Setup for studying quasi-free neutron-neutron scattering in the energy range of 20–60 MeV

A setup installed on the RADEX neutron beam channel (Institute for Nuclear Research, Russian Academy of Sciences) and designed to study quasi-free nn scattering in the n + d → p + n + n reaction is described. The setup is a two-arm time-of-flight spectrometer composed of scintillation neutron hodoscope (in the left arm), a scintillation neutron detector (in the right arm), and an active scintillation deuterated target for detecting protons. Secondary neutrons are detected at angles corresponding to the kinematic conditions of quasi-free nn scattering. Events are selected at low energies of the outgoing proton spectator. It is shown that data on neutron-neutron quasi-free scattering can be obtained in a wide range of primary-neutron energies.     

Phase-shift analysis of π+ p-scattering in the energy region from 194 to 600 MeV

An energy-independent phase-shift analysis ofπ ⁺ p-scattering has been carried out at 16 energies in the region 194–600 MeV. The new data on elastic polarization, obtained in LNPI up to 1983, were included.     

Microscopic analysis of the energy dependence of the 6He, 6Li + 28Si total reaction cross sections in the energy range E = 5−50 A MeV

The experimental data on the total cross sections of the ^{4, 6}He, ^{6, 7}Li + ²⁸Si reactions at energies E=5−50 A MeV are reported. The data for the ⁶Li, ⁶He + ²⁸Si reactions have been analyzed within the microscopic model of double-folding optical potential, in which the real and imaginary parts are calculated at different densities of the projectile nucleus. The cross sections calculated with the microscopic double-folding Coulomb potential and the standard Coulomb potential for uniform charge distribution are compared with each other. Semimicroscopic potentials providing agreement with experimental data have been constructed on the basis of renormalized microscopic potentials and their derivatives, added to take into account collective effects. Original Russian Text ￠ K.V. Lukyanov, E.V. Zemlyanaya, V.K. Lukyanov, I.N. Kukhtina, Yu.E. Penionzhkevich, Yu.G. Sobolev, 2008, published in Izvestiya Rossiiskoi Akademii Nauk. Seriya Fizicheskaya, 2008, Vol. 72, No. 3, pp. 382–386.     

Study of the reactione + e −→K + K − in the energy range1350 \leqq \sqrt s \leqq 2400 MeV

Thee ⁺ e ^?→K ⁺ K ^? cross section has been measured from about 750 events in the energy interval \(1350 \leqq \sqrt s \leqq 2400 MeV\) with the DM2 detector at DCI. TheK ^± form factor |F _F ^±| cannot be explained by the ρ, ω, ? and ρ′(1600). An additional resonant amplitude at 1650 MeV has to be added as suggested by a previous experiment.     

Search for a transient electric field gradient in the system90Zr→148Nd with the crystal ball spectrometer

The particle- angular correlation of the 2⁺0⁺ transition in¹⁴⁸Nd, Coulomb excited by⁹⁰Zr projectiles, was investigated to search for a transient electric field gradient expected to be present during the stopping of the recoils in²⁰⁸Pb. An upper limit of V_zz <>¹⁹V/cm² was obtained for¹⁴⁸Nd recoiling with initial velocities of 0.05 c.     

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     

Partial-wave analysis of elastic <Superscript>4</Superscript>He<Superscript>4</Superscript>He scattering in the energy range 40–50 MeV

A partial-wave analysis of elastic ⁴He⁴He scattering is performed in the energy range 40–50 MeV.     

Energy dependence of the optical potential for 16O + 28Si,elastic scattering in the energy range of E = 55–215 MeV

The energy dependence of an optical potential which reasonably fits all of the existing experimental data on ¹⁶O + ²⁸Si elastic scattering in the energy range of E = 54.7–215.2 MeV is studied. The real part of the potential found for this system shows a transition from a proximity to a double-folding type of the potential as a result of quenching of the Pauli principle effects with an increase of the incident energy. The imaginary part shows a transition from a surface-transparent to a strongly absorptive type of the potential.     

Experimental results on cross sections for 7Be photoproduction on 12C, 14N,and 16O nuclei in the energy range of 40–90 MeV

The yields of A(Γ,X)⁷Be reactions induced by bremsstrahlung photons were measured at the endpoint electron energies of 40, 50, 60, 70, 80, and 90MeV. The spectra of bremsstrahlung incident to the targets used were calculated via a simulation based on the GEANT 4 code passage. The cross sections for the A(γ,X)⁷Be reactions on ¹²C, ¹⁴N, and ¹⁶O nuclei were evaluated on the basis of the measured reaction yields and the calculated bremsstrahlung spectra. The experimental cross sections for the photonuclear reactions of ⁷Be production were comparedwith their counterparts calculated on the basis of the TALYS 1.4 package. Agreement of the experimental and evaluated results was demonstrated for ¹²C nuclei and partly for ¹⁴N nuclei.     

