16 research outputs found
Combining Stochastics and Analytics for a Fast Monte Carlo Decay Chain Generator
Various Monte Carlo programs, developed either by small groups or widely
available, have been used to calculate the effects of decays of radioactive
chains, from the original parent nucleus to the final stable isotopes. These
chains include uranium, thorium, radon, and others, and generally have
long-lived parent nuclei. Generating decays within these chains requires a
certain amount of computing overhead related to simulating unnecessary decays,
time-ordering the final results in post-processing, or both. We present a
combination analytic/stochastic algorithm for creating a time-ordered set of
decays with position and time correlations, and starting with an arbitrary
source age. Thus the simulation costs are greatly reduced, while at the same
time avoiding chronological post-processing. We discuss optimization methods
within the approach to minimize calculation time
A Model for the Secondary Scintillation Pulse Shape from a Gas Proportional Scintillation Counter
Proportional scintillation counters (PSCs), both single- and dual-phase, can
measure the scintillation (S1) and ionization (S2) channels from particle
interactions within the detector volume. The signal obtained from these
detectors depends first on the physics of the medium (the initial scintillation
and ionization), and second how the physics of the detector manipulates the
resulting photons and liberated electrons. In this paper we develop a model of
the detector physics that incorporates event topology, detector geometry,
electric field configuration, purity, optical properties of components, and
wavelength shifters. We present an analytic form of the model, which allows for
general study of detector design and operation, and a Monte Carlo model which
enables a more detailed exploration of S2 events. This model may be used to
study systematic effects in currents detectors such as energy and position
reconstruction, pulse shape discrimination, event topology, dead time
calculations, purity, and electric field uniformity. We present a comparison of
this model with experimental data collected with an argon gas proportional
scintillation counter (GPSC), operated at 20 C and 1 bar, and irradiated with
an internal, collimated 55Fe source. Additionally we discuss how the model may
be incorporated in Monte Carlo simulations of both GPSCs and dual-phase
detectors, increasing the reliability of the simulation results and allowing
for tests of the experimental data analysis algorithms.Comment: 10 pages, 9 figure
Comparison of Lithium Gadolinium Borate Crystal Shards in Scintillating and Nonscintillating Plastic Matrices
We present a method for detecting neutrons using scintillating lithium
gadolinium borate crystal shards in a plastic matrix while maintaining high
gamma rejection. We have procured two cylindrical detectors, 5"\times5",
containing 1% crystal by mass. Crystal shards have a typical dimension of 1 mm.
One detector was made with scintillating plastic, and one with nonscintillating
plastic. Pulse shape analysis was used to reject gamma ray backgrounds. The
scintillating detector was measured to have an intrinsic fast fission neutron
efficiency of 0.4% and a gamma sensitivity of less than 2.3 \times 10-9, while
the nonscintillating detector had a neutron efficiency of 0.7% and gamma
sensitivity of (4.75\pm3.94)\times10-9. We determine that increasing the
neutron detection efficiency by a factor of 2 will make the detector
competitive with moderated 3He tubes, and we discuss several simple and
straightforward methods for obtaining or surpassing such an improvement. We end
with a discussion of possible applications, both for the scintillating-plastic
and nonscintillating-plastic detectors.Comment: 32 pages, 17 Figures, 3 Table
Using Cyclotron Radiation Emission for Ultra-high Resolution X-Ray Spectroscopy
Cyclotron Radiation Emission Spectroscopy (CRES) is an approach to measuring
the energy of an electron trapped in an externally applied magnetic field. The
bare electron can come from different interactions, including photoelectric
absorption, Compton scatters, beta decay, and pair production. CRES relies on
measuring the frequency of the electron's cyclotron motion, and because the
measurement times extend over - cycles, the energy resolution is on
the order of a single electronvolt. To date, CRES has only been performed on
internal beta-emitting radioisotopes, but the technology can be applied to
X-ray spectrometery through appropriate selection of a target gas and
sufficient intensity of the distinct X-ray source. The applications of this
technology range from high-precision measurements of atomic energy levels, to
calibrations of basic science experiments, to trace element identification. In
this work we explore the use of CRES for X-ray spectroscopy within the rubric
of measuring the energy levels of argon, although the principles are broadly
applicable to many other situations. The issues we explore include target
material, density, electron trapping depth, noise levels, and overall
efficiency. We also discuss spectral deconvolution and how the multiple peaks
obtained from a single target / source pair can be used to enhance the
robustness of the measurement.Comment: 11 pages, 9 figure
A Global Analysis of Light and Charge Yields in Liquid Xenon
We present an updated model of light and charge yields from nuclear recoils
in liquid xenon with a simultaneously constrained parameter set. A global
analysis is performed using measurements of electron and photon yields compiled
from all available historical data, as well as measurements of the ratio of the
two. These data sweep over energies from 1 - 300 keV and external applied
electric fields from 0 - 4060 V/cm. The model is constrained by constructing
global cost functions and using a gradient descent minimizer, a simulated
annealing algorithm, and a Markov Chain Monte Carlo approach to optimize and
find confidence intervals on all free parameters in the model. This analysis
contrasts with previous work in that we do not unnecessarily exclude data sets
nor impose artificially conservative assumptions, do not use spline functions,
and reduce the number of parameters used in NEST v0.98. We report our results
and the calculated best-fit charge and light yields. These quantities are
crucial to understanding the response of liquid xenon detectors in the energy
regime important for rare event searches such as the direct detection of dark
matter particles.Comment: 9 pages, 11 figure
Replacement of a Photomultiplier Tube with Silicon Photomultipliers for use in Safeguards Applications
We compared the performance of a SiPM array and a PMT in a laboratory setting
using a single 5.08x5.08-cm cylindrical sodium iodide scintillating crystal.
