Measuring fluence of fast neutrons with planar silicon detectors

The results of measurements of 1-MeV (Si) equivalent fast neutron fluence with silicon planar detectors are reported. The measurement method is based on the linear dependence of the reverse detector current increment on the neutron fluence: ΔI = α _I × Φ × V. This technique provides an opportunity to measure the equivalent fluence in a wide dynamic range from 108 to 10¹⁶ cm^–2 with an unknown neutron energy spectrum and without detector calibration. The proposed method was used for monitoring in radiation resistance tests of different detector types at channel no. 3 of IBR-2 and for determining the fluence of fission and leakage neutrons at the KVINTA setup.     

E1,ΔK=0−Übergänge in deformierten Kernen ungerader Massenzahl

The half lives of the 5/2 5/2^?[523] level at 25.7 keV in ₆₆ ¹⁶¹ Dy and the 5/2 5/2⁺[642] level in ₆₈ ¹⁶³ Er, found in this work to lie at 69.2 keV, have been determined by the delayed coincidence method to be T_1/2=27.8± 1.5 nsec, and T_1/2=8.8± 0.5 nsec, respectively. The following hindrance factors relative to the single particle Weisskopf estimate (F _W and the Nilsson estimate (F_N were obtained: ₆₆ ¹⁶¹ Dy 5/2 5/2^?[523] → 5/2 5/2⁺[642]:F_W=(6.6± 1.3) × 10³, F_N=0.48± 0.10 ₆₈ ¹⁶³ Er 5/2 5/2⁺[642] → 5/2 5/2^?[523]:F_W=(2.4± 0.5)× 10⁴, F_N=1.8 ± 0.4 A systematic difference between transitions in odd proton nuclei and odd neutron nuclei was found: E1, ΔK=0 transitions in odd neutron nuclei have hindrance factors F_N from 2.9 to 0.16, this means, these transitions are in agreement with the predictions of the Nilsson model within a factor of 10. For transitions in odd proton nuclei one has hindrance factors F_N from 75 to 9.9 × 10^?4. It is shown that a small difference between the deformation of the initial and the final state changes the transition probability of both, proton and neutron transitions, considerably.     

The continuum shell-model neutron states of209Pb

The neutron strength distributions of the three high-spin 1k _17/2, 2h _11/2 and 1j_13/2 states of²⁰⁹Pb have been obtained within the formalism of the core-polarisation effect where the effect of interaction of the neutron shell-model states of²⁰⁹Pb with the collective vibrational states (originating also from the giant resonances) have been taken into consideration. The theoretical results have been discussed in the light of works on 1k _17/2, 2h1_11/2 and 1j_13/2 neutron orbitals of²⁰⁹Pb. The shell-model energies of the neutron states have been obtained by Skyrme-Hartree-Fock method     

Determination of fine structure intervals in a series of excited sodium D states using doppler free two-photon spectroscopy

Using Doppler free two-photon spectroscopy technique, we have measured the absolute values of fine-structure (fs) intervals in a series of excited sodium n²D states (n = 3,6,7, and 8). We have shown the structures are inverted and our measured values for these states are: Δ_fs(3²D) = -1523 ± 8 MHz, Δ_fs(6²D) = -385 ± 5 MHz, Δ_fs(7²D) = -253 ± MHz, and Δ_fs(8²D) = -173 ± 10 MHz.     

A pilgrimage through superheavy valley

We searched for the shell closure proton and neutron numbers in the superheavy region beyond Z = 82 and N = 126 within the framework of non-relativistic Skryme–Hartree–Fock (SHF) with FITZ, SIII, SkMP and SLy4 interactions. We have calculated the average proton pairing gap Δ_p, average neutron pairing gap Δ_n, two-nucleon separation energy S _2q and shell correction energy E _shell for the isotopic chain of Z = 112–126. Based on these observables, Z = 120 with N = 182 is suggested to be the magic numbers in the present approach.     

