Always, whether we notice it or not. It's a law of nature.
You are correct it is translucent because opaque let’s no light through but transparent lets almost all light through
Iodine-131 has a half life of 8 days, so half of it is gone every 8 days.
10 grams of iodine-131 is left for 24 days.
At 8 days: 10/2=5 grams left
At 16 days: 5/2=2.5 grams left
At 24 days: 2.5/2=1.25 grams left.
**
Your mistake is that you stopped at 16 days.
Answer: 37.5 nm
Explanation: speed of light c= 3.00·10^8 m/s.
I use same accuracy to speed of light as it's for frequency.
Frequency f= 8.01·10^15 1/s
Speed c = wavelength · frequency
Wavelength = c/f = 3.745·10^-8 m
