Edims: an event-driven internal memory synchronized readout prototype ASIC chip developed for HFRS-TPC

HFRS(HIAF FRagment Separator) will be the radioactive secondary beam separation line on High-Intensity heavy-ion Accelerator Facility(HIAF) in China. Several TPC detectors, with high count rates, are planned for particle identification and beam monitoring at HFRS. This paper presents an event-driven internal memory and synchronous readout(EDIMS)prototype ASIC chip. The aim is to provide HFRS-TPC with high-precision time and charge measurements with high count rates and a large dynamic range. The first prototype EDIMS chip integrated 16 channels and is fabricated using a 0.18-μm CMOS process. Each channel consists of a charge-sensitive amplifier, fast shaper, slow shaper, peak detect-and-hold circuit, discriminator with time-walk compensation, analog memory, and FIFO. The token ring is used for clock-synchronous readout. The chip is taped and tested.

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.

Properties of Z=114 super-heavy nuclei

The center of the stability island of super-heavy nuclei(SHN)is the subject of intense experimental and theoretical investigations and has potential technological applications.^(298)^(114) Fl lies in the Z=114 isotopic chain as a persuasive candidate of the spherical double-magic nucleus in SHN,and in this study,the calculations of nuclear binding energies,one-nucleon and two-nucleon separation energies,a-decay energies,and the corresponding halflives provide strong evidence for this point.These calculations within an improved Weizsacker-Skyrme nuclear mass model(WS*)were performed and compared with the calculations of the finite-range droplet model(FRDM2012)and experimental data for Z=114 isotopes and N=184 isotones.Concurrently,the corresponding single-particle levels in a Woods-Saxon potential well with a spin-orbit term are calculated,which can be used as a powerful indicator to identify the shell effects existing in114298Fl.Both the study of the properties of the isotopic chain and microphysical quantities provide a vital signal that ^(298)^(114) Fl is a spherical double-magic nucleus and also the center of the SHN.

The NUBASE2016 evaluation of nuclear properties

This paper presents the NUBASE2016 evaluation that contains the recommended values for nuclear and decay properties of 3437 nuclides in their ground and excited isomeric （T1/2〉 100 ns） states. All nuclides for which any experimental information is known were considered. NUSASE2016 covers all data published by October 2016 in primary （journal articles） and secondary （mainly laboratory reports and conference proceedings） references, together with the corresponding bibliographical information. During the development of NUBASE2016, the data available in the ＂Evaluated Nuclear Structure Data File＂ （ENSDF） database were consulted and critically assessed for their validity and completeness. Furthermore, a large amount of new data and some older experimental results that were missing from ENSDF were compiled, evaluated and included in NUBASE2016. The atomic mass values were taken from the ＂Atomic Mass Evaluation＂ （AME2016, second and third parts of the present issue）. In cases where no experimental data were available for a particular nuclide, trends in the behavior of specific properties in neighboring nuclides （TNN） were examined. This approach allowed to estimate values for a range of properties that are labeled in NUBASE2016 as ＂non-experimental＂ （flagged ＂#＂）. Evaluation procedures and policies used during the development of this database are presented, together with a detailed table of recommended values and their uncertainties.

A method for determination of deuterium impurity in the helium beam

Both the LUNA(Laboratory for Underground Nuclear Astrophysics)collaboration in Europe and the JUNA(Jinping Underground Laboratory for Nuclear Astrophysics)collaboration in China are planning to study the key reactions during the stellar helium burning at or close to their stellar energies in deep underground laboratories[1-3].The success of such experiments relies on the ratio of the reaction

α particle preformation and shell effect for heavy and superheavy nuclei

The α particle preformation factor is extracted within a generalized liquid drop model for Z=84-92 isotopes and N=126, 128, 152, 162, 176, 184 isotones. The calculated results show clearly that the shell effects play a key role in α particle preformation. The closer the proton and neutron numbers are to the magic numbers, the more difficult the formation of the α cluster inside the mother nucleus is. The preformation factors of the isotopes reflect that N=126 is a magic number for Po, Rn, Ra, and Th isotopes, but for U isotopes the weakening of the influence of the N=126 shell closure is evident. The trend of the factors for N=126 and N=128 isotones also support this conclusion. We extend the calculations for N=152, 162, 176, 184 isotones to explore the magic numbers for heavy and superheavy nuclei, which are probably present near Z=108 to N=152, 162 isotones and Z=116 to N=176, 184 isotones. The results also show that another subshell closure may exist after Z=124 in the superheavy nuclei. This is useful for future experiments.

