首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 31 毫秒
1.
Continuing earlier investigations we studied the energy dependence of the cross sections of the following nuclear reactions produced by neutrons in the energy range from 12 to 19 MeV: P31(n, 2n)P32, P31(n,α)Al28, Cu65(n, 2n)Cu64, Cu65(n, p)Ni65, Zn64(n, 2n)Zn63, Zn64(n, p)Cu64, V51(n, p)Ti51, Br79(n, α)As76, O16(n, α)C13. The results were compared with cross sections calculated according to the statistical theory, considering the competition ofγ-ray emission and particle (predominantly neutron) emission from the excited residual nucleus.  相似文献   

2.
The nuclide Be7 was produced by irradiating graphite and water with bremsstrahlung from the Darmstadt 60 MeV linear accelerator. Yield curves and approximate cross-sections are presented up to 57 MeV. Integrated cross-sections at 57 MeV are 6,0 MeV mbarn for C12(γ, x) Be7 and about 0,7 MeV mbarn for O16(γ, x) Be7. At 51,4 MeV maximum bremsstrahlung energy the yield of Si30(γ, 2p Mg28) is 1,6% of the C12 (γ, n) C11 yield, and about 3,8 times as much Na24 as Mg28 is produced in a natural silicon target.  相似文献   

3.
The cross sections for the reactions N14(n, α)B11 and N14(n, t)C12 have been measured in the neutron energy range 4.0 to 6.4 MeV and at 2.5 MeV. Mono-energetic neutrons were produced in the D(d, n) He3 reaction using a gas target. The (n, α) and (n, t) disintegrations were detected in a gridded ionization chamber filled with an argonnitrogen mixture. The response of the chamber under different operation conditions is described. The excitation functions, measured with a neutron energy resolution of 40 to 50 keV, are given for theα 0 group from the N14(n,α)B11 reaction over the entire neutron energy range and for theα 1 group and the t0 group from N14(n, t) C12 for neutron energies above 4.3 and 5.6 MeV, respectively.  相似文献   

4.
Explicit formulasfor strongly forbidden magnetic-dipole transitiions between states njl and n′jl in the hydrogen atom and light hydrogen-like ions are derived. The expressions for transition probabilities are presented in the form W n′jl; njl (M1) = D n′n lj αm e Z)10 (in relativistic units), where m e is the electron mass, α is the fine-structure constant, and Z is the nuclear charge; the constants D n′n lj are presented in an analytical form. Before now, only the D 21 01/2 coefficient corresponding to the 1s 1/2–2s 1/2 transition was known in explicit form. The results obtained can be used in designing an experiment on parity violation in the hydrogen atom.  相似文献   

5.
Standard enthalpies of formation for solid solutions of composition Nd1 + x Ba2 ? x Cu3O y (x = 0–0.8, y = 6.65–7.24) from oxides were determined by solution calorimetry. The heat capacity of NdBa2Cu3O6.87 phase was measured in the range 5–320 K by low-temperature adiabatic calorimetry. The absolute entropy S o(T), the difference of enthalpies H o(T)-H o(0 K), and the reduced Gibbs energy Φo(T) = S o(T)–[H o(T)–H o(0)]/T were calculated on the basis of smoothed dependence C p (T) in the 0–320 K range. An assessment was made for the heat capacities and the absolute entropies of solid solutions Nd1+x Ba2?x Cu3O y . The obtained set of thermodynamic parameters can be used for the calculation of phase equilibria in the Nd-Ba-Cu-O system.  相似文献   

6.
This paper presents the results of conduction band discontinuities calculation for strained/relaxed Si1?x Ge x /Si1?y Ge y heterointerfaces in Γ 15C , Γ 2′C and L upper bands minima, as well as the room-temperature strained (vs. relaxed) band gaps deduced from the classical model-solid theory. Based upon the obtained data, we propose a type-I W-like Si1?y Ge y /Si1?x Ge x /Ge/Si1?x Ge x /Si1?y Ge y quantum wells heterostructure optimized in terms of compositions and thicknesses. Electronic states and wave functions are found by solving Schrödinger equation without and under applied bias voltage. An accurate investigation of the optical properties of this heterostructure is done by calculating the energies of the interband transitions and their oscillator strengths. Moreover, a detailed computation of the bias-voltage evolution of the absorption spectra is presented. These calculations prove the existence of type-I band alignment at Γ 2′C point in compressively strained Ge quantum wells grown on relaxed Ge-rich Si1?y Ge y buffers. The strong absorption coefficient (> 8 × 103 cm-1) and the large Stark effect (0.1 eV @ 2 V) of the Γ 2′C transitions thresholds open up perspectives for application of these heterostructures for near-infrared optical modulators.  相似文献   

