A radioactive isotope has an initial decay rate of 51.29 dps (disintegrations per second) for a sample. After an elapsed time of 7.86 days, the rate has decreased to 19.9 dps. What is the half-life (in days) of this isotope?
A Watt (W) is a unit of power equal to 1J/s. A kilowatt is 1000 watts. How many kilowatt hours (1000 watts/s for one hour) of energy would be produced by the complete conversion to energy of 0.62 mg of matter? Error tolerance: ±1%
2007-04-30 14:30:05 · 1 answers · asked by Anonymous in Science & Mathematics ➔ Chemistry
Half-life = 5.7544 days. You calculate this as follows:
2*-(7.86 / halflife) = 19.9 / 51.29
logbase2(19.9 / 51.29) = -7.86 / halflife
logbase2(x) = log(x) / log(2)
halflife = -7.86 / [log(19.9 / 51.29) / log(2)]
According to Einstein, total conversion of mass to energy means e=m*c^2.
e = 6.2E-8 kg * (3E9 m/s)^2 = 5.58E11 J =
5.58E11 J / (1000 J/kw-s * 3600 s/hr) = 155000 kwh.
2007-05-04 12:46:44 · answer #1 · answered by kirchwey 7 · 0⤊ 0⤋