研制了一种新型的液氩纯度监测器，其灵敏度可达ppb级（O $_2$当量）。这种高纯度例如在LAr漂移室中是需要的。其原理是测量LAr中准自由电子的寿命，因为这是漂移室操作的重要参数。自由电子是通过用$α$ -粒子电离LAr产生的，该粒子由同位素$^{210}Pb$源的$^{210}Po$链子体发射。通过测量漂移路径开始和结束时电子云的电荷以及漂移时间，可以获得电子的寿命。$α$ -粒子具有约50 μ $m in LAr and the ionization density is very high, typically between $ 750 <$1500 \rm MeV/cm $, leading to a high recombination rate. To suppress the recombination of the argon ions with the electrons, the $ α $-source was put in a strong electric field of $ 40 <$150 $ kV/cm的非常短的范围。这是通过将源沉积在直径约为0.5 mm的球形高压阴极的表面上来实现的。阳极也被制成与阴极直径大致相同的球体，因此，靠近两个电极之间的轴，电漂移场近似为偶极场。
英文摘要：
A novel liquid argon (LAr) purity monitor was developed with a sensitivity to electronegative impurities of the order of ppb (O$_2$ equivalent). Such a high purity is e.g. needed in a LAr drift chamber. The principle is to measure the lifetime of quasifree electrons in LAr, since this is the important parameter for the operation of a drift chamber. Free electrons are produced by ionizing the LAr with $α$-particles emitted by the $^{210}Po$ chain daughter of an isotope $^{210}Pb$ source. From a measurement of the charge of the electron cloud at the beginning and at the end of a drift path, together with the drift time, the lifetime of the electrons is obtained. The $α$-particles have a very short range of about 50 μ$m in LAr and the ionization density is very high, typically between $750÷1500\rm MeV/cm$, leading to a high recombination rate. To suppress the recombination of the argon ions with the electrons, the $α$-source was put in a strong electric field of $40÷150$ kV/cm. This was achieved by depositing the source on the surface of a spherical high voltage cathode with a diameter of about 0.5 mm. The anode was also made as a sphere of about the same diameter as the cathode, thus, close to the axis between the two electrodes the electric drift field was approximately a dipole field.
Purity monitor devices are increasingly used in noble gas time projection chambers to measure the lifetime of drifting electrons. Purity monitors work by emitting electrons from a photocathode material via the photoelectric effect. The electrons are then drifted towards an anode by means of an applied electric drift field. By measuring the difference in charge between the cathode and the anode, one can extract the lifetime of the drifting electrons in the medium. For the first time, we test the performance of different photocathode materials-- silver, titanium, and aluminium--and compare them …
In neutron transmutation doped germanium, the thermal neutron fluence of reactor irradiation is as high as 10$^{18}$~n$\cdot$cm$^{-2}$. For radiological safety reasons, general Co or Au neutron flux monitors cannot be easily used. We have experimentally demonstrated the feasibility of measuring the X-rays emitted by the NTD-Ge itself to determine the absolute thermal neutron fluence for the first time. A Micro-Megas Detector (MMD) and a Silicon Drift Detector (SDD) are set up to detect the tagging KX-rays with 9.2 keV and 10.3 keV cascading from the decays of $^{71}$Ge. Combined the detection …
Linear polarization analysis of hard x-rays is employed to probe electronic anisotropies in metal-containing complexes with very high selectivity. We use the pronounced linear dichroism of nuclear resonant x-ray scattering to determine electric field gradients in an iron(II) containing compound as they evolve during a temperature-dependent high-spin/low-spin phase transition. This method constitutes a novel approach to analyze changes in the electronic structure of metal-containing molecules as function of external parameters or stimuli. The polarization selectivity of the technique allows us …
Radiation detectors constructed from large volume high purity Ge (HPGe) single crystals are widely used for gamma-ray spectroscopy. The detectors for this application can be simple in that they need only have two electrical contacts for voltage application and signal readout. Such HPGe based detectors have been commercially produced for many decades using standard semiconductor fabrication processes. For the applications of gamma-ray imaging and particle tracking, however, interaction position measurement within the detector as well as the measurement of the deposited energy is required. This …
Procurement and Purification of Liquid Argon for the LEGEND-200 Experiment
Jagiellonian University（雅盖隆大学）；Technical University of Munich（慕尼黑工业大学）；Istituto Nazionale di Fisica Nucleare, Laboratori Nazionali del Gran Sasso（意大利国家核物理研究所，格兰萨索国家实验室）
High-purity germanium crystals approximately 12 cm in diameter were grown in a hydrogen atmosphere using the Czochralski method. The dislocation density of the crystals was determined to be in the range of 2000 - 4200 cm-2, which meets a requirement for use as a radiation detector. The axial and radial distributions of impurities in the crystals were measured and are discussed. A planar detector was also fabricated from one of the crystals and then evaluated for electrical and spectral performance. Measurements of gamma-ray spectra from Cs-137 and Am-241 sources demonstrate that the detector h…
Single-electron detection in a high-purity Ge device
IP2I-Lyon, Univ. Lyon, Université Lyon 1, CNRS/IN2P3（里昂第一大学国家科学研究中心/法国原子能和替代能源委员会第二粒子物理研究所）；IJCLab, Université Paris-Saclay, CNRS/IN2P3（巴黎萨克雷大学国家科学研究中心/法国原子能和替代能源委员会第二粒子物理研究所）；Department of Physics, University of Zurich（苏黎世大学物理系）；LPSC-IN2P3, Univ. Grenoble Alpes, CNRS, Grenoble INP（格勒诺布尔阿尔卑斯大学国家科学研究中心/法国原子能和替代能源委员会第二粒子物理研究所格勒诺布尔国立理工学院）；Argonne National Laboratory（阿贡国家实验室）；Department of Physics, University of California Berkeley（加州大学伯克利分校物理系）；Amherst Center for Fundamental Interactions and Department of Physics, University of Massachusetts（马萨诸塞大学基础相互作用中心及物理系）；Lawrence Berkeley National Laboratory（劳伦斯伯克利国家实验室）
