共查询到20条相似文献,搜索用时 31 毫秒
1.
D.C. Biswas R.K. Choudhury M. Cinausero B. Fornal D.V. Shetty G. Viesti D. Fabris E. Fioretto M. Lunardon G. Nebbia G. Prete D. Bazzacco M. DePoli D.R. Napoli C.A. Ur G. Vedovato 《The European Physical Journal A - Hadrons and Nuclei》2000,7(2):189-195
Measurements of fission fragment yields and neutron multiplicities have been carried out for the Mo-Ba fragment pairs in
the spontaneous fission of 252Cf, using the γ-ray spectroscopy technique to analyze γ-γ-γ coincidence data. Prompt γ -ray multiplicities were also measured
as a function of the number of neutrons emitted in the fission process leading to the Mo-Ba partition. We do not observe the
enhancement in the yields of events with high neutron emission multiplicity (νn > 7) that has been associated to a second fission mode leading to the production of hyperdeformed Ba fragments, as reported
in some earlier studies. The average γ-ray multiplicity is found to be rather weakly dependent on the number of neutrons emitted
in the fission process.
Received: 21 July 1999 / Revised version: 19 November 1999 相似文献
2.
J. H. Hamilton A. V. Ramayya J. K. Hwang G. M. Ter-Akopian A. V. Daniel J. O. Rasmussen S. -C. Wu R. Donangelo C. J. Beyer J. Kormicki X. Q. Zhang A. M. Rodin A. S. Fomichev G. S. Popeko J. Kliman L. Krupa M. Jandel Yu. Ts. Oganessian G. Chubarian D. Seweryniak R. V. F. Janssens W. C. Ma R. B. Piercey W. Greiner J. D. Cole 《Physics of Atomic Nuclei》2002,65(4):645-652
The spontaneous fission (SF) of 252Cf has been studied via γ-γ-γ coincidence and light charged particle—γ-γ coincidence with Gammasphere. The yields of correlated Mo-Ba pairs in binary fission with 0–10 neutron emission have been remeasured with an uncompressed cube. The previous hot fission mode with 8–10 neutron emission seen in the Mo-Ba split is found to be smaller than earlier results but still present. New 0n binary SF yields are reported. By gating on the light charged particles detected in ΔE-E detectors and γ-γ coincidence with Gammasphere, the relative yields of correlated pairs in alpha ternary fission with zero to 6n emission are observed for the first time. The peak occurs around the α2n channel. A number of correlated pairs are identified in ternary fission with 10Be as the light charged particle. We observed only cold, 0n 10Be and little, if any, hot, xn 10Be channels. 相似文献
3.
J. H. Hamilton A. V. Ramayya J. K. Hwang G. M. Ter-Akopian A. V. Daniel T. N. Ginter C. J. Beyer J. Kormicki X. Q. Zhang A. M. Rodin A. S. Fomichev J. Kliman L. Krupa J. Jandel Yu. Ts. Oganessian W. Greiner D. N. Poenaru G. Chubaryan D. Seweryniak R. V. F. Janssens J. O. Rasmussen S. C. Wu R. Donangelo W. C. Ma R. B. Piercey J. D. Cole 《Acta Physica Hungarica A》2001,14(1-4):161-168
The spontaneous fission of 252Cf has been studied via γ-γ-γ coincidence and γ-γ light charged particle coincidence with Gammasphere. The binary fission yields of correlated Mo?Ba pairs with 0–10 neutron emission have been remeasured. The existence of “hot” fission mode with 8–10 neutron emission seen previously in the Mo?Ba split is confirmed but with lower intensities. By gating on the light charged particles detected in ΔE-E detectors and a γ ray in one partner, the relative yields of correlated pairs in alpha ternary SF with zero to 6n emission are observed for the first time with the distribution peaked at 2.5n. New correlated pairs are identified in 10Be ternary SF. We observed essentially only cold, On 10Be and little, if any, hot, xn 10Be. New γ-γ-γ data with 2.3 times the total events show weak non-Doppler broadened high energy peaks in coincidence with transitions in correlated pairs in 10Be SF shifted by the same 6,1 to 26 keV from the 2-0 energy in 10Be as seen earlier. 相似文献
4.
