First proof-of-principle experiment with the post-accelerated isotope separator on-line beam at BRIF:measurement of the angular distribution of ^(23)Na+^(40)Ca elastic scattering

The reaction dynamics of exotic nuclei near the drip line is one of the main research topics of current interest.Elastic scattering is a useful probe for investigating the size and surface diffuseness of exotic nuclei.The development of rare isotope accelerators offers opportunities for such studies.To date,many relevant measurements have been performed at accelerators using the projectile fragmentation technique,while the measurements at accelerators using isotope separator on-line(ISOL)systems are still quite scarce.In this work,we present the first proof-of-principle experiment with a post-accelerated ISOL beam at the Beijing Radioactive Ion Beam Facility(BRIF)by measuring the angular distribution of elastic scattering for the stable nucleus^(23)Na from the doubly magic nucleus^(40)Ca at energies above the Coulomb barrier.The angular distribution measured by a silicon strip detector array in a scattering chamber using the ISOL beam at BRIF is in good agreement with that measured by the high-precision Q3 D magnetic spectrograph using the nonISOL beam at nearly the same energy.This work provides useful background for making BRIF a powerful tool for the investigation of the reaction dynamics of exotic nuclei.

Silicon detector array for radioactive beam experiments at HIRFL-RIBLL

A new and innovative detector system based on a silicon strip detector dedicated to the study of the reaction induced by lighter radioactive beams is described herein.The detector system consists of five sets of three types of telescopes,which are successfully used to measure the angular distributions of both elastic scattering and breakup simultaneously, on the Radioactive Ion Beam Line in Lanzhou at Heavy Ion Research Facility in Lanzhou. This silicon detector array is used to measure the elastic scattering angular distributions of ^(11) Be on a ^(208) Pb target at E_(lab) = 140 and 209 MeV. A comparison of the Monte Carlo simulations with the experimental results shows a reasonable consistency.

Compact 16-channel integrated charge-sensitive preamplifier module for silicon strip detectors

In this study,a compact 16-channel integrated charge-sensitive preamplifier named the smart preamplifier(SPA)was developed to support the large-scale detector array used in modern nuclear physics experiments.Two types of SPA,namely SPA02 and SPA03(with external field effect transistor),have been manufactured to match silicon detectors with small and large capacitances,respectively.The characteristics of the SPA include fast response of typically less than 6 ns for pulse rising time and low equivalent noise of 1.5 keV at zero input capacitance.The energy sensitivity and pulse decay time can be easily adjusted by changing the feedback capacitance Cfand resistance Rfin various applications.A good energy resolution of 24.4 keV for 5.803-MeV alpha particles from 244 Cm was achieved using a small-sized Si-PIN detector;for the silicon strip detectors in the test with the alpha source,a typical energy resolution of 0.6–0.8%was achieved.The integrated SPA has been employed in several experiments of silicon strip detectors with hundreds of channels,and a good performance has been realized.

A detector setup for the measurement of angular distribution of heavy-ion elastic scattering with low energy on RIBLL

A detector setup for the measurement of angular distribution of heavy-ion elastic scattering at energies around Coulomb barrier on the radioactive ion beam line in Lanzhou at the heavy-ion research facility in Lanzhou is designed.The beam profile and the scattering angles on the target are deduced by two parallel plate avalanche counters,and four sets of detector telescopes(including doublesided silicon strip detectors) are placed systematically with the beam line,incorporating with Monte Carlo simulations.The data of ^(16)O on ^(89)Y target were analyzed to compare with the simulation results.It is found that the simulated distribution is agreeable with the experimental data.By assuming the pure Rutherford scattering at small scattering angles,the angular distribution of elastic scattering of^(16)O+^(89)Y at low energies can be reasonably obtained.It indicates that this set of detector setup can be used for the measurement of angular distributions of heavy-ion elastic scattering at energies around Coulomb barrier.

