Alpha a Decay

When an element emits an alpha particle, the number of protons in its nnclens changes, transforming the element into a different element. We symbolize this phenomenon with a nuclear equation, an equation that represents nuclear processes such as radioactivity. For example, the nuclear equation for the alpha decay of uranium-238 is  

The original atom is called the parent nuclide, and the product of the decay is called the daughter nuclide. In this case, uranium-238 (the parent nucUde) becomes thorium-234 (the daughter nuclide). Unlite a chemical reaction, in which elements retain their identities, in a nuclear reaction elements often change their identities. Like a chemical equation, however, a nuclear equation must be balanced. TTie sum of the atomic numbers on both sides of a nuclear equation must be equal, and the sum of the mass numbers on both sides must also be equal. 

We can deduce the identity and symbol of the daughter nuclide in any alpha decay from the mass and atomic number of the parent nuclide. During alpha decay, the mass number decreases by 4 and the atomic number decreases by 2, as shown in Example 19.1. 

EXAMPLE 19.1 Writing Nuclear Equations for Alpha Decay Write the nuclear equation for the alpha decay of Ra-224. SOLUTION  

Begin with the symbol for Ra-224 on the left side of the equation and the symbol for an alpha particle on the right side. isRa 1 + He 

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Figure 1 Chart showing the decay chain of the U-Th decay series isotopes. Vertical arrows define alpha (a) decays while beta (/ ) decays are illustrated by diagonal arrows...

Alpha (a.) decay. As we shall see later, the alpha particle, which is a helium nucleus, is a stable particle. For some unstable heavy nuclei, the emission of this particle occurs. Because the a particle contains a magic number of both protons and neutrons (2), there is a tendency for this particular combination of particles to be the one emitted rather than some other combination such as s3Li. In alpha decay, the mass number decreases by 4 units, the number of protons decreases by 2, and the number of neutrons decreases by 2. An example of alpha decay is the following ... 

Deduce the identity of the unknown daughter nuclide from the atomic number. Since the atomic number is 86, the daughter nuclide is radon (Rn). SKILLBUILDER 17.1 Writing Nuclear Equations for Alpha (a) Decay Write a nuclear equation for the alpha decay of Po-216. FOR MORE PRACTICE Example 17.6 Problems 59,60. Rn -r He... 

Alpha (a) decay involves the loss of an a particle from a nucleus. For each a particle emitted by the parent, A decreases by 4 and Z decreases by 2 in the daughter. Every element beyond bismuth (Bi Z = 83) is radioactive and exhibits a decay, which is the most common means for a heavy, unstable nucleus to become more stable. For example, radium undergoes a decay to yield radon (Rn Z = 86) ... 

Alpha (a) decay occurs when an unstable nucleus emits a particle composed of two protons and two neutrons (Figure 19.2 ). Since two protons and two neutrons combined are identical to a helium-4 nucleus, the symbol for alpha radiation is the symbol for heUum-4 ... 

The major types of natural radioactivity are alpha (a) decay, beta (jS) decay, gamma (7) ray emission, and positron emission. 

The third type of decay is alpha (a) decay, which primarily occurs among heavy elements. In a decay the nucleus ejects an a particle, a particle consisting of two protons and two neutrons. Thus, the number of protons and number of neutrons are each decreased by two and the atomic mass is decreased by four. 

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