Sci-Afric Journal of Scientific Issues, Research and Essays.Vol. 2 (11), Pp. 479-490, November, 2014.
www.sci-africpublishers.org
Research Paper
RADIATION LEVEL MEASUREMENT IN DELTA STATE UNIVERSITY,
CAMPUS I, ABRAKA, Nigeria.
Osiga-Aibangbee Damaris
School of Science and Technology, Department of Science Laboratory Technology, Delta State Polytechnic, Ozoro,
PMB 5, Delta State, Nigeria.
Author’s E-mail: [email protected]
Accepted October 29th, 2014
-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------ABSTRACT
The natural background radiation has been measured in Delta State University Campus I, Abraka using Radiation levels
monitor FS2011+ to conduct Outdoor and indoor survey. A total of 11 outdoor and 11 indoor points was surveyed. The
minimum dose rate is 0.18µSv/hr and the maximum dose rate is 0.24µSv/hr for the outdoor measurement and 0.12µSv/hr
and 0.18µSv/hr for the indoor measurement. The outdoor and the indoor mean dose rate of the surveyed areas are found
to be 0.22µSv/hr and 0.14µSv/hr respectively. The result obtained shows the background radiation in the study area.
Thus, we have pointed out that no healthy risks have been around owing to the data/result obtained. This study is useful
as it can serve as baseline data of natural background radiation levels and also show the way to the background radiation
studies in the future.
Key words: Background radiation, Health, Radiation, Ultraviolet, Sun, Environment, Delta state.
INTRODUCTION
Life evolved in an environment with higher radiation levels than exist today, and background radiation levels today are lower
than at any time in the history of life on Earth. Since life first evolved, background radiation levels have decreased by a factor of
about 10, although there has been a negligible reduction since the evolution of humans (Prasad et al 2004). At present, natural
background radiation levels on Earth vary by at least two orders of magnitude today, so humans and other organisms are subject
to a wide range of background radiation levels. These do not include contributions from radon progeny in the lungs, which are
estimated to be even greater than the absorbed doses shown if the radiation weighting factor of alpha particles is taken into
account. Areas with unusually high background (high background radiation areas, or HBRAs) are found in Yangjiang, China;
Kerala, India; Guarapari, Brazil; and Ramsar, Iran (Abdel-Rassoul et al 2007). Some areas of Ramsar, a city in northern Iran, have
among the highest known background radiation levels in the world. For the purposes of this paper, “dose” will be used to mean
absorbed beta/ gamma radiation dose because the contribution of alpha emitters is not considered.
The background level of radiation in the natural environment surrounds us at all times. Since the Earth formed and life
developed, background radiation has been our constant companion.
Background radiation (which scientists call “ubiquitous background radiation”) is emitted from both natural and human-made
radioactive chemicals (radionuclides). Some naturally occurring radionuclides are found in the earth beneath our feet, while others
are produced in the atmosphere by radiation from space (Abdel-Rassoul et al 2007). Human-made radionuclides have entered the
environment from activities such as medical procedures that use radionuclides to image the body and electricity generation that
uses radioactive uranium as fuel.
Humans are continuously irradiated by sources outside and inside their bodies. Outside sources include space radiation and
terrestrial radiation. Inside sources include the radionuclides that enter our bodies in the food and water people ingest and the air
they breathe. Whatever its origin, radiation is everywhere (or “ubiquitous”) in the environment (Malathi et al 2005).
Radiation is energy in motion, in the form of waves or streams of particles. Radiation has always been present and is all
around us in many forms.
When people hear the word radiation, they often think of atomic energy, nuclear power and radioactivity, but radiation has
many different forms and comes from many other sources. Sound and visible light are familiar forms of radiation; other types
include ultraviolet radiation (that produces a suntan), infrared radiation (a form of heat energy), and radio and television signals.
These are examples of non-ionizing radiation.
Ionizing radiation has the ability to knock electrons out of orbit around atoms, upsetting the electron/proton balance and
potentially damaging cells. Examples include alpha, beta, gamma and neutron radiation and x-rays.
Life has evolved in a world with significant levels of ionizing radiation, and our bodies have adapted to it (Malathi et al 2005).
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Figure 1: Distribution of the population dose among the various sources of background radiation (Taher et al 2007).
SOURCES OF BACKGROUND RADIATION
Radiations sources are classified into natural background radiation sources and man-made radiation sources. The natural
background radiation sources are further classified into cosmic radiation, terrestrial radiation, internal radiation which further divided
into other sources. These sources of radiation will be discussed in this section (Taher et al 2007).