Angular distributions and anisotropy of the fragments from neutron-induced fission of <Superscript>233</Superscript>U and <Superscript>209</Superscript>Bi in the intermediate energy range of 1–200 MeV

New results of the neutron-induced fission experiments carried out at the neutron time-of-flight spectrometer GNEIS of the PNPI are given. Angular distributions of fission fragments from the neutron-induced fission of ²³³U and ²⁰⁹Bi nuclei have been measured in the energy range 1–200 MeV using position sensitive multiwire proportional counters as fission fragment detector. The recent improvements of the measurement and data processing procedures are described. The data on anisotropy of fission fragments deduced from the measured angular distributions are presented in comparison with the experimental data of other authors.     

Cross sections for the photofission of <Superscript>243</Superscript>Cm, <Superscript>245</Superscript>Cm, <Superscript>249</Superscript>Bk,and <Superscript>249</Superscript>Cf isotopes in the energy range from the threshold to 10–12 MeV

The relative method was used to measure the photofission cross sections for ²⁴³Cm and ²⁴⁹Cf isotopes in the energy range from 6 to 12 MeV, for ²⁴⁵Cm in the energy range from 5 to 10 MeV, and for ²⁴⁹Bk in the energy range from 5.5 to 10 MeV. The measurements were performed with an energy step of 50 to 200 keV by using the microtron installed at the Institute of Physics and Power Engineering (Obninsk). The cross section for ²³⁸U photofission was used as a reference in these measurements. Data on the cross sections for ²⁴³Cm, ²⁴⁵Cm, and ²⁴⁹Bk photofission were obtained for the first time, while data on the cross section for ²⁴⁹Cf photofission were obtained for the first time only in the energyregion E<10 MeV. The data on the ²⁴⁵Cm nucleus suggest that, in the energy region around 6 MeV, the cross section for its photofission has a maximum, which is likely to be due to the low-energy resonance structure of the dipole-photoabsorption cross section. For ²⁴⁹Cf, an anomalously large value of the photo fission cross section is observed in the region of the first maximum of the giant dipole resonance (E≈11 MeV). By comparing the energy dependences obtained for the fissilities of the ²⁴³Cm and ²⁴⁹Bk isotopes from photofission data with the fissilities from direct-reaction data, it is found that the observed fission thresholds agree and that there is a plateau-like dependence at energies above 7.5 MeV. For the ²⁴⁵Cm and ²⁴⁹Cf nuclei, there are no similar data for performing such a comparison. Data on the fissilities as obtained from the present series of relative measurements that employ the microtron bremsstrahlung spectrum are analyzed.     

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.     

Deperturbation study of the 0u+ symmetry states of As2 observed in the energy range 39 000–45 000 cm−1

The mutual perturbations of the A¹Σ_u⁺ and b0_u⁺ states of As₂ are due to a strong spin-orbit interaction. The numerical treatment of these perturbations leads to the following parameters:

     

17.

Nuclear vertex constants for the virtual decay <Superscript>7</Superscript>Be → <Superscript>3</Superscript>He + <Superscript>4</Superscript>He of the 7Be bound states from a phase-shift analysis in the effective-range theory     

Yu. V. Orlov  L. I. Nikitina 《Physics of Atomic Nuclei》2011,74(11):1610-1614

The phase-shift-analysis data for the ³He⁴He scattering are analyzed using the effective-range theory, with the Coulomb interaction taken into account. We find both the renormalized nuclear vertex constants for the vertex ⁷Be → ³He + ⁴He in the ground (3/2⁻) and in the first excited (1/2⁻) bound states of ⁷Be, and the corresponding asymptotic normalization constants of the radial wave functions in these states. The results obtained can be used in an astrophysical S-factor calculation for radiative capture reaction ⁴He(³He, γ)⁷Be     

18.

Description of cross sections for photonucleon reactions on tin isotopes at photon energies in the range 2 ≤ <Emphasis Type="Italic">E</Emphasis><Subscript><Emphasis Type="Italic">γ</Emphasis></Subscript> ≤ 140 MeV     

B. S. Ishkhanov  V. N. Orlin 《Physics of Atomic Nuclei》2009,72(12):2010-2026

A modified model of preequilibrium decay is considered. This model makes it possible to calculate cross sections for multiparticle photonucleon reactions with allowance for the impact of collective isospin effects. Features of the photodisintegration of 101 ≤ A ≤ 135 tin isotopes in the energy range 2 ≤ E _γ ≤ 140 MeV are studied on the basis of this model.     

19.

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     

M. N. Achasov  K. I. Beloborodov  A. V. Berdyugin  A. G. Bogdanchikov  D. A. Bukin  A. V. Vasiljev  V. B. Golubev  T. V. Dimova  V. P. Druzhinin  L. V. Kardapoltsev  I. A. Koop  A. A. Korol  S. V. Koshuba  E. V. Pakhtusova  S. I. Serednyakov  Z. K. Silagadze  A. N. Skrinsky  A. G. Kharlamov  Yu. M. Shatunov 《Journal of Experimental and Theoretical Physics》2011,113(1):75-79

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.     

20.

