Proportional electroluminescence (EL) in noble gases is a physical process routinely used in two-phase (liquid–gas) detectors for low-energy astroparticle-physics experiments. In this work, the time ...properties of visible-light EL in two-phase argon detectors have been systematically studied for the first time. In particular, two unusual slow components in the EL signal, with their contributions and time constants increasing with electric field, were observed. This puzzling property is not expected in any of the known mechanisms of photon and electron emission in two-phase media. Time constants of these components is about 4–5
μ
s and 50
μ
s. In addition, a specific threshold behavior of the slow components was revealed: they emerged at a threshold in reduced electric field of 4.8 ± 0.2 Td regardless of the gas phase density, which is about 1 Td above the onset of standard (excimer) EL. There is a conspicuous similarity between this threshold and reduced field threshold of EL in NIR occurring via higher atomic excited states Ar
∗
(
3
p
5
4
p
)
. An unexpected temperature dependence of slow components was also observed: their contribution decreased with temperature, practically disappearing at room temperature. We show that the puzzling properties of slow components can be explained in the framework of hypothesis that these are produced in the charge signal itself due to trapping of drifting electrons on metastable negative argon ions.
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DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
The effect of proportional electroluminescence (EL) is used to record the primary ionization signal (S2) in the gas phase of two-phase argon detectors for dark matter particle (WIMP) searches and ...low-energy neutrino experiments. Our previous studies of EL time properties revealed the presence of two unusual slow components in S2 signal of two-phase argon detector, with time constants of about 4–5
μ
s and 50
μ
s. The puzzle of slow components is that their time constants and contributions to the overall signal increase with electric field (starting from a certain threshold), which cannot be explained by any of the known mechanisms of photon and electron emission in two-phase media. There are indications that these slow components result from delayed electrons, temporarily trapped during their drift in the EL gap on metastable negative argon ions of yet unknown nature. In this work, this hypothesis is confirmed by studying the time properties of electroluminescence in a Thick Gas Electron Multiplier (THGEM) coupled to the EL gap of two-phase argon detector. In particular, an unusual slow component in EL signal, similar to that observed in the EL gap, was observed in THGEM itself. In addition, with the help of THGEM operated in electron multiplication mode, the slow component was observed directly in the charge signal, confirming the effect of trapped electrons in S2 signal. These results will help to unravel the puzzle of slow components in two-phase argon detectors and thus to understand the background in low-mass WIMP searches.
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DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
A recent discovery of additional mechanism of electroluminescence (EL) in noble gases due to the neutral bremsstrahlung (NBrS) effect led to a prediction that NBrS EL should be present in noble ...liquids as well. A theoretical model of NBrS EL in noble liquids was developed accordingly in the frameworks of Cohen-Lekner and Atrazhev. In this work, we confirm this prediction: For the first time, visible-range EL has been observed in liquid argon at electric fields reaching 90 kV/cm, using gas electron multiplier (GEM) and thick GEM structures. Absolute light yields of the EL were measured and found to be in excellent agreement with the theory, provided that the momentum-transfer cross section of electron scattering is used for calculation of the NBrS cross section (instead of the energy-transfer one).
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CMK, CTK, FMFMET, IJS, NUK, PNG, UL, UM
Our recent studies of electroluminescence (EL) properties in two-phase argon detectors for dark matter searches have revealed the presence of unusual delayed pulses in the EL signal in the form of ...two slow components with time constants of about 5 and 50
μ
s
. These components were shown to be present in the charge signal itself, which clearly indicates that drifting electrons are temporarily trapped on two states of metastable negative argon ions which have never been observed before. In this work, using the pressure dependence of the ratio of slow component contributions measured in experiment, it is deduced that these states are those of two types of metastable negative molecular ions,
Ar
2
∗
-
(
b
4
Σ
u
-
)
and
Ar
2
∗
-
(
a
4
Σ
g
+
)
for the higher and lower energy level respectively.
