Light Charged Particle Emission Research Articles

Performance study of the Multi-purpose Time Projection Chamber (MTPC) using a four-component alpha source

The Multi-purpose Time Projection Chamber (MTPC) is a gas-filled detector designed to measure cross sections of neutron-induced light-charged particle emission and fission reactions at the Back-streaming white neutron facility (Back-n) at the China Spallation Neutron Source. A prototype MTPC has been constructed with a drift volume, a resistive Micromegas charge amplification structure, and a high-density pixelated anode readout plane with 1519 hexagonal pads. Test measurements have been performed using a four-component alpha source. Alpha-particle track reconstruction is performed to obtain the deposited energy and length information of the trajectory. The performance test and characterization of the detector have served as the basis for the optimized design of the MTPC, which is currently undergoing commissioning at Back-n.

The light charged particle detector array at the CSNS Back-n white neutron source

The Back-n white neutron source at the China Spallation Neutron Source (CSNS) provides neutrons in the continuous energy region from 0.5 eV to 200 MeV. A spectrometer named Light charged Particle Detector Array (LPDA) is designed for the study of (n, lcp) reactions at Back-n. The main detector of the LPDA spectrometer, a 16-unit ΔE-ΔE-E telescope array, is composed of two arrays of 8-unit ΔE-ΔE-E telescope. Each telescope unit consists of a Low-Pressure Multi-Wire Proportional Chamber (LPMWPC), a Si-PIN detector, and a CsI(Tl) scintillator detector. In 2021, a neutron-proton (n-p) scattering reaction cross-section measurement experiment was accomplished as the first experiment of the telescope array. Protons can be clearly identified in the ΔE-E spectrum (LPMWPC + Si-PIN) and the ΔE-E spectrum (Si-PIN + CsI(Tl)). Cross sections of the n-p scattering reaction in the neutron energy range of several MeV are extracted. The ΔE-E method also provides new measurement opportunities for many-body neutron induced light charged-particle emission reactions.

Research on the application of pulse shape discrimination method in (n, lcp) reaction cross-section measurements

The China Spallation Neutron Source Back-n white neutron source supplies neutrons with a wide energy range for nuclear data measurements and nuclear techniques. In cross-section measurements of neutron induced light charged-particle emission (n, lcp) reactions at Back-n, the identification of charged particles are usually achieved with the ΔE-E method or a two-dimensional spectrum of the signal amplitude of the particles deposited in the detector and the corresponding neutron energies derived from the time of flight, called amplitude-En method. Nevertheless, a deficiency still exists in the measurement range and the identification performance with these methods. The pulse shape discrimination (PSD) method with a silicon detector is supposed to be a supplement to the amplitude-En and ΔE-E methods. With silicon detectors, experiments have been performed to compare the performance of the amplitude-En and the PSD methods. The PSD method shows a good performance in identifying light charged particles in the MeV neutron energy region. Alphas and tritons emitted from 6Li(n, t) reaction can be identified with the low energy threshold around 2.5 MeV. This provides an effective method for the cross-section measurement of (n, lcp) reactions at Back-n.

Detector Development for a Double-Differential Cross Section Experiment with the Emission of Light Charged Particles from High Energy Neutrons

Detector Development for a Double-Differential Cross Section Experiment with the Emission of Light Charged Particles from High Energy Neutrons

Gap uniformity study of a resistive Micromegas for the Multi-purpose Time Projection Chamber (MTPC) at Back-n white neutron source

A Multi-purpose Time Projection Chamber prototype based on a resistive Micromegas technique has been proposed, designed and fabricated at China Spallation Neutron Source to measure the cross sections of neutron-induced light-charged particle emission reactions and fission reactions at the Back-n white neutron source. For the requirements of working stability with high voltage and high granularity of readout, the prototype is fabricated by applying a resistive Micromegas with high-density pixelated anode plane. In order to fully understand the process of charge spreading and signal induction on the anode plane covered by a resistive layer, a simulation method is developed and the energy correction function is then obtained, which can be used in the further energy correction in the experimental data analysis. Measured with a 55Fe X-ray source, the uniformity of gain and avalanche gap are specially analyzed by combining the simulated gas avalanche parameters with fitting of experimental data in which the parallel plate avalanche model is adopted.

