共查询到20条相似文献,搜索用时 15 毫秒
1.
V. V. Varlamov B. S. Ishkhanov V. N. Orlin S. Yu. Troshchiev 《Bulletin of the Russian Academy of Sciences: Physics》2010,74(6):842-849
The results from experimental and theoretical studies of the total and partial cross sections of photoneutron reactions on
the 197Au isotope were analyzed. The cross sections for reactions σ(γ, nX) = σ(γ, n) + σ(γ, np) + … + σ(γ, 2nX) = σ(γ, 2n) + σ(γ, 2np) + … were evaluated in the energy range 7 ≤ E
γ ≤ 30 MeV using an approach free of the shortcomings of experimental photoneutron multiplicity sorting methods. The total
photoneutron reaction cross sections σexp(γ, xn) = σexp(γ, nX) + 2σexp(γ, 2nX) + … = σexp(γ, n) + σexp(γ, np) + 2σexp(γ, 2n) + 2σexp(γ, 2np) + … were used as the initial experimental data. The contributions from the cross sections σ(γ, nX) and σ(γ, 2nX) to the cross sections σexp(γ, xn) were separated using the multiplicity transition functions F
1
theor = σtheor(γ, 1nX)/σtheor(γ, xn) and F
2
theor = σtheor(γ, 2nX)/σtheor(γ, xn), calculated within an updated version of the pre-equilibrium model of photonuclear reactions. New evaluated data for both
partial reaction cross sections, i.e., σeval (γ, 1nX) = F
1
theorσexp(γ, xn) and σeval(γ, 2nX) = F
2
theorσexp(γ, xn), were obtained. The cross sections σeval(γ, nX) and σeval.(γ, 2nX) evaluated using the theoretically calculated functions F
1,2theor are consistent with the Livermore data, but substantially contradict the Saclay data. 相似文献
2.
V. V. Varlamov B. S. Ishkhanov V. N. Orlin V. A. Chetvertkova 《Bulletin of the Russian Academy of Sciences: Physics》2010,74(6):833-841
A combined analysis of experimental data on total and partial photoneutron reaction cross sections, obtained using bremsstrahlung
γ-radiation and quasi-monoenergetic annihilation photon beams, was performed for nine Sn isotopes. The partial reactions σeval(γ, nX) and σeval(γ, 2nX) cross sections were evaluated using an approach free of the shortcomings of experimental neutron multiplicity sorting methods.
This approach involves calculations within the photonuclear reaction model, based on Fermi gas densities and considering the
effects of nucleus deformation, the isospin splitting of its giant dipole resonance (GDR), and experimental data on the total
photoneutron cross sections σexp(γ, xn) = σexp(γ, nX) + 2σexp(γ, 2nX) = σexp(γ, n) + σexp(γ, np) + … + 2σexp(γ, 2n) + 2σexp(γ, 2np) + …. The evaluated σeval(γ, nX) and σeval(γ, 2nX) reactions cross sections were obtained using the introduced transition multiplicity functions F
theor = σtheor(γ, 2nX)/σtheor(γ, xn) = σtheor(γ, 2nX)/[σtheor(γ, nX) + 2σtheor(γ, 2nX) + …]; and σeval.(γ, 2nX) = F
theor.σexp.(γ, xn) = σeval(γ, nX) = (1 − 2F
theor)σexp(γ, xn). The evaluated partial reaction cross sections were used to assess the total photoneutron reaction cross sections σeval(γ, sn) = σeval(γ, nX) + σeval(γ, 2nX) + … as functions of the mass number A. The GDR features of 112, 114, 116, 117, 118, 119, 120, 122, 124Sn isotopes were studied and are discussed here. 相似文献
3.
Line strengthS and radial matrix elementσ for the dipole allowed transitions withinn=2 complex of ions in the Be isoelectronic sequence have been fitted in the formsZ
2
S=A+B/(Z − C) andZσ=A′ + B′/(Z − C′). The constantsA, B, C andA′, B′, C′ have been calculated by employing a non-linear least square method. The relevant data forS andσ have been taken from calculations which includes correlation effects. It is shown that the fitted yalues ofA andA′ are in excellent accord with their hydrogenic values (Z →α) provided that we express the zeroth-order wavefunction of the ground state 1s22s2
1
S as a quantum-mechanical admixture of the Hartree-Fock (HF) state 1s22s2
1
S and the near-degenerate state 1s22p2
1
S. 相似文献
4.
