Neutral Particle Detector Research Articles

Application of Time Projection Chambers with GEMs and Pixels to WIMP Searches and Fast Neutron Detection

We present work on the detection of neutral particles via nuclear recoils in gas-filled Time Projection Chambers (TPCs). We employ Gas Electron Multipliers (GEMs) to amplify the signal and silicon pixel electronics to detect the avalanche charge. These technologies allow ionization in the target gas to be detected with low noise, improved position and time resolution, and high efficiency. We review experimental results obtained in previous years, and report on ongoing simulation studies and construction of the first prototype at the University of Hawaii. We also present prospects of using such detectors to perform direction-sensitive searches for WIMP dark matter and fast neutron from fissionable material.

Particle identification for the [formula omitted] detector

Cooled antiproton beams of unprecedented intensities in the momentum range of 1.5–15 GeV/ c will be used for the P ¯ ANDA experiment at FAIR to perform high precision experiments in the charmed quark sector. The proposed P ¯ ANDA detector is a 4 π internal target spectrometer at the HESR allowing the detection and identification of neutral and charged particles generated within the total energy range of the antiproton annihilation products. The detector is divided in a forward spectrometer and a target spectrometer. The charged particle identification in the latter is performed by ring imaging Cherenkov counters employing the DIRC principle.

The AMADEUS experiment – precision measurements of low-energy antikaon nucleus/nucleon interactions

The planned series of measurements with AMADEUS will provide a high precision data set to study antikaon nucleus/nucleon dynamics at low energy. To achieve these goals AMADEUS will make use of the KLOE detector system at LNF, which is ideally suited for our measurements due to their large drift chamber with excellent charge particle tracking and identification probability. An almost 4 π calorimeter is available for the detection of neutral particles. R&D work has already started to construct a dedicated target and trigger system for further improvements on kaon stopping efficiency and background suppression.

Towards hot electron mediated charge exchange in hyperthermal energy ion–surfaceinteractions

We have made Na + and He + ions incident on the surface of solid state tunnel junctions and measured the energy lossdue to atomic displacement and electronic excitations. Each tunnel junction consists of anultrathin film metal–oxide–semiconductor device which can be biased to create a band ofhot electrons useful for driving chemical reactions at surfaces. Using the binary collisionapproximation and a nonadiabatic model that takes into account the time-varying natureof the ion–surface interaction, the energy loss of the ions is reproduced. The energy loss forNa + ions incident on the devices shows that the primary energy loss mechanism is the atomicdisplacement of Au atoms in the thin film of the metal–oxide–semiconductor device. Wepropose that neutral particle detection of the scattered flux from a biased device could be aroute to hot electron mediated charge exchange.

Nearly complete isobar suppression by photodetachment

The efficiency of selective suppression of negative ions by photodetachment in a gas-filled radio frequency quadrupole ion cooler was investigated with a new detection method. A neodymium doped yttrium aluminum garnet laser beam at 1064 nm was used to remove Co− ions in the radio frequency quadrupole cooler and the remaining ions were then probed by photodetachment and neutral particle detection. More than 99.99% suppression of the Co− ions was observed. Under identical conditions, only 20% of a Ni− beam was suppressed. The results demonstrate that this isobar suppression technique can lead to nearly complete elimination of certain isobaric contaminants in negative ion beams, opening up new experimental possibilities in nuclear and atomic research and accelerator mass spectrometry.

Development of the PANDA barrel DIRC

Cooled antiproton beams of unprecedented intensities of L = 2 × 1032 s-1cm-2 in the momentum range of 1.5–15 GeV/c will be used for the PANDA experiment at FAIR to perform high precision experiments in the charmed quark sector. The major physical research topics will be: Spectroscopy of resonances in the energy region of charmonium and above the D̄D threshold, in-medium effects of open and hidden charm, glueballs, and single and double hypernuclei. The proposed PANDA detector is a 4π spectrometer working with a fixed target in the internal beam of the HESR. It will allow the detection and identification of neutral and charged particles generated within the total energy range of the antiproton annihilation products. The charged particle identification at polar angles from 22° to 140° will be performed with a detector barrel working with the Detection of Internally Reflected Cherenkov light (DIRC).