A. V. Daniel J. H. Hamilton A. V. Ramayya A. S. Fomichev Yu. Ts. Oganessian G. S. Popeko A. M. Rodin G. M. Ter-Akopian J. K. Hwang D. Fong C. Goodin K. Li J. O. Rasmussen D. Seweryniak M. Carpenter C. J. Lister Sh. Zhu R. V. F. Janssens J. Batchelder J. Kliman L. Krupa W. -C. Ma S. J. Zhu L. Chaturvedi J. D. Cole 《Physics of Atomic Nuclei》2006,69(8):1405-1408
A new experiment devoted to the fission of 252Cf is described. It continued a series of our experiments based on correlation measurements of γ rays emitted by fission fragment pairs. The measurements of γ-γ and γ-γ-γ coincidences were done at Gammasphere with closed 252Cf sources. The open source was used for the first time in the last experiment. Fission fragment detectors were arranged in
the center hole of Gammasphere. Correlations between fission fragment masses, total kinetic energy, and γ rays were observed. The first, preliminary results of data analysis are discussed.
The text was submitted by the authors in English. 相似文献
5.
N. Nenoff P. Bringel A. Bürger S. Chmel S. Dababneh M. Heil H. Hübel F. Käppeler A. Neußer-Neffgen R. Plag 《The European Physical Journal A - Hadrons and Nuclei》2007,32(2):165-173
An activation technique was used to investigate relative yields of fission products from the reaction 232Th(n, f ) for neutron energies between 1.3 and 1.8MeV covering the region around the first hyperdeformed resonances. Intensities
of characteristic γ-ray transitions were analyzed to search for changes in the mass distribution for neutron energies corresponding to the resonances
and below the resonances. Relative increases in yield between 7 and 23% are observed for A ≈ 100 and 132 in the resonance region around 1.6MeV. It is proposed that the yield enhancement of daughter nuclei of the
preformed fragments 132Sn and 101Zr arises from cold fission of a di-cluster configuration. The experimental results support theoretical predictions for the
existence of hyperdeformed octupole shapes based on the di-nuclear configuration 132Sn + 101Zr. 相似文献
6.
The yield and energy distribution of long-range alpha-particles (lra) emitted from neutron-induced fission of235U have been measured at neutron energies; thermal, 125±12, 155±11, 185±10, 210±9, 240±9, 365±50 and 480±45 keV. The long-range
alpha-particles were detected in cellulose nitrate track detector foils. Results showed an increase of about 50% in the yield
at neutron energies in the region 150 keV≤E
n≤220 keV as compared to that of thermal neutrons. A calculation has been carried out to extract thelra to binary fission ratio forp-wave neutron induced fission. 相似文献
7.
G. V. Danilyan J. Klenke V. A. Krakhotin Yu. N. Kopach V. V. Novitsky V. S. Pavlov P. B. Shatalov 《Physics of Atomic Nuclei》2011,74(5):671-674
Study of the T-odd three-vector correlation in the emission of prompt neutrons from 235U fission by polarized cold neutrons has been continued at the facility MEPHISTO of the FRM II reactor (Technical University
of Munich). The sought correlation was not found within experimental error of 2.3 × 10−5. The upper limit for the asymmetry coefficient has been set to |D
n
| < 6 × 10−5 at 99% confidence level, whereas for ternary fission correlation coefficient D
α
= (170±20) × 10−5. This limit casts doubt on a model that explains the three-vector correlation in ternary fission by the Coriolis mechanism.
At the same time, five-vector correlation in the emission of prompt fission neutrons has been measured, which describes the
rotation of the fissioning nucleus at the moment it breaks (ROT effect). At the angle 22.5° to the fission axis, the correlation
coefficient was found to be (1.57 ± 0.20) × 10−4, while at the angle of 67.5° it is zero within the experimental uncertainty. The existence of ROT effect in the emission
of prompt fission neutrons can be explained by the anisotropy of neutron emission in the rest frame of the fragment (fission
fragments are aligned with respect to the axis of deformation of the fissioning nucleus), similar to the mechanism of ROT
effect in the emission of prompt γ-rays. 相似文献
8.
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
9.
D. E. Lyubashevsky S. G. Kadmenskii 《Bulletin of the Russian Academy of Sciences: Physics》2010,74(6):791-794
The principal values for the even and odd components of the amplitudes of the angular distributions of α particles emitted
as the third particles in true low-energy ternary fission of nuclei are calculated within the quantum theory of fission using
natural approximations for the dependence of the potential scattering phases of the α particle on its orbital momenta and
experimental angular distributions, unperturbed by the fissioning nucleus rotation, of these third α particles. Knowing the
angular dependences of these components, we can estimate the angular dependences of the T-odd ROT and TRI asymmetry coefficients for the ternary fission of actinide nuclei induced by cold polarized neutrons. 相似文献
10.
