XENON Project Research Articles

Source Term Analysis of Xenon (STAX): An effort focused on differentiating man-made isotope production from nuclear explosions via stack monitoring

An overview of the hardware and software developed for the Source Term Analysis of Xenon (STAX) project is presented which includes the data collection from two stack monitoring systems installed at medical isotope production facilities, infrastructure to transfer data to a central repository, and methods for sharing data from the repository with users. STAX is an experiment to collect radioxenon emission data from industrial nuclear facilities with the goal of developing a better understanding of the global radioxenon background and the effect industrial radioxenon releases have on nuclear explosion monitoring. A final goal of this work is to utilize collected data along with atmospheric transport modeling to calculate the contribution of a peak or set of peaks detected by the International Monitoring System (IMS) to provide desired discriminating information to the International Data Centre (IDC) and National Data Centers (NDCs). Types of data received from the STAX equipment are shown and collected data was used for a case study to predict radioxenon concentrations at two IMS stations closest to the Institute for RadioElements (IRE) in Belgium. The initial evaluation of results indicate that the data is very valuable to the nuclear explosion monitoring community.

First STAX detector installation at the National Institute for Radioelements (IRE)

The Source Term Analysis of Xenon (STAX) project has been installing stack detectors at medical isotope production facilities to measure radioxenon emissions to investigate the effect of radioxenon releases on nuclear explosion monitoring. This paper outlines the installation of the first STAX detection system at the National Institute for Radioelements (IRE) in Fleurus, Belgium which has been operating for over three years and transferring collected data to the STAX repository. Information about the equipment installed, the data flow established, and calculations for determination of radioxenon releases from the facility are presented. Data quality was investigated to confirm values reported by STAX automated data processing and in a comparison of collected STAX data with data collected by IRE for regulatory reporting.

The Xenon Road to Direct Detection of Dark Matter at LNGS: The XENON Project

Dark matter is a milestone in the understanding of the Universe and a portal to the discovery of new physics beyond the Standard Model of particles. The direct search for dark matter has become one of the most active fields of experimental physics in the last few decades. Liquid Xenon (LXe) detectors demonstrated the highest sensitivities to the main dark matter candidates (Weakly Interactive Massive Particles, WIMP). The experiments of the XENON project, located in the underground INFN Laboratori Nazionali del Gran Sasso (LNGS) in Italy, are leading the field thanks to the dual-phase LXe time projection chamber (TPC) technology. Since the first prototype XENON10 built in 2005, each detector of the XENON project achieved the highest sensitivity to WIMP dark matter. XENON increased the LXe target mass by nearly a factor 400, up to the 5.9 t of the current XENONnT detector installed at LNGS in 2020. Thanks to an unprecedentedly low background level, XENON1T (predecessor of XENONnT) set the world best limits on WIMP dark matter to date, for an overall boost of more than 3 orders of magnitude to the experimental sensitivity since the XENON project started. In this work, we review the principles of direct dark matter detection with LXe TPCs, the detectors of the XENON project, the challenges posed by background mitigation to ultra-low levels, and the main results achieved by the XENON project in the search for dark matter.

Latest results from the XENON1T experiment

The most successful class of direct detection of WIMPs with masses from few GeV/c2 to TeV/c2 have utilized Liquid Xenon time projection chambers (TPCs). The XENON project adopted dual phase TPCs using ultra-pure liquid Xenon as both target and detection medium for WIMPs. The first ton-scale Liquid Xenon based TPC, XENON1T, is running at the Gran Sasso Laboratory. With an active mass inside the TPC of 2 tonnes, data were collected for 278.8 days live time. Within a fiducial mass of 1.3 tonne, this results in 1.0 tonne×year exposure. In the energy region of interest, the detector exhibits the lowest background ever obtained in direct dark matter search experiment. In these data no significant excess over background is found and the most stringent limits on WIMP-nucleon spin-independent elastic scattering cross section has been set for masses above 6 GeV/c2 with a minimum of 4.1×10−47cm2 at 30 GeV/c2.

The XENON project for dark matter direct detection at LNGS

The XENON project at INFN Laboratori Nazionali del Gran Sasso, Italy, aims at dark matter direct detection with liquid xenon dual-phase time projection chambers. Latest results of XENON100 detector exclude various models of leptophilic dark matter. A search for low mass weakly interacting massive particles was also performed, lowering the energy threshold for detection to 0.7 keV for nuclear recoils. The multi-ton XENON1T detector is fully installed and operating. It is expected to reach a sensitivity a factor 100 better than XENON100 with a 2 ton·year exposure.

