Low-pressure Gaseous Detectors Research Articles

Flexible algorithms for background suppression in heavy ion induced nuclear reactions

A new algorithm for the analog spectrometer of the DGFRS-2 setup installed at DC-280 cyclotron is presented. The main goal of application of this algorithm is to search an optimal time correlation recoilalpha parameter directly during the acquisition C++ code execution. A new real-time flexible algorithm in addition to the conventional ER − a algorithm, which has been used for a several years at the DGFRS-1 setup installed at the U-400 FLNR cyclotron, is presented. The main parts of the spectrometer are a 48×128 strip DSSD detector (Double Side Strip Detector) and a low-pressure gaseous detector. They are presented schematically. Nuclear reactions for synthesis of element Z=119 at the DGFRS-2 are under consideration. Some attention is paid to computer simulation of the heavy recoil spectra, taking into account its pulse height defect in silicon. First beam test results are also presented. A new formula for half-life time using recent data for superheavy nuclei is obtained.

Beam tracking with micromegas & wire chambers in secondary electron detection configuration

The focal plane of S3 (Super Separator Spectrometer), a new experimental area of SPIRAL2 at GANIL, will be used for identification of nuclei, and requires the reconstruction of their trajectories and velocities by the Time Of Flight (TOF) method. Classical tracking detectors used in-beam would generate a lot of angular and energy straggling due to their thickness. One solution is the use of a SED (Secondary Electron Detection), which consists of a thin emissive foil in beam coupled to a low pressure gaseous detector out of the beam, for the detection of secondary electrons ejected from the foil. Moreover, this type of detector can be used for classical beam tracking at low energies, or for example at NFS (GANIL) for the FALSTAFF experiment for the reconstruction of fission fragments trajectories. Several low pressure gaseous detectors such as wire chambers and Micromegas have been constructed and tested since 2008. High counting rate capabilities and good time resolution obtained in previous tests motivated the construction of a new real-size 2D prototype wire chamber and a 2D bulk Micromegas at low pressure. For the first time, spatial resolution of the Micromegas at low pressure (below 20 mbar) in the SED configuration was measured. Different tests have been performed in order to characterize time and spatial properties of both prototypes, giving spatial resolution in the horizontal (X) direction of 0.90(0.02) mm FWHM for the real size prototype and 0.72(0.08) mm FWHM for Micromegas, and a time resolution of ∼ 110(25) ps for the real size prototype.

Micromegas at low pressure for beam tracking

New facilities like FAIR at GSI or SPIRAL2 at GANIL, will provide radioactive ion beams at low energies (less than 10 MeV/n). Such beams have generally a large emittance, which requires the use of beam tracking detectors to reconstruct the exact trajectories of the nuclei. To avoid the angular and energy straggling that classical beam tracking detectors would generate in the beam due to their thickness, we propose the use of SED (Secondary Electron Detectors). It consists of a low pressure gaseous detector placed outside the beam coupled to an emissive foil in the beam. Since 2008, different low pressure gaseous detectors (wire chambers and micromegas) have been constructed and tested. The performances achievable at low pressure are similar to or even better than the ones at atmospheric pressure. The fast charge collection leads to excellent timing properties as well as high counting rate capabilities. Several micromegas at low pressure were tested in the laboratory demonstrating a good time resolution, 130±30 ps, which is compatible with the results obtained with wire chambers.

Production and measurement of neutron reference fields : the AMANDE facility and MIMAC prototype as neutron detection system

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.

Secondary electrons detectors for beam tracking: micromegas and wire chamber

SPIRAL2 or FAIR will be able to deliver beams of radioactive isotopes of low energy (less than 10 MeV/n). The emittance of these new beams will impose the use of beam tracking detectors to reconstruct the exact impact position of the nuclei on the experimental target. However, due to their thickness, the classical detectors will generate a lot of energy and angular straggling. A possible alternative is the SED principle (Secondary Electron Detector). It consists of an emissive foil placed in beam and a detector for the secondary electrons ejected by the passing of the nuclei through the foil. An R&D program has been initiated at CEA Saclay to study the possibility to use low pressure gaseous detectors as SED for beam tracking. Some SED have been already used on the VAMOS spectrometer at GANIL since 2004. We have constructed new detectors on this model to measure their performances in time and spatial resolution, and counting rate. Other detector types are also under study. For the first time, a test with different micromegas detectors at 4 Torr has been realized. A comparison on the time resolution has been performed between wire chamber and micromegas at very low pressure. The use of micromegas could be promising to improve the counting rate capability and the robustness of beam tracking detectors.

