Advertisements
Advertisements
Question
The half-life of 35S is 87.8 d. What percentage of 35S sample remains after 180 d?
Advertisements
Solution
Given: t1/2 = 87.8 d, N0 = 100, t = 180 d
To find: % of 35S that remains after 180 days
Formulae:
- `lambda = 0.693/("t"_(1//2))`
- `lambda = 2.303/"t" log_10 ("N"_0/"N")`
Calculation:
- `lambda = 0.693/("t"_(1//2)) = 0.693/(87.8 "d") = 7.893 xx 10^-3 "d"^-1`
- Now, `lambda = 2.303/"t" log_10 ("N"_0/"N")`
`log_10 ("N"_0/"N") = (lambda"t")/2.303`
`= (7.893 xx 10^-3 xx 180)/2.303`
= 0.617
Taking antilog on both sides we get,
`"N"_0/"N" = 4.140`
N = `100/4.140`
= 24.155 ≈ 24.2%
Percentage of 35S that remains after 180 d is 24.2%.
APPEARS IN
RELATED QUESTIONS
Sample of carbon obtained from any living organism has a decay rate of 15.3 decays per gram per minute. A sample of carbon obtained from very old charcoal shows a disintegration rate of 12.3 disintegrations per gram per minute. Determine the age of the old sample given the decay constant of carbon to be 3.839 × 10−12per second.
Complete the following equation describing nuclear decay.
\[\ce{_8^19O->e^- { +}}\] _____
Complete the following equation describing nuclear decay.
\[\ce{_90^228Th->\alpha { +}}\] _____
Write relation between decay constant of a radioelement and its half-life.
Decay constant of 197Hg is 0.017 h-1. What is its half-life?
The half-life of 18F is 110 minutes. What fraction of 18F sample decays in 20 minutes?
The half-life of 67Ga is 78 h. How long will it take to decay 12% of the sample of Ga?
65% of 111In sample decays in 4.2 d. What is its half-life?
A 3/4 of the original amount of radioisotope decays in 60 minutes. What is its half-life?
A sample of 32P initially shows activity of one Curie. After 303 days, the activity falls to 1.5 × 104 dps. What is the half-life of 32P?
The half-life of radon is 3.82 d. By what time would 99.9% of radon will be decayed?
A radioactive substance decays to (1/10)th of its original value in 56 days. Calculate its decay constant.
The rate of radioactive disintegration at an instant for a radioactive sample of half-life 2.2 x 109 s is 1010 s-1. The number of radioactive atoms in that sample at that instant is, ______
Most excited states of an atom have life times of about ____________.
The activity of a radioactive sample ____________.
A radioactive substance has half life of 3 hours. 75 % of the substance would decay in ____________.
What is beta decay?
The radioactivity of a sample is R1 at a time T1 and R2 at a time T2. If the half-life of the specimen is T, the number of atoms that have disintegrated in the time (T1 - T2) is proportional to ______.
A radioactive sample S1 having the activity A1 has twice the number of nuclei as another sample S2 of activity A2 If A2 = 2A1 then the ratio of half-life of S1 to the half-life of S2 is ______.
The half-life of a radioactive substance is 10 days. The time taken for the `(7/8)^"th"` of the sample of disintegrates is ______.
The disintegration rate of a radio-active sample is 1010 per hour at 20 hours from the start. It reduces to 5 × 109 per hour after 30 hours. Calculate the decay constant.
Define half-life period.
In one mean lifetime of a radioactive element the fraction of the nuclei that has disintegrated is ______. [e is the base of natural logarithm]
