共查询到20条相似文献,搜索用时 31 毫秒
1.
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
2.
Within the framework of the single-channel approximation, an {αtd} model of the 9
Be nucleus is presented. A comparative analysis of the t 6
Li wave functions describing relative motion of bound states constructed in {ααn} and {αtd} cluster representations is carried out on the example of calculations of the 9
Be(γ,t0)6
Li process characteristics.
__________
Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 85–89, January, 2008. 相似文献
3.
K. Manimaran M. Balasubramaniam 《The European Physical Journal A - Hadrons and Nuclei》2010,45(3):293-300
The ternary fragmentation of 252Cf for all possible third fragments has been investigated using the recently proposed three-cluster model within a spherical
approximation and satisfying the condition A
1
3 \geq
A
2
3 \geq
A
3 . The most probable ternary configurations in the fission of 252Cf accompanied with all possible third fragment mass numbers from A
3 = 1 to 84 are predicted and their independent and overall relative yields are calculated. The calculations of the properly
charge minimized potential energy surface (PES) and yield reveal that even-mass third fragments are more favored than odd
ones. In the most probable configuration having the minimum in the potential energy and the maximum in yield, among the three
fragments, at least one (or two) of the fragment(s) associates itself with the neutron (or proton) closed shell and in some
cases even with the doubly closed shell. The calculated relative yields imply that next to 14C (the heaviest third fragment observed in the spontaneous ternary fission of 252Cf , 34, 36, 38Si , 46, 48Ar , and 48, 50Ca are presenting themselves as the most favoured cases to be observed as the third particle in the spontaneous ternary fission
of 252Cf . 相似文献
4.
B. Cameron Reed 《Central European Journal of Physics》2005,3(1):1-7
The ground-state energy of neutral helium is estimated variationally with a trial wavefunction of the form ϕ≈e
−γ(rA/a
o)ne−γ(rB/a
o)n. This model represents a modification of traditional textbook examinations of this problem via inclusion of the power “n”
as a second nonlinear variational parameter in addition to the usual effective nuclear charge γ and leads to an upper-limit
on the ground state energy of −2.86107 E
h
(E
h
=1 hartree) in comparison with the traditional (n=1) result of −2.84766 E
h
. This result represents a reduction of the percentage overestimate from the true ground-state energy (−2.90373 E
h
) of from 1.93 to 1.47. In comparison with the maximum accuracy obtainable from an uncorrelated trial wavefunction, −2.86168
E
h
, the present trial wavefunction reduces the percentage overestimate from 0.49 (n=1) to 0.021. The optimum values of (n, γ)
are determined to be ≈(0.897, 1.825). 相似文献
5.
P. Jesinger Yu. N. Kopatch M. Mutterer F. Gönnenwein A. M. Gagarski J. v. Kalben V. Nesvizhevsky G. A. Petrov W. H. Trzaska H. -J. Wollersheim 《The European Physical Journal A - Hadrons and Nuclei》2005,24(3):379-388
Experiments have been performed for studying quaternary fission (QF) in spontaneous fission of 252Cf, on the one hand, and for the neutron-induced fission reactions 233, 235U(nth, f ), on the other hand. In this higher-multiplicity fission mode, by definition, four charged products appear in the final state. In other words, as a generalization of the ternary-fission process, not only one but two light charged particles (LCPs) are accompanying the splitting of an actinide nucleus into the customary pair of fission fragments. In the two sets of measurements, which have used quite different approaches, the yields of several QF reactions with α-particles and tritons as the LCPs have been determined and the corresponding kinetic-energy distributions of the α-particles measured. The QF process can appear in two basically different ways: i) the simultaneous creation of two LCPs in the act of fission (“true” QF) and ii) via a fast sequential decay of a single but particle-unstable LCP in common ternary fission (“pseudo” QF). Experimentally the two varieties of QF have been distinguished by exploiting the different patterns of angular correlations between the two outgoing LCPs. The experiments described in the present paper are the first to demonstrate that both types of reactions, true and pseudo QF, occur with quite comparable probabilities. As a new result also, the kinetic-energy distributions related to the two processes have been shown to be significantly different. For all QF reactions which could be explored, the yields for 252Cf(sf) were found to be roughly by an order of magnitude larger than the yields found in the 233U(nth, f ) and 235U(nth, f ) reactions. An interesting by-product has been the measurement of yields of excited LCPs which allows to deduce nuclear temperatures at scission by comparison to the respective yields in the ground state. 相似文献
6.
