Indoor Air Pollution - Air Pollution and Global Warming: History, Science, and Solutions - page 210

Figure 9.1. Antoine Henri Becquerel (1871-1937).
Edgar Fahs Smith Collection, University of
Pennsylvania Library.

Figure 9.2. Ernest Rutherford (1871-1937). American
Institute of Physics Emilio Segr `eVisualArchives,
William G. Myers Collection.

234 Pa decays further to uranium-234 ( 234 U), then to
thorium-230 ( 230 Th), then to radium-226 ( 226 Ra), and
then to radon-222 ( 222 Rn).
Whereas radon precursors are bound in minerals
(Lyman, 1997), 222 Rn is a gas and can escape through

beta particles. Rutherford later discovered the gamma
ray as well.
Equation 9.1 summarizes the radioactive decay path-
way of 238 Uto 206 Pb. Numbers shown are half-lives of
each decay process.

(9.1)

When it decays to produce radon, 238 Ufirstreleases
an alpha particle, producing thorium-234 ( 234 Th), which
decays to protactinium-234 ( 234 Pa), releasing a beta par-
ticle. 234 Pa has the same number of protons and neutrons
in its nucleus as does 234 Th, but 234 Pa has one less elec-
tron than does

soil and unsealed floors into houses, where its mixing
ratio builds up in the absence of ventilation. 222 Rn has a
half-life of 3.8 days. It decays to polonium-218 ( 218 Po),
which has a half-life of 3 minutes and decays to lead-214
( 214 Pb). 218 Po and 214 Pb, referred to as radon progeny ,
are electrically charged and can be inhaled or attach to

234 Th, giving 234 Pa a positive charge.