The PANDA detector at FAIR

Cooled antiproton beams of unprecedented intensities in the momentum range of 1.5–15 GeV/c will be used for the PANDA experiment at FAIR to perform high precision experiments in the charmed quark sector. Four major physical research topics will be addressed: Spectroscopy of resonances in the energy region of charmonium and above, In-medium effects of open and hidden charm, glueballs, predicted by QCD, and single and double hypernuclei. The proposed PANDA detector is a 4π internal target spectrometer at the HESR allowing the detection and identification of neutral and charged particles generated within the total energy range of the antiproton annihilation products.

Detection of long-lived neutral particles with ATLAS

A number of extensions of the Standard Model result in particles that are neutral, weakly coupled and have macroscopic decay lengths comparable with LHC detector dimensions. These long-lived particles occur in many models: gauge-mediated SUSY extensions of the MSSM (addition of one singlet field), MSSM with R-parity violation, split SUSY, inelastic dark matter and Hidden Valley (HV) Scenarios in which a new sector is weakly coupled to the Standard Model. In the HV models long-lived particles decaying to heavy quark pairs and tau pairs can be produced in SUSY processes, Z' decays and Higgs boson decays. For the purpose of exploring the challenges to the trigger posed by long-lived neutral particles, the Hidden Valley scenario serves as an excellent setting. Results are presented of a first study of the ATLAS Detector performance for the Higgs decay h0 → π0 vπ0 v, where π0 v is neutral and has a displaced decay mainly to bottom quarks. The initial goal of the study is to obtain benchmark triggers for processes with such non-standard signatures in the ATLAS apparatus.

Space weathering on near-Earth objects investigated by neutral-particle detection

The ion-sputtering (IS) process is active in many planetary environments in the solar system where plasma precipitates directly on the surface (for instance, Mercury, Moon and Europa). In particular, solar wind sputtering is one of the most important agents for the surface erosion of a near-Earth object (NEO), acting together with other surface release processes, such as photon stimulated desorption (PSD), thermal desorption (TD) and micrometeoroid impact vaporization (MIV). The energy distribution of the IS-released neutrals peaks at a few eVs and extends up to hundreds of eVs. Since all other release processes produce particles of lower energies, the presence of neutral atoms in the energy range above 10 eV and below a few keVs (sputtered high-energy atoms (SHEA)) identifies the IS process. SHEA easily escape from the NEO, due to NEO's extremely weak gravity. Detection and analysis of SHEA will give important information on surface-loss processes as well as on surface elemental composition. The investigation of the active release processes, as a function of the external conditions and the NEO surface properties, is crucial for obtaining a clear view of the body's present loss rate as well as for getting clues on its evolution, which depends significantly on space weather. In this work, an attempt to analyze processes that take place on the surface of these small airless bodies, as a result of their exposure to the space environment, has been realized. For this reason, a new space weathering model (space weathering on NEO-SPAWN) is presented. Moreover, an instrument concept of a neutral-particle analyzer specifically designed for the measurement of neutral density and the detection of SHEA from a NEO is proposed.

Calibration of charge state conversion surfaces for neutral particle detectors

Molecular oxygen and hydrogen ions were scattered off hydrogen terminated diamondlike carbon (DLC) charge state conversion surfaces at incident grazing angles. The energy range of the scattered particles was 390–1000 eV, and the surface roughness of the DLC surface was of the order of 1 Å rms. For all surfaces almost equal angular scattering and negative ion fractions were found within the uncertainties of the measurement. This result supports the fact that charge state conversion with DLC surfaces is a reliable technology for neutral particle sensing instruments. Furthermore, these instruments can work in the laboratory as well as in the harsh environment on board a satellite.The surfaces measured here are used in the IBEX-lo sensor, a neutral particle sensing instrument on the NASA IBEX mission, which is scheduled for launch into orbit around Earth in July 2008.

