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A Geiger counter and a source of radioactive particles are so situated that the probability that a particle emanating from the radioactive source will be registered by the counter is \(1 / 10000\). Assume that during the time of observation, 30000 particles emanated from the source. What is the probability that the number of particles registered was (a) zero, (b) three, (c) more than five?

Short Answer

Expert verified
(a) 0.0498, (b) 0.2240, (c) 0.1841.

Step by step solution

01

Define the Problem using the Poisson Distribution

The Poisson distribution is suitable for calculating the probability of a given number of events (particles registered) happening in a fixed interval of time, given the average number of times the event occurs over that interval. Here, it’s given that the probability of a particle being detected is \( \frac{1}{10000} \), and 30000 particles have emanated from the source. Thus, the mean number of detected particles \( \lambda \) is \( \lambda = \frac{30000}{10000} = 3 \).
02

Calculate Probability of Zero Particles Registered

For a Poisson distribution, the probability of \( k \) events is given by the formula \( P(k, \lambda) = \frac{e^{-\lambda} \lambda^k}{k!} \). To find the probability of zero particles being registered, substitute \( k = 0 \) and \( \lambda = 3 \):\[ P(0, 3) = \frac{e^{-3} \cdot 3^0}{0!} = e^{-3} \approx 0.0498 \].
03

Calculate Probability of Three Particles Registered

Now use the same Poisson formula for \( k = 3 \) and \( \lambda = 3 \):\[ P(3, 3) = \frac{e^{-3} \cdot 3^3}{3!} = \frac{e^{-3} \cdot 27}{6} = \frac{27 \cdot e^{-3}}{6} \approx 0.2240 \].
04

Calculate Probability of More Than Five Particles Registered

To find the probability of more than 5 particles registered, calculate the probability of \( 0 \) through \( 5 \) particles registered and subtract from 1:\[ P(>5) = 1 - (P(0) + P(1) + P(2) + P(3) + P(4) + P(5)) \].Using the Poisson formula, compute:- \( P(1, 3) \approx 0.1494 \)- \( P(2, 3) \approx 0.2240 \)- \( P(4, 3) \approx 0.1680 \)- \( P(5, 3) \approx 0.1008 \)Sum these and subtract from 1:\[ P(>5) \approx 1 - (0.0498 + 0.2240 + 0.2240 + 0.2240 + 0.1680 + 0.1008) = 0.1841 \].

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Key Concepts

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

Probability Calculation
Understanding how to calculate probabilities is an essential part of working with Poisson distributions. This type of distribution is handy when we need to determine the likelihood of a particular number of events occurring within a fixed interval. The events are assumed to occur independently and with a constant mean rate.
For Poisson distributions, a key formula is used:
  • \( P(k, \lambda) = \frac{e^{-\lambda} \lambda^k}{k!} \)
here, \( P(k, \lambda) \) gives the probability of \( k \) events occurring when the mean number of events is \( \lambda \).
In our exercise, we're asked to find the probability of a Geiger counter registering a specific number of radioactive particles established in time intervals.
  • To find zero particles registered: Substitute \( k = 0 \) into the formula.
  • To find three particles registered: Substitute \( k = 3 \).
  • For more than five particles registered: Calculate and sum the probabilities for 0 to 5 particles and subtract from 1.
These calculations provide us with understanding on how likely certain numbers of events are to happen, based on a given average.
Radioactive Particles
Radioactive particles are tiny bits of matter that result from the decay of unstable atomic nuclei. The process is random and occurs naturally over time. We often study these particles to understand properties of radioactive materials and to assess safety in environments where radiation is present.
The emission of these particles is what we are concerned with in the given problem. Despite the complexity of radiation, using statistical methods like Poisson distributions allows us to predict certain behaviors.
When working with radioactive sources:
  • Detectors, like Geiger counters, are used to measure the activity by counting the number of particles detected over time.
  • The randomness of emission means not every particle will be detected.
  • Tools like Poisson distributions help in approximating the expected outcomes in these scenarios.
This understanding is crucial in environments such as laboratories or nuclear facilities where accurate detection and interpretation of radiation levels are vital.
Mean of Distribution
In statistics, the mean, or average, gives a central value for a set of numbers. The concept of the mean is slightly different in a Poisson distribution context. Here, the mean \( \lambda \) represents the average number of occurrences of an event in a fixed interval.
In the context of our exercise, the mean is derived by multiplying the total number of particles by the probability of being detected by the Geiger counter. Here, 30000 particles are emitted, and each has a \( \frac{1}{10000} \) chance of detection. This gives \( \lambda = 3 \).
  • \( \lambda \) is key, as it determines the shape and spread of the distribution.
  • A high mean would indicate that many events are likely to occur.
  • A low mean suggests fewer events are expected.
Understanding this mean helps in accurately predicting the number of particles likely to be registered, which is critical in monitoring and managing radioactive sources.

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Most popular questions from this chapter

If \(Z\) is a random variable having the standard normal distribution, find the probabilities that \(Z\) will have a value (a) greater than \(1.14\), (b) less than \(-0.36\) (c) between \(-0.46\) and \(-0.09\), (d) between \(-0.58\) and \(1.12\).

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