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1.
A. Goswami S. B. Manohar S. K. Das A. V. R. Reddy B. S. Tomar S. Prakash 《Zeitschrift für Physik A Hadrons and Nuclei》1992,342(3):299-301
Mass resolved fission fragment angular distribution was measured in the 28.5 MeV alpha induced fission of233U using recoil catcher technique and direct gamma spectrometry. The angular distribution of 8 fission products were obtained. The angular anisotropies of asymmetric fission products were found to be higher than those of symmetric products indicating a correlation between the fragment angular distribution and the mass distribution.The authors are grateful to Dr. S.K. Kataria and Dr. T. Datta for fruitful discussions. We thank the operation crew of the variable energy cyclotron, Calcutta for their help in carrying out the irradiations. Thanks are due to Dr. P.R. Natarajan, Head of the Radiochemistry Division for his keen interest in the work. 相似文献
2.
A. Díaz-Torres F. Guzmán-Martínez O. Rodríguez-Hoyos 《The European Physical Journal A - Hadrons and Nuclei》1999,4(1):51-59
An interpretation of the cold fission events in thermal-neutron-induced fission of heavy nuclei is given. The descent from
the saddle point is considered as a dynamical process with reversible coupling between collective and intrinsic degrees of freedom. The distribution function for the collective variables is expressed
as a product of two terms: the adiabatical and the dynamical factors. A simple model for symmetric fission to study the mass distribution is presented. As example, the calculations are performed
for the nucleus 264Fm. Gross features of the cold fission are discussed as well as the dependence of the theoretical mass distribution on the
parameters of the model.
Received: 29 April 1998 / Revised version: 11 September 1998 相似文献
3.
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
4.
Th. Rubehn W. F. J. Müller R. Bassini M. Begemann-Blaich Th. Blaich A. Ferrero C. Groß G. Imme I. Iori G. J. Kunde W. D. Kunze V. Lindenstruth U. Lynen T. Möhlenkamp L. G. Moretto B. Ocker J. Pochodzalla G. Raciti S. Reito H. Sann A. Schüttauf W. Seidel V. Serfling W. Trautmann A. Trzcinski G. Verde A. Wörner E. Zude B. Zwieglinski 《Zeitschrift für Physik A Hadrons and Nuclei》1995,353(2):197-204
Electromagnetic fission of238U projectiles at E/A =600 and 1000 MeV was studied with the ALADIN spectrometer at the heavy-ion synchrotron SIS. Seven different targets (Be, C, Al, Cu, In, Au and U) were used. By considering only those fission events where the two charges added up to 92, most of the nuclear interactions were excluded. The nuclear contributions to the measured fission cross sections were determined by extrapolating from beryllium to the heavier targets with the concept of factorization. The obtained cross sections for electromagnetic fission are well reproduced by extended Weizsäcker-Williams calculations which include E1 and E2 excitations. The asymmetry of the fission fragments' charge distribution gives evidence for the excitation of the double giant-dipole resonance in uranium.Communicated by V. Metag 相似文献
5.
U. Graf F. Gönnenwein P. Geltenbort K. Schreckenbach 《Zeitschrift für Physik A Hadrons and Nuclei》1995,351(3):281-288
The parity nonconserving (PNC) asymmetry coefficient for the angular distribution of fragment emission from binary fission of233U irradiated by polarized thermal neutrons has been measured. Complementary fragments were detected by a double ionization chamber with high resolving power. The experiment was carried out at the high flux reactor of the ILL, Grenoble. Integrated over all masses and energies of light fragments from asymmetric fission of234Uh, the PNC asymmetry coefficient is found to be =(3.29±0.31) × 10–4.The positive sign of indicates a preferential emission of light fragments parallel to the spin of neutrons inducing fission. Theory claims that PNC effects are sensitive to the properties of the fission barrier. On the other hand, one may wonder whether characteristics of eventual fragments are already specified at the barrier. The measurement of PNC asymmetries for distinct mass-energy ranges of fragments has been utilized to answer this question. Mass-energy distributions of fragments were analyzed along the lines of the Brosa model of fission as a superposition of individual modes. Within experimental uncertainty no mode dependence of asymmetric fission could be disclosed. The result is in keeping with the Brosa model where asymmetric modes bifurcate only once the standard fission barrier has been passed. 相似文献
6.