7.
A silicon semiconductor detector was irradiated with betatron bremsstrahlung of different end point energies and the energy distributions of the protons originating in the detector itself by the reaction Si28(γ,p) Al27 were measured with good statistical accuracy. The end point energies were varied in 1 MeV steps from 15 to 30 MeV. Using the known spectral distribution of theγ-rays the energy dependence of the total cross section of the studied reaction could be derived from the measured proton spectra. The resulting cross section shows a peak at 20, 5 MeV and a half width of 4 MeV. Approximate values for the branching ratios for transitions to excited states of the residual nucleus could also be obtained.  相似文献   

8.
The temperature behavior of the EPR spectra of the Gd3+ impurity center in single crystals of SrMoO4 in the temperature range T = 99–375 K is studied. The analysis of the temperature dependences of the spin Hamiltonian b 2 0 (T) = b2(F) + b2(L) and P 2 0 (T) = P2(F) + P2(L) (for Gd157) describing the EPR spectrum and contributing to the Gd3+ ground state splitting ΔE is carried out. In terms of the Newman model, the values of b2(L) and P2(L) depending on the thermal expansion of the static lattice are estimated; the b2(F) and P2(F) spin-phonon contributions determined by the lattice ion oscillations are separated. The analysis of b 2 0 (T) and P 2 0 (T) is evidence of the positive contribution of the spin-phonon interaction; the model of the local oscillations of the impurity cluster with close frequencies ω describes well the temperature behavior of b2(F) and P2(F).  相似文献   

9.
Let H(?)=?? 2d2/dx 2+V(x) be a Schrödinger operator on the real line, W(x) be a bounded observable depending only on the coordinate and k be a fixed integer. Suppose that an energy level E intersects the potential V(x) in exactly two turning points and lies below V =lim?inf?|x|→∞ V(x). We consider the semiclassical limit n→∞, ?=? n →0 and E n =E where E n is the nth eigenenergy of H(?). An asymptotic formula for 〈n|W(x)|n+k〉, the non-diagonal matrix elements of W(x) in the eigenbasis of H(?), has been known in the theoretical physics for a long time. Here it is proved in a mathematically rigorous manner.  相似文献   

10.
Argon gas has been irradiated with 34 MeV bremsstrahlung. The yields of the reactions A40(γ, p) Cl39 and A40 (γ, np) Cl33 were determined relative to C12(γ, n) by β-counting. The resulting upper limits for the cross sections integrated to 28 MeV are 160 MeVmbarns for (γ, p), and 35 MeV mbarns for (γ, np). This does not confirm the anomalously high A40 (γ, p)-cross section reported in the literature.  相似文献   

11.
In order to quantify contextuality of empirical models, the quantity of contextuality (QoC) of empirical models is introduced in terms of the trace-distance. Let Q C(e) denote the QoC of an empirical model e. The following conclusions are proved. (i) An empirical model e is non-contextual if and only if Q C(e)=0, and then it is contextual if and only if Q C(e)>0; (ii) the QoC function QC is convex, contractive and continuous. Finally, the QoC of some famous models is computed, including PM-isotropic boxes P M α , M-isotropic boxes M α , C H n -isotropic boxes \(CH_{n}^{\alpha }\) as well as K box, where α∈[0,1]. Moreover, P M α is non-contextual if and only if \(\alpha \in [\frac {1}{6},\frac {5}{6}]\); M α is non-contextual if and only if \(\alpha \in [0,\frac {4}{5}]\); when n is even, \(CH_{n}^{\alpha }\) is non-contextual if and only if \(\alpha \in [\frac {1}{n},\frac {n-1}{n}]\), and when n is odd, \(CH_{n}^{\alpha }\) is non-contextual if and only if \(\alpha \in [0,\frac {n-1}{n}]\). The most important thing is that it is very easy to compare the QoC of any two isotropic boxes discussed in the above.  相似文献   