N. Kh. Dzhemilev S. F. Kovalenko L. F. Lifanova S. E. Maksimov Sh. T. Khozhiev 《Bulletin of the Russian Academy of Sciences: Physics》2008,72(7):910-914
The spectra of kinetic energies of positive Si
n
O
m
+ cluster ions (n = 2–5, m = 2–7) have been measured using a double focusing ion microanalyzer with reverse geometry at instants 10−5 to 10−4 s after emission. The dissociation energies have been determined within the evaporative ensemble model and the theory of
unimolecular decay reactions. The results obtained are compared with the binding energies of neutral Si
n
O
m
clusters. 相似文献
7.
K. R. Vijayaraghavan W. von Oertzen M. Balasubramaniam 《The European Physical Journal A - Hadrons and Nuclei》2012,48(3):27
The kinetic energy distribution and potential energies of fragments from the collinear cluster tripartition (CCT), the “true”
ternary fission of 252Cf, have been calculated. It is assumed that the breakup of the nucleus into three fragments happens sequentially in two steps
from a hyper-deformed shape. In the first step a first neck rupture occurs of the parent radioactive nucleus, forming two
fragments (one of them is usually 132Sn) and, in the second step, one of the two fragments breaks into two other fragments, resulting finally in three fragments
(the experiment is based on a binary coincidence where a missing mass is determined). We show the result for the principal
combination of the three spherical fragments (semi-magic isotopes of Sn, Ca, Ni) observed recently experimentally. These isotopes
are clusters with high Q -values, which produce the highest yields in the ternary fission bump. It is shown that the kinetic energies of the middle
fragments have very low values, making their experimental detection quite difficult. This fact explains why the direct detection
of true ternary fission with three fragments heavier than A > 40 has escaped experimental observation. 相似文献
8.
A. Yu. Buki I. S. Timchenko N. G. Shevchenko 《The European Physical Journal A - Hadrons and Nuclei》2012,48(2):17
The Coulomb sums S
L(q) of the 6Li nucleus have been obtained from electron scattering measurements at 3-momentum transfers q = 1.125–1.625 fm−1. It is found that at q > 1.35 fm−1 the Coulomb sum of the nucleus becomes saturated: S
L(q) = 1 . 相似文献
9.
V. M. Apatin V. O. Kompanets V. N. Lokhman N. -D. D. Ogurok D. G. Poydashev E. A. Ryabov S. V. Chekalin 《JETP Letters》2011,94(7):570-573
Intracluster reactions that are induced in (CF3I)
n
clusters by femtosecond ultraviolet radiation, including the reaction of the formation of the I2+ molecular ion, have been directly observed. It has been shown that there are two channels of the formation of I2+ ions with the characteristic times τ1 ≈ 1 ps and τ2 ≈ 7 ps. A model of these reactions has been proposed that is in good agreement with the experimental data. 相似文献
10.
T.?Raghavendra Rao Ch.?Rama Krishna U.?S.?Udayachandran Thampy Ch.?Venkata Reddy Y.?P.?Reddy P.?Sambasiva Rao
Physical and spectral studies on 20ZnO + xLi2O + (30-x)Na2O + 50B2O3 (5 ≤ x ≥ 25) doped with 0.1 mol% of paramagnetic CuO impurity are carried out. Powder X-ray diffraction patterns of the glass samples
confirm the amorphous nature. The physical parameters of all the glasses were also evaluated with respect to the composition.
The electron paramagnetic resonance spectra of all these glasses exhibit resonance signals that are characteristic of Cu2+ ions. The optical absorption spectra also confirm the Cu2+ ion in tetragonally elongated octahedral site. Various crystal field, spin-Hamiltonian and bonding parameters are evaluated.
It is observed that the mixed alkali effect is significant. 相似文献
11.
S. Kar Y. K. Ho 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,44(1):1-8
We have investigated the ground state and the doubly excited 1,3P○ resonance states of plasma-embedded Li+ ion. The plasma effect is taken care of by using a screened Coulomb potential obtained from the Debye model. A correlated
wave function has been used to represent the correlation effect between the charged particles. The ground state of Li+ in plasmas for different screening parameters has been estimated in the framework of Rayleigh-Ritz variational principle.
In addition, a total of 18 resonances (9 each for 1P○ and 3P○ states) below the n=2 Li+ thresholds has been estimated by calculating the density of states using the stabilization method. For each spin state, this
includes four members in the 2snp+ (2≤n ≤5) series, three members in the 2snp- (3≤n ≤5) series, and two members in the 2pnd (n=3, 4) series. The resonance energies and widths for various Debye parameters
ranging from infinity to a small value for these 1,3P○ resonance states along with the ground state energies of Li+ and the Li2+ (1S), Li2+ (2S) threshold energies are reported. Furthermore, the wavelengths for the photo-absorption of lithium ion from its ground
state to such 1P○ resonance states for different Debye lengths are also reported. 相似文献
12.
