Active Target Time Projection Chamber Research Articles

Cluster structure of 3α+p states in N13

Cluster states in N13 are extremely difficult to measure due to the unavailability of B9+α elastic-scattering data. Using β-delayed charged-particle spectroscopy of O13, clustered states in N13 can be populated and measured in the 3α+p decay channel. One-at-a-time implantation and decay of O13 was performed with the Texas Active Target Time Projection Chamber. 149β3αp decay events were observed and the excitation function in N13 reconstructed. Four previously unknown α-decaying excited states were observed in N13 at an excitation energy of 11.3, 12.4, 13.1, and 13.7 MeV decaying via the 3α+p channel. These states are seen to have a [9B(g.s)⨂α/p+C12(02+)], [9B(12+)⨂α], [9B(52+)⨂α], and [9B(52+)⨂α] structure, respectively. A previously seen state at 11.8 MeV was also determined to have a [p+C12(g.s.)/p+C12(02+)] structure. The overall magnitude of the clustering is not able to be extracted, however, due to the lack of a total width measurement. Clustered states in N13 (with unknown magnitude) seem to persist from the addition of a proton to the highly α-clustered C12. Evidence of the 12+ state in B9 was also seen to be populated by decays from N★13.Published by the American Physical Society2024

Performance of prototype dual gain multilayer thick gas electron multiplier with high-intensity heavy-ion beam injections in low-pressure hydrogen gas

Abstract A prototype Dual Gain Multilayer Thick Gas Electron Multiplier (DG-M-THGEM) with an active area of 10 cm × 10 cm was manufactured aiming at the production of a large-volume active-target time projection chamber which can work under the condition of high-intensity heavy-ion beam injections. The DG-M-THGEM has an alternating structure of electrodes and insulators. Effective gas gains of two regions, which are called beam and recoil regions, are separately controlled. Performance of the prototype DG-M-THGEM in hydrogen gas at a pressure of 40 kPa was evaluated. Irradiating a 132Xe beam, an effective gas gain lower than 100 with a charge resolution of 3% was achieved in the beam region while an effective gas gain of 2000 was maintained in the recoil region. Position distributions of measured charges along the beam axis were investigated in order to evaluate gain uniformity in the high-intensity beam injection. The gain shift was estimated by simulations considering space charges in the drift region. The gain shift was suppressed within 3% even at the beam intensity of 2.5 × 106 particles per second.

Machine learning method for 12C event classification and reconstruction in the active target time-projection chamber

Active target time projection chambers are important tools in low energy radioactive ion beams or gamma rays related researches. In this work, we present the application of machine learning methods to the analysis of data obtained from an active target time projection chamber. Specifically, we investigate the effectiveness of Visual Geometry Group (VGG) and the Residual neural Network (ResNet) models for event classification and reconstruction in decays from the excited 22+ state in 12C Hoyle rotation band. The results show that machine learning methods are effective in identifying 12C events from the background noise, with ResNet-34 achieving an impressive precision of 0.99 on simulation data, and the best performing event reconstruction model ResNet-18 providing an energy resolution of σE<77 keV and an angular reconstruction deviation of σθ<0.1 rad. The promising results suggest that the ResNet model trained on Monte Carlo samples could be used for future classifying and predicting experimental data in active target time projection chambers related experiments.

β^{+} Gamow-Teller Strengths from Unstable ^{14}O via the (d,^{2}He) Reaction in Inverse Kinematics.

For the first time, the (d,^{2}He) reaction was successfully used in inverse kinematics to extract the Gamow-Teller transition strength in the β^{+} direction from an unstable nucleus. The new technique was made possible by the use of an active-target time-projection chamber and a magnetic spectrometer, and opens a path to addressing a range of scientific challenges, including in astrophysics and neutrino physics. In this Letter, the nucleus studied was ^{14}O, and the Gamow-Teller transition strength to ^{14}N was extracted up to an excitation energy of 22MeV. The data were compared to shell-model and state-of-the-art coupled-cluster calculations. Shell-model calculations reproduce the measured Gamow-Teller strength distribution up to about 15MeV reasonably well, after the application of a phenomenological quenching factor. In a significant step forward to better understand this quenching, the coupled-cluster calculation reproduces the full strength distribution well without such quenching, owing to the large model space, the inclusion of strong correlations, and the coupling of the weak interaction to two nucleons through two-body currents.

First Observation of the β3αp Decay of ^{13}O via β-Delayed Charged-Particle Spectroscopy.

