Germanium (Ge) detectors with ability of measuring a single electron–hole (e–h) pair are needed in searching for light dark matter (LDM) down to the MeV scale. We investigate the feasibility of Ge ...detectors with amorphous-Ge (a-Ge) contacts to achieve the sensitivity of measuring a single e-h pair, which requires extremely low leakage current. Three Ge detectors with a-Ge contacts are used to study the charge barrier height for blocking electrons and holes. Using the measured bulk leakage current and the Döhler–Brodsky model, we obtain the values for charge barrier height and the density of localized energy states near the Fermi energy level for the top and bottom contacts, respectively. We predict that the bulk leakage current is extremely small and can be neglected at helium temperature (
∼
4 K). Thus, Ge detectors with a-Ge contacts possess the potential to measure a single e–h pair for detecting LDM particles.
Light, MeV-scale dark matter (DM) is an exciting DM candidate that is undetectable by current experiments. A germanium (Ge) detector utilizing internal charge amplification for the charge carriers ...created by the ionization of impurities is a promising new technology with experimental sensitivity for detecting MeV-scale DM. We analyze the physics mechanisms of the signal formation, charge creation, charge internal amplification, and the projected sensitivity for directly detecting MeV-scale DM particles. We present a design for a novel Ge detector at helium temperature (
∼
4 K) enabling ionization of impurities from DM impacts. With large localized E-fields, the ionized excitations can be accelerated to kinetic energies larger than the Ge bandgap at which point they can create additional electron–hole pairs, producing intrinsic amplification to achieve an ultra-low energy threshold of
∼
0.1 eV for detecting low-mass DM particles in the MeV scale. Correspondingly, such a Ge detector with 1 kg-year exposure will have high sensitivity to a DM-nucleon cross section of
∼
5
×
10
-
45
cm
2
at a DM mass of
∼
10 MeV/c
2
and a DM-electron cross section of
∼
5
×
10
-
46
cm
2
at a DM mass of
∼
1 MeV/c
2
.
The detection of low-energy deposition in the range of sub-eV through ionization using germanium (Ge) with a bandgap of
∼
0.7 eV requires internal amplification of the charge signal. This can be ...achieved through high electric field that accelerates charge carriers, which can then generate more charge carriers. The minimum electric field required to generate internal charge amplification is derived for different temperatures. We report the development of a planar point contact Ge detector in terms of its fabrication and the measurements of its leakage current and capacitance as a function of applied bias voltage. With the determination of the measured depletion voltage, the field distribution is calculated using GeFiCa, which predicts that the required electric field for internal charge amplification can be achieved in proximity to the point contact. The energy response to an Am-241 source is characterized and discussed. We conclude that such a detector with internal charge amplification can be used to search for low-mass dark matter.
For the first time, electrical conduction mechanisms in the disordered material system is experimentally studied for p-type amorphous germanium (a-Ge) used for high-purity Ge detector contacts. The ...localization length and the hopping parameters in a-Ge are determined using the surface leakage current measured from three high-purity planar Ge detectors. The temperature dependent hopping distance and hopping energy are obtained for a-Ge fabricated as the electrical contact materials for high-purity Ge planar detectors. As a result, we find that the hopping energy in a-Ge increases as temperature increases while the hopping distance in a-Ge decreases as temperature increases. The localization length of a-Ge is on the order of
2
.
13
+
0.07
-
0.05
A
∘
to
5
.
07
+
2.58
-
0.83
A
∘
, depending on the density of states near the Fermi energy level within bandgap. Using these parameters, we predict that the surface leakage current from a Ge detector with a-Ge contacts can be much smaller than one yocto amp (yA) at helium temperature, suitable for rare-event physics searches.
By studying charge trapping in germanium detectors operating at temperatures below 10 K, we demonstrate for the first time that the formation of cluster dipole states from residual impurities is ...responsible for charge trapping. Two planar detectors with different impurity levels and types are used in this study. When drifting the localized charge carriers created by α particles from the top surface across a detector at a lower bias voltage, significant charge trapping is observed when compared to operating at a higher bias voltage. The amount of charge trapping shows a strong dependence on the type of charge carriers. Electrons are trapped more than holes in a p-type detector, while holes are trapped more than electrons in an n-type detector. When both electrons and holes are drifted simultaneously using the widespread charge carriers created by γ rays inside the detector, the amount of charge trapping shows no dependence on the polarity of bias voltage.
