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High-sensitivity measurement of He 3 − He 4 isotopic ratios for ultracold neutron experiments
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Nuclear Physics: The Ultracold Neutron Source
This report provides an overview of Ultracold neutrons (UCNs) which provide a unique tool for researchers seeking a better understanding of the fundamental particles and interactions that govern the universe. Los Alamos National Laboratory’s Ultracold Neutron Source provides those researchers with the world’s highest density source of ultracold neutrons. Ultracold
Improved limits on Fierz interference using asymmetry measurements from the Ultracold Neutron Asymmetry (UCNA) experiment
The Ultracold Neutron Asymmetry (UCNA) experiment was designed to measure the β-decay asymmetry parameter, A 0 , for free neutron decay. In the experiment, polarized ultracold neutrons are transported into a decay trap, and their β-decay electrons are detected with ≈4π acceptance into two detector packages which provide position and energy reconstruction. The experiment also has sensitivity to b n , the Fierz interference term in the neutron β-decay rate. In this work, we determine bn from the energy dependence of A 0 using the data taken during the UCNA 2011–2013 run. In addition, we present the same type of analysis using the earlier 2010 A dataset. Furthermore, motivated by improved statistics and comparable systematic errors compared to the 2010 data-taking run, we present a new b n measurement using the weighted average of our asymmetry dataset fits, to obtain b n = 0.066 ± 0.041 stat ± 0.024 syst which corresponds to a limit of -0.012 < b n < 0.144 at the 90% confidence level.
Simulation of Experiment on Measurement of Neutron Lifetime Using the Big Gravitational Trap of Ultracold Neutrons with the Absorber
At present, the experiment on measuring neutron lifetime using a big gravitational trap is being performed at Petersburg Nuclear Physics Institute. It is planned to achieve a measurement precision of 0.2 s, which is four times better than the best existing level of precision. The modified installation is simulated using the Monte Carlo method. It has been shown that the application of the absorber in the installation design increases the number of stored ultracold neutrons in the trap by a factor of approximately three and reduces the duration of the measurement cycle.
Program of Fundamental-Interaction Research for the Ultracold-Neutron Source at the the WWR-M Reactor
The use of ultracold neutrons opens unique possibilities for studying fundamental interactions in particles physics. Searches for the neutron electric dipole moment are aimed at testing models of CP violation. A precise measurement of the neutron lifetime is of paramount importance for cosmology and astrophysics. Considerable advances in these realms can be made with the aid of a new ultracold-neutron (UCN) supersource presently under construction at Petersburg Nuclear Physics Institute. With this source, it would be possible to obtain an UCN density approximately 100 times as high as that at currently the best UCN source at the high-flux reactor of the Institute Laue–Langevin (ILL, Grenoble, France). To date, the design and basic elements of the source have been prepared, tests of a full-scale source model have been performed, and the research program has been developed. It is planned to improve accuracy in measuring the neutron electric dipole moment by one order of magnitude to a level of 10{sup −27} to 10{sup −28}e cm. This is of crucial importance for particle physics. The accuracy in measuring the neutron lifetime can also be improved by one order of magnitude. Finally, experiments that would seek neutron–antineutron oscillations by employing ultracold neutrons will become possible upon reaching an UCN density of 10{sup 3} to 10{sup 4} cm{sup −3}. The current status of the source and the proposed research program are discussed.
Quantum levitation of nanoparticles seen with ultracold neutrons
Analyzing new experiments with ultracold neutrons (UCNs) we show that physical adsorption of nanoparticles/nanodroplets, levitating in high-excited states in a deep and broad potential well formed by van der Waals/Casimir-Polder (vdW/CP) forces results in new effects on a cross-road of the fields of fundamental interactions, neutron, surface and nanoparticle physics. Accounting for the interaction of UCNs with nanoparticles explains a recently discovered intriguing so-called 'small heating' of UCNs in traps. It might be relevant to the striking conflict of the neutron lifetime experiments with smallest reported uncertainties by adding false effects there.
