Question

Primary radiation barriers require ___ inches of lead shielding.

1) 2
2) 4
3) 6
4) 8

Answer 1

The required thickness of lead shielding to absorb all but one in 1000 gamma rays from a radioactive source is approximately 1.70 mm.

Step-by-step explanation:

The question is asking about the thickness of lead shielding required to reduce the intensity of gamma rays from a radioactive source. We know that a certain thickness of lead can absorb a specific percentage of gamma rays. The challenge here is to find the total thickness that will result in only 0.1% of the original gamma rays passing through.

Consider lead's effectiveness in blocking gamma radiation: if 0.170 mm of lead absorbs half of the rays, then, to find the thickness that leaves one in 1000 unabsorbed (0.10% of the original rays), we repeatedly halve the initial radiation amount until we reach the desired fraction.

With each 0.170 mm thickness of lead, the radiation is halved, so:

1. 0.170 mm reduces to 50%
2. 0.170 mm * 2 (0.340 mm) reduces to 25%
3. 0.170 mm * 3 (0.510 mm) reduces to 12.5%
4. ...
5. 0.170 mm * 10 (1.70 mm) reduces to 0.0977%, slightly less than 0.1%

Therefore, to reduce the gamma rays to one in 1000, we would need a lead shielding of approximately 1.70 mm thick.