Investigation on symmetry and characteristic properties of the fragmenting source in heavy-ion reactions through reconstructed primary isotope yields

In this report,a kinematical focusing technique will be briefly described,and using this technique,the primary hot isotope yields from the multiplicities of evaporated light particles,associated with isotopically identified intermediate mass fragments,are reconstructed.Symmetry energy and characteristic properties of the fragmenting source at the time of the intermediate mass fragment formation are extracted from these reconstructed primary isotope yields using a self-consistent manner.The extracted density-dependent symmetry energy is further compared with those experimentally extracted from other heavy-ion reactions in literatures.A direct connection between the freeze-out concept and transport model simulations in a multifragmenting regime of heavy-ion collisions is also demonstrated quantitatively in the present work.

Development of a low-background neutron detector array

A low-background neutron detector array was developed to measure the cross section of the ^(13)C(a,n)^(16)O reaction,which is the neutron source for the s-process in AGB stars,in the Gamow window(E_(c.m.)=190±40 keV)at the China Jinping Underground Laboratory(CJPL).The detector array consists of 24^(3)He proportional counters embedded in a polyethylene cube.Owing to the deep underground location and a borated polyethylene shield around the detector array,a low background of 4.5(2)/h was achieved.The ^(51)V(p,n)^(51)Cr reaction was used to determine the neutron detection efficiency of the array for neutrons with energies E_(n)<1 MeV.Geant4 simulations are shown to effectively reproduce the experimental results.They were used to extrapolate the detection efficiency to higher energies for neutrons emitted in the ^(13)C(α,n)^(16)O reaction.The theoretical angular distributions of the ^(13)C(α,n)^(16)O reaction were shown to be important in the estimation of the uncertainties of the detection efficiency.

A simulation study of a windowless gas-stripping room in an E//B neutral particle analyzer

The neutral particle analyzer(NPA)is one of the crucial diagnostic devices in a Tokamak facility.The stripping unit is one of the main parts of the NPA.A windowless gas-stripping room with two differential pipes has been constructed in a parallel electric and magnetic fields(E//B)NPA.The pressure distributions in the stripping chamber are simulated by ANSYS Fluent together with MolFlow+.Based on the pressure distributions obtained from the simulation,the stripping efficiency of the E//B NPA is studied using GEANT4.Hadron reaction physics is modified to track the charge state of each particle in a cross-section-based method in GEANT4.The transmission rates(R)and stripping efficiencies f_(+1)are examined for particle energies ranging from 20 to 200 keV with the input pressure(P_(0)),ranging from 20 to 400 Pa.According to the combined global efficiency,R×f_(+1),P_(0)=240 Pa is obtained as the optimum pressure for the maximum global efficiency in the incident energy range investigated.

An active base designed in high-counting-rate applications for Hamamatsu R1924A photomultiplier tube

Hamamatsu R1924A is one of the most widely used photomultiplier tubes(PMTs) in nuclear physics.Since the active base suitable for R1924A is still not available in market, an active base is designed for Hamamatsu R1924A PMT, and the test results at high counting rates are presented. The active bases with two different sets of resistor chains were tested and compared by a frequency-controlled green straw hat LED light. A stable signal output up to 100 kHz is achieved using frequency-controlled LED pulsed light. The temperature of bases, which reflects the power consumption and is crucial for applications in vacuum, is also monitored with the same LED pulsed light. The temperature of the active base with smaller resistances reaches about twice of that of the active base with larger resistances in the resistor chain. For the applications in vacuum, the active base with resistance between the two sets of resistor chains may be preferable.

Interaction of supersonic molecular beam with low-temperature plasma

The interaction between the supersonic molecular beam(SMB)and the low-temperature plasma is a critical issue for the diagnosis and fueling in the Tokamak device.In this work,the interaction process between the argon SMB and the argon plasma is studied by a high-speed camera based on the Linear Experimental Advanced Device(LEAD)in Southwestern Institute of Physics,China.It is found that the high-density SMB can extinct the plasma temporarily and change the distribution of the plasma density significantly,while the low-density SMB can hardly affect the distribution of plasma density.This can be used as an effective diagnostic technique to study the evolution of plasma density in the interaction between the SMB and plasma.Moreover,the related simulation based on this experiment is carried out to better understand the evolution of electron density and ion density in the interaction.The simulation results can be used to analyze and explain the experimental results well.

Towards the full realization of the RIBLL2 beam line at the HIRFL-CSR complex

More than 99%of the mass in the visible universe—the material that makes up ourselves,our planet,stars—is in the atomic nucleus.Although the matter has existed for billions of years,only over the past few decades have we had the tools and the knowledge necessary to get a basic understanding of the structure and dynamic of nuclei.Nuclear physicists around the world have made tremendous strides by initiating a broad range of key