An experiment for p( 14 C, 14 C * → 10 Be + α)p inelastic excitation and decay was performed in inverse kinematics at a beam energy of 25.3 MeV/u. A series of 14 C excited states, including a new one at 18.3(1) MeV, were observed which decay to various states of the final nucleus of 10 Be. A specially designed telescope-system, installed around the zero degree, played an essential role in detecting the resonant states near the α-separation threshold. A state at 14.1(1) MeV is clearly identified, being consistent with the predicted band-head of the molecular rotational band characterized by the π-bond linear-chain-configuration. Further clarification of the properties of this exotic state is suggested by using appropriate reaction tools.

Background: For the deeply-bound one-nucleon removal at intermediate energies using a 9 Be or 12 C target, a strong reduction of cross section was observed relative to the prediction of eikonal theoretical model. The large disagreement has not been explained and the systematic trend is inconsistent with results from transfer reactions. The recently observed asymmetric parallel momentum distribution of the knockout residue indicates the significant dissipative core-target interaction in the knockout reaction with a composite target, implying new reaction mechanisms beyond the eikonal reaction descriptions. Purpose: To investigate the reaction mechanism for deeply-bound nucleon removal at intermediate energies. Method: The neutron removal from14 O using a 12 C target at 60 MeV/nucleon was performed. Nucleon knockout cross sections were measured. The unbound excited states of 13 O were reconstructed using invariant mass method with the residues and the associated decay protons measured in coincidence. The measured cross sections are compared with an Intra-Nuclear Cascade (INC) prediction. Results: The measured cross section of ( 14 O, 11 C) is 60(9) mb, which is 3.5 times larger than that of ( 14 O, 13 O) channel. This 2pn-removal cross section is consistent with INC prediction, which is 66 mb mainly contributed by the non-direct reaction processes. On the other hand, the upper limit of the cross section for one-neutron removal from 14 O followed by proton evaporation is 4.6(20) mb, integrated up to 6 MeV above the proton separation energy of 13 O. The calculated total cross section for such reaction processes by INC model is 2.5 mb, which is within the measured upper limit. Conclusions: The data provide the first constraint on the role of core excitation and evaporation processes in the deeply-bound nucleon removal from asymmetric nuclei. The experiment results suggest that non-direct reaction processes, which are not considered in the eikonal model, play an important role in the deeply-bound nucleon removal from asymmetric nuclei at intermediate energies.

To perform a kinematically complete measurement of the dissociation reaction for neutron-rich nuclei, a multi-neutron correlation spectrometer is proposed at Peking University. A Monte Carlo simulation code based on GEANT4 is developed for a single scintillation bar which processes not only the energy deposition but also the light propagation in the scintillator and the light collection and conversion to signal at the end of the bar in a realistic way. The simulating method is described in detail in this paper, and the timing and position resolutions and detector efficiency are studied based on the simulation and compared with the experimental results. A new method of crosstalk rejection has been demonstrated to be important for the design of the whole spectrometer.

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