共查询到20条相似文献,搜索用时 31 毫秒
1.
D. O. Eremenko A. A. Dermenev V. A. Drozdov S. Yu. Platonov O. V. Fotina O. A. Yuminov 《Physics of Atomic Nuclei》2009,72(10):1651-1658
A combined dynamical and statistical approach to describing induced fission of heavy nuclei is proposed. This approach takes
into account the nuclear-dissipation phenomenon and the double-humped structure of the fission barrier. A method that is intended
for calculating the angular distribution of fission fragments and which is applicable over a broad range of excitation energies
is discussed. The potential of the approach is demonstrated by addressing the problems of self-consistently describing experimental
data on fission probabilities for plutonium and americium isotopes, the yields of shape isomers in the α+238U reaction at alpha-particle energies in the range E
α
= 20–32 MeV and the d+242,240Pu reactions at deuteron energies in the range E
d
= 20–30 MeV, fission times in the α + 238U reaction at alpha-particle energies in the range E
α
= 20–32 MeV, and angular distributions of fission fragments in the α + 238U, 237Np reactions at alpha-particle energies in the range E
α
= 20–100 MeV. 相似文献
2.
S. Sodaye K. Sudarshan B.S. Tomar A. Goswami S. Mukherjee K. Mahata 《The European Physical Journal A - Hadrons and Nuclei》2002,14(3):371-376
Kinetic-energy spectra and angular distribution of projectile-like fragments have been measured in the reaction of 84 MeV
12C on 169Tm, using the surface barrier silicon-based ΔE-E telescopes. The fragments close to the projectile show typical spectra of quasi-elastic transfer reactions, which were found
to be in agreement with the calculations based on the direct surface transfer reaction model. A significant cross-section
of fast alpha-particles was found at forward angles, reminiscent of incomplete fusion reactions, which could be explained
in terms of the direct surface transfer reaction model after taking into account the level density of continuum states in
the heavy reaction product. The results have been explained in terms of the continuous evolution of the reaction mechanism
as a function of the mass transfer.
Received: 13 March 2002 / Accepted: 3 May 2002 相似文献
3.
W. von Oertzen B. Gebauer G. Efimov V. Zherebchevsky Tz. Kokalova S. Thummerer Ch. Schulz H. G. Bohlen D. Kamanin C. Beck D. Curien P. Papka M. Rousseau G. Royer G. de Angelis 《The European Physical Journal A - Hadrons and Nuclei》2008,36(3):279-288
Coincidences between two heavy fragments have been measured from the fission of 56Ni compound nuclei formed in the 32S + 24Mg reaction at E
lab( ^32S ) = 165.4 MeV. A unique experimental set-up consisting of two large-area position-sensitive (x, y) gas detector telescopes has been used allowing the complete determination of the observed fragments and their momentum vectors.
In addition to binary fission events with subsequent particle evaporation, narrow out-of-plane correlations are observed for
two fragments emitted in purely binary events and in events with a missing charge consisting of 2α - and 3α -particles (12C). These events are interpreted as ternary cluster decay from 56Ni nuclei at high angular momenta through hyper-deformed shapes. 相似文献
4.
With the help of a combined LEED- and Auger-investigation, the surface of a platinum (111) crystal was cleaned first. Then,
the spectrum of the characteristic energy losses for both contaminated and cleaned surfaces is studied. On the cleaned surface
the following losses were found: ΔE
1=7.4 eV, ΔE
2=13.5 eV, ΔE
3=24.8 eV, ΔE
4=31.8 eV, ΔE
5=45.1 eV, ΔE
6=54.1 eV, ΔE
7=71.2 eV.
The present results are compared with the measurement of other investigators. In particular, in good agreement with optical
measurements we identify ΔE
1 and ΔE
2 as interband transitions, and ΔE
3 and ΔE
4 as surface and volume plasma loss, respectively. 相似文献
5.
Abstract Annealing behaviour of heavy ion radiation damage in muscovite is studied at different temperatures. The activation energies Ea for annealing of heavy ion tracks of different energies, viz. 93Nb(18.0 MeVn ?1), 208Pb(17.0MeVn ?1), 238U(10.0MeVn ?1) and 252Cf(fission fragments), are found to be the same (~0.97 eV). The concept of a single activation energy as an intrinsic property of the detector seems to be fully justified. 相似文献
6.
Ž. Todorović S. Savović S. Jokić 《The European Physical Journal A - Hadrons and Nuclei》1998,2(3):295-300
The processes of production of fragments with Z≥ 8 in the interaction of 12.7 GeV 4He with U, Pb, Au and Ag have been analyzed using the polycarbonate track detector Makrofol. The sandwich technique was used
which enables direct observation of multiply charged fragment emission by a single nucleus. The decay channels ending with
one, two, or more (three, four) fragments were detected. A classification scheme based on the multiplicity of heavy fragments
with Z > 20 was used in order to identify the events belonging to the different reaction channels. The cross sections, excitation
energies and multiplicities of intermediate-mass fragments 8 ≤Z≤ 20 have been determined for the various reaction mechanisms, and their variation as a function of the target mass has been
investigated.
