Clustering Effect of Nucleonic Matter in the Low-Density Region

We investigate clusterization of nuclear matter in low-density region. Single-particle states of nucleons in nuclear matter with a crystal structure are described by Bloch functions, which have two extreme states, an aggregation of isolated clusters and uniform matter in low- and high-density limit, respectively. For the purpose of investigating clusterization under neutron-rich situation, we introduce the Bloch function of the linear combination of p orbit orthogonal to that of s orbit to describe states of excess neutrons. Here, the width parameter of clusterings can be determined variationally depending on the density. We find that ¹⁰He cluster-like density fluctuation arises below about one-fifth of the nuclear saturation density in asymmetric nuclear matter with N/A = 0.8. We also study α- and ¹⁶O-cluster-like ones in symmetric nuclear matter.