We report on a search for a bound di-neutron by comparing electron-induced proton-knockout (e,e′p) measurements from Helium-3 (3He) and Tritium (3H). The measurements were performed at Jefferson Lab ...Hall A with a 4.326 GeV electron beam, and kinematics of large momentum transfer (〈Q2〉≈1.9 (GeV/c)2) and xB>1, to minimize contributions from non quasi-elastic (QE) reaction mechanisms. Analyzing the measured 3He missing mass (Mmiss) and missing energy (Emiss) distributions, we can distinguish the two-body break-up reaction, in which the residual proton-neutron system remains bound as a deuteron. In the 3H mirror case, under the exact same kinematic conditions, we do not identify a signature for a bound di-neutron with similar binding energy to that of the deuteron. We calculate exclusion limits as a function of the di-neutron binding energy and find that, for binding equivalent to the deuteron, the two-body break-up cross section on 3H is less than 0.9% of that on 3He in the measured kinematics at the 95% confidence level. This limit implies that the di-neutron content of the tritium spectral function is less than 1.5%. With a dedicated measurement using similar high resolution spectrometers, but lower beam energy and vacuum coupling, significantly better energy missing energy resolution could be achieved, extending the sensitivity of the method to search for a di-neutron with far smaller binding energy.
A 90° bend curved light-guide for TOF scintillating detectors Olivenboim, M.; Cohen, E. O.; Burshtein, L. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
09/2021, Letnik:
1018, Številka:
C
Journal Article
Recenzirano
Odprti dostop
We report here a bench study of TOF resolution using a 90° bend curved solid light-guide (LG) used to transport the light from a plastic scintillator counter to a photomultiplier (PMT). The 90° LG ...allows the rotation of the PMT axis to be vertical to the detector axis, in an environment featured by a strong magnetic field along the detector surface, or other geometrical constrains. We show that with a TOF counter of 2000 x 100 x 60 mm3 and light read-out by PMTs at its two 100 × 60 mm2 sides, when 90° LG benders are used between the scintillating bar and the PMTs on both sides, the TOF resolution is worsen, by 5–10%.
A new technique to measure the lifetime τ of a neutron-radioactive nucleus that decays in-flight via neutron emission is presented and demonstrated utilizing MonteCarlo simulations. The method is ...based on the production of the neutron-unbound nucleus in a target, which at the same time slows down the produced nucleus and the residual nucleus after (multi-) neutron emission. The spectrum of the velocity difference of neutron(s) and the residual nucleus has a characteristic shape, that allows to extract the lifetime. If the decay happens outside the target there will be a peak in the spectrum, while events where the decay is in the target show a broad flat distribution due to the continuous slowing down of the residual nucleus. The method itself and the analysis procedure are discussed in detail for the specific candidate 26O. A stack of targets with decreasing target thicknesses can expand the measurable lifetime range and improve the sensitivity by increasing the ratio between decays outside and inside the target. The simulations indicate a lower limit of measurable lifetime τ∼0.2ps for the given conditions.
A 90° bend curved light-guide for TOF scintillating detectors Olivenboim, M.; Cohen, E.O.; Burshtein, L. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
12/2021, Letnik:
1018, Številka:
C
Journal Article
Recenzirano
We report here a bench study of TOF resolution using a 90° bend curved solid light-guide (LG) used to transport the light from a plastic scintillator counter to a photomultiplier (PMT). The 90° LG ...allows the rotation of the PMT axis to be vertical to the detector axis, in an environment featured by a strong magnetic field along the detector surface, or other geometrical constrains. We show that with a TOF counter of 2000×100×60 mm3 and light read-out by PMTs at its two 100 × 60 mm2 sides, when 90° LG benders are used between the scintillating bar and the PMTs on both sides, the TOF resolution is worsen, by 5–10%.
Direct proton-knockout reactions of 55Sc at ∼ 220 MeV / nucleon were studied at the RIKEN Radioactive Isotope Beam Factory. Populated states of 54Ca were investigated through γ -ray and ...invariant-mass spectroscopy. Level energies were calculated from the nuclear shell model employing a phenomenological internucleon interaction. Theoretical cross sections to states were calculated from distorted-wave impulse approximation estimates multiplied by the shell model spectroscopic factors, which describe the wave function overlap of the 55Sc ground state with states in 54Ca . Despite the calculations showing a significant amplitude of excited neutron configurations in the ground-state of 55Sc , valence proton removals populated predominantly the ground state of 54Ca . This counterintuitive result is attributed to pairing effects leading to a dominance of the ground-state spectroscopic factor. Owing to the ubiquity of the pairing interaction, this argument should be generally applicable to direct knockout reactions from odd-even to even-even nuclei.