12.
Using the activation method investigations on the fluctuation of the total reaction cross sections for the reactions F19(n, 2n)F18, Al27(n, α)Na24 and Cu65(n, 2n)Cu64 were performed in the 14 MeV region under similar conditions as in the experiments reported byStrohal et al. and byCsikai on the same subject. In disagreement to the results of these authors no considerable fluctuation amplitudes were found.  相似文献   

13.
Let \({\mathfrak{D}}\) be the space consists of pairs (f, g), where f is a univalent function on the unit disc with f(0) = 0, g is a univalent function on the exterior of the unit disc with g(∞) = ∞ and f′(0)g′(∞) = 1. In this article, we define the time variables \({t_n, n\in \mathbb{Z}}\), on \({\mathfrak{D}}\) which are holomorphic with respect to the natural complex structure on \({\mathfrak{D}}\) and can serve as local complex coordinates for \({\mathfrak{D}}\) . We show that the evolutions of the pair (f, g) with respect to these time coordinates are governed by the dispersionless Toda hierarchy flows. An explicit tau function is constructed for the dispersionless Toda hierarchy. By restricting \({\mathfrak{D}}\) to the subspace Σ consists of pairs where \({f(w)=1/\overline{g(1/\bar{w})}}\), we obtain the integrable hierarchy of conformal mappings considered by Wiegmann and Zabrodin [31]. Since every C 1 homeomorphism γ of the unit circle corresponds uniquely to an element (f, g) of \({\mathfrak{D}}\) under the conformal welding \({\gamma=g^{-1}\circ f}\), the space Homeo C (S 1) can be naturally identified as a subspace of \({\mathfrak{D}}\) characterized by f(S 1) = g(S 1). We show that we can naturally define complexified vector fields \({\partial_n, n\in \mathbb{Z}}\) on Homeo C (S 1) so that the evolutions of (f, g) on Homeo C (S 1) with respect to ? n satisfy the dispersionless Toda hierarchy. Finally, we show that there is a similar integrable structure for the Riemann mappings (f ?1g ?1). Moreover, in the latter case, the time variables are Fourier coefficients of γ and 1/γ ?1.  相似文献   

14.
We consider mass-conserving self-similar solutions for Smoluchowski’s coagulation equation with kernel K(ξ,η)=(ξη) λ with λ∈(0,1/2). It is known that such self-similar solutions g(x) satisfy that x ?1+2λ g(x) is bounded above and below as x→0. In this paper we describe in detail via formal asymptotics the qualitative behavior of a suitably rescaled function h(x)=h λ x ?1+2λ g(x) in the limit λ→0. It turns out that \(h \sim 1+ C x^{\lambda/2} \cos(\sqrt{\lambda} \log x)\) as x→0. As x becomes larger h develops peaks of height 1/λ that are separated by large regions where h is small. Finally, h converges to zero exponentially fast as x→∞. Our analysis is based on different approximations of a nonlocal operator, that reduces the original equation in certain regimes to a system of ODE.  相似文献   

15.
The new VEPP-2000 e+e? collider of maximum energy 2000 MeV, which is under construction at the Budker Institute of Nuclear Physics (Siberian Division, Russian Academy of Sciences, Novosibirsk), is briefly described. Experiments at VEPP-2000 will be performed with two upgraded detectors, CMD-2M and SND. A precise measurement of the total cross section for the process e+e? → hadrons and of the partial cross sections for its exclusive hadronic channels is the main point of the physics program for this machine. These measurements will be aimed at testing QCD and the VMD and CVC models, as well as at refining the hadron contribution to fundamental constants such as the muon anomalous magnetic moment \(a_\mu = \frac{{g - 2}}{2}\) and the fine-structure constant αem(M Z 2 ). Measurements of the nucleon form factors in the reactions e+e?p\(\bar p\), n\(\bar n\) at their threshold will also be of great importance.  相似文献   

