Research on mechanism of nuclear fusion reaction below Coulomb barrier energy

The report describes some studies carried out as part of the joint research project implemented by Tsukuba University, Japan, and Legnaro National Nuclear Research Institute, Italy, focusing on heavy ion fusion reaction near the Coulomb barrier, isotope dependence of nuclear fusion reaction cross section enhancement, and optical potential abnormality below the Coulomb barrier. Measured nuclear fusion reaction cross sections below the Coulomb barrier are greater than theoretical values derived by taking the tunnel effect into account. This fact suggests that some degrees of freedom other than those associated with the tunnel effect are contributing to the mechanism of nuclear fusion reaction. Another study is carried out to make systematic measurements of nuclear fusion reactions, nucleon migration reactions, and cross sections of elastic/non-elastic scattering, and investigate their relations with the mechanism of nuclear fusion near the Coulomb barrier energy. The fact that active fusion reactions take place in energy regions below the Coulomb barrier must be reflected in the profile of the nuclear potential (optical potential) that describes the reactions. (N.K.)