Crystal field splitting in γ-cerium

Results are reported on an inelastic neutron scattering experiment to determine the crystal field splitting and level scheme for the ²F_{$\text{5}\text{2}$} multiplet in γ-cerium. For the first time in a metallic cerium system the inelastic peak is well resolved and the splitting, Δ, can be accurately determined. As a next logical step in improving the point charge model we consider the screened point charge model. We find a Γ₇ ground state and Δ = 67 K.     

Is there neutron-proton pairing in medium heavy nuclei?

Present knowledge of the proton and neutron pairing energies Δ_p and Δ_n, deduced from nuclear masses, is reviewed and an attempt is made to find general trends in the data. The analysis shows that, besides the well-known smooth slow decrease with A, the pairing energies also contain a symmetry energy-like dependence on the neutron excess $\text{(N?Z)}\text{A}$. The trends is most pronounced in the shell 50<Z<82, 82<N<126 where both pairing energies decrease by a factor of almost two between the most neutron deficient and the most neutron rich nuclei. The same tendency persists in other mass regions, but is not a universal one. An empirical expression for Δ, that is more accurate than the value $\text{12A}{}^{\mathrm{<mtext>?</mtext><mtext>1</mtext><mtext>2</mtext>}}\text{MeV}$ usually assumed, is proposed.     

Quantum beats in two-photon resonance fluorescence

The two-photon resonance fluorescence spectrum of a three-level atom is shown to consist of the low frequency modes in addition to the high frequency ones in the limit of high photon densities. The spectral function for the low frequency modes consists of two lorentzian lines describing: the peak occuring at the renormalized beat frequency Δ₊ and that of the zero-photon excitation at the frequency Δ_-, where Δ_±=Δ-3Ω²/2ω_a±Ω²u/2ω_a, u²=1+(2Δω_a/Ω ²)². Here, 2Δ is the energy splitting between the two excited states, ω_a is the photon energy of the pump field and Ω is the Rabi frequency. The peak at the renormalized beat frequency Δ₊ occurs provided that the condition (2Δω_a/Ω²)² > 1 is satisfied. The two-photon laser spectroscopy is expected to be a useful tool for the observation of the low frequency modes in question.     

Damping of the high-spin neutron hole orbitals of the207Pb

The neutron strength functions of the high-spin 1g _7/2 and 1h _11/2 hole states of the²⁰⁷Pb have been deduced within the formalism of the hole-core vibrational coupling scheme. The attenuation of the shell-model strengths of these two high-spin hole states have been compared with the distribution of the neutron strength functions of the discrete 1h _9/2 and 1i _13/2 states. The theoretical results have been discussed in the light of the recent experimental findings on the neutron hole orbitals of the²⁰⁷Pb nucleus. Side by the side the implication of the present research works has been reviewed on the basis of the other existing theoretical calculations on the high-spin neutron hole states of the²⁰⁷Pb.     

中子辐照对AlGaN/GaN高电子迁移率晶体管器件电特性的影响

本文采用能量为1 MeV的中子对SiN钝化的AlGaN/GaN HEMT(高电子迁移率晶体管)器件进行了最高注量为1015cm-2的辐照.实验发现:当注量小于1014cm-2时,器件特性退化很小,其中栅电流有轻微变化(正向栅电流IF增加,反向栅电流IR减小),随着中子注量上升,IR迅速降低.而当注量达到1015cm-2时,在膝点电压附近,器件跨导有所下降.此外,中子辐照后,器件欧姆接触的方块电阻退化很小,而肖特基特性退化却相对明显.通过分析发现辐照在SiN钝化层中引入的感生缺陷引起了膝点电压附近漏电流和反向栅泄漏电流的减小.以上结果也表明,SiN钝化可以有效地抑制中子辐照感生表面态电荷,从而屏蔽了绝大部分的中子辐照影响.这也证明SiN钝化的AlGaN/GaN HEMT器件很适合在太空等需要抗位移损伤的环境中应用.     

