The tenth-value layer for Co-60 gamma rays using lead is:

The tenth-value layer for Co-60 gamma rays using lead is:

• A. 0.50 inches
• B. 1.50 inches
• C. 1.0 inches
• D. 2.0 inches

Answer: (B)

A tenth-value layer is the thickness of shielding required to cut the gamma exposure by a factor of ten. For Co-60 gamma rays shielding with lead, the attenuation of the photons follows N = N0 e^{-μx}, so the thickness that yields N/N0 = 0.1 is x_TVL = (ln 10)/μ. In lead at the energies emitted by Co-60, this results in a TVL of about 1.5 inches. That’s why 1.50 inches is the best choice. In practice, TVL is typically a bit over three times the half-value layer in this material-energy combination, which aligns with roughly 1.5 inches for Co-60 in lead.

A tenth-value layer is the thickness of shielding required to cut the gamma exposure by a factor of ten. For Co-60 gamma rays shielding with lead, the attenuation of the photons follows N = N0 e^{-μx}, so the thickness that yields N/N0 = 0.1 is x_TVL = (ln 10)/μ. In lead at the energies emitted by Co-60, this results in a TVL of about 1.5 inches. That’s why 1.50 inches is the best choice. In practice, TVL is typically a bit over three times the half-value layer in this material-energy combination, which aligns with roughly 1.5 inches for Co-60 in lead.