Belt of stability

The ratios of stable isotopes (red dots) fall within a narrow range, referred to as the "belt of stability." For light isotopes of small atomic number the stable ratio is 1 1. For heavier isotopes the ratio gradually increases to about 1.5 1. Isotopes outside the band of stability are unstable and radioactive. There are no stable isotopes for elements of atomic number greater than 83 (Bi). 

As you can see from Figure 2.5, the neutron-to-proton ratio required for stability varies with atomic number. For light elements (Z < 20), this ratio is close to 1. For example, the isotopes C, N, and are stable. As atomic number increases, the ratio increases the belt of stability shifts to higher numbers of neutrons. With very heavy isotopes such as 2j Pb, the stable neutron-to-proton ratio is about 1.5 ... 

Basic ion An anion that forms OH- ions in water the CO32- ion is basic because of the reaction CO32 (aq) + H20 <— OH (aq) + HCO3 (aq), 372 Basic solution An aqueous solution with a pH greater than 7 (at 25°C), 369 Belt of stability, 30... 

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. 

For each different element, there are a few specific values of A that result in stable nuclei. Figure 2-20 shows all the stable nuclei on a plot of the number of neutrons (iV) versus the number of protons (Z). These data show a striking pattern All stable nuclei fall within a belt of stability. Any nucleus whose ratio of neutrons to protons falls outside the belt of stability is unstable and decomposes spontaneously. Lighter nuclei lie along the JV = Z line, but the N jZ ratio of stable nuclei rises slowly until it reaches 1.54. The trend is illustrated by the N j Z... 

As described in Chapter 2 (see Figure ), stable nuclides fall within a belt of stability with roughly equal numbers of neutrons and protons. Lighter nuclides lie along the = Z line, but as the mass of the nuclide increases, the... 

Within the belt of stability. Table 22-2 shows that nuclides with even numbers of protons and neutrons are more prevalent than those with odd numbers of protons or neutrons. Almost 60% of all stable nuclides have even numbers of both protons and neutrons, whereas fewer than 2% have odd numbers of both. Moreover, of the five... 

A detailed view of one portion of the N vs. Z plot of nuclides, illustrating the modes of nuclear decay for nuclides on either side of the belt of stability. 

Nuclides that lie below the belt of stability have low neutron-proton ratios and must reduce their nuclear charges to become stable. These nuclides can convert protons into neutrons by positron emission. Positrons (symbolized jS ) are particles with the same mass as electrons but with a charge of -Ft instead of-1. Here are three examples ... 

Neutrons readily induce nuclear reactions, but they always produce nuclides on the high neutron-proton side of the belt of stability. Protons must be added to the nucleus to produce an unstable nuclide with a low neutron-proton ratio. Because protons have positive charges, this means that the bombarding particle must have a positive charge. Nuclear reactions with positively charged particles require projectile particles that possess enough kinetic energy to overcome the electrical repulsion between two positive particles. 

C22-0094. Two isotopes used in positron-emission imaging are C and O. On which side of the belt of stability are these nuclides located Write the nuclear reactions for their disintegrations. 

C22-0125. Erom the mass number distribution given in Eigure 22-10 and the belt of stability shown in Eigures 22-5 and 2-20, predict which elements should be found in greatest abundance in the remains of a fission event like that of the Oklo reactor (Box). 

A plot of the neutrons (n) versus the protons (p) for the known stable isotopes gives the nuclear belt of stability. (See your textbook for a figure of the belt of stability.) At the low end of this belt of stability (Z < 20), the n/p ratio is 1. At the high end (Z 80), the n/p ratio is about 1.5. We can then use the n/p ratio of the isotope to predict if it will be stable. If it is unstable, then the isotope will utilize a decay mode that will bring it back onto the belt of stability. 

Isotopes that are neutron-rich, that have too many neutrons or not enough protons, lie above the belt of stability and tend to undergo beta emission because that decay mode converts a neutron into a proton. 

By plotting a graph between number of neutrons and protons for the nuclei of various elements it has been found that most stable nuclei (non-radioactive nuclei) lie within the shaded area which is called the zone or belt of stability because it contains the stable nuclei. Nuclei that fall above or below this belt are unstable. Nuclei that fall above the stability belt have more neutrons while those lying below have more protons. Such unstable nuclei would attain stability by undergoing change that would produce a nucleus with n/p ratio within the stability zone. 

Nuclei lying above the belt of stability are richer in neutrons and hence they disintegrate is such a manner that one of their neutrons is converted into a protons i.e.,... 

The nucleide near the belt of stability are probably stable, those above the belt are beta emitters, those below, positron emitters. Thus the stable hucleides are 208p 3 emitters are Ca, aI... 

When the proton number is graphed versus the neutron number for a stable nuclei, a belt of stability emerges (Figure 14.2). Nuclei outside this belt tend to be unstable and therefore radioactive. 

No, this one-to-one neutron-to-proton ratio is outside the belt of stability. Ni-58 yes (p = 28 n = 30 both even)... 

Alpha decay improves the stability of radioactive nuclei that lie to the right of the belt of stability. Emission of an alpha particle moves the nucleus diagonally toward the belt of stability because the numbers of both protons and neutrons are decreased by 2. The alpha particle is the least dangerous form of radiation as it has little ability to penetrate tissue. 

For each nuclei, there are some isotopes that are more stable than others. The stability of each nucleus is determined by the ratio of neutrons to protons. The belt of stability can be used to estimate the stability of any given nucleus. 

Figure 23.1 shows a plot of the number of neutrons versns the number of protons in various isotopes. The stable nuclei are located in an area of the graph known as the belt of stability. Most radioactive nnclei lie ontside this belt. Above the stability belt, the nuclei have higher neutron-to-proton ratios than those within the belt (for the same number of protons). To lower this ratio (and hence move down toward the belt of stability), these nnclei nndergo the following process, called -particle emission ... 

FIGURE 23.1 Plot of neutrons versus protons for various stable isotopes, represented by dots. The straight line represents the points at which the neutron-to-proton ratio equals I. The shaded area represents the belt of stability. 

Below the stability belt the nuclei have lower neutron-to-proton ratios than those in the belt (for the same number of protons). To increase this ratio (and hence move up toward the belt of stability), these nuclei either emit a positron... 

Nuclei outside the belt of stability, as well as nuclei with more than 83 protons, tend to be unstable. The spontaneous emission by unstable nuclei of particles or electromagnetic radiation, or both, is known as radioactivity. The main types of radiation are a particles (or doubly charged helium nuclei, He " ) /3 particles (or electrons) y rays, which are very-short-wavelength (0.1 nm to 10 " nm) electromagnetic waves positron emission and electron capture. 

When an isotope is above the belt of stability, the neutron/proton ratio is too high. The only mechanism to... 

The neutron-to-proton ratio for tritium equals 2 and is thus outside the belt of stability. In a more elaborate... 

When alpha decay occurs, it stabilizes the nuclei that lie on the right of the band of stability (Figure 4-2). Upon a particle emission, the nucleus moves diagonally (left and down) toward the belt of stability as both the number of protons and neutrons are decreased by two. 

The dark blue dots in HGU RE 21.2 represent stable (nonradioactive) isotopes. The region of the graph covered by these dark blue dots is known as the belt cf stability. The belt of stability ends at element 83 (bismuth), which means that all nudei widi 84 or more protons are radioactive. For example, all isotopes of uranium, Z = 92, are radioactive. 

The type of radioactive decay that a particular radionuclide undergoes depends largely on how its neutron-to-proton ratio compares with those of nearby nuclei that lie within the belt of stability. We can envision three general situations ... 

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