The joint probability density functions of the normalized structure amplitudes of the structure and the model (i.e.,y
N andy
p
c
) are derived for triclinic crystals containing heavy atoms (1, 2 and many) by taking the model to consist of the heavy atoms
and a part of the light atoms in the unit cell. These functions are derived for the two cases where the model is completely
correct (i.e., the related case) and where the model is completely wrong (i.e., the unrelated case) in terms of the fractional contributions to the local mean intensity from the heavy atoms and all known
atoms (i.e., σ
1h
/2
and σ
1
2
) as parameters. These functions are then used to obtain the theoretical local values of 〈y
N〉 and 〈|y
N
n
− σ
1
n
(y
P
c
)
n
|〉,n=1, 2. A method of using these results to compute the theoretical overall values ofR(F) andR(I) for the related and unrelated cases is briefly described. A comparison of the observed values of these indices with their
theoretical values for the related and unrelated cases would help in determining the correctness of the proposed trial structure.
Contribution No. 548 相似文献
5.
Theoretical expressions of 〈y
N〉, 〈|y
N − σ1
y
P
c
|〉 and 〈|y
N
2
−σ
1
2
(y
P
c
)2|〉 (wherey
N andy
P
c
are the normalized structure amplitudes of the structure and the model respectively) are derived in terms of the heavy atom
contributionσ
1
2
for monoclinic and orthorhombic crystals containing a few (i.e., 1 or 2) heavy atoms of the same kind per asymmetric unit by taking the heavy atom part alone as the model. Results are obtained
for both the related and unrelated cases. The local values of 〈y
N〉 and 〈|y
N
n
− σ
1
n
(y
P
c
)
n
|〉, (n=1, 2) calculated from these expressions can be used to calculate the overall values of the conventionalR-indicesR(F) andR(I) for the related and unrelated cases. These overall values could be used to check the correctness of heavy atoms located
in the structure.
Contribution No. 550 相似文献
6.
I. S. Dmitriev Ya. A. Teplova Yu. A. Fainberg 《Journal of Experimental and Theoretical Physics》1999,89(5):830-836
The electron loss and electron capture cross sections σ
i,i+m and σ
i,i−m for boron ions and atoms traveling at the velocities V=1.19 and 1.83 a.u. in H2, He, N2, Ne, Ar, and Xe are measured. The known experimental data on these cross sections at velocities near the cross-section maximum
are analyzed. It is found that the electron loss cross sections can be described by a formula which was previously derived
in the free-collision approximation and takes into account features of both the ions and the ambient atoms. As the nuclear
charge Z
t of the ambient atoms increases, the cross sections vary nonmonotonically, increasing on average as Zt
t
1/2
. A formula based on the model of independent electrons is proposed for electron capture by ions with small values of the
charge i. It describes the dependence of the electron capture cross section σ
i,i−1 on the mean binding energy of an electron in an ion with the charge i−1. The total electron capture cross section σ
i,i−1 is proportional to the number of vacancies in the unfilled electron shell nearest the nucleus. The cross sections 0σ
i,i−1 exhibit substantially nonmonotonic variation with Z
t, increasing on average as Z
t
1/3
.
Zh. éksp. Teor. Fiz. 116, 1539–1550 (November 1999) 相似文献
7.
M. V. Eremin S. I. Nikitin N. I. Silkin S. Yu. Prosvirin R. V. Yusupov 《Journal of Experimental and Theoretical Physics》1998,87(4):771-775
Studies involving the piezospectroscopy method have shown that the symmetry of the pair centers of Cr3+-Cr2+ ions in the KZnF3 crystal is tetragonal. In this paper we develop a microscopic model of a pair center. We use the temperature dependence of
the integrated intensity of the absorption line to find the effective hopping integral for an e
g electron, t
σσ=205 ± 10 cm−1, and the polaron reduction factor, equal to 0.11. By analyzing the selection rules for exchange-induced electric dipole transitions
under double-exchange conditions we identify all the absorption lines of Cr3+-Cr2+ pairs.