Radiation that enters the Earth’s atmosphere from space can come from as close as the Earth’s radiation belts and the sun or
as far away as beyond the boundaries of the solar system and even beyond the Milky Way galaxy (Taher et al 2007). Radiation
from beyond the solar system has enough energy to generate additional radiation as it passes through Earth’s atmosphere,
creating either radionuclides in the air or secondary particles. Some secondary particles reach the Earth’s surface—most readily
near the magnetic poles where the Earth’s magnetic field is weakest and at high altitudes where the Earth’s atmosphere is
thinnest. Radionuclides created by space radiation are called cosmogenic radionuclides. They include tritium (hydrogen-3),
beryllium-7, carbon-14, and so-dium-22.
NATURAL RADIATION SOURCES
Terrestrial Radiation
Radiation that originates on Earth is called terrestrial radiation. Primordial radionuclides (radioactive chemicals that were
present when the Earth formed about 4.5 billion years ago) are found around the globe in igneous and sedimentary rock. From
rocks, these radionuclides migrate into soil, water, and even air. Human activities such as uranium mining have also redistributed
these radionuclides. Primordial radionuclides include the series of radionuclides produced when uranium and thorium decay, as
well as potassium-40 and rubidium-87.
In the past, one human activity that contributed to terrestrial radiation was production of nuclear weapons. Today, an
atmospheric weapon testing is not a significant contributor to background radiation because fallout has decayed since weapons
testing were stopped. The reactor accident at Chernobyl in 1986 is also not a significant source of background radiation in the
United States (Taher et al 2007).
Radionuclides in the Body
Terrestrial and cosmogenic radionuclides enter the body through the food we eat, water we drink, and air we breathe. As with
all chemicals, radionuclides are used and eliminated by the body during normal metabolism. Some radionuclides decay away
quickly but are re-placed through fresh ingestion or inhalation. Other radionuclides decay more slowly and may concentrate in
specific body tissues (such as radium in bone); others are not readily absorbed by the gut and are quickly eliminated.
The most important radionuclides that enter the body are terrestrial in origin. Primary among them are the radon gases (and
their decay products) that a person constantly inhales. Radon levels depend on uranium and thorium content of the soil, which
varies widely across the United States. The highest levels are found in the Appalachians, the upper Midwest, and the Rocky
Mountain states. Other radionuclides in the body include uranium and thorium and their decay products, as well as potassium-40.
These terrestrial radionuclides are in the soil where food grows and eventually find their way into the water supply.
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Most drinking-water sources have very low levels of terrestrial radionuclides, including radium-226, radium-228, and uranium
(Taher et al 2007). These radionuclides may be higher in some areas of the United States than in others—for ex-ample, radium
levels are higher in some Midwestern states, while uranium levels are higher in some Western states. Typically these levels are
less than the limits set by the United States Environmental Protection Agency.
Cosmic Radiation
The earth’s outer atmosphere is continually bombarded by cosmic radiation. Usually it originates from a variety of sources,
including the sun and other celestial events in the universe. Some ionizing radiation will penetrate the earth’s atmosphere and
become absorbed by humans which results in natural radiation exposure.
Man-made Radiation
We are also exposed to ionizing radiation from man-made sources, mostly through medical procedures. On the average, doses
from a diagnostic X-ray are much lower, in dose effective terms, than natural background radiation. Radiation therapy, however,
can reach levels many times higher than natural background radiation but this is usually targeted only to the affected tissues
(Taher et al 2007). Beside medical applications, extremely small amounts of man-made background radiation are received from
consumer products and facilities using radioactive material including research and teaching institutions, nuclear reactors and their
supporting facilities such as uranium mills and fuel preparation plants, and Federal facilities involved in nuclear weapons
production apart of their normal operation. People who smoke receive additional radiation from radionuclides in tobacco smoke
(Taher et al 2007). Other sources of man-made radiation include, computers, television, light bulb, mobile phone, etc.
Dose from Background Radiation
A person receives a radiation dose from exposure to radiation sources outside the body (for example, external radiation from
uranium in concrete used to build homes) and inside the body (for example, internal radiation from radioactive potassium absorbed
by the cells when a person eats food). Here the term “dose” is used to mean effective dose, which describes the amount of
radiation energy absorbed by the body.
When scientists describe dose, they use the units of sievert (Sv), one-thousandth of a sievert (millisievert or mSv), or onemillionth of a sievert (microsievert or µSv), much in the way units of meters are used to describe distance. Another dose unit is the
gray (Gy) and one-trillionth of a gray (nanogray or nGy).
Each year, a resident of the United States receives an average total dose from background radiation of about 3.1 mSv. Some
people receive less (although no one re-ceives zero), some people receive more, and a few per-cent of the population receive
much more.
