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.     

Optical-model analysis for 3He scattering from some light nuclei in the energy range 18–20 MeV

Angular distributions for ³He elastic scattering by ²⁴Mg, ²⁸Si, ³⁰Si and ³²S have been measured at 18 and 20 MeV incident energy in the angular range 15° ≦ θ ≦ 100° and analysed in terms of an optical model. A detailed optical model analysis of the ²⁸Si-data showed the existence of ambiguities, due to different numbers of half-waves inside the potential well. The influence of experimental uncertainties on optical parameter determination has been investigated as well as the effect of a spin-orbit term on the shape of the angular distribution.     

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.     

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.     

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:

     

15.

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     

A. S. Soldatov 《Physics of Atomic Nuclei》2003,66(3):547-557

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.     

16.

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.     

17.

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.     

	$\text{T}{}_{\mathrm{e}}\text{(}\text{cm}{}^{\mathrm{?1}}\text{)}$	$\text{ω}{}_{\mathrm{e}}\text{(}\text{cm}{}^{\mathrm{?1}}\text{)}$	$\text{ω}{}_{\mathrm{e}}\text{x}{}_{\mathrm{e}}\text{(}\text{cm}{}^{\mathrm{?1}}\text{)}$	$\text{B}{}_{\mathrm{e}}\text{(}\text{cm}{}^{\mathrm{?1}}\text{)}$
$\text{A}{}^1\text{Σ}{}_{\mathrm{u}}{}^{\mathrm{+}}$	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)

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.     

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.