Observation of a correlated free four-neutron system.

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 decades1, with a particular focus on the four-neutron system called the tetraneutron, resulting in only a few indications of its existence so far2-4, 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 8He beam was key.

Mass, Spectroscopy, and Two-Neutron Decay of

The structure and decay of the most neutron-rich beryllium isotope, ^{16}Be, has been investigated following proton knockout from a high-energy ^{17}B beam. Two relatively narrow resonances were observed for the first time, with energies of 0.84(3) and 2.15(5) MeV above the two-neutron decay threshold and widths of 0.32(8) and 0.95(15) MeV, respectively. These were assigned to be the ground (J^{π}=0^{+}) and first excited (2^{+}) state, with E_{x}=1.31(6) MeV. The mass excess of ^{16}Be was thus deduced to be 56.93(13) MeV, some 0.5 MeV more bound than the only previous measurement. Both states were observed to decay by direct two-neutron emission. Calculations incorporating the evolution of the wave function during the decay as a genuine three-body process reproduced the principal characteristics of the neutron-neutron energy spectra for both levels, indicating that the ground state exhibits a strong spatially compact dineutron component, while the 2^{+} level presents a far more diffuse neutron-neutron distribution.

Nuclear structure opportunities with GeV radioactive beams at FAIR.

The Facility for Antiproton and Ion Research (FAIR) is in its final construction stage next to the campus of the Gesellschaft für Schwerionenforschung Helmholtzzentrum for heavy-ion research in Darmstadt, Germany. Once it starts its operation, it will be the main nuclear physics research facility in many basic sciences and their applications in Europe for the coming decades. Owing to the ability of the new fragment separator, Super-FRagment Separator, to produce high-intensity radioactive ion beams in the energy range up to about 2 GeV/nucleon, these can be used in various nuclear reactions. This opens a unique opportunity for various nuclear structure studies across a range of fields and scales: from low-energy physics via the investigation of multi-neutron systems and halos to high-density nuclear matter and the equation of state, following heavy-ion collisions, fission and study of short-range correlations in nuclei and hypernuclei. The newly developed reactions with relativistic radioactive beams (R3B) set up at FAIR would be the most suitable and versatile for such studies. An overview of highlighted physics cases foreseen at R3B is given, along with possible future opportunities, at FAIR. This article is part of the theme issue 'The liminal position of Nuclear Physics: from hadrons to neutron stars'.

Validation of the

The cluster structure of the neutron-rich isotope ^{10}Be has been probed via the (p,pα) reaction at 150 MeV/nucleon in inverse kinematics and in quasifree conditions. The populated states of ^{6}He residues were investigated through missing mass spectroscopy. The triple differential cross section for the ground-state transition was extracted for quasifree angle pairs (θ_{p},θ_{α}) and compared to distorted-wave impulse approximation reaction calculations performed in a microscopic framework using successively the Tohsaki-Horiuchi-Schuck-Röpke product wave function and the wave function deduced from antisymmetrized molecular dynamics calculations. The remarkable agreement between calculated and measured cross sections in both shape and magnitude validates the molecular structure description of the ^{10}Be ground-state, configured as an α-α core with two valence neutrons occupying π-type molecular orbitals.

Multiple Mechanisms in Proton-Induced Nucleon Removal at ∼100 MeV/Nucleon.

We report on the first proton-induced single proton- and neutron-removal reactions from the neutron-deficient ^{14}O nucleus with large Fermi-surface asymmetry S_{n}-S_{p}=18.6 MeV at ∼100 MeV/nucleon, a widely used energy regime for rare-isotope studies. The measured inclusive cross sections and parallel momentum distributions of the ^{13}N and ^{13}O residues are compared to the state-of-the-art reaction models, with nuclear structure inputs from many-body shell-model calculations. Our results provide the first quantitative contributions of multiple reaction mechanisms including the quasifree knockout, inelastic scattering, and nucleon transfer processes. It is shown that the inelastic scattering and nucleon transfer, usually neglected at such energy regime, contribute about 50% and 30% to the loosely bound proton and deeply bound neutron removal, respectively. These multiple reaction mechanisms should be considered in analyses of inclusive one-nucleon removal cross sections measured at intermediate energies for quantitative investigation of single-particle strengths and correlations in atomic nuclei.

