In connection with commissioning of the IREN pulsed resonance neutron source new electronics and appropriate software are developed for registration of time-of-flight spectra with small width of the channel (21 ns). The hardware-software system is intended for research of the IREN neutron beam characteristics, properties of new detectors, and also for performance of precision experiments under conditions of low intensity or registration of rare events.

A new method of extracting the neutron-electron scattering length b(ne), which is directly connected with the fundamental physical Value of neutron mean squared charge radius, from the Slow neutron diffraction on noble gases was developed and verified by the analysis of literature data on structure factors for gaseous Kr and (36)Ar and for liquid Kr.Different variants of analysis of these experimental data allow us to obtain b(ne) value with the statistical accuracy of 10-20%, but in some of them the real possibility for the accessible accuracy no worse than 2-3% was shown. In order to remove some systematical uncertainties and to reach such a good accuracy the execution of comparative diffraction measurements is proposed with a pair of gases having close atomic properties and different n,e-scattering contributions, such as Ar-(36)Ar or Xe-Kr. (C) 2009 Elsevier B.V. All rights reserved.

A novel method to extract the neutron-electron scattering length b ne from the precise neutron scattering data measured for a noble gas at several different densities n is proposed. The main point of this method is dividing the experimental data into two parts: the first, nearly proportional to n, corresponding to diffraction on neighboring atoms and the second one, a small contribution of n, e scattering independent on n. The proposed technique is demonstrated using the structure factor S(q) for gaseous krypton.

As a preparation for the new experiment to measure the ne scattering length ane the total neutron cross section of gaseous argon has been obtained by the time-of-flight method at the Dubna booster IBR-30 in the energy range from ∼5 eV to ∼30 keV. A combined one-level analysis of the newly obtained and other known data on cross sections of Ar and 36Ar has made it possible to improve some neutron parameters and calculate the scattering cross section σs and the scattering length a separately for 36Ar and 40Ar at any energy.

The new neutron spectrometer UGRA has been put into operation on the 250 m long time-of-flight path of the IBR-30 booster in Dubna. It has been constructed for the determination of the electric polarizability of the neutron which will be derived from the precise measurement of the angular dependence of neutron scattering on heavy nuclei at energies ∼0.5–60 keV. The spectrometer is situated in a vacuum chamber of ∼3m lateral dimensions, capable of holding up to 3 scattering samples and 163He-detectors (of ∼7l volume each) in shielding tanks on a rotary platform. Some characteristics of the instrument are reported.

A new method is proposed for setting a lower or upper limit a α n * on the neutron electric polarizability α an . It is based on the fact that the real part of the s -wave scattering amplitude changes sign near the s -wave neutron resonance at E=E *. The methods consist of the observation of the energy behavior of the forward-backward scattering asymmetry ω 1 which experiences a jump at E=E *. If the jump is such that dω 1 / dE >0, then α n > α n *, while if dω 1 / dE <0, then α n < α n *, and if dω 1 / dE ∼0, then α n ∼ α n *. Seven even-even nuclei are found with α n * from 0.5 to 3.1 in 10 −3 fm 3 . Some details of a possible experiment with 182 W are described.

Strict comprehensive treating the generalized Dirak equation for nucleon in external electro-magnetic field argues quite clear that there is no physical reason to bring into consideration so-called “Foldy-term” while obtaining the neutron mean square charge radius < r n 2 >, caused by an electric charge distribution inside a nucleon, from the experimental value of the (ne) — scattering length b ne , that term being, as a matter of fact, fictitious one. Consequently, the representing of the experimental quantity b ne as a sum of “Foldy length” b F and “intrinsic” one bI, even so splitting the total value of < r n 2 > in “Foldy” and “intrinsic” < r in 2 >, turn out of having no profound physical sense, being rather ambiguous in actual fact. The formal phenomenological relation, originated from the generalized Dirak equation for nucleon, of the quantities b ne , < r n 2 >, and neutron anomalous magnetic moment μ is inquired. Concise treating < r n 2 > in the frame-work of up-to-date nucleon cloudy bag model (CBM) is presented, no “Foldy term” being emerged, and < r n 2 >, calculated according this approach, provides b ne -value which is in agreement with experimental result within accuracy of about 10%. On the other hand, the experimental b ne -value proves to be described phenomenologically through solely the neutron anomalous magnetic moment μ with the same accuracy ∼ 10%. Then the necessity of obtaining b ne -value with more reliable accuracy then in previous experiments becomes obvious, corrections have to be reduced to the level of the precise declared. For these aims, two new proposed experiments have been Monte-Carlo modelled. The first renders the measurement of the energy dependence of an elastic scattering cross-section on 86 Kr, having the unique small capture cross-section. The second one is to measure the energy dependence of neutron scattering angle anisotropy for natural Xe.