V. E. Bunakov S. G. Kadmenskii S. S. Kadmenskii 《Bulletin of the Russian Academy of Sciences: Physics》2010,74(4):522-527
Conditions for the appearance and observation of prescission γ-rays emitted by a fissioning nucleus before its separation
into fission fragments were investigated within the quantum theory of fission. It was demonstrated that these conditions can
be fulfilled in the γ-decay of giant electric isovector dipole resonances in a fissioning nucleus that become excited due
to the nonadiabaticity of the collective deformation motion of the nucleus at the final stages of its prefission evolution.
Angular and energy distributions of prescission γ-rays emitted by unpolarized fissioning nuclei were analyzed. Characteristics
of T-odd asymmetries in angular distributions of prescission γ-rays were investigated for fission of unpolarized target nuclei
induced by polarized cold neutrons, and these correlations were shown to be similar in nature to the T-odd ROT correlations earlier found for α-particles emitted in ternary nuclear fission. 相似文献
11.
A. V. Andreev G. G. Adamian N. V. Antonenko S. P. Ivanova S. N. Kuklin W. Scheid 《The European Physical Journal A - Hadrons and Nuclei》2006,30(3):579-589
The ternary system with a light nucleus between two heavy fragments is assumed to appear from the binary configuration near
scission. The formation of a third light nucleus in the binary system is considered. The calculated charge distributions in
spontaneous ternary fission of 252Cf and in induced ternary fission of 56Ni are compared with the available experimental data. The neutron multiplicity from the fission fragments is described. The
fine structures of the TKE-mass distribution are predicted. 相似文献
12.
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
13.
Yu. P. Gangrsky V. I. Zhemenik N. N. Kolesnikov V. G. Lukashik B. N. Markov G. V. Myshinskiy O. D. Maslov G. A. Bozhikov 《Physics of Atomic Nuclei》2010,73(9):1477-1481
The yields of 135Cs nuclei in a high-spin (19/2) isomeric state and of nuclei neighboring it were measured for photonuclear reactions of the
(γ, f) and (γ, α) types. The experiments in question were performed by using bremsstrahlung from a microtron at the maximum electron energy
of 25 MeV. The product nuclei were identified by their half-lives and by the lines of gamma radiation emitted in their decay,
and the reaction yields R were determined by the ratios of the intensities of these lines to the bremsstrahlung flux. The cross sections for isomer
production were calculated, and the angular momenta of product nuclei immediately before the cascade of gamma transitions
populating the ground or an isomeric nuclear state were evaluated on the basis of these results. An enhanced yield of the
high-spin isomer of 135Cs in the fission reaction in relation to the respective (γ, α) reaction and in relation to the results of the calculations is found. 相似文献
14.
Y. Toh S. Yamada A. Taniguchi Y. Kawase 《The European Physical Journal A - Hadrons and Nuclei》1999,4(3):233-238
The structure of 152Nd, produced via β− decay of 152Pr, has been investigated using γ-γ coincidence, γ-γ angular correlation, and β-γ-γ triple coincidence measurements. Praseodymium
activities were obtained by the thermal neutron fission of 235U and collected by the on-line isotope separator KUR-ISOL. Nineteen γ-rays and four excited states were newly found. The spins
of six exited states were determined and the parities of three of them were also deduced. The spin and parity of the 152Pr ground state, which were previously considered as 4−, are proposed to be 4+ by the present study.
Received: 19 October 1998 / Revised version: 22 December 1998 相似文献
15.
F.P. Heßberger S. Hofmann I. Kojouharov D. Ackermann S. Antalic P. Cagarda B. Kindler B. Lommel R. Mann A.G. Popeko S. Saro J. Uusitalo A.V. Yeremin 《The European Physical Journal A - Hadrons and Nuclei》2002,15(3):335-342
The radioactive decay of 217Pa was investigated by means of α-γ-spectroscopy. Fine structure in the ground-state α-decay was established. Ambiguities
in the fine structure of the α-decay of the previously known isomeric state could be clarified by α-γ-coincidence measurements.
A previously unknown α-transition of E
α = (8306 ± 5) keV was detected and identified by means of delayed α-α- and α-γ-γ-coincidence measurements. A second isomeric
state decaying by α-emission was not observed. The quality of the previously reported data of the α-decay fine structure of
217Th was improved.