Zh. éksp. Teor. Fiz. 114, 1421–1429 (October 1998) 相似文献
8.
The Harari-Shupe model of quarks and leptons is viewed, not as a gauge theory, but as a quantum-mechanical three-body problem
of the extreme relativistic type involving massless preons. Considerations based onS
3-symmetry in the available degrees of freedom (spin, isospin, space and hypercolour) are employed in conjunction with a spin-dependence
ansatz on the three-preon forces (Σ
a
=σ
μv
(1)
σ
λμ
(3)
) for an understanding of the three basic issues of (i) spin-1/2, (ii) generation structure and (iii) steeply rising mass
patterns of quark-lepton families. The Σ
a
-dynamics is compatible with the interpretation of colour as a manifestation ofS
3-symmetry, as envisaged in the original Harari-Shupe proposal, while the interpretation of the generation structure devolves
on the role of a certain quantum numberN which takes on three different classes of values (3n, 3n ± 1;n = 0, 1, 2, ...) according to theS
3-symmetry of thespatial wavefunction. 相似文献
9.
V. I. Arnold 《Mathematical Physics, Analysis and Geometry》2006,9(2):95-108
Linear combinations x
1
a
1 ⋯ x
n
a
n
of n given natural numbers a
s
(with nonnegative integral coefficients x
s
) attain all the integral values, starting from some integer N(a), called the Frobenius number of vector a (provided that the integers a
s
have no common divisor, greater than 1). The growth rate of N(a) with the large value of σ = ta
1 ⋯ a
n
depends peculiarly from the direction α of the vector a = σα. The article proves the lower bound of order and the upper bound of order σ
2. Both orders are reached from some directions α. The averaging of N(a) along all directions, performed for σ = 7, 19, 41 and 97, provides the values, confirming the rate σ
p
for some p between 3/2 and 2 (for n = 3), excluding neither 3/2 nor 2, for the asymptotic behaviour at large σ. One gets check p ≈ 1, 66 for σ between 100 and 200. These unexpected results, based on some strange relations of the Frobenius numbers to the higher-dimensional continued fractions geometry, lead to many facts of this arithmetic trubulence theory, discussed in this article both as theorems and as conjectures.
★ Partially supported by RFBR grant 05-01-00104. 相似文献
10.
H. Naik R.J. Singh R.H. Iyer 《The European Physical Journal A - Hadrons and Nuclei》2003,16(4):495-507
Charge distribution studies for heavy-mass fission products were carried out in the fast-neutron-induced fission of 232Th, 238U, 240Pu and 244Cm using radiochemical and gamma-ray spectrometric techniques. The width parameter( σZ/σA), the most probable charge/mass ( Z
P/A
P), the charge polarization (ΔZ) and the slope of charge polarization [ δ(ΔZ)/δA
′] as a function of the fragment mass (A
′) were deduced. The average charge dispersion parameter ( 〈σZ〉) and proton odd-even effect ( δp) were also obtained for these fissioning systems. The 〈σZ〉 and δp values in the fissioning systems 241Pu * and 245Cm * were determined for the first time. The δ(ΔZ)/δA
′ value is also determined for the first time in the fissioning systems 239U * , 241Pu * and 245Cm * . These data along with the literature data for even-Z fissioning systems such as 230Th * , 232Th * , 233U * , 234U * , 236U * , 238U * , 239Pu * , 240Pu*, 242Pu * , 246Cm * , 250Cf * and 252Cf(SF) are discussed in terms of nuclear structure effect and dynamics of descent from the saddle to the scission point. The
role of the excitation energy in low-energy fission is also discussed.
Received: 26 July 2002 / Accepted: 3 December 2002 / Published online: 3 April 2003
RID="a"
ID="a"Present address: Emeritus Scientist (CSIR) Bhabha Atomic Research Centre, Nuclear Recycle Group, WIP Building, Trombay, Mumbai-400085, India;
e-mail: rhiyer@magnum. barc.ernet.in
Communicated by D. Schwalm 相似文献
11.
