Limin Duan

A BGO detector array and its application in intermediate energy heavy ion experiments

A BGO crystal (Bi4Ge3O12) as the E detector of ΔE-E for identification of reaction products has been used for detecting the charged particles emitting from the 25 MeV/u 40Ar induced reaction. The responses of the BGO crystal to various light charged particles were measured. A close-packed hexagonal array consisting of thirteen ΔE-E telescopes (Si-BGO) has been developed to detect the light charged particles interfering with each other in intermediate-energy heavy-ion induced reactions. Some applications of this telescope array are also described.

7Be, 8B+208Pb Elastic Scattering at Above-Barrier Energies

Angular distributions for the elastic scattering of 7Be and 8B by an enriched 208Pb target were measured at the Radioactive Ion Beam Line at Lanzhou (RIBLL). The incident energies of the radioactive beams were about three times the respective Coulomb barriers. A suppressed Coulomb-nuclear Interference Peak (CNIP) is not observed for 8B, a pronounced proton halo nucleus. Optical model fits were performed using Woods-Saxon potentials and the total reaction cross sections deduced. The results are discussed.

Plastic scintillation detectors for precision Time-of-Flight measurements of relativistic heavy ions

Plastic scintillation detectors for Time-of-Flight (TOF) measurements are almost essential for event-by-event identification of relativistic rare isotopes. In this work, a pair of plastic scintillation detectors of dimensions 50 × 50 × 3t mm3 and 80 × 100 × 3t mm3 have been set up at the External Target Facility (ETF), Institute of Modern Physics (IMP). Their time, energy and position responses are measured with the 18O primary beam at 400 MeV/nucleon. After off-line corrections for walk effect and position, the time resolutions of the two detectors are determined to be 27 ps (σ) and 36 ps (σ), respectively. Both detectors have nearly the same energy resolution of 3.1% (σ) and position resolution of about 3.4 mm (σ). The detectors have been used successfully in nuclear reaction cross section measurements, and will be be employed for upgrading the RIBLL2 beam line at IMP as well as for the high energy branch at HIAF.

Temperature and excitation energy of hot nuclei in the reaction of 40Ar+197Au at 25 MeV/nucleon

Abstract The coincidence measurements between heavy fission fragments and light charged particles with Z ⩽ 2 were carried out for the 40 Ar+ 197 Au reaction at 25 MeV/nucleon, to study the properties of hot nuclei in heavy ion induced reactions. The linear momentum transfers (LMTs) were deduced from the folding angle and the time-of-flight difference between two fission fragments of heavy residues. The relationship of the nuclear temperature (slope parameter of the energy spectrum) and the excitation energy was determined independently from the measurement of the kinetic energy spectra in the frames of the emitting sources and from the LMT analysis. Both the temperature and the excitation energy increase with decreasing impact parameter, which suggests that a plateau temperature of 5.5 MeV is reached at an excitation energy of 3.1 MeV/nucleon. The result was also compared with various statistical models that explain the plateau by the multifragmentation process, where the excitation energy is assumed to be stored in compression and expansion effects.

Breakup of 33.4 MeV/u 17N on a 9Be Target

Correlation measurements of neutrons and fragments have been performed in a reaction of 33.4 MeV/u 17N on a 9Be target. Energy spectra of n and nitrogen fragments were obtained at different angles. Based on the nuclear diffraction dissociation model, the measured energy spectra and the neutron angular distributions were reproduced quite well assuming that 17N was composed of 16N and n or 15N and 2n interacting with the nonlocal separable potential. The satisfactory agreement between the theoretical calculations and the experimental data shows that the contribution of Coulomb dissociation is negligible in the reaction concerned.

A BGO hodoscope for intermediate mass fragments

Abstract A BGO hodoscope was developed to detect intermediate mass fragments (IMF) emitted from the intermediate energy heavy ion collisions. It consists of 13 Δ E – E telescopes (Si–BGO). The responses of the BGO detector for charged particles and IMF were tested. The results indicate that charge resolution for helium, IMF and isotope resolution for hydrogen are achieved for this hodoscope. Some applications of this hodoscope are also described.

The 4-fold fission in 40Ar + 209Bi, 197Au and 159Tb reactions at 25 MeV/u

Abstract The paper presents the 4-fold fission or fragmentation of hot nuclei produced in 25 MeV/u 40 Ar + 209 Bi , 197Au and 159Tb reactions. The events with 4 massive fragments emitted with angles larger than 36 ° were detected by 8 PPACs with area of 25 × 20 cm2. The TKE, distributions of mass and velocity for the four fragments have been obtained.

Comparison of Experiment and Simulation of the triple GEM-Based Fast Neutron Detector

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.

Nuclear Physics Programs at HIRFL‐CSRm: A Status Report

An internal and an external target experiment, ETE and HPLUS, respectively, will be built at the HIRFL‐CSRm complex covering various nuclear physics programs. This talk introduces briefly the conceptual designs and the main physical interests of these two experiments. Parallel R&D works for the sub‐detectors of ETE and HPLUS have been started. The current status is documented.

Which sort of particles was emitted earlier during decay of highly excited nuclei

Emission orders of light charged particles and Li fragments from highly excited fissioning nuclei in the reaction of40Ar +197Au atEbeam/A = 25 MeV have been studied by measuring difference velocity distributions of two correlated particles at small relative angles in coincidence with two fission fragments. By comparing the data with three-body trajectory calculations, it is found that high-velocity light particles (tritons and He particles) are emitted prior to high-velocity Li fragments but low-velocity light particles are emitted after low-velocity Li fragments. On the other hand, no preferential emission was observed among light particles, such as deuterons and tritons.