B

5 B Boron 10.81

Physical Properties at STP

Density: 2.3 g/cm³
Electronegativity 2.0
Boiling Point: 4273K
Melting Point: 2348K
Specific Heat Capacity: 1.03 J/gK
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Summary

Boron has two naturally occurring isotopes; Boron-10 and Boron-11. Boron-10 is the most efficient of all the elements as a neutron absorber. Absorbing an neutron Boron-10 emits an alpha particle according to the reaction:

B¹⁰ + n¹ -> Li⁷ + He²⁺ +2e^-+ 2.5 MeV

For this reason Boron is used in control rods in nuclear power plants.

Boron is also useful in alloys and began being used in WWII. Quantities as low as .0005% are sufficient to significantly increase the strength of steel alloys. It also serves this purpose in non-heat treated aluminum alloys.

Sources

Massey, A. G. (1966). Boron and Compounds. In The Encyclopedia of Chemistry second edition (pp. 147-150). New York: Van Nostrand Reinhold Company.

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Boron at The Periodic Table of Videos (Alternate Version)