piont-wise cross section

Dear Alberto,
     Thanks for your last return. I have tried the large radius cavity according to your advice. And there is not unreasonable peak
in the pulse height spectrum.But when the cavity radius shrink to several cm, the unreasonable peaks will appear,even there is no
wall. why this happen?
    I hope the point wise cross section used for the low energy neutron transportation. As you said, the point-wise cross section
are not available for any of the materials in my input file. I didnot know how to set the card.Could you help me? I attached my
input file in which I deleted the unnecessary cards.
Best regards,
                                  Zhang Weihua

2012-02-20

Xu Lijun