Question

Uranium-235 undergoes fission to produce two neutrons per fission event. A neutron-absorbing material is mixed in with this sample. This causes the number of neutrons that can initiate fission events to decrease. Which of the following will be effective at achieving a critical mass? Check all that apply.

A. Surround the sample with a deflective material to prevent neutrons from escaping to the surroundings.
B. Add more absorbent material.
C. Compress the uranium-235 sample.

Answer 1

To achieve a critical mass for uranium-235, adding more absorbent material and compressing the uranium-235 sample are effective methods.

Step-by-step explanation:

A critical mass refers to the minimum amount of fissionable material needed to sustain a self-sustaining chain reaction. In order to achieve a critical mass for uranium-235, the following options would be effective:

1. Add more absorbent material: By increasing the amount of neutron-absorbing material mixed with the uranium-235 sample, the number of neutrons available to initiate fission events decreases, making it easier to achieve a critical mass.
2. Compress the uranium-235 sample: Applying pressure to the uranium-235 sample can increase its density, which can reduce the number of neutrons that escape and increase the probability of fission events.

Surrounding the sample with a deflective material to prevent neutron escape would actually hinder the achievement of a critical mass because it would prevent the necessary number of neutrons from interacting with the fissionable material.