Photomultiplier tubes (PMTs) are the most commonly used device to monitor
scintillating materials for radiation detection purposes. The systems are
sometimes limited by disadvantages in the PMTs that may degrade their
performance, including temperature dependence and variation with magnetic
field. Instrumentation engineering must also contend with a potentially large
volume relative to the active scintillator volume, fragility, and high voltage
requirements. One possible alternative is an array of silicon photomultipliers
(SiPMs). Measurements were made with a 5.04x5.04-cm sensL J-series SiPM array
and a 7.62cm Hamamatsu PMT. We demonstrated how the SiPM bias can be
sufficiently altered to remove the effects of temperature variation encountered
in environments where nuclear safeguards work is often performed. Finally, we
evaluated a method of determining enrichment levels of at various
levels and shielding configurations, using both the PMT-mounted and
SiPM-mounted scintillator.Comment: 7 pages, 7 figure
Electron extraction efficiency study for dual-phase xenon dark matter experiments
Dual-phase xenon detectors are widely used in dark matter direct detection
experiments, and have demonstrated the highest sensitivities to a variety of
dark matter interactions. However, a key component of the dual-phase detector
technology--the efficiency of charge extraction from liquid xenon into gas--has
not been well characterized. In this paper, we report a new measurement of the
electron extraction efficiency (EEE) in a small xenon detector using two
mono-energetic decay features of Ar. By achieving stable operation at
very high voltages, we measured the EEE values at the highest extraction
electric field strength reported to date. For the first time, an apparent
saturation of the EEE is observed over a large range of electric field; between
7.5 kV/cm and 10.4 kV/cm extraction field in the liquid xenon the EEE stays
stable at the level of 1%(kV/cm). In the context of electron transport
models developed for xenon, we discuss how the observed saturation may help
calibrate this relative EEE measurement to the absolute EEE values. In
addition, we present the implications of this result not only to current and
future xenon-based dark matter searches, but also to xenon-based searches for
coherent elastic neutrino-nucleus scatters
Modeling Pulse Characteristics in Xenon with NEST
A comprehensive model for describing the characteristics of pulsed signals,
generated by particle interactions in xenon detectors, is presented. An
emphasis is laid on two-phase time projection chambers, but the models
presented are also applicable to single phase detectors. In order to simulate
the pulse shape due to primary scintillation light, the effects of the ratio of
singlet and triplet dimer state populations, as well as their corresponding
decay times, and the recombination time are incorporated into the model. In a
two phase time projection chamber, when simulating the pulse caused by
electroluminescence light, the ionization electron mean free path in gas, the
drift velocity, singlet and triplet decay times, diffusion constants, and the
electron trapping time, have been implemented. This modeling has been
incorporated into a complete software package, which realistically simulates
the expected pulse shapes for these types of detectors
Measurement of the ionization yield from nuclear recoils in liquid xenon between 0.3 -- 6 keV with single-ionization-electron sensitivity
Dual-phase xenon TPC detectors are a highly scalable and widely used
technology to search for low-energy nuclear recoil signals from WIMP dark
matter or coherent nuclear scattering of MeV neutrinos. Such experiments
expect to measure O(keV) ionization or scintillation signals from such sources.
However, at keV and below, the signal calibrations in liquid xenon
carry large uncertainties that directly impact the assumed sensitivity of
existing and future experiments. In this work, we report a new measurement of
the ionization yield of nuclear recoil signals in liquid xenon down to
0.3keV-- the lowest energy calibration reported to date -- at which
energy the average event produces just 1.1~ionized~electrons. Between 2 and
6keV, our measurements agree with existing measurements, but significantly
improve the precision. At lower energies, we observe a decreasing trend that
deviates from simple extrapolations of existing data. We also study the
dependence of ionization yield on the applied drift field in liquid xenon
between 220V/cm and 6240V/cm, allowing these measurements to apply to a broad
range of current and proposed experiments with different operating parameters.Comment: 13 pages, 8 figure
MaGe - a Geant4-based Monte Carlo framework for low-background experiments
A Monte Carlo framework, MaGe, has been developed based on the Geant4
simulation toolkit. Its purpose is to simulate physics processes in low-energy
and low-background radiation detectors, specifically for the Majorana and Gerda
Ge neutrinoless double-beta decay experiments. This jointly-developed
tool is also used to verify the simulation of physics processes relevant to
other low-background experiments in Geant4. The MaGe framework contains
simulations of prototype experiments and test stands, and is easily extended to
incorporate new geometries and configurations while still using the same
verified physics processes, tunings, and code framework. This reduces
duplication of efforts and improves the robustness of and confidence in the
simulation output