Detailed γ-ray spectroscopy of the exotic neon isotope 28Ne has been performed for the first time using the one-neutron removal reaction from 29Ne on a liquid hydrogen target at 240 MeV/nucleon. ...Based on an analysis of parallel momentum distributions, a level scheme with spin-parity assignments has been constructed for 28Ne and the negative-parity states are identified for the first time. The measured partial cross sections and momentum distributions reveal a significant intruder p-wave strength providing evidence of the breakdown of the N=20 and N=28 shell gaps. Only a weak, possible f-wave strength was observed to bound final states. Large-scale shell-model calculations with different effective interactions do not reproduce the large p-wave and small f-wave strength observed experimentally, indicating an ongoing challenge for a complete theoretical description of the transition into the island of inversion along the Ne isotopic chain.
First observation of 28 O Kondo, Y.; Achouri, N. L.; Falou, H. A. ...
Nature (London),
2023, Letnik:
620, Številka:
7976
Journal Article
Recenzirano
Odprti dostop
Subjecting a physical system to extreme conditions is one of the means often used to obtain a better understanding and deeper insight into its organization and structure. In the case of the atomic ...nucleus, one such approach is to investigate isotopes that have very different neutron-to-proton (N/Z) ratios than in stable nuclei. Light, neutron-rich isotopes exhibit the most asymmetric N/Z ratios and those lying beyond the limits of binding, which undergo spontaneous neutron emission and exist only as very short-lived resonances (about 10−21s), provide the most stringent tests of modern nuclear-structure theories. Here we report on the first observation of 28O and 27O through their decay into 24O and four and three neutrons, respectively. The 28O nucleus is of particular interest as, with the Z = 8 and N = 20 magic numbers1,2, it is expected in the standard shell-model picture of nuclear structure to be one of a relatively small number of so-called ‘doubly magic’ nuclei. Both 27O and 28O were found to exist as narrow, low-lying resonances and their decay energies are compared here to the results of sophisticated theoretical modelling, including a large-scale shell-model calculation and a newly developed statistical approach. In both cases, the underlying nuclear interactions were derived from effective field theories of quantum chromodynamics. Finally, it is shown that the cross-section for the production of 28O from a 29F beam is consistent with it not exhibiting a closed N = 20 shell structure.
NeuLAND (New Large-Area Neutron Detector) is the next-generation neutron detector for the R3B (Reactions with Relativistic Radioactive Beams) experiment at FAIR (Facility for Antiproton and Ion ...Research). NeuLAND detects neutrons with energies from 100 to 1000 MeV, featuring a high detection efficiency, a high spatial and time resolution, and a large multi-neutron reconstruction efficiency. This is achieved by a highly granular design of organic scintillators: 3000 individual submodules with a size of 5 × 5 × 250 cm3 are arranged in 30 double planes with 100 submodules each, providing an active area of 250 × 250 cm2 and a total depth of 3 m. The spatial resolution due to the granularity together with a time resolution of σt≤ 150 ps ensures high-resolution capabilities. In conjunction with calorimetric properties, a multi-neutron reconstruction efficiency of 50% to 70% for four-neutron events will be achieved, depending on both the emission scenario and the boundary conditions allowed for the reconstruction method. We present in this paper the final design of the detector as well as results from test measurements and simulations on which this design is based.
Detailed spectroscopy of the neutron-unbound nucleus 28F has been performed for the first time following proton/neutron removal from 29Ne/29F beams at energies around 230 MeV / nucleon . The ...invariant-mass spectra were reconstructed for both the 27F(*) + n and 26F(*) + 2n coincidences and revealed a series of well-defined resonances. A near-threshold state was observed in both reactions and is identified as the 28F ground state, with Sn(28F) = -199(6) keV, while analysis of the 2n decay channel allowed a considerably improved Sn(27F) = 162(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 28F. Importantly, in the case of the ground state, the reconstructed 27F + n momentum distribution following neutron removal from 29F indicates that it arises mainly from the 1p3/2 neutron intruder configuration. Finally, this demonstrates that the island of inversion around N = 20 includes 28F, and most probably 29F, and suggests that 28O is not doubly magic.
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