Measurements Of Reaction Cross Sections Research Articles

Measurements of neutron-induced light-charged particle emission reactions

In the past two decades cooperating with Frank Laboratory of Neutron Physics (FLNP), Joint Institute for Nuclear Research (JINR) measurements of (n, α) reaction cross sections for 6Li, 10B, 25Mg, 39K, 40Ca, 54,56,57 Fe, 58Ni, 63Cu, 64,67 Zn, 95Mo, 143Nd and 147,149 Sm nuclei were performed in the MeV neutron energy region based on the 4.5 MV Van de Graaff accelerator at Peking University. In recent years, our measurements were extended in three aspects. Firstly, measurements were expanded from two-body reactions to three-body reactions such as 10B (n, t2 α). Secondly, the neutron energy region was extended from below 8 MeV to 8 - 11 MeV by using the HI-13 tandem accelerator of China Institute of Atomic Energy (CIAE), with which cross sections of 54,56 Fe(n, α)53,51Cr reactions were measured. Thirdly, based on the newly-built China Spallation Neutron Source (CSNS) Back-n WNS (White Neutron Source), differential and angle-integrated cross sections for 6Li(n, t) and 10B(n, α) reactions were measured in the neutron energy region from 1 eV to 3 MeV.

A 4π γ-summing method for cross-section measurements of capture reactions

Capture reaction cross sections at energies far below the Coulomb barrier are of major importance for the understanding of stellar nucleosynthesis. Since the cross sections of the majority of these reactions are very small, the use of high efficiency detectors is essential. In this work, a new method for capture reaction cross section measurements based on a large volume 4π NaI detector is presented.

58Ni(n,p)58Co and 58Ni(n,2n)57Ni reactions at the neutron energy of 14.54 MeV with covariance analysis

The 58 Ni(n,p) 58 Co and 58 Ni(n,2n) 57 Ni reactions cross sections have been estimated relative to 197 Au(n,2n) 196 Au monitor reaction at the incident neutron energy of 14.54±0.0024 MeV from the D-T fusion nuclear reaction using Purnima neutron generator carried through methods of activation and off-line γ-ray spectrometry. The uncertainty propagation and correlation for measured cross sections have been estimated using covariance analysis through considering the partial uncertainties in different attributes. The present measured reaction cross sections data have been analyzed by comparing with the literature data, with various libraries of evaluated data, like ENDF/B-VIII.0, JEFF-3.3, JENDL/AD-2017, ROSFOND-2010 and TALYS-1.9 theoretical calculations.

Cross section of α -induced reactions on Au197 at sub-Coulomb energies

Statistical model calculations have to be used for the determination of reaction rates in large-scale reaction networks for heavy-element nucleosynthesis. A basic ingredient of such a calculation is the a-nucleus optical model potential. Several different parameter sets are available in literature, but their predictions of a-induced reaction rates vary widely, sometimes even exceeding one order of magnitude. This paper presents the result of a-induced reaction cross-section measurements on gold which could be carried out for the first time very close to the astrophysically relevant energy region. The new experimental data are used to test statistical model predictions and to constrain the a-nucleus optical model potential. For the measurements the activation technique was used. The cross section of the (a,n) and (a,2n) reactions was determined from g-ray counting, while that of the radiative capture was determined via X-ray counting. The cross section of the reactions was measured below E$_a=20.0$~MeV. In the case of the $^{197}$Au(a,2n)$^{199}$Tl reaction down to 17.5~MeV with 0.5-MeV steps, reaching closer to the reaction threshold than ever before. The cross section of $^{197}$Au(a,n)$^{200}$Tl and $^{197}$Au(a,g)$^{201}$Tl was measured down to E$_a=13.6$ and 14.0~MeV, respectively, with 0.5-MeV steps above the (a,2n) reaction threshold and with 1.0-MeV steps below that. The new dataset is in agreement with the available values from the literature, but is more precise and extends towards lower energies. Two orders of magnitude lower cross sections were successfully measured than in previous experiments which used g-ray counting only, thus providing experimental data at lower energies than ever before. The new precision dataset allows us to find the best-fit a-nucleus optical model potential and to predict cross sections in the Gamow window with smaller uncertainties.

