Anatomy and Specific Gravity of Wood Samples from Six Nigerian Tree Species in Relation to their Diagnostic X-ray Shielding Capabilities

Abstract

The basic principle of protection against nuclear radiation is to keep radiation exposure as  much as possible below the maximum permissible dose equivalent (MPD). In order to redress the dependence on costly shielding materials such as lead, steel, glass and gypsum, cheaper and readily available  materials  such as wood have been brought under focus as potential resources for shielding hazardous radiations. Making use of the relative transmission of 60 kVp X-rays by the wood of six Nigerian tree species as reference data, this study examined the wood anatomy of the tree  species (i.e Syzygium guinense (Willd.) DC., Tectona grandis L., Afzelia pachyloba Harms., A.  africana Pers., Gmelina arborea Roxb. and Daniellia oliveri (Rolfe) Hutch. & Dalziel with a view to providing information on the wood anatomical basis for their X-ray shielding capabilities. T. grandis and G. arborea were  the two most fibrous of  the six species studied, with their fibre-to-non-fibrous tissue ratios (F/NF) being 1.24 and 1.01 respectively. Incidentally, these two species transmitted  the least amounts of radiation at an average wood thickness of 5 cm.   Tyloses were observed in the wood of all but G. arborea and D. oliveri, and the % of vessels with tylose ranged  from 20.64 to 50.36.  At  0.05 level of probability, the reference data on relative X-ray transmission showed significant positive correlation  with % axial parenchyma content (r = 0.754), but significant negative correlations with % fibre content (-0.734), %  of vessels with tylose (-0.864), vessel diameter (-0.757), vessel lumen width (-0.753) and F/NF (-0.742). The diagnostic X-ray attenuation capability of the  wood samples examined can therefore be anatomically explained by these six  parameters, and their evaluation in prospective wood samples for shielding hazardous radiations can be useful.

Key words: Gmelina arborea, hardwood, hazardous radiation, Tectona grandis, tylose,  wood anatomy, X-ray.