Liquid Argon Ionization Chamber Research Articles

Application and development of liquid argon detector in rare event detection

Rare event detection is a frontier subject in particle physics and nuclear physics. In particular, dark matter detection, neutrino-free double beta decay and neutrino-nucleon coherent elastic scattering are being planned and implemented gradually. Rare event detection requires not only the detectors to possess excellent performances but also extremely low environmental background, so the selection of detectors and related materials is an important issue in rare event detection. Liquid argon has become an important scintillator material for scintillator detectors because of its low cost, good scintillation performance and large volume. Liquid argon was first studied in the 1940s as a sensitive material for ionizing radiation detectors. The first measurements of high-energy beta particles were obtained by using a liquid argon ionization chamber in 1953. The ICARUS group put forward the idea of constructing liquid argon temporal projection chamber, and made attempt to construct liquid argon temporal projection chamber in 1977. The scintillation light signals were collected for the first time in a liquid argon temporal projection chamber in 1999. Thus, the drift time of the particle can be obtained to determine the particle track. After development, single-phase liquid argon scintillator detector and two-phase argon time projection chamber have become two common types of liquid argon detectors, and have been extensively used in rare event detection experiments in recent years. For dark matter detection, the DEAP group and DarkSide group have achieved good results with single-phase liquid argon scintillation detector and two-phase argon time projection chamber, respectively. For neutrino-free double beta decay experiments, the GERDA group has done a lot of researches of liquid argon anti-coincidence system and applied the said system to experiments. The LEGEND group, which is the combination of GERDA and MAJORANA experimental group, upgraded the liquid argon anti-coincidence system which was applied to the following LEGEND-200 project. For neutrino-nucleon elastic scattering experiments, COHERENT obtained the latest results by using the liquid argon detectors. The Taishan neutrino-nucleon coherent elastic scattering project of the High Energy Institute of Chinese Academy of Sciences has also begun to study the feasibility of liquid argon anti-coincidence system. Finally, this paper discusses the direction of optimizing the liquid argon detector, such as exposure, background level and optical readout scheme, and gives a good prospect of liquid argon detector applied to rare event detection in the future.

On concentration of 42Ar in the Earth's atmosphere

Data from the DBA liquid argon ionization chamber experiment have been used to obtain an estimate on the concentration of 42Ar in the Earth's atmosphere, 6.8−3.2+1.7·10−21 atoms of 42Ar per atom of 40Ar corresponding to the 42Ar activity of 1.2−0.5+0.3μBq per cubic meter of air.

On concentration of 42Ar in liquid argon

Data from the DBA liquid argon ionization chamber experiment were used to obtain an estimate on the concentration of 42Ar in the Earth’s atmosphere, 9.2+2.2-4.6. 10-21 atoms of 42 Ar/ atom of 40Ar. This corresponds to a specific activity of freshly produced liquid argon of 92+22-46 /µBq/kg.

Space-charge effects in liquid argon ionization chambers

We have uniformly irradiated liquid argon ionization chambers with betas from high-activity 90Sr sources. The radiation environment is similar to that in the liquid argon calorimeters which are part of the ATLAS detector installed at CERN׳s Large Hadron Collider (LHC). We measured the resulting ionization current over a wide range of applied potential for two different source activities and for three different chamber gaps. These studies provide operating experience at exceptionally high ionization rates. In particular they indicate a stability at the 0.1% level for these calorimeters over years of operation at the full LHC luminosity when operated in the normal mode at an electric field E=1.0kV/mm. We can operate these chambers in the normal mode or in the space-charge limited regime and thereby determine the transition point between the two. This transition point is parameterized by a positive argon ion mobility of μ+=0.08±0.02mm2/Vs at a temperature of 88.0±0.5K and at a pressure of 1.02±0.02bar. In the space-charge limited regime the ionization currents are degraded and show signs of instability. At the highest electric fields in our study (6.7kV/mm) the ionization current is still slowly rising with increasing electric field.

First demonstration of a sub-keV electron recoil energy threshold in a liquid argon ionization chamber

We describe the first demonstration of a sub-keV electron recoil energy threshold in a dual-phase liquid argon time projection chamber. This is an important step in an effort to develop a detector capable of identifying the ionization signal resulting from nuclear recoils with energies of order a few keV and below. We obtained this result by observing the peaks in the energy spectrum at 2.82keV and 0.27keV, following the K- and L-shell electron capture decay of 37Ar respectively. The 37Ar source preparation is described in detail, since it enables calibration that may also prove useful in dark matter direct detection experiments. An internally placed 55Fe x-ray source simultaneously provided another calibration point at 5.9keV. We discuss the ionization yield and electron recombination in liquid argon at those three calibration energies.