Study of the Extracted Beam Energy as a Function of Operational Parameters of a Medical Cyclotron

The medical cyclotron at the Bern University Hospital (Inselspital) is used for both routine 18 F production for Positron Emission Tomography (PET) and multidisciplinary research. It provides proton beams of variable intensity at a nominal fixed energy of 18 MeV. Several scientific activities, such as the measurement of nuclear reaction cross-sections or the production of non-conventional radioisotopes for medical applications, require a precise knowledge of the energy of the beam extracted from the accelerator. For this purpose, a study of the beam energy was performed as a function of cyclotron operational parameters, such as the magnetic field in the dipole magnet or the position of the extraction foil. The beam energy was measured at the end of the 6 m long Beam Transfer Line (BTL) by deflecting the accelerated protons by means of a dipole electromagnet and by assessing the deflection angle with a beam profile detector.

Investigating the link between proton reaction cross sections and the quenching of proton spectroscopic factors in 48Ca

The nucleon self-energies of 40Ca and 48Ca are determined using a nonlocal dispersive optical model (DOM). By enforcing the dispersion relation connecting the real and imaginary part of the self-energy, scattering and structure data are used to constrain these self-energies. The ability to calculate both bound and scattering states simultaneously puts these self-energies in a unique position to consistently describe exclusive knockout reactions such as (e,e′p). The present analysis reveals the importance of high-energy proton reaction cross-section data in constraining spectroscopic factors required for the description of the (e,e′p) cross sections. In particular, it is imperative that high-energy proton reaction cross-section data are measured for 48Ca in the near future so that the quenching of the spectroscopic factors in the 48Ca(e,e′p)47K reaction can be unambiguously constrained using the DOM. Measurements of proton reaction cross sections in inverse kinematics employing rare isotope beams with large neutron excess will provide corresponding constraints on proton spectroscopic factors for exotic nuclei. Moreover, DOM generated spectral functions indicate that the quenching of spectroscopic factors compared to 40Ca is not only due to long-range correlation, but also partly due to the increase in high-momentum protons in 48Ca on account of the strong neutron-proton interaction. Single-particle momentum distributions of protons and neutrons in 48Ca calculated from these spectral functions confirm that neutron excess causes a higher fraction of high-momentum protons than neutrons.

Total reaction cross sections of neutron-rich light nuclei measured by the COMBAS fragment-separator

Preliminary results of measurements of the total reaction cross sections σ R for nuclei 4 He, 6 He, 8 He, 7 Li, 8 Li, 9 Li, 11 Li, 7 Be, 9 Be, 10 Be, 11 Be, 12 Be, 8 B, 10 B, 11 B and 12 B nuclei at energy range (10-50) AMeV with 28 Si target is presented. The secondary beams of light nuclei were produced by bombardment of the 15N (50 AMeV) primary beam on Be target and separated by COMBAS fragment- separator. In dispersive focal plane a horizontal slit defined the momentum acceptance as 1% and a wedge degrader of 600 µm Al was installed. The B ρ of the second section of the fragment-separator was adjusted for measurements in energy range (10-45) AMeV. The strong absorption model reproduces the A-dependence of σ R , but not the detailed structure. We are comparing our experimental data with predictions of microscopic (dashed line) and strong absorption model, Glauber multiple scattering theory and preliminary results are obtained.

Fusion reactivity of the pB11 plasma revisited

Fusion reactivity for the pB11 fuel has been reassessed for magnetic confinement devices. This study is based on two factors: new measurements of the fusion reaction cross-sections and an accounting of the kinetic effects that lead to the increase of the number of protons at higher energies (with respect to a pure Maxwellian). The net effect leads to an approximately 30% increase of the fusion yield for the same global plasma parameters compared to the previous assessments.

Investigation of (n,2n) reactions using the high energy neutron facility at NCSR “Demokritos”

In the high energy neutron facility at the 5.5MV tandem T11/25 Accelerator of NCSR "Demokritos", the neutron beam is produced by means of the 3H(d,n)4He reaction in the energy range ~15-21 MeV and at a flux of the order of 105 -106 n/cm2s. The beam has been characterized by means of the NeuSDesc and MCNP5 Monte Carlo simulations along with the multiple foil activation technique at various neutron energies. The neutron flux has been deduced using reference reactions, such as the 27Al(n,α) reaction, while the flux variation of the neutron beam was monitored by using a BF3 detector. After the characterization, the neutron beam has been used for (n,2n) reaction cross section measurements on Hf, Au and Ir isotopes via the activation technique. The irradiations were carried out at 15.3 and 17.1 MeV.