F. Schümann S. Zavatarelli L. Gialanella U. Greife M. Junker D. Rogalla C. Rolfs F. Strieder H.P. Trautvetter 《The European Physical Journal A - Hadrons and Nuclei》1998,2(4):337-342
Abstact: The elastic scattering cross sections, σ (E,θ), for the systems He+Ta and He+W have been measured at θlab=165° and E
lab=76.1 keV to 3.988 MeV using targets with a thickness of a few atomic layers. The results are smaller than the results given
by the Rutherford scattering law, σR(E,θ), due to the effects of electron screening and can be described by σ(E,θ)/σR(E,θ)=(1+Ue/E)−1, where U
e is an atomic screening potential energy. The deduced average value, U
e=28 ± 3 keV, is consistent with the Moliére- and Lenz-Jensen-models as well as electron binding energies.
Received: 25 May 1998 相似文献
12.
The isomeric ratios of the 197m,g
Pt and 197m,g
Hg yields in the respective (γ, n) reactions are measured for the first time in the energy range 8–17 MeV. The isomeric ratios σ
m/σg for 197m,g
Hg in the (d, 2n) reaction are measured in the energy range 8–50 MeV. The experimental data are compared with the results of theoretical calculations.
The effect of the structure of low-lying states and of the yrast line on the behavior of σ
m/σg is revealed.
__________
Translated from Yadernaya Fizika, Vol. 67, No. 5, 2004, pp. 899–905.
Original Russian Text Copyright ? 2004 by Zheltonozhsky, Mazur, Bigan. 相似文献
13.
Nathalie Besson Maarten Boonekamp Esben Klinkby Sascha Mehlhase Troels Petersen 《The European Physical Journal C - Particles and Fields》2008,57(3):627-651
We present a study of the LHC sensitivity to the W boson mass based on simulation studies. We find that both experimental and phenomenological sources of systematic uncertainties
can be strongly constrained with Z measurements: the lineshape, dσ
Z
/dm, is robustly predicted, and its analysis provides an accurate measurement of the detector resolution and absolute scale,
while the differential cross-section analysis, d2
σ
Z
/dydp
T
, absorbs the strong interaction uncertainties. A sensitivity δ
m
W
∼7 MeV for each decay channel (W→e
ν, W→μ
ν), and for an integrated luminosity of 10 fb−1, appears as a reasonable goal. 相似文献
14.
Y. Zhang C. Y. Chen M. Huang Y. S. Wang Y. M. Zou 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2010,56(2):157-166
Ab initio calculations of the total dielectronic
recombination (DR) rate coefficients for thirteen ions along the NiI
isoelectronic sequence in the ground state (Kr8+, Mo14+,
Ag19+, Sn22+, Xe26+, Nd32+, Gd36+,
Yb42+, W46+, Au51+, Pb54+, At57+, and
U64+) have been performed using the flexible atomic code. The
level-by-level calculations are performed for evaluating the DR
contributions through the relevant Cu-like autoionizing inner-shell
excited 3l174l′n′′l′′ and 3l175l′n′′l′′ configuration complexes with n′′
≤15, which are associated with Δn=1 and Δn=2
core-excitations, respectively. The usual (n′′)-3 scaling
law is found to be invalid for low-Z ions. A level-by-level
extrapolation procedure is employed to obtain the contributions
through higher n′′ complexes. The decays to autoionizing
levels followed possibly by radiative cascades could enlarge the
rates at relatively high temperature by a factor up to about 23%.
For the whole isoelectronic ions the contributions from
3s23p63d9 4l′n′′l′′ dominate the total DR
rates while the contributions from the 3s23p63d9 5l′n′′l′′ configuration complexes are about 10-20% at
relatively high temperature. On the basis of the calculated results,
a general analytic formula for the total DR rate coefficients of all
the ions with 36≤Z ≤92 along the NiI isoelectronic
sequence is constructed. The comparisons of the rates obtained from
the general formula with those from the detailed calculations show
that the formula is of high precision, generally better than 3%
accuracy for electron temperatures kT≥0.1EI, where EI is
the ionization energy of the Cu-like ion. The present DR rates at
temperature above 1.0EI are larger than the previously published
data by a factor above 30%. The commonly used semiempirical formula
proposed by Burgess and modified by Merts may overestimate the rates
at high temperature by a factor of about 2 for low-Z ions. 相似文献
15.
