Book excerpt: Excerpt from Study of a Halpern-Type 4π Neutron Detector The study of photonuclear interactions by measurements of photoneutron cross sections has been very fruitful. This is primarily because the photoneutron cross section represents a large percentage of the total absorption cross section; the percentage ranges from about 50% for the light elements to about 90% for the heavier elements such as lead. Of almost equal importance, however, is the fact that neutrons weakly interact with matter. This allows the use of thick targets and compensates for the relatively low photon yield available from accelerators such as the betatron. Unfortunately, the magnitude of the photoneutron cross sections, as measured in different laboratories, show differences of as much as The problem may be due, in part at least, to the detectors used to measure the photoneutron yields. The most commonly used system is a relatively simple 4h neutron detector which moderates and then captures the neutrons emitted from the target. It is possible that variations in the designs of these detectors resulting in non-uniform responses as a function of neutron energy may have caused the discrepancies in the measured neutron cross sections. About the Publisher Forgotten Books publishes hundreds of thousands of rare and classic books. Find more at www.forgottenbooks.com This book is a reproduction of an important historical work. Forgotten Books uses state-of-the-art technology to digitally reconstruct the work, preserving the original format whilst repairing imperfections present in the aged copy. In rare cases, an imperfection in the original, such as a blemish or missing page, may be replicated in our edition. We do, however, repair the vast majority of imperfections successfully; any imperfections that remain are intentionally left to preserve the state of such historical works.