Received: 28 November 1997 / Revised version: 24 April 1998 相似文献
7.
D.C. Biswas B.K. Nayak M. Cinausero B. Fornal G. Viesti D. Bazzacco M. DePoli D. Fabris E. Fioretto M. Lunardon D.R. Napoli G. Nebbia G. Prete C.A. Ur G. Vedovato 《The European Physical Journal A - Hadrons and Nuclei》1999,4(4):343-348
The high energy γ-ray emission accompanying the spontaneous fission of 252Cf has been measured in coincidence with individual fission fragments selected by discrete γ-ray transitions. The enhancement
of the γ-ray emission probability in the energy range Eγ= 3–8 MeV has been observed for the fission fragments in the region of nearly symmetric mass splitting, confirming results
reported in previous investigations. The γ-γ coincidence technique employed in the present work clearly demonstrate that the
major contribution to this enhancement is caused by the fission channels where one fragment is near to the N= 82 or Z= 50 shell closures. The high energy γ-ray emission probability does not show any significant dependence on the number of
neutrons emitted in the fission process, supporting the hypothesis that high energy γ-rays are mainly emitted from the fragments
after the neutron evaporation.
Received: 22 December 1998 相似文献
8.
The fission decay of highly neutron-rich uranium isotopes is investigated which shows interesting new features in the barrier
properties and neutron emission characteristics in the fission process. 233U and 235U are the nuclei in the actinide region in the beta stability valley which are thermally fissile and have been mainly used
in reactors for power generation. The possibility of occurrence of thermally fissile members in the chain of neutron-rich
uranium isotopes is examined here. The neutron number N = 162 or 164 has been predicted to be magic in numerous theoretical studies carried out over the years. The series of uranium
isotopes around it with N = 154–172 are identified to be thermally fissile on the basis of the fission barrier and neutron separation energy systematics;
a manifestation of the close shell nature of N = 162 (or 164). We consider here the thermal neutron fission of a typical representative 249U nucleus in the highly neutron-rich region. Semiempirical study of fission barrier height and width shows that 250U nucleus is stable against spontaneous fission due to increase in barrier width arising out of excess neutrons. On the basis
of the calculation of the probability of fragment mass yields and the microscopic study in relativistic mean field theory,
this nucleus is shown to undergo exotic decay mode of thermal neutron fission (multi-fragmentation fission) whereby a number
of prompt scission neutrons are expected to be simultaneously released along with the two heavy fission fragments. Such properties
will have important implications in stellar evolution involving r-process nucleosynthesis.
相似文献
9.
Several characteristics of fission accompanied by long range alpha particles (LRA) have been studied in the thermal neutron
induced fission of235U. The kinetic energies of fission fragments and the LRA were measured with a back-to-back ionization chamber and semiconductor
detectors respectively. The kinetic energies of the two fragments and the LRA in LRA fission, along with the energies of pair
fragments in the normal binary fissions, were recorded event by event on a magnetic tape by means of a four-parameter data
acquisition system. The data were analysed to study the dependence of different quantities in LRA fission on the fragment
mass ratio, LRA energy and the total kinetic energy of the fission fragments. It is seen that the most probable energy of
LRA increases significantly for near symmetric mass divisions. The total kinetic energy for all mass ratios in LRA fission
is found to be (2.6±0.7) MeV larger than that in binary fission. The difference in the total kinetic energies in LRA and binary
fissions is seen to be dependent on mass ratio. This result may suggest that the scission configuration in LRA fission is
different for different mass ratios. Correlations between the fission fragment and LRA energies have been studied for several
mass ratios. It is seen that the most probable fragment kinetic energyĒ
k varies nearly linearly with the LRA energyE
a for various mass divisions but the variation of the most probable LRA energyĒ
a with fragment kinetic energyE
k is found to deviate from linearity for several mass ratios. From a least square fit to the variation ofĒ
k withE
a it is found that the slope (dĒ
k/dEa) increases with the increase in mass ratio. The present results are discussed to arrive at a better understanding of the
scission configuration in the fission accompanied by LRA emission. 相似文献
10.