Zhang XiaoAn Xiao GuoQing Yang ZhiHu Chen XiMeng Zhao YongTao Li FuLi Wang Li Cui Ying Zhang HongQiang Zhan WenLong 《中国科学G辑(英文版)》2008,51(1):82-89
Using the slow highly charged ions 129Xe
q+ (q = 25, 26, 27; initial kinetic T
0⩽4.65 keV/a.u.) to impact Au surface, the Au atomic Mα characteristic X-ray spectrum is induced. The result shows that as
long as the charge state of projectile is high enough, the heavy atomic characteristic X-ray can be effectively excited even
though the incident beam is very weak (nA magnitude), and the X-ray yield per ion is in the order of 10−8 and increases with the kinetic energy and potential energy of projectile. By measuring the Au Mα-X-ray spectra, Au atomic
N-level lifetime is estimated at about 1.33×10−18 s based on Heisenberg uncertainty relation.
Supported by the National Natural Science Foundation of China (Grant Nos. 10574132, 10274088 and 10405025), the Talent Introduction
Project of Xianyang Normal University (Grant No. 05XSYK103) and the Education Commission Foundation of Shaanxi Province (Grant
No. 04JK300) 相似文献
13.
The electron paramagnetic resonance (EPR) parameters (g-factors g
‖, g
⊥ and zero-field splitting D) of two tetragonal 3d3 impurity centers M3d-VMg and M3d-Li+ (where M3d = Cr3+ or Mn4+, VMg is the Mg2+ vacancy) in M3d-doped MgO crystals are calculated from the high-order perturbation formulas including both the crystal-field (CF) and the
charge-transfer (CT) mechanisms for 3d3 ions in the tetragonal symmetry. The calculated results are in reasonable agreement with the experimental values. From the
calculations, it can be found that the relative importance of the CT mechanism for EPR parameters increases with increasing
valence state of the 3d3 ion. So, for the high-valence 3d
n
ions in crystals, a reasonable explanation of EPR parameters should take into account both CF and CT mechanisms. The defect
structures (characterized by the displacement ΔR of O2− in the intervening M3d and VMg or Li+ at the Mg2+ site) for these tetragonal impurity centers are obtained from the calculations. The results are consistent with the expectations
based on the electrostatic interactions. 相似文献
14.
A. M. Gagarski I. S. Guseva V. E. Sokolov G. V. Val’ski G. A. Petrov D. O. Krinitsin D. V. Nikolaev T. A. Zavarukhina V. I. Petrova 《Bulletin of the Russian Academy of Sciences: Physics》2008,72(6):773-777
An experiment has been carried out to study neutron-neutron angular correlations in spontaneous fission of 252Cf. Angular dependences of the number of neutron-neutron coincidences obtained in the experiment were compared with the results of the Monte Carlo calculations for various neutron detection thresholds in the range 425–1600 keV. It was inferred that 10–11% of the total number of prompt neutrons from 252Cf (s.f.) in the laboratory system were emitted isotropically and may probably be interpreted as neutrons directly associated with the instant of scission of the nucleus. The analysis allowed their energy distribution to be determined as well. A similar method was also used to describe the angular correlation of prompt neutrons that accompanied the reaction 235U(n th ,f). 相似文献
15.
A. Sibirtsev J. Haidenbauer H. -W. Hammer U. -G. Meißner 《The European Physical Journal A - Hadrons and Nuclei》2007,32(2):229-241
We utilize existing inclusive data on K+-meson momentum spectra of the reaction pp→K
+
X at T
p = 2.3-2.85GeV to deduce total cross-sections for pp→K
+
Σ
+
n. The method used to extract those cross-sections is explained and discussed in detail. Our result for T
p = 2.85GeV is consistent with the data point from a direct measurement at the same beam energy. The cross-section obtained
for T
p = 2.3GeV is with 13.7±2.3μb considerably smaller than the value found in a recent experiment by the COSY-11 Collaboration
at a somewhat lower beam energy, indicating that the pp→K
+
Σ
+
n reaction cross-section could exhibit a rather unusual energy dependence. 相似文献
16.