Luminosity limits for liquid argon calorimetry

We have irradiated liquid argon ionization chambers with betas using high-activity Strontium-90 sources. The radiation environment is comparable to that in the liquid argon calorimeters which are part of the ATLAS detector installed at CERN's Large Hadron Collider. We measure the ionization current over a wide range of applied potential for two different source activities and for three different chamber gaps. These studies provide operating experience at exceptionally high ionization rates. We can operate these chambers either in the normal mode or in the space-charge limited regime and thereby determine the transition point between the two. From the transition point we indirectly extract the positive argon ion mobility.

A correction to Birks' Law in liquid argon ionization chamber simulations for highly ionizing particles

We present a study of the performance of Birks' Law in liquid argon ionization chamber simulations as applied to highly ionizing particles, such as particles with multiple electric charges or with magnetic charge. We used Birks' Law to model recombination effects in a Geant4 simulation of heavy ions in a liquid argon calorimeter. We then compared the simulation to published heavy-ion data to extract a highly ionizing particle correction to Birks' Law.

Onset of space charge effects in liquid argon ionization chambers

Using a thin-gap liquid argon ionization chamber and Strontium-90 beta sources we have measured ionization currents over a wide range of gap potentials. These precision “HV plateau curves” advance the understanding of liquid argon sampling calorimeter signals, particularly at high ionization rates. The order of magnitude differences in the activities of the beta sources allow us to estimate where the ionization chamber is driven into the space-charge dominated regime.

Double beta decay of 100Mo

Using a liquid argon ionization chamber the 2νββ decay of 100Mo was detected with its half-life of [7.2 ± 0.9( stat) ± 1.8( syst)] · 10 18 y. The limits on half-lives for 0ν- and 0νχ 0 -decays of 100Mo were estimated as 8.4(4.9) · 10 21 y and 4.1(3.2) · 10 20 y respectively at 68(90)% CL. Available world data for the 2νββ decay of 100Mo lead to the average “world” value of the half-life, T 1 2 = (8.0 ± 0.7) · 10 18 y, that corresponds to the nuclear matrix element, M GT = 0.118 ± 0.005.

Double beta decay of 100Mo

Two-neutrino double beta decay of 100Mo with half-life T 1/2=[7.2±0.9(stat)± 1.8(syst)]×1018 yr was detected using a liquid argon ionization chamber. With a C.L. of 68% (90%), the bounds on neutrinoless decay and decay with majoron emission were found to be 8.4(4.9)×1021 and 4.1(3.2)×1020 yr, respectively. An analysis of all available results provides the average “world” value T 1/2=(8.0±0.7)×1018 yr for the two-neutrino decay of 100Mo, and the corresponding nuclear matrix element is M GT=0.118±0.005.

Method for background reduction in an experiment devoted to WIMP searches with a liquid-xenon (liquid-argon) ionization chamber

A method for detecting ultraviolet photons from Xe 2 * deexitation with an efficiency of nearly 100% is proposed. This method allows a reliable discrimination between Xe (Ar) recoil nuclei and background electrons. As a result, the β and γ background is almost completely suppressed. The neutron background can be reduced by water shielding and by selection of events involving only one recoil nucleus. The developed grid screen will remove the photon feedback. The small prototype TPC with a preliminary multiplication of ionization electrons in a proportional gap and a subsequent detection of the multiplied charges in the induction gap is constructed. The shape of an electron component of the proportional signal is obtained in this chamber for Penning mixtures. A chamber 636 mm long is now being prepared for WIMP searches. A background of about 10−5 event/(keV kg d) can be obtained in this experiment.

An Allene-Doped Liquid Argon Ionization Chamber for O and Ne Ions at 100 MeV/n

An allene-doped liquid argon ionization chamber with a sensitive volume of 48 mm×48 mm×40 mm has been constructed and investigated for precise measurement of the heavy ion energies at around 100 MeV/n. An energy resolution of 1% (full width at half maximum [FWHM]) was achieved for the 99 MeV/n 16O and 125 MeV/n 20Ne ion beams. However, the energy resolution was found to deteriorate as the beam intensity increased. To understand this phenomenon, a simple model is proposed, in which a space-charge electric field due to the positive ions left along the track of an incident ion is taken into consideration. The estimated electric field is strong enough to worsen the energy resolution when the incident beam intensity is only 100 particles/s.