V. A. Rubchenya A. A. Alexandrov S. V. Khlebnikov V. G. Lyapin V. A. Maslov Yu. E. Penionzhkevich G. Prete Yu. G. Sobolev G. P. Tyurin W. H. Trzaska D. N. Vakhtin E. Vardaci 《Physics of Atomic Nuclei》2006,69(8):1388-1398
The dynamics of the excited superheavy system with Z = 118 in the reaction 86Kr + 208Pb at E
Kr = 460, 500, and 600 MeV has been investigated. The mass and kinetic energy of binary fragments were measured by the time-of-flight
method. Double-differential distributions of protons and α particles were measured in coincidence with fragments. The proton
spectra can be described considering only evaporation from fragments. Evidence of the neck fragmentation was obtained from
analysis of double-differential α spectra. Properties of the α-particle neck fragmentation component are close to those known
from the ternary fission of actinide nuclei, but the multiplicity is much larger than can be expected from extrapolation of
the ternary fission data.
The text was submitted by the authors in English. 相似文献
11.
Binary and ternary cluster decay of 60Zn compound nuclei at high angular momentum, formed in the 36Ar + 24Mg reaction at E
lab(36Ar) = 195 MeV, has been measured in a unique kinematic coincidence setup consisting of two large area position sensitive (x, y) gas detector telescopes with Bragg-ionization chambers (BRS). The BRS provides the opportunity to measure the reaction angles
in-and out-of-plane, and through Bragg-curve spectroscopy to achieve a complete identification of the nuclear charge for different
final channels. We observed very narrow out-of-plane angular correlations for two heavy fragments emitted either in purely
binary events or in events with a missing mass consisting of 2 and 3α particles. These narrow correlations are interpreted
as ternary fission decay from compound nuclei at high angular momenta through an elongated (hyperdeformed) shape with a very
large moment of inertia. In these stretched configurations, the lighter mass in the neck region remains at rest or with very
low momentum in the center of mass.
The text was submitted by the authors in English. 相似文献
12.
S. V. Zuev E. S. Konobeevskii V. M. Lebedev M. V. Mordovskoi A. V. Spasskii S. I. Potashev I. M. Sharapov 《Bulletin of the Russian Academy of Sciences: Physics》2012,76(4):396-399
A procedure for and the results from the energy calibration of a ΔE-E scintillation telescope used in experiments performed at the INR to study the nd-breakup reaction are described. The telescope
was calibrated using a beam of α particles with an energy of 30 MeV of the U-120 cyclotron (INP). Secondary protons from the
10,11B(α, p) reaction were recorded by the ΔE-E telescope at several recording angles and with the application of different absorbing foils. The calibration results from
the ΔE-E telescope were obtained over the interval E
p
= 10–30 MeV, allowing us to measure the energies of secondary protons in the ndbreakup reaction when the energy of primary
neutrons is 20–60 MeV. 相似文献
13.
The effect of doping CdIn2S4 single crystals by copper (3 mol %) on their X-ray dosimetric characteristics is investigated. It is found that the characteristic
X-ray conductivity of CdIn2S4〈Cu〉 single crystals increases 3–16 times compared with undoped CdIn2S4 at effective radiation hardness V
a = 25−50 keV and dose rate E = 0.75−78.05 R/min. Moreover, the persistence of the crystal characteristics completely disappears and the supply voltage
of a CdIn2S4〈Cu〉 X-ray detector decreases fivefold. The dependence of the steady X-ray-induced current in CdIn2S4〈Cu〉 on the X-ray dose is described as ΔI
E, 0 ∝ E
α, where 0.6 ≤ α ≤ 1.8. 相似文献
14.
RK Choudhury 《Pramana》2001,57(2-3):585-600
Nuclear fission process involves large scale shape changes of the nucleus, while it evolves from a nearly spherical configuration
to two separated fission fragments. The dynamics of these shape changes in the nuclear many body system is governed by a strong
interplay of the collective and single particle degrees of freedom. With the availability of heavy ion accelerators, there
has been an impetus to study the nuclear dynamics through the investigations of nucleus-nucleus collisions involving fusion
and fission process. From the various investigations carried out in the past years, it is now well recognized that there is
large scale damping of collective modes in heavy ion induced fission reactions, which in other words implies that nuclear
motion is highly viscous. In recent years, there have been many experimental observations in heavy ion induced fission reactions
at medium bombarding energies, which suggest possible occurrence of various non-equilibrium modes of fission such as quasi-fission,
fast fission and pre-equilibrium fission, where some of the internal degrees of freedom of the nucleus is not fully equilibrated.
