The experimental group of nuclear reaction and structure from Peking University has been studying exotic phenomena in light neutron-rich nuclei for several decades and has developed a large number of professor teams, detection devices, and research methods. Zhu Hongyu from this group studies new magic numbers, shell evolutions, spectroscopic factors, halo structures, and clusters through methods like the transfer, elastic/inelastic reactions, and more.

Spectroscopic factors are generally quenched relative to the occupancy numbers predicted by the independent particle model (IPM) due to nucleon-nucleon correlations, which is quantified by the reduction/quenching factor Rs. Rs extracted from knock-out reactions were found to be strongly dependent on the isospin asymmetry (ΔS = Sn- Sp / Sp- Sn for neutron/proton removing reaction). However, Rs deduced from the transfer reactions induced by stable nuclei were found to be independent of ΔS. What about unstable nuclei with larger absolute values of ΔS in transfer reactions?

In order to answer this question, a combined experiment with radioactive beams of 15C and 16N was performed at Radioactive Beam Line in Lanzhou (RIBLL), China in 2022. The differential cross sections of the single-nucleon transfer reactions 15C(p, d)14C, ¹⁵C(d, ³He)¹⁴B, ¹⁶N(p, d) ¹⁵N, and ¹⁶N(d, ³He)¹⁵C were obtained. By comparing the experimental angular distributions to the DWBA theoretical calculations, the spectroscopic factors and the corresponding Rs with ΔS = -19.86-20.14 MeV were extracted. Significant dependencies of Rs on ΔS were found in this experiment.

In the same experiment, a new measurement of the ²H(¹⁵C,³He)¹⁴B reaction was conducted to study the proton shell evolution in neutron-rich carbon and boron isotopes. The experiment employed a radioactive beam of ¹⁵C with a higher energy at 28.3 MeV/u and LACPU, a large-acceptance charged particle detector array, enabling coincident measurement of high-lying unbound states in ¹⁴B that include π0p1/2-π0p3/2 transitions. A newly observed 3.69(41)-MeV resonance with a statistical significance of 3.4σ in 14B exhibits π0p1/2 rather than π0p3/2-dominant character according to structural model predictions. The extracted proton spectroscopic factor of 0.14 ± 0.06 for ¹⁵Cg.s. not only follows the systematic decreasing trend in neutron-rich carbon isotopes but also agrees with theoretical predictions, providing clear evidence for the Z = 6 magicity in ¹⁵C.

In the future, Peking University and FLNR will be committed to leverage each other’s advantages to carry out more and deeper cooperation and experiments in China and Russia.