What if during DNA replication we could label the new pieces of DNA and track where they went?

What if during DNA replication we could label the new pieces of DNA and track where they went? Let's say you were replicating the following DNA strand:

5' XXXXXXXXXXXXXXXXXXXXXXXXXXXXX

3' XXXXXXXXXXXXXXXXXXXXXXXXXXXXX

While the strand was replicating you added radioactive nucleotides so that any new nucleotides used by polymerase were radioactive (I'm labelling them N here). 

When replication was finished you'd have:

5' XXXXXXXXXXXXXXXXXXXXXXXXXXXXX

3' NNNNNNNNNNNNNNNNNNNNNNNNNNN

3' XXXXXXXXXXXXXXXXXXXXXXXXXXXXX

5' NNNNNNNNNNNNNNNNNNNNNNNNNNN

Now, in your cells DNA usually only replicates when the cell is dividing. In these experiments you always wash the 'extra' radiation away, so the cell will only be radioactive if the DNA strand (with all the Ns, above) is in the cell. 

You started with one cell, you performed the radioactive replication as noted above and now the cell has divided into two. How many of those two cells are radioactive?

In other words: 1 parent cell ------DNA replication followed by cell division ---> two daughter cells (how many of these daughter cells are radioactive?)

ANSWER__________

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You started with one cell, you performed the radioactive replication as noted above and the cell divided into two. In those two cells DNA was replicated and then they divided. No new radiation was added, so the DNA strands with 'N' are still radioactive but nothing else is. How many of the four cells are radioactive?

1 parent cell ------DNA replication followed by cell division ---> two daughter cells ------DNA replication followed by cell division ---> four 'grand'-daughter cells (each of the two daughter cells has split into two).

ANSWER_____