The β-delayed proton decay of ^{13}O has previously been studied, but the direct observation of β-delayed 3αp decay has not been reported. Rare 3αp events from the decay of excited states in ^{13}N^{⋆} provide a sensitive probe of cluster configurations in ^{13}N. To measure the low-energy products following β-delayed 3αp decay, the Texas Active Target (TexAT) time projection chamber was employed using the one-at-a-time β-delayed charged-particle spectroscopy technique at the Cyclotron Institute, Texas A&M University. A total of 1.9×10^{5} ^{13}O implantations were made inside the TexAT time projection chamber. A total of 149 3αp events were observed, yielding a β-delayed 3αp branching ratio of 0.078(6)%. Four previously unknown α-decaying excited states were observed in ^{13}N at 11.3, 12.4, 13.1, and 13.7MeV decaying via the 3α+p channel.

Performance study of novel micro-Resistive WELL (μ-RWELL) detector in different gas mixtures

Versatility of micro-pattern gaseous detectors (MPGD) make them suitable for the use in various fields of study, e.g. nuclear physics, particle physics, dark matter physics along with a wide range of medical and security applications. Our primary interest was to implement the novel μ-RWELL (micro-Resistive WELL) detector as the gas amplification stage in TACTIC, a cylindrical active target time projection chamber (TPC) designed to study nuclear reactions with astrophysical significance. In preparation towards their installation inside TACTIC, the performance and characteristics of μ-RWELL were studied in a test chamber, a planar analogue of TACTIC. This work reports the high gas gains achieved in Ar:CH4 and He:CO2 and a study of the charging-up effect in He:CO2.

Simulations and analysis tools for charge-exchange (d, 2He) reactions in inverse kinematics with the AT-TPC

Charge-exchange (d,2He) reactions in inverse kinematics at intermediate energies are a very promising method to investigate the Gamow–Teller transition strength in unstable nuclei. A simulation and analysis software based on the attpcroot package was developed to study this type of reactions with the active-target time projection chamber (AT-TPC). The simulation routines provide a realistic detector response that can be used to understand and benchmark experimental data. Analysis tools and correction routines can be developed and tested from simulations in attpcroot, because they are processed in the same way as the real data. In particular, we study the feasibility of using coincidences with beam-like particles to unambiguously identify the (d,2He) reaction channel, and to develop a kinematic fitting routine for future applications. More technically, the impact of space-charge effects in the track reconstruction, and a possible correction method are investigated in detail. This analysis and simulation package constitutes an essential part of the software development for the fast-beams program with the AT-TPC.

Compact 3-T superconducting magnet for nucleosynthesis reaction experiments

A compact 3-T superconducting magnet with an active-target time projection chamber and a gamma-ray detector array was constructed for stellar nucleosynthesis studies. This magnet was newly developed based on the previous 1.5-T Helmholtz magnet (Kim and Ahn, 2021) to achieve higher magnetic field and larger space for the detector system. Conduction-cooled Helmholtz coils with an inner diameter of 40 cm generate a central magnetic field of up to 3.0 T at a current of 90.5 A. The operational goal is 2.5 T in nucleosynthesis experiments. The magnet has a large opening between two coils to accommodate the active-target time projection chamber and the gamma-ray detector array. The magnet operates at ramping rates of 0.008–0.02 A/s without quenching and generates highly uniform magnetic field strength within 1% of the central value over a volume of 10 × 10 × 10 cm3, covering a size of active-target time projection chamber. Herein, we report the results of the first excitation test and the field mapping.

Warsaw Active-Target TPC: A new detector for photonuclear reactions studies at astrophysical energies

An active-target time-projection chamber (TPC) optimised for studying nuclear reactions of astro-physical interest was developed by the University of Warsaw for studying photo-disintegration reactions using intense, monochromatic γ-ray beams. Different reactions can be studied by tuning composition and density of the gaseous target for particular energy of the gamma beam. The Warsaw TPC detector, with its active volume of about 33x20x20 cm3 centred around the beam axis and micro-pattern structures (GEMs) employed to amplify the primary ionisation induced by charged particles produced in reactions in the gaseous target, is characterised by a readout based on signal strips, arranged into 3-coordinate redundant system. The 3D kinematics of charged particles in the event are reconstructed from a total of about 103 channels read out by digitising front-end electronics based on the General Electronics for TPCs (GET). In this paper the principles of detector operation and basic track reconstruction methods are discussed and illustrated by means of preliminary results from pilot measurements conducted in 2021-22.