Dose from Terrestrial Radiation
People living in the Northern part of Nigeria receive an average dose from terrestrial radiation (not including the dose from
ingested and inhaled radionuclides) of about 0.2mSv per year. The dose from terrestrial radiation also varies with location: doses
on the Atlantic and Gulf coastal plains are lowest.
Nuclear fallout from past weapons testing is not a significant contributor to terrestrial radiation. In fact, the dose from fallout is
so low today those instruments can’t measure it (Everaert and Bauwens 2007). The average terrestrial radiation dose (not
including the dose from radionuclides in the body, discussed below) is about 7 percent of the average total dose from background
radiation.
Dose from Space Radiation
Most people living in the North-Eastern receive an average dose from space radiation of about 0.3mSv each year. This dose
depends on where a person lives the latitude and altitude. In the Southern part of Nigeria, (at sea level and near the equator) the
average dose from space radiation is 0.2mSv (200µSv), while in high altitude and latitude the average space radiation dose is
0.7mSv (700µSv). The average space radiation dose makes up about 11 percent of the average total dose from background
radiation.
Traveling by airplane can expose people to slightly more space radiation because at high altitudes, there are fewer
atmospheres to shield the incoming radiation. For example, one study found that on a flight from New York to Chicago, travelers
would receive a dose of about 0.009mSv. This dose can vary significantly, too, depending on flight path and the sun’s 11year cycle
of solar flares (Everaert and Bauwens 2007).
Dose from Radionuclides in the Body
Inhaled radionuclides include cosmogenic radionuclides and terrestrial radionuclides that become air-borne. Of all sources of
background radiation, radon (the gas emitted by uranium and thorium in soil and rocks) and its decay products result in the
greatest dose to humans. Yet indoor radon concentrations are also the most variable dose components, since they depend on how
a house is built, the soil it is built on, where in the house the radon is measured, and more. Even granite countertops can contribute
Osiga-Aibangbee 481
to the radon levels in a house, but this contribution is typically very small com-pared to the radon from the soil under the house.
The average dose from all inhaled radionuclides is about 2.3mSv per year, which is about 73 percent of the average total dose
from background radiation (Everaert and Bauwens 2007).
People ingest radionuclides when they eat food grown in soil that contains uranium, thorium, potassium, and rubidium; drink
milk from animals fed crops that grow in the soil; and drink water containing dissolved terrestrial radionuclides. The average dose
from all ingested radionuclides is about 0.3mSv per year (about 9 percent of the average total dose from background radiation).
HEALTH EFFECTS OF BACKGROUND RADIATION
Exposure to high levels of radiation is known to cause cancer. But the effects on human health from very low doses of radiation
such as the doses from back-ground radiation are very hard to determine because there are so many other factors that can mask
or distort the effects of radiation. For example, among people exposed to high radon levels, cigarette smokers are much more likely
to get lung cancer than non-smokers. Lifestyle choices, geographic locations, and individual sensitivities are difficult to account for
when trying to understand the health effects of back-ground radiation (Everaert and Bauwens 2007).
A United Nations committee concluded that exposure to varying levels of background radiation does not significantly affect
cancer incidence. A committee of the National Academy of Sciences suggested that while there may be some risk of cancer at the
very low doses from background radiation, that risk is small.
Still, while the overall risk is low for all cancers, it is not zero and it is greater for some types of cancer than others. For lung
cancer caused by breathing radon (and its decay products), the Environmental Protection Agency estimates that there are about
21,000 deaths each year, which is about 13 percent of all lung-cancer deaths. There is no evidence of increased risk of diseases
other than cancer.
Objective of Project
The objective of this project is measure the background radiation level and the absorbed dose rate to the students, staffers and
member of the general public within Delta State University, Abraka, Campus III campus of the tertiary institution. The values
obtained for background radiation from this work will form part of the baseline data for environmental radiation in study area.
Importance of Project
This project is important because the data from this work could also be used as base line for radiation impact in the campus.
This project is also a source of material to other research.
Scope of Study
The radiation level in DELSU Abraka campus III has been assessed using radiation level monitor FS2011+ and Global Position
System (GPS) to determine the coordinates of the sample area. The instrument is capable of measuring gamma dose rates in the
range 0-20mR/hr. These features make this FS2011+ an ideal choice for the measurement of radiation dose rate from
environmental radiation and also for geological prospecting for radioactive minerals.
The areas chosen for background radiation measurement in the institutions were randomly selected but evenly distributed to
cover campus. They include areas which record high population flux throughout the day. These include: Staff School (SS),
Business Center (BC), Physical Health Education Lecture Room (PHELR), Sport Complex (SP), Canon Marson Hall (CMH), Delsu
Consult (CH), Vocational Education Lection Room (VELR), Skill Acquisition Centre (SAC), Staff Quarter (SQ), Delsu Staff Club
(DSC) and Football Field.
