▁additional ▁ 4 ▁v eto ▁layers ▁of ▁the ▁sc int ill ator ▁surr ound ▁the ▁module ▁on ▁the ▁sides ▁to ▁distinguish ▁particles ▁entering ▁from ▁the ▁outside ▁from ▁those ▁produced ▁by ▁interactions ▁inside ▁the ▁module . ▁The ▁total ▁mass ▁of ▁iron ▁in ▁one ▁module ▁is ▁ 7 . 1 ▁tons ▁and ▁constit utes ▁ 9 6 % ▁of ▁the ▁module ▁weight . ▁On ▁the ▁neut r ino ▁beam ▁axis , ▁in ▁the ▁middle ▁of ▁the ▁cross ▁between ▁the ▁vertical ▁and ▁horizontal ▁arm , ▁there ▁is ▁an ▁additional ▁module ▁built ▁only ▁from ▁layers ▁of ▁the ▁pl astic ▁sc int ill ator ▁( Pro ton ▁Module ) ▁with ▁a ▁mass ▁of ▁ 0 . 5 5 ▁tons . ▁Its ▁purpose ▁is ▁to ▁register ▁qu as iel astic ▁interactions ▁and ▁compare ▁the ▁obtained ▁results ▁with ▁the ▁simulations . ▁ ▁N D 2 8 0 ▁det ector ▁ ▁The ▁N D 2 8 0 ▁det ector ▁is ▁used ▁to ▁measure ▁the ▁flux , ▁energy ▁spectrum ▁and ▁electron ▁neut r ino ▁beam ▁poll ution ▁for ▁the ▁same ▁off - axis ▁angle ▁as ▁for ▁the ▁far ▁det ector . ▁N D 2 8 0 ▁also ▁investig ates ▁various ▁types ▁of ▁mu on ▁and ▁electron ▁neut r ino ▁and ▁ant ine ut r ino ▁interactions . ▁All ▁this ▁allows ▁estim ating ▁the ▁expected ▁number ▁and ▁type ▁of ▁interactions ▁in ▁the ▁far ▁det ector , ▁reducing ▁the ▁system atic ▁error ▁in ▁the ▁neut r ino ▁oscill ations ▁analysis ▁associated ▁with ▁models ▁of ▁neut r ino ▁interactions ▁and ▁flux . ▁ ▁N D