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Lead-210 has a half-life of \(20.4\) years. This isotope decays by beta particle emission. A counter registers \(1.3 \times 10^{4}\) disintegrations in five minutes. How many grams of \(\mathrm{Pb}-210\) are there?

Short Answer

Expert verified
Answer: The mass of Lead-210 present in the sample is approximately 1.39x10^-12 grams.

Step by step solution

01

Calculate the decay constant

The decay constant \(\lambda\) can be found using the formula relating half-life \(T_{1/2}\) and decay constant(lambda): \(\lambda = \frac{ln 2}{T_{1/2}}\) The half-life of Lead-210 is given as \(20.4\) years. Use this value to calculate the decay constant: \(\lambda = \frac{ln 2}{20.4} = 0.033915\) (per year).
02

Find the number of Lead-210 nuclei

The number of disintegrations in five minutes is given as \(1.3 \times 10^4\). Using this information together with the decay constant, we can determine the number of Lead-210 nuclei, \(N\): \(Disintegrations = \lambda \times N \times time\) The given disintegrations are recorded in five minutes, but the decay constant was calculated in years. Therefore, we need to convert the time to years: \(5 \text{ minutes} = \frac{5}{60\times24\times365} = 9.506x10^{-6} \text{ years}\) Now, replacing the known values in the equation and solving for \(N\): \(1.3 \times 10^4 = 0.033915 \times N \times 9.506x10^{-6}\) \(N = \frac{1.3 \times 10^4}{0.033915 \times 9.506x10^{-6}} = 4.015x10^{9}\) nuclei
03

Convert the number of nuclei to grams

With the number of nuclei calculated, now it is necessary to convert it into grams. Using Avogadro's number, the molar mass of Lead-210, and the calculated number of nuclei, we can find the grams of Lead-210: \( grams = \frac{Number\_of\_nuclei \times Molar\_Mass\_of\_Pb\_210}{Avogadro's\_Number}\) \( grams = \frac{4.015x10^{9} \text{ nuclei} \times 210 \text{ g/mol}}{6.022x10^{23} \text{ nuclei/mol}}\) \( grams = 1.39x10^{-12}\) g The mass of Lead-210 present in the sample is approximately \(1.39x10^{-12}\) grams.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Lead-210
Lead-210 is a radioactive isotope of the element lead, commonly represented as \(\mathrm{Pb}-210\). It undergoes a process known as radioactive decay, where it emits beta particles and transforms into a more stable element, eventually becoming bismuth-210. This process is a part of the natural decay series that begins with uranium-238 and progresses through various elements before arriving at stable lead isotopes.

Understanding Lead-210 is essential in fields like environmental science and geochronology. It is used to date sediments and can provide insights into sedimentation rates over time. In the context of radiological studies, Lead-210's presence can help assess radiation exposure risk because it is a precursor to the radioactive radon gas, a potential health hazard.

In terms of practical applications, researchers rely on Lead-210's decay to study ecological systems, monitor pollution, and even understand climate patterns from previous centuries. Its long half-life makes it a particularly useful isotope for studies covering historical periods spanning multiple decades.
Half-life Calculation
The concept of half-life is fundamental to understanding radioactive decay. It represents the time it takes for half of a sample of radioactive material to decay.

In the case of Lead-210, the half-life is given as \(20.4\) years. This means that if you start with \(100\) grams of Lead-210, only \(50\) grams will remain undecayed after \(20.4\) years. This attrition continues, reducing the amount by half, every \(20.4\) years.

Half-life calculations are crucial in estimating the age of a sample in radiometric dating techniques. Knowing the half-life and current composition of a substance allows scientists to backtrack to when a certain event occurred, such as sediment deposition or artifact formation. It’s also vital for determining the decay rate or how quickly the sample is losing its radioactive strength.

To calculate the half-life mathematically, you use the formula:
  • \(\lambda = \frac{\ln 2}{T_{1/2}}\)
where \(\lambda\) is the decay constant, and \(T_{1/2}\) is the half-life of the radioactive isotope.
Decay Constant
The decay constant, often symbolized by \(\lambda\), is a crucial value in the study of radioactive decay. It denotes the probability per unit time that a given nucleus will decay.

For Lead-210, we calculated \(\lambda\) using the formula \(\lambda = \frac{\ln 2}{T_{1/2}}\). With Lead-210's half-life of \(20.4\) years, the decay constant comes out to \(0.033915\) per year. This value indicates how quickly the material is losing its radioactive particles on a yearly basis.

The decay constant helps quantify the rate of decay and is used in various calculations to predict the behavior of radioactive materials. When multiplied by the number of radioactive nuclei, it defines the activity or the rate of disintegrations per second. Knowing \(\lambda\) can be essential for safely managing materials that release radiation, as it allows precise predictions of decay rates over time.

In practical terms, understanding and calculating the decay constant is vital for applications ranging from medical treatments, such as in radiotherapy, to determining the age of archaeological finds through carbon dating.

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Most popular questions from this chapter

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