The radiation parameter is determined from the field data obtained during survey. The data are then analyzed using Microsoft
Excel or SPSS software to interpreter the data. The average dose and the standard deviation are obtained from the analysis.
Study Area
Delta State University, Abraka, Campus I, is located in Ethiope East Local Government Area of DELSU. The population of
these areas has increased tremendously over recent years due to many factors. These may factors include, relative peace,
increase in business activities in the town due to the increasing numbers of students being admitted each year. Although the town
does not boast of any manufacturing company which utilizes radioactive materials, the geology of the state suggests that
environmental radiation level in the state could be significant. The study area is dominated by moderate vegetation cover and slight
flat topography. The area is covered by three major formations; the Benin, Akata and Abada formations. The sedimentary rocks to
the south are characterized by sandstones and alluvial deposits. This subarea also contains the extensive flood plains of the River
Niger and this has made the state to be one of the largest and most fertile agricultural lands in the country.
Figure 2 show the map of Delta State showing the study area.
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Study Area
Figure 2: Map of Delta State.
RADIATION BASICS
Radiation is energy that comes from a source and travels through space and may be able to penetrate various materials. Light,
radio, and microwaves are types of radiation that are called non-ionizing. The kind of radiation discussed in this document is called
ionizing radiation because it can produce charged particles (ions) in matter (NRPB 2005).
Ionizing radiation is produced by unstable atoms. Unstable atoms differ from stable atoms because unstable atoms have an
excess of energy or mass or both. Radiation can also be produced by high-voltage devices (e.g., x-ray machines).
Unstable atoms are said to be radioactive. In order to reach stability, these atoms give off, or emit, the excess energy or mass
(NRPB 2005). These emissions are called radiation (NRPB 2005). The kinds of radiation are electromagnetic (like light) and
particulate (i.e., mass given off with the energy of motion). Gamma radiation and x rays are examples of electromagnetic radiation.
Gamma radiation originates in the nucleus while x rays come from the electronic part of the atom. Beta and alpha radiation are
examples of particulate radiation (NRPB 2005).
DEFINITION OF TERMS
Alpha particle: A specific particle ejected from a radioactive atom. It has low penetrating power and short range. Alpha particles
will generally fail to penetrate the skin. Alpha-emitting atoms can cause health effects if introduced into the lungs or wounds.
Atom: The smallest piece of an element that cannot be divided or broken up by chemical means.
Background radiation: The radiation in man's natural environment, including cosmic rays and radiation from the naturally
radioactive elements, both outside and inside the bodies of humans and animals. It is also called natural radiation. Man-made
sources of radioactivity contribute to total background radiation levels.
Becquerel: The SI unit of activity 1 disintegration per second; 37 billion Bq = 1 curie.
Beta particle: A small particle ejected from a radioactive atom. It has a moderate penetrating power and a range of up to a few
meters in air. Beta particles will penetrate only a fraction of an inch of skin tissue.
Controlled area: An area where entry and exit activities are controlled to help ensure radiation protection and to prevent the
spread of contamination.
Cosmic rays: High-energy radiation that originates outside the Earth's atmosphere.
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Contamination: Deposition of radioactive material in any place where it is not desired, particularly where its presence can be
harmful.
Curie: A unit of measure used to describe the amount of radioactivity in a sample of material.
Decontamination: The reduction or removal of contaminating radioactive material from a structure, area, object, or person.
Detector: A device that is sensitive to radiation and can produce a response signal suitable or measurement or analysis.
Dose: A general term for the quantity of radiation or energy absorbed.
Dose rate: The dose delivered per unit of time. It is usually expressed as rads per hour or in multiples or submultiples of this unit
such as millirads per hour. The dose rate is commonly used to indicate the level of hazard from a radioactive source.
Dosimeter: A small, pocket-sized device used for monitoring radiation exposure of personnel. Before use, it is given a charge,
and the amount of discharge that occurs is a measure of the accumulated radiation exposure.
Electromagnetic radiation: A traveling wave motion that results from changing electric and magnetic fields. Types of
electromagnetic radiation range from those of short wavelength, like x rays and gamma rays, through the ultraviolet, visible, and
infrared regions, to radar and radio waves of relatively long wavelengths.
Exposure: A quantity used to indicate the amount of ionization in air produced by x- or gamma-ray radiation. The unit is the
roentgen (R). For practical purposes, one roentgen is comparable to 1 rad or 1 rem for X and gamma radiation. The SI unit of
exposure is the coulomb per kilogram (C/kg). One R = 2.58 x 10-4 C/kg.
Gamma rays, or gamma radiation: Electromagnetic radiation of high energy. Gamma rays are the most penetrating type of
radiation and represent the major external hazard.
