Tritium, (^3H) is used in glowing \"EXIT\" signs located where there is no elect

Question

Tritium, (^3H) is used in glowing "EXIT" signs located where there is no electricity for light bulbs. If the 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? a. 0.632% b. 63.2% c. 35.1% d. 1.51% e. 25.0% positron emission, 1 degree beta of a large isotope can give increased nuclear stability by: a) increasing the n/p ratio b) decreasing the n/p ratio c) decreasing the # of ns The purpose of a Boron Rod in a nuclear reactor is to control the fission chain reaction by: a) changing U-235 to U-238 b) slowing down the neutrons c) absorbing neutrons The half-life of C-14 is 5730 years. The measurement of the percentage of the C-14 remained in a tree that died was found to be 10.8%, how long the tree was left undisturbed after it died? a) 19, 680 yrs b) 945 yrs c) 18, 400 yrs

Explanation / Answer

26) we know that

K = 0.693 / t1/2

t1/2 = half life = 12.26 years

K = rate constant = 0.693 / 12.26 = 0.05652 years-1

Now

ln[A]=kt+ln[A0]

ln [A] = - 0.0552 X 18.5 + ln [A0]

ln [At] / [A0] = -1.04571

taking antilog

[At] / [A0] = 0.351

At = 35.1 %

27) It increased n/p ratio

28) Boron rods absrobs neutron and check further decay

29) Half life = 5730 years

K = 0.693 / t1/2

t1/2 = half life = 5730years

K = rate constant = 0.693 / 5730 = 1.2094 X 10^-4 years-1

Now

ln[A]=kt+ln[A0]

ln [At/ A0] = - kt

ln (0.108) = - kt

-2.226 = -kt

time = 18402 = 18400 years approx

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