What technique can effectively reduce the amount of black scattered radiation reaching the film?

Backing the cassette with a sheet of lead is an effective technique to reduce the amount of black scattered radiation reaching the film. Lead acts as a barrier to scatter radiation, which is generated when the primary X-ray beam interacts with the subject being radiographed. This scatter can degrade the quality of the radiographic image by adding undesired blackness or fog to the film. By placing a layer of lead behind the film, only the useful, primary radiation can expose the film while minimizing the impact of scatter. This technique is particularly useful in improving the contrast and quality of the radiographs.

The other options, while they may influence aspects of radiography, do not effectively address the reduction of scattered radiation in the same way. For instance, using a higher film speed can increase the sensitivity of the film to radiation, which may result in shorter exposure times but does not inherently reduce scatter. Lowering the kV setting, while it may reduce energy levels in the X-ray beam, can also increase the amount of scatter radiation due to increased interactions in the subject. Increasing the exposure time can lead to more exposure to both primary and scattered radiation, potentially making the issue of scatter worse rather than alleviating it. Therefore, backing the cassette with lead provides a direct and