Relativistic Hartree-Fock model and its recent progress on the description of nuclear structure

Regarding the stage progress on the relativistic Hartree-Fock(RHF)model achieved recently,we review the extensive developments of the model itself,including the descriptions of axially deformed unstable nuclei and nuclear spin-isospin excitations,which shows that a complete RHF framework is now available for exploring the tensor force effects in both ground state and excited states of unstable nuclei.Meanwhile,the recent RHF descriptions of the pseudo-spin symmetry restoration and the new magicity are also reviewed.It shows that the Fock terms,particularly theρ-tensor coupling and naturally introduced tensor force components,bring about significant improvements in maintaining the delicate in-medium balance of nuclear attractions and repulsions,and uniformly interpreting the emergence of new magicity inCa.The revealed microscopic mechanisms not only deepen our understanding on the properties of nuclear structure,but also help to guide the further development of the effective nuclear force.

Stability of super heavy nuclei associated with the updated nuclear data

The stability of super heavy nuclei（SHN） from Z =104 to Z =126 is analyzed systematically,associated with the following theoretical mass tables： FRDM2012 [At.Data Nucl.Data Tables 109-110（2016）],WS2010 [Phys.Rev.C 82,044304（2010）],WS-LZ-RBF [J.Phys.G： Nucl.Part.Phys.42,095107（2015）] and the updated experimental data AME2016 [Chinese Physics C 41,040002（2017）].The nucleus with the biggest mean binding energy in each isotopic chain shows systematic regular behavior,indicating that the mean binding energy is a good criterion to classify SHN by their stability.Based on binding energy,the α-decay energy Qα,two-proton separation energy S2p,and two-neutron separation energy S2n are extracted and analyzed.It is found that N =152 and N =162 are sub-magic numbers,N = 184 is a neutron magic number,and Z = 114 is a proton magic number,which may provide useful information for the synthesis and identification of SHN.

Exploring effects of tensor force and its strength via neutron drops

The tensor-force effects on the evolution of spin-orbit spittings in neutron drops are investigated within the framework of the relativistic Hartree-Fock theory.For a fair comparison on the pure mean-field level,the results of the relativistic Brueckner-Hartree-Fock calculation with the Bonn A interaction are adopted as meta-data.Through a quantitative analysis,we certify that theπ-pscudovector(π-PV)coupling affects the evolutionary trend through the embedded tensor force.The strength of the tensor force is explored by enlarging the strength fr of theπ-PV coupling.It is found that weakening the density dependence of fn is slightly better than enlarging it with a factor.We thus provide a semiquantitative support for the renormalization persistency of the tensor force within the frame-work of density functional theory.This will serve as important guidance for further development of relativistic effective interactions with particular focus on the tensor force.

Improved empirical formula for α particle preformation factor

In this contribution,the α preformation factors of 606 nuclei are extracted within the framework of the generalized liquid drop model(GLDM).Through the systematic analysis of the α preformation factors of even-even Po-U isotopes,we found that there is a significant weakening of influence of N=126 shell closure in uranium,which is consistent with the results of a recent experiment [J.Khuyagbaatar et al.,Phys.Rev.Lett.115,242502(2015)],implying that N=126 may not be the magic number for U isotopes.Furthermore,we propose an improved formula with only 7 parameters to calculate α preformation factors suitable for all types of α-decay;it has fewer parameters than the original formula proposed by Zhang et al.[H.F.Zhang et al.,Phys.Rev.C 80,057301(2009)]with higher precision.The standard deviation of the α preformation factors calculated by our formula with extracted values for all 606 nuclei is 0.365 with a factor of 2.3,indicating that our improved formula can accurately reproduce the α preformation factors.Encouraged by this,the α-decay half-lives of actinide elements are predicted,which could be useful in future experiments.Notably,the predicted α-decay half-lives of two new isotopes 220 Np [Z.Y.Zhang,et al.,Phys.Rev.Lett.122,192503(2019)] and 219 Np [H.B.Yang et al.,Phys.Lett.B 777,212(2018)] are in good agreement with the experimental α-decay half-lives.

Unified mechanism behind the even-parity ground state and neutron halo of^(11)Be

Using the axially deformed relativistic Hartree-Fock-Bogoliubov(D-RHFB)model,we explore the mechanism behind the parity inversion and halo occurrence in^(11)Be,which are well reproduced by the RHF Lagrangian PKA1.It is illustrated that evidently enhanced deformation effects by theπ-pseudo-vector andρ-tensor couplings in PKA1 are crucial for correctly describing both the even-parity ground state(GS)and the neutron halo of^(11)Be.Coupling with the deformation,the intrude 1d_(5/2)component largely enhances the couplings between the evenparity orbit 1/2_(2)^(+)and the nuclear core to ensure an even-parity GS,whereas the 2s_(1/2)component therein dominates the halo formation in^(11)Be.Moreover,the deformed halo in^(11)Be is found to be stabilized by the attractive inherent correlations between the 1d_(5/2)and 2s_(1/2)components of the halo orbit 1/2_(2)^(+),instead of pairing correlations,which paves a new way for understanding the halo pictures in deformed unstable nuclei.

