# alpha decay

## how dangerous is alpha decay

All types of radioactive decay pose risks to living things, but alpha decay is the least dangerous. Thats because alpha particles are relatively heavy, so they can travel only a few centimeters through the air. They also are not very penetrating. For example, they cant pass through a sheet of paper or thin layer of clothing. They may burn the skin, but they cant penetrate to the tissues underneath the skin. However, if alpha particles are emitted inside the body, they can do more damage. One way this can happen is by inhaling cigarette smoke. People who smoke actually inhale the radioactive element polonium-210. It undergoes alpha decay in the lungs. Over time, exposure to alpha particles may cause lung cancer.

## what is alpha decay

Alpha decay occurs when a nucleus is unstable because it has too many protons. The Figure 1.1 shows what happens during alpha decay. The nucleus emits an alpha particle and energy. An alpha particle consists of two protons and two neutrons, which is actually a helium nucleus. Losing the protons and neutrons makes the nucleus more stable.

## equations for alpha decay

Radioactive nuclei and particles are represented by nuclear symbols that indicate their numbers of protons and neutrons. For example, an alpha particle (helium nucleus) is represented by the symbol 42 He, where He is the chemical symbol for helium, the subscript 2 is the number of protons, and the superscript 4 is the mass number (2 protons + 2 neutrons). Nuclear symbols are used to write nuclear equations for radioactive decay. Lets consider an example. Uranium-238 undergoes alpha decay to become thorium-234. (The numbers following the chemical names refer to the number of protons plus neutrons.) In this reaction, uranium-238 loses two protons and two neutrons to become the element thorium-234. The reaction can be represented by this nuclear equation: 238 U 92 4 234 90 Th + 2 He + Energy If you count the number of protons (subscripts) as well as the number of protons plus neutrons (superscripts), youll see that the total numbers are the same on both sides of the arrow. This means that the equation is balanced. The thorium-234 produced in this reaction is also unstable, so it will undergo radioactive decay as well. The alpha particle (42 He) produced in the reaction can join with two free electrons to form the element helium. This is how most of Earths helium formed. Q: Fill in the missing subscript and superscript to balance the following nuclear equation for alpha decay of Polonium-210. 210 Po 84 ?? Pb + 42 He + Energy A: The subscript of Pb is 82, and the superscript is 206. This means that the new element produced in the reaction has 82 protons. You can find the element with this number of protons in the periodic table. It is the element lead (Pb). The new element also has 124 neutrons (206 - 82 protons = 124 neutrons).

## why some nuclei decay

Radioactive elements and isotopes have unstable nuclei. To become more stable, the nuclei undergo radioactive decay. In radioactive decay, the nuclei give off, or emit, radiation in the form of energy and often particles as well. There are several types of radioactive decay, including alpha, beta, and gamma decay. Energy is emitted in all three types of decay, but only alpha and beta decay also emit particles.

## instructional diagrams

No diagram descriptions associated with this lesson

## questions

an alpha particle is a

a) packet of energy.

b) single electron.

-->  c) helium nucleus.

d) none of the above

what does the following nuclear symbol represent?

-->  a) alpha particle

b) helium atom

c) helium ion

d) none of the above

in the nuclear symbol 6 c, the superscript represents the

a) atomic number.

-->  b) mass number.

c) valence number.

d) group number.

in the following nuclear equation for alpha decay, what is the missing subscript that will balance the equation? th + 42 he + energy 238 234

a) 94

b) 92

-->  c) 90

d) 88

an alpha particle consists of one proton and one neutron.

a. true

-->  b. false

alpha decay is the least dangerous type of radioactive decay.

-->  a. true

b. false

## diagram questions

No diagram questions associated with this lesson