Neutron Knockout Research Articles

Quenching of single-particle strengths of carbon isotopes 9-12,14-20C with knockout reactions for incident energies 43–2100 MeV/nucleon * *Supported by National Natural Science Foundation of China (U2067205,11775013,11775316), Fundamental Research Funds for the Central Universities (2020MS033) and Natural Science Foundation of Shanxi Province, China (202103021223047)

To study the quenching of single-particle strengths of carbon isotopes, a systematic analysis is performed for 9-12,14-20C, with single neutron knockout reactions on Be/C targets, within an energy range from approximately 43 to 2100 MeV/nucleon, using the Glauber model. Incident energies do not show any obvious effect on the resulting values across this wide energy range. The extracted quenching factors are found to be strongly dependent on the proton-neutron asymmetry, which is consistent with the recent analysis of knockout reactions but is inconsistent with the systematics of transfer and quasi-free knockout reactions.

Single-nucleon knockout cross sections for reactions producing resonance states at or beyond the drip line

Single-nucleon knockout cross sections from fast secondary beams of the proton-drip-line nuclei $^{9}\mathrm{C}$, $^{13}\mathrm{O}$, and $^{17}\mathrm{Ne}$ on a $^{9}\mathrm{Be}$ target have been studied with emphasis on the production of resonance states. These states were identified by their invariant mass, and resonances with two-, three-, and five-body exit channels were examined. The measured cross sections for these states were compared with eikonal-model predictions using shell-model or variational Monte Carlo spectroscopic factors. The experimental yields were found to be suppressed relative to the model predictions, especially when a well-bound neutron or proton is removed. This suppression exceeds that found systematically in measured inclusive cross sections to particle-bound final states. In neutron knockout from $^{9}\mathrm{C}$ and $^{13}\mathrm{O}$ projectiles, this suppression of the unbound ground-state residuals yield is a factor of two to three times larger than that found in the bound final-state studies. Modifications to the structure of these systems due to coupling of the shell-model configurations to the continuum is expected to contribute to this extra suppression, especially when the final state is a near-threshold resonance. However, other considerations including the role of nuclear dynamics may be required to explain all the observed trends.

Quasi-free neutron and proton knockout reactions from light nuclei in a wide neutron-to-proton asymmetry range

The quasi-free scattering reactions 11C(p,2p) and 10,11,12C(p,pn) have been studied in inverse kinematics at beam energies of 300–400 MeV/u at the R3B-LAND setup. The outgoing proton-proton and proton-neutron pairs were detected in coincidence with the reaction fragments in kinematically complete measurements. The efficiency to detect these pairs has been obtained from GEANT4 simulations which were tested using the 12C(p,2p) and 12C(p,pn) reactions. Experimental cross sections and momentum distributions have been obtained and compared to DWIA calculations based on eikonal theory. The new results reported here are combined with previously published cross sections for quasi-free scattering from oxygen and nitrogen isotopes and together they enable a systematic study of the reduction of single-particle strength compared to predictions of the shell model over a wide neutron-to-proton asymmetry range. The combined reduction factors show a weak or no dependence on isospin asymmetry, in contrast to the strong dependency reported in nucleon-removal reactions induced by nuclear targets at lower energies. However, the reduction factors for (p,2p) are found to be 'significantly smaller than for (p,pn) reactions for all investigated nuclei.

Photonuclear production of yttrium-88 – A high energy gamma emitter for hydrocarbon extraction applications

The use of fracing has risen over the past decade and revolutionized energy production in the US. However, there is still an impetus for further optimization of the extraction of oil and natural gas from vast shale reservoirs. In this work, we discuss photonuclear production of yttrium-88 as a promising radiotracer for fracing operations. Single neutron knock-out from natural monoisotopic yttrium-89 is an inexpensive process resulting in high activity of 88Y with minimal impurities. MCNPX simulations were performed to estimate the 88Y yield. Irradiations of natural yttrium using a 32 MeV electron linac equipped with a tungsten bremsstrahlung converter were done to benchmark the simulations. Activities of 88Y, 87gY, and 87mY were measured and found to be in good agreement with the predictions.

Critical Phenomena: Coexistence of Valence Single Particle- and Core- Excitations in the $$^\mathbf{11}$$ 11 Be Halo Nucleus

Neutron knockout from $$^{11}$$ Be due to the collision with a proton target is evaluated at 300 MeV/u using the three-body Faddeev/Alt-Grassberger-Sandhas (Faddeev/AGS) equations. The results for the Quasi-Free-Scattering reaction mechanism are discussed.

