Nuclear Decay Processes

Ck12 Science

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Printed: July 20, 2014

AUTHORCk12 Science

www.ck12.org Chapter 1. Nuclear Decay Processes

CHAPTER 1 Nuclear Decay Processes• List the decay processes.• Describe the alpha decay process.• Describe the beta decay process.• Describe gamma emission.• Describe positron emission.

You did what to my hamburger?

Food irradiation is a sensitive subject for many people. The practice involves exposing the food to ionizing radiationin order to kill harmful bacteria (such as salmonella) that cause sickness. The food is essentially unchanged anddoes not lose any nutritive value. Parasites and insect pests are easily destroyed by this process, while bacteria takelonger to kill. Viruses are not affected by the radiation treatment. But don’t worry –the food is not radioactive andyou will not glow in the dark if you eat it.

Nuclear Decay Processes

Radioactive decay involves the emission of a particle and/or energy as one atom changes into another. In mostinstances, the atom changes its identity to become a new element. There are four different types of emissions thatoccur.

Alpha Emission

Alpha (α) decay involves the release of helium ions from the nucleus of an atom. This ion consists of two protonsand two neutrons and has a 2+ charge. Release of an α-particle produces a new atom that has an atomic number twoless than the original atom and an atomic weight that is four less. A typical alpha decay reaction is the conversion ofuranium-238 to thorium:

23892U→ 234

90Th+ 42α

+

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We see a decrease of two in the atomic number (uranium to thorium) and a decrease of four in the atomic weight (238to 234). Usually the emission is not written with atomic number and weight indicated since it is a common particlewhose properties should be memorized. Quite often the alpha emission is accompanied by gamma (γ) radiation, aform of energy release. Many of the largest elements in the periodic table are alpha-emitters.

FIGURE 1.1Emission of an alpha particle from thenucleus.

Beta Emission

Beta (β) decay is a more complicated process. Unlike the α-emission, which simply expels a particle, the β-emissioninvolves the transformation of a neutron in the nucleus to a proton and an electron. The electron is then ejected fromthe nucleus. In the process, the atomic number increases by one while the atomic weight stays the same. As is thecase with α-emissions, β-emissions are often accompanied by γ-radiation.

FIGURE 1.2Beta emission.

A typical beta decay process involves carbon-14, often used in radioactive dating techniques. The reaction formsnitrogen-14 and an electron:

146C→ 14

7N+ 0−1e

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Again, the beta emission is usually simply indicated by the Greek letter β; memorization of the process is necessaryin order to follow nuclear calculations in which the Greek letter β without further notation.

Gamma Emission

Gamma (γ) radiation is simply energy. It may be released by itself or more commonly in association with otherradiation events. There is no change of atomic number or atomic weight in a simple γ-emission. Often, an isotopemay produce γ-radiation as a result of a transition in a metastable isotope. This type of isotope may just “settle,” witha shifting of particles in the nucleus. The composition of the atom is not altered, but the nucleus could be consideredmore “comfortable” after the shift. This shift increases the stability of the isotope from the energetically unstable (or“metastable”) isotope to a more stable form of the nucleus.

Positron Emission

A positron is a positive electron (a form of antimatter). This rare type of emission occurs when a proton is convertedto a neutron and a positron in the nucleus, with ejection of the positron. The atomic number will decrease by onewhile the atomic weight does not change. A positron is often designated by β+.

Carbon-11 emits a positron to become boron-11:

116C→ 11

5B+ 0+1β

Summary

• Radioactive decay processes are described.

Practice

Read the material at the link below and answer the questions at Practice Problem 3.

Review

Questions

1. What is gamma emission?2. What isotope is formed when U-238 emits an alpha particle?3. What isotope produces boron-11 when it emits a positron?

• alpha decay: Emission of two protons plus two neutrons.• beta decay: Emission of an electron.• gamma emission: Emission of energy.• positron emission: Emission of a positive electron.

References

1. Courtesy of United States Department of Agriculture, Food Safety and Inspection Service. http://commons.wikimedia.org/wiki/File:Radura-Symbol.svg .

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2. User:Inductiveload/Wikimedia Commons, modified by CK-12 Foundation. http://commons.wikimedia.org/wiki/File:Beta-minus_Decay.svg .

3. User:Inductiveload/Wikimedia Commons, modified by CK-12 Foundation. http://commons.wikimedia.org/wiki/File:Beta-minus_Decay.svg .

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