Thorium, a rare element in the earth's crust, has over seven radioactive isotopes. Of of these Th has a half-life of 18.68 days. 227 90 Calculate the decay constant. What percent of Th-227 will be left after 43 days? % When o.355 % is left, how much time has passed? days

If 25%(1/4)of a radioactive element remains after1,000years, what is the half-life?

Iodine-131 is a radionuclide that is frequently used in nuclear medicine. Among other things, it is used to detect fluid build up in the brain. The half-life of iodeine-131 is 8.0 days. How much of a 0.16-g sample of iodine-131 will remain undecayed after a period of 32 days?   a.) 0.020g b.) 0.080g c.) 0.010g d.) 0.040g

The radioactive isotope I-131is used in the treatment of hyperthyroidism. When administeredto a patient, I-131 accumulates in the thyroid gland, where it decays and kills part of thatgland. Consider the half-life of 8 days.a) Suppose that it takes 72 hours to ship I-131 from the producer to the hospital. Whatpercentage of the original amount shipped actually arrives at the hospital.b) If the I-131 is stored at the hospital for an addition 48 hours before it is used, how muchof the original amount shipped from the producer is left when it is used?c) How long will it take for the I-131 to decay completely so that the remnants can be thrownaway without special precautions?

What is the half‑life of an isotope that decays to 3.125%3.125% of its original activity in 41.8 h?

How many hours are needed for a 16.0 g sample of Si-31 to decay to 2.0 g? The half-life for Si-31 is 2.6 h.

Radioactive vanadium-48 decays with a half-life of 16.0 days. a. What is the value of k in s? k = b. A sample contains 84.0 mg *°V. How many decay events will be produced in the first second? Assume the atomic mass of **V is 48.0 u. decays/s c. A chemist obtains a fresh sample of 48 V and measures its radioactivity. She then determines that to do an experiment, the radioactivity cannot fall below 25% of the initial measured value. How long does she have to do the experiment? days