00:01
To answer this question, we'll first write the balanced nuclear reaction.
00:06
If phosphorus 32 with an atomic number of 15 decays via beta emission, it'll produce a beta particle with no mass and an atomic number of minus 1 because of its minus 1 charge, plus something with a mass number of 32, so 32 plus 0 gives us 32, and an atomic number of minus 1 charge, and an atomic number.
00:31
Of 16, so 16 minus 1 gives us 15.
00:35
Element 16 is sulfur.
00:39
Next we'll calculate the decay constant from the half -life by dividing the half -life into the natural log of 2, giving us 4 .85 times 10 to the minus 2, 1 over days.
00:51
So the natural log of the amount remaining after 35 days, divided by the amount that we originally have, will be equal to negative 4 .85 times 10 to the minus 2, negative k value, multiplied by the time that has elapsed 35 days.
01:08
If the half -life is 14 .28 days, 35 days is a little bit more than two half -lives.
01:17
Two half -lifes should result in 25 % remaining, so we should get something less than 25%...