共查询到20条相似文献,搜索用时 33 毫秒
1.
A. P. Serebrov I. A. Kuznetsov I. V. Stepanenko A. V. Aldushchenkov M. S. Lasakov Yu. A. Mostovoi B. G. Erozolimskii M. S. Dewey F. E. Wietfeldt O. Zimmer H. Börner 《Journal of Experimental and Theoretical Physics》1998,86(6):1074-1082
The result of a new run of measurements of the antineutrino escape asymmetry with respect to the spin of the decaying neutron
is presented. The asymmetry coefficient is B=0.9821±0.0040, which is consistent with the prediction of the standard model of weak interactions. The prospects for increasing the
accuracy of the measurements are discussed.
Zh. éksp. Teor. Fiz. 113, 1963–1978 (June 1998) 相似文献
2.
F. M. Abzaev S. A. Bel’kov A. V. Bessarab S. V. Bondarenko V. A. Gaidash S. G. Garanin G. V. Dolgoleva N. V. Zhidkov V. M. Izgorodin G. A. Kirillov G. G. Kochemasov D. N. Litvin S. P. Martynenko V. M. Murugov L. S. Mkhitar’yan A. V. Pinegin S. I. Petrov A. V. Senik N. A. Suslov V. S. Bushuev V. M. Dorogotovtsev Yu. A. Merkul’ev 《Journal of Experimental and Theoretical Physics》1998,87(6):1080-1086
Experiments on the indirect (x-ray) irradiation of high-aspect-ratio capsules (with a diameter-to-thickness ratio ≈900) filled
with DT gas are performed on the Iskra-5 laser facility. It is shown that all the characteristics measured (neutron yield,
ion temperature, shell implosion time, etc.) are faithfully reproduced in calculations based on the one-dimensional SNDA (spectral
nonequilibrium diffusion of absorption) program for nonequilibrium radiation gas dynamics. The calculations provide an explanation
for the experimentally detected generation of a smaller number of neutrons in an experiment with a higher measured value for
the ion temperature of DT gas.
Zh. éksp. Teor. Fiz. 114, 1993–2003 (December 1998) 相似文献
3.
S. G. Kadmenskii V. E. Bunakov S. S. Kadmenskii 《Bulletin of the Russian Academy of Sciences: Physics》2010,74(4):517-521
T-odd asymmetries in angular distributions of evaporation γ-rays emitted by thermalized fragments resulting from the fission
of axially symmetric deformed nuclei induced by cold polarized neutrons are investigated within the quantum theory of fission.
The asymmetries in question are due to the anisotropy of the angular distributions of evaporation γ-rays, caused by zero wriggling
vibrations of the fissioning nucleus and associated with the orientation of large fission fragment spins in the direction
perpendicular to the direction n
0 of the symmetry axis of the fissioning nucleus at the time of its separation into fragments. The angle of rotation of the
vector n
0 with respect to the asymptotic direction of the light fission fragment emission is calculated with allowance for the interference
of fission amplitudes of neutron resonances excited in the fissioning nucleus as it captures the incident neutron. It is shown
that the angular and energy characteristics of the T-odd asymmetry calculated for evaporation γ-rays agree with the characteristics of the experimentally investigated T-odd asymmetry in angular distributions of all γ-rays emitted by a fissioning 236U nucleus. 相似文献
4.
The order-disorder model has been used to explain asymmetry of mass and charge division and related phenomena in fission.
According to this model the fission process involves two steps consisting of charge polarisation into two ‘impending fragment
clusters’ with beta stable neutron numbers and subsequent distribution of the balance neutrons between the two. Mode of elemental
division of the fissioning nuclei is attributed to the charge polarisation in the first step. Theory of reaction rate has
been applied to the system.
The frequency term is obtained by applying the conditional stochastic process under charge polarisation constraint and the
energy-dependent term is given by the condition of minimum in free energy of the system. Using this, the relative probability
of polarisation into given charge pair is arrived at.
The model uses stable neutron numbers for the charges as the only input. No explicit assumption or quantification on the preference
of formation of shell closure species in fission is necessary. The statistics developed on the principle of equala priori probability of all charge polarisation is used. The shell effects come into play only in deciding a stable neutron number
for the charges. The total isotopic yield distribution for a number of fission reactions shows asymmetry in the actinide region
which reduces with increasing mass/charge of the fissioning nuclide and bunching of the higherz peaks. Although the mass yields obtained therefrom for a number of fission reactions agree with experimental results, the
peaks of the distributions are slightly shifted away from the symmetric point and the distributions are somewhat narrower.