Storage of Ultracold Neutrons in the Magneto-Gravitational Trap of the UCN Experiment
The UCN experiment is designed to measure the lifetime n of the free neutron by trapping ultracold neutrons (UCN) in a magneto-gravitational trap. An asymmetric bowl-shaped NdFeB magnet Halbach array confines low-field-seeking UCN within the apparatus, and a set of electromagnetic coils in a toroidal geometry provides a background holding field to eliminate depolarization-induced UCN loss caused by magnetic field nodes. We present a measurement of the storage time store of the trap by storing UCN for various times and counting the survivors. The data are consistent with a single exponential decay, and we find store = 860 19 s, within 1 of current global averages for n. The storage time with the holding field deactivated is found to be store = 470 160 s; this decreased storage time is due to the loss of UCN, which undergo Majorana spin flips while being stored. We discuss plans to increase the statistical sensitivity of the measurement and investigate potential systematic effects.
A high-field adiabatic fast passage ultracold neutron spin flipper for the UCNA experiment
The UCNA collaboration is making a precision measurement of the {beta} asymmetry (A) in free neutron decay using polarized ultracold neutrons (UCN). A critical component of this experiment is an adiabatic fast passage neutron spin flipper capable of efficient operation in ambient magnetic fields on the order of 1 T. The requirement that it operate in a high field necessitated the construction of a free neutron spin flipper based, for the first time, on a birdcage resonator. The design, construction, and initial testing of this spin flipper prior to its use in the first measurement of A with UCN during the 2007 run cycle of the Los Alamos Neutron Science Center's 800 MeV proton accelerator is detailed. These studies determined the flipping efficiency of the device, averaged over the UCN spectrum present at the location of the spin flipper, to be {epsilon}=0.9985(4).
Specifics of Preparation of Storage Chambers for Ultracold Neutrons and EDM Spectrometer Sensitivity
Storage cells for ultracold neutrons (UCNs) are crucial parts of the experimental setup used to measure the electric dipole moment (EDM) of a neutron. The effect of the technology of preparation and sputtering of elements of UCN storage cells on the limiting operating voltage and on the capacity of these cells for long-term operation under high voltage with polarity switching was studied. A voltage magnitude of ±250 kV was obtained in tests of a neutron storage cell for the EDM spectrometer with a cell height of 9 cm.
Ultracold neutrons
This series of slides describes ultracold neutrons (UCN) and their properties, various UCN sources, and an overview of UCN-based experiments. Numerous diagrams and photographs are included.
Measurement of spin-flip probabilities for ultracold neutrons interacting with nickel phosphorus coated surfaces
In this paper, we report a measurement of the spin-flip probabilities for ultracold neutrons interacting with surfaces coated with nickel phosphorus. For 50 μm thick nickel phosphorus coated on stainless steel, the spin-flip probability per bounce was found to be β NiP on SS = (3.3 +1.8, -5.6) X 10 -6 . For 50 μm thick nickel phosphorus coated on aluminum, the spin-flip probability per bounce was found to be β NiP on Al = (3.6 +2.1, -5.9) X 10 -6 . For the copper guide used as reference, the spin flip probability per bounce was found to be β Cu = (6.7 + 5.0, -2.5) X 10 -6 . The results on the nickel phosphorus-coated surfaces may be interpreted as upper limits, yielding β NiP on SS < 6.2 X 10 -6 (90% C.L.) and β NiP on Al < 7.0 X 10 -6 (90% C.L.) for 50 μm thick nickel phosphorus coated on stainless steel and 50 μm thick nickel phosphorus coated on aluminum, respectively. Finally, nickel phosphorus coated stainless steel or aluminum provides a solution when low-cost, mechanically robust, and non-depolarizing UCN guides with a high Fermi potential are needed.
Ultracold Neutrons. Fundamental physics and more
This presentation describes the Ultracold Neutrons program.
Status of the Ultracold neutron source upgrade at LANSCE [PowerPoint]
Several slides show the source and flux of ultracold neutrons produced. In summary, an upgraded UCN source has been designed, and parts are currently being fabricated. Nickel phosphorus-coated guides will improve transport to the experiment hall. The source will be installed in the spring of 2016 and commissioned in the fall of 2016.