H. Chamati 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,24(2):241-249
The finite-size critical properties of the (n) vector ϕ4 model, with long-range interaction decaying algebraically with the interparticle distance r like r
-d - σ, are investigated. The system is confined to a finite geometry subject to periodic boundary condition. Special attention
is paid to the finite-size correction to the bulk susceptibility above the critical temperature T
c. We show that this correction has a power-law nature in the case of pure long-range interaction i.e. 0 < σ < 2 and it turns out to be exponential in case of short-range interaction i.e.σ = 2. The results are valid for arbitrary dimension d, between the lower ( d
< = σ) and the upper ( d
> = 2σ) critical dimensions.
Received 2 July 2001 and Received in final form 4 Septembre 2001 相似文献
16.
Andre Toom 《Journal of statistical physics》1997,88(1-2):347-364
We consider space- and time-uniformd-dimensional random processes with linear local interaction, which we call harnesses and which may be used as discrete mathematical
models of random interfaces. Their components are rea random variablesa
s
t
, wheres ∈ Z
d
andt=0, 1, 2.,... At every time step two events occur: first, every component turns into a linear combination of itsN neighbors, and second, a symmetric random i.i.d. “noise”v is added to every component. For any σ ∈Z
d
+
define Δσ
a′
s
as follows. If σ=(0,...,0), σ=(0,...,0), Δσ
a
s
t
=a
s
t
. Then by induction,
wheree
i is thed-dimensional vector, whoseith component is one and other components are zeros. Denote |σ| the sum of components of σ. Call a real random variable ϕ symmetric
if it is distributed as −ϕ. For any symmetric random variable ϕpower decay or P-decay is defined as the supremum of thoser for which therth absolute moment of ϕ is finite. Convergence a.s., in probability and in law whent→∞ is examined in terms of P-decay(v): Ifd=1, σ=0 ord=2, σ=(0,0), Δσ
a
s
t
diverges. In all the other cases: If P-decay(v)<(d+2)/(d+|σ|), Δσ
a
s
t
diverges; if P-decay(v)>(d+2)/(d+|σ|), Δσ
a
s
t
, converges and P-decay(ν) For any symmetric random variable ϕexponential decay or E-decay is defined as the supremum of thoser for which the expectation of exp(|x|r) is finite. Let E-decay(v)>0. Whenever Δσ
a
s
t
converges (that is, ifd>2 or |σ|>0: Ifd>2, E-decay(lima
s
t
)=min(E-decay(v),d+2/2); if |σ|=1, E-decay (lim Δσ
a
s
t
)=min(E-decay(ν),d+2); if |σ| ⩾, E-decay (lim Δσ
a
s
t
)=E-decay(ν). 相似文献
17.
Living polymers are formed by reversible association of primary units (unimers). Generally the chain statistical weight involves
a factor σ < 1 suppressing short chains in comparison with free unimers. Living polymerization is a sharp thermodynamic transition
for σ ≪ 1 which is typically the case. We show that this sharpness has an important effect on the kinetics of living polymerization
(one-dimensional association). The kinetic model involves i) the unimer activation step (a transition to an assembly-competent
state); ii) the scission/recombination processes providing growth of polymer chains and relaxation of their length distribution.
Analyzing the polymerization with no chains but unimers at t = 0 , with initial concentration of unimers M ≳ M
* (M* is the critical polymerization concentration), we determine the time evolution of the chain length distribution and find
that: 1) for M
* ≪ M ≪ M
*/σ the kinetics is characterized by 5 distinct time stages demarcated by 4 characteristic times t1, t2, t3 and t*; 2) there are transient regimes (t
1 ≲ t ≲ t
3) when the molecular-weight distribution is strongly non-exponential; 3) the chain scissions are negligible at times shorter
than t2. The chain growth is auto-accelerated for t
1 ≲ t ≲ t
2 : the cut-off chain length (= polymerization degree 〈n〉w
N
1 ∝ t
2 in this regime. 4) For t
2 < t < t
3 the length distribution is characterized by essentially 2 non-linear modes; the shorter cut-off length N1 is decreasing with time in this regime, while the length scale N2 of the second mode is increasing. (5) The terminal relaxation time of the polymer length distribution, t*, shows a sharp maximum in the vicinity of M*; the effective exponent
is as high as ∼ σ-1/3 just above M*. 相似文献
18.