Extended p_{3/2} Neutron Orbital and the N=32 Shell Closure in

The one-neutron knockout from ^{52}Ca in inverse kinematics onto a proton target was performed at ∼230 MeV/nucleon combined with prompt γ spectroscopy. Exclusive quasifree scattering cross sections to bound states in ^{51}Ca and the momentum distributions corresponding to the removal of 1f_{7/2} and 2p_{3/2} neutrons were measured. The cross sections, interpreted within the distorted-wave impulse approximation reaction framework, are consistent with a shell closure at the neutron number N=32, found as strong as at N=28 and N=34 in Ca isotopes from the same observables. The analysis of the momentum distributions leads to a difference of the root-mean-square radii of the neutron 1f_{7/2} and 2p_{3/2} orbitals of 0.61(23) fm, in agreement with the modified-shell-model prediction of 0.7 fm suggesting that the large root-mean-square radius of the 2p_{3/2} orbital in neutron-rich Ca isotopes is responsible for the unexpected linear increase of the charge radius with the neutron number.

Quasifree Neutron Knockout Reaction Reveals a Small s-Orbital Component in the Borromean Nucleus

A kinematically complete quasifree (p,pn) experiment in inverse kinematics was performed to study the structure of the Borromean nucleus ^{17}B, which had long been considered to have a neutron halo. By analyzing the momentum distributions and exclusive cross sections, we obtained the spectroscopic factors for 1s_{1/2} and 0d_{5/2} orbitals, and a surprisingly small percentage of 9(2)% was determined for 1s_{1/2}. Our finding of such a small 1s_{1/2} component and the halo features reported in prior experiments can be explained by the deformed relativistic Hartree-Bogoliubov theory in continuum, revealing a definite but not dominant neutron halo in ^{17}B. The present work gives the smallest s- or p-orbital component among known nuclei exhibiting halo features and implies that the dominant occupation of s or p orbitals is not a prerequisite for the occurrence of a neutron halo.

Pairing Forces Govern Population of Doubly Magic

Direct proton-knockout reactions of ^{55}Sc at ∼220 MeV/nucleon were studied at the RIKEN Radioactive Isotope Beam Factory. Populated states of ^{54}Ca 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 ^{55}Sc ground state with states in ^{54}Ca. Despite the calculations showing a significant amplitude of excited neutron configurations in the ground-state of ^{55}Sc, valence proton removals populated predominantly the ground state of ^{54}Ca. 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.

Surface Localization of the Dineutron in

The formation of a dineutron in the ^{11}Li nucleus is found to be localized to the surface region. The experiment measured the intrinsic momentum of the struck neutron in ^{11}Li via the (p,pn) knockout reaction at 246 MeV/nucleon. The correlation angle between the two neutrons is, for the first time, measured as a function of the intrinsic neutron momentum. A comparison with reaction calculations reveals the localization of the dineutron at r∼3.6 fm. The results also support the density dependence of dineutron formation as deduced from Hartree-Fock-Bogoliubov calculations for nuclear matter.

How Robust is the N=34 Subshell Closure? First Spectroscopy of

The first γ-ray spectroscopy of ^{52}Ar, with the neutron number N=34, was measured using the ^{53}K(p,2p) one-proton removal reaction at ∼210 MeV/u at the RIBF facility. The 2_{1}^{+} excitation energy is found at 1656(18) keV, the highest among the Ar isotopes with N>20. This result is the first experimental signature of the persistence of the N=34 subshell closure beyond ^{54}Ca, i.e., below the magic proton number Z=20. Shell-model calculations with phenomenological and chiral-effective-field-theory interactions both reproduce the measured 2_{1}^{+} systematics of neutron-rich Ar isotopes, and support a N=34 subshell closure in ^{52}Ar.

Quasifree Neutron Knockout from

Exclusive cross sections and momentum distributions have been measured for quasifree one-neutron knockout reactions from a ^{54}Ca beam striking on a liquid hydrogen target at ∼200 MeV/u. A significantly larger cross section to the p_{3/2} state compared to the f_{5/2} state observed in the excitation of ^{53}Ca provides direct evidence for the nature of the N=34 shell closure. This finding corroborates the arising of a new shell closure in neutron-rich calcium isotopes. The distorted-wave impulse approximation reaction formalism with shell model calculations using the effective GXPF1Bs interaction and ab initio calculations concur our experimental findings. Obtained transverse and parallel momentum distributions demonstrate the sensitivity of quasifree one-neutron knockout in inverse kinematics on a thick liquid hydrogen target with the reaction vertex reconstructed to final state spin-parity assignments.

[Relevant aspects of identification and interpretation of the glycated hemoglobin research findings.]