Evaluation of commercial nickel-phosphorus coating for ultracold neutron guides using a pinhole bottling method
We report on the evaluation of commercial electroless nickel phosphorus (NiP) coatings for ultracold neutron (UCN) transport and storage. The material potential of 50μm thick NiP coatings on stainless steel and aluminum substrates was measured to be V F =213(5.2)neV using the time-of-flight spectrometer ASTERIX at the Lujan Center. The loss per bounce probability was measured in pinhole bottling experiments carried out at ultracold neutron sources at Los Alamos Neutron Science Center and the Institut Laue-Langevin. For these tests a new guide coupling design was used to minimize gaps between the guide sections. The observed UCN loss in the bottle was interpreted in terms of an energy independent effective loss per bounce, which is the appropriate model when gaps in the system and upscattering are the dominate loss mechanisms, yielding a loss per bounce of 1.3(1)×10 –4 . In conclusion, we also present a detailed discussion of the pinhole bottling methodology and an energy dependent analysis of the experimental results.
Performance of the upgraded ultracold neutron source at Los Alamos National Laboratory and its implication for a possible neutron electric dipole moment experiment
We report the ultracold neutron (UCN) source at Los Alamos National Laboratory (LANL), which uses solid deuterium as the UCN converter and is driven by accelerator spallation neutrons, has been successfully operated for over 10 years, providing UCN to various experiments, as the first production UCN source based on the superthermal process. It has recently undergone a major upgrade. This paper describes the design and performance of the upgraded LANL UCN source. Measurements of the cold neutron spectrum and UCN density are presented and compared to Monte Carlo predictions. The source is shown to perform as modeled. The UCN density measured at the exit of the biological shield was 184(32) UCN / cm 3 , a fourfold increase from the highest previously reported. Finally, the polarized UCN density stored in an external chamber was measured to be 39(7) UCN / cm 3 , which is sufficient to perform an experiment to search for the nonzero neutron electric dipole moment with a one-standard-deviation sensitivity of σ(d n ) = 3 × 10 -27 e cm.
Consideration of a ultracold neutron source in two-dimensional cylindrical geometry by taking simulated boundaries
A new idea to calculate ultracold neutron (UCN) production by using Monte Carlo simulation method to calculate the cold neutron (CN) flux and an analytical approach to calculate the UCN production from the simulated CN flux was given. A super-thermal source (UCN source) was modeled based on an arrangement of D{sub 2}O and solid D{sub 2} (sD{sub 2}). The D{sub 2}O was investigated as the neutron moderator, and sD{sub 2} as the converter. In order to determine the required parameters, a two-dimensional (2D) neutron balance equation written in Matlab was combined with the MCNPX simulation code. The 2D neutron-transport equation in cylindrical (ρ − z) geometry was considered for 330 neutron energy groups in the sD{sub 2}. The 2D balance equation for UCN and CN was solved using simulated CN flux as boundary value. The UCN source dimensions were calculated for the development of the next UCN source. In the optimal condition, the UCN flux and the UCN production rate (averaged over the sD{sub 2} volume) equal to 6.79 × 10{sup 6} cm{sup −2}s{sup −1} and 2.20 ×10{sup 5} cm{sup −3}s{sup −1}, respectively.
A boron-coated CCD camera for direct detection of Ultracold Neutrons (UCN)
A new boron-coated CCD camera is described for direct detection of ultracold neutrons (UCN) through the capture reactions 10 B (n,α0γ) 7 Li (6%) and 10 B(n,α1γ) 7 Li (94%). The experiments, which extend earlier works using a boron-coated ZnS:Ag scintillator, are based on direct detections of the neutron-capture byproducts in silicon. The high position resolution, energy resolution and particle ID performance of a scientific CCD allows for observation and identification of all the byproducts α, 7 Li and γ (electron recoils). A signal-to-noise improvement on the order of 10 4 over the indirect method has been achieved. Sub-pixel position resolution of a few microns is demonstrated. The technology can also be used to build UCN detectors with an area on the order of 1 m 2 . The combination of micrometer scale spatial resolution, few electrons ionization thresholds and large area paves the way to new research avenues including quantum physics of UCN and high-resolution neutron imaging and spectroscopy.