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DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
We further study the effect of neutral bremsstrahlung (NBrS) in two-phase argon electroluminescence (EL), revealed recently in Buzulutskov et al. (2018). The absolute EL yield due to NBrS effect, in ...the visible and NIR range, was remeasured in pure gaseous argon in the two-phase mode, using a two-phase detector with EL gap read out directly by cryogenic PMTs and SiPMs. Possible applications of the NBrS effect in detection science are discussed, including those in two-phase dark matter detectors.
•Electroluminescence in gaseous Ar in the two-phase mode.•Non-VUV spectral component in electroluminescence.•Electroluminescence below the Ar excitation threshold.•Neutral bremsstrahlung as a mechanism of proportional electroluminescence.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Abstract
In liquid argon TPCs for dark matter search and neutrino detection experiments, primary scintillation light is used as a prompt signal of particle scattering, being intensively produced in ...the vacuum ultraviolet (VUV) due to excimer emission mechanism. On the other hand, there were indications on the production of visible-light emission in liquid argon, albeit at a much lower intensity, the origin of which is still not clear. The closely related issue is visible-light emission in liquid argon doped with methane, the interest in which is due to the possible use in neutron veto detectors for those experiments. In this work we study in detail the properties of such light emission in pure liquid argon and its mixtures with methane. In particular, the absolute photon yield of visible-light emission in pure liquid argon was measured to be about 200 and 90 photon/MeV for X-rays and alpha particles respectively. In liquid argon doped with methane the photon yield dropped down significantly, by about an order of magnitude at a methane molar content varying from 0.01 to 1%, and then almost did not change when further increasing the methane content up to 10%.
OBJECTIVE:to study the dynamics of the central (aortic) hemodynamics parameters in patients with STEMI, depending on the achieving the LDL-C target values at the 48-weeks atorvastatin therapy.
DESIGN ...AND METHOD:The study included 97 patients (mean age 47.9 ± 6.2 years) with STEMI confirmed by biomarkers, ECG, coronary angiography. An applanation tonometry by Sphygmocor device (AtCorMedical, Australia) was performed at 7–9th day from the disease onset and after 48 weeks of follow-up. Parameters were analyzedSBPao, DBPao, PPao and cfPWV. Patients were treated with atorvastatin throughout the follow-up period. The patients were divided into two groups depending on the LDL-C level after 48 weeks. Group 1 consisted of 49 patients with LDL-C < 1.5 mmol/L and/or a reduction by 50% of the baseline values. The second group - 48 people who did not acheive target LDL-C level.
RESULTS:The aortic pressure parameters increased in group 1 after 48-weeks therapySBPao from 102 ± 8.9 to 108.5 ± 11mmHg (p = 0.001), PPao from 29.5 ± 6.8 to 32.7 ± 7.8mmHg (p = 0.01). DBPao initially - 71 (66; 81)mmHg; after therapy - 73 (66; 81)mmHg (p = 0.05). An increase of SBPao from 102.4 ± 10.9 to 109.9 ± 11.8mmHg (p = 0.001), PPao from 26 (22; 31) to 32.1 ± 7.9 mmHg (p = 0.001) was found in group 2. DBPao has not changedfrom 75 (70; 81); to 76 (71; 81) mmHg. Initially low SBPao in group 1 was diagnosed in 46.9%, PPao in 36.7%, normal values - in 53.1% and 63.3%; after 48 weeks a low SBPao and PPao level was in 30.6% and 20.4%, normal - in 69.4% and 79.6%. In group 2 initially low SBPao was in 57.3%, PPao in 44.8%, normal in 42.7% and 55.2%. Low values were observed in 25% and 18.8%, normal -in 66.7% and 72.9%, high values -in 8.3% and 8.3%(p < 0.05) in 48 weeks. PWV decreased from 6.9 (6.1, 8.3)m/s to 6.1 (5.4, 7.8)m/s (p = 0.01). In Group 2 PWV initially - 7.1 (6.2, 7.7)m/s, follow-up - 6.9 (6.1, 7.8)m/s (p = 0.2).
CONCLUSIONS:In group 2 an increase of central pressure is associated with normalization of the parameters and pathological values appearance. While in group 1 an increase of SBPao and PPao was due to their normalization, with a favorable decrease of cfPWV.
