I think you can get it by doing a experiment by yourself.

Thermal n cross sec

1H(n,g)2H: 0.32barn

10B(n,a): 3840barn

11B(b,g): 5 mbarn

14N(n,g): 0.080 barn

Thermal n absorption cross sec is a nuclear property and hence does not depend upon particle size (i.e. nano or micro)

Dear Debasish Saha

Thanks

Could you please give me any reference from the published work for your statement, "Thermal n absorption cross sec is a nuclear property and hence does not depend upon particle size (i.e. nano or micro)". Because I am thinking otherwise. Also if neutron only interact with 10B then what is the role of nitrogen in h-BN.

Neutron cross section for all atoms can be found data sheets.  Also, it's not depend on particle size because neutron is inreact directly with the nucleus. the particle size is grain size of additives/materials.  

The response of Mr. Debasish is OK. For this material thermal neutron interact principaly with 10B.

You can get any answer you like if you choose the isotopic composition.  It's quite easy to get enriched 10B for high absorption or deplected for low absorption.  The nuclear power industry drives the isotope separation because of the use of 10B in reactor control rods.  The semiconductor process industry piggybacks off this and prefers the use of 11B to minimise soft error events due to alpha particles.