public int NeutronFreeSpaces()
  {
     int result=0;
     if (board[neutron_x-1][neutron_y-1]==EMPTY) result++; 
     if (board[neutron_x-1][neutron_y  ]==EMPTY) result++; 
     if (board[neutron_x-1][neutron_y+1]==EMPTY) result++; 
     if (board[neutron_x  ][neutron_y  ]==EMPTY) result++; 
     if (board[neutron_x  ][neutron_y  ]==EMPTY) result++; 
     if (board[neutron_x+1][neutron_y-1]==EMPTY) result++; 
     if (board[neutron_x+1][neutron_y  ]==EMPTY) result++; 
     if (board[neutron_x+1][neutron_y+1]==EMPTY) result++; 
    
     return result;
   }