Activation cross section measurement of the (n,2n) reactions on natural Ir isotopes

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Highlights of the day-one experimental program at the gamma-beam system of ELI-NP

The emerging experimental program with brilliant gamma beams at the Extreme Light Infrastructure - Nuclear Physics facility (ELI-NP) is presented with emphasis on the prepared day-one experiments. Ex- periments at ELI-NP will cover nuclear resonance fluorescence measurements, studies of large-amplitude motions in nuclei, photo-fission and photonuclear reactions of astrophysics interest, and measurements of photonuclear reaction cross sections. The physics cases of the flagship experiments at ELI-NP and the performance of the related instruments, which are under construction for their realization, are discussed.

High-energy neutron facility at the Athens Tandem Accelerator NCSR “Demokritos”

In the 5.5 MV tandem T11/25 Accelerator Laboratory of NCSR “Demokritos” monoenergetic neutron beams have been produced in the energy range ∼16–19 MeV using a new Ti-tritiated target of 373 GBq activity, by means of the 3H(d,n)4He reaction. The corresponding beam energies obtained from the accel- erator, were 0.8–3.7 deuterons. The maximum flux has been determined to be of the order of 106 n/s·cm2, implementing reference reactions. An investigation of the energy dependence of the neutron fluence has been carried out with the multiple foil activation technique. The beam has been used for the measurement of (n,2n) reaction cross section on several isotopes at 16.7 and 17 MeV.

Cross-section measurement of (n,2n) reactions for Nd isotopes induced by 14 MeV neutrons

Cross-sections of the (n,2n) reactions for neodymium (Nd) isotopes induced by 14 MeV neutrons were measured in this work by using the activation and relative methods. The measured cross-sections of the 150Nd(n,2n)149Nd, 148Nd(n,2n)147Nd, and 142Nd(n,2n)141Nd reactions were 1854 ± 81, 1789 ± 119, and 1559 ± 98 mb, respectively, at a neutron energy of 14.2 ± 0.2 MeV, and 1485 ± 74, 1726 ± 85, and 1670 ± 119 mb, respectively, at 14.9 ± 0.2 MeV. The results were compared with the experimental values from the reported literature, with the evaluated data from the ENDF/B-VII.1, CENDL-3.1, and JENDL-4.0 libraries, and with the curves calculated by the Talys-1.8 code.

Fractionation of copper activation products in debris samples from the National Ignition Facility

Nuclear fusion experiments performed at the National Ignition Facility produce radioactive debris, arising in reactions of fast neutrons with the target assembly. We have found that postshot debris collections are fractionated, such that isotope ratios in an individual debris sample may not be representative of the radionuclide inventory produced by the experiment. We discuss the potential sources of this fractionation and apply isotope-correlation techniques to calculate unfractionated isotope ratios that are used in measurements of nuclear reaction cross sections.

Consistent account of deuteron-induced reactions on natCr up to 60 MeV

Purpose: Accurate new measurements of low-energy deuteron-induced reaction cross sections for natural Cr target can enhance the related database and the opportunity for an unitary and consistent account of the involved reaction mechanisms. Methods: The activation cross sections of $^{51,52,54}$Mn, $^{51}$Cr, and $^{48}$V nuclei for deuterons incident on natural Cr at energies up to 20 MeV, were measured by the stacked-foil technique and high resolution gamma spectrometry using U-120M cyclotron of the Center of Accelerators and Nuclear Analytical Methods (CANAM) of the Nuclear Physics Institute of the Czech Academy of Sciences (NPI CAS). They as well as formerly available data for deuteron interactions with Cr isotopes up to 60 MeV are the object of an extended analysis of all processes from elastic scattering until the evaporation from fully equilibrated compound system, but with a particular attention given to the BU and DR mechanisms. Results: The new measured activation excitation functions proved essential for the enrichment of the deuteron database, while the theoretical analysis of all available data strengthens for the first time their consistent account provided that (i) a suitable BU and DR assessment is completed by (ii) the assumption of PE and CN contributions corrected for decrease of the total-reaction cross section due to the leakage of the initial deuteron flux towards BU and DR processes. Conclusions: The suitable description of nuclear mechanisms involved within deuteron-induced reactions on chromium, taking into account especially the BU and DR direct processes, is validated by an overall agreement of the calculated and measured cross sections including particularly the new experimental data at low energies.