The dark matter search project by means of ultra high purity NaI(Tl) scintillator is now underdevelopment. An array of large volume NaI(Tl) detectors whose volume is 12.7 cm$ϕ\times$12.7 cm is applied to search for dark matter signal. To remove radioactive impurities in NaI(Tl) crystal is one of the most important task to find small number of dark matter signals. We have developed high purity NaI(Tl) crystal which contains small amounts of radioactive impurities, $<4$ ppb of $^{nat}$K, 0.3 ppt of Th chain, 58 $μ$Bq/kg of $^{226}$Ra and 30 $μ$Bq/kg of $^{210}$Pb. Future prospects to search for …
Large, high-purity, germanium (HPGe) detectors are needed for neutrinoless double-beta decay and dark matter experiments. Currently, large (> 4 inches in diameter) HPGe crystals can be grown at the University of South Dakota (USD). We verify that the quality of the grown crystals is sufficient for use in large detectors by fabricating and characterizing smaller HPGe detectors made from those crystals. We report the results from eight detectors fabricated over six months using crystals grown at USD. Amorphous germanium (a-Ge) contacts are used for blocking both electrons and holes. Two types of…
The MEG-II experiment searches for the lepton flavor violating decay: mu in electron and gamma. The reconstruction of the positron trajectory uses a cylindrical drift chamber operated with a mixture of He and iC4H10 gas. It is important to provide a stable performance of the detector in terms of its electron transport parameters, avalanche multiplication, composition and purity of the gas mixture. In order to have a continuous monitoring of the quality of gas, we plan to install a small drift chamber, with a simple geometry that allows to measure very precisely the electron drift velocity in a…
A high purity and large volume NaI(Tl) scintillator was developed to search for cosmic dark matter. The required densities of radioactive impurities (RIs) such as U-chain, Th-chain are less than a few ppt to establish high sensitivity to dark matter. The impurity of RIs were effectively reduced by selecting raw materials of crucible and by performing chemical reduction of lead ion in NaI raw powder. The impurity of $^{226}$Ra was reduced less than 100 $μ$Bq/kg in NaI(Tl) crystal. It should be remarked that the impurity of $^{210}$Pb, which is difficult to reduce, is effectively reduced by chem…
For the first time, planar high-purity germanium detectors with thin amorphous germanium contacts were successfully operated directly in liquid nitrogen and liquid argon in a cryostat at the Max-Planck-Institut fuer Physics in Munich. The detectors were fabricated at the Lawrence Berkeley National Laboratory and the University of South Dakota, using crystals grown at the University of South Dakota. They survived long-distance transportation and multiple thermal cycles in both cryogenic liquids and showed reasonable leakage currents and spectroscopic performance. Also discussed are the pros and…
In order to recuperate the ultra-high purity xenon from PandaX-4T dark matter detector to high-pressure gas cylinders in emergency or at the end-of-run situation, a high speed ultra-high purity xenon recuperation system is designed and developed. This system includes a diaphragm pump, the heat management system, the main recuperation pipeline, the reflux pipeline, the auxiliary recuperation pipeline and the automatic control system. The liquid xenon in the detector is vaporized by the heat management system, and the gaseous xenon is compressed to 6 MPa at the flow rate of 200 standard litres p…
Semiconductor detector fabrication technologies developed decades ago are widely employed today to produce gamma-ray detectors from large volume, single crystals of high purity Ge (HPGe). Most all of these detectors are used exclusively for spectroscopy measurements and are of simple designs with only two impurity based electrical contacts produced with B implantation and Li diffusion. Though these technologies work well for the simple spectroscopy detectors, the Li contact in particular is thick and lacks room temperature stability in a manner that makes it inappropriate for many of the more …
A dark matter search project needs and extremely low background radiation detector since the expected event rate of dark matter is less than a few events in one year in one tonne of the detector mass. The authors developed a highly radiopure NaI(Tl) crystal to search for dark matter. The best combination of the purification methods was developed, resulting $^{\mathrm{nat}}$K and $^{210}$Pb were less than 20 ppb and 5.7 $μ$Bq/kg, respectively. The authors will construct a large volume detector system with high-purity NaI(Tl) crystals. The design and the performance of the prototype detector mod…
We describe the design, installation, and operation of a purification system that is able to provide large volumes of high purity ASTM (D1193-91) Type-I water to a high energy physics experiment. The water environment is underground in a lightly sealed system, and this provides significant challenges to maintaining high purity in the storage pools, each of which contains several thousand cubic meters. High purity is dictated by the need for large optical absorption length, which is critical for the operation of the experiment. The system is largely successful, and the water clarity criteria ar…
Bayesian inference of high-purity germanium detector impurities based on capacitance measurements and machine-learning accelerated capacitance calculations
We investigate the idea of detecting pure neutrino-hydrogen interactions in a multinuclear target using the transverse kinematic imbalance technique [Lu et al., Phys. Rev. D 92, 051302 (2015)] in a high-pressure time projection chamber (HPTPC). With full solid-angle acceptance, MeV-level proton tracking threshold, state-of-the-art tracking resolution, and an O(100 m^3) gas volume at 10 bar, an HPTPC could provide an opportunity to realize this technique. We propose the use of hydrogen-rich gases in the TPC to achieve high detection purity with large hydrogen mass. With the projected neutrino b…