Fission Fragment Angular Correlation in the Reaction Induced by 84.0MeV 16O Bombarded 238U 下载免费PDF全文
QIAN Xing ZHANG Huan-Qiao LIU Zu-Hua XU Jin-Cheng CHEN Shao-Lin XU Kan LU Li-Xin 《中国物理C(英文版)》1993,17(2):173-178
Fission fragment angular distribution and angular correlation in the reaction induced by 84.0MeV 16O bombarded 238U have been measured by using two position-sensitive PPAC with large area.Transfer fission has been removed from total fission using fission fragment angular correlation technique.The contribution to the total fission cross section arising from transfer is about 10%.The anisotropy of fission fragment for transfer-fission is rather small,thus the removal of the transfer fission has little effect on the total fragment angular distribution.Indeed the anisotropy becomes larger by about 5% and anomalously anisotropies still persist. 相似文献
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8.
G. Lhersonneau P. Dendooven G. Canchel J. Huikari P. Jardin A. Jokinen V. Kolhinen C. Lau L. Lebreton A.C. Mueller A. Nieminen S. Nummela H. Penttilä K. Peräjärvi Z. Radivojevic V. Rubchenya M.-G. Saint-Laurent W.H. Trzaska D. Vakhtin J. Vervier A.C.C. Villari J.C. Wang J. Äystö 《The European Physical Journal A - Hadrons and Nuclei》2000,9(3):385-396
In the context of a parameter study conducted by several laboratories for future European radioactive beam facilities based
on fast-neutron induced fission, in particular for the SPIRAL-II project at GANIL, we have measured the yields of neutron-rich
isotopes in the mass range of 88 to 144. These nuclei were obtained as fission products of natural uranium bombarded by neutrons
of 20 MeV average energy emitted by a thick carbon target irradiated by 50 MeV deuterons. Yields have been measured using
on-line mass separation with the ion-guide method. Compared with proton-induced fission at 25 MeV the magnitude of cross-sections,
except for the symmetric region, is similar. Z-distributions of isobars have the same width, 0.7 charge units, but their maxima are shifted by about 0.8 charge units, favouring
production of the neutron-richer isobars. Our data allow calculations of absolute cross-sections for fission of natural uranium
induced by neutrons of about 20 MeV.
Received: 10 July 2000 / Accepted: 27 October 2000 相似文献
9.
H. Baba N. Takahashi A. Yokoyama T. Saito 《The European Physical Journal A - Hadrons and Nuclei》1998,3(3):281-292
The reaction of 238U with 12C was studied radiochemically with the purpose of elucidating fast fission characteristics. From the difference in the mass
distribution below and above the critical energy where fast fission is predicted to set in, fast fission component was extracted
in far-asymmetric mass region and interpreted as the mass diffusion following the Fokker-Planck equation. Anomalous charge
dispersion widths in the corresponding mass region and a sudden increase of the whole mass distribution width at the critical
energy were also observed to support the above result. The reaction time of fast fission deduced from the width and position
of the mass distribution was 5×10−21s as well by taking into account the effect of neutron emission during the diffusion process, which turned out to be more
than one order of magnitude longer than the corresponding life time of typical deep inelastic scattering but substantially
short compared to ordinary fusion-fission life time. Evaluation of the driving potential for mass drift required dinuclear
configuration be of an elongated or deformed form for fast fission in contrast to a more compact form for the deep-inelastic
process.
Received: 11 November 1997 相似文献
10.
C. Donzaud S. Czajkowski P. Armbruster M. Bernas C. Böckstiegel P. Dessagne H. Geissel E. Hanelt A. Heinz C. Kozhuharov C. Miehé G. Münzenberg M. Pfützner W. Schwab C. Stéphan K. Sümmerer L. Tassan-Got B. Voss 《The European Physical Journal A - Hadrons and Nuclei》1998,1(4):407-426
Projectile fission of 750 AMeV 238U-ions interacting with a Pb target was studied by means of the spectrometer FRS, GSI-Darmstadt. One of the two fission fragments
was detected with a transmission of few percent and identified in mass and charge. Low-energy fission (E* < 25 MeV) events were selected by their magnetic rigidity. Whereas the production of asymmetric fission events is dominated
by the GDR excitation, very asymmetric fission and symmetric fission take place after a GQR or DGDR excitation or after a
nuclear interaction. Cross sections of more than 250 isotopes were measured. Isotopic distributions of low-energy fission
were reconstructed for elements from Se to Te. The fission modes SI, SII and SL were clearly shown in these distributions
and in the mass and TKE distributions. Charge polarization and mass dispersion were deduced for each fission mode. Finally,
the characteristics of the low-energy fission process explain the production rates of neutron-rich species.
Received: 14 July 1997 / Revised version: 6 October 1997 相似文献
11.