Geiger counter or G-M meter: An instrument used to detect and measure radiation.
Gray: The SI unit of absorbed dose; 1 gray = 100 rads.
Inverse square law: The relationship that states that electromagnetic radiation intensity is inversely proportional to the square of
the distance from a point source.
Ionization: Production of charged particles in a medium. An orbital electron is stripped from a neutral atom, producing an ion pair
(a negatively charged electron and a positively charged atom).
Ionizing radiation: Electromagnetic (X ray and gamma) or particulate (alpha, beta) radiation capable of producing ions or charged
particles.
Irradiation: Exposure to ionizing radiation.
Monitoring: Determining the amount of ionizing radiation or radioactive contamination present. Also referred to as surveying.
Rad: The unit of radiation absorbed dose.
Radiation: Energy traveling through space. Some types of radiation associated with radioactivity are alpha and beta particles and
gamma and X rays.
Radioactivity: The spontaneous emission of radiation from the nucleus of an unstable atom. As a result of this emission, the
radioactive atom is converted, or decays, into an atom of a different element that might or might not be radioactive.
Rem: A measure of radiation dose related to biological effect.
Roentgen: The unit of exposure from X or gamma rays (see exposure).
Sealed source: A radioactive source sealed in an impervious container that has sufficient mechanical strength to prevent contact
with and dispersion of the radioactive material under the conditions of use and wear for which it was designed. Generally used for
radiography or radiation therapy. May be classified "Special Form" on shipping papers and packages.
Sievert: The SI unit of dose equivalent; 1 Sv = 100 rem.
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X rays: Penetrating electromagnetic radiation whose wavelengths are shorter than those of visible light.
Shine: Radiation detected that is from a source some distance away is called shine. Shine will make it more difficult to determine
the levels of radiation from nearby objects. The meter readings are higher than if the shine radiation did not exist. An example of a
shine source is a large pile of radioactive tailings or a large radioactive ore pile. Shine fields are also created by strong local
radioactive sources such as density gauges or metal weld x-ray devices.
External dose: There are several ways of measuring doses from ionizing radiation. People in occupational contact with radioactive
substances or who may be exposed to radiation routinely carry personal dosimeters. These are specifically designed to record and
indicate the dose received (Ivanovich and Harmon, 1982). Traditionally these were badges containing photographic film (film badge
dosimeter), which would be chemically developed following exposure to indicate the total dose received. Film badges have now
been largely replaced with other devices such as the TLD badge which uses Thermoluminescent dosimetry or optically stimulated
luminescence (OSL) badges (Herman, 1996).
A number of electronic devices known as Electronic Personal Dosimeters (EPDs) have come into general use using
semiconductor detection and programmable processor technology. These are worn as badges, but can give an indication of
instantaneous dose rate and an audible and visual alarm if a dose rate or a total integrated dose is exceeded (Herman, 1996). A
good deal of information can be made immediately available to the wearer of the recorded dose and current dose rate via a local
display. They can be used as the main stand-alone dosimeter, or as a supplement to such as a TLD badge. These devices are
particularly useful for real-time monitoring of dose where a high dose rate is expected which will time-limit the wearer's exposure.
The ICRP states that if a personal dosimeter is worn on a position on the body representative of its exposure, assuming wholebody exposure, the value of ambient dose equivalent H(10) is sufficient to provide an effective dose value suitable for radiological
protection (ICRP, 2003).
In certain circumstances dose can be inferred from readings taken by fixed instrumentation in an area in which the person
concerned has been working. This would generally only be used if personal dosimetry had not been issued, or a personal
dosimeter has been damaged or lost. Such calculations would take a pessimistic view of the likely received dose.
Internal Dose: Internal dosimetry is used to evaluate the committed dose due to the intake of radionuclides into the human body.
Medical dosimetry: Medical dosimetry is the calculation of absorbed dose and optimization of dose delivery in radiation therapy. It
is often performed by a professional medical dosimetrist with specialized training in the field. In order to plan the delivery of
radiation therapy, the radiation produced by the sources is usually characterized with percentage depth dose curves and dose
profiles measured by medical physicists (ICRP, 2003)..
Environmental dosimetry: Environmental Dosimetry is used where it is likely that the environment will generate a significant
radiation dose. An example of this is radon monitoring. Radon is a radioactive gas generated by the decay of uranium, which is
present in varying amounts in the earth's crust (Herman, 1996). Certain geographic areas, due to the underlying geology,
continually generate radon which permeates its way to the earth's surface. In some cases the dose can be significant in buildings
where the gas can accumulate. A number of specialized dosimetry techniques are used to evaluate the dose that a building's
occupants may receive (Herman, 1996).