Selective detection of 13C by laser photodetachment mass spectrometry

In this paper, we demonstrate how laser photodetachment mass spectrometry (LPMS) can be used to selectively detect 13C − ions in the presence of 12C − ions in a low energy ion beam. An isotopically enriched beam of carbon ions consisting of equal amounts of 13C − and 12C − ions was extracted from an ion source. The ions interacted with a laser beam in a collinear geometry over a distance of 70 cm. Residual atoms produced in the photodetachment process were detected in a neutral particle detector placed downstream of the collinear interaction region. By making use of the Doppler effect we were able to selectively photodetach 13C − ions. The number of detected 13C atoms was 13 times larger than the number of detected 12C atoms. The population of the excited, weakly bound 2D excited state of the C − ion was depleted by the use of a second laser. This significantly reduced the background accompanying the signal arising from the photodetachment of the 4S ground state C − ion. Different applications of the LPMS method will be discussed in the paper.

ENA detection in the dayside of Mars: ASPERA-3 NPD statistical study

The Analyzer of Space Plasma and EneRgetic Atoms (ASPERA-3) on board Mars Express is designed to study the interaction between the solar wind and the atmosphere of Mars and to characterize the plasma and neutral gas environment in near-Mars space. Neutral Particle Detectors (NPD-1 and 2), which form part of the ASPERA-3 instrument suite, are Energetic Neutral Atom (ENA) detectors which use the time-of-flight (ToF) technique to resolve the energy of detected particles. In the present study, we perform a statistical analysis of NPD ToF data collected between 14 March 2004 and 17 June 2004 when Mars Express was located at the dayside of Mars looking toward the planet. After pre-processing and removal of UV contamination, the ToF spectra were fitted with simple analytical functions so as to derive a set of parameters. The behavior of these parameters, as a function of spacecraft position and attitude, is compared with a model, which describes ENA generation by charge exchange between shocked solar wind protons and extended Martian exosphere. The observations and the model agree well, indicating that the recorded signals are charge-exchanged shocked solar wind.

The Analyser of Space Plasmas and Energetic Atoms (ASPERA-4) for the Venus Express mission

The general scientific objective of the ASPERA-4 (Analyser of Space Plasmas and Energetic Atoms) experiment is to study the solar wind–atmosphere interaction and characterise the plasma and neutral gas environment in the near-Venus space through energetic neutral atom (ENA) imaging and local charged particle measurements. The studies to be performed address the fundamental question: How strongly do the interplanetary plasma and electromagnetic fields affect the Venusian atmosphere? The ASPERA-4 instrument comprises four sensors; two ENA sensors, electron and ion spectrometers. The neutral particle imager (NPI) provides measurements of the integral ENA flux (0.1–60 keV) with no mass and energy resolution but relatively high angular resolution. The neutral particle detector (NPD) provides measurements of the ENA flux, resolving velocity (0.1–10 keV) and mass (H and O) with a coarse angular resolution. The electron spectrometer (ELS) is a standard top-hat electrostatic analyser in a very compact design. These three sensors are located on a scanning platform providing a 4 π coverage. The instrument also contains an ion mass composition sensor, IMA (ion mass analyser). Mechanically, IMA is a separate unit electrically connected with the ASPERA-4 main unit. IMA provides ion measurements in the energy range 0.01–36 keV/ q for the main ion components H + , He ++ , He + , and the ion group with M / q 20 – 80 amu / q .

