ASNT Radiographic Testing Practice Test 2025 – Comprehensive All-in-One Guide for Exam Success!

Question: 1 / 400

After how many half-lives is approximately 2% of the original radioactivity remaining?

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To determine how many half-lives it takes for the remaining radioactivity to be around 2%, it's essential to understand the concept of half-lives in radioactive decay. After each half-life, the amount of radioactive substance reduces to half of its previous amount.

The general formula to find the remaining percentage of a radioactive substance after a certain number of half-lives is:

Remaining Activity = (1/2)^n * 100%

where n represents the number of half-lives.

To find when approximately 2% is remaining, we set up the equation:

(1/2)^n * 100% = 2%

This simplifies to:

(1/2)^n = 0.02

Now if we calculate this, we can convert 0.02 to a fraction:

0.02 = 2/100 = 1/50

So we need to determine n where (1/2)^n = 1/50.

Taking logarithms can help us solve for n:

n * log(1/2) = log(1/50)

Now using the value of log(1/2) and log(1/50):

log(1/50) can be approximated as log(

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