Readout system for a prototype multi-purpose time projection chamber at CSNS Back-n

This paper presents a readout system for a prototype multi-purpose Time Projection Chamber (MTPC), which is developed for the research of neutron-induced light-charged particles emission reaction. The prototype MTPC consists of 1521 readout channels for charge measurements, track reconstruction, and neutron time-of-flight measurement. The main function of the readout system is to perform 1521-channel waveform digitization based on multi-channel analog to digital converters (ADCs). Digital waveform compression, multi-board time synchronization, and many other efforts have been made to ensure system performance and stability. Test results show that the readout system has a time resolution better than 10 ns at a trigger rate of 20 kHz. With a 2.8 pC dynamic range of charge measurement, the noise without any input load is around 0.76 fC (in RMS), and the nonlinearity of each channel is less than 0.35%. A beam test with 6Li target has been carried out at the back-streaming white neutron source (Back-n) of China Spallation Neutron Source. The tracks of particles from neutron-induced reactions have been successfully reconstructed. The time-of-flight distribution of the 6Li(n,α)3H reaction reveals the resonance peak at about 240 keV. These results indicate that the readout system fulfils the requirements of the prototype MTPC.

The New Physics in LILITA_N21: An Improved Description of the Reaction 190 MeV 40Ar + 27Al

In this paper, light charged particle emission in the evaporation residue channel for the 190 MeV 40Ar + 27Al reaction leading to 67Ga composite nuclei at Ex = 91 MeV and angular momentum up to 46 ℏ has been re-analyzed. The main goal was to study the decay of 67Ga on the basis of an extended set of observables in order to provide a description of the evaporative decay cascades using the multistep Monte Carlo approach. The proton and α-particle energy spectra along with their angular distributions and ratios of differential multiplicities have been considered. The measured observables were compared with statistical model calculations. Having used a single-step Monte Carlo approach and standard parameters decades ago, the model does not provide a good description of the full dataset. Only a subset of the data was reproduced by assuming emitting nuclei with very large deformed shapes in a previous work published in the late 1980s. In the reported analysis, better agreement has been observed. Using the new transmission coefficients from the Optical Model, the parameters of which have recently been derived, the multi-step approach and the introduction of a nuclear shape description based on the nuclear stratosphere allowed us to realize a significant improvement.

Light charged particle emission from Pb isotopes formed in n-induced channel and related structural analysis

Light charged particle emission from Pb isotopes formed in n-induced channel and related structural analysis

Nuclear reaction measurements of 80.5 MeV/u [formula omitted]C beam bombarding on C, Cu, W, Au, Pb targets

To get the energy distributions and cross sections of emitted light charged particles, and to explore the nuclear reaction, experiments of 80.5 MeV/u 12C beam bombarding on C, Cu, W, Au, Pb targets have been carried out at Institute of Modern Physics, Chinese Academy of Sciences. 30°, 60°, and 120° relative to the incident beam have been detected using three sets of telescope detectors. The method of ΔE−ΔE−E was used for particle identification. Results indicate that heavier targets have larger double differential cross sections, and the emitted fragments tend to go forward. Besides, the decrease of cross sections of fragments produced with the increasing emitted angles follows a kind of pattern.

Nonequilibrium information entropy approach to ternary fission of actinides

Ternary fission of actinides probes the state of the nucleus at scission. Light clusters are produced in space and time very close to the scission point. Within the nonequilibrium statistical operator method, a generalized Gibbs distribution is constructed from the information given by the observed yields of isotopes. Using this relevant statistical operator, yields are calculated taking excited states and continuum correlations into account, in accordance with the virial expansion of the equation of state. Clusters with mass number $A \le 10$ are well described using the nonequilibrium generalizations of temperature and chemical potentials. Improving the virial expansion, in-medium effects may become of importance in determining the contribution of weakly bound states and continuum correlations to the intrinsic partition function. Yields of larger clusters, which fail to reach this quasi-equilibrium form of the relevant distribution, are described by nucleation kinetics, and a saddle-to-scission relaxation time of about 7000 fm/c is inferred. Light charged particle emission, described by reaction kinetics and virial expansions, may therefore be regarded as a very important tool to probe the nonequilibrium time evolution of actinide nuclei during fission.

Isospin transport phenomena for the systems Kr80+Ca40,48 at 35 MeV/nucleon

Experimental data concerning isospin transport phenomena for the systems Kr80+Ca40,48 at 35 MeV/nucleon are presented. Data have been collected with four FAZIA blocks; this data set is the same analyzed in S. Piantelli , Phys. Rev. C 101, 034613 (2020)2469-998510.1103/PhysRevC.101.034613. The isotopic composition of the QuasiProjectile residue (up to Z around 25) and of its decay products in the two reactions are compared, finding a neutron enrichment when the target is Ca48. The isotopic composition of the emitted light charged particles (LCP) and intermediate mass fragments (IMF) was also investigated in different windows of velocity. The obtained results have been compared with the prediction of the transport model AMD followed by the statistical code GEMINI (used as an afterburner), with different recipes for the density dependence of the symmetry energy term in the nuclear equation of state. A weak indication in favor of a stiff symmetry energy emerges when the fragments emitted at midvelocity are examined.