Observations of the Martian Subsolar ENA Jet Oscillations

The Neutral Particle Detector (NPD) of the ASPERA-3 experiment (Analyser of Space Plasmas and Energetic Atoms) on board the Mars Express (MEX) spacecraft observed an intense flux of H ENAs (energetic neutral atoms) with average energy of about 1.5 keV emitted anisotropically from the subsolar region of Mars. The NPD detected the ENA jet near the bow shock at radial distances of about 1 R M from the Martian surface as the spacecraft moved outbound, while the NPD continuously pointed towards the subsolar region. The jet intensity shows oscillative behavior. These intensity variations occur on two clearly distinguishable time scales. The majority of the identified events have an average oscillation period of about 50 sec. The second group consists of events with long-scale variations with a time scale of approximately 300 sec. The fast oscillations of the first group exhibit a periodic structure and are detected in every orbit, while the slow variations of the second group are identified in ∼40% of orbits. The intensity of the fast oscillations have a peak-to-valley ratio about 20 to 30% of the peak intensity. One of the possible mechanisms to explain fast oscillations is the formation of the low frequency ion waves at the subsolar region of Mars. Slow variations may be explained by either temporal variations in the ENA generation source or by a specific structure of the ENA generation source, in which hair-like ENA subjets can be present.

Energetic Hydrogen and Oxygen Atoms Observed on the Nightside of Mars

We present measurements of energetic hydrogen and oxygen atoms (ENAs) on the nightside of Mars detected by the neutral particle detector (NPD) of ASPERA-3 on Mars Express. We focus on the observations for which the field-of-view of NPD was directed at the nightside of Mars or at the region around the limb, thus monitoring the flow of ENAs towards the nightside of the planet. We derive energy spectra and total fluxes, and have compiled maps of hydrogen ENA outflow. The hydrogen ENA intensities reach 105 cm−2 sr−1 s−1, but no oxygen ENA signals above the detection threshold of 104 cm−2 sr−1 s−1 are observed. These intensities are considerably lower than most theoretical predictions. We explain the discrepancy as due to an overestimation of the charge-exchange processes in the models for which too high an exospheric density was assumed. Recent UV limb emission measurements (Galli et al., this issue) point to a hydrogen exobase density of 1010 m−3 and a very hot hydrogen component, whereas the models were based on a hydrogen exobase density of 1012 m−3 and a temperature of 200 K predicted by (1996). Finally, we estimate the global atmospheric loss rate of hydrogen and oxygen due to the production of ENAs.

The Analyzer of Space Plasmas and Energetic Atoms (ASPERA-3) for the Mars Express Mission

The general scientific objective of the ASPERA-3 experiment is to study the solar wind – atmosphere interaction and to characterize the plasma and neutral gas environment with within the space near Mars through the use of energetic neutral atom (ENA) imaging and measuring local ion and electron plasma. The ASPERA-3 instrument comprises four sensors: two ENA sensors, one electron spectrometer, and one ion spectrometer. The Neutral Particle Imager (NPI) provides measurements of the integral ENA flux (0.1–60 keV) with no mass and energy resolution, but high angular resolution. The measurement principle is based on registering products (secondary ions, sputtered neutrals, reflected neutrals) of the ENA interaction with a graphite-coated surface. The Neutral Particle Detector (NPD) provides measurements of the ENA flux, resolving velocity (the hydrogen energy range is 0.1–10 keV) and mass (H and O) with a coarse angular resolution. The measurement principle is based on the surface reflection technique. The Electron Spectrometer (ELS) is a standard top-hat electrostatic analyzer in a very compact design which covers the energy range 0.01–20 keV. These three sensors are located on a scanning platform which provides scanning through 180∘ of rotation. The instrument also contains an ion mass analyzer (IMA). Mechanically IMA is a separate unit connected by a cable to the ASPERA-3 main unit. IMA provides ion measurements in the energy range 0.01–36 keV/charge for the main ion components H+, He++, He+, O+, and the group of molecular ions 20–80 amu/q. ASPERA-3 also includes its own DC/DC converters and digital processing unit (DPU).

