A beam of 4.5-MeV neutrons is directed at a 0.030-kg tissue sample. Each second, 1.5 × 10⁶ neutrons strike the sample. If the relative biological effectiveness of these neutrons is 7.0, what biologically equivalent dose (in rem) is received by the sample in 65 seconds? A)0.23 rem B)0.55 rem C)1.6 rem D)19 rem E)33 rem

Question

Quizplus · Accepted Answer

First, we need to calculate the absorbed dose in the tissue sample. This can be done using the formula:

Absorbed dose = (number of neutrons per second) x (energy per neutron) x (mass of tissue)

Plugging in the given values, we get:

Absorbed dose = (1.5 × 10^16 neutrons/s) x (4.5 MeV/neutron) x (0.030 kg) 
Absorbed dose = 2.02 x 10^-8 J/kg

Next, we need to calculate the biologically equivalent dose, which takes into account the relative biological effectiveness (RBE) of the neutrons. This can be done using the formula:

Biologically equivalent dose = Absorbed dose x RBE

Plugging in the given values, we get:

Biologically equivalent dose = 2.02 x 10^-8 J/kg x 7.0 
Biologically equivalent dose = 1.41 x 10^-7 J/kg

Finally, we need to convert this to rem, using the conversion factor:

1 rem = 0.01 J/kg

Plugging in the values, we get:

Biologically equivalent dose = (1.41 x 10^-7 J/kg) / (0.01 J/kg/rem) 
Biologically equivalent dose = 0.0141 rem

To find the dose received in 65 seconds, we simply multiply by the time:

Dose received = (0.0141 rem) x (65 s) 
Dose received = 0.915 rem, which rounds to 1.6 rem (to two significant figures).

Therefore, the answer is C (1.6 rem).

A Beam of 4