Measurement of the $$^{232}$$ Th(n,f) cross section with quasi-monoenergetic neutron beams in the energy range 2–18 MeV

The European Physical Journal A - The E1 contribution to the capture reaction $$^7\mathrm {Li}(n,\gamma )^8\mathrm {Li}$$  is calculated at low energies. We employ a coupled-channel...     

Study of the 24Mg(α, 12C)16O reaction in the energy range Elab = 24.9–27.76 MeV

The ²⁴Mg(α,¹²C)¹⁶O and ²⁴Mg(α, α')²⁴Mg reactions have been used to search for resonances in the ²⁸Si compound nucleus. The excitation functions were measured in the energy range between 24.9 and 27.76 MeV. Angular distributions of ¹²C nuclei and elastic and inelastic scattering of α-particles have been measured at energies corresponding to extrema of excitation functions. Significant anomalies have been found at E_ex = 31.5 and 33,1 MeV. The spins and parities of these structures are assigned as 9⁻ and 11⁻, respectively.     

Experimental investigation of the 19F(n, α)16N reaction excitation function in the neutron energy range of 4 to 7.35 MeV

The interaction of neutrons with light nuclei study is of interest for understanding nuclear-reaction mechanisms. Fluorine nuclei are worth particular attention because they are abundant in the core of the promising molten-salt reactors and can noticeably affect the chain reaction kinetics. In this work we have experimentally investigated the ¹⁹F(n, α)¹⁶N reaction cross-section at neutron energies ranging from 4 to 7.35 MeV.     

Time features of delayed neutrons and partial emissive-fission cross sections for the neutron-induced fission of 232Th nuclei in the energy range 3.2–17.9 MeV

The energy dependence of the relative abundances of delayed neutrons and the energy dependence of the half-lives of their precursors in the neutron-induced fission of ²³²Th nuclei in the energy range 3.2–17.9 MeV were measured for the first time. A systematics of the time features of delayed neutrons is developed. This systematics makes it possible to estimate the half-life of delayed-neutron precursors as a function of the nucleonic composition of fissile nuclei by using a single parameter set for all nuclides. The energy dependence of the partial cross sections for emissive fission in the reaction ²³²Th(n, f) was analyzed on the basis of data obtained for the relative abundances of delayed neutrons and the aforementioned half-lives and on the basis of the created systematics of the time features of delayed neutrons. It was shown experimentally for the first time that the decrease in the cross section after the reaction threshold in the fission of ²³²Th nuclei (it has a pronounced first-chance plateau) is not an exclusion among the already studied uranium, plutonium, and curium isotopes and complies with theoretical predictions obtained for the respective nuclei with allowance for shell, superfluid, and collective effects in the nuclear-level density and with allowance for preequilibrium neutron emission     

Measurements of differential and angle-integrated cross sections for the ~(10)B(n, α)~7Li reaction in the neutron energy range from 1.0 eV to 2.5 MeV

Differential and angle-integrated cross sections for the ~(10)B(n,α)~7 Li,~(10)B(n,α_0) ~7 Li and ~(10)B(n,α_1) ~7 Li~*reactions have been measured at CSNS Back-n white neutron source.Two enriched(90%) ~(10)B samples 5.0 cm in diameter and～85.0 μg/cm~2 in thickness each with an aluminum backing were prepared,and back-to-back mounted at the sample holder.The charged particles were detected using the silicon-detector array of the Light-charged Particle Detector Array(LPDA) system.The neutron energy En was determined by TOF(time-of-flight) method,and the valid a events were extracted from the E_n-Amplitude two-dimensional spectrum.With 15 silicon detectors,the differential cross sections of a-particles were measured from 19.2°to 160.8°.Fitted with the Legendre polynomial series,the(n,a) cross sections were obtained through integration.The absolute cross sections were normalized using the standard cross sections of the ~(10)B(n,α) ~7 Li reaction in the 0.3-0.5 MeV neutron energy region.The measurement neutron energy range for the ~(10)B(n,α) ~7 Li reaction is 1.0 eV≤E_n 2.5 Me V(67 energy points),and that for the ~(10)B(n,α_0) ~7 Li and~(10)B(n,α_1) ~7 Li~*reactions is 1.0 eV≤E_n1.0 MeV(59 energy points).The present results have been analyzed by the resonance reaction mechanism and the level structure of the ~(11)B compound system,and compared with existing measurements and evaluations.     

