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We developed a Dual-PPACs detector for fast neutron measurements that consists of two sets of PPAC: conventional PPAC and fission PPAC. A238U(U3O8) coating is placed in the fission PPAC’s anode, which is used as the neutrons conversion layer. An experiment was performed to measure neutron time-of-flight (TOF) in which 252Cf spontaneous fission source was used. An excellent time resolution of 164ps has been observed at 6 mbar in isobutene gas. With the excellent time resolution of Dual-PPACs detector, exact neutron energy can be extracted from the timing measurement. The experimental detection efficiency was 1.9 × 10−7, consistent with the efficiency of 2.5 × 10−7 given by a Geant4 simulation. Ultimately, the results show that the Dual-PPACs detector is a suitable candidate for measuring fast neutrons in the future CiADS system.

We have developed a position-sensitive Parallel Plate Avalanche Counter (PPAC) to detect the fission fragments and reconstruct the fission reaction plane in the experiment of studying nuclear equation of state (nEOS) by means of heavy ion collision (HIC). This experiment put forward high requirements for the performances of PPAC, such as the time resolution, efficiency and position resolution. According to these requirements we designed the PPAC with an active area of 240 mm × 280 mm working at low gas pressure. The results show that time resolution could be less than 300 ps. Position resolution is consistent with the theoretical calculation about 1.35 mm. Detection efficiency could be approaching 100% gradually with the voltage increasing in different gas pressures. The performances of PPAC have also been verified in beam experiment. Each set of anode wires can be accurately separated in the position spectrum. In the beam experiment, we also got the back-to-back correlation of fission fragments which is one of the direct signals characterizing binary decay. Keywords: PPAC, nEOS, Time resolution, Position resolution, Efficiency

The External Target Facility (ETF) has been constructed for reaction studies with high-energy secondary beams of several hundred MeV/u. The charged fragment detector system of ETF consists of a dipole magnet, tracking drift chambers, ionization chambers and plastic scintillators for particle identification (PID) via B ρ - Δ E-TOF method. The system is now ready for physics experiments. Before physics runs, it has been tested using 280 MeV/u 18O primary beam as well as the secondary beams produced by projectile fragmentation. The system used as a magnetic spectrometer has exhibited satisfying PID capability in identifying fragments ranging from nitrogen to beryllium.

A gas detector 140 $$\times$$ 140 $$\times$$ 140 mm $$^3$$ in size, termed the compact active target time projection chamber (CAT-TPC), was developed in this study to measure resonant scattering associated with cluster structures in unstable nuclei. The CAT-TPC consists of an electronic field cage, double-thick gas-electron-multiplier foils, a general-purpose digital data acquisition system, and a newly developed two-dimensional strip-readout structure. The CAT-TPC was operated using a $$^4$$ He (96%) + CO $$_2$$ (4%) gas mixture at 400 mbar. The working gas also serves as an active target for tracking charged particles. The overall performance of the CAT-TPC was evaluated using a collimated $$\alpha$$ -particle source. A time resolution of less than 20 ns and a position resolution of less than 0.2 mm were observed along the electron drift direction. Three-dimensional images of incident trajectories and scattering events can be clearly reconstructed under an angular resolution of approximately 0.45 degree.

A consistent measurement of the inclusive single-neutron removal cross sections of $^{14,15,16}\mathrm{C}$ on a carbon target at around 240 MeV/nucleon has been performed at the External Target Facility, HIRFL-CSR, and compared with Glauber model predictions using shell-model spectroscopic strengths between the initial projectile ground state and configurations of bound core state $+$ valence neutron state as input. For the dependence of the spectroscopic factor reduction characterized by the ratio ${R}_{s}$ of the experimental over theoretical single-nucleon removal cross section on the bounding depth $\mathrm{\ensuremath{\Delta}}S$ of the removed nucleon established in single-nucleon removals with beam energies mainly over 80--120 MeV/nucleon, our measurement gives ${R}_{s}$ values that conform to the earlier ${R}_{s}\text{\ensuremath{-}}\mathrm{\ensuremath{\Delta}}S$ systematics, where the relatively higher incident beam energy facilitates the applicability of the eikonal and sudden approximation used in the Glauber model.

A drift chamber array at the External Target Facility in HIRFL-CSR has been constructed for three-dimensional particle tracking in high-energy radioactive ion beam experiments. The design, readout, track reconstruction program and calibration procedures for the detector are described. The drift chamber array was tested in a 311 AMeV 40Ar beam experiment. The detector performance based on the measurements of the beam test is presented. A spatial resolution of 230 μ m is achieved.

