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A new Frisch-grid ionization chamber has been built to explore the appropriate choice of Frisch-grid. Detailed studies of the relationship between grid geometries and detector performance have been performed with an 241Am source. This paper describes and compares the energy resolution of ionization chambers with parallel-wire and mesh grids of different grid parameters. Some specific recommendations for grid selection are provided based on the data currently available. To obtain optimal energy resolution, the operating voltage of the chamber must satisfy the condition of minimum electron collection on the grid with distinct geometries and parameters, respectively. Since there is no established theory applicable to both types of grids, we have devised a careful simulation procedure incorporating the COMSOL and Garfield++ codes to search for the conditions of the minimum electron collection on the grid. The simulation results fit the experimental data well, suggesting that this simulation method successfully predicts the suitable voltage setting when using a mesh grid or parallel wires grid as the shielding electrode.

The charge exchange (CE) reaction is an effective probe to study the structure of atomic nuclei in the isospin dimension, which has been studied for decades. To expand the range of nuclei studied by CE reactions to a wider range and research the structure characteristics of unstable nuclei, including the isospin symmetry, spin-isospin excitation, and nuclear symmetry energy, a semi-cylindrical time projection chamber (scTPC) prototype was designed and constructed to probe ( 3 He, t ) CE reactions in inverse kinematics. The 266 nm UV laser was used to achieve electron-drift-velocity calibration. The scTPC has an energy resolution (FWHM) of 5.6% for α particles emitted by 241 Am radioactive source. The position resolution of scTPC is described by the residual method. The spatial resolution on the pad plane is 409 μ m. And the position resolution in the drift direction is 326 μ m, equivalent to an angular resolution of 0.4 ∘ . These performances suggest that the scTPC can measure Δ E and particle tracks precisely. The successful development of the scTPC prototype provides better conditions for the next step of experimental data analysis and processing.

In the NνDEx collaboration, a high-pressure gas TPC is being developed to search for the neutrinoless double beta decay. The use of electronegative 82SeF6 gas mandates an ion-TPC. The reconstruction of the z coordinate is to be realized by exploiting the feature of multiple species of charge carriers. As the initial stage of the development, we studied the properties of the SF6 gas, which is non-toxic and has a similar molecular structure to SeF6. In the paper, we present the measurement of drift velocities and mobilities of the majority and minority negative charge carriers found in SF6 at a pressure of 750 Torr, slightly higher than the local atmospheric pressure. The reduced fields range between 3.0 and 5.5 Td. This was performed using a laser beam to ionize the gas inside a small TPC, with a drift length of 3.7 cm. A customized charge-sensitive amplifier was developed to read out the anode signals induced by the slowly drifting ions. The closure test of the reconstruction of the z coordinate using the difference in the velocities of the two carriers was also demonstrated.

A new trapezoid-shaped Frisch-grid ionization chamber (TFG-IC) has been built as a part of a ΔE-E telescope system for the detection and identification of charged particles at energies down to a few MeV. To study the effect of the drift electric field uniformity, two types of sealed windows, namely a pair of SSA (split-strip aluminized mylar film) and a pair of DSA (double-sided aluminized mylar film) sealed windows have been investigated. The detector’s performances were studied using a standard 241Am source at different gas pressures, and the total energy-deposit resolution achieved is about 1.1%(FWHM). The ΔE-E telescope, which was composed of TFG-IC and a DSSSD (double-sided silicon strip detector), has been tested using a three-component α source and the 241Am source under laboratory conditions. The results show that the energy resolution with the SSA sealed windows which provide uniform drift electric field has a smaller fluctuation than that with the DSA ones; the fluctuations are about 1% and 4% for the former and the latter, respectively. Simulations using the COMSOL software also confirmed the electric-field distortion at the edge of the detector with the DSA windows. A correlation curve between energy resolution and energy deposit of charged particles at various gas pressures and for two gas species is derived for TFG-IC with the SSA sealed windows using the measurement with the 241Am source. Incorporating the above results, we performed Monte Carlo simulations to evaluate the particle-identification capability of the telescope. The results show that the telescope can be extended to the identification of low-energy particles.

The Heavy Ion Research Facility in Lanzhou-Cooling Storage Ring (HIRFL-CSR) external-target experiment (CEE) under construction is expected to provide novel opportunities for the studies of the thermodynamic properties of nuclear matter, in particular the nuclear matter equation of state (nEOS), with heavy ion collisions at a few hundreds MeV/u beam energies. Based on Geant 4 packages, the simulations of the detector responses to the collision events generated using transport model are conducted. The overall performance of CEE, including the geometric coverage, the momentum resolution of tracks and the particle identification ability has been investigated. Various observables proposed to probe the nEOS, such as the production of light clusters, 3 H / 3 He yield ratio, radial flow, π - / π + yield ratio and neutral kaon yields, have been reconstructed. The feasibility of studying nEOS beyond the saturation density via the aforementioned observables to be measured with CEE has been demonstrated by using the ultra relativistic quantum molecular dynamics (UrQMD) simulation data.