Neutron knockout from 68,70Ni ground and isomeric states.

Neutron-rich isotopes are an important source of new information on nuclear physics. Specifically, the spin-isospin components in the nucleon-nucleon (NN) interaction, e.g., the proton-neutron tensor force, are expected to modify shell structure in exotic nuclei. These potential changes in the intrinsic shell structure are of fundamental interest. The study of the excitation energy of states corresponding to specific configurations in even-even isotopes, together with the single-particle character of the first excited states of odd-A, neutron-rich Ni isotopes, probes the evolution of the neutron orbitals around the Fermi surface as a function of the neutron number a step forward in the understanding of the region and the nature of the NN interaction at large N/Z ratios.In an experiment carried out at the National Superconducting Cyclotron Laboratory [1], new spectroscopic information was obtained for 68Ni and the distribution of single-particle strengths in 67,69Ni was characterized by means of single-neutron knockout from 68,70Ni secondary beams. The spectroscopic strengths, deduced from the measured partial cross sections to the individual states tagged by their de-exciting gamma rays, is used to identify and quantify configurations that involve neutron excitations across the N = 40 harmonic oscillator shell closure. The de-excitation γ rays were measured with the GRETINA tracking array [2].The results challenge the validity of the most current shell-model Hamiltonians and effective interactions, highlighting shortcomings that cannot yet be explained. These results suggest that our understanding of the low-energy states in such nuclei is not complete and requires further investigation.

Analysis of spectroscopic factors in Be11 and Be12 in the Nilsson strong-coupling limit

Spectroscopic factors in 10Be, 11Be and 12Be, extracted from (d,p), one neutron knockout, and (p,d) reactions are interpreted within the rotational model. Assuming that the ground state and first excited state of 11Be can be associated with the 1/2[220] and 1/2[101] Nilsson levels, the strong coupling limit gives simple expressions that relate the amplitudes of these wavefunctions (in the spherical basis) with the measured cross-sections and derived spectroscopic factors. We obtain good agreement with both the measured magnetic moment of the ground state in 11Be and the reaction data.

Neutron knockout from 68,70Ni ground and isomeric states.

Neutron knockout from 68,70Ni ground and isomeric states.

Quasi-elastic neutrino reactions on carbon and lead nuclei

We examine neutral-current quasi-elastic neutrino–nucleus reactions on 12C and 208Pb targets. We use the relativistic mean field theory approach to describe the nuclear dynamics. We compute the cross sections for the scattering of 150, 500 and 1000 MeV neutrinos on a 12C target and study the effect of the strange-quark content of the nucleon which appears in these reactions via the isoscalar weak current. We compare our results with the data of the MiniBooNE experiment for mineral oil (CH2). We also calculate the cross section for the quasi-elastic neutron knockout reaction of 20–60 MeV neutrinos on a 208Pb target which is relevant to plans to use lead as a target material in future supernova neutrino detectors.

Probing short-range correlations in asymmetric nuclei with quasi-free pair knockout reactions

Short-range correlations (SRC) in asymmetric nuclei with an unusual neutron-to-proton ratio can be studied with quasi-free two-nucleon knockout processes following the collision between accelerated ions and a proton target. We derive an approximate factorized cross section for those SRC-driven p(A,p′N1N2) reactions. Our reaction model hinges on the factorization properties of SRC-driven A(e,e′N1N2) reactions for which strong indications are found in theory-experiment comparisons. In order to put our model to the test we compare its predictions with results of C12(p,p′pn) measurements conducted at Brookhaven National Laboratory (BNL) and find a fair agreement. The model can also reproduce characteristic features of SRC-driven two-nucleon knockout reactions, like back-to-back emission of the correlated nucleons. We study the asymmetry dependence of nuclear SRC by providing predictions for the ratio of proton–proton to proton–neutron knockout cross sections for the carbon isotopes 9−15C thereby covering neutron excess values (N−Z)/Z between −0.5 and +0.5.