Using experimental data from the neutron transmission measurements on enriched 206,207,208Pb, natural Pb and Bi targets, the potential scattering radii R' and the electric polarizability of the neutron αn were determined by general least squares fit at fixed neutron-electron bound scattering length values: bne = −1.32 × 10−3 fm (Garching) and bne = −1.59 × 10−3 fm (Dubna). The evaluations were performed in two versions: (1) The potential scattering radii R' were taken as fitted parameters; (2) R' values were deduced from optical model calculations. The obtained potential scattering radii values are in the range R' = 9.0 − 10.0 fm. The electric polarizability of the neutron in the first version resulted in αn = +(0.12 ± 0.44) × 10−3 fm3 with the Garching bne value and αn = −(0.97 ± 0.44) × 10−3 fm3 with the Dubna bne value, but in the second calculation version - in αn = −(0.14 ± 0.37) × 10−3 fm3 with both bne values. On the basis of obtained results we give preference to the Garching bne value.

A method for determining neutron electric polarizability and the only meaningful result alpha(n) = (1.20 +/- 0.15 +/- 0.20) x 10(-3) fm(3) are analyzed in detail. Since some inexactitudes in obtaining this result are found, the conclusion that its systematic error must be 3-4 times higher is made. A complex method for determining a,, from the total cross section for neutrons scattered by Pb-208 nuclei is proposed. This method involves taking into account both the k(3) term in the cross section (k is neutron wave number) and the negative neutron resonance at -1.91 MeV.

The electric properties of the neutron have been deduced from precise measurements of coherent scattering lengths and of total cross sections of Pb, of its isotopes with A=208, 207, and 206, and of Bi. Their energy dependences are due to nuclear properties, to nuclear and atomic charges as well as to the neutron's electric polarizability and to the neutron-electron interaction. We investigated in detail the different evaluations used in the past by German and Russian scientist groups. By means of both data handling methods we found consistent results of ${\mathrm{\ensuremath{\alpha}}}_{\mathit{n}}$=(0.0\ifmmode\pm\else\textpm\fi{}0.5)${10}^{\mathrm{\ensuremath{-}}3}$ ${\mathrm{fm}}^{3}$ for the electric polarizability and of ${\mathit{b}}_{\mathit{n}\mathit{e}}$=-(1.32\ifmmode\pm\else\textpm\fi{}0.03)${10}^{\mathrm{\ensuremath{-}}3}$ fm for the neutron-electron scattering length. This result agrees with quark-core models of the neutron.

The neutron strength functions S1/2(1) and S3/2(1) and scattering radii R1' for p waves are determined from measurements of the differential cross section for the scattering of neutrons of energy up to approximately 300 keV at three angles on the isotopes Te-128 and Te-130. As for the natural mixture of Te isotopes studied earlier, the p-wave scattering radii are much smaller than for neighboring nuclei, but the average R1' for the other Te isotopes is apparently ''normal.'' The possibility of explaining the anomaly in terms of the formation of doorway states in Te-129 and Te-131 compound nuclei with spins and parities of 1/2- and (or) 3/2- is demonstrated.

Differential cross sections for elastic scattering of neutrons with energies up to approximately 300 keV by gaseous krypton and xenon have been measured. Oxygen was used as a calibration element. The neutron strength functions S0, S1/2(1), and S3/2(1) and the remote-level contributions R0 infinity and R1 infinity were determined from the experimental cross sections by the method of least squares. The experimental values found for these parameters fill some gaps in the experimental results on 34 nuclei over the mass-number interval 48 < A < 144. The krypton measurements refine the curve describing the experimental scattering lengths for p-wave scattering in the region A congruent-to 70-90, in which the phase shift of the neutron p wave is found to have an anomalous positive sign. The results on neutron scattering by xenon provide additional information near the upper boundary of the mass-number interval of interest.

The measurements were carried out of angle distributions of neutrons with energies up to 250 keV elastically scattered by the even cadmium isotopes. The strength functions and potential scattering parameters S°, S1 ½, S1 3/2, Re∞ l were determined. The paper also includes data obtained for other nuclei in the range 50