RADIATION DETECTING INSTRUMENT AND METHODOLOGY
Radiation Detecting Instrument
Radiation cannot be detected by human senses. A variety of handheld and laboratory instruments is available for detecting and
measuring radiation. The most common handheld or portable instruments are:
GEIGER COUNTER, WITH GEIGER-MUELLER (G-M) TUBE OR PROBE: A G-M tube is a gas-filled device that, when a high
voltage is applied, creates an electrical pulse when radiation interacts with the wall or gas in the tube. These pulses are converted
to a reading on the instrument meter. If the instrument has a speaker, the pulses also give an audible click. Common readout units
are roentgens per hour (R/hr), milliroentgens per hour (mR/hr), rem per hour (rem/hr), millirem per hour (mrem/hr), and counts per
minute (cpm). G-M probes (e.g., "pancake" type) are most often used with handheld radiation survey instruments for contamination
measurements. However, energy-compensated G-M tubes may be employed for exposure measurements. Further, often the
meters used with a G-M probe will also accommodate other radiation-detection probes. For example, a zinc sulfide (ZnS)
scintillator probe, which is sensitive to just alpha radiation, is often used for field measurements where alpha-emitting radioactive
materials need to be measured.
MICROR METER, WITH SODIUM IODIDE DETECTOR: A solid crystal of sodium iodide creates a pulse of light when radiation
interacts with it. This pulse of light is converted to an electrical signal by a photomultiplier tube (PMT), which gives a reading on the
instrument meter. The pulse of light is proportional to the amount of light and the energy deposited in the crystal. These
instruments most often have upper and lower energy discriminator circuits and, when used correctly as single-channel analyzers,
can provide information on the gamma energy and identify the radioactive material. If the instrument has a speaker, the pulses also
give an audible click, a useful feature when looking for a lost source. Common readout units are microroentgens per hour (µR/hr)
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and/or counts per minute (cpm). Sodium iodide detectors can be used with handheld instruments or large stationary radiation
monitors. Special plastic or other inert crystal scintillator materials are also used in place of sodium iodide.
PORTABLE MULTICHANNEL ANALYZER: A sodium iodide crystal and PMT described above, coupled with a small multichannel
analyzer (MCA) electronics package, are becoming much more affordable and common. When gamma-ray data libraries and
automatic gamma-ray energy identification procedures are employed, these handheld instruments can automatically identify and
display the type of radioactive materials present. When dealing with unknown sources of radiation, this is a very useful feature.
IONIZATION (ION) CHAMBER: This is an air-filled chamber with an electrically conductive inner wall and central anode and a
relatively low applied voltage. When primary ion pairs are formed in the air volume, from x-ray or gamma radiation interactions in
the chamber wall, the central anode collects the electrons and a small current is generated. This in turn is measured by an
electrometer circuit and displayed digitally or on an analog meter (Merdanoglu and Altinsoy, 2006). These instruments must be
calibrated properly to a traceable radiation source and are designed to provide an accurate measure of absorbed dose to air which,
through appropriate conversion factors, can be related to dose to tissue. In that most ion chambers are open air, they must be
corrected for change in temperature and pressure. Common readout units are milliroentgens and roentgen per hour (mR/hr or
R/hr).
NEUTRON REM METER, WITH PROPORTIONAL COUNTER: A boron trifluoride or helium-3 proportional counter tube is a gasfilled device that, when a high voltage is applied, creates an electrical pulse when a neutron radiation interacts with the gas in the
tube. The absorption of a neutron in the nucleus of boron-10 or helium-3 causes the prompt emission of a helium-4 nucleus or
proton respectively. These charged particles can then cause ionization in the gas, which is collected as an electrical pulse, similar
to the G-M tube (Merdanoglu and Altinsoy, 2006). These neutron-measuring proportional counters require large amounts of
hydrogenous material around them to slow the neutron to thermal energies. Other surrounding filters allow an appropriate number
of neutrons to be detected and thus provide a flat-energy response with respect to dose equivalent. The design and characteristics
of these devices are such that the amount of secondary charge collected is proportional to the degree of primary ions produced by
the radiation. Thus, through the use of electronic discriminator circuits, the different types of radiation can be measured separately.
For example, gamma radiation up to rather high levels is easily rejected in neutron counters.
RADON DETECTORS: A number of different techniques are used for radon measurements in home or occupational settings (e.g.,
uranium mines) (Nwankwo and Akoshile, 2005). These range from collection of radon decay products on an air filter and counting,
exposing a charcoal canister for several days and performing gamma spectroscopy for absorbed decay products, exposure of an
electret ion chamber and read-out, and long-term exposure of CR39 plastic with subsequent chemical etching and alpha track
counting. All these approaches have different advantages and disadvantages which should be evaluated prior to use.