A new neutron detector designed for (n,2n) and (n,3n) reaction cross section measurements

A large 4π liquid scintillator was commonly used as the neutron detector to measure nucleus (n,2n) and (n,3n) reaction cross sections in the past direct neutron counting method. However, this type of detector was often criticized for its high γ-rays background. Hence we constructed a new 4π3He array detector to substitute the large liquid scintillation detector, which can effectively suppress the γ-rays. This work mainly studies the detection efficiency and moderation time of this new detector through experimental and simulational methods. Due to its spherical configuration, a relatively stable and weak angular dependence detection efficiency is obtained for the secondary neutrons from (n,2n) and (n,3n) reactions. In addition, the character that the moderation time is nearly independent of neutron energy guarantees gate width has a same influence on the detection efficiency of the secondary neutrons from different samples. These features make it a good candidate detector for (n,2n) and (n,3n) reaction cross section measurements. At last, the preliminary experiment plan and the corresponding calculation method are briefly described.

Erratum: “Formalism for Inclusion of Measured Reaction Cross Sections in Stellar Rates including Uncertainties and its Application to Neutron Capture in the s-process” (2012, ApJL, 755, L10)

Abstract The final rate uncertainty factors presented in the original Letter have been calculated using an inappropriate value for the ground-state contribution in some cases. Revised rate uncertainty factors are presented here. Furthermore, the full version of Equation (6), incomplete in the original Letter, is given.

Measurement and covariance analysis of 59Co(n, 2n)58Co reaction cross sections at the effective neutron energies of 11.98 and 15.75 MeV

Abstract The 59Co(n, 2n)58Co reaction cross sections relative to the cross sections of the 115In(n, n′)115mIn reaction have been measured at the effective neutron energies of 11.98 and 15.75 MeV by using activation and off-line γ-ray spectrometric technique. Neutron beam used in the present experiment was generated from the 7Li(p, n)7Be reaction with the proton energies of 14 and 18 MeV at the 14UD BARC-TIFR Pelletron facility, Mumbai. We also present the covariance information by taking into account the sources of error and the correlations between the attributes influencing the measurements. The 59Co(n, 2n)58Co reaction cross sections from the present work are then compared with the values from different evaluated nuclear data libraries. The micro-correlation technique suggested by Smith was modified to generate the covariance matrix for the measurements of reaction cross sections as the efficiencies of detector for the sample and monitor are correlated.

Superhalo of C22 reexamined

An unusually large value of the C22 matter radius, extracted by Tanaka et al. [Phys. Rev. Lett. 104, 062701 (2010)PRLTAO0031-900710.1103/PhysRevLett.104.062701] from measured reaction cross sections, attracted great attention of scientific community. Since that time, several experimental works related to the C22 nucleus have appeared in the literature. Some of the experimental data, measured with high accuracy, allow us to fix C22 structure more reliably. Two limiting models reproducing C22 nuclear structure within the three-body cluster approach, that allow us to describe all existing experimental data, are presented. The C22 ground state, continuum structure, and geometry are obtained. With fixed C22 wave function, the prediction for the soft dipole mode in C22, which is studied in the process of Coulomb fragmentation, is performed.

The RIB facility EXOTIC and its experimental program at INFN-LNL

In this contribution, I will present a review about the EXOTIC facility and the research field accessible by using its Radioactive Ion Beams. The EXOTIC facility, installed at the INFN-Laboratori Nazionali di Legnaro, is devoted to the in-flight production of light Radioactive Ion Beams in the energy range between 3-5 MeV/nucleon. The scientific activity performed at EXOTIC concerns different aspects of nuclear physics and nuclear astrophysics, such as, the investigation of reaction mechanisms and nuclear structure, resonant scattering experiments and measurements of nuclear reaction cross sections of astrophysical interest.