# Understanding the determination of Radon activity

• user1139
In summary: At any time the amount of daughter isotopes naturally occurring is constant.This is a conceptual question.
user1139
Homework Statement
This is a conceptual question.
Relevant Equations
As it is conceptual in nature, no equations will be used in the question.
When we want to determine the radioactivity of a nucleus, we usually determine the counts detected using say a Geiger counter. The count rate is then usually used as the disintegration rate i.e. the activity of the nucleus.

However, say now we wish to measure the activity of Radon 222 using alpha spectroscopy. Here is the part I don't understand:

If we use say RAD7, a detector with inbuilt alpha spectroscopy, we have to wait for activity equilibrium between the parent Radon nucleus and the daughter nuclei (those who decay via alpha particle emission) before an accurate Radon concentration (measured in ##\mathrm{Bq/m}^3##) can be calculated. Why do we have to wait for equilibrium? And if we do wait for equilibrium, then the Radon concentration will only involved counts obtained from Po-218 after around 10mins and only after 3h will counts from both Po-214 and Po-218 be involved. Why is it okay to calculate the Radon concentration this way even though different contributions occur at different times?

Last edited:
Even if you had an isotopically pure sample of Rn222 how would the production of Po218 affect the rate of decay of Rn?

Besides ever since the formation of the Earth's supply of U238 daughter nuclei have been/are being produced
Because of the extremely long half-life of U238 and the relatively short half-lives of the daughters an equilibrium has occurred in the population of the daughters. At any time the amount of daughter isotopes naturally occurring is constant.

Thomas1 said:
Homework Statement:: This is a conceptual question.
Relevant Equations:: As it is conceptual in nature, no equations will be used in the question.

If we use say RAD7, a detector with inbuilt alpha spectroscopy, we have to wait for activity equilibrium between the parent Radon nucleus and the daughter nuclei (those who decay via alpha particle emission) before an accurate Radon concentration (measured in ) can be calculated. Why do we have to wait for equilibrium?
One should look at 'secular equilibrium', where the parent isotope decays slower (has a longer half-life) than the daughter radionuclide.
https://en.wikipedia.org/wiki/Secular_equilibrium
Secular equilibrium can occur in a radioactive decay chain only if the half-life of the daughter radionuclide B is much shorter than the half-life of the parent radionuclide A. In such a case, the decay rate of A and hence the production rate of B is approximately constant, because the half-life of A is very long compared to the time scales considered. The quantity of radionuclide B builds up until the number of B atoms decaying per unit time becomes equal to the number being produced per unit time. The quantity of radionuclide B then reaches a constant, equilibrium value. Assuming the initial concentration of radionuclide B is zero, full equilibrium usually takes several half-lives of radionuclide B to establish.

## 1. What is Radon activity?

Radon activity refers to the amount of the radioactive gas Radon present in a given area. It is measured in units of activity per volume, typically in Becquerels per cubic meter (Bq/m3).

## 2. How is Radon activity determined?

Radon activity is determined through the use of specialized equipment, such as a Radon detector, which measures the concentration of Radon in the air. This measurement is then used to calculate the activity level.

## 3. Why is it important to understand Radon activity?

Radon is a known carcinogen and exposure to high levels of Radon gas can increase the risk of developing lung cancer. Understanding Radon activity can help identify areas with high levels of Radon and take necessary measures to reduce exposure.

## 4. What factors can affect Radon activity levels?

The main factor that affects Radon activity levels is the geological composition of the area. Radon is naturally present in soil and rocks, and certain types of soil and rocks have higher concentrations of Radon. Other factors such as ventilation, temperature, and building materials can also impact Radon activity levels.

## 5. How can we reduce Radon activity levels?

There are several ways to reduce Radon activity levels, including increasing ventilation, sealing cracks and openings in buildings, and installing a Radon mitigation system. It is important to consult a professional for proper mitigation techniques and to regularly test for Radon levels to ensure they are within safe limits.

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