The origin of the background radioactive isotope 127Xe in the sample of Xe enriched in 124Xe

The results of investigation of 127Xe radioactive isotope production in the xenon sample enriched in 124Xe, 126Xe, 128Xe are presented. The isotope is supposed to be the source of the background events in the low-background experiment on search for 2K-capture of 124Xe. In this work we consider two channels of 127Xe production: the neutron knock-out from 128Xe nucleus by cosmogenic muons and the neutron capture by 126Xe nucleus. For the first channel the upper limit of the cross section of 127Xe production was found to be σ ≤ 0.007 × 10−24 cm2 at 95% C.L. For the second channel the value obtained for the cross section was found to be equal to σ = (2.74 ± 0.4) × 10−24 cm2, which coincides well, within the statistical error, with reference value.

Neutron single-particle strengths at N=40 , 42: Neutron knockout from Ni68,70 ground and isomeric states

The distribution of single-particle strength in 67,69Ni was characterized with one-neutron knockout reactions from intermediate-energy 68,70Ni secondary beams, selectively populating neutron-hole configurations at N = 39 and 41, respectively. The spectroscopic strengths deduced from the measured partial cross sections to the individual final states, as tagged by their γ-ray decays, are used to identify and quantify neutron configurations in the wave functions. While 69Ni compares well to shell-model predictions, the results for 67Ni challenge the validity of current effective shell-model Hamiltonians by revealing discrepancies that cannot be explained so far. These results suggest that our understanding of the low-lying states in the neutron-rich, semi-magic Ni isotopes may be incomplete and requires further investigation on both the experimental and theoretical sides.

Production of the PET isotope 11C in hadron therapy via neutron knockout

PurposePositron emitting isotopes such as 11C and 10C can be used for vital dose verification in hadron therapy. These isotopes are produced when the high energy 12C primary beam particles undergo nuclear reactions within the patient. MethodsWe discuss a model for calculating cross sections for the production 11C in 12C+12C collisions, applicable at hadron therapy energies. ResultsGood agreement with the available cross section measurements is found for 12C(−1n), though more detailed, systematic measurements would be very valuable. ConclusionsNuclear structure plays a crucial role in the reactions of light nuclei, particularly when those reactions are peripheral and involve only a few nucleons. For such reactions, nuclear structure has a strong influence on the energy and angular distribution of the cross section, and is an important consideration for reliable dose verification using 11C in hadron therapy.

Determination of a dineutron correlation in Borromean nuclei via a quasi-free knockout (p,pn) reaction

To discuss the dineutron correlation in the ground state, the quasi-free neutron knockout reaction on $^6$He is investigated.In the present work, the momentum distribution of the two emitted neutrons is calculated with the $\alpha$~+~$n$~+~$n$ three-body model and a simple reaction model to assess the effects of the knockout process via the $^5$He resonance and the target dependence in the momentum distribution. A clear signature of the dineutron correlation can be obtained by choosing the kinematical condition so the process via the $^5$He resonance is excluded because the $^5$He resonance drastically changes the momentum distribution. Using the proton target is important in the quantitative discussion on the dineutron correlation by the knockout reaction. In addition to theoretical arguments, a possible experimental setup to determine the dineutron correlation via the quasi-free knockout reaction is considered.

Distortion effects on the neutron knockout from exotic nuclei in the collision with a proton target

Background: Reaction theory plays a major role in the interpretation of experimental data and one needs to identify and include accurately all the relevant dynamical effects in order to extract reliable structure information. The knockout of a nucleon (neutron/proton) from a high energy exotic nucleus projectile colliding with a proton target allows to get insight on the structure of its valence and inner shells.Purpose: We aim to clarify the role of the distortion on the calculated observables for nucleon knockout, in particular, the dependence of the calculated observables on the binding energy ${\ensuremath{\epsilon}}_{b}$ and angular momentum $L$ of the knockout particle, and on the mass of the projectile core, ${A}_{c}$. We consider mainly the knockout of a neutron that may be either in the valence or in the inner shell of the projectile nucleus.Method: Exact three-body Faddeev/Alt-Grassberger-Sandhas (Faddeev/AGS) calculations are performed for the nucleon knockout from stable and exotic nuclei in the collision of 420 MeV/u projectile beams with a proton target. Results are compared with plane-wave impulse approximation (PWIA) calculations.Results: The Faddeev/AGS formalism accurately predicts: (i) a systematic nearly logarithmic dependence of the distortion parameter on the separation energy; (ii) roughly linear dependence of the ratio of the full to the PWIA cross section on the asymmetry parameter; (iii) a distinct behavior between the calculated transverse core momentum distribution from the PWIA and full Faddeev/AGS exact approach which indicates that distortion effects do not modify fully exclusive observables through a common renormalization factor.Conclusions: To extract structure information on deeper shells one needs to include distortion effects accurately. A systematic analysis enables to estimate the total cross section for knockout of a nucleon from a given shell of nuclei at/away the stability line of the nuclear landscape. The comparison with experimental results may provide understanding on the used interaction and structure model.