Measurement of the range component directional signature in a DRIFT-II detector using 252Cf neutrons

The Directional Recoil Identification From Tracks (DRIFT) collaboration utilizes low-pressure gaseous detectors to search for Weakly Interacting Massive Particle (WIMP) dark matter with directional signatures. A 252Cf neutron source was placed on each of the principal axes of a DRIFT detector in order to test its ability to measure directional signatures from the three components of very low-energy (∼keV/amu) recoil ranges. A high trigger threshold and the event selection procedure ensured that only sulfur recoils were analyzed. Sulfur recoils produced in the CS 2 target gas by the 252Cf source closely match those expected from massive WIMP induced sulfur recoils. For each orientation of the source, with a threshold of ∼50 keV, a directional signal from the range components was observed, indicating that the detector has directional capability along all three axes, though in one direction the directionality was marginal. An analysis of these results yields an optimal orientation for DRIFT detectors when searching for a directional signature from WIMPs. Additional energy dependent information is provided to aid in understanding this effect.

Detection of neutron-induced nuclear recoils in a low-pressure gaseous detector for particle dark matter searches

Recent neutron beam tests of a prototype detector to search for weakly interacting massive particles in the Galactic Halo are presented. The detector is an optically imaged time-projection chamber using various low-pressure gas mixtures. This technique potentially offers significant advantages for the detection of galactic dark matter in that it measures both the energy and direction of the nuclear recoil. In this paper we present measurements of ranges of neutron-induced nuclear recoils in different target gasses which are then used to determine the sensitivity of the device in a dark matter search. We also demonstrate the ability to accurately determine the direction of the recoil which can be used to discriminate signal from background using the expected diurnal modulation in the average recoil direction, which is unique to particle dark matter interactions.

A study of relativistic charged particle identification by primary cluster counting

Abstract The possibility to identify charged particles in the relativistic rise region by primary cluster counting in low-pressure gaseous detectors is discussed. Based on experimental parameters measured with a single detector module and with minimum ionizing electrons, the response of a full detection system to relativistic particles was simulated. Particle separation with a realistic device, comprising 20 consecutive detector modules, was evaluated in terms of total system length and momentum range. The estimated performance is compared to that of some existing d E d x detectors.

Low pressure gaseous detector for particle dark matter.

The results of recent testing of a prototype detector to search for weakly interacting massive particles in the galactic halo are presented. The detector is an optically imaged, low pressure time projection chamber. This technique offers significant advantages for the detection of dark matter in that it measures both the energy and direction of the nuclear recoil. Using neutron and x-ray sources we also demonstrate that this detector has substantial electron background rejection capability (greater than 99.8%) and can utilize various target nuclei, such as hydrogen and argon.

Progress in low-pressure gaseous detectors

Abstract Some outstanding properties of low-pressure MWPCs open new prospects in the domain of heavy as well as light particle detection. In the present mode of operation, the mechanism of avalanche formation is divided into two steps: it combines an amplification process in a high, constant, electric field region with a second one, occurring in the vicinity of the proportional wires. Large gains associated with fast charge-collection times are reached at pressures as low as a fraction of a Torr, leading to excellent timing properties and to a high counting-rate capability. Transmission timing detectors, having a total thickness in the 100 μg/mm 2 range, have been designed for heavy-ion detection and offer time resolutions of the order of 100 ps (fwhm) at rates as high as 10 5 c/cm 2 s. The properties of this type of detectors are summarized and localization and multitrack detection capabilities are discussed. Present and future heavy-ion detection systems based on this simple, efficient and low cost technique are described. Possible applications in nuclear and particle physics are also discussed.