No errors in my code but the program stays busy forever?

Hello

I'm trying to write a program that simulates a radioactive decay. Given a certain number of initial atoms, I need to know how many atoms of each isotope is left and then plot it vs. time. However something seems to be wrong with my first loop and I don't know what it is since MATLAB wont show me any error statements. here is the question

    % initial number of atoms  
  NA_0  = 20000000;   
  NA1_0 = 10000000;
  NA2_0 = 20000000;
  NB_0  = 1000000;

% number of remaining atoms
NA  = NA_0;        
NA1 = NA1_0;
NA2 = NA2_0;
NB  = NB_0;

% decay constants
LA    = 0.7;
LA1   = 0.7;
LA2   = 0.3;

% number of A atoms at i-1 unit of time
i = 1;
A_atoms(i)= NA;

% number of A1 atoms at j-1 unit of time
j = 1;
A1_atoms(j)= NA1; 

% number of A2 atoms at k-1 unit of time
k = 1;
A2_atoms(k) = NA2; 

% number of B atoms at m-1 unit of time
m = 1;
B_atoms(m) = NB;   

while NA_0 > 0;

      for i = 0:NA;
          x = rand;

          if x < LA
            NA = NA - 1;

           if x < 0.2
            A1_atoms(j) = A1_atoms(j) + 1;

           else if (x>0.2) && (x<0.7)
            A2_atoms(k) = A2_atoms(k)+ 1;
               end 

          end
         end

      i = i + 1;
      A_atoms(i)  = NA;

      j = j + 1;
      A1_atoms(j) = NA1;

      k = k + 1;
      A2_atoms(k) = NA2;
      end
  end

j1 = 1; 
k1 = 1;

      while NA1 > 0 || NA2 > 0

      if NA1 > 0
      N1 = NA1;

      for k1 = 1:N1
          y = rand;

          if y <= LA1
          NA1 = NLA1 - 1;
          end

      end
      j1 = j1 + 1;
      A1_atoms(j1)= NA1;

      end

      if NA2 > 0
      N2 = NA2;

      for k1 = 1:N2
          z = rand;
          if z <= L2
          NA2 = NA2 - 1;
          end
      end

      k1 = k1 + 1;
      A2_atoms(k1)= NA2;

      end

      % number of B atoms after adding the decayed atoms from A1 and A2
      NB = NB +(N1-NA1)+(N2-NA2); 
      B_atoms(m) = NB;

      end