55 research outputs found
Scintillation of liquid neon from electronic and nuclear recoils
We have measured the time dependence of scintillation light from electronic
and nuclear recoils in liquid neon, finding a slow time constant of 15.4+-0.2
us. Pulse shape discrimination is investigated as a means of identifying event
type in liquid neon. Finally, the nuclear recoil scintillation efficiency is
measured to be 0.26+-0.03 for 387 keV nuclear recoils
Preparation of Neutron-activated Xenon for Liquid Xenon Detector Calibration
We report the preparation of neutron-activated xenon for the calibration of
liquid xenon (LXe) detectors. Gamma rays from the decay of xenon metastable
states, produced by fast neutron activation, were detected and their activities
measured in a LXe scintillation detector. Following a five-day activation of
natural xenon gas with a Cf-252 (4 x 10^5 n/s) source, the activities of two
gamma ray lines at 164 keV and 236 keV, from Xe-131m and Xe-129m metastable
states, were measured at about 95 and 130 Bq/kg, respectively. We also observed
three additional lines at 35 keV, 100 keV and 275 keV, which decay away within
a few days. No long-lifetime activity was observed after the neutron
activation.Comment: to be published in NIM A, corrected typos in Table 1 and Fig.6 of the
previous versio
Neutrino Detection With CLEAN
This article describes CLEAN, an approach to the detection of low-energy
solar neutrinos and neutrinos released from supernovae. The CLEAN concept is
based on the detection of elastic scattering events (neutrino-electron
scattering and neutrino-nuclear scattering) in liquified noble gases such as
liquid helium, liquid neon, and liquid xenon, all of which scintillate brightly
in the ultraviolet. Key to the CLEAN technique is the use of a thin film of
wavelength-shifting fluor to convert the ultraviolet scintillation light to the
visible. This allows the same liquid to be used as both a passive shielding
medium and an active self-shielding detector, allowing lower intrinsic
radioactive backgrounds at low energies. Liquid neon is a particularly
promising medium for CLEAN. Because liquid neon has a high scintillation yield,
has no long-lived radioactive isotopes, and can be easily purified by use of
cold traps, it is an ideal medium for the detection of rare nuclear events. In
addition, neon is inexpensive, dense, and transparent to its own scintillation
light, making it practical for use in a large self-shielding apparatus. Monte
Carlo simulations of gamma ray backgrounds have been performed assuming liquid
neon as both shielding and detection medium. Gamma ray events occur with high
probability in the outer parts of the detector. In contrast, neutrino
scattering events occur uniformly throughout the detector. We discriminate
background gamma ray events from events of interest based on a spatial Maximum
Likelihood method estimate of event location. Background estimates for CLEAN
are presented, as well as an evaluation of the sensitivity of the detector for
neutrinos. Given these simulations, the physics potential of the CLEAN
approach is evaluated.Comment: 21 pages, 3 figures. Submitted to Astroparticle Physic
Scintillation and charge extraction from the tracks of energetic electrons in superfluid helium-4
An energetic electron passing through liquid helium causes ionization along
its track. The ionized electrons quickly recombine with the resulting positive
ions, which leads to the production of prompt scintillation light. By applying
appropriate electric fields, some of the ionized electrons can be separated
from their parent ions. The fraction of the ionized electrons extracted in a
given applied field depends on the separation distance between the electrons
and the ions. We report the determination of the mean electron-ion separation
distance for charge pairs produced along the tracks of beta particles in
superfluid helium at 1.5 K by studying the quenching of the scintillation light
under applied electric fields. Knowledge of this mean separation parameter will
aid in the design of particle detectors that use superfluid helium as a target
material.Comment: 10 pages, 8 figure
Observation of Crossover from Ballistic to Diffusion Regime for Excimer Molecules in Superfluid He
We have measured the temperature dependence of the time of flight of helium
excimer molecules He2* in superfluid 4He and find that the molecules behave
ballistically below 100mK and exhibit Brownian motion above 200 mK. In the
intermediate temperature range the transport cannot be described by either of
the models.Comment: 8 pages, 6 figures, submitted to the Proceedings of the International
Conference on Quantum Fluids and Solids 201
Magnetically Stabilized Luminescent Excitations in Hexagonal Boron Nitride
Magnetically stabilized luminescence is observed in hexagonal boron nitride.