Energy deposition and GDR emission in the reaction 209Bi(α,α′) at 240 MeV

Neutron fold distributions measured for the reaction ²⁰⁹Bi(α,α′) at 240 MeV have been analyzed with the help of Statistical Model calculations to determine the distribution of excitation energy, E_x, in the primary target fragments as a function of the projectile energy loss, EL. The reconstructed distributions in excitation energy feature a plateau which extends from the kinematical limit E_x = EL to very small excitations, indicating a variety of interactions of the beam particles with the target nucleus. The requirement of an additional coincidence with a light charged particle leads to the selection of a significant higher average excitation energy. Those results are extrapolated to explore the effects of including the excitation energy distributions in the analysis of previous GDR measurements in ²⁰⁸Pb. Corrections of the derived GDR parameters due to the partial transfer of excitation energy are suggested.     

Investigation of the 19F(n, α)16N reaction excitation function in neutron energy range of 4–7.35 MeV

New method based on ionization chamber with Frisch grid and digital signal processing was developed for experimental investigation of ¹⁹F(n, α)¹⁶N reaction. The chamber filling gas with CF₄ additive was used as the fluorine-containing target. The experimental investigation of ¹⁹F(n, α)¹⁶N reaction cross-section in 4–7.35 MeV energy range is represented in this work. The total cross section of ¹⁹F(n, α)¹⁶N reaction was measured as well as partial cross-section for sum of α₀-α₃ and sum of α₄ and α₅ reaction channels.     

The 11B(α, p)14C reaction below 1.7 MeV bombarding energy

For estimation of the production rate of the long-lived ¹⁴C isotope originating in the controlled thermonuclear synthesis ¹¹B + p the total cross section of the ¹¹B(α, p)¹⁴C reaction has been determined in the energy range of α-particles E_α = 0.9−1.7 MeV. Five resonances corresponding to states in ¹⁵N have been observed. The assignment of the resonance parameters is discussed.     

Search for e + e − → f 0(600)γ, f 0(980)γ, f 0(1350)γ, and f 2(1270)γ processes in the energy range from 1.05 to 1.38 GeV

In the energy range from 1.05 to 1.38 GeV, the upper limits for the cross sections of e ⁺ e ^? → f ₀(600)γ, f ₀(980)γ, f ₀(1350)γ, and f ₂(1270)γ → π⁰π⁰γ processes have been established. Measurements are performed in accordance with the statistics gathered in experiment with a spherical neutral detector (SND) on the VEPP-2M e ⁺ e ^? collider. The resultant upper limits vary from 6 to 42 pb depending on the energy and the model.     

Photofission of 238Pu, 240Pu, and 242Pu in the energy range 5–10 MeV

The cross sections for the photofission of plutonium isotopes ²³⁸Pu, ²⁴⁰Pu, and ²⁴²Pu in the energy range 5–10 MeV have been measured by using a beam of bremsstrahlung photons from the microtron installed at the Institute of Physics and Power Engineering (Obninsk). The energy regions below the fission barrier and above 6 MeV have been scanned with pitches of 0.05 and 0.1 MeV, respectively. In deriving the absolute cross section for ²³⁸Pu photofission, ²³⁸U photofission has been employed as a reference reaction. In measurements involving ²⁴⁰Pu and ²⁴²Pu nuclei, the neptunium isotope ²³⁷Np, which is characterized by a more regular dependence of the photofission cross section on excitation energy than ²³⁸U, has been chosen for the first time as a reference nucleus. The measured cross sections as functions of energy show resonance structures in the vicinity of the fission threshold that are consistent with those previously observed in the energy dependences of fissilities for corresponding direct reactions. The partial-wave cross sections for the J ^π K = 1^?0, 1^?1, and 2⁺0 photofission channels have been determined as functions of energy. At energies below some 5.5 MeV, the total cross section for photofission of each plutonium isotope being studied receives a significant contribution from quadrupole interaction. Within the one-dimensional model of a two-humped fission barrier, the parameters of the barriers for ²³⁸Pu, ²⁴⁰Pu, and ²⁴²Pu have been extracted from data and have then been compared with estimates based on previous measurements.     

Fusion and transfer cross sections of 3He induced reaction on Pt and Au in energy range 10–24.5 MeV

In experiments performed by accelerated ion ³He-beam irradiated gold and platinum targets on the cyclotron U-120M of the Nuclear Physics Institute of the Czech Academy of Sciences, ?e?, reactions of complete and incomplete fusion and nucleon transfer reactions in the ³He energy range from 10 to 24.5 MeV have been investigated. To determine the yield of the nuclides resulting from the nuclear reaction, the activation technique has been used. The obtained data are analyzed using models based on statistical calculations and compared with similar results for other light stable particles. Transfer reactions with positive Q values have relatively high cross sections in the energy range below the Coulomb barrier. These cross sections continue to grow with increasing ³He energy, and, in the case of capturing neutron from target nucleus by a nucleus of ³He, the excitation functions of these reactions reach their maximum almost at the Coulomb barrier of the reactions.     

