A complete dedicated electronics, from front-end to back-end, was developed to instrument a MIMAC prototype. A front end ASIC able to monitor 64 strips of pixels and to provide their individual “Time ...Over Threshold” information has been designed. An associated acquisition electronics and a real time track reconstruction software have been developed to monitor a 512 channel prototype. This auto-triggered electronic uses embedded processing to reduce the data transfer to its useful part only, i.e. decoded coordinates of hit tracks and corresponding energy measurements. The electronic designs, acquisition software and the results obtained are presented.
The measurement of the ionization produced by particles in a medium presents a great interest in several fields from metrology to particule physics and cosmology. The ionization quenching factor is ...defined as the fraction of energy released by ionisation by a recoil in a medium compared with its kinetic energy. At low energy, in the range of a few keV, the ionization fall rapidly and systematic measurement are needed. We have developped an experimental setup devoted to the measurement of low energy (keV) ionization quenching factor for the MIMAC project. The ionization produced in the gas has been measured with a Micromegas detector filled with Helium gas mixture.
The XENON1T experiment aims for the direct detection of dark matter in a detector filled with 3.3 tons of liquid xenon. In order to achieve the desired sensitivity, the background induced by ...radioactive decays inside the detector has to be sufficiently low. One major contributor is the
β
-emitter
85
Kr which is present in the xenon. For XENON1T a concentration of natural krypton in xenon
nat
Kr
/
Xe
<
200
ppq
(parts per quadrillion,
1
ppq
=
10
-
15
mol
/
mol
) is required. In this work, the design, construction and test of a novel cryogenic distillation column using the common McCabe–Thiele approach is described. The system demonstrated a krypton reduction factor of
6.4
·
10
5
with thermodynamic stability at process speeds above 3 kg/h. The resulting concentration of
nat
Kr
/
Xe
<
26
ppq
is the lowest ever achieved, almost one order of magnitude below the requirements for XENON1T and even sufficient for future dark matter experiments using liquid xenon, such as XENONnT and DARWIN.
Growth, cadmium accumulation and potassium and calcium status were studied in two halophytes from Aizoaceae family:
Sesuvium portulacastrum and
Mesembryanthemum crystallinum. After multiplication, ...the seedlings were cultivated on nutrient solution supplemented with NaCl (100
mM) and CdCl
2 (0, 50, 100, 200 and 300
μM). After 1 month of treatment, plants were harvested and the dry weight, as well as the Cd, K and Ca concentrations in tissues were determined. Results showed that
S. portulacastrum, a perennial halophyte with slow growth, is significantly more tolerant to Cd than
M. crystallinum, an annual plant. Cd severely inhibited
Mesembryanthemum growth even at the lowest Cd concentration in culture medium (50
μM), and did not modify significantly that of
Sesuvium. For both halophytes, Cd accumulation was significantly higher in the roots than in the shoots. However, Cd concentration reached 350–700
μg
g
−1 DM in the shoots, values characteristic of Cd hyperaccumulator plants. The addition of Cd in the culture medium led to a disturbance of Ca and especially K nutrition, suggesting the possibility to improve plant growth and Cd phytoextraction of both halophytes by increasing nutrient availability in the culture medium.
The AMANDE facility produces mono-energetic neutron fields from 2 keV to 20 MeV with a metrological quality (Gressier et al. 2004). To be considered as a standard facility, fluence and energy ...distributions of neutron fields have to be mastered, i.e. measured by primary detector standards. For this purpose, a new gaseous Time Projection Chamber (μTPC) is being developed within the MIMAC project devoted to directional Dark Matter search (Billard et al. 2010). The μTPC is dedicated to measure neutron fields from 2 keV up to 1 MeV. The measurement strategy requires track reconstruction of recoiling nuclei down to a few keV, which can be achieved with low pressure gaseous detectors. Hence the energy must be measured precisely and the track of the recoiling nucleus must be 3D reconstructed. This is achieved with a low pressure micropattern gaseous detector (a pixelized bulk micromegas) equipped with a self triggered electronics able to perform the anode sampling at a 50 MHz frequency. Methods to measure fluence and neutron energy with the TPC have been described.
Soybeans (Glycine max L. Merr., cv Kingsoy) were grown on media containing NO3
- or urea. The enrichments of shoots in K+, NO3
-, and total reduced N ($\text{N}_{\text{r}}$), relative to that in ...Ca2+, were compared to the ratios $\text{K}^{+}/\text{Ca}^{2+}$,$\text{NO}_{3}{}^{-}/\text{Ca}^{2+}$, and $\text{N}_{\text{r}}/\text{Ca}^{2+}$ in the xylem saps, to estimate the cycling of K+, and $\text{N}_{\text{r}}$. The net production of carboxylates ($\text{R}^{-}$) was estimated from the difference between the sums of the main cations and inorganic anions. The estimate for shoots was compared to the theoretical production of $\text{R}^{-}$ associated with NO3
- assimilation in these organs, and the difference was attributed to export of $\text{R}^{-}$ to roots. The net exchange rates of H+ and OH- between the medium and roots were monitored. The shoots were the site of more than 90% of total NO3
- reduction, and $\text{N}_{\text{r}}$ was cycling through the plants at a high rate. Alkalinization of the medium by NO3
--fed plants was interrupted by stem girdling, and not restored by glucose addition to the medium. It was concluded that the majority of the base excreted in NO3
- medium originated from $\text{R}^{-}$ produced in the shoots, and transported to the roots together with K+. As expected, cycling of K+ and reduced N was favoured by NO3
- nutrition as compared to urea nutrition.
The aim of the MIMAC project is to detect non-baryonic Dark Matter with a directional TPC. The recent Micromegas efforts towards building a large size detector will be described, in particular the ...characterization measurements of a prototype detector of 10 × 10 cm2 with a 2 dimensional readout plane. Track reconstruction with alpha particles will be shown.
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