The article contains the literature review on laboratory criteria of detection and monitoring of the progression of the disease in patients with the diagnosis of diabetes mellitus. It also covers the issues of methodical approaches to the identification of glycated hemoglobin (HbA1c). The findings of author's researches of glycated hemoglobin in 149 patients have been given within the framework of comparison of two methodical approaches and comparison of the results with the subsequent classification of the received data. A random laboratory finding of qualitative hemoglobinopathy has been demonstrated, and the results recognized as unqualifiable and the approach to classification of such values have been discussed.Comparison of the results of glycated hemoglobin identification performed by different methods. 149 patients underwent a one-stage identification of glycated hemoglobin from plasma stabilized with K2-EDTA on Bio-Rad D10 and Sebia Capillarys Flex Piercing 2. Comparative study of the results of glycated hemoglobin identification has shown a difference in absolute values. However, a statistically reliable (p < 0.05) correlation between the values of glycated hemoglobin, expressed as a percentage obtained by different methods, has been revealed. In this case, the choice of a method for identifying glycated hemoglobin is not a matter of principal but it is important to adhere to the same method in treatment and long-term monitoring.

Quasifree (p, 2p) Reactions on Oxygen Isotopes: Observation of Isospin Independence of the Reduced Single-Particle Strength.

Quasifree one-proton knockout reactions have been employed in inverse kinematics for a systematic study of the structure of stable and exotic oxygen isotopes at the R^{3}B/LAND setup with incident beam energies in the range of 300-450 MeV/u. The oxygen isotopic chain offers a large variation of separation energies that allows for a quantitative understanding of single-particle strength with changing isospin asymmetry. Quasifree knockout reactions provide a complementary approach to intermediate-energy one-nucleon removal reactions. Inclusive cross sections for quasifree knockout reactions of the type ^{A}O(p,2p)^{A-1}N have been determined and compared to calculations based on the eikonal reaction theory. The reduction factors for the single-particle strength with respect to the independent-particle model were obtained and compared to state-of-the-art ab initio predictions. The results do not show any significant dependence on proton-neutron asymmetry.

Strong Neutron Pairing in core+4n Nuclei.

The emission of neutron pairs from the neutron-rich N=12 isotones ^{18}C and ^{20}O has been studied by high-energy nucleon knockout from ^{19}N and ^{21}O secondary beams, populating unbound states of the two isotones up to 15 MeV above their two-neutron emission thresholds. The analysis of triple fragment-n-n correlations shows that the decay ^{19}N(-1p)^{18}C^{*}→^{16}C+n+n is clearly dominated by direct pair emission. The two-neutron correlation strength, the largest ever observed, suggests the predominance of a ^{14}C core surrounded by four valence neutrons arranged in strongly correlated pairs. On the other hand, a significant competition of a sequential branch is found in the decay ^{21}O(-1n)^{20}O^{*}→^{18}O+n+n, attributed to its formation through the knockout of a deeply bound neutron that breaks the ^{16}O core and reduces the number of pairs.

Extraction of the Landau-Migdal Parameter from the Gamow-Teller Giant Resonance in

The key parameter to discuss the possibility of the pion condensation in nuclear matter, i.e., the so-called Landau-Migdal parameter g^{'}, was extracted by measuring the double-differential cross sections for the (p,n) reaction at 216 MeV/u on a neutron-rich doubly magic unstable nucleus, ^{132}Sn with the quality comparable to data taken with stable nuclei. The extracted strengths for Gamow-Teller (GT) transitions from ^{132}Sn leading to ^{132}Sb exhibit the GT giant resonance (GTR) at the excitation energy of 16.3±0.4(stat)±0.4(syst) MeV with the width of Γ=4.7±0.8 MeV. The integrated GT strength up to E_{x}=25 MeV is S_{GT}^{-}=53±5(stat)_{-10}^{+11}(syst), corresponding to 56% of Ikeda's sum rule of 3(N-Z)=96. The present result accurately constrains the Landau-Migdal parameter as g^{'}=0.68±0.07, thanks to the high sensitivity of the GTR energy to g^{'}. In combination with previous studies on the GTR for ^{90}Zr and ^{208}Pb, the result of this work shows the constancy of this parameter in the nuclear chart region with (N-Z)/A=0.11 to 0.24 and A=90 to 208.

[Resistant cytomegalovirus infection in related donor kidney allograft recipients].