Mesoscopic structure of Ni<Subscript>2 + <Emphasis Type="Italic">x</Emphasis></Subscript>Mn<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>Ga alloys in the concentration range corresponding to a coupled magnetic-structural phase stransition     

V.?V.?Runov  M.?K.?Runova  V.?V.?Khova?lo 《Physics of the Solid State》2010,52(7):1333-1337

The Ni_{2 + x} Mn_{1 − x} Ga magnetic shape memory alloys at concentrations x = 0.18–0.36 have been studied using small-angle polarized neutron scattering in magnetic fields 0 < H ≤ 5.7 kOe. In this concentration range, the alloy undergoes a coupled magnetic-structural phase transition. At x < 0.18, the martensitic phase transition occurs, as usual, in the ferromagnetic state, i.e., T _m < T _C (T _m and T _C are the temperatures of the martensitic and magnetic phase transitions, respectively). However, at x > 0.27, the relationship between the characteristic temperatures is changed, i.e., T _m > T _C. The small-angle polarized neutron scattering data indicate that, in the concentration range under investigation, there occurs a complex transformation of the magnetic and atomic structures. All phase transitions exhibit a temperature hysteresis of scattering and polarization, which is characteristic of first-order phase transitions. A comparative analysis of the mesoscopic structures of the Ni_{2 + x} Mn_{1 − x} Ga and Ni_{2 + x + y} Mn_{1 − x} Ga_{1 − y} alloys studied using the small-angle polarized neutron scattering technique has been carried out.     

	$\text{T}{}_{\mathrm{e}}\text{(}\text{cm}{}^{\mathrm{?1}}\text{)}$	$\text{ω}{}_{\mathrm{e}}\text{(}\text{cm}{}^{\mathrm{?1}}\text{)}$	$\text{ω}{}_{\mathrm{e}}\text{x}{}_{\mathrm{e}}\text{(}\text{cm}{}^{\mathrm{?1}}\text{)}$	$\text{B}{}_{\mathrm{e}}\text{(}\text{cm}{}^{\mathrm{?1}}\text{)}$
$\text{A}{}^1\text{Σ}{}_{\mathrm{u}}{}^{\mathrm{+}}$	40 806 (3)	297 (2)	5.1 (2)	0.0798 (12)
$\text{b0}{}_{\mathrm{u}}{}^{\mathrm{+}}$	38 884 (3)	422 (1)	8.8 (1)	0.0783 (12)

Nuclear vertex constants for the virtual decay <Superscript>7</Superscript>Be → <Superscript>3</Superscript>He + <Superscript>4</Superscript>He of the 7Be bound states from a phase-shift analysis in the effective-range theory

The phase-shift-analysis data for the ³He⁴He scattering are analyzed using the effective-range theory, with the Coulomb interaction taken into account. We find both the renormalized nuclear vertex constants for the vertex ⁷Be → ³He + ⁴He in the ground (3/2⁻) and in the first excited (1/2⁻) bound states of ⁷Be, and the corresponding asymptotic normalization constants of the radial wave functions in these states. The results obtained can be used in an astrophysical S-factor calculation for radiative capture reaction ⁴He(³He, γ)⁷Be     

Description of cross sections for photonucleon reactions on tin isotopes at photon energies in the range 2 ≤ <Emphasis Type="Italic">E</Emphasis><Subscript><Emphasis Type="Italic">γ</Emphasis></Subscript> ≤ 140 MeV

A modified model of preequilibrium decay is considered. This model makes it possible to calculate cross sections for multiparticle photonucleon reactions with allowance for the impact of collective isospin effects. Features of the photodisintegration of 101 ≤ A ≤ 135 tin isotopes in the energy range 2 ≤ E _γ ≤ 140 MeV are studied on the basis of this model.     

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.     

Mesoscopic structure of Ni<Subscript>2 + <Emphasis Type="Italic">x</Emphasis></Subscript>Mn<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>Ga alloys in the concentration range corresponding to a coupled magnetic-structural phase stransition

The Ni_{2 + x} Mn_{1 − x} Ga magnetic shape memory alloys at concentrations x = 0.18–0.36 have been studied using small-angle polarized neutron scattering in magnetic fields 0 < H ≤ 5.7 kOe. In this concentration range, the alloy undergoes a coupled magnetic-structural phase transition. At x < 0.18, the martensitic phase transition occurs, as usual, in the ferromagnetic state, i.e., T _m < T _C (T _m and T _C are the temperatures of the martensitic and magnetic phase transitions, respectively). However, at x > 0.27, the relationship between the characteristic temperatures is changed, i.e., T _m > T _C. The small-angle polarized neutron scattering data indicate that, in the concentration range under investigation, there occurs a complex transformation of the magnetic and atomic structures. All phase transitions exhibit a temperature hysteresis of scattering and polarization, which is characteristic of first-order phase transitions. A comparative analysis of the mesoscopic structures of the Ni_{2 + x} Mn_{1 − x} Ga and Ni_{2 + x + y} Mn_{1 − x} Ga_{1 − y} alloys studied using the small-angle polarized neutron scattering technique has been carried out.