Heavy-ion fusion reactions, such as 12 C+ 12 C, play crucial roles in stellar evolution and nucleosynthesis in massive stars . However, limited by the low cross section and large background, it is very challenging to study the reactions at stellar energies. We have developed a 1024-channel prototype TPC named MATE (Multi-purpose time projection chamber for nuclear AsTrophysical and Exotic beam experiments) to study these reactions at stellar energies. The design of our prototype TPC and its performance are described, and the preliminary results of a commissioning experiment for measuring the 12 C( 12 C, α 0 ) 20 Ne reaction at E cm = 3.0 MeV are presented. Perspectives of future experiments for the 12 C+ 12 C fusion cross section measurement are also provided.

The cross section for one-proton knockout from $^{16}\mathrm{C}$ with a large neutron-proton separation energy asymmetry on a carbon target has been measured at an intermediate beam energy of around 240 MeV/nucleon. The measured cross section is compared to the predictions based on the eikonal reaction model with shell-model structure inputs. The beam-energy dependence of the reduction on the extracted spectroscopic strength for strongly bound nucleon removal is derived from combining the existing intermediate-energy data with the present measurement. The deduced reduction factor ${R}_{s}$, defined as the ratio of the measured and theoretical cross sections, for the strongly bound nucleon removal at around 240 MeV/nucleon is consistent with the systematics observed from knockout reactions induced by light nuclear targets at intermediate energies of around 80 MeV/nucleon.

A fission chamber with two layers of 238U fissile materials has been developed for the measurements of fast neutrons. The developed fission chamber has been tested by 60Co gamma source and 252Cf neutron source. The results have indicated that it is very easy to cut off the gamma rays from the neutrons by using a discriminator, when the fission chamber works in the pulse mode. The detector works well, even if the static air is used as the filling gas. To discuss the application of the detector, Monte Carlo simulations have been performed by considering four 238U-coated fission chambers located outside the spallation target for the fast neutron measurement from spallation reaction. The simulation results have indicated that the detector can be used to measure the fast neutron flux and neutron flux ratio of four fission chambers. Furthermore, a 238U-coated fission chamber can be used within a reactor for longer time, in comparison with a 235U-coated fission chamber.

To obtain the angular distributions of 12C + 12C elastic scatterings with the incident energies of 200–400A MeV for the study of three-body forces, a detector system was constructed at second Radioactive Ion Beam Line in Lanzhou (RIBLL2) of Institute of Modern Physics (IMP). This system was composed of five plastic scintillation detectors with two read-outs for each detector, a Multi Wire Proportional Chamber (MWPC) and a 4×4 CsI(Tl) array. The 12C beam with the incident energy of 200A MeV on a natural carbon target was used to test this detector system. It is found that the plastic scintillation detector can give the good energy loss (ΔE) and time of flight (TOF) signals, it can also reflect the position information of scattered 12C events. MWPC can precisely provide the trajectories of scattered particles. This system has a very good particle identification ability and can clearly distinguish the scattered 12C particles from the fragments. It can be used for the study of the three-body forces effect for high energy heavy-ion scattering.

The cross sections for two-neutron removal from $^{15,16}\mathrm{C}$ on a carbon target have been measured at around 240 MeV/nucleon. The measured cross section for $^{15}\mathrm{C}$ is smaller than for $^{16}\mathrm{C}$. The trends of the cross sections for $^{15,16}\mathrm{C}$ are inconsistent with the previously reported experimental data, but in agreement with the theoretical predictions based on eikonal-model calculations. Based on the present results of $^{15,16}\mathrm{C}$ combined with the available experimental data on $^{17--20}\mathrm{C}$, an odd-even staggering of the two-neutron removal cross sections along the neutron-rich carbon isotopic chain from $^{15}\mathrm{C}$ to $^{20}\mathrm{C}$ is observed, and this feature is well reproduced by the theoretical calculations.

In typical nuclear physics experiments with radioactive ion beams (RIBs) selected by the in-flight separation technique, Si detectors or ionization chambers are usually equipped for the charge determination of RIBs. The obtained charge resolution relies on the performance of these detectors for energy loss determination, and this affects the particle identification capability of RIBs. We present an approach on improving the resolution of charge measurement for heavy ions by using the abundant energy loss information from different types of existing detectors along the beam line. Without altering the beam line and detectors, this approach can improve the charge resolution by more than 12\% relative to the multiple sampling ionization chamber of the best resolution., Comment: 8 pages, 5 figures

A multiple sampling ionization chamber used as a particle identification device for high energy heavy ions has been developed for the External Target Facility. The performance of this detector was tested with a 239Pu α source and RI beams. A Z resolution (FWHM) of 0.4–0.6 was achieved for nuclear fragments of 18O at 400 AMeV.