AIM: To clarify whether cytomegalovirus (CMV) infection can affect the results of living related donor kidney transplantation. SUBJECTS AND METHODS: A study group included 17 (7.27%) patients (10 men and 7 women; 8 children and 9 adults) aged 3 to 51 years who had developed resistant CMV infection. For comparative analysis, a control group was formed from 113 patients (61 men and 52 women; 40 children and 73 adults) aged 1 to 61 years, whose CMV polymerase chain reaction (PCR) had always been negative, i.e. CMV DNA was absent. The duration of CMV infection episodes was 44 to 232 days. RESULTS: The patients were given valganciclovir in a dose of 450 mg/day. CMV PCR was negative in all the patients at the end of therapy. None of the patients died; one graft was lost. In the control (negative CMV PCR) group, 6 grafts were lost in 113 patients lost and 4 patients died. Statistical analysis showed that the results of related donor kidney transplantation were virtually equal. CONCLUSION: Suppression of resistant CMV infection can be achieved with the longer use of valganciclovir or its higher dose. CMV infection fails to affect the results of related donor kidney transplantation.

[Kidney allotransplantation from alive related donor in patients with Alport syndrome].

AIM: To evaluate the results of kidney transplantation from alive related donor in patients with Alport syndrome and to compare with those in patients with kidney hypoplasia. MATERIAL AND METHODS: We have analyzed 8 and 27 medical records of patients with Alport syndrome and kidney hypoplasia respectively. Following parameters were used - Kaplan-Meier survival analysis, Wilcox overall risk, percentage of transplants loss and mortality (Fisher's exact test calculation). RESULTS: It is concluded that percentage of transplants loss and mortality rate as well as overall survival and risk were similar in both groups. CONCLUSION: Despite risk of anti-GBM nephritis development in patients with Alport syndrome results are comparable with those after transplatation for chronic renal failure caused by other reasons.

[The effect of gender on the results of related kidney transplantation].

AIM: To define the effect of donor and recipient gender on the results of kidney transplantation from living related donor. MATERIAL AND METHODS: Group of 271 patients who underwent kidney transplantation from living related donor was analyzed. There were 115 women and 156 men. Age varied from 1 to 63 years (mean 21.30±12.32). There were 127 children aged 1-18 years (mean 11.28±4.63) and 144 adults aged 19-63 years (mean 29.81±11.24). Donors included 162 women and 109 men. Overall survival was calculated using Kaplan-Mayer. Mortality and incidence of transplants failure were determined using Fisher's exact test. RESULTS: All patients were divided into 2 groups depending on recipients' gender and then into 4 subgroups depending on gender of donors and recipients. Comparative statistical analysis showed that transplants survival was higher in women vs. men (T=2.7, p=0.007). Survival of patients was similar in both groups. Moreover it was the best in subgroup of recipients-women with kidneys from donors-men. Difference was statistically significant (T=2.16, p=0.03). There was no significant difference in all other cases. CONCLUSION: The results of kidney transplantation are better in recipients-women than in men.

[Vaccination in patients with chronic renal failure in the pre- and posttransplantation period].

AIM: To clarify whether vaccination provokes renal graft rejection. SUBJECTS AND METHODS: A total of 131 vaccinations were performed in 92 patients with chronic kidney failure (CKF), including 7 and 85 patients vaccinated before and in different periods after kidney transplantation, respectively. The patients were examined using needle graft biopsy, measurement of proteinuria, and estimation of changes in blood creatinine levels and glomerular filtration rate. RESULTS: Vaccination was not fount to provoke rejection, as suggested by the results of needle biopsy of renal allografts and examination of their function. CONCLUSION: Vaccination is safe for patients with CKF as it causes no rejection episodes.

[THE INFLUENCE OF CYTOMEGALOVIRUS ON THE RESULTS OF KIDNEY TRANSPLANTATION].

To understand whether the presence of cytomegalovirus in blood influences the results of kidney transplantation from live relative donors, we analysed materials from 258 recipients divided into 2 groups. Group 1 included 113 patients with negative results of PCR for cytomegalovirus, group 2 contained 139 patients with positive PCR. We evaluated lethality, the loss of transplanted kidneys, frequency of rejection and infectious complications. Statistical treatment of the data obtained included Kaplan-Meier survival analysis, the Wilcoxon test showing the cumulative hazard risk, and comparative analysis by Fisher's and Student's tests. It was shown that cytomegalovirus present in blood increases lethality and the frequency of infectious complications in recipients of transplanted kidneys but does not influence their rejection. The cumulative survival rate was significantly higher and cumulative risk lower in group 1 than in group 2.