as an X-ray.
Explain, in terms of [link] , how unstable heavy nuclides (atomic number>83) may decompose to form nuclides of greater stability (a) if they are below the band of stability and (b) if they are above the band of stability.
Which of the following nuclei is most likely to decay by positron emission? Explain your choice.
(a) chromium-53
(b) manganese-51
(c) iron-59
Manganese-51 is most likely to decay by positron emission. The n:p ratio for Cr-53 is = 1.21; for Mn-51, it is = 1.04; for Fe-59, it is = 1.27. Positron decay occurs when the n:p ratio is low. Mn-51 has the lowest n:p ratio and therefore is most likely to decay by positron emission. Besides, is a stable isotope, and decays by beta emission.
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