The AME2016 atomic mass evaluation (Ⅱ).Tables,graphs and references

This paper is the second part of the new evaluation of atomic masses, AME2016. Using least-squares adjustments to all evaluated and accepted experimental data, described in Part I, we derive tables with numerical values and graphs to replace those given in AME2012. The first table lists the recommended atomic mass values and their uncertainties. It is followed by a table of the influences of data on primary nuclides, a table of various reaction and decay energies, and finally, a series of graphs of separation and decay energies. The last section of this paper lists all references of the input data used in the AME2016 and the NUBASE2016 evaluations （first paper in this issue）.

Systematic study ofαdecay half-lives within the Generalized Liquid Drop Model with various versions of proximity energies

It is universally acknowledged that the Generalized Liquid Drop Model(GLDM)has two advantages over otherαdecay theoretical models:introduction of the quasimolecular shape mechanism and proximity energy.In the past few decades,the original proximity energy has been improved by numerous works.In the present work,the different improvements of proximity energy are examined when they are applied to the GLDM for enhancing the calculation accuracy and prediction ability ofαdecay half-lives for known and unsynthesized superheavy nuclei.The calculations ofαhalf-lives have systematic improvements in reproducing experimental data after choosing a more suitable proximity energy for application to the GLDM.Encouraged by this,theαdecay half-lives of even-even superheavy nuclei with Z=112-122 are predicted by the GLDM with a more suitable proximity energy.The predictions are consistent with calculations by the improved Royer formula and the universal decay law.In addition,the features of the predictedαdecay half-lives imply that the next double magic nucleus after ^(208)Pb is ^(298)Fl.

The AME2016 atomic mass evaluation

This paper is the first of two articles （Part I and Part II） that presents the results of the new atomic mass evaluation, AME2016. It includes complete information on the experimental input data （also including unused and rejected ones）, as well as details on the evaluation procedures used to derive the tables of recommended values given in the second part. This article describes the evaluation philosophy and procedures that were implemented in the selection of specific nuclear reaction, decay and mass-spectrometric results. These input values were entered in the least-squares adjustment for determining the best values for the atomic masses and their uncertainties. Details of the calculation and particularities of the AME are then described. All accepted and rejected data, including outweighted ones, are presented in a tabular format and compared with the adjusted values obtained using the least-squares fit analysis. Differences with the previous AME2012 evaluation are discussed and specific information is presented for several cases that may be of interest to AME users. The second AME2016 article gives a table with the recommended values of atomic masses, as well as tables and graphs of derived quantities, along with the list of references used in both the AME2016 and the NUBASE2016 evaluations （the first paper in this issue）.

Studies of the 2α and 3α channels of the ^(12)C+^(12)C reaction in the range of E_(c.m.)=8.9 MeV to 21 MeV using the active target Time Projection Chamber

The ^(12)C+^(12)C fusion reaction was studied in the range of E_(c.m.)=8.9 to 21 MeV using the active-target Time Projection Chamber.With full information on all tracks of the reaction products,cross sections of the^(12)C(^(12)C,^(8)Be)^(16)O_(g.s.)channel and the ^(12)C(^(12)C,3a)^(12)C channel could be measured down to the level of a few milibarns.The ^(12)C(^(12)C,^(8)Be)^(16)O_(g.s.)reaction channel was determined to be 10_(-8)^(+24) mb at E_(c.m.)=11.1 MeV,supporting the direct a transfer reaction mechanism.The ^(12)C(^(12)C,3α)^(12)C reaction channel was studied for the first time using an exclusive measurement.Our result does not confirm the anomaly behavior reported in the previous inclusive measurement by Kolata et al.[Phys.Rev.C 21,579(1980)].Our comparisons with statistical model calculations suggest that the 3 a channel is dominated by the fusion evaporation process at E_(c.m.)>19 MeV.The additional contribution of the 3 a channel increases the fusion reaction cross section by 10% at energies above 20 MeV.We also find that an additional reaction mechanism is needed to explain the measured cross section at E_(c.m.)<15 MeV at which point the statistical model prediction vanishes.

Effects of shell correction on α decay properties

The shell correction effects on the α decay properties of heavy and superheavy nuclei have been studied in a macroscopic-microscopic manner. The macroscopic part is constructed from the generalized liquid drop model（GLDM）, whereas the microscopic part, namely, the shell correction energy, brings about certain effects on the potential barriers and half-lives under a WKB approximation, which is emphasized in this work. The results show that the shell effects play a significant role in the estimation of the α decay half-lives within the actinide region.Predictions of the α decay half-lives are then generated for superheavy nuclei, which will provide useful information for future experiments.