Spectrum of the high spin neutron hole states of205Pb

The high resolution (³He,α) reaction on²⁰⁶Pb shows the distribution of the 2f _7/2, 1h _9/2 and 1i _{1 3/2} neutron states of²⁰⁵Pb within the 6 MeV excitation energy of²⁰⁵Pb. The spectrum of these three-hole states is obtained within the hole-core vibrational coupling scheme. The shell model energies of the neutron hole states arising from the core-polarization effect are compared with the Bansal-French energy weighted sum rule. The possible implication of the present neutron hole energies has been discussed in the light of the deduced shell model wave functions of the collective states of²⁰⁶Pb.     

Inelasticα-scattering from100Mo

The level scheme of¹²³Ba has been extended. Bands based on the [523]7/2^? and [402]5/2⁺ Nilsson configurations were established to spins 59/2 (67/2 tentatively) and 29/2, respectively. The first backbend in this region is found to be caused by the alignment of a pair of h_11/2 protons. For the first time in this mass region there is evidence for a second crossing due to the alignment of an h_11/2 neutron pair in a neutron h_11/2 band. The experimental results are compared with self-consistent cranking calculations. A previous suggestion that large γ-deformation is needed to explain the observed bandheads is not supported.     

Theg-factor of 19− isomer in202Pb

The half-life and the g-factor of the 19^– isomer at (5241.9+) keV in²⁰²Pb have been measured through the in-beam time differential perturbed angular distribution technique as T_1/2=105(2) ns and g(19^–)=0.099(3). The value of the g-factor indicates predominantly four neutron hole configurations involving three i ₁₃ ^2/–1 neutron holes coupled to a f ₅ ^2/–1 neutron hole for the 19^– isomer.     

3PF2 neutron superfluidity in neutron stars and three-body force effect

We investigate the ^3PF2 neutron superfluidity in H-stable neutron star matter and neutron stars by using the BCS theory and the Brueckner-Hartree-Fock approach. We adopt the Argonne V18 potential supplemented with a microscopic three-body force as the realistic nucleon-nucleon interaction. We have concentrated on studying the threebody force effect on the ^3PF2 neutron pairing gap. It is found that the three-body force effect is to enhance remarkably the ^3PF2 neutron superfluidity in neutron star matter and neutron stars.     

Effect of γ irradiation on the thermochromic phase transition in [(C<Subscript>2</Subscript>H<Subscript>5</Subscript>)<Subscript>2</Subscript>NH<Subscript>2</Subscript>]<Subscript>2</Subscript>CuCl<Subscript>4</Subscript> crystals (as derived from heat capacity measurements)

The heat capacity of [(C₂H₅)₂NH₂]₂CuCl₄ crystals, both nonirradiated and γ-irradiated to a dose of 10⁷R, was studied in the temperature interval 90–330 K by adiabatic calorimetry. The temperature dependence of C_p(T) was found to have a peak-shaped anomaly in the region of the thermochromic phase transition (PT) at T = 322.7 K. Smoothened experimental heat capacity data were used to calculate the changes in the thermodynamic functions. The changes in the entropy and enthalpy of the thermochromic PT were determined to be ΔS = 42 J K^?1 mol^?1 and ΔH = 13653 J mol^?1 for the nonirradiated crystals and ΔS = 39 J K^?1 mol^?1 and ΔH = 12120 J mol^?1 for the irradiated crystals, respectively. Irradiation of a [(C₂H₅)₂NH₂]₂CuCl₄ crystal by γ rays to a dose of 10⁷ R was shown to shift the PT point toward lower temperatures by ΔT ≈ 1.7 K.     

15N16O的激光磁共振谱与同位素分子15N17O和15N18O的光谱分析

采用内腔式饱和吸收技术获得Lamb凹陷,使CO激光磁共振谱仪的灵敏度及分辨率大大提高.利用该技术对自然丰度下¹⁵N¹⁶O的X²Π(υ=1)←X²Π(υ=0)塞曼跃迁进行测量,实现了包括Λ双分裂在内的各种精细结构的谱分辨.结合已发表的¹⁵NO同位素分子光谱实验数据进行分析计算,拟合得到迄今最完备、最精确的各相关同位素分子¹⁵N^mO(m=16—18)的结构参 关键词：     

Pressure change dynamics of plasma focus chambers as a part of the pulse neutron generators

