2. Tritium, (3 H) is used in glowing "EXIT" signs located where there is no electricity for light bulbs. If the half-life of tritium 12.26 years, what percentage of the original quantity of the isotope is left in the sign after 18.5 years?

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Chapter1: Units, Trigonometry. And Vectors
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PROBLEM SOLVING HELP NUMBER 2 ONLY 

Another equation relating the half-life, T1/2 and Activity, R can
be expressed as:
R=0.693N Tia
If a radioactive sample contains N radioactive nuclei in some
instant, we can solve for the number of nuclei, AN, that decays in time
At, is proportional to N. This is given by the equation:
VNY--NV
The number of nuclei present varies with time according to the
equation: N = NOe -At where e 2.718
Sample Problems
The half-life of a radioactive sample is 30minutes. If the sample
originally contains 3x1018 nuclei, how many of these nuclei remain
after 2 hours?
The half-life of the sample is 30minutes. In 2 hours, the number of half-
life would be:
2 hours
= 4 half-life periods
2 hours
3 0家
The remaining sample after 2hours is equal to
1xxx+r(3x1018 nuclei)
= 1.85x 1017 nuclei
2. The activity of a radioactive sample is 1.6 Ci and its half-life is 2.5
days. What will be the activity after 10 days?
The half-life of the sample is 2.5 days. To determine the number of
half-life the sample undergone:
10 days
2.5 days
= 4 half-life periods
The initial activity of the sample is 1.6 Ci. The activity after 10 days
=0.1 Ci
The initial mass of an lodine isotope was 200g. Determine the lodine
mass after 30 days if the half-life of the isotope is 8 days.
The decay constant is equal to A= 0.693 T1/2 where T1/2 8days
ori s /ceerol- a10
N= 200e -2.6
N= 200x0.074
N= 14.9grams
Activity 2: What's
Activity 2: What's my life?
Directions: Analyze the problem below. Show all your solutions on the answer sheet provided for you at the last page of this
module.
1. Uranium-238 decays to form thorium-234 with a half-life of 4.5 x 10° years. How many years will it take for 75% of the
uranium-238 to decay?
2. Tritium, (3 H) is used in glowing "EXIT" signs located where there is no electricity for light bulbs. If the half-life of tritium is
12.26 years, what percentage of the original quantity of the isotope is left in the sign after 18.5 years?
(Write you final answer on the answer sheet)
4 | Page
Transcribed Image Text:Another equation relating the half-life, T1/2 and Activity, R can be expressed as: R=0.693N Tia If a radioactive sample contains N radioactive nuclei in some instant, we can solve for the number of nuclei, AN, that decays in time At, is proportional to N. This is given by the equation: VNY--NV The number of nuclei present varies with time according to the equation: N = NOe -At where e 2.718 Sample Problems The half-life of a radioactive sample is 30minutes. If the sample originally contains 3x1018 nuclei, how many of these nuclei remain after 2 hours? The half-life of the sample is 30minutes. In 2 hours, the number of half- life would be: 2 hours = 4 half-life periods 2 hours 3 0家 The remaining sample after 2hours is equal to 1xxx+r(3x1018 nuclei) = 1.85x 1017 nuclei 2. The activity of a radioactive sample is 1.6 Ci and its half-life is 2.5 days. What will be the activity after 10 days? The half-life of the sample is 2.5 days. To determine the number of half-life the sample undergone: 10 days 2.5 days = 4 half-life periods The initial activity of the sample is 1.6 Ci. The activity after 10 days =0.1 Ci The initial mass of an lodine isotope was 200g. Determine the lodine mass after 30 days if the half-life of the isotope is 8 days. The decay constant is equal to A= 0.693 T1/2 where T1/2 8days ori s /ceerol- a10 N= 200e -2.6 N= 200x0.074 N= 14.9grams Activity 2: What's Activity 2: What's my life? Directions: Analyze the problem below. Show all your solutions on the answer sheet provided for you at the last page of this module. 1. Uranium-238 decays to form thorium-234 with a half-life of 4.5 x 10° years. How many years will it take for 75% of the uranium-238 to decay? 2. Tritium, (3 H) is used in glowing "EXIT" signs located where there is no electricity for light bulbs. If the half-life of tritium is 12.26 years, what percentage of the original quantity of the isotope is left in the sign after 18.5 years? (Write you final answer on the answer sheet) 4 | Page
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