We evaluate the cosmogenic production rates in some materials that are commonly used as targets and shielding/supporting components for detecting rare events. The results from Geant4 simulations and ...the calculations of ACTIVIA are compared with the available experimental data. We demonstrate that the production rates from the Geant4-based simulations agree with the available data reasonably well. As a result, we report that the cosmogenic production of several isotopes in various materials can generate potential backgrounds for direct detection of dark matter and neutrinoless double-beta decay.
Half of all new human papillomavirus (HPV) infections occur in adolescents and young adults, and this population has poor HPV vaccination rates. Rural areas of the U.S. have high rates of HPV-related ...diseases and low vaccination rates as well. The purpose of this study was to determine the perceived barriers and facilitators to HPV vaccination among adolescents and their caregivers in rural south Alabama.
Vaccinated and non-vaccinated adolescents ages 11–18 years old and primary caregivers were recruited from three rural counties in south Alabama. Participants completed individual interviews to discuss perceived barriers to vaccination and factors influencing their decision to vaccinate. Discussion groups were held to determine potential solutions to barriers elucidated from the interviews. Interview and discussion group transcripts were analyzed, and themes were identified.
Approximately 62.5% of adolescents had not initiated the HPV vaccine series. Of those adolescents who started the vaccine series (n = 9, 37.5%), about half completed it (n = 5). Few participants in this study reported speaking with their health care provider (HCP) about the vaccine in the past year. Lack of information about the vaccine, its side effects, and no HCP recommendation were common barriers cited by non-vaccinators. Facilitators to vaccination included cancer prevention, discussion with HCP, and peer testimonials. Potential solutions to barriers were also discussed.
Proposed strategies to increase HPV vaccination were similar between vaccinated and non-vaccinated groups. Education about HPV and the HPV vaccine is needed throughout these rural south Alabama communities to ensure informed decisions are made about vaccination and to increase vaccination rates.
We report a measurement of muon annual modulation in a 12-l liquid scintillation detector with a live-time of more than 4 years at the Soudan Underground Laboratory. Muon minimum ionization in the ...detector is identified by its observed pulse shape and large energy deposition. The measured muon rate in the detector is
28.69
±
2.09
muons per day with a modulation amplitude of (
2.64
±
0.07
)% and a phase at Jul
22
±
36.2
days. This annual modulation is correlated with the variation of the effective atmospheric temperature in the stratosphere. The correlation coefficient,
α
T
, is determined to be
0.898
±
0.025
. This can be interpreted as a measurement of the atmospheric charged kaon to pion (
K
/
π
) ratio of
0
.
094
-
0.061
+
0.044
for
E
p
>
7
TeV, consistent with the measurement from the MINOS far detector. To further constrain the value of
K
/
π
ratio, a Geant4 simulation of the primary cosmic-ray protons with energy up to 100 TeV is implemented to study the correlation of
K
/
π
ratio and the muon annual modulation for muon energy greater than 0.5 TeV. We find out that a charged
K
/
π
ratio of 0.1598, greater than the upper bound (0.138) from this work at the production point 30 km above the Earth surface in the stratosphere cannot induce muon annual modulation at the depth of Soudan.
For the first time, planar high-purity germanium detectors with thin amorphous germanium contacts were successfully operated directly in liquid nitrogen and liquid argon in a cryostat at the ...Max-Planck-Institut für Physics in Munich. The detectors were fabricated at the Lawrence Berkeley National Laboratory and the University of South Dakota, using crystals grown at the University of South Dakota. They survived long-distance transportation and multiple thermal cycles in both cryogenic liquids and showed reasonable leakage currents and spectroscopic performance. Also discussed are the pros and cons of using thin amorphous semiconductor materials as an alternative contact technology in large-scale germanium experiments searching for physics beyond the Standard Model.
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