Application of a silicon detector array in [formula omitted] reaction cross-section measurements at the CSNS Back-n white neutron source

The Back-n white neutron source at the China Spallation Neutron Source (CSNS) was put into operation in 2018, providing a good platform for the cross-section measurement of neutron induced light charged particle (lcp) emission (n,lcp) reactions. Currently, in order to detect and identify light charged particles produced in (n,lcp) reactions at Back-n, a silicon detector array has been developed as a part of Light-charged Particle Detector Array. Composed of 15 silicon detectors, the array can detect the emitted particles ranging from 19.2°to 160.8°. The energy resolution of each silicon detector unit is better than 1% for 5.499 MeV α particles. Adopting this silicon detector array, several experimental measurements have been completed. Differential cross sections and angle-integrated cross sections in the neutron energy region ranging from the eV to the MeV range are extracted. Compared with previous measurements and evaluations, new results are obtained in the present measurements. These experiments indicate the feasibility of the silicon detector array in (n,lcp) reaction cross-section measurements.

Measurements of neutron-induced light-charged particle emission reactions

In the past two decades cooperating with Frank Laboratory of Neutron Physics (FLNP), Joint Institute for Nuclear Research (JINR) measurements of (n, α) reaction cross sections for 6Li, 10B, 25Mg, 39K, 40Ca, 54,56,57 Fe, 58Ni, 63Cu, 64,67 Zn, 95Mo, 143Nd and 147,149 Sm nuclei were performed in the MeV neutron energy region based on the 4.5 MV Van de Graaff accelerator at Peking University. In recent years, our measurements were extended in three aspects. Firstly, measurements were expanded from two-body reactions to three-body reactions such as 10B (n, t2 α). Secondly, the neutron energy region was extended from below 8 MeV to 8 - 11 MeV by using the HI-13 tandem accelerator of China Institute of Atomic Energy (CIAE), with which cross sections of 54,56 Fe(n, α)53,51Cr reactions were measured. Thirdly, based on the newly-built China Spallation Neutron Source (CSNS) Back-n WNS (White Neutron Source), differential and angle-integrated cross sections for 6Li(n, t) and 10B(n, α) reactions were measured in the neutron energy region from 1 eV to 3 MeV.

Progress of experimental researches on neutron induced light charged-particle emission nuclear reactions

Progress of experimental researches on neutron induced light charged-particle emission (n,lcp) reactions, as well as the scientific significance, research methods and measurement difficulties, are comprehensively summarized. International investigations based on the n_TOF, LANSCE, ORELA and GELINA neutron sources are systematically introduced. Domestic investigations are presented entirely. The investigations performed by the Peking University group based on the 4.5 MV Van de Graaff accelerator for years are presented extensively, and recent developments based on Beijing HI-13 tandem accelerator and CSNS Back-n neutron sources are also introduced. Future domestic developments in this area are prospected.

Comparison between calculations with the AMD code and experimental data for peripheral collisions of Nb93+93Nb,116Sn at 38 MeV/nucleon

Experimental data concerning binary events in peripheral collisions for the systems 93Nb+93Nb and 93Nb+116Sn at 38 MeV/nucleon, collected with the Fiasco setup, are compared with calculations performed with the dynamic code AMD, coupled with the statistical code Gemini used as an afterburner. The comparison focuses on the properties of the quasiprojectile (QP) and on the total multiplicities of the emitted light charged particles. A good reproduction of the average mass ratio, charge Z and c.m. angle of the QP is obtained in the examined impact parameter range (b~7-12 fm). Concerning the light charged particles, a general agreement is found for the total emitted charge, while some discrepancy remains for the multiplicities of the various species, especially for the protons which are always overestimated by the calculations.

Intermediate Energy Reactions Versus Heavy-Ion Fusion: Light Particle Emission and Post-Saddle Friction in the Presence of Deformation Effects**Supported by the National Nature Science Foundation of China under Grant No. 11575044 and the Foundation of Nanjing University of Finance & Economics under Grant No. JGY1859

