Measurement of the neutron total cross sections for Bi and 208 Pb

The results of measuring the neutron total cross sections for Bi and Si in the energy range from 1 eV up to 100 eV and those for 208 Pb and C in the range from 1 eV up to 20 keV are reported. The total cross section measurements for silicon and carbon isotopes are carried out as a zero-test of the experiment. For Si and C the polarizability influence should be negligibly small as compared with that for Bi and 2'0'8 Pb because the polarizability contribution to the cross section is proportional to the square of nuclear charge Z2. The measurements are realized using the GNEIS time-of-flight facility with an accuracy of the order of 10-3. The schematic layout of the experiment is shown. An estimated value of the neutron electric polarizability is found to be less than αn < 1.1 x 10-3 fm3. It is shown that a further progress in increasing the precision of αn measurements can be related with the substitution of neutron detector for more effective one, and in conjunction with detailed background analysis and therefore increasing the high-energy boundary of measured cross section