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.

Performance of the CAT-TPC based on two-dimensional readout strips

A gas detector 140×140×140 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 a-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.Threedimensional images of incident trajectories and scattering events can be clearly reconstructed under an angular resolution of approximately 0.45 degree.

An efficient method for mapping the 12C+12C molecular resonances at low energies

The 12C+12C fusion reaction is famous because of its complication of molecular resonances,and it plays an important role in both nuclear structural research and astrophysics. It is extremely difficult to measure the cross sections of 12C+12C fusions at energies of astrophysical relevance because of the very low reaction yields. To measure the complicated resonant structure that exists in this important reaction, an efficient thick target method has been developed and applied for the first time at energies Ec.m.<5.3 MeV. A scan of the cross sections over a relatively wide range of energies can be carried out using only a single beam energy. The result of measurement at Ec.m.=4.1 MeV is compared with results from previous work.This method will be useful for searching for potentially existing resonances of 12C+12C in the energy range 1 MeV<Ec.m.<3 MeV.