~ 14 ~
Original Article
Determination of - Radiation Shielding Characteristics of
some Woods in Western Nigeria
Ero F.A
2
and Adebo B.A
1,2
Department of Physics, University of Ibadan, Nigeria
1
Lead City University, Ibadan, Nigeria
2
ABSTRACT
This study compares the shielding characteristics of twenty-two tropical woods by using gamma scintillation detection
method.
The intensities of the emergent radiation were measured, when each of these woods were placed between a scintillation
detector and a standard radioactive source. Analysis of result obtained shows an appreciable evidence of radiation
attenuation due to the changes in the chemical composition of the woods and the dependence of the attenuation coefficient
on energy and densities of these woods. The descending order of attenuation coefficient determined for each wood type are ;
Ayin, Oro, Anuje, Ako, Asunrun, Apa-igbo Gedu, Agbonyin , Opepe Oganwo, Iroko Odogi , Ayo, Ayunre , Afara , Omo, Melania,
Akomu, Arere, Pine, Araba. For a constant energy of 0.101MeV, the attenuation coefficient are 0.190cm
-1
, 0.165cm
-1
,
0.163cm
-1
, 0.156cm
-1
, 0.149cm
-1
, 0.143cm
-1
, 0.133cm
-1
, 0.132cm
-1
, 0.127cm
-1
, 0-124cm
-1
, 0.085cm
-1
0-123cm
-1
, 0-122cm
-1
,
0.113cm
-1
,0.101cm
-1
, 0.088cm
-1
,0.087cm
-1
, 0.086cm
-1
, 0-082cm
-1
respectively.
The wood in descending order of dependence of attenuation coefficient on density are : Ayin,Oro, Anunje,Ako,Asunrun,Apa-
Igbo, Gedu, Agbonyin, Opepe, Oganwo, Iroko, Odogi, Ijebo,
Ayo, Ayunre, Afara, Omo, Melania, Akomu, Arere, Pine and Araba. The half value layer shows the thickness at various energy
regions.
Result shows that attenuation coefficient depends on the energy of incident photons and the nature of the absorbing woods.
Key words: Gamma Scintillation, Radiation, Attenuation Coefficient, Half Value Layer (HVL), Density
INTRODUCTION
Gamma rays (-rays) are electromagnetic waves. Their wavelengths run from about 10
-10
m to well
below 10
-14
m, with corresponding frequency range from 310
18
Hz to more than 310
22
Hz. -rays
are produced by many radioactive substances. They can also be found in nuclear reactors and in
cosmic radiation. There are many useful applications of gamma ray such as radiotherapy, medical
tracer and sterilization. Nevertheless when -rays are absorbed by a living organism (e.g. human),
they may cause serious effects. Therefore, it is necessary to find out some substances that can
effectively absorb and block -rays. Gamma radiation from radionuclides, such as 40K and the
232Th and 238U series and their decay products, represents the main external source of
irradiation to the human body [1] .
The penetrating power of -rays, however, is very high so that most substances cannot effectively
absorb them.
In order to ensure radiation safety in the various application of ionizing radiation technology
certain procedures must be put in place to reserve exposure levels to their maximum. These
procedures include, designing work schedule in a way that the safest possible distance is kept from
the source. However, there are limitations to the above procedures.
Perhaps the most effective radiation protection is the use of shielding materials between the
workers and the source and also to curtail the radiation to where it is being applied without
constituting danger to the general public.
A shield material is expected to have high gamma ray attenuation coefficient in orders that a small
thickness will produce significant reduction in intensity. The practice for instance is to use lead
(Pb) lining on doors of X-rays rooms. However, the observation is that a large number of X-rays
centres use wooden doors of different thickness without Pb lining. The aim of his project is to
answer the question “how safe are these wooden doors”.
This was done by collecting samples of wood commonly used in Nigeria and determining their
gamma attenuation characteristics. By comparing this, especially at low gamma ray energies with
International Archive of Applied Sciences and Technology
Volume 3 [2] June 2012: 14 - 20
ISSN: 0976-4828
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