Numerical Studies on Primary Ionization in TPC

Identification followed by directionality measurement using reconstruction of tracks is very crucial for studying the reaction vertex kinematics. In the field of low-energy nuclear physics, Active-Target Time Projection Chambers (AT-TPCs) can be used to study the nuclear reaction kinematics through tracking of the reaction products which is important for cross-section measurement. Ions produced in primary ionization by any charged particle along their track in the active gas volume of TPC can be utilized for track reconstruction with position-sensitive electron collection system placed inside an electric field. The TPC gas volume acts as the tracker of the reaction products and the target for the reaction with the incoming projectile simultaneously which is advantageous to conventional detector arrays. In this context, the design of the electric field in the drift volume of the TPC is an important criterion for precise tracking as the tracking capability of the TPC is strongly governed by the homogeneity of the electric field. Due to the lesser mobility of positive ions produced in primary ionization, their accumulation in the drift volume can distort the local electric field. In low-energy nuclear physics, this effect may be substantial due to the significant amount of ionization produced by the low-energy projectile and reaction products. Here we report the spatial information of primary space charges produced by cosmic muon and alpha particle obtained with geant4 [1] and Heed [2] simulation packages. We have used photo absorption and ionization physics lists in geant4 for the simulation and compared the results with that of the Heed. The simulation results for the change in pressure of gas volume will be reported. These results can be used for finding the distortion of the electric field due to the space charge in the drift region of the TPC which can be helpful for designing an AT-TPC for low-energy nuclear reaction experiments.

Studies of the 2α and 3α channels of the 12C+12C reaction in the range of E c.m.=8.9 MeV to 21 MeV using the active target Time Projection Chamber* *Supported in part by the Strategic Priority Research Program of Chinese Academy of Sciences (XDB34020200), the National Key Research and Development program (MOST 2016YFA0400501) from the Ministry of Science and Technology of

The 12C+12C 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 12C(12C,8Be)16Og.s. channel and the 12C(12C,3α)12C channel could be measured down to the level of a few milibarns. The 12C(12C,8Be)16Og.s. reaction channel was determined to be 10 mb at E c.m.=11.1 MeV, supporting the direct α transfer reaction mechanism. The 12C(12C,3α)12C 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 3α channel is dominated by the fusion evaporation process at E c.m. > 19 MeV. The additional contribution of the 3α 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.

Neutron-upscattering enhancement of the triple-alpha process

The neutron inelastic scattering of carbon-12, populating the Hoyle state, is a reaction of interest for the triple-alpha process. The inverse process (neutron upscattering) can enhance the Hoyle state’s decay rate to the bound states of 12C, effectively increasing the overall triple-alpha reaction rate. The cross section of this reaction is impossible to measure experimentally but has been determined here at astrophysically-relevant energies using detailed balance. Using a highly-collimated monoenergetic beam, here we measure neutrons incident on the Texas Active Target Time Projection Chamber (TexAT TPC) filled with CO2 gas, we measure the 3α-particles (arising from the decay of the Hoyle state following inelastic scattering) and a cross section is extracted. Here we show the neutron-upscattering enhancement is observed to be much smaller than previously expected. The importance of the neutron-upscattering enhancement may therefore not be significant aside from in very particular astrophysical sites (e.g. neutron star mergers).

Digital signal analysis based on convolutional neural networks for active target time projection chambers

An algorithm for digital signal analysis using convolutional neural networks (CNN) was developed in this work. The main objective of this algorithm is to make the analysis of experiments with active target time projection chambers more efficient. The code is divided in three steps: baseline correction, signal deconvolution and peak detection and integration. The CNNs were able to learn the signal processing models with relative errors of less than 6%. The analysis based on CNNs provides the same results as the traditional deconvolution algorithms, but considerably more efficient in terms of computing time (about 65 times faster). This opens up new possibilities to improve existing codes and to simplify the analysis of the large amount of data produced in active target experiments.

The Notre-Dame Cube: An active-target time-projection chamber for radioactive beam experiments and detector development

Active-target detectors have the potential to address the difficulties associated with the low intensities of radioactive beams. We have developed an active-target detector, the Notre Dame Cube (ND-Cube), to perform experiments with radioactive beams produced at TwinSol and to aid in the development of active-target techniques. Various aspects of the ND-Cube and its design were characterized. The ND-Cube was commissioned with a 7Li beam for measuring 40Ar + 7Li fusion reaction cross sections and investigating 7Li(α, α)7Li scattering events. The ND-Cube will be used to study a range of reactions using light radioactive ions produced at low energy.