The most common laboratory instruments are:
LIQUID SCINTILLATION COUNTERS: A liquid scintillation counter (LSC) is a traditional laboratory instrument with two opposing
PMTs that view a vial that contains a sample and liquid scintillator fluid, or cocktail. When the sample emits a radiation (often a lowenergy beta) the cocktail itself, being the detector, causes a pulse of light. If both PMTs detect the light in coincidence, the count is
tallied (Nwankwo and Akoshile, 2005). With the use of shielding, cooling of PMTs, energy discrimination, and this coincidence
counting approach, very low background counts can be achieved, and thus low minimum detectable activities (MDA). Most modern
LSC units have multiple sample capability and automatic data acquisition, reduction, and storage.
PROPORTIONAL COUNTER: A common laboratory instrument is the standard proportional counter with sample counting tray and
chamber and argon/methane flow through counting gas. Most units employ a very thin (microgram/cm2) window, while some are
windowless. Shielding and identical guard chambers are used to reduce background and, in conjunction with electronic
discrimination, these instruments can distinguish between alpha and beta radiation and achieve low MDAs. Similar to the LSC units
noted above, these proportional counters have multiple sample capability and automatic data acquisition, reduction, and storage
(Nwankwo and Akoshile, 2005). Such counters are often used to count smear/wipe or air filter samples. Additionally, large-area gas
flow proportional counters with thin (milligram/cm2) mylar windows are used for counting the whole body and extremities of workers
for external contamination when exiting a radiological control area.
MULTICHANNEL ANALYZER SYSTEM: A laboratory MCA with a sodium iodide crystal and PMT (described above), a solid-state
germanium detector, or a silicon-type detector can provide a powerful and useful capability for counting liquid or solid matrix
samples or other prepared extracted radioactive samples. Most systems are used for gamma counting, while some silicon
detectors are used for alpha radiation. These MCA systems can also be utilized with well-shielded detectors to count internally
deposited radioactive material in organs or tissue for bioassay measurements. In all cases, the MCA provides the capability to bin
and tally counts by energy and thus identify the emitter. Again, most systems have automatic data acquisition, reduction, and
storage capability (Nwankwo and Akoshile, 2005).
Osiga-Aibangbee 486
DATA PRESENTATION, INTERPRETATION AND DISCUSSION
DATA PRESETATION
Table 1 and 2 Shows the Radiation Field Data. Table 1 shows the outdoor radiation level while table 2 shows the indoor radiation
level.
Date: 0/06/2013
Observer: Osiga-Aibangbee; Site Location: DELSU Campus III; Instrument: Radiation levels monitor FS2011+ and ETREX Germin
GPS
Table 1: Outdoor Radiation Level.
S/N
Geographical
Location
1
2
0
N05 47.461'
E006006.318'
N05047.459'
E006006.374'
3
N05047.485'
E006006.397'
4
N05 47.525'
E006006.407'
5
6
7
0
N05047.579'
E006006.476'
N05047.452'
E006006.410'
N05047.484'
E006006.463'
Dose Rate
Elevation
Sample Location
16
SPC
0.23
15
PHELR
0.21
11
SAC
0.24
17
CMH
0.22
13
VELR
0.21
14
SS
0.21
14
FF
0.24
15
DC
0.18
15
DSC
0.18
14
SQ
0.21
13
BC
0.24
mSvh-1
0
8
N05 47.454'
0
E006 06.485'
0
9
10
11
N05 47.486'
E006006.496'
0
N05 47.489'
0
E006 07.471'
N05047.451'
0
E006 06.388'
Mean
0.22
Osiga-Aibangbee 487
Table 2: Indoor Radiation Level.
S/N
1
2
Geographical
Location
N05047.455'
E006006.298'
N05047.457'
E006006.377'
Dose Rate
Elevation (m)
Sample Location
19
SPC
0.12
13
PHELR
0.14
mSvh-1
3
N05047.472'
E006006.406'
14
SAC
0.18
4
N05047.543'
E006006.415'
16
CMH
0.13
12
VELR
0.13
12
SS
0.13
17
FF
0.13
15
DC
0.18
15
DSC
0.12
15
SQ
0.13
12
BC
0.18
0
5
6
7
8
9
10
11
N05 47.587'
E006006.471'
N05047.443'
E006006.399'
N05047.467'
E006006.445'
N05047.456'
E006006.493'
N05047.491'
E006006.490'
N05047.497'
E006007.477'
N05047.458'
E006006.382'
Mean
0.14
RESULT AND DISCUSSION
A total of 22 points was surveyed, 11 outdoor and 11 indoor across the campus for background environmental radiation. The
dose rate obtained at each point is presented in table 1 and 2. The dose rate ranges from 0.18µSv/hr to 0.24µSv/hr for the outdoor
measurement and 0.12µSv/hr to 0.18µSv/hr for the indoor measurement.
