Random number list with only two numbers

This is really simple, but I keep getting stuck! I am trying to create a list in R of 1000 zeros with the number 1.5 added 20 times at random intervals, to look like:

0.000
0.000
1.500
0.000
1.500
0.000
0.000

But am stuck on how to keep it as just the two numbers? I have been using the seq command but can't get the arguments right...