The drift of the isospin degree of freedom (IDOF) is experimentally visualized through the wide-range angular distribution and the beam energy dependence of the isospin composition of light charged particles (LCP) produced in heavy ion collisions. It is evidenced that the net isospin transport is presented in the whole process from early dynamic emission to the statistical evaporation lasting to very late stage. Due to the long-time accumulation of the isospin effect, the angular distribution of the relative neutron excess summing over the LCPs is utilized as a sensitive probe to the symmetry energy. With S fixed at 28.3 MeV, a soft density dependence with L=33–61 MeV (0.95 confidential level) at ρ0 is circumstantially deduced using an improved quantum molecular dynamics transport model attached with a statistical emission afterburner.

A tracking system composed of three multi-wires proportional chambers (MWPCs) for the external target facility of the Cooler Storage Ring is reported in this paper. The active areas of the MWPCs are 518 mm × 400 mm, 582 mm × 450 mm, and 710 mm × 500 mm. Each MWPC consists of a series of alternately placed cathode and anode wire planes and can measure position along the directions of −30°, 0°, and 30° relative to horizontal. The construction and operation of the detectors are described, and a method for track reconstruction is introduced. A track-finding efficiency of about 62% and a spatial resolution of 1.21 mm have been achieved. The pion and proton can be identified clearly with the tracking system combined with a time-of-flight system.

The RIBLL2 in-flight separator at IMP, the secondary beam line between two storage rings at the \blue{\uwave{Heavy Ion Research Facility in Lanzhou (HIRFL-CSR)}}, has been commissioned to study the rare-isotope beam (RIB) physics at around 300 MeV/nucleon for the first time, in combination of the external target facility (ETF). The unambiguous particle identification in mass and charge states for $^{18}$O and $^{40}$Ar fragments has been achieved in recent experiments. A full realization of RIBLL2 will open many potentials to address important RIB physics problems at around 300 MeV/nucleon., Comment: 3 pages, 2 figures

The non-uniformity effect of the inter-foil distance has been studied using a gaseous electron multiplication (GEM) detector with sensitive area of 50mm × 50mm. A gradient of the inter-foil distance is introduced by using spacers with different heights at the two ends of the foil gap. While the cluster size and the intrinsic spatial resolution show insignificant dependence on the inter-foil distance, the gain exhibits an approximately linear dependence on the inter-foil distance. From the slope, a quantitative relationship between the change of the inter-foil distance and the change of the gain is derived, which can be used as a method to evaluate the non-uniformity of the foil gap in the application of large-area GEM detectors.

A detector for fast neutrons based on a 10 x 10 cm(2) triple gas electron multiplier (GEM) device is developed and tested. A neutron converter, which is a high density polyethylene (HDPE) layer, is combined with the triple GEM detector cathode and placed inside the detector, in the path of the incident neutrons. The detector is tested by obtaining the energy deposition spectrum with an Am Be neutron source in the Institute of Modern Physics (IMP) at Lanzhou. In the present work we report the results of the tests and compare them with those of simulations. The transport of fast neutrons and their interactions with the different materials in the detector are simulated with the GEANT4 code, to understand the experimental results. The detector displays a clear response to the incident fast neutrons. However, an unexpected disagreement in the energy dependence of the response between the simulated and measured spectra is observed. The neutron sources used in our simulation include deuterium-tritium (DT, 14MeV), deuterium-deuterium (DD, 2.45MeV), and Am Be sources. The simulation results also show that among the secondary particles generated by the incident neutron, the main contributions to the total energy deposition are from recoil protons induced in hydrogen-rich HDPE or Kapton (GEM material), and activation photons induced by neutron interaction with Ar atoms. Their contributions account for 90% of the total energy deposition. In addition, the dependence of neutron deposited energy spectrum on the composition of the gas mixture is presented.

A prototype of the forward tracking array consisting of three multiwire drift chambers (MWDC) for the external target experiment (CEE) at the Heavy Ion Research Facility at the Lanzhou -Cooling Storage Ring (HIRFL-CSR) has been assembled and tested using cosmic rays. The signals from the anode wires are amplified and fed to a Flash-ADC to deliver the drift time and charge integration. The performances of the array prototype are investigated under various high voltages. For the tracking performances, after the space-time relation (STR) calibration and the detector displacement correction, the standard deviation of 223 μm of the residue is obtained. The performances of the forward MWDCs tracking array meets the requirements of CEE in design.