We have carried out extensive investigations on the fission fragment angular distributions at near barrier bombarding energies
using heavy fissile targets. The measured fragment anisotropies when compared with the standard saddle point model (SSPM)
calculations show that for projectile-target systems having zero or low ground state spins, the angular anisotropy exhibits
a peak-like behaviour at the sub barrier energies, which cannot be explained by the SSPM calculations. For projectiles or
targets with large ground state spins, the anomalous peaking gets washed out due to smearing of the K-distribution by the intrinsic entrance channel spins. Recently studies have been carried out on the spin distributions of
fission fragments through the gamma ray multiplicity measurements. The fission fragments acquire spin mainly from two sources:
(i) due to rigid rotation of the nascent fragments at scission and (ii) due to statistical excitation of the spin bearing
collective modes in the fissioning nucleus. One of the collective modes — the tilting mode depends on the K quantum number and is responsible for the emission angle dependence of fragment spin. In our studies, we have shown conclusively
that the collective statistical spin modes get strongly suppressed for high K values corresponding to large rotational frequencies along the fission axis. These results bring out the importance of the
dynamical effects in the heavy ion induced fusion-fission reactions. The present article will review the work carried out
on the above aspects in heavy ion fission reactions as well as on the fission time scales, and some of the recent studies
on the mass-energy correlations of fission fragments at near-barrier bombarding energies. 相似文献
15.
E. N. Elekina A. A. Krutov A. P. Martynenko 《Physics of Particles and Nuclei Letters》2011,8(4):331-336
On the basis of quasi-potential approach to the bound state problem in QED we calculate the vacuum polarization, recoil and
structure corrections of orders α5 and α6 to the fine splitting interval ΔE
fs = E(2P
3/2) − E(2P
1/2) in muonic 24He ion. The resulting value ΔE
fs = 146180.68 μeV provides reliable guideline in performing a comparison with the relevant experimental data. 相似文献
16.
D. Fong J. H. Hamilton A. V. Ramayya J. K. Hwang C. Goodin K. Li J. Kormicki J. O. Rasmussen Y. X. Luo S. C. Wu I. Y. Lee A. V. Daniel G. M. Ter-Akopian G. S. Popeko A. S. Fomichev A. M. Rodin Yu. Ts. Oganessian M. Jandel J. Kliman L. Krupa J. D. Cole M. A. Stoyer R. Donangelo W. C. Ma 《Physics of Atomic Nuclei》2006,69(7):1161-1167
The hot bimodal fission of 252Cf is reexamined with new high-statistics data. We constructed a γ-γ-γ coincidence cube for binary fission and LCP-gated γ-γ matrix for ternary fission. By identifying the secondary fission fragments from their γ-ray transitions, we measured the yields for various fission splits. The normal neutron yield distribution is found to be
Gaussian for Xe-Ru. However, the binary fission split of Ba-Mo is found to exhibit a bimodal neutron distribution with the
“hot mode” corresponding to ≈3.1% of the total yield. In α ternary fission, the first measurements of yields for specific fission splits are presented. The Te-α-Ru and Xe-α-Mo neutron yields fit well with a single mode, but the Ba-α-Zr split shows evidence for an enhanced hot mode with an intensity of ≈13.8% of the normal mode.
The text was submitted by the authors in English. 相似文献
17.
Exotic decay of some heavy nuclei with Z≥100 formed in heavy ion ‘cold fusion’ reaction were studied taking interacting barrier consisting of Coulomb and proximity
potential. Calculated half-life time shows that some modes of decay are well within the present upper limit for measurements
(T
1/2<1030 s). Cluster formation probabilities are calculated for different clusters within fission model. It is found that transition
from cluster mode to fission mode take place at mass of the cluster, A
2=20 in exotic decay which is comparable with the value A
2=16 of Shanmugam et al based on cubic plus Yukawa plus exponential model (CYEM). 相似文献
18.
On the basis of quasipotential approach to the bound state problem in QED we calculate the vacuum polarization, relativistic,
recoil, structure corrections of orders α
5 and α
6 to the fine structure interval ΔE
fs = E(2P
3/2) − E(2P
1/2) and to the hyperfine structure of the energy levels 2P
1/2 and 2P
3/2 in muonic 23He ion. The resulting values ΔE
fs = 144 803.15 μeV, Δ$
\tilde E
$
\tilde E
hfs(2P
1/2) = −58 712.90 μeV, Δ$
\tilde E
$
\tilde E
hfs(2P
3/2) = −24 290.69 μeV provide reliable guidelines in performing a comparison with the relevant experimental data. 相似文献
19.
HADI ESLAMIZADEH 《Pramana》2012,78(2):231-236
Data on shape isomer yield for α + 235U reaction at Ea lab = E_\alpha ^{\rm lab} =\,\,20–29 MeV are analysed in the framework of a combined dynamical–statistical model. From this analysis, information on the
double humped fission barrier parameters for some Pu isotopes has been obtained and it is shown that the depth of the second
potential well should be less than the results of statistical model calculations. 相似文献
20.
A powder diffractometer with a linear position sensitive detector (PSD) has been designed and fabricated at BARC. The system
is in operation at Dhruva reactor. The PSD has been tested for the position linearity and the uniformity of efficiency. The
resolution Δd/d of the diffractometer has been found to be 1·3%. The data can be analyzed using profile refinement technique. 相似文献