We introduce a simulation framework for the transport of high and low energy electrons in xenon-based optical time projection chambers (OTPCs). The simulation relies on elementary cross sections ...(electron–atom and electron–molecule) and incorporates, in order to compute the gas scintillation, the reaction/quenching rates (atom–atom and atom–molecule) of the first 41 excited states of xenon and the relevant associated excimers, together with their radiative cascade. The results compare positively with observations made in pure xenon and its mixtures with CO2 and CF4 in a range of pressures from 0.1 to 10 bar. This work sheds some light on the elementary processes responsible for the primary and secondary xenon-scintillation mechanisms in the presence of additives, that are of interest to the OTPC technology.
As the amount of digital data grows, so does the theft of sensitive data through the loss or misplacement of laptops, thumb drives, external hard drives, and other electronic storage media. Sensitive ...data may also be leaked accidentally due to improper disposal or resale of storage media. To protect the secrecy of the entire data lifetime, we must have confidential ways to store and delete data. This survey summarizes and compares existing methods of providing confidential storage and deletion of data in personal computing environments. PUBLICATION ABSTRACT
The amount of sensitive data stored on electronic media increases as the use of computers and mobile devices becomes more prevalent. For example, home computers and devices may store financial ...information (e.g., Quicken files or tax documents), usernames and passwords, private correspondence (e.g., emails or chat logs), and personal media files (e.g., pictures or videos). Business computers and devices may store sensitive client data and trade secrets. Government computers and devices may store personally identifiable data on citizens and various classified materials. As the amount of digital sensitive information accrues, the need for the ability to securely remove this information increases. Short of physically destroying the entire storage medium, existing secure-deletion solutions tend to be piecemeal at best – they may only work for one type of storage or file system, may force the user to delete all files instead of selective files, may require the added complexities of encryption and key storage, may require extensive changes and additions to the computer's operating system or storage firmware, and may not handle system crashes gracefully. This dissertation introduces TrueErase, a holistic secure-deletion framework that irrevocably deletes data and metadata. At heart, TrueErase is an information-propagation framework that works alongside of legacy operating system components for easier integration. Through its design, implementation, verification, and evaluation on both a hard drive and emerging solid-state storage, TrueErase shows that it is possible to construct a holistic, per-file, encryption-free, secure-deletion framework that accommodates different storage media and legacy file systems, requires limited changes to legacy systems, and handles common crash scenarios. The experience of building TrueErase further contributes insight into the mechanisms and complexities of the legacy operating system storage data path.
We present evidence of non-excimer-based secondary scintillation in gaseous xenon, obtained using both the NEXT-White TPC and a dedicated setup. Detailed comparison with first-principle calculations ...allows us to assign this scintillation mechanism to neutral bremsstrahlung (NBrS), a process that has been postulated to exist in xenon that has been largely overlooked. For photon emission below 1000 nm, the NBrS yield increases from about 10\(^{-2}\) photon/e\(^{-}\) cm\(^{-1}\) bar\(^{-1}\) at pressure-reduced electric field values of 50 V cm\(^{-1}\) bar\(^{-1}\) to above 3\(\times\)10\(^{-1}\) photon/e\(^{-}\) cm\(^{-1}\) bar\(^{-1}\) at 500 V cm\(^{-1}\) bar\(^{-1}\). Above 1.5 kV cm\(^{-1}\) bar\(^{-1}\), values that are typically employed for electroluminescence, it is estimated that NBrS is present with an intensity around 1 photon/e\(^{-}\) cm\(^{-1}\) bar\(^{-1}\), which is about two orders of magnitude lower than conventional, excimer-based electroluminescence. Despite being fainter than its excimeric counterpart, our calculations reveal that NBrS causes luminous backgrounds that can interfere, in either gas or liquid phase, with the ability to distinguish and/or to precisely measure low primary-scintillation signals (S1). In particular, we show this to be the case in the "buffer" and "veto" regions, where keeping the electric field below the electroluminescence (EL) threshold will not suffice to extinguish secondary scintillation. The electric field in these regions should be chosen carefully to avoid intolerable levels of NBrS emission. Furthermore, we show that this new source of light emission opens up a viable path towards obtaining S2 signals for discrimination purposes in future single-phase liquid TPCs for neutrino and dark matter physics, with estimated yields up to 20-50 photons/e\(^{-}\) cm\(^{-1}\).
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