Question
The mean lives of a radioactive substance are 1620 years and 405 years foremission and emission respectively. Find out the time during which threefourth of a sample will decay if it is decaying both by emission andemission simultaneously.
.

449 years

435 years

475 years

None of these
medium
Solution
449 years
The decay constants for emission are respectively per year.
.
After th part has been disintegrated,
= 449 years.
SIMILAR QUESTIONS
The disintegration rate of a certain radioactive sample at any instant is 4750 disintegrations per minute. 5 minute after, the rate becomes 2700 disintegrations per minute. Calculate the halflife of the sample. .
At a given instant are 25% undecayed radioactive nuclei in a sample. After 10 seconds, the number of undecayed nuclei reduces to 12.5%. Calculate the time in which the number of undecayed nuclei will further reduce to 6.25% of the reduced number.
The normal activity of a living mater containing radioactive carbon C^{14} is found to be 15 decays per minute per gram of carbon. An archaeological specimen shows an activity of 9 decays per minute per gram of carbon. Estimate the age of the specimen. The halflife of C^{14} is 5730 years.
A radioactivity sample contains 2.2 mg of pure which has halflife period of 1224 seconds. Calculate the number of atoms present initially.
A small quantity of solution containing radionuclide (halflife 15 hours) of activity 1.0 microcurie is injected into the blood of a person. A sample of the blood of volume 1 cm^{3} taken after 5 hours show an activity of 296 disintegrations per minute. Determine the total volume of blood in the body of the person.
.
The isotopes occur in nature in the ratio 140 : 1. Assuming that at the time of earth’s formation they were present in equal ratio, make an estimation of the age of the earth. The halflives of respectively.
A radioactive isotope X has a halflife of 3 seconds. At t = 0 second, a given sample of this isotope X contains 8000 atoms. Calculate the number of decays per second in the sample at t = t_{1} second.
A radioactive element of atomic weight 99 has a halflife of 6 hours. Find the activity in a solution containing 1 gram of the element in the beginning. The Avogadro’s number is .
In an ore containing uranium, the ratio of nuclei is 3. Calculate the age of the ore, assuming that all the lead present in the ore is the final stable product of . Take the halflife of .
Calculate the energy in joule equivalent to the mass of one proton. The mass of proton is 1.00728 u. Express the energy in kilowatthour also.