A double-phase argon Time Projection Chamber (TPC), with an active mass of 185 g, has been designed and constructed for the Recoil Directionality (ReD) experiment. The aim of the ReD project is to ...investigate the directional sensitivity of argon-based TPCs via columnar recombination to nuclear recoils in the energy range of interest (20–
200
keV
nr
) for direct dark matter searches. The key novel feature of the ReD TPC is a readout system based on cryogenic Silicon Photomultipliers (SiPMs), which are employed and operated continuously for the first time in an argon TPC. Over the course of 6 months, the ReD TPC was commissioned and characterised under various operating conditions using
γ
-ray and neutron sources, demonstrating remarkable stability of the optical sensors and reproducibility of the results. The scintillation gain and ionisation amplification of the TPC were measured to be
g
1
=
(
0.194
±
0.013
)
photoelectrons/photon and
g
2
=
(
20.0
±
0.9
)
photoelectrons/electron, respectively. The ratio of the ionisation to scintillation signals (S2/S1), instrumental for the positive identification of a candidate directional signal induced by WIMPs, has been investigated for both nuclear and electron recoils. At a drift field of 183 V/cm, an S2/S1 dispersion of 12% was measured for nuclear recoils of approximately 60–
90
keV
nr
, as compared to 18% for electron recoils depositing 60 keV of energy. The detector performance reported here meets the requirements needed to achieve the principal scientific goals of the ReD experiment in the search for a directional effect due to columnar recombination. A phenomenological parameterisation of the recombination probability in LAr is presented and employed for modeling the dependence of scintillation quenching and charge yield on the drift field for electron recoils between 50–500 keV and fields up to 1000 V/cm.
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DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Proportional electroluminescence (EL) in noble gases is used in two-phase detectors for dark matter searches to record (in the gas phase) the ionization signal induced by particle scattering in the ...liquid phase. The “standard” EL mechanism is considered to be due to noble gas excimer emission in the vacuum ultraviolet (VUV). In addition, there are two alternative mechanisms, producing light in the visible and near infrared (NIR) ranges. The first is due to bremsstrahlung of electrons scattered on neutral atoms (“neutral bremsstrahlung”, NBrS). The second, responsible for electron avalanche scintillation in the NIR at higher electric fields, is due to transitions between excited atomic states. In this work, we have for the first time demonstrated two alternative techniques of the optical readout of two-phase argon detectors, in the visible and NIR range, using a silicon photomultiplier matrix and electroluminescence due to either neutral bremsstrahlung or avalanche scintillation. The amplitude yield and position resolution were measured for these readout techniques, which allowed to assess the detection threshold for electron and nuclear recoils in two-phase argon detectors for dark matter searches. To the best of our knowledge, this is the first practical application of the NBrS effect in detection science.
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DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Silicon photomultipliers (SiPMs) are extensively used in different fields now. They exceed photomultiplier tubes in the quantum efficiency, size and resistance to magnetic field. However, because of ...structure features, their dark noise rate is higher and they have additional sources of noise: cross-talk and after-pulsing. In addition, these parameters may be temperature dependent. In this article we present results of an evaluation of the dark noise rate, probabilities of cross-talk and after-pulses at different voltages and temperatures for two modern SiPMs: S13360-3050CS (HAMAMATSU) and PM1125NS-SB0 (KETEK). For comparison, the data for a previous-generation SiPM, S10362-11-100C (HAMAMATSU), are presented. To find these parameters, we performed a waveform analysis to determine the amplitude and time distributions of the pulses generated by a SiPM without an external light source. We evaluated the temperature and voltage dependences of these parameters. The measured cross-talk probability for PM1125NS-SB0 and S13360-3050CS at their optimal operating voltage is about 6%. It is two times smaller than that for S10362-11-100C. The fast component of the after-pulsing probability for PM1125NS-SB0 and S13360-3050CS is about 10%, which is also almost 2 times smaller than the sum of the fast and slow components of the after-pulsing probability for S10362-11-100C. The dark noise rate for S13360-3050CS at 20°C is just 45 kHz/mm2 in comparison with 60 kHz/mm2 for PM1125NS-SB0.
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