Data on the cross sections for single-electron charge exchange and excitation in collisions of He+ ions with C5+, N6+, and O7+ ions in the He+ ion energy range of 0.2–3.0 MeV are obtained for the first time. The cross sections for the single-electron charge transfer
into the singlet and triplet 1snl states of C4+, N5+, and O6+ (2≤n≤5) ions and for the 1s → 2p
0, ±1 electronic excitation of He+(1s) ions are calculated. The calculations were performed by solving close-coupling equations on the basis of ten two-electron
quasi-molecular states. 相似文献
17.
G. N. Lovchikova A. M. Trufanov M. I. Svirin V. A. Vinogradov A. V. Polyakov 《Physics of Atomic Nuclei》2004,67(7):1246-1263
The time-of-flight technique is used to measure the ratios R(E, E n )=N(E, E n )/NCf(E) of the normalized (to unity) spectra N(E, E n ) of neutrons accompanying the neutron-induced fission of 238U at primary-neutron energies of E n =6.0 and 7.0 MeV to the spectrum NCf(E) neutrons from the spontaneous fission of 252Cf. These experimental data and the results of their analysis are discussed together with data that were previously obtained for the neutron-induced fission of 238U at the primary energies of E n =2.9, 5.0, 13.2, 14.7, 16.0, and 17.7 MeV. 相似文献
18.
S. Singh R. Chandra P. K. Rath P. K. Raina J. G. Hirsch 《The European Physical Journal A - Hadrons and Nuclei》2007,33(4):375-388
The two-neutrino double-beta decay of 124, 126Xe , 128, 130Te , 130, 132Ba and 150Nd isotopes is studied in the Projected Hartree-Fock-Bogoliubov (PHFB) model. Theoretical 2ν β-β- half-lives of 128, 130Te , and 150Nd isotopes, and 2ν β+β+ , 2ν β+
EC and 2ν ECEC for 124, 126Xe and 130, 132Ba nuclei are presented. Calculated quadrupolar transition probabilities B(E2 : 0+ → 2+) , static quadrupole moments and g -factors in the parent and daughter nuclei reproduce the experimental information, validating the reliability of the model
wave functions. The anticorrelation between nuclear deformation and the nuclear transition matrix element M
2ν is confirmed. 相似文献
19.
V.V. Anisovich A.V. Sarantsev 《The European Physical Journal A - Hadrons and Nuclei》2003,16(2):229-258
We present the results of the current analysis of the partial wave IJ
PC = 00+ + based on the available data for meson spectra ( ππ, KˉK,ηη,η,ππππ). In the framework of the K-matrix approach, the analytical amplitude has been reconstructed in the mass region 280 MeV < < 1900 MeV. The following scalar-isoscalar states are seen: comparatively narrow resonances f
0(980), f
0(1300), f
0(1500), f
0(1750) and the broad state f0(1200-1600). The positions of the amplitude poles (masses and total widths of the resonances) are determined as well as pole
residues (partial widths to meson channels ππ, KˉK,ηη,η,ππππ). The fitted amplitude gives us the positions of the K-matrix poles (bare states) and the values of bare-state couplings to meson channels thus allowing the quark-antiquark nonet
classification of bare states. On the basis of the obtained partial widths to the channels ππ, KˉK,ηη,η, we estimate the quark/gluonium content of f
0(980), f
0(1300), f
0(1500), f
0(1750), f0(1200-1600). For f
0(980), f
0(1300), f
0(1500) and f
0(1750), their partial widths testify the qˉq origin of these mesons though being unable to provide precise evaluation of the possible admixture of the gluonium component
in these resonances. The ratios of the decay coupling constants for the f0(1200-1600) support the idea about the gluonium nature of this broad state.
Received: 14 May 2002 / Accepted: 20 August 2002 / Published online: 11 February 2003
RID="a"
ID="a"e-mail: anisovic@thd.pnpi.spb.ru
Communicated by A. Sch?fer 相似文献
20.
L. S. Danelyan S. N. Korshunov A. N. Mansurova V. V. Zatekin V. S. Kulikauskas I. V. Borovitskaya L. I. Ivanov V. V. Paramonova M. M. Lyakhovitskii 《Journal of Surface Investigation: X-ray, Synchrotron and Neutron Techniques》2012,6(2):236-240
Changes in the surface properties of vanadium and its alloys irradiated by Ar+ ions with the energy 20 keV, to a dose of 1022 m−2 at T
irr ≈ 700K have been studied. The radiation effect consists of material surface hardening, increasing the lattice parameters
of the irradiated samples, and radiation erosion of the surface layers in the form of flaking. Features of radiation damage
to the material’s surface irradiated by gas ions with high sputtering coefficients are discussed. 相似文献