The neutron-neutron (\\(nn\\)) correlation function has been measured in 25 MeV/u \\(^124\\)Sn+\\(^124\\)Sn reactions. Using the Lednický-Lyuboshitz approach, the \\(nn\\) scattering length and effective range (\\(f_0^nn\\), \\(d_0^nn\\)), as well as the reduced space-time size \\(R^(0)\\) of the neutron emission source are simultaneously extracted as (\\(18.9^+1.3_-1.2\\) fm, \\(1.9^+1.3_-1.0\\) fm) and \\(4.12 0.12\\) fm, respectively. The measured \\(nn\\) scattering length is consistent with the results obtained in the low-energy scattering \\(^2 H(^-,)2n\\), indicating heavy-ion collisions can serve as an effective approach for measuring \\(nn\\) interactions and further investigating the charge symmetry breaking of nuclear force. The space-time size extracted from momentum-gated correlation functions exhibits clear dependence on the pair momentum, with \\(R^(0)=2.8 0.1 \\) fm and \\(4.9 0.2\\) fm being determined for the high and low momentum neutrons, respectively.

The emission of neutrons from heavy ion reactions is an important observable for studying the asymmetric nuclear equation of state and the reaction dynamics. A 20-unit neutron array has been developed and mounted on the compact spectrometer for heavy ion experiments (CSHINE) to measure the neutron spectra, neutron-neutron and neutron-proton correlation functions. Each unit consists of a \\( 15 15 15~cm^3\\) plastic scintillator coupled to a \\( =52 ~ mm\\) photomultiplier. The Geant4 simulation with optical process is performed to investigate the time resolution and the neutron detection efficiency. The inherent time resolution of 212 ps is obtained by cosmic ray coincidence test. The n-\\(\\) discrimination and time-of-flight performance are given by \\( ^252Cf\\) radioactive source test and beam test. The neutron energy spectra have been obtained in the angle range \\(30^ _ lab 51^\\) in the beam experiment of \\(^124\\)Sn+\\(^124\\)Sn at 25 MeV/u with CSHINE.

Bremsstrahlung \\(\\gamma\\) production in heavy ion reactions at Fermi energies carries important physical information including the nuclear symmetry energy at supra-saturation densities. In order to detect the high energy Bremsstrahlung \\(\\gamma\\) rays, a hodoscope consisting of 15 CsI(Tl) crystal read out by photo multiplier tubes has been built, tested and operated in experiment. The resolution, efficiency and linear response of the units to \\(\\gamma\\) rays have been studied using radioactive source and \\(({\\rm p},\\gamma)\\) reactions. The inherent energy resolution of \\(1.6\\%+2\\%/E_{\\gamma}^{1/2}\\) is obtained. Reconstruction method has been established through Geant 4 simulations, reproducing the experimental results where comparison can be made. Using the reconstruction method developed, the whole efficiency of the hodoscope is about \\(2.6\\times 10^{-4}\\) against the \\(4\\pi\\) emissions at the target position, exhibiting insignificant dependence on the energy of incident \\(\\gamma\\) rays above 20 MeV. The hodoscope is operated in the experiment of \\(^{86}\\)Kr + \\(^{124}\\)Sn at 25 MeV/u, and a full \\(\\gamma\\) energy spectrum up to 80 MeV has been obtained.

Two-body correlations of the isotope-resolved light and heavy clusters are measured in \\(^{86}\\)Kr+\\(^{\\rm 208}\\)Pb reactions at 25 MeV/u. The yield and kinetic variables of the \\(A=3\\) isobars, triton and \\(^3\\)He, are analyzed in coincidence with the heavy clusters of \\(7\\le A \\le 14\\) emitted at the earlier chance. While the velocity spectra of both triton and \\(^3\\)He exhibit scaling behavior over the type of the heavy clusters, the yield ratios of \\({\\rm t/^3He}\\) correlate reversely to the neutron-to-proton ratio \\(N/Z\\) of the latter, showing the ping-pong modality of the \\(N/Z\\) of emitted clusters. The commonality that the \\(N/Z\\) of the residues keeps the initial system value is extended to the cluster emission in heavy ion reactions. The comparison of transport model calculations to the data is discussed.