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Question
World War II aircraft had instruments with glowing radium- painted dials (see Figure 31.2). The activity of one such instrument was $1.0\times 10^{5}\textrm{ Bq}$ when new. (a) What mass of $^{226}\textrm{Ra}$ was present? (b) After some years, the phosphors on the dials deteriorated chemically, but the radium did not escape. What is the activity of this instrument 57.0 years after it was made?
1. $2.73 \textrm{ ng}$
2. $9.8\times 10^{4}\textrm{ Bq}$
Solution Video

# OpenStax College Physics Solution, Chapter 31, Problem 59 (Problems & Exercises) (3:49)

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