1998 Volume 47 Issue 9 Pages 678-685
Long term (three years from Aug. 1994 up to Sep. 1997) irradiated prechemically etched CR-39 solid state nuclear track detectors were used for the estimation of recoil proton track densities and related dose equivalent of atmospheric neutrons whose energies (Enabove-0.5 MeV which we call the effective fast neutrons) cause observable recoil proton tracks. The CR-39 detectors were exposed to the ordinary atmosphere and to up and down sides of building ceilings to estimate the total effect of buildings, ceilings and air voids, on the effective fast neutrons fluences. Also the attenuation of such neutrons within concrete was investigated. It was found that atmospheric cosmic neutrons of fluences above -0.5 Me V decrease with the increasing of concrete thicknesses (0-12 cm) . The average build up factor B times the attenuation terme-Σt.d (build up-attenuation coefficient) B⋅e-Σt.dwas calculated for each ceiling and for concrete blocks. The results give agreements with experiments done hitherto.
