Target Time Projection Chamber Research Articles

CO2 operation of an active target detector readout based on THGEM.

We present and discuss a systematic study of the operation of THick Gaseous Electron Multipliers (THGEM)-like structures in pure CO2, in view of possible applications as Active Target Time Projection Chambers (AT-TPC) readout. The ultimate goal is to use oxygen-rich gas as active medium to perform nuclear physics/astrophysics experiments on stable oxygen isotopes (16O,17O,18O). We report the measurement of the effective avalanche gain of ceramic Multi-layer THGEMs (M-THGEMs), for different geometries (two- and three-layers M-THGEM) at various pressures. In addition, we report the analysis of the tracking performance of a large-volume AT-TPC equipped with a position-sensitive MICROMEGAS detector and double-cascade THGEMs pre-amplification stage. The AT-TPC was irradiated with 6.1 MeV α-particles from a 252Cf source mounted inside the detector vessel, filled with pure CO2 at 50 torr. High gain operation was achieved in CO2 at relative low pressure (0< 15 torr), of interest for AT-TPC experiments. For higher pressure the operation of the detector became unstable. The maximum achievable gain decreased to lower value—below 103 at 450 torr. Through the image analysis of the α-particle tracks we computed an energy resolution of around 3% (FWHM) based on the α-particle range, while the energy resolution from the collected charge is around 5% (FWHM).

The Active Target Time Projection Chamber at NSCL

Reactions in inverse kinematics close to the Coulomb barrier offer unique opportunities to study exotic nuclei, but they are plagued by the difficulty to efficiently and precisely measure the characteristics of the emerging particles. The Active Target Time Projection Chamber (AT-TPC) offers an elegant solution to this dilemma. In this device, the detector gas of the time projection chamber is at the same time the target in which nuclear reactions take place. The use of this new paradigm offers several advantages over conventional inert target methods, the most significant being the ability to increase the luminosity of experiments without loss of resolution. The AT-TPC and some results obtained on resonant α scattering to explore the clustering properties of neutron-rich nuclei are presented, as well as fusion cross section results using a 10 Be radioactive beam. In addition, the first re-accelerated radioactive beam experiment using the fully commissioned ReA3 linac was conducted recently at the NSCL with the AT-TPC, where proton resonant scattering of a 4.6 MeV/u 46 Ar beam was used to measure the neutron single-particle strength in 47 Ar.

3-D tracking in a miniature time projection chamber

The three-dimensional (3-D) detection of millimeter-scale ionization trails is of interest for detecting nuclear recoils in directional fast neutron detectors and in direction-sensitive searches for weakly interacting massive particles (WIMPs), which may constitute the Dark Matter of the universe. We report on performance characterization of a miniature gas target Time Projection Chamber (TPC) where the drift charge is avalanche-multiplied with Gas Electron Multipliers (GEMs) and detected with the ATLAS FE-I3 Pixel Application Specific Integrated Circuit (ASIC). We report on measurements of gain, gain resolution, point resolution, diffusion, angular resolution, and energy resolution with low-energy X-rays, cosmic rays, and alpha particles, using the gases Ar:CO2 (70:30) and He:CO2 (70:30) at atmospheric pressure. We discuss the implications for future, larger directional neutron and Dark Matter detectors. With an eye to designing and selecting components for these, we generalize our results into analytical expressions for detector performance whenever possible. We conclude by demonstrating the 3-D directional detection of a fast neutron source.

Operation of a THGEM-based detector in low-pressure Helium

In view of a possible application as a charge-particle track readout for an Active Target Time Projection Chamber (AT-TPC), the operating properties of THick Gaseous Electron Multipliers (THGEM) in pure low-pressure Helium were investigated. This paper includes the effective gain dependence on pressure for different detector configurations (single-, double-, triple-cascade setup), long-term gain stability and energy resolution from tracks of 5.5 MeV alpha particles. Stable operational conditions and maximum detector gains of 104–107 have been achieved in pure Helium at pressure ranging from 100 torr up to 760 torr. Energy resolution of 6.65% (FWHM) for 690 keV of energy deposited by 5.5 MeV alpha particles at 350 torr was measured. The expected energy resolution for the full track is around 2.4% (FWHM). These results, together with the robustness of THGEM electrodes against spark damage, make THGEM structures highly competitive compared to other technologies considered for TPC applications in an active target operating with pure noble gases, requiring a high dynamic range and a wide operating pressure range down to few hundred torr.

Tests of Micro-Pattern Gaseous Detectors for active target time projection chambers in nuclear physics

Active target detection systems, where the gas used as the detection medium is also a target for nuclear reactions, have been used for a wide variety of nuclear physics applications since the eighties. Improvements in Micro-Pattern Gaseous Detectors (MPGDs) and in micro-electronics achieved in the last decade permit the development of a new generation of active targets with higher granularity pad planes that allow spatial and time information to be determined with unprecedented accuracy. A novel active target and time projection chamber (ACTAR TPC), that will be used to study reactions and decays of exotic nuclei at facilities such as SPIRAL2, is presently under development and will be based on MPGD technology. Several MPGDs (Micromegas and Thick GEM) coupled to a 2×2mm2 pixelated pad plane have been tested and their performances have been determined with different gases over a wide range of pressures. Of particular interest for nuclear physics experiments are the angular and energy resolutions. The angular resolution has been determined to be better than 1° FWHM for short traces of about 4cm in length and the energy resolution deduced from the particle range was found to be better than 5% for 5.5MeV α particles. These performances have been compared to Geant4 simulations. These experimental results validate the use of these detectors for several applications in nuclear physics.

Prototype AT-TPC: Toward a new generation active target time projection chamber for radioactive beam experiments

The Prototype AT-TPC, a detector based on time projection chamber (TPC) technology was built at the National Superconducting Cyclotron Laboratory, Michigan State University. The chamber gas, called the active target, of the Prototype AT-TPC is utilized simultaneously as a reaction target and a tracking medium of charged particles for measuring low-energy nuclear reactions. In pursuit of luminosity, efficiency and resolution for reaction studies at a new generation of radioactive isotope facilities, the Prototype AT-TPC provides one of the largest active volumes in the world measuring 25cm in diameter and 50cm long along the beam axis, millimeter-precision tracking capability, and a high electric field of 1kV/cm/atm for fast electron drift, which limits the detector dead time. Commissioning of the detector using standard alpha sources and radioactive 6He beams has demonstrated the detector's long-term stability as well as its performance, which allowed good reconstruction of reaction kinematics.

Test of a micromegas detector with helium-based gas mixtures for active target time projection chambers utilizing radioactive isotope beams

Abstract A Micromegas detector was tested in a helium–carbon dioxide mixture at atmospheric pressure. A stable operation of the detector was confirmed at a gain of over 103 for a standard alpha source of 241Am. In order to realize a position-dependent gain, an anode strip was biased while keeping the other strips at the ground potential. The gain of the biased strip was reduced by one order of magnitude without affecting the gains of the neighboring strips. The energy spectra at 3.7 MeV, the energy deposited by Am alpha particles in the sensitive region of the Micromegas, were obtained from the total charge and the charge deposit profile along the track. The energy resolutions for helium:carbon dioxide 90:10 mixture at a gas gain of about 100 were 11% FWHM for the former and 4% FWHM for the latter. The present results highlight the Micromegas as a promising electron amplifier of the forthcoming active target time projection chambers that will be dedicated to nuclear reactions with radioactive isotope beams.