Received: 29 April 2002 / Accepted: 17 June 2002 / Published online: 19 November 2002
RID="a"
ID="a"e-mail: f.p.hessberger@gsi.de
Communicated by J. ?yst? 相似文献
16.
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
17.
J. K. Hwang D. Fong A. V. Ramayya J. H. Hamilton M. Jandel C. J. Beyer J. Kormicki Y. X. Luo P. Gore J. Kliman L. Krupa M. Morhac G. M. Ter-Akopian Yu. Ts. Oganessian A. M. Rodin A. S. Fomichev G. S. Popeko A. V. Daniel J. O. Rasmussen A. O. Macchiavelli I. Y. Lee M. A. Stoyer R. Donangelo J. D. Cole 《Acta Physica Hungarica A》2003,18(2-4):383-391
He and Be ternary fission processes of 252Cf have been studied in two experiments with the Gammasphere detector array with light charged particle detectors surrounding the source. From α-γ double gated spectra, neutron multiplicity distributions were determined for related α ternary fission pairs. In going from binary to α ternary SF for approximately the same mass splittings (A ≈ 104–146) the average neutron multiplicity decreases about 0.7 AMU. In the first light charged particle (LCP) γ-γ experiment, the 10Be spectrum was cutoff below 27 MeV and in the recent experiment, below 18 MeV. For high energy (E > 27 MeV) 10Be ternary fission, the data indicate that the largest yields go via the cold process (zero neutron evaporation). In the recent experiment with E cutoff of 18 MeV, the 10Be ternary SF was observed for zero to 4n emissions. It seems that in some cases like 136Te, the On channel is the strongest and in the other cases like 100Zr the 1n or 2n channel dominates. Clearly, there is a shift to lower average number of neutrons emitted for 10Be compared to α ternary SF. The 104Zr and 136Te cases where zero neutron emission occurs may be related to the fact that these nuclei are near the limits of the more neutron rich Zr and Te nuclei observed. The 136Te is more spherical than the heavy partners in the other pairs and this may influence the 0n channel. Finally, the 0n channel may be more enhanced in the first data with the higher 10Be energy cutoff, leading to lower excitation energy. Also, we confirmed the 3368 keV peak with the FWHM of 60 keV emitted from the moving Be particles in the Doppler effect corrected spectrum. 相似文献
18.
G. V. Danilyan 《JETP Letters》1999,70(9):565-568
Some experimental possibilities of establishing the nature of the recently observed T-odd angular correlation in ternary fission of 233U by polarized neutrons are discussed. Specifically, investigation of the neutron energy dependence of the correlation coefficient
in the ternary fission of 239Pu and 235U could shed light on the problem under discussion.
Pis’ma Zh. éksp. Teor. Fiz. 70, No. 9, 561–564 (10 November 1999) 相似文献
19.
M. Jandel J. Kliman L. Krupa M. Morháč J. H. Hamilton J. Kormicki A. V. Ramayya J. K. Hwang Y. X. Luo D. Fong P. Gore G. M. Ter-Akopian Yu. Ts. Oganessian A. M. Rodin A. S. Fomichev G. S. Popeko A. V. Daniel J. O. Rasmussen A. O. Macchiavelli M. A. Stoyer R. Donangelo J. D. Cole 《The European Physical Journal A - Hadrons and Nuclei》2005,24(3):373-378
For the first time, average angular momenta of the ternary fission fragments 100, 102Zr, 106Mo, 144, 146Ba and 138, 140, 142Xe from the α-accompanied fission of 252Cf were obtained from relative intensities of prompt γ-ray transitions with the use of the statistical model calculation. Average values of the angular momenta were compared with the corresponding values for the same fission fragments from the binary fission of 252Cf. Results indicate the presence of a decreasing trend in the average values of angular momenta induced in ternary fission fragments compared to the same binary fission fragments. On the average, the total angular momentum extracted for ternary fission fragments is ∼1.4 ℏ lower than in binary fission. Consequently, results indicate that the mechanism of the ternary α-particles emission may directly effect an induction of angular momenta of fission fragments, and possible scenarios of such mechanisms are discussed. Further, the dependence of the angular momenta of 106Mo and 140Xe on the number of emitted neutrons from correlated pairs of primary fragments was obtained also showing a decreasing dependence of average angular momenta with increasing number of emitted neutrons. Consequences are briefly discussed. 相似文献
20.
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