An allene-doped liquid argon ionization chamber for Ar and Ca ions at around 100 MeV/n

Abstract An allene-doped liquid argon ionization chamber with 48 mm×48 mm×40 mm sensitive volume has been constructed for precise energy measurement of heavy ions at around 100 MeV/n. An energy resolution of 0.6%–0.7% (FWHM) was achieved for Ca and Ar ions both at 78 MeV/n.

Search for double beta decay of 100Mo with liquid argon ionization chamber (first results)

First two runs with 138.7 g of 100Mo were done 9202 h and 238 h). Limits on half-lives for 0ν- and 0νχ 0-decays of 100Mo were obtained, > 2.3 · 10 21 y and 0.8 · 10 20 y, respectively at 90% CL. Also the limit on the content of radioactive 42Ar in the natural Ar was obtained, < 5 · 10 −21 g/g. Perspectives for the future are discussed.

New experimental limit on the 42Ar content in the Earth’s atmosphere

Using a liquid argon ionization chamber a new experimental limit on the 42Ar content in the Earth’s atmosphere was found to be less than 6×10 −21 parts of 42Ar per part of natAr at the 90% CL.

Search for double beta decay of 100Mo and 116Cd with a liquid argon ionization chamber (present status)

An experiment on the search for the double beta decay of 100Mo and 116Cd with sensitivity (5–7)×10 23 yr for neutrinoless decay, 5×10 22 yr for decay with majoron emission and 5×10 21 yr for two-neutrino mode is described. The detector is multisection liquid argon ionization chamber surrounded by a passive shielding.

Multisection liquid argon ionization chamber for double beta decay

The construction of a multisection liquid argon ionization chamber for the double beta decay experiment is presented. Its volume is 904. The Ti-sponge purification system and the purity control detector were specially constructed for this chamber. A single passage of commercial argon through the purification system at a rate of ≈0.6 m 3/h yields a gas of purity 1.9 × 10 −9 equivalent O 2. Measurement range of the purity control detector is 10 −1−10 −12 equivalent O 2.

Design, construction and performance of a liquid xenon and liquid argon ionization chamber

We have constructed an ionization chamber for liquid xenon and liquid argon and have conducted studies of initial ion-electron recombination. Using a 392 keV 113 Sn source, we find in xenon a charge collection of (90±5)% at an electric drift field of 1.6 kV/cm and (10±3)% at 10 V/cm. In argon we collect (78±5)% of the charge in a field of 1.6 kV/cm. We have developed a method for measuring the concentration of electronegative impurities in the detector liquid. The purity of the liquid was always better than 2 ppb O 2 equivalent. Under these conditions, the energy resolution observed with either liquid in the detector is (12±1)% FWHM at 380 keV in an electric drift field of 1.8 kV/cm for argon and 1.6 kV/cm for xenon. This appears to be a fundamental limit imposed by the statistics of delta electron production.

Limited energy resolution in liquid argon due to δ-ray production

The measured energy resolution of electrons and γ-rays detected in liquid argon ionization chambers is about an order of magnitude worse than the prediction based on the calculated Fano factor. It is suggested that along the path of an ionizing particle low energy δ-rays are copiously produced. They ionize the argon much more strongly than the primary electron, and the liberated charges experience a correspondingly higher recombination rate. The loss of ionization electrons from these δ-rays causes fluctuations in the detectable signal, which dominate the observed energy resolution. Measurements with a liquid argon filled gridded ionization chamber are presented that support this assumption.

Use of a pulse shape analysis of recoil electron signals in a liquid ionization chamber for indication of the direction of incidence of low energy photons and neutrinos

It is shown that the direction of incidence of photons and neutrinos with energies above 0.5 MeV can be determined by pulse shape analysis of recoil electron signals in a liquid ionization chamber. The experiments were carried out using a liquid argon ionization chamber. For 0.622–3.2 MeV photons the direction of incidence can be determined within the cone ±(40°−70°) depending on energy. A detailed Monte-Carlo calculation demonstrated the possibility of the suppression of the isotropic background by an order of magnitude for a recoil electron energy above 2–3 MeV.