Charge distribution parameters obtained from these results are also presented. 相似文献
5.
K.W. Krämer H.U. Güdel P. Fischer F. Fauth M.T. Fernandez-Diaz T. Hauß 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,18(1):39-47
ErCl3 crystallizes in the AlCl3-type layer structure. The crystal structure was refined in the paramagnetic state by powder neutron diffraction. The monoclinic
lattice parameters at 1.5 K are a
= 6.8040(3)?, b
= 11.7456(5)?, c
= 6.3187(3)? and . The space group is C2/m. Short-range, predominantly in-plane, magnetic ordering occurs above 350 mK up to several Kelvin.
Below mK a three-dimensional antiferromagnetic order with a propagation vector of sets in. The magnetic structure of ErCl3 was determined by powder and single-crystal neutron diffraction at temperatures down to 45 mK. The Er3+ ions are located on two-dimensional honeycomb layers in the a–b plane. There are two antiferromagnetically coupled triangular sublattices which form right- and left-handed helices along the c-axis. The magnetic moments are oriented in the a–b plane and amount to 3.3(1) at saturation. From the temperature dependence of the integrated neutron magnetic peak intensity a critical exponent (2) was derived for the magnetic phase transition.
Received 1 December 1999 and Received in final form 21 July 2000 相似文献
6.
D. G. Haase C. R. Gould J. E. Koster N. R. Roberson L. W. Seagondollar J. P. Soderstrum M. B. Schneider X. Zhu 《Hyperfine Interactions》1988,43(1-4):133-138
We describe searches for parity and time reversal violations in the scattering of polarized neutrons from polarized and aligned165Ho targets. We have completed a search with 7.1 and 11.0 MeV neutrons for PoddTodd terms in the elastic scattering forward amplitude of the form s. (I×K), wheres is the neutron spin,I is the target spin andk is the neutron momentum vector. The target was a single crystal of holmium, polarized horizontally along itsb axis by a 1 Tesla magnetic field. The neutrons were polarized vertically. Differences in the neutron transmission were measured
for neutrons with spins parallel (antiparallel) toI×k. The P,T violating analyzing powers were found to be consistent with zero at the few 10−3 level: ρP,T(7.1 MeV)=−0.88 (±2.02) x 10−3, ρP,T(11.0 MeV)=−0.4 (±2.88) x 10−3. We have also attempted to find enhancements with MeV neutrons in P-violation due to the term s\k. We are preparing an aligned target cryostat for investigations of PevenTodd terms {bd(I\k)(I×k)\s} in neutron scattering. The target will be a single crystal cylinder of165Ho cooled to 100 mK in a bath of liquid helium and rotated by a shaft from a room temperature stepping motor. The cylinder
will be oriented vertically and the alignment (c) axis oriented horizontally. Warming or rotation of the sample allows one to separate effects that mimic the sought-after
time reversal violating term. 相似文献
7.
V. N. Lazukov P. A. Alekseev E. S. Klement’ev E. V. Nefedova I. P. Sadikov J. -M. Mignot N. B. Kol’chugina O. D. Chistyakov 《Journal of Experimental and Theoretical Physics》1998,86(5):943-952
To examine the effect of hybridization of 4f electrons with conduction electrons on the crystal field potential using neutron spectroscopy, we studied the effects of
the crystal electric field (CEF) in intermetallic compounds of the type ReNi, in which chemical substitution is followed by
a transition of the cerium ions from an intermediate valence state to the Kondo state. Measurements were performed both on
cerium ions in the compounds Ce1−x
LaxNi (x=0.5, 0.8), where they have a whole-number population of the 4f shell, and on the paramagnetic impurity ion Nd in the series of compounds Re1−x
NdxNi (Re=Ce, La, Y), in which the cerium ions are found either in an intermediate valence state or in the Kondo state. From
the neutron inelastic magnetic scattering spectra on Nd ions, we have reconstructed the crystal field parameters in ReNi compounds
and calculated the CEF level diagram of Ce ions in these compounds as functions of the interion distances Re-Ni. The results
of our calculations are in good agreement with the experimentally determined splitting diagram of the ground-state multiplet
of the Ce ions. We have determined that as the degree of hybridization with the conduction electrons grows the CEF potential
varies considerably and the effective splitting of the 4f shell of the cerium ions increases. The estimated energy scale of the splitting of the ground-state multiplet of the Ce3+ ions in the ReNi CEF (ΔCEF∼15 meV) turns out to be commensurate with the Kondo temperature (T
K
;140 K for CeNi. Analysis indicates that the CEF potential has a substantial effect on the formation of the valence-unstable
ground state of the f shell in this compound.
