The half-life of Na-24 is 15 hours. When there are 1,000 atoms of Na-24 in a sample, a scientist starts a stopwatch. The scientist stops the stopwatch at 45 hours; there are ______ atoms of Na-24 remaining. This is an example problem to the section. I just am unsure of the process. Thanks in advance

The approach is basically the same as you need for the gold question you posted ealier.

 

The half-life describes the time taken for half of the atoms to decay. So you need to halve the number of atoms X times, where X is the number of half-life intervals that fit into the measured time period.

 

Does that make sense?

Element X, half life 500 hours, 64 atoms present. After 500 hours: 32 atoms present, or 0.5 x 64. After 1000 hours: 16 atoms present, or 0.5 x 0.5 x 64. After 1500 hours: 8 atoms present, or 0.5 x 0.5 x 0.5 x 64.

Total number of hours

divided by half-life time

= a number.

 

Total number of atoms in sample

halve that total a few times.

 

I'll let you work out how many times to halve it.

 

It's all math. There's no "science" knowledge needed.

You still need to get the "hey i did this with a little help, lets try the next one myyself"-spark, afer that, nuclear physics may be fun to do