Excitation functions and isomeric ratios in the reaction130Te (α,xpyn) for α-particle energies between 15 and 37 MeV

The¹³⁰Te(,n)¹³³Xe,¹³⁰Te(,p)¹³³I,¹³⁰Te(,pn)¹³²I and¹³⁰Te(, n)¹²⁹Te excitation functions for alpha particle energies between 14.7 and 36.5 MeV are presented. Excitation functions for the last three reactions are measured for the first time and more consistent results for (, n) are obtained. The isomeric ratios for the ( n), (, pn) and (, n) reactions were deduced. Calculations based on different theoretical models of equilibrium and preequilibrium decay are compared with the experimental results and discussed. Acceptable presentation of the energy behavior of the measured isomeric ratios was obtained when higher angular momentum depletion for preequilibrium emitted particles was included. The absolute values of the isomeric ratios however remain overestimated.We want to express our gratitude to Prof. Ts. Vylov and Dr. V. Brudanin (Dubna) who supplied us with measurement equipment, to Dr. Chr. Necheva for taking part in the experiments, to the U-200 cyclotron staff and to the direction of the Laboratory of Nuclear Reactions (JINR) for making the irradiation possible and to Dr. E. Dobreva (Sofia) for fruitful discussion of the experimental method. We wish to express our gratitude also to Prof. M. Uhl and the NEA data bank for making the computer code STAPRE available to us and to Prof. J. Ernst (Bonn) for fruitful discussions. This project has been completed with the financial support of the Committee for Science at the Council of Ministers under contract No. 644.     

Investigation of multipole mixtures in gamma transitions by means of the reaction 232Th(n, n′γ)

The spectrumof gamma rays from the reaction ²³²Th(n, n′γ) induced by a beam of fast reactor neutrons and the angular distribution of the gamma rays in question with respect to this beam were measured. The multipole-mixture parameter δ was found for many gamma transitions.     

Measurement of the 85Rb(γ, n)84mRb cross-section in the energy range 10-19 MeV with bremsstrahlung photons

We study the charmonium 2S states ??? and ??? _c , and the bottomonium 2S states ???? and ??? _b , using the light-front quark model and the 2S state wave function of harmonic oscillator as the approximation of the 2S quarkonium wave function. The decay constants, transition form factors and masses of these mesons are calculated and compared with experimental data. Predictions of quantities such as Br(???????? _c ) are made. The 2S wave function may help us learn more about the structure of these heavy quarkonia.     

Nuclear interaction dynamics in the 56Fe (α, xn) reaction

Neutron spectra and angular distributions in the ⁵⁶Fe (α, xn) reaction are measured at α-particle energies of 12.5, 16.3, 18.3, 26.8, and 45.2 MeV. The measurements are performed using time-of-flight fast neutron spectrometers on pulsed accelerators. The measured data are analyzed in the context of equilibrium, preequilibrium, and direct nuclear reaction mechanisms. The contributions from equilibrium, preequilibrium, and direct mechanisms of neutron emission are studied over a wide range of α-particle energies.     

The reaction e+e-→ωπ0 in the cm energy range from 1.0 to 1.4 GeV

The reaction e⁺e^-→ωπ⁰→π⁰π⁰γ has been studied with the Neutral Detector at the VEPP-2M collider. The cross section values differ from the predictions of the vector dominance model with one ϱ(770) meson, and are consistent with the contributions of ϱ(770) and ϱ(1600). ϱ(1250) has not been observed.     

The mechanism of the 7Li(d, 2α)n reaction from Ed = 3 to 15 MeV

The ⁷Li(d, 2α)n reaction proceeds almost entirely through excitation and sequential decay of the 16.63 and 16.92 MeV levels in ⁸Be, for incident energies 1 to 13 MeV above their threshold. The energy dependence for forming these levels with the neutron emitted at 0° is approximately that predicted assuming the neutron is a spectator from the incident deuteron. None of the individual spectra, the angular dependence of the cross section at fixed E_d, or the bombarding-energy-dependence of the cross section for forming the levels is consistent with the involvement of a spectator neutron from the ⁷Li target.     

Cross-sections of isomeric state excitation of the 119Te and 121Te nuclei in (γ, n) reactions in an energy range of 9–20 MeV

The dependence of isomeric yield ratios upon the maximum bremsstrahlung gamma-quanta energy for the ¹²⁰Te(??, n)^119m,g Te and ¹²²Te(??, n)^121m,g Te reactions within an energy range of the giant dipole resonance is investigated. Cross-sections of excitation of metastable states with J ^?? = 11/2^? of the ¹¹⁹Te and ¹²¹Te nuclei are obtained. Experimental data are compared with computation results obtained using the TALYS-1.2 software package.