Zh. éksp. Teor. Fiz. 113, 1731–1747 (May 1998) 相似文献
8.
A method is proposed to deduce the shell correction energy corresponding to the fission transition state shape of nuclei in
the mass region around 200, from an analysis of the first chance fission values of the ratio of fission to neutron widths,
(Γ
f
/Γ
n
)1. The method is applied to the typical case of the fissioning nucleus212Po, formed by alpha bombardment of208Pb. For the calculation of the neutron width, the level densities of the daughter nucleus after neutron emission were obtained
from a numerical calculation starting from shell model single particle energy level scheme. It is shown that with the use
of standard Fermi gas expression for the level densities of the fission transition state nucleus in the calculation of the
fission width, an apparent energy dependence of the fission barrier height is required to fit the experimental data. This
energy dependence, which arises from the excitation energy dependence of shell effects on level densities, can be used to
deduce the shell correction energy at the fission transition state point. It is found that in the case of212Po, the energy of the actual transition state point is higher than the energy of the liquid drop model (LDM) saddle point
by (3 ± 1) MeV, implying significant positive shell correction energy at the fission transition state. Further, the liquid
drop model value of level density parametera is found to be a few per cent smaller for the saddle point shape as compared to its spherical shape. 相似文献
9.
在神光Ⅲ原型装置上利用八路6400J/1ns激光注入1100μm×1850μm的黑腔内产生210eV的高温辐射场,均匀辐照填充氘氘燃料的靶丸实现内爆。实验中选择高气压薄壳靶丸实现纯冲击波聚心内爆。通过闪烁体探测器、中子条纹相机等多套诊断设备获取了中子产额、聚变反应时刻等关键内爆参数。结合一维数值模拟表明,实验测量的中子产额与干净一维数值模拟计算的中子产额之比达到90%;同时通过人为破坏内爆对称性等方式表明,该设计下内爆中子产生机制集中于冲击波聚心,其内爆性能受到高维因素影响极低,从而实现了准一维内爆。 相似文献
10.
G. G. Bunatyan 《Journal of Experimental and Theoretical Physics》1999,89(5):811-820
Since the emission of γ grays unavoidably accompanies β decay, the final state after the β decay of a neutron includes a photon along with a proton, an electron, and an antineutrino, i.e., four particles, rather
than three. Therefore, when only the electron and proton momenta are detected and the γ-ray momentum is not detected in an experiment, the antineutrino momentum cannot be uniquely reconstructed, and only its mean
value over a γ-ray momentum distribution determined from corresponding calculations can be considered. The γ grays are significant for finding the asymmetry parameter B of the antineutrino angular distribution from experiments on the β decay of polarized neutrons, where the electron momentum p directed along the x axis and the projection of the proton momentum P
x onto the x axis are detected, and the neutron polarization vector ξ is parallel or antiparallel to x. Since the γ rays are not detected in such experiments, the antineutrino kinematics are not uniquely specified by the observables p and P
x and can be reconstructed only on the average, so that the antineutrino momentum distribution averaged over a γ-ray momentum distribution is considered. Thus, the exact value of B cannot be obtained from these experiments, but the true value of B can be estimated on the average by considering the mean (most likely) value 〈B〉 and the dispersion (rms deviation) ΔB. The unavoidable uncertainty in the estimate of B amounts to several percent and is thus significant for present-day experiments, which are intended to obtain the value of
B to a very high accuracy of ∼ (0.1–1)%. If electromagnetic interactions are taken into account, measurements of the electron
and proton momentum distributions can also be used to obtain g
A, i.e., the axial β-decay amplitude, to high accuracy.
Zh. éksp. Teor. Fiz. 116, 1505–1522 (November 1999) 相似文献
11.
P. Guazzoni M. Jaskola L. Zetta J.N. Gu A. Vitturi G. Graw R. Hertenberger P. Schiemenz B. Valnion U. Atzrott G. Staudt 《The European Physical Journal A - Hadrons and Nuclei》1998,1(4):365-378
The (p,α) reaction on 90Zr has been studied in a high resolution experiment at an incident proton energy of 22 MeV. The cross section and asymmetry
angular distributions for transitions to 36 levels of 87Y with an excitation energy up to 3 MeV have been measured. DWBA analyses of experimental angular distributions, using either
Woods-Saxon or Double Folded potentials for the exit channel, have been done, allowing either the confirmation of previous
spin and parity values or the assignment of new spin and parity to a large number of states. The structure of low lying states
of 87Y has been studied in the framework of the shell model, using the OXBASH code. With the interaction PMM90 reasonable agreement
is obtained for part of the negative parity spectrum.
