Commissioning of the Active-Target Time Projection Chamber Bradt, J.; Bazin, D.; Abu-Nimeh, F. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
12/2017, Letnik:
875
Journal Article
Recenzirano
Odprti dostop
The Active-Target Time Projection Chamber (AT-TPC) was recently built and commissioned at the National Superconducting Cyclotron Laboratory at Michigan State University. This gas-filled detector uses ...an active-target design where the gas acts as both the tracking medium and the reaction target. Operating inside a 2T solenoidal magnetic field, the AT-TPC records charged particle tracks that can be reconstructed to very good energy and angular resolutions. The near-4π solid angle coverage and thick target of the detector are well-suited to experiments with low secondary beam intensities. In this paper, the design and instrumentation of theAT-TPC are described along with the methods used to analyze the data it produces. A simulation of the detector’s performance and some results from its commissioning with a radioactive 46Ar beam are also presented.
Shell closures and their associated magic numbers of nucleons provide a unique means for studying the structure of exotic nuclei far from stability. An experiment was recently performed at the ...National Superconducting Cyclotron Laboratory to measure resonant elastic proton scattering on 46Ar in inverse kinematics in the region containing isobaric analogue states of 47Ar, an N=29 nucleus with one neutron above the N=28 shell closure. Four candidate resonances were observed: one corresponding to the 3/2− ground state of 47Ar, another corresponding to its 1/2− first excited state, and two that likely correspond to states in the 47K compound nucleus. The observed properties of the ground state resonance were compatible with values from the literature, but a significantly lower spectroscopic factor was found for the 1/2− state resonance.
.
Many nuclear structure studies are presently performed with secondary radioactive beams to explore the nuclear chart far from stability. This entails a large decrease of available intensities, as ...compared to stable beam experiments, even with the highest power primary beam accelerators. To compensate for this intensity loss, thick targets and high detection efficiency are needed. Using secondary beams implies a change from direct kinematics to inverse kinematics: the target becomes the light reaction partner and the beam the heavy reaction partner. In quasi-elastic processes, the light reaction partner carrying most of the information emerges with very low recoil energy. In these conditions Time Projections Chambers (TPCs) filled with a gas that serves as both target and tracking medium (Active Target) have very unique properties that mitigate these difficulties. By construction, a TPC has a solid angle coverage of
4
π
, and even short tracks of low energy particles can be precisely measured if the readout has a high enough granularity. Due to the reaction characteristics large dynamics of the electronics and gas multipliers are needed, and specific data analysis methods of the 3-dimensional tracks have to be developed.
Weakly bound nuclear systems can be considered to represent a good testing-ground of our understanding of non-perturbative quantum systems. Reactions leading to bound and unbound states in systems ...with very unbalanced neutron-to-proton ratios are used to understand the properties of these systems. Radioactive beams with energies from below the Coulomb barrier up to several hundreds MeV/nucleon are now available, and with these beams, a broad variety of studies of nuclei near the drip-line can be performed. To compensate for the low intensity of secondary beams as compared to primary beams, thick targets and high efficiency detection is necessary. In this context, a new generation of detectors was developed, called active target detectors: the detector gas is used as target, and the determination of the reaction vertex in three dimensions allows for good resolution even with thick targets. The reaction products can be measured over essentially 4π. The physics explored with these detectors together with the technology developed will be described.
General Electronics for TPCs (GET) is a generic, reconfigurable and comprehensive electronics and data-acquisition system for nuclear physics instrumentation of up to 33792 channels. The system ...consists of a custom-designed ASIC for signal processing, front-end cards that each house 4 ASIC chips and digitize the data in parallel through 12-bit ADCs, concentration boards to read and process the digital data from up to 16 ASICs, a 3-level trigger and master clock module to trigger the system and synchronize the data, as well as all of the associated firmware, communication and data-acquisition software. An overview of the system including its specifications and measured performances are presented.
The study of low-energy reactions with radioactive-ion beams has been greatly enhanced by the recent use of active-target detectors, which have high efficiency and low thresholds to detect low-energy ...charged-particle decays. Both of these features have been used in experiments with the Prototype Active-Target Time-Projection Chamber to study α-cluster structure in unstable nuclei and 3-body charged-particle decays after implantation. Predicted α-cluster structures in 14C were probed using resonant α scattering and the nature of the 3-α breakup of the 02+ Hoyle state in 12C after the beta decay of 12N and 12B was studied. These experiments used in-flight radioactive-ion beams that were produced using the dual superconducting solenoid magnets TwinSol at the University of Notre Dame. Preliminary results from these experiments as well as the development of future radioactive beams to be used in conjunction with the PAT-TPC are presented.
Isobaric single charge-exchange reactions, changing nuclear charges by one unit but leaving the mass partitions unaffected, have been for the first time investigated by peripheral collisions of 112Sn ...ions accelerated up to 1A GeV at the GSI facilities. The high-resolving power of the FRS spectrometer allows us to obtain (p,n)-type isobaric charge-exchange cross sections with an uncertainty of 3.5% and to separate quasi-elastic and inelastic components in the missing-energy spectra of the ejectiles. The inelastic component is associated to the excitation of the Δ(1232) isobar resonance and the emission of pions in s-wave both in the target and projectile nucleus, while the quasi-elastic contribution is associated to the nuclear spin-isospin response of nucleon-hole excitations. An apparent shift of the Δ-resonance peak of ∼63 MeV is observed when comparing the missing-energy spectra obtained from the measurements with proton and carbon targets. A detailed analysis, performed with a theoretical model for the reactions, indicates that this observation can be simply interpreted as a change in the relative magnitude between the contribution of the excitation of the resonance in the target and in the projectile.
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.
Abstract
Isobaric charge-exchange reactions induced by beams of
112
Sn have been investigated at the GSI facility using the fragment separator FRS. The high-resolving power of this spectrometer makes ...it possible to obtain the isobaric charge-exchange cross sections with an uncertainty of 3.5% and to separate quasi-elastic and inelastic contributions in the missing-energy spectra, in which the inelastic component is associated to the in-medium excitation of baryonic resonances such as the Δ resonance. We report on the results obtained for the (
p,n
) channel excited by using different targets that cover a large range in neutron excess. In addition, we also compare the missing-energy spectra with an intranuclear cascade model coupled to a de-excitation code to investigate the in-medium effects in the production of baryonic resonances.
PDF