A decaying nucleus undergoes a change in deformation when it fissions. This affects the particle emission in the fission process. Using the dynamical Langevin model, we investigate the role of deformation in the sensitivity of post-saddle neutrons and light charged particles (LCPs) to the post-saddle friction strength (β) for heavy nuclei 240Am produced with different initial conditions: (i) a low excitation energy E* and a large spin ℓ (provided via a fusion mechanism) and (ii) a high E* and a large ℓ as well as a higher E* but a small ℓ (provided in peripheral and near-central intermediate energy heavy-ion reactions, respectively). It is shown that deformation obviously enhances the sensitivity of post-saddle neutrons to β at intermediate-energy peripheral collisions and that for case (i), the drop of LCPs emission due to deformation makes post-saddle LCPs to be almost insensitive to β, but for case (ii) LCPs still have a significant change with β. Furthermore, we find that post-saddle LCPs display a greater sensitivity to β for near-central collisions than for peripheral collisions. These results suggest that given the deformation effects, to better probe post-saddle dissipation properties with neutrons (LCPs) in experiments, it is best to choose those excited heavy nuclear systems populated in peripheral (near-central) collisions at intermediate energies.

Emission of light charged particles and fission fragments from Hf⁎ and Pt⁎ nuclei

Using dynamical cluster-decay model, the time scale of fission and light charged particles emitted in the decay of Hf⁎ and Pt⁎ nuclei is estimated. The decay analysis is carried out for isotopes and isobars of 170,174Hf⁎ and 170,174Pt⁎ nuclei. The structural information from the excited Hf⁎ and Pt⁎ nuclei is extracted using the fragmentation potential and preformation probability, which in turn accordingly influence the cross section yields. The cross sections of evaporation residue and fission-fragments are calculated by optimizing the neck length ΔR with in the frame work of dynamical cluster-decay model (DCM). The neck length ΔR provides significant information about the shape elongation of decaying fragments and in turn provides an insight of the reaction time scale. Applying momentum conservation, the velocity and time scale of fission fragments is calculated for 170Hf⁎ nucleus at temperature T=2.011MeV, which comes out of the order of (0.7–1)×10−21 s and the same for light charged particle is 0.5×10−21 s.

Comparative study of four reactions at onset of pre-equilibrium emission

The study of the emitted particles, comparing pre-equilibrium and thermal components, is a useful tool to examine the nuclear structure of emitters. Possible clustering effects, which may change the expected decay chain probability, could be highlighted on the competition between different reaction mechanisms. The NUCL-EX collaboration (INFN, Italy) has carried out an extensive research campaign on pre-equilibrium emission of light charged particles from hot nuclei. In this framework, the reactions 16O+30Si, 18O+28Si, 19F+27Al at 7 AMeV and 16O+30Si at 8 AMeV have been carried out using the GARFIELD+RCo array at Legnaro National Laboratories. Some anomalies in the α-particle emission channels have been evidenced in the measurement reported above, showing in an exclusive way the observed effects related to the entrance channels. The experimental results are compared to model prediction, for which the same filtering and complete event selection have been applied.

Effect of clustering on the emission of light charged particles

Energy spectra of light charged particles emitted in the reaction $p + {}^{27}\mathrm{Al} \rightarrow {}^{28}\mathrm{Si}^{\ast}$ have been studied and compared with statistical model calculation. Unlike 16O + 12C where a large deformation was observed in 28Si*, the energy spectra of $\alpha$ -particles were well explained by the statistical model calculation with standard “deformability parameters” obtained using the rotating liquid drop model. It seems that the $\alpha$ -clustering in the entrance channel causes extra deformation in 28Si* in the case of 16O + 12C, but the reanalysis of other published data shows that there are several cases where extra deformation was observed for composites produced via non- $\alpha$ -cluster entrance channels also. An empirical relation was found between mass-asymmetry in the entrance channel and deformation, which indicates that along with $\alpha$ -clustering, mass-asymmetry may also affect the emission of a light charged particle.

A STUDY ON 4 REACTIONS FORMING 46Ti*

The NUCL-EX collaboration is carrying out an extensive research program on preequilibrium emission of light charged particles from hot nuclei. The ultimate goal is to study how cluster structures affect nuclear reactions [1,2,3,4]. Indeed, a strong correlation between nuclear structure and reaction dynamics emerges when some nucleons or clusters of nucleons are emitted or captured [5]. At this purpose, the four reactions 16O+30Si, 16O+30Si, 18O+28Si and 19F +27Al have been measured at about 120 MeV projectile energy. Experimental data were collected at Legnaro National Laboratories, using the GARFIELD+RCo array, fully equipped with digital electronics [6]. Following an initial identification of particles and the energy calibration procedures, the complete analysis is being performed on an event-by-event basis. Experimental data are then compared to the theoretical predictions where events are generated by numerical codes based on pre-equilibrium and statistical models and then filtered through a software replica of the setup. Differences between the experimental data and the predicted data put into evidence effects related to the entrance channel and to the cluster nature of the colliding ions. After a general introduction on the experimental campaign, this contribution will focus on the preliminary results obtained so far.