The luminescence is induced by absorption of cold neutrons and is in the
visible region. In the absence of a magnetic field, the photon emission level
is observed to decay over several hundred seconds. A fraction of this
luminescence can be suppressed if the temperature is T <~ 0.6 K and the
magnetic field is B >~ 1.0 T. Subsequent to irradiation and suppression,
luminescence can be induced by an increase in T or lowering of B. Possible
explanations include stabilization of triplet states or the localization and
stabilization of excitons.Comment: 11 pages, 7 figures, to appear in the Journal of Luminescenc
Electron - nuclear recoil discrimination by pulse shape analysis
In the framework of the ``ULTIMA'' project, we use ultra cold superfluid 3He
bolometers for the direct detection of single particle events, aimed for a
future use as a dark matter detector. One parameter of the pulse shape observed
after such an event is the thermalization time constant. Until now it was
believed that this parameter only depends on geometrical factors and superfluid
3He properties, and that it is independent of the nature of the incident
particles. In this report we show new results which demonstrate that a
difference for muon- and neutron events, as well as events simulated by heater
pulses exist. The possibility to use this difference for event discrimination
in a future dark matter detector will be discussed.Comment: Proseedings of QFS 2007, Kazan, Russia; 8 pages, 4 figures. Submited
to J. Low Temp. Phy
Magnetic trapping of ultracold neutrons
Three-dimensional magnetic confinement of neutrons is reported. Neutrons are
loaded into an Ioffe-type superconducting magnetic trap through inelastic
scattering of cold neutrons with 4He. Scattered neutrons with sufficiently low
energy and in the appropriate spin state are confined by the magnetic field
until they decay. The electron resulting from neutron decay produces
scintillations in the liquid helium bath that results in a pulse of extreme
ultraviolet light. This light is frequency downconverted to the visible and
detected. Results are presented in which 500 +/- 155 neutrons are magnetically
trapped in each loading cycle, consistent with theoretical predictions. The
lifetime of the observed signal, 660 s +290/-170 s, is consistent with the
neutron beta-decay lifetime.Comment: 17 pages, 18 figures, accepted for publication in Physical Review
Homestake result, sterile neutrinos and low energy solar neutrino experiments
The Homestake result is about ~ 2 \sigma lower than the Ar-production rate,
Q_{Ar}, predicted by the LMA MSW solution of the solar neutrino problem. Also
there is no apparent upturn of the energy spectrum (R \equiv N_{obs}/N_{SSM})
at low energies in SNO and Super-Kamiokande. Both these facts can be explained
if a light, \Delta m^2_{01} ~ (0.2 - 2) \cdot 10^{-5} eV^2, sterile neutrino
exists which mixes very weakly with active neutrinos: \sin^2 2\alpha ~ (10^{-5}
- 10^{-3}). We perform both the analytical and numerical study of the
conversion effects in the system of two active neutrinos with the LMA
parameters and one weakly mixed sterile neutrino. The presence of sterile
neutrino leads to a dip in the survival probability in the intermediate energy
range E = (0.5 - 5) MeV thus suppressing the Be, or/and pep, CNO as well as B
electron neutrino fluxes. Apart from diminishing Q_{Ar} it leads to decrease of
the Ge-production rate and may lead to decrease of the BOREXINO signal and
CC/NC ratio at SNO. Future studies of the solar neutrinos by SNO, SK, BOREXINO
and KamLAND as well as by the new low energy experiments will allow us to check
this possibility. We present a general analysis of modifications of the LMA
energy profile due to mixing with new neutrino states.Comment: Figures 5 and 6 modified, shorter version will be published in PR
The scintillation and ionization yield of liquid xenon for nuclear recoils
XENON10 is an experiment designed to directly detect particle dark matter. It
is a dual phase (liquid/gas) xenon time-projection chamber with 3D position
imaging. Particle interactions generate a primary scintillation signal (S1) and
ionization signal (S2), which are both functions of the deposited recoil energy
and the incident particle type. We present a new precision measurement of the
relative scintillation yield \leff and the absolute ionization yield Q_y, for
nuclear recoils in xenon. A dark matter particle is expected to deposit energy
by scattering from a xenon nucleus. Knowledge of \leff is therefore crucial for
establishing the energy threshold of the experiment; this in turn determines
the sensitivity to particle dark matter. Our \leff measurement is in agreement
with recent theoretical predictions above 15 keV nuclear recoil energy, and the
energy threshold of the measurement is 4 keV. A knowledge of the ionization
yield \Qy is necessary to establish the trigger threshold of the experiment.
The ionization yield \Qy is measured in two ways, both in agreement with
previous measurements and with a factor of 10 lower energy threshold.Comment: 8 pages, 9 figures. To be published in Nucl. Instrum. Methods
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