The knockout reaction of 15C on a 9Be target at intermediate energies

In this work, neutron knockout reactions of 15C on a 9Be target at energy 103 and 250 MeV/nucleon are studied. Using the Eikonal approximation of the Glauber model, total neutron removal cross sections, the stripping and diffractive cross sections as well as 14C longitudinal momentum distributions are determined in both 15C ground state and exited states of the wave function. We compared the results of our calculations with the available experimental data obtained recently. The calculated cross sections of 15C and 14C reactions, as well as the momentum distribution are in relatively good agreement with available data.

Differences Between a Single- and a Double-Folding Nucleus- $$^\mathbf{9}$$ 9 Be Optical Potential

We have recently constructed two very successful n- $$^9$$ Be optical potentials (Bonaccorso and Charity in Phys Rev C89:024619, 2014). One by the Dispersive Optical Model (DOM) method and the other (AB) fully phenomenological. The two potentials have strong surface terms in common for both the real and the imaginary parts. This feature makes them particularly suitable to build a single-folded (light-) nucleus- $$^9$$ Be optical potential by using ab-initio projectile densities such as those obtained with the VMC method (Wiringa http://www.phy.anl.gov/theory/research/density/ ). On the other hand, a VMC density together with experimental nucleon–nucleon cross-sections can be used also to obtain a neutron and/or proton- $$^9$$ Be imaginary folding potential. We will use here an ab-initio VMC density (Wiringa http://www.phy.anl.gov/theory/research/density/ ) to obtain both a n- $$^9$$ Be single-folded potential and a nucleus-nucleus double-folded potential. In this work we report on the cases of $$^8$$ B, $$^8$$ Li and $$^8$$ C projectiles. Our approach could be the basis for a systematic study of optical potentials for light exotic nuclei scattering on such light targets. Some of the projectiles studied are cores of other exotic nuclei for which neutron knockout has been used to extract spectroscopic information. For those cases, our study will serve to make a quantitative assessment of the core-target part of the reaction description, in particular its localization.

Neutron single-particle strengths at N=40, 42: Neutron knockout from Ni 68,70 ground and isomeric states

Neutron single-particle strengths at N=40, 42: Neutron knockout from Ni 68,70 ground and isomeric states

Observation of long-range three-body coulomb effects in the decay of (16)Ne.

The interaction of an E/A=57.6-MeV ^{17}Ne beam with a Be target is used to populate levels in ^{16}Ne following neutron knockout reactions. The decay of ^{16}Ne states into the three-body ^{14}O+p+p continuum is observed in the High Resolution Array (HiRA). For the first time for a 2p emitter, correlations between the momenta of the three decay products are measured with sufficient resolution and statistics to allow for an unambiguous demonstration of their dependence on the long-range nature of the Coulomb interaction. Contrary to previous measurements, our measured limit Γ<80 keV for the intrinsic decay width of the ground state is not in contradiction to the small values (of the order of keV) predicted theoretically.

Neutron occupancy of the [formula omitted] orbital and the [formula omitted] shell closure in 24O

One-neutron knockout from 24O leading to the first excited state in 23O has been measured for a proton target at a beam energy of 62 MeV/nucleon. The decay energy spectrum of the neutron unbound state of 23O was reconstructed from the measured four momenta of the 22O fragment and emitted neutron. A sharp peak was found at Edecay=50±3 keV, corresponding to an excited state in 23O at 2.78±0.11 MeV, as observed in previous measurements. The longitudinal momentum distribution for this state was consistent with d-wave neutron knockout, providing support for a Jπ assignment of 5/2+. The associated spectroscopic factor was deduced to be C2S(0d5/2)=4.1±0.4 by comparing the measured cross section (σ−1nexp=61±6 mb) with a distorted wave impulse approximation calculation. Such a large occupancy for the neutron 0d5/2 orbital is in line with the N=16 shell closure in 24O.