Radioactive decay can be described by the following equation in a = in ao- kt where ao is the original amount of the substance, a is the amount of the substance remaining after time t, and k is a constant that is characteristic of the substance. minutes for the radioactive isotope chromium-56, k is 1.17 x 10 if the original amount of chromium-56 in a sample is 34.5 mg, how much time is needed for the amount of chromium- 56 that remains to fall to 20.3 mg?

The amount of time needed is 4.53 minutes.

Explanation:

The equation used to calculate time period follows:

where,

= initial mass of Cr-56 isotope = 34.5 mg

A = mass of the Cr-56 isotope left after the time = 20.3 mg

t = time = ? min

k = rate constant =

Putting values in above equation, we get:

Hence, the amount of time needed is 4.53 minutes.

most historians agree that gabriel mouton, the vicar of st. paul’s church in lyons, france, is the “founding father” of the metric system. he proposed a decimal system of measurement in 1670. mouton based it on the length of one minute of arc of a great circle of the earth (now called a nautical mile, 1852 meters). he also proposed the swing-length of a pendulum with a frequency of one beat per second as the unit of length (about 25 cm). a pendulum beating with this length would have been fairly easy to produce, thus facilitating the widespread distribution of uniform standards. over the years, his work was revised, improved, and extended by a number of french scientists.

the political sponsor of weights and measures reform in the french revolutionary national assembly was the bishop of autun, better known as talleyrand. under his auspices, the french academy appointed several committees to carry out the work of developing a usable system of weights and measures for france. one of the committees recommended a decimalized measurement system based upon a length equal to one ten-millionth of the length of a quadrant of the earth’s meridian (i.e., one ten-millionth of the distance between the equator and the north pole).