The activity of a stock isotope is 10,000 DPM/0.10mL. If 0.25 ml of this stock is placed in 2.50 ml of water, what is the activity in the diluted specimen?

My guess is that I just multiply the 10,000 DPM by the 1/10 dilution factor. I then come up with 1,000DPM/0.10ml. Does this sound right?

Your approach is close, but the dilution factor is actually 0.025 (0.25 mL / 10 mL). To calculate the activity in the diluted specimen, you need to apply the dilution factor to the activity of the stock isotope.

Here's how to calculate it step by step:

1. Calculate the dilution factor: 0.25 mL / 2.50 mL = 0.10
Note: The dilution factor represents the ratio of the final volume to the initial volume.

2. Multiply the dilution factor by the activity of the stock isotope:
Diluted activity = Dilution factor * Stock activity
Diluted activity = 0.025 * 10,000 DPM/0.10 mL

By multiplying the dilution factor (0.025) with the stock activity (10,000 DPM/0.10 mL), you'll get the activity in the diluted specimen.