Received: 17 November 1997 相似文献
12.
Zurab Berezhiani 《The European Physical Journal C - Particles and Fields》2009,64(3):421-431
It was pointed out recently that oscillation of the neutron n into a mirror neutron n′, a sterile twin of the neutron with exactly the same mass, could be a very fast process with baryon number violation, even
faster than the neutron decay itself. This process is sensitive to magnetic fields and it could be observed by comparing the
neutron loss rates in the UCN storage chambers for different magnetic backgrounds. We calculate the probability of the n−n′ oscillation in the case when a mirror magnetic field B′ is non-zero and show that in this case it can be suppressed or resonantly enhanced by applying the ordinary magnetic field B, depending on its strength and on its orientation with respect to B′. The recent experimental data, under this hypothesis, still allow for an n−n′ oscillation time of order 1 s or even smaller. Moreover, they indicate that the neutron losses are sensitive to the orientation
of the magnetic field. If these hints will be confirmed in future experiments, this would point to the presence of a mirror
magnetic field on the Earth of the order of 0.1 G, or some equivalent spin-dependent force of other origin that makes a difference
between the neutron and mirror neutron states. 相似文献
13.
F. F. Karpeshin 《Physics of Atomic Nuclei》2011,74(7):951-957
It is shown that the Strutinsky-Denisov induced polarization mechanism leads to the appearance of the prompt electric dipole
radiation from fission fragments of 235Uby thermal neutrons in the domain of around 5 MeV. The probability of the radiation is at the level of 0.001 per fission,
which is in agreement with experiment. The angular distribution exhibits left-right asymmetry with respect to the direction
of the neutron polarization axis. That means that the emission of gamma quanta at the given angle depends on the neutron polarization.
The asymmetry is at the level of 10−3. The study of this effect will give a direct information about the scission configuration, nuclear viscosity, and dissipation
properties of the collective energy of the surface vibration in fragments with large amplitude. This will give a complete
picture of the process of snapping back the nuclear surface. 相似文献
14.
W. Zuo A. Lejeune U. Lombardo J.F. Mathiot 《The European Physical Journal A - Hadrons and Nuclei》2002,14(4):469-475
Brueckner calculations including a microscopic three-body force have been extended to isospin-asymmetric nuclear matter. The
effects of the three-body force on the equation of state and on the single-particle properties of nuclear matter are discussed
with a view to possible applications in nuclear physics and astrophysics. It is shown that, even in the presence of the three-body
force, the empirical parabolic law of the energy per nucleon vs. isospin asymmetry β = (N - Z)/A is fulfilled in the whole asymmetry range 0≤β≤1 up to high densities. The three-body force provides a strong enhancement
of the symmetry energy which increases with density in good agreement with the predictions of relativistic approaches. The
Lane's assumption that proton and neutron mean fields linearly vary vs. the isospin parameter is violated at high density due to the three-body force, while the momentum dependence of the mean
fields turns out to be only weakly affected. Consequently, a linear isospin split of the neutron and proton effective masses
is found for both cases with and without the three-body force. The isospin effects on multifragmentation events and collective
flows in heavy-ion collisions are briefly discussed along with the conditions for direct URCA processes to occur in the neutron
star cooling.
Received: 18 February 2002 / Accepted: 16 May 2002 相似文献
15.
The neutron flux distribution on the wall of a toroidal CTR device with strongly elongated cross section is calculated. On the inner and outer cylindrical walls (belt-pinch device) the flux distribution has a plateau region with a half-width equal to about the height of the plasma. The maximum flux is found on the outer cylinder and in the symmetry plane (z 0=0). The neutron flux asymmetry and reductionη of the mean wall loading are determined. For standard data anη of 57% is computed. This is mainly due to the flux profiles on the cylindrical walls and does not depend sensitively on the toroidal curvature. For standard parameters the inner cylinder absorbs 22.6%, the outer cylinder 68.6% and the end plates together 8.8% of the total neutron emission. The corresponding values for a straight device with the same coil and plasma cross section are 44%, 44% and 12%. A reduction of toroidal curvature diminishes flux asymmetry between the inner and outer cylinders. The maximum flux and minimumη-value are obtained at a large torus radius equal to two times the coil width. For small aspect ratios (R t W0.5) the neutron flux through the inner cylinder becomes so small that its interior may be filled with a material other than a blanket material, e.g. with an iron core. 相似文献
16.
