76 research outputs found
Ultra-stable implanted 83Rb/83mKr electron sources for the energy scale monitoring in the KATRIN experiment
The KATRIN experiment aims at the direct model-independent determination of
the average electron neutrino mass via the measurement of the endpoint region
of the tritium beta decay spectrum. The electron spectrometer of the MAC-E
filter type is used, requiring very high stability of the electric filtering
potential. This work proves the feasibility of implanted 83Rb/83mKr calibration
electron sources which will be utilised in the additional monitor spectrometer
sharing the high voltage with the main spectrometer of KATRIN. The source
employs conversion electrons of 83mKr which is continuously generated by 83Rb.
The K-32 conversion line (kinetic energy of 17.8 keV, natural line width of 2.7
eV) is shown to fulfill the KATRIN requirement of the relative energy stability
of +/-1.6 ppm/month. The sources will serve as a standard tool for continuous
monitoring of KATRIN's energy scale stability with sub-ppm precision. They may
also be used in other applications where the precise conversion lines can be
separated from the low energy spectrum caused by the electron inelastic
scattering in the substrate.Comment: 30 pages, 10 figures, 1 table, minor revision of the preprint,
accepted by JINST on 5.2.201
Melting of Partially Fluorinated Graphene: From Detachment of Fluorine Atoms to Large Defects and Random Coils
The melting of fluorographene is very unusual and depends strongly on the
degree of fluorination. For temperatures below 1000 K, fully fluorinated
graphene (FFG) is thermo-mechanically more stable than graphene but at
T2800 K FFG transits to random coils which is almost twice lower
than the melting temperature of graphene, i.e. 5300 K. For fluorinated graphene
(PFG) up to 30 % ripples causes detachment of individual F-atoms around 2000 K
while for 40-60 % fluorination, large defects are formed beyond 1500 K and
beyond 60% of fluorination F-atoms remain bonded to graphene until melting. The
results agree with recent experiments on the dependence of the reversibility of
the fluorination process on the percentage of fluorination.Comment: 16 pages, 6 figure
Space weathering simulations through controlled growth of iron nanoparticles on olivine
Airless planetary bodies are directly exposed to space weathering. The main spectral effects of space weathering are darkening, reduction in intensity of silicate mineral absorption bands, and an increase in the spectral slope towards longer wavelengths (reddening). Production of nanophase metallic iron (npFe0) during space weathering plays major role in these spectral changes. A laboratory procedure for the controlled production of npFe0 in silicate mineral powders has been developed. The method is based on a two-step thermal treatment of low-iron olivine, first in ambient air and then in hydrogen atmosphere. Through this process, a series of olivine powder samples was prepared with varying amounts of npFe0 in the 7-20 nm size range. A logarithmic trend is observed between amount of npFe0 and darkening, reduction of 1 µm olivine absorption band, reddening, and 1 µm band width. Olivine with a population of physically larger npFe0 particles follows spectral trends similar to other samples, except for the reddening trend. This is interpreted as the larger, ~40-50 nm sized, npFe0 particles do not contribute to the spectral slope change as efficiently as the smaller npFe0 fraction. A linear trend is observed between the amount of npFe0 and 1 µm band center position, most likely caused by Fe2+ disassociation from olivine structure into npFe0 particles.Peer reviewe
A UV LED-based fast-pulsed photoelectron source for time-of-flight studies
We report on spectroscopy and time-of-flight measurements using an 18 keV
fast-pulsed photoelectron source of adjustable intensity, ranging from single
photoelectrons per pulse to 5 photoelectrons per microsecond at pulse
repetition rates of up to 10 kHz. Short pulses between 40 ns and 40
microseconds in length were produced by switching light emitting diodes with
central output wavelengths of 265 nm and 257 nm, in the deep ultraviolet (or
UV-C) regime, at kHz frequencies. Such photoelectron sources can be useful
calibration devices for testing the properties of high-resolution electrostatic
spectrometers, like the ones used in current neutrino mass searches.Comment: 16 pages, 11 figure
Effect of a sweeping conductive wire on electrons stored in the Penning trap between the KATRIN spectrometers
The KATRIN experiment is going to search for the mass of the electron
antineutrino down to 0.2 eV/c^2. In order to reach this sensitivity the
background rate has to be understood and minimised to 0.01 counts per second.
One of the background sources is the unavoidable Penning trap for electrons due
to the combination of the electric and magnetic fields between the pre- and the
main spectrometer at KATRIN. In this article we will show that by sweeping a
conducting wire periodically through such a particle trap stored particles can
be removed, an ongoing discharge in the trap can be stopped, and the count rate
measured with a detector looking at the trap is reduced.Comment: Final version published in EPJ A, 14 pages, 19 figures (21 files
Melting of Partially Fluorinated Graphene: From Detachment of Fluorine Atoms to Large Defects and Random Coils
The melting of fluorographene is very unusual and depends strongly on the degree of fluorination. For temperatures below 1000 K, fully fluorinated graphene (FFG) is thermo-mechanically more stable than graphene but at T m ≈ 2800 K FFG transits to random coils which is almost twice lower than the melting temperature of graphene, i.e. 5300 K. For fluorinated graphene (PFG) up to 30% ripples causes detachment of individual F-atoms around 2000 K while for 40-60% fluorination, large defects are formed beyond 1500 K and beyond 60% of fluorination F-atoms remain bonded to graphene until melting. The results agree with recent experiments on the dependence of the reversibility of the fluorination process on the percentage of fluorination.Fil: Singh, Sandeep Kumar. Universiteit Antwerpen. Department of Physics; BélgicaFil: Costamagna, Sebastian. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Rosario. Instituto de Física de Rosario (i); Argentina. Universidad Nacional de Rosario. Facultad de Ciencias Exactas, Ingeniería y Agrimensura; ArgentinaFil: Neek Amal, M.. Universiteit Antwerpen. Department of Physics; BélgicaFil: Peeters, F. M.. Universiteit Antwerpen. Department of Physics; Bélgic
Improved Upper Limit on the Neutrino Mass from a Direct Kinematic Method by KATRIN
We report on the neutrino mass measurement result from the first four-week science run of the Karlsruhe Tritium Neutrino experiment KATRIN in spring 2019. Beta-decay electrons from a high-purity gaseous molecular tritium source are energy analyzed by a high-resolution MAC-E filter. A fit of the integrated electron spectrum over a narrow interval around the kinematic end point at 18.57 keV gives an effective neutrino mass square value of . From this, we derive an upper limit of 1.1 eV (90% confidence level) on the absolute mass scale of neutrinos. This value coincides with the KATRIN sensitivity. It improves upon previous mass limits from kinematic measurements by almost a factor of 2 and provides model-independent input to cosmological studies of structure formation
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