Unsupervised learning for identifying events in active target experiments

This article presents novel applications of unsupervised machine learning methods to the problem of event separation in an active target detector, the Active-Target Time Projection Chamber (AT-TPC) (Bradt, 2017). The overarching goal is to group similar events in the early stages of the data analysis, thereby improving efficiency by limiting the computationally expensive processing of unnecessary events. The application of unsupervised clustering algorithms to the analysis of two-dimensional projections of particle tracks from a resonant proton scattering experiment on 46Ar is introduced. We explore the performance of autoencoder neural networks and a pre-trained VGG16 (Simonyan and Zisserman, 2015) convolutional neural network. We study clustering performance on both data from a simulated 46Ar experiment, and real events from the AT-TPC detector. We find that a k-means algorithm applied to simulated data in the VGG16 latent space forms almost perfect clusters. Additionally, the VGG16+k-means approach finds high purity clusters of proton events for real experimental data. We also explore the application of clustering the latent space of autoencoder neural networks for event separation. While these networks show strong performance, they suffer from high variability in their results.

First Direct Measurement of ^{22}Mg(α,p)^{25}Al and Implications for X-Ray Burst Model-Observation Comparisons.

Type-I x-ray bursts can reveal the properties of an accreting neutron star system when compared with astrophysics model calculations. However, model results are sensitive to a handful of uncertain nuclear reaction rates, such as ^{22}Mg(α,p). We report the first direct measurement of ^{22}Mg(α,p), performed with the Active Target Time Projection Chamber. The corresponding astrophysical reaction rate is orders of magnitude larger than determined from a previous indirect measurement in a broad temperature range. Our new measurement suggests a less-compact neutron star in the source GS1826-24.

Conduction-Cooled Superconducting Magnet for Active-Target TPC Experiments at RAON

A compact superconducting magnet was constructed for low-energy nuclear physics experiments at the RAON heavy-ion accelerator facility. Conduction-cooled Helmholtz coils with a radius of 40 cm generate a uniform magnetic field of up to 1.51 Tat a current of 71 A. The magnet has two crossing beam windows that allows the beam to pass either parallel (solenoid mode) or perpendicular (dipole mode) to the field direction. The magnet operates at a ramping rate of 0.01 A/s without quenching and generates a highly uniform magnetic induction within 0.1% of the central value of 1.51 T over the volume of 10 × 10 × 10 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> corresponding to the size of an active target time projection chamber. Herein, we report our first excitation test and field mapping results.

Texas Active Target (TexAT) detector for experiments with rare isotope beams

The TexAT (Texas Active Target) detector is a new active-target time projection chamber (TPC) that was built at the Cyclotron Institute Texas A&M University. The detector is designed to be of general use for nuclear structure and nuclear astrophysics experiments with rare isotope beams. TexAT combines a highly segmented Time Projection Chamber (TPC) with two layers of solid state detectors. It provides high efficiency and flexibility for experiments with low intensity exotic beams, allowing for the 3D track reconstruction of the incoming and outgoing particles involved in nuclear reactions and decays.

Beam-induced space-charge effects in time projection chambers in low-energy nuclear physics experiments

Tracking capabilities in Time Projection Chambers (TPCs) are strongly dictated by the homogeneity of the drift field. Ion back-flow in various gas detectors, mainly induced by the secondary ionization processes during amplification, has long been known as a source of drift field distortion. Here, we report on beam-induced space-charge effects from the primary ionization process in the drift region in low-energy nuclear physics experiment with Active Target Time Projection Chamber (AT-TPC). A qualitative explanation of the observed effects is provided using detailed electron transport simulations. As ion mobility is a crucial factor in the space-charge effects, the need for a careful optimization of gas properties is highlighted. The impact of track distortion on tracking algorithm performance is also discussed.

Direct Observation of Proton Emission in ^{11}Be.

The elusive β^{-}p^{+} decay was observed in ^{11}Be by directly measuring the emitted protons and their energy distribution for the first time with the prototype Active Target Time Projection Chamber in an experiment performed at ISAC-TRIUMF. The measured β^{-}p^{+} branching ratio is orders of magnitude larger than any previous theoretical model predicted. This can be explained by the presence of a narrow resonance in ^{11}B above the proton separation energy.