B. R. Meshcherov A. I. Fomin S. M. Chernyavskii P. Geltenbort R. I. Zakharchenya 《JETP Letters》1998,67(5):307-311
The spectral dependence of the transmission of a collimated neutron beam by disordered quartz microstructures is measured.
The observed mean free paths are very short, down to 200 nm. The results show that scattering with a characteristic value
of the parameter kl⩽10 is realized near the neutron total external reflection edge.
Pis’ma Zh. éksp. Teor. Fiz. 67, No. 5, 291–295 (10 March 1998) 相似文献
17.
M. V. Sazhin S. D. Ustyugov V. M. Chechetkin 《Journal of Experimental and Theoretical Physics》1998,86(4):629-635
This paper discusses the gravitational radiation that accompanies the formation of a rotating protoneutron star. Mainly large-scale
entropy inhomogeneities develope inside the star. As a result, bubbles of hot nuclear substance are formed, and convective
motions arise: bubbles of hot neutron matter float to the surface of the star, while cold matter sinks to its center. Such
large-scale motions of material give rise to an inhomogeneous mass distribution inside the star. Variable asymmetry appears
in the mass distribution, and this causes gravitational radiation.
Zh. éksp. Teor. Fiz. 113, 1153–1166 (April 1998) 相似文献
18.
S. G. Kadmenskii S. S. Kadmenskii D. E. Lyubashevskii 《Bulletin of the Russian Academy of Sciences: Physics》2010,74(4):528-530
T-odd asymmetries in the angular distributions of evaporation neutrons emitted by thermalized fission fragments in the fission
of axially symmetric deformed nuclei by cold polarized neutrons are investigated within the quantum theory of fission. The
asymmetries in question are due to the anisotropy of angular distributions of evaporation neutrons in the center-of-mass systems
of the fission fragments, and this anisotropy arises from the orientation of large-value fission fragment spins in the direction
perpendicular to the direction K
0 of the symmetry axis of the fissioning nucleus at the time of its scission, caused by zero wriggling vibrations of the fissioning
nucleus. The angle of rotation of the vector k
0 with respect to the asymptotic direction k
0 of the fissioning nucleus symmetry axis is calculated with allowance for the interference of fission amplitudes of neutron
resonances excited in a fissioning nucleus as it captures an incident neutron. It is shown that the T-odd asymmetry coefficient for evaporation neutrons is close in structure and value to the analogous coefficient for evaporation
γ-rays. 相似文献
19.
M. Lindroos J. Billowes C. Broude G. Goldring H. Haas M. Hass L. Mueller M.R. Pearson L. Weissman 《Hyperfine Interactions》2000,129(1-4):109-118
We report here on an ongoing experimental program initiated at the ISOLDE facility at CERN for the measurement of magnetic
moments of short-lived radionuclides, with the emphasis on magnetic moments of mirror nuclei in far-from-stability regions.
The nuclei are polarized by the tilted foil technique and the resulting 0–180○ βasymmetry is monitored as a function of rf frequency applied in an NMR setup. In order to achieve sufficiently high energy
for transmission through the foils, the experimental setup is mounted on a high voltage platform. The first experiment in
this program was the measurement of the βasymmetry and the NMR resonance for the ground state of 23Mg (I=3/2, T1/2=11.3 s), yielding μ=−0.533(6) nm. Improvements to the experimental setup are presently being designed, to be used in conjunction
with the new developments at ISOLDE for obtaining high charge-state ions from the EBIS (REX-ISOLDE) ion source. This will
help pave the way for measurements of magnetic moments of T=3/2 nuclei in the s–d shell and of T=1/2 f-shell nuclei. The study
of relaxation times and other solid-state phenomena in semiconductors and other materials of interest using this technique
is also contemplated.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
20.
J. E. Koster E. D. Davis C. R. Gould D. G. Haase N. R. Roberson L. W. Seagondollar 《Hyperfine Interactions》1992,75(1-4):165-172
We describe a search for the time reversal non-invariant five-fold correlation (s·Ixk)(I·k) in the scattering of 2 MeV polarized neutrons from an aligned165Ho target. Here s is the neutron spin,I is the target spin, andk is the neutron momentum vector. Differences in transmission were sought when s was reversed. The target was a single crystal
of holmium, cryogenically aligned with a specially built dilution refrigerator. Rotating the target axis of alignment while
cold permits the parity-even, five-fold correlation to be identified among other spin-dependent correlations in the forward
elastic scattering amplitude. An analyzing power was found to be (1±6)×10−4, consistent with time reversal invariance.We obtain a bound of 5×10−3 for αT, the ratio of T-odd to T-even couplings in the effective nucleon-nucleon interaction. 相似文献