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Ch.20 - Nuclear Chemistry
Chapter 20, Problem 112

Nitrogen-16 is formed in the cooling water flowing through a hot reactor core in a nuclear power plant. It is formed when oxygen captures a neutron and then emits a b par-ticle. Determine the activity of 50.0 mg of 16N in units of Bq and Ci.

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1
Identify the decay process of Nitrogen-16 (16N). It decays by beta emission, and you need to know its half-life to proceed. The half-life of 16N is approximately 7.13 seconds.
Calculate the number of moles of 16N in 50.0 mg. Use the molar mass of 16N, which is approximately 16 g/mol. Number of moles = mass (g) / molar mass (g/mol).
Convert the number of moles of 16N to the number of atoms. Use Avogadro's number (approximately 6.022 x 10^23 atoms/mol). Number of atoms = moles x Avogadro's number.
Calculate the decay constant (\(\lambda\)) using the formula \(\lambda = \frac{\ln(2)}{t_{1/2}}\), where \(t_{1/2}\) is the half-life of the isotope.
Determine the activity (A) of the sample in becquerels (Bq) using the formula A = \(\lambda \times \) number of atoms. To convert the activity to curies (Ci), use the conversion factor 1 Ci = 3.7 x 10^10 Bq.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Radioactive Decay

Radioactive decay is the process by which unstable atomic nuclei lose energy by emitting radiation. This can occur in various forms, including alpha particles, beta particles, and gamma rays. Understanding this concept is crucial for calculating the activity of a radioactive substance, as it directly relates to the rate at which the substance decays over time.
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Activity of a Radioactive Sample

The activity of a radioactive sample is defined as the number of decays per unit time, typically measured in becquerels (Bq) or curies (Ci). One Bq corresponds to one decay per second, while one Ci is equivalent to 3.7 x 10^10 decays per second. This concept is essential for quantifying the radioactivity of a sample, such as the nitrogen-16 in the question.
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Mass-Energy Equivalence

Mass-energy equivalence, expressed by Einstein's equation E=mc², indicates that mass can be converted into energy and vice versa. In nuclear reactions, such as the formation of nitrogen-16 from oxygen capturing a neutron, a small amount of mass is converted into energy, which can affect the stability and decay of the resulting isotope. This principle underlies the processes occurring in nuclear reactors.
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Related Practice
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Open Question
Determine the activity of 10.0 mg of ²²⁶Ra in units of Bq and Ci. The half-life of ²²⁶Ra is 1600 years.
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The maximum allowable radiation dose for recovery workers at the Fukushima nuclear plant in Japan was set to 100 mSv. A gastrointestinal (GI) tract X-ray is 5 mSv. The radiation exposure of a Fukushima worker is equivalent to how many GI tract X-rays?
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A proposed nuclear theory suggests that the relative abun-dances of the uranium isotopes 235U and 238U were approximately equal at the time they were formed. Today, the observed ratio of these isotopes is 7.25 x 10^-3. Give that the half-lives for radioactive decay are 7.04 x 19^8 are y for and 4.47 x 10^9 y for , calculate the age of the elements.
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Textbook Question
A small sample of wood from an archaeological site in Clo-vis, New Mexico, was burned in O2 and the CO2 produced was bubbled through a solution of Ba(OH)2 to produce a precipitation of BaCO3. When the BaCO3 was collected by filtration, a 1.000 g sample was found to have a radioactivity of 4.0 x 10^-5 Bq. The half-life of 14C is 5715 y, and living organisms have a radioactivity due to 14C if 15.3 disintegrations/min per gram of carbon. If the analysis was carried out in 1960, what is the date of the Clovis site?
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