The dynamics of working gas pressure changes in the plasma focus (PF) chambers were studied by using the chamber with a built-in manometer as part of the ING-102 neutron generator (2.5 MeV neutron yield 10⁶÷10⁷ neutrons/pulse). Investigations were carried out during high-voltage training and neutron emission operation mode. The studies were executed while filling the chamber with various gas mixtures. For operation with a deuterium-tritium mixture, a sealed-off chamber with a built-in gas generator was used. After the primary filling of the PF chambers with a gas mixture, there is a systematic decrease in pressure by Δp = (5 ÷ 50) ·10⁻³ Torr (∼0,7 ÷ 7 Pa) after each shot of the chamber.The change in the shape of breakdown curves U_br(p) in the interelectrode gap of the chamber after each series of shots was studied. That made it possible to assess the optimal number of shots during high-voltage training of the PF chamber.     

Etude par spectrometrie Mössbauer (57Fe) de FeMo2S4

We have investigated FeMo₂S₄ by transmission Mössbauer spectroscopy on the ⁵⁷Fe nucleus between 4.2 and 1037 K, using both powdered and single crystal samples.The temperature dependences of the isomer shift and the quadrupole splitting indicate the existence of ferrous ions with well localized 3d electrons. The two different crystallographic Fe sites cannot be separated over the experimental temperature range. The local symmetry of the iron site is lower than axial (η ~ 0.47) and the crystal field splittings Δ₁ and Δ₂ of the Fe²⁺ ? T_2g Orbitals, estimated by the Ingalls' method, are close to 250 and 900 cm^?1.The hyperfine field makes an angle of 14° with the normal on the plane (a, b), deviating a little from the direction of the magnetic moments determined to be perpendicular to (a, b) by neutron diffraction study.At higher temperatures, and more particularly near T_N, a line broadening is observed, and the spectra have to be fitted by a hyperfine field distribution. The broadening comes from the presence of about 7% “abnormal” Fe-sites observed in the paramagnetic spectra, and whose origin is discussed.The Néel temperature was determined to be 112 ± 1 K for the powdered sample and 106 ± l K for the single crystal.     

High-K band structures in 164Er

High-spin states of the doubly-odd ¹¹²Sb were studied by in-beam spectroscopy using the ⁸⁸Sr (²⁸Si, p3n) and ⁸⁹Y (²⁹Si, α2n) fusion-evaporation reactions at beam energies of 120 and 108 MeV, respectively. γ?γ, charged particle-γ?γ coincidences, and γ?γ angular correlation analyses were employed for determining the level scheme of ¹¹²Sb. In the present work, all the levels except for low-lying states in ¹¹²Sb were newly established. Two ΔI = 1 strongly coupled bands were observed; one is a negative-parity band that is similar to those observed in the neighboring doubly-odd Sb isotopes and the other is a positive-parity band that has a new type structure not observed in the other isotopes. From the similarity of the properties of these ΔI = 1 bands to the bands built on 9/2⁺ 2p?1h states in the odd-A Sb isotopes, we suggest that these two ΔI = 1 bands should be associated with the [π(g_9/2)^?1 ? νh_11/2] and [π(g_9/2)^?1νg_7/2] configurations, respectively.     

Fine and hyperfine structure of <Emphasis Type="Italic">P</Emphasis>-wave levels in muonic hydrogen

Corrections of order α ⁵ and α ⁶ are calculated for muonic hydrogen in the fine-structure interval ΔE ^fs = E(2P _3/2) − E(2P _1/2) and in the hyperfine structure of the 2P _1/2-and 2P _3/2-wave energy levels. The resulting values of ΔE ^fs = 8352.08 μeV, ΔẼ ^hfs(2P _1/2) = 7819.80 μeV, and ΔẼ ^hfs(2P _3/2) = 3248.03 μeV provide reliable guidelines in performing a comparison with relevant experimental data and in more precisely extracting the experimental value of the (2P–2S) Lamb shift in the muonic-hydrogen atom. Original Russian Text ? A.P. Martynenko, 2008, published in Yadernaya Fizika, 2008, Vol. 71, No. 1, pp. 126–136.