N. Takahashi N. Yukawa H. Kobayashi A. Yokoyama T. Saito H. Baba 《Zeitschrift für Physik A Hadrons and Nuclei》1995,353(1):35-42
We attempted to confirm the existence of two-mode-fission mechanism in the232Th and238U plus4He systems. Angular distributions and differential ranges of the fission fragments were measured for both systems. Two distinct groups, symmetric and asymmetric, were observed in the anisotropy of the fragments obtained from the angular distributions in either systems. Kinetic energies of the fragments were deduced from the measured ranges and the effective distances were calculated from the data. The distribution of the resulting distances was classified into two groups also, indicating the existence of the symmetric and asymmetric modes. This strongly suggests existence of two independent paths in the fission process.Communicated by: P. Armbruster 相似文献
12.
H.-G. Clerc K.-H. Schmidt H. Wohlfarth W. Lang H. Schrader K.E. Pferdekämper R. Jungmann M. Asghar J.P. Bocquet G. Siegert 《Nuclear Physics A》1975,247(1):74-90
The nuclear charge distribution of fission products with mass numbers A = 90, 91, 94, 99, 100, 101 and 104 provided by the mass separator “Lohengrin” was measured. Adjacent elements in the group of the light fission products could be separated by their different energy loss in a carbon absorber. The Z-yields were found to be strongly dependent on the kinetic energy of the fission products. The widths of the nuclear charge distributions are very small, in general, and strongly dependent on A as well as on the kinetic energy. The influence of the neutron evaporation and odd-even effects are clearly detected. An asymmetric nuclear charge distribution was found for A = 104 indicating the suppression of fission fragments with Z = 43. The average nuclear charges of the fission products at their average kinetic energy are in good agreement with the results from measurements of the number of β-decays and K X-ray measurements. The average nuclear charge of the isobar A = 132 was measured at its average kinetic energy with a calibrated secondary electron detector to be Z = 51.14 ± 0.15 which is in very good agreement with the radiochemical results. Thus previous physical measurements indicating a large independent yield for the doubly magic nucleus 132Sn could not be confirmed. 相似文献
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15.
L. Nowicki E. Piasecki J. Sobolewski A. Kordyasz M. Kisieliński W. Czarnacki H. Karwowski P. Koczoń C. Signarbieux 《Nuclear Physics A》1982,375(2):187-216
The energy distributions and relative intensities of protons, deuterons, tritons and α-particles emitted along the fission axis during spontaneous fission of 252Cf were measured simultaneously with both fission fragment energies. The absolute intensity of particles, the mass distribution of fragments, the total kinetic energy and total excitation energy of both fragments were subsequently deduced from the experimental data. Statistical model calculations based on a hypothesis that the polar particles are evaporated from fission fragments have been performed for 252Cf and 236U fission. Although some experimental results agree remarkably well with the evaporation hypothesis, the considered model cannot describe many features of the polar emission phenomenon. 相似文献
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17.
The first and the second moments of the multiplicity distribution of prompt gamma rays in spontaneous ternary fission of252Cf have been measured by the multiple coincidence technique. While both these moments were found to be nearly independent
of the energy of the light charged particle accompanying the fission fragments, the width of the multiplicity distribution
was larger than that in the case of normal binary fission by about 20%. 相似文献
18.
J. Galy B. Fogelberg F. Storrer H. Mach 《The European Physical Journal A - Hadrons and Nuclei》2000,8(3):331-354
A comprehensive study has been carried out of the yield pattern of fission products formed in fast neutron-induced fission
of 233U. The isotope separator on-line facility at Studsvik to the R2-0 nuclear reactor was used for rapid separation of the fission
products. At a target temperature of 2250 °C fission products of the elements from zinc (Z = 30) to barium (Z = 56) are released, with the exception of yttrium, zirconium, niobium, molybdenum, technetium, ruthenium and rhodium. The
individual isotopes are then available for study, implying that an almost complete mapping of the yield distribution can be
made. In the analysis, the delay between production and measurement and the overall separator efficiency for three consecutive
elements (the one under study and its parent and grand parent) are taken into account. Independent and/or cumulative yields
have been obtained for 203 nuclear species, among them 59 isomeric states.
Received: 19 April 2000 / Accepted: 19 June 2000 相似文献
19.
Ternary fission in ^197Au+^197Au collisions at 15 A MeV is investigated by using the improved quantum molecular dynamical (ImQMD) model. The experimental mass distributions for each of the three fragments are reproduced for the first time without any freely adjusting parameters. The mechanisms of ternary fission in central and semicentral collisions are dynamically studied. In direct prolate ternary fission, two necks are found to be formed almost simultaneously and rupture sequentially in a very short time interval. Direct oblate ternary fission is a very rare fission event, in which three necks are formed and rupture simultaneously, forming three equally sized fragments along space-symmetric directions in the reaction plane. In sequential ternary fission a binary division is followed by another binary fission event after hundreds of fm/c. 相似文献
20.
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