Radioactive Decay
World War II aircraft had instruments with glowing radium-painted dials. The activity of one such instrument was \(1.0 \times 10^{5} \mathrm{~Bq}\) when new. (a) What mass of \({ }^{226} \mathrm{Ra}\) 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?
Text Transcription:
1.0 times 10^5 Bq
^226 Ra
The Celestial Sphere Points of light in the sky o Jupiter o Saturn o Mars o Venus o Mercury o Sun Large sources of light o Moon o Venus o Sun o Spica Occasional visitors o Comets o Meteors Practical astronomy o Zenith Directly above your head o Nadir Directly below your feet The sun’s motion in the sky o The setting sun does not like to set o Solstices and equinoxes mark the beginnings of their seasons o Ecliptic The path the sun travels o Zodiac The constellations the sun travels through o Solar day 24 hours o Sidereal day 23 hours 56 minutes o There are 365 days in a year and the sun travels just about 1 degree per day against the celestial sphere o In the course of 1 year the sun makes 1 fewer revolution than the star’s do Solstices and equinoxes o Specific points on the celestial sphere o Specific instants during the year when the sun is exactly at those points o Solstice Sun stops o Equinox Equal night and day The seasons o The sun goes around the celestial sphere in 1 year o The seasons are connected to where the sun is on the celestial sphere o In winter the sun is above the horizon for a smaller fraction of the day o In winter even when it is up the sun hits the ground