The Hydrogen Exospheric Density Profile Measured with ASPERA-3/NPD

We have evaluated the Lyman-α limb emission from the exospheric hydrogen of Mars measured by the neutral particle detector of the ASPERA-3 instrument on Mars Express in 2004 at low solar activity (solar activity index = 42, F10.7=100). We derive estimates for the hydrogen exobase density, n H = 1010 m−3, and for the apparent temperature, T > 600 K. We conclude that the limb emission measurement is dominated by a hydrogen component that is considerably hotter than the bulk temperature at the exobase. The derived values for the exosphere density and temperature are compared with similar measurements done by the Mariner space probes in the 1969. The values found with Mars Express and Mariner data are brought in a broader context of exosphere models including the possibility of having two hydrogen components in the Martian exosphere. The present observation of the Martian hydrogen exosphere is the first one at high altitudes during low solar activity, and shows that for low solar activity exospheric densities are not higher than for high solar activity.

Global Response of Martian Plasma Environment to an Interplanetary Structure: From Ena and Plasma Observations at Mars

As a part of the global plasma environment study of Mars and its response to the solar wind, we have analyzed a peculiar case of the subsolar energetic neutral atom (ENA) jet observed on June 7, 2004 by the Neutral Particle Detector (NPD) on board the Mars Express satellite. The “subsolar ENA jet“ is generated by the interaction between the solar wind and the Martian exosphere, and is one of the most intense sources of ENA flux observed in the vicinity of Mars. On June 7, 2004 (orbit 485 of Mars Express), the NPD observed a very intense subsolar ENA jet, which then abruptly decreased within ∼10 sec followed by quasi-periodic (∼1 min) flux variations. Simultaneously, the plasma sensors detected a solar wind structure, which was most likely an interplanetary shock surface. The abrupt decrease of the ENA flux and the quasi-periodic flux variations can be understood in the framework of the global response of the Martian plasma obstacle to the interplanetary shock. The generation region of the subsolar ENA jet was pushed towards the planet by the interplanetary shock; and therefore, Mars Express went out of the ENA jet region. Associated global vibrations of the Martian plasma obstacle may have been the cause of the quasi-periodic flux variations of the ENA flux at the spacecraft location.

First ENA observations at Mars: ENA emissions from the martian upper atmosphere

The neutral particle detector (NPD) on board Mars Express has observed energetic neutral atoms (ENAs) from a broad region on the dayside of the martian upper atmosphere. We show one such example for which the observation was conducted at an altitude of 570 km, just above the induced magnetosphere boundary (IMB). The time of flight spectra of these ENAs show that they had energies of 0.2–2 keV/amu, with an average energy of ∼1.1 keV/amu. Both the spatial distribution and the energy of these ENAs are consistent with the backscattered ENAs, produced by an ENA albedo process. This is the first observation of backscattered ENAs from the martian upper atmosphere. The origin of these ENAs is considered to be the solar wind ENAs that are scattered back by collision processes in the martian upper atmosphere. The particle flux and energy flux of the backscattered ENAs are 0.9 – 1.3 × 10 7 cm −2 s −1 and ∼ 9.5 × 10 9 eV cm −2 s −1 , respectively.

First ENA observations at Mars: Subsolar ENA jet

The Neutral Particle Detector (NPD), an Energetic Neutral Atom (ENA) sensor of the Analyzer of Space Plasmas and Energetic Atoms (ASPERA-3) on board Mars Express, detected intense fluxes of ENAs emitted from the subsolar region of Mars. The typical ENA fluxes are (4–7) × 10 5 cm −2 sr −1 s −1 in the energy range 0.3–3 keV. These ENAs are likely to be generated in the subsolar region of the martian exosphere. As the satellite moved away from Mars, the ENA flux decreased while the field of view of the NPD pointed toward the subsolar region. These decreases occurred very quickly with a time scale of a few tens of seconds in two thirds of the orbits. Such a behavior can be explained by the spacecraft crossing a spatially constrained ENA jet, i.e., a highly directional ENA emission from a compact region of the subsolar exosphere. This ENA jet is highly possible to be emitted conically from the subsolar region. Such directional ENAs can result from the anisotropic solar wind flow around the subsolar region, but this can not be explained in the frame of MHD models.