Laser test of the prototype of CEE time projection chamber

A prototype thick-GEM-based cooling storage ring external-target experiment(CEE) time projection chamber(TPC) is constructed and tested with the pulsed ultraviolet laser beams. The results indicate that the prototype TPC has a good performance in three-dimensional track resolution. In X direction the position resolution is about 0.2 mm, and in Y direction the position resolution is about 0.5 mm. The results also determine that the energy resolution is about 5.4%, which achieve the requirements of the CEE experiment and can be used to study the nuclear state equation and the quantum chromo dynamics.

The effects of beam drifts on elastic scattering measured by the large solid-angle covered detector array

A new detector array characterized by compact structure and large solid-angle coverage was designed for radioactive ion beam(RIB)experiments and measuring multi-particle correlations.A Monte Carlo simulation was performed to explore the effects of beam drifts in different directions and distances on the angular distribution of the Rutherford scattering,as measured by the detector array.The results indicate that when the beam drift distance is less than 2.0 mm,the symmetry of the detector array can maintain a count error of less than 5%.This confirms the property of the detector array for RIB experiments.Furthermore,the simulation was validated through the elastic scattering angular distributions of 6;7 Li measured by the detector array in 6;7Li t209 Bi experiments at different energies.

Characterization of CIAE developed double-sided silicon strip detector for charged particles

A double-sided silicon strip detector(DSSD)with active area of 48 mm x 48 mm and thickness of300μm has been developed. Each side of DSSD consists of48 strips, each with width of 0.9 mm and inter-strip separation of 0.1 mm. Electrical properties and detection performances including full depletion bias voltage, reverse leakage current, rise time, energy resolution and cross talk have been studied. At a bias of 80 V, leakage current in each strip is less than 15 nA, and rise time for alpha particle at 5157 keV is approximately 15 ns on both sides.Good energy resolutions have been achieved with0.65-0.80% for the junction strips and 0.85-1.00% for the ohmic strips. The cross talk is found to be negligible on both sides. The overall good performance of DSSD indicates its readiness for various nuclear physics experiments.

Implantation-decay method to study the β-delayed charged particle decay

In this paper,the implantation-decay method is introduced to study the β-delayed charged particle decay.A silicon detector array was used for the implantation of the incident beams and for the detection of the emitted particles.An experimental measurement on the β-delayed particle emission from ^(22)Al was used to demonstrate the method.The half-life value,charged particle spectroscopy,γ ray spectrum,and γ particle coincidence for the decay process were obtained and compared with previous experimental results for ^(22)Al.The results show that the implantation-decay method,using a silicon detector array,is a suitable experimental method to study the β-delayed charged particle decay for proton-rich nuclei.

New measurement of 4^(H)e and proton decays from resonant states in^(19)Ne

A^(6)Li(^(16)O,^(19)Ne^(∗))^(3)H multi-nucleon transfer-reaction experiment was performed to populate the highly excited states in^(19)Ne.The subsequent decay particles,^(4)He or protons from the^(19)Ne resonant states,were detected in coincidence with the recoil 3 H.The excitation-energy spectra of^(19)Ne were reconstructed using the detected proton or^(4)He and the deduced^(18)F or^(15)O data,respectively.A broad resonance at about 7.85 MeV(1/2^(+))was observed,with partial decay widths different from the previously reported values,which may have a significant impact on the destruction of 18 F in astrophysical processes.Several resonances up to very high excitation energies have been identified with a largeα-clustering strength,which confirm the formation of the cluster structure with a one-hole configuration in light nuclei and encourage further systematic studies of the cluster structure in^(19)Ne.

Systematic extraction of the strong absorption distance and Coulomb barrier from elastic scattering

The reduced strong absorption distance d_(S) and Coulomb barrier height V_(B) are extracted from the quarter-point recipe from a series of experimental elastic scattering angle distributions.The nuclei with different binding energies are systematically studied as the projectile,including the tightly bound,weakly bound,and halo nuclei.It is found that the mean d_(S) for halo nuclei is significantly larger than that of tightly and weakly bound nuclei.The complex behavior of d_(S) regarding the binding energy and properties of the target is observed for halo nuclei.The linear relationship of the reduced distance with system size may be used to estimate the Coulomb barrier radius R_(B),which is difficult to obtain from fusion reactions.The rule of V_(B) concerning the Coulomb parameter z is in agreement with other theoretical barrier laws extracted from the fusion reaction.Furthermore,the reason why the binding energy or deformation has little effect on the linear relationship of V_(B) as a function of z is clarified.

