Environmental Engineering Reference
In-Depth Information
26
NeutroN-FlueNce NaNoseNsors Based
oN BoroN-coNtaiNiNg Materials
Levan Chkhartishvili
Department of Engineering Physics, Georgian Technical University, Tbilisi, Georgia
Laboratory for Boron and Powdered Composite Materials, F. Tavadze Institute of Metallurgy and Materials Science, Tbilisi, Georgia
Neutron-fluence nanosensors are nanotech-integrated monitoring tools that are helpful in reducing environmental risks. Concern
over the consequences of harsh radionuclide pollution has resulted in an increasing demand for suitable means of monitoring
neutron radiation sources: radioactive pollutants generated directly or indirectly, as a result of nuclear waste, influence different
substances used in nuclear power stations (water, gases, metals, etc.) or places existing near radioactive materials. The
development of a range of neutron-sensor materials has provided devices with enhanced selectivity and sensitivity for neutron
radiation by a number of substances from harsh sites.
On the one hand, boron-containing materials possess extraordinary potential for solid-state neutron detector applications
because boron
10
B isotope has a capture cross section of ~3835 barns for thermal neutrons, which is several orders of magnitude
larger than isotopes of other chemical elements. On the other hand, state-of-the-art nanotechnology offers multiple benefits for
neutron radiation-sensing applications: the ability to incorporate nano-sized radiation indicators into widely used materials
such as paints, coatings, and ceramics to create nanocomposite materials; the development of ultralow-power, flexible detection
systems that can be portable or embedded in clothing or other systems; and so on.
Boron belongs to the group of least abundant chemical elements: B content in the earth's crust makes up no more than about
0.005wt.%. However, its role in forming the various molecular and solid-state structures is incommensurably great.
Understanding the structural diversity of boron-containing solid phases comes down to the B atom's electronic structure: it is a
strongly distinct acceptor and elemental boron structures should be electron-deficient. This is why all-boron crystalline forms,
as well as amorphous ones, exhibit very complex, clustered structures, in which icosahedron B
12
serves as a main building
block. Besides, elemental boron forms diatomic molecule B
2
, small molecular clusters B
n
, and some nanophases that are also
constructed from the interconnected icosahedra. Acceptor behavior of B atoms and their clusters favors the formation of a huge
number of borides, that is, compounds of boron with metals, which are usually characterized by the donor behavior. Only binary
B/Me crystalline compounds with chemical formulas from Me
5
B to MeB
66
can be counted as approximately 250. Higher
borides are characterized by the clustered structures based on icosahedron and/or other 3D boron cages, while among the lower
borides one can find a wide variety of 1D and 2D structural motifs—various chains and plane networks of boron atoms. Boron
compounds with nonmetals that are characterized by a higher electron affinity, that is, boron carbides, nitrides, oxides, etc.,
show less complicated structures. They also form nanosystems like nanotubes and fullerenes. Strong B-B bonds makes all the
boron-rich solids refractory and resistant against aggressive environments, while the diversity of geometric and electronic struc-
tures and, consequently, the diversity of sets of their physical properties, enable their usage in large spheres of technical and
technological applications.
