Radon under normal conditions is gaseous and it is easily inhaled. Radon is a single largest contributor to an individual's background radiation dose and it is thereby considered as being hazardous to health.

There is a clear link between breathing high concentrations of radon and incidence of lung cancer as shown by Epidemiological studies.

Read more on Radon from my previous posts here 1, 2.

Imagine a condition in which all products from soil are contaminated by radon 222.

The main source of radon is soil and rocks. Soil and rocks are very significant and important material found on the surface of the earth that is composed of both organic and inorganic substance. We make use of soil for farming which is considered as a source of food production and a paramount source of livelihood. Soil and rocks are used as construction materials for building, it is also the source of all clean, fresh or steam water.

Let's just think about the consequences of a contaminated soil, in a nutshell, the consequence of a contaminated soil is so disastrous. All vegetables and fruits from the primary producer (plant) will be contaminated, buildings and homes will also be contaminated due to contaminated raw materials such as ties, cement, sand, iron rods e.t.c used for construction and to cap it all, all types and forms of water either fresh or sea water are contaminated, invariably, all sea lives are contaminated.

From the fore mentioned examples, it is cleared that effects of soil contamination have direct consequences on lives on earth, including humans. Therefore investigation and assessment of soil sample for radon from farm lands, construction sites, industrial estates, buildings and infrastructures e.t.c are of most importance.

Determination of Radon 222 in soil sample

Assessment and determination of radon in soil from farm land of Ladoke Akintola University of Technology (LAUTECH) Ogbomoso, Oyo State Nigeria was mainly due to the consideration of over 5000 Agricultural students who make use of the farmland for farming practices per annum and also to be sure how safe it is to consume farm products produces from the farm land.

How to sample soil from investigated location
A total number of 24 samplings were observed at 6 different sample locations on the farm land. Random sampling method was adopted. In each sampling locations, four different forms of measurements of sampling point were taken. At each location points, measurements were taken at the surface (0cm) and a depth of 10cm, 20cm and 30cm.

Before measurements, all weeds, roots, and gravels were removed from the relevant location points of the measuring station.
A sharp-edged metallic container was inserted into the ground at different depths for measurement. A half hour counting time for each depth in all sampling points was employed. The average radon activity concentration was measured and recorded in Bq/m3.

The Detector: AlphaGuard system

AlphaGuard DF2000Pro device

AlphaGuard DF2000Pro device was used for the measurement of radon concentration in soil samples. The AlphaGuard radon monitor is an active electronic device that makes use of an ionization chamber and allows detection through alpha spectroscopy. It is attached a pump that pumps air into a 0.56-liter cell by means of diffusion.

The two common isotopes of radon which are 222 Rn and 220 Rn are identified by their respective energies from the alpha decays. The signal received from the alpha detection is filtered and converted into a digital output that can be readily processed with the AlphaGuard system, it can be connected to a PC using a RS-232 cable.

AlphaGuard PQ2000Pro detector can be used to determine radon concentrations, radon soil-gas, outdoor radon content, indoor radon concentration, in mining environments and in water storage radon measurements. It can simultaneously monitor air temperature (in the range from –10˚C to +50˚C), air humidity (from 0% to 99%) and air pressure (from 700 mbar to 1100 mbar). It functions on internal battery of life span of atleast 10 days.

Mode of operation
The measuring radon gas gets into an ionization chamber in a diffusion mode via a large surface glass filter. Only the gaseous 222radon is allowed to pass, while the radon daughter products (progeny products) are prevented from entering the ionization chamber.

At the same time, the filter protects the interior of the chamber from contamination of aerosol particles. A PC Software support allows a graphic presentation and calculation of the average concentration in the measured radon. Each depth in all sampling points takes half hour counting time for radon detection and measurement. The average radon activity concentration was measured and recorded in Bq/m3.

The most important feature of the Alpha Guard is displayed in its ability to respond from 2 Bq/m3 to 2 MBq/m3 of 222Rn concentration known as a linear response, while the disadvantage of the device is observed in its capable to detect alpha emitters without energy discrimination.

My investigations and findings (My final year project work)

The research work I am about to share with you was my final year project in the University, that was like 6 years ago. My project supervisor gave to me another work entirely for my project work but I convinced him to let me work on the school farm land.

I vividly remember the question he asked me, he asked me to convince him why he should allow me to embark on my desired project. The reply was that I needed to know the extent of radon exposure to my co-students who usually engage in various activities on the farm land as Agricultural students, so that a proper recommendation can be made to the school authorities based on the outcome of the research work.

Table showing various radon concentrations in soil samples of LAUTECH farm land

Various radon concentrations detected and measure from four different sample locations on LAUTECH farmland following procedures and methods described earlier are shown in the table above. It was observed that radon concentration increases as the sampling depth increases, that is, radon concentration is minimal or reduces at the surface compared to concentrations in various depth as investigated.

The result of the research work shows that radon concentrations are below the action levels of 200 - 600 Bq m-3 as recommended by ICRP. Therefore the areas of study are safe and do not pose health risks to the populace especially LAUTECH Agricultural students (over 5000 of them) who make use of the land for various farming purposes.

It should be noted that there is more to the assessment of natural radioactivity in soil than investigating only the effects of radon. It is also important to investigate effects of other natural radionuclides like 238U and 232Th parent series and natural 40K because they largely contribute to Annual effective dose to occupants.

Health effects of these natural radionuclides in soil sample will be considered as also investigated in LAUTECH farm land come next series of this post.

Don't miss out.

Thanks for reading!

LAUTECH MAIN ENTRANCE

References
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