Status of the XENON Project

Astronomical and cosmological observations indicate that a large amount of the energy content of the Universe is made of dark matter. The most promising dark matter candidates are the so-called Weakly Interacting Massive Particles. The search for these particles is performed with various experimental approaches. The XENON Project, at the Gran Sasso National Laboratory, is devoted to the direct search of dark matter particles. It consists in operating a double-phase time projection chamber using ultra-pure liquid Xenon as both target and detection medium for dark matter particle interactions. The WIMPs can be indeed detected via their elastic scattering off Xenon nuclei.The XENON100 detector with 160 kg of liquid Xenon has reached in 2012 the sensitivity of 2×10-45 cm2 at 55 GeV/c2 and 90% confidence level on spin-independent elastic WIMP-nucleon scattering cross section. The next generation XENON1T detector, that will host 3.3 tonnes of ultra-pure liquid Xenon, is in its final stage of construction and will likely start taking data by the end of 2015. The detector is designed to increase the sensitivity by two orders of magnitude.

Status of the solid xenon project at Fermilab

The solid (crystalline) phase of xenon possesses many of the same advantages of liquid xenon as a particle detector material including good transparency and ionization drift, self-shielding, low intrinsic background, and high scintillation light yield. Many of the properties of solid xenon have been measured previously employing small volumes and thin films. However, few systematic studies have been successfully produced using large volumes of solid xenon. Two major R&D issues must be addressed to make a solid xenon particle detector; the demonstration of the scalability of solid xenon and the capability to readout solid xenon signals. Both issues are being addressed with a dedicated cryogenic system at Fermilab. The first phase of this project entailed growing approximately a kilogram of transparent solid phase xenon and was successfully completed in 2010 at Fermilab. The second phase of this project is underway where the signals from scintillation light and electron drift in solid xenon will be measured. These measurements are expected to be completed this year. In this talk, we will discuss the recent progress of solid xenon detector R&D performed at Fermilab.

Limits on the release of Rb isotopes from a zeolite based 83mKr calibration source for the XENON project

The isomer 83mKr with its half-life of 1.83 h is an ideal calibration source for a liquid noble gas dark matter experiment like the XENON project. However, the risk of contamination of the detector with traces of the much longer lived mother isotope 83Rb(T½ = 86.2 d) has to be ruled out. In this work the release of 83Rb atoms from a 1.8 MBq 83Rb source embedded in zeolite beads has been investigated. To do so, a cryogenic trap has been connected to the source for about 10 days, after which it was removed and probed for the strongest 83Rbγ-rays with an ultra-sensitive Germanium detector. No signal has been found. The corresponding upper limit on the released 83Rb activity means that the investigated type of source can be used in the XENON project and similar low-background experiments as 83mKr generator without a significant risk of contaminating the detector. The measurements also allow to set upper limits on the possible release of the isotopes 84Rb and 86Rb, traces of which were created alongside the production of 83Rb at the Rez cyclotron.

Formal methods for security in the Xenon hypervisor

This paper reports on the Xenon project’s use of formal methods. Xenon is a higher-assurance secure hypervisor based on re-engineering the Xen open-source hypervisor. The Xenon project used formal specifications both for assurance and as guides for security re-engineering. We formally modelled the fundamental definition of security, the hypercall interface behaviour, and the internal modular design. We used three formalisms: CSP, Z, and Circus for this work. Circus is a combination of Standard Z, CSP with its semantics given in Hoare and He’s unifying theories of programming. Circus is suited for both event-based and state-based modelling. Here, we report our experiences to date with using these formalisms for assurance.

Re-engineering Xen internals for higher-assurance security

The Xenon project is investigating the construction of a higher-assurance open source separation kernel based on the Xen open source hypervisor. Just as the Xen open source hypervisor was initially developed from the open source Linux operating system, by simplifying Linux and modifying its design, the Xenon separation kernel is being developed from Xen. The primary goal of the Xenon project is to investigate issues in creating an open source software product with higher security assurance than conventional open source software. The Xenon project is also focused on (1) problems relating to separation kernels that support unmodified uninterpreted commercial off the shelf (COTS) guests and (2) distinctions between these kinds of separation kernels and hypervisors. This paper explains the Xenon project's approach to re-engineering Xen's internal structure into a higher-assurance form. If conventional open source software cannot be brought into this form with moderate amounts of re-engineering then higher-assurance open source software is probably not practical. Our results indicate that moderate amounts of re-engineering will be sufficient for all but a small part of the code. The remaining code is small enough to be addressed in a reasonable time, even though more effort is required.