Abstract
A long-standing question in nuclear physics is whether chargeless nuclear systems can exist. To our knowledge, only neutron stars represent near-pure neutron systems, where neutrons are ...squeezed together by the gravitational force to very high densities. The experimental search for isolated multi-neutron systems has been an ongoing quest for several decades
1
, with a particular focus on the four-neutron system called the tetraneutron, resulting in only a few indications of its existence so far
2–4
, leaving the tetraneutron an elusive nuclear system for six decades. Here we report on the observation of a resonance-like structure near threshold in the four-neutron system that is consistent with a quasi-bound tetraneutron state existing for a very short time. The measured energy and width of this state provide a key benchmark for our understanding of the nuclear force. The use of an experimental approach based on a knockout reaction at large momentum transfer with a radioactive high-energy
8
He beam was key.
Full text
Available for:
EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Abstract
Ultra-high resolution particle-in-cell coupled to Monte-Carlo collisions modelling unveils microscale instabilities in non-equilibrium plasmas fulfilling Penrose’s instability criterion. The ...spontaneous development of ion turbulence in the phase-space generated by charge exchange collisions leads to finite amplitude modulations of the local electric field. The latter are responsible for the trapping of low energy electrons and their transport from the plasma volume to the sheath vicinity. Electrostatic tidal effect occurring near the sheath is responsible for the release of the trapped electrons as a monochromatic bunch, accelerated back towards the source. This instability provides an additional theoretical ground for the anomalous enrichment of low-energy electrons observed by Langmuir probes in similar conditions. The present results demonstrate that marginally fulfilling PIC criteria is insufficient to study the microscale instabilities effects on the electrons dynamics in non-equilibrium low temperature plasmas.
A 19-year-old thalassemic woman had tissue from one of her ovaries cryopreserved prior to bone marrow transplantation, total body irradiation and sterilizing chemotherapy. As expected, premature ...ovarian failure resulted from this treatment. Transplantation of her thawed ovarian tissue resulted in return of menstrual cycling and the patient then underwent several IVF cycles. The patient, however, had poor ovarian response to hyperstimulation. We thus considered an alternative approach based on the observation that very thin ovarian fragments that preserve the basic ovarian structure ovarian micro-organs (MOs) induce angiogenesis and remained viable after autologous transplantation in animals. We report that preparation of autologous tiny ovarian fragments (MO)s and reimplantation into our patient resulted in IVF pregnancy and delivery of a healthy baby.
The ionization efficiency of High Power Impulse Magnetron Sputtering (HiPIMS) discharges is the key parameter leading to (i) gas ion production and consequently controlling the sputtering ...effectiveness and (ii) sputtered vapor ionization, self-consistently linked to self-sputtering and thin film properties.
To study the HiPIMS discharge time dependent two dimensional Particle in Cell (2D PIC) modelling coupled with Monte Carlo treatment of the plasma kinetics is discussed in terms of numerical scheme and stability criteria. The first microscopic results are presented for very short pulses (~5μs) using superimposed DC pre-ionization.
During this modeled HiPIMS short-pulse the plasma density increases at least two orders of magnitude driven by the pulse voltage, which also continues for a short time in the afterglow. During the pulse voltage plateau, the plasma potential shows a linear dependency going away from the target with two slopes over two space regions. First region is very narrow (<0.5mm), corresponding to the cathode sheath in front of the race-track, while the second region, much larger, corresponds to the pre-sheath or Ionization Region (IR). Modeling results show an increasing electric field in the sheath with the voltage rise of the pulse, while it stays almost constant in the IR, corresponding to about 150Vcm−1, in agreement with reported probe measurements. The local electron energy distribution functions in the IR and further out in the Diffusion Region (DR) are very different. IR electrons are much more energetic compared to the ones found in the DR, which have an important low energy population as a result of the ionization processes.
The transport of sputtered metal vapor from the target is simulated by 3D Monte Carlo (MC) modeling, in the intermediary pressure range — between ballistic and diffusive. Using the self-consistent output of plasma density maps from PIC with MC transport of sputtered vapor including their possible ionization when they cross the HiPIMS dense plasma, it is possible to estimate the metal ionization fraction, found here slightly lower than in previous reported works.
•Very first results were obtained with 2D PIC–MCC of the HiPIMS plasma.•OHIPIC code gives 2D maps of the plasma density as high as 1019m−3.•Plasma density rises by two orders of magnitude applying the high power pulse.•eedf clearly shows more energetic in the IR with respect to the DR.•A posteriori Monte Carlo gives the ionization fraction of the sputtered metal.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Abstract
A self-consistent iterative Monte Carlo model to simulate electron cyclotron resonance ion source (ECRIS) plasma is presented. It computes the species’ spatial and energy distribution in the ...whole plasma chamber in a three-dimensional mesh. A number of electrons and ions are propagated independently considering the static magnetic field, injected microwave field and local electrical potential field. The species trajectories populate the mesh allowing to compute their local density and velocity. Each species is pushed until it undergoes a destructive collision or after a fixed time limit. After each propagation phase, the local plasma potential and the heating electromagnetic microwave field are updated. This process is then iterated until convergence of species distributions and fields is reached. This method is intended to be a faster alternative to other methods to characterise the species distributions in the plasma for a specified ECRIS design and aid with their conception. The model and software development status are presented, along with prospects.
The heavy-ion inelastic scattering of the neutron-rich nucleus 29Ne to its excited states was studied using a 100.1 MeV/u 29Ne rare isotope beam on 181Ta and 9Be targets. The combined setup ...consisting of the GRETINA array, the TRIPLEX device and the S800 Spectrograph facilitates the simultaneous measurements of the two inelastic reactions, providing the first measurement of the transition strengths for this isotope. A sizable E2 strength B(E2↑) which amounts to 163(30) e2fm4 was determined in the excitation to the 931-keV state, demonstrating a large degree of collectivity. The present results of B(E2↑) are compared to various shell-model calculations, confirming the role of intruder configurations in 29Ne at the boundary of the island of inversion.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Detailed spectroscopy of the neutron-unbound nucleus F28 has been performed for the first time following proton/neutron removal from Ne29/F29 beams at energies around 230 MeV/nucleon. The ...invariant-mass spectra were reconstructed for both the F(*)27+n and F(*)26+2n coincidences and revealed a series of well-defined resonances. A near-threshold state was observed in both reactions and is identified as the F28 ground state, with Sn(F28)=−199(6) keV, while analysis of the 2n decay channel allowed a considerably improved Sn(F27)=1620(60) keV to be deduced. Comparison with shell-model predictions and eikonal-model reaction calculations have allowed spin-parity assignments to be proposed for some of the lower-lying levels of F28. Importantly, in the case of the ground state, the reconstructed F27+n momentum distribution following neutron removal from F29 indicates that it arises mainly from the 1p3/2 neutron intruder configuration. This demonstrates that the island of inversion around N=20 includes F28, and most probably F29, and suggests that O28 is not doubly magic.
Full text
Available for:
CMK, CTK, FMFMET, IJS, NUK, PNG, UL, UM
PDF
