Alpha emission capture

There are five main types of emissions alpha emission, beta emission, positron emission, electron capture, and gamma emission. Four of these produce changes in the elements undergoing decay, and the end result is a more stable atomic structure. 

To gain stability, neutrons undergo decay reactions alpha emission, beta emission, positron emission, and electron capture are possible. 

The arrows in Figure 19.1 show the directions of the types of decay discussed so far. Nuclei whose values of N/Z are too great move toward the line of stability by beta emission, whereas those whose values are too small undergo positron emission or electron capture. Nuclei that are simply too massive can move to lower values of both N and Z by alpha emission. The range of stable nuclides is limited by the interplay of attractive nuclear forces and repulsive Coulomb forces between protons in the nucleus. Scientists believe that it is unlikely that additional stable elements will be found, although long-lived radioactive nuclides may well exist at still higher Z. 

E.C. stands for electron capture e for positron alpha emission. emission e for beta emission a, for... 

To gain stability, neutrons undergo decay reactions alpha emission, beta emission, positron emission, and electron capture are possible. Although it is not possible to predict when a single decay will occur, the overall rate of decay for any isotope is relatively consistent. 

Write nuclear equations for (a) alpha emission hy polonium-210, used in radiation therapy, (b) beta emission by gold-198, used to assess kidney activity, (c) positron emission by nitrogen-13, used in making brain, heart, and liver images, and (d) electron capture by gallium-67, used to do whole body scans for tumors. 

This is the last chapter in Part I of the general chemistry review. In this chapter, we will discuss the different aspects of radioactivity. Radioactivity is a nuclear phenomenon. It results from natural nuclear instability or externally induced nuclear instability. We will limit our discussion of nuclear chemistry to the basic aspects of radioactivity involving radioactive emissions such as alpha emission, beta emission, gamma rays, positron emission, and electron capture. We will also review other ideas such as the half-lives of radioactive substances and the mass-energy equation. 

Figure 21.3 Results of alpha emission ( He), beta emission ( e), positron emission (°e), and electron capture on the number of protons and neutrons in a nucleus. Moving from left to right or from bottom to top, each square represents an additional proton or neutron, respectively. Moving in the reverse direction indicates the loss of a proton or neutron. 

The first two reactions are found for many of the heavy radioactive nucleides. Alpha emission has been observed also for a number of the neutron-rich nucleides in the rare-earth region. The third reaction, positron emission, occurs for most neutron-rich nucleides, many of which also decompose by electron capture (the fourth reaction). (Electron capture is classed as a spontaneous decomposition because the electrons are always available in the atom for capture it is the s electrons, principally l5, that are captured they are the only electrons with finite probability at the nucleus.) The last two reactions, proton and neutron emission, occur only rarely. 

Figure 22-1 A plot of the number of neutrons, A/, versus the number of protons,Z, in nuclei.The stable nuclei (green dots) are located in an area known as the band of stability. All other nuclei in the white, pink, and blue regions are unstable and radioactive. No nuclei exist in the large gray shaded region. Most unstable, radioactive nuclei occur outside the band of stability. As atomic number increases, the N/Z ratio of the stable nuclei increases. Unstable nuclei above the band of stability are referred to as neutron-rich nuclei (Woe shad/ng) those below the band of stability are called neutron-poor nuclei (pinkshading). Unstable (radioactive) nuclei decay by alpha emission, beta emission, positron emission, or electron capture. Lighter neutron-poor nuclei usually decay by positron emission or electron capture, either of which converts a proton into a neutron. Heavier neutron-poor nuclei usually decay by alpha emission, which decreases the neutron/proton ratio. Neutron-rich nuclei decay by beta emission, which transforms a neutron into a proton. Decay by alpha emission is by far the most predominant mode of decay for nuclei with atomic numbers beyond 83 (bismuth).

The stable nuclides,indicated by black dots, cluster in a band. Nuclides to the left of the band of stability usually decay by beta emission, whereas those to the right usually decay by positron emission or electron capture. Nuclides ofZ> 83 often decay by alpha emission. 

There are three common ways by which nuclei can approach the region of stability (1) loss of alpha particles (a-decay) (2) loss of beta particles (/3-decay) (3) capture of an orbital electron. We have already encountered the first type of radioactivity, a-decay, in equation (/0). Emission of a helium nucleus, or alpha particle, is a common form of radioactivity among nuclei with charge greater than 82, since it provides a mechanism by which these nuclei can be converted to new nuclei of lower charge and mass which lie in the belt of stability. The actinides, in particular, are very likely to decay in this way. 

Radioactivity—Spontaneous nuclear transformations that result in the formation of new elements. These transformations are accomplished by emission of alpha or beta particles from the nucleus or by the capture of an orbital electron. Each of these reactions may or may not be accompanied by a gamma photon. 

Alpha, beta, and gamma emission are the most common types of natural decay modes, but we do occasionally observe positron emission and electron capture. 

Make sure that in alpha, beta, gamma, and positron emission the particle being emitted is on the right-hand side of the reaction arrow. In electron capture, the electron should be on the left side of the arrow. 

Know that nuclear stability is best related to the neutron-to-proton ratio (n/p), which starts at about 1/1 for light isotopes and ends at about 1.5/1 for heavier isotopes with atomic numbers up to 83- All isotopes of atomic number greater than 84 are unstable and will commonly undergo alpha decay. Below atomic number 84, neutron-poor isotopes will probably undergo positron emission or electron capture, while neutron-rich isotopes will probably undergo beta emission. 

The ion Es1 is stable. The isotopes of mass numbers 245. 252. 253 and 254 decay by alpha-particle emission that of mass number 250 by electron capture, those of mass numbers 24ft. 248. 249. and 251 by both of these processes, while those of mass numbers 255 and 256 emit electrons to form the corresponding fermium isotopes. 

Another isotope. Lr. hall-life about 45 seconds, was reported by the Soviet Union in 1965. It was produced by impact of oxygen atoms (l

alpha-particle emission and electron capture to form Fm See also Chemical Elements. 



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