16.
It is shown how several discrepancies in the optical hfs of the Eu can be understood as consequences of the exchange polarization of the inner and outers-electrons by the spin of the half filled (4f 7)-subshell, an effect which should produce additional magnetic fields at the nucleus. Thus from the two different values of the electronic splitting constanta 6s in the two Eu-II ground states the polarization field from the 6s-shell (Δ H 6s ) is determined to be ca. +260 KG, and the formal splitting constantσ (??3 mK) of the (4f 7)-subshell yields ca. ?350 KG for the fieldΔ H (1?5) from the five innern s-shells (n=1?5) in good agreement with the strength of the inner field obtained from recent Mössbauer effect studies.Δ H (1?5) is deduced to be approximately equal in all sufficiently analysed ground and excited configurations of the neutral and ionised Eu atom ((4f 7) 6s, 6p, 5d, 6s 2 and 6s 6p). Other elements with half filled subshells (Am, Mn) show similar features in their optical hfs. For Am+ ((5f 7) 7s) ca. ?2200 KG are found for the inner field (Δ H (1?6)). For several 3d-elements it was found that the agreement between the calculated polarization fields and those following from experimental results is better than assumed so far.  相似文献   

17.
We discuss the scenario where the X(3872) resonance is the \(c\bar c\) = χc1(2P) charmonium which “sits on” the D*0\({\bar D^0}\) threshold. We explain the shift of the mass of the X(3872) resonance with respect to the prediction of a potential model for the mass of the χc1(2P) charmonium by the contribution of the virtual D*\(\bar D\) + c.c. intermediate states into the self energy of the X(3872) resonance. This allows us to estimate the coupling constant of the X(3872) resonance with the D*0\({\bar D^0}\) channel, the branching ratio of the X(3872) → D*0\({\bar D^0}\) + c.c. decay, and the branching ratio of the X(3872) decay into all non-D*0\({\bar D^0}\) + c.c. states. We predict a significant number of unknown decays of X(3872) via two gluon: X(3872) → gluongluonhadrons. We suggest a physically clear program of experimental researches for verification of our assumption.  相似文献   

18.
With a recording photoelectric Fabry-Perot spectrometer and an atomic-beam light source the hyperfine structure of the Mn I-resonance linesλ=4031 Å,λ=4033 Å,λ=4034 Å (3d 54s 2 a 6 S 5/2?3d 54s4p z 6 P 7/2,5/2,3/2 0)and of the inter-combination linesλ=5395 Å andλ=5433 Å (3d 54s 2 a 6 S 5/2?3d 54s4p z 8 P 7/2,5/2 0) was measured. Furthermore the resonance lines have been measured with a pulsed atomic-beam in absorption. In this case the quotient (I 0(ν)?I(ν))/I 0(ν) was recorded, whereI(ν)=I 0(ν) exp(?α(ν)d) is the observed intensity with absorption andI 0(ν) the intensity of the light source. From the hyperfine structure splitting the value of the electric quadrupole moment of Mn55 was derived to be:Q(Mn55)=+(0.35±0.05)·10?24 cm2.  相似文献   

19.
In this paper, we derived the equations for the hypersurface \({M^{n}_{r}}\) of a pseudo-Riemannian space form \(N^{n+1}_{q}(c)\) to satisfy τ 2(?) = η τ(?) (η a constant) with τ(?) and τ 2(?) be the tension and bitension fields of \({M^{n}_{r}}\). As applications, we prove that a hypersurface \({M^{n}_{r}}\) satisfying τ 2(?) = η τ(?) in \(N^{n+1}_{q}(c)\) has constant mean curvature, under the assumption that \({M^{n}_{r}}\) has diagonalizable shape operator with at most three distinct principal curvatures. Then, using this result, we classify partially such hypersurface. We also make a preliminary study of hypersurfaces satisfying τ 2(?) = f τ(?) with f be function.  相似文献   

20.
Simple expressions have been derived for three photon distribution functions w N M (T), w N Z (T), and w N O (T) corresponding to three different methods for counting fluorescence photons from a single nanoparticle excited by continuous laser radiation. In contrast to the previously derived expressions represented in the form of N multiple integrals, the new expressions contain only single or double integrals of Poisson functions, which makes it possible to easily perform the numerical calculation of the photon distribution. The simplest photon counting method corresponds to the lengthiest function w N M (T); on the contrary, the simplest function w N O (T) corresponds to the most complex photon counting method. The functions w N M (T), w N Z (T), and w N O (T) are noticeably different in short time intervals T; however, the distributions calculated using these functions are almost indistinguishable from each other in long T intervals. This circumstance makes it possible to use the simplest function w N O (T) to consider the photon statistics measured by the simplest method. This possibility is particularly important for investigating the fluorescence photon statistics, where the intensity fluctuates.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号