α-cluster decay from ^(24)Mg resonances produced in the ^(12)C(^(16)O,^(24)Mg)α reaction

A transfer reaction and cluster-decay experiment,12C(16O,24Mg→ α+20Ne)α, was performed at a beam energy of 96 MeV. Both recoil and decay α particles were detected in coincidence, allowing us to deduce the energymomentum of a20Ne fragment. A number of resonant states of24Mg were reconstructed up to an excitation energy of approximately 30 MeV. Owing to the experimentally achieved excellent resolutions of the Q-value and excitationenergy spectra, the relative decay widths for each resonant state in24Mg to various final states of20Ne were extracted, along with the total decay width. The obtained results provide good testing ground for theoretical descriptions of multiple clustering configurations in24Mg.

质子滴线核^(17)F在近库仑势垒能区的反应机制研究进展

质子滴线核在近库仑势垒能区的反应机制研究是当前核物理领域的热点问题.本文对国内外开展的^(17)F在近库仑势垒能区的实验研究进行了回顾和总结.为了深入探索^(17)F的反应机制,本课题组相继开展了^(17)F+^(12)C,89Y和^(208)Pb的弹性散射研究以及^(17)F+^(58)Ni的全反应道研究.目前的弹性散射研究表明,在大范围的靶区内,^(17)F的破裂连续态对弹性散射的耦合效应并不显著.对于破裂反应,在近垒能区只有^(17)F+^(58)Ni体系的细致研究.研究表明,去弹破裂是主要的^(16)O产生机制.而对于熔合反应,目前只有^(17)F+^(58)Ni和^(208)Pb两个体系的实验结果.^(17)F+^(58)Ni体系在垒下表现出明显的总熔合截面增强现象.理论计算表明,这种增强主要是由^(17)F连续态的耦合效应导致.而对于^(17)F+^(208)Pb,其总熔合激发函数与^(19)F+^(208)Pb基本相同.^(17)F+^(58)Ni和^(208)Pb体系熔合激发函数的差异还需要进一步研究.

Bayesian analysis on non-resonant behavior of 12C+12C fusion reaction at sub-barrier energies

Controversies exist among experiments and theories on the S^(*)factor of the astrophysical important reaction ^(12)C+^(12)C for energies below 3 MeV.Only frequentist approaches have been used so far for data analysis,and the confidence levels or theoretical errors are not available from previous theoretical predictions.In this study,the Bayesian method is employed to provide theoretical predictions and its 1σconfidence level based on all the currently available experimental data for the first time.The improved coupled-channels model CCFULL-FEM implemented with the finite element method as well as the Markov chain Monte Carlo approach emcee are adopted to analyze the non-resonant behavior of this reaction.The posterior distribution of the Woods-Saxon potential parameters is investigated.Compared with the widely used frequentist method MIGRAD within the Minuit minimization program,the Bayesian method has a significant advantage for exploring the potential parameter space.When the existing experimental data measured down to subbarrier energies are considered,the potential parameters are constrained to a very narrow range,and the predictions of the S^(*) factor showed no sharp decrease in the low-energy region.

Relative probabilities of breakup channels in reactions of^(6.7)Li with^(209)Biat energies around and above the Coulomb barrier

Coincidence measurements of breakup fragments in reactions of^(6.7)with^(209)Bi at energies around and above the Coulomb barrier were carried out using a large solid-angle covered detector array.Through the Q values along with the relative energies of the breakup fragments,different breakup components(prompt breakups and delayed breakups)and different breakup modes(α+t,α+d,α+p,andα+α)are distinguished.A new breakup mode,α+t,is observed in^(6)Li-induced reactions at energies above the Coulomb barrier.Correlations between breakup modes and breakup components as well as their variations with the incident energy are investigated.The results will help us better understand the breakup effects of weakly bound nuclei on the suppression of a complete fusion,particularly for the above-barrier energies.