Question

An unknown radioactive element decays into non-radioactive
substances. In 860 days the radioactivity of a sample decreases by
54 percent.

(a) What is the half-life of the element?

half-life: (days)

(b) How long will it take for a sample of 100 mg to decay to 91
mg?

time needed: (days)

Answer #1

An unknown radioactive element decays into non-radioactive
substances. In 860 days the radioactivity of a sample decreases by
49 percent.
(a) What is the half-life of the element?
half-life: (days)
b) How long will it take for a sample of 100 mg to decay to 78
mg?
time needed: (days)

An unknown radioactive element decays into non-radioactive
substances. In 520 days the radioactivity of a sample decreases by
35 percent.
(a) What is the half-life of the element? (days)
(b) How long will it take for a sample of 100 mg to decay to 44
mg? time needed: (days)

(1 point) An unknown radioactive element decays into
non-radioactive substances. In 500 days the radioactivity of a
sample decreases by 39 percent.
(a) What is the half-life of the element?
half-life: (days)
(b) How long will it take for a sample of 100 mg to decay to 57
mg?
time needed: (days)

An unknown radioactive element decays into non-radioactive
substances. In 640 days the radioactivity of a sample decreases by
50 percent. What is the half-life of the element? How long will it
take for a sample of 100 mg to decay to 70 mg?

A sample of a certain radioactive material decays to 89.36% of
its mass after 2 years.
a. What is the half-life of the material? Show your calculations
and keep four significant figures of accuracy.
b. How long would it take for the sample to decay to 10% of its
original mass? How much longer after that would it take to decay to
1% of its original mass?

The radioactive isotope 32P decays by first-order kinetics and
has a half-life = 14.3 days. How many atoms of a 1.0000 ug sample
of 32P would decay in 1.0000 second? (Assume 1 decay per atom.)

You have a 9.8 mol pure sample of an unknown material.
After 1.3 h, you discover that 22% has decayed. Determine the
half-life, decay constant, mean life, & initial decay rate.
Also determine what the decay rate is at 1.3 h.
T1/2 =
λ = ________ h-1
τ =
Ro = __________ decays/h
R = __________ decays/h
The decay rate of a radioactive source decreases by
70.6% in 6 h. Determine the half-life, decay constant, & mean
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Plutonium-239 can be used to make nuclear weapons and is found
in nuclear waste, but radioactive waste from nuclear reactors
contains large amounts of undesirable contaminants. Radioactive
waste can be stored in deep geological storage. Over many years the
fission products decay, decreasing the radioactivity of the waste.
However, the undesirable contaminant Pu-240 decays faster than the
Pu-239, and thus the quality of the bomb material increases with
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A radioactive substance decays at a continuous rate of 8.6% per
day. After 15 days, what amount of the substance will be left if
you started with 100 mg? (a) First write the rate of decay in
decimal form. r= (b) Now calculate the remaining amount of the
substance. Round your answer to two decimal places

Q.1 Radioactive 68Ge decays by β+ with a 271 day half-life. How
many grams of an initial 2.50 g sample of 68Ge remain after 365
days of radioactive decay?
Q.2 A particular reaction has an initial concentration of 4.302
M and a final concentration of 3.978 M after 1.08 seconds. The rate
constant is 0.0175 M-1s-1. What is the half-life at the initial
concentration?

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