The outdoor dose rate and the indoor dose rate are compared to one another and it was observed that the outdoor radiation
level is higher than the indoor radiation level. The radiation level measured in the study area could be attributed to natural sources
as there are no radiation generators around the campus. The outdoor and the indoor mean dose rate of the surveyed areas are
found to be 0.22µSv/hr and 0.14µSv/hr respectively. Figure 2 and figure 3 shows the variation in the various radiation level
measured in the campus.
According to Ballinger (1991), most radiation biology researches describing the quantitative relationship between the radiation
dose and biological affect indicates a threshold dose level below which no health side-effects occurs. The results obtained this
measurement show that the radiation level did not exceed the normal background level which is placed at 1mSv/annum by
International Commission on Radiation Protection (ICRP, 1990). The average effective dose for the outdoor and indoor point
studied is 0.22µSv/hr and 0.14µSv/hr respectively is less than the ICRP limit value for non occupational population exposure.
Osiga-Aibangbee 488
Figure 3: outdoor Dose rate for locations at campus I
Figure 4: Indoor Dose rate for locations at Campus I
Figure 5: Indoor Dose rate for locations at Campus I using line graph
Osiga-Aibangbee 489
Figure 6: outdoor Dose rate for locations at Campus I using line graph
Figure 7: comparison on outdoor an indoor Dose rate for locations at Campus I
Figure 8: comparison on outdoor an indoor Dose rate for locations at Campus I
Osiga-Aibangbee 490
CONCLUSION
In this study, the natural background radiation/dose rate has been measured in Delta State University Campus I, Abraka using
Radiation levels monitor FS2011+ to conduct Outdoor and indoor survey. A total of 11 outdoor and 11 indoor points was surveyed.
The dose rate ranges from 0.18µSv/hr to 0.24µSv/hr for the outdoor measurement and 0.12µSv/hr to 0.18µSv/hr for the indoor
measurement. The outdoor and the indoor mean dose rate of the surveyed areas are found to be 0.22µSv/hr and 0.14µSv/hr
respectively. The result obtained shows the background radiation in the study area.Thus, we have pointed out that no healthy risks
have been around owing to the data/result obtained. To sum up, it can be said that these kinds of studies are useful to serve as
baseline data of natural background radiation levels and also show the way to the background radiation studies in the future.
References
Abdel-Rassoul GO. Abou El-Fateh, M. Abou Salem, A. Michael, F. Farahat, M. El-Batanouny and E. Salem, K. (2005)
Neurobehavioral effects among inhabitants around mobile phone base stations, Journal of NeuroToxicology 28:434-440
Ballinger A, (1991). Radiation Monitoring and Protection Methods, Journal of Radiation and Epistemology of Northern Ireland,
13(2):125-138.
El-Taher AMAM. Uosif and AA. Orabi, (2007). Natural Radioactivity Levels And Radiation Hazard Indices In Granite From Aswan
Towadi El-Allaqi Southeastern Desert, Egypt’, Journal of Radiation Protection Dosimetry 112:148-154.
Everaert J. and D. Bauwens, (2007) A Possible Effect of Electromagnetic Radiation from Mobile Phone Base Stations on the
Number of Breeding House Sparrows, Journal of Electromagnetic Biology and Medicine, 26:63-72.
International Commission on Radiological Protection, (1991) Recommendations of the International Commission on Radiological
Protection, ICRP Publication 60:1–3.
JMalathi AKV. Andal, A. Paramesvaran, R. Vijayshankar and S. Selvasekarapandian, J. (2005) Study of indoor gamma radiation
in Coimbatore City, Tamilnadu, India’, International Congress Series 12(6):344-345.
M. Siegrist TC. Earle, H. Gutscher and C. Keller, ‘Perception of Mobile Phone and Base Station Risks’, Risk Analysis, 25 (2005),
pp.1253-1264.
Moulder KR. Foster, LS. Erdreich and JP. Mcnamee JE. (2005) ‘Mobile phones, mobile phone base stations and cancer: a
review’, International Journal of Radiation, 81:189-203.
Prasad WC. Cole and GM. Haase KN. ‘Radiation protection in humans: extending the concept of as low as reasonably achievable
(ALARA) from dose to biological damage’, The British Journal of Radiology, 77 (2004), pp.97-99.
Radiation Alert, Operation Manual for the Monitor 4/4EC. S.E. International, Inc., Summertown, USA, (1998).
The National Radiological Protection Board (NRPB), (2005) Mobile Phones and Health National Radiation Protection Board
Report15:5-88