W. J. Kossler X. H. Yu A. Greer H. E. Schone C. E. Stronach M. Davis R. S. Cary J. E. Crow W. F. Lankford J. Oostens 《Hyperfine Interactions》1991,63(1-4):81-86
Transverse and zero-field μSR measurements were made on YBa2(Cu1−xNix)3O7−y withx=0.1 and 0.2, and YBa2(Cu1−x
Zn
x
)3O7−y
withx=0.03, 0.06, 0.1, and 0.16, wherey≈0.1. Since doping may lead to magnetic ordering this was searched for with both zero and transverse field μSR, but no evidence
was found over the temperature range studied: 10–100 K. However, depolarization rates as functions of temperature were obtained,
and the low temperature values of these are σ=3.2 μs−1.1.6μs−1, and 1 μs−1 forx=0.01, and 0.2 Ni, respectively, and σ=0.8 μs−1, 0.75 μs−1, 0.65 μs−1, and 0.4 μs−1 forx=0.03, 0.06, 0.1, and 0.16 Zn, respectively. Estimates for the effect of decreasing electron concentration for Zn are made,
but these alone do not account for the drop in σ. Estimates for the effect of scattering on λ and hence σ are made. The reduction
in σ for Ni dopant is in surprisingly good agreement with these estimates. For Zn the order of magnitude is correct, but the
relative lack of further change in σ after the effect of the first 0.03 addition seems to imply a saturation of the effect
of scattering. 相似文献
19.
A Goswami B K Srivastava Alok Srivastava S B Manohar Satya Prakash M V Ramaniah 《Pramana》1986,26(3):179-189
Fractional independent yields of fission products in the thermal neutron-induced fission of233U,235U,239Pu,241Pu and in the spontaneous fission of252Cf have been correlated with the neutron-to-proton ratio of the fission products. The yields of the products from a fissioning
system, when plotted as a function of neutron-to-proton (N/Z) ratio of fission preducts, fall on two Gaussian distribution corresponding to light and heavy fission products. The centroids
of the distribution or the most probable value of neutron-to-proton ratio is found to be very close to theN/Z of the fissioning nucleus. From the most probable value ofN/Z the various parameters of charge distribution e.g. most probable massA
p, most probable chargeZ
p, the mass dispersionσ
Aand the charge dispersionσ
Zhave been obtained and are in good agreement with the experimental values ofA
pandZ
p. 相似文献
20.
J. Castillo E. M. Materón R. Castillo R. A. Vargas P. R. Bueno J. A. Varela 《Ionics》2009,15(3):329-336
We report on electrical relaxation measurements of (1 − x)NH4H2PO4-xTiO2 (x = 0.1) composites by admittance spectroscopy, in the 40-Hz–5-MHz frequency range and at temperatures between 303 and 563 K.
Simultaneous thermal and electrical measurements on the composites identify a stable crystalline phase between 373 and 463 K.
The real part of the conductivity, σ’, shows a power-law frequency dependence below 523 K, which is well described by Jonscher’s expression , where σ
0 is the dc conductivity, ω
p
/2π = f
p
is a characteristic relaxation frequency, and n is a fractional exponent between 0 and 1. Both σ
0 and f
p
are thermally activated with nearly the same activation energy in the II region, indicating that the dispersive conductivity
originates from the migration of protons. However, activation energies decrease from 0.55 to 0.35 eV and n increases toward 1.0, as the concentration of TiO2 nanoparticles increases, thus, enhancing cooperative correlation among moving ions. The highest dc conductivity is obtained
for the composite x = 0.05 concentration, with values above room temperature about three orders of magnitude higher than that of crystalline
NH4H2PO4 (ADP), reaching values on the order of 0.1 (Ω cm) − 1 above 543 K. 相似文献