共查询到20条相似文献,搜索用时 31 毫秒
1.
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
2.
A. Ya. Rusanov M. G. Itkis N. A. Kondratiev V. V. Pashkevich I. V. Pokrovsky V. S. Salamatin G. G. Chubarian 《Physics of Atomic Nuclei》2008,71(6):956-981
The mass-energy distributions of fragments originating from the fission of the compound nucleus 226Th and their correlations with the multiplicity of gamma rays emitted from these fragments are measured and analyzed in 18O + 208Pb interaction induced by projectile oxygen ions of energy in the range E lab = 78–198.5 MeV. Manifestations of an asymmetric fission mode, which is damped exponentially with increasing E lab, are demonstrated. Theoretical calculations of fission valleys reveal that only two independent valleys, symmetric and asymmetric, exist in the vicinity of the scission point. The dependence of the multiplicity of gamma rays emitted from both fission fragments on their mass, Mγ(M), has a complicated structure and is highly sensitive to shell effects in both primary and final fragments. A two-component analysis of the dependence Mγ(M) shows that the asymmetric mode survives in fission only at low partial-wave orbital angular momenta of compound nuclei. It is found that, for all E lab, the gamma-ray multiplicity Mγ as a function of the total kinetic energy (TKE) of fragments, Mγ(TKE), decreases linearly with increasing TKE. An analysis of the energy balance in the fission process at the laboratory energy of E lab = 78 MeV revealed the region of cold fission of fragments whose total kinetic energy is TKE ~Q max. 相似文献
3.
P. David J. Hartfiel H. Janszen T. Mayer-Kuckuk R. von Mutius C. Petitjean H. W. Reist S. M. Polikanov J. Konijn C. T. A. M. de Laat A. Taal T. Krogulski T. Johansson G. Tibell J. F. M. d'Achard van Enschut 《Zeitschrift für Physik A Hadrons and Nuclei》1987,328(1):37-47
Mass yield and total kinetic energy release (TKE) distributions of fragments from prompt and delayed muon induced fission, separately, have been measured for the isotopes235U,238U,237Np and242Pu. The distributions from prompt muon induced fission are compared with the corresponding distributions from hadronic reactions and from spontaneous fission (s.f.). The distributions from the delayed muonic fission processes are compared to the distributions for neutron and proton-induced fission. No mass distributions measured in the prompt muonic fission process show any signature, which can be attributed to the presence of the muon. Differences observed between the TKE distributions of prompt muon induced and hadron induced fission can be explained by the screening effect of the negative charge of the muon bound in the orbit of one of the fission fragments. The observed yield of symmetric muon induced fission was found to be defined merely by the value of the excitation energy. 相似文献
4.
Angular distributions of light charged particles from 252Cf fission in the ranges 0–46° and 134–180°
A.J. Kordyasz E. Piasecki L. Nowicki P. Koczoń J. Sobolewski M. Kisieliński W. Czarnackif 《Nuclear Physics A》1985,439(1):28-44
Alpha particles, tritons, deuterons and protons accompanying 252Cf fission were registered in coincidence with both fission fragments by means of a system containing two-dimensional position-sensitive silicon detectors. Angular distributions, kinetic energy spectra of light charged particles as well as mass distributions of fission fragments in coincidence with light charged particles were measured. The experimental results are compared with some theoretical models. 相似文献
5.
P. David J. Debrus F. Lübke H. Mommsen E. Schmitt R. Schoenmackers H. Simons 《Physics letters. [Part B]》1976,61(2):158-160
Mass and energy distributions of 238U fragments following fission induced by inelastic scattering of α-particles were obtained in a triple coincidence experiment. The total kinetic energy (TKE) of the fragments is observed to decrease with excitation energy. 相似文献
6.
Ewald Konecny Helmut Gunther Helmut Rösler Günter Siegert Heinz Ewald 《Zeitschrift für Physik A Hadrons and Nuclei》1970,231(1):59-97
Fragments from thermal-neutron induced fission of235U have been separated by a mass spectrometer with respect to their masses and kinetic energies within 1 μsec. The separation principles are briefly described. For masses 130 to 139 amu the charge distributions have been determined by counting the number of beta tracks emitted from the individual mass selected fission fragments in a nuclear photographic emulsion. In another method, the average number of beta particles for each fragment mass is determined by use of a 4π-proportional counter. The mean nuclear charge as a function of mass is compared with other experimental results and theoretical curves. Contradictory to the radiochemical results, this experiment yields a dip in the mean nuclear charge versus mass curve at mass 132 amu corresponding to the doubly magic nucleus (N=82,Z=50)132Sn. Recent theoretical calculations of Nörenberg are in agreement with this finding. 相似文献
7.
V. A. Khryachkov I. P. Bondarenko T. A. Ivanova B. D. Kuzminov N. N. Semenova A. I. Sergachev 《Physics of Atomic Nuclei》2013,76(3):259-262
The masses, total kinetic energies (TKE), and emission angles of fragments originating from the fission of 238U nuclei that was induced by 5- and 6.5-MeV neutrons were measured by using digital methods for processing signals. A detailed analysis of the shape of digital signals made it possible to reduce substantially the contribution of fragments whose TKE values were distorted because of a superimposition of signals from recoil protons and from alpha particles produced in the spontaneous decay of uranium. The total statistics exceeded two million events for either neutron energy, and this permitted performing a detailed analysis of fission-fragment yields in the region of the highest attainable TKE values. An analysis of fragment yields made it possible to draw specific conclusions on the structure of the potential surface of fissile nuclei. 相似文献
8.
The shape parameters of the multiplicity distribution of prompt gamma rays emitted in spontaneous fission of252Cf were obtained using the multiple coincidence technique. The multiplicity distribution is well represented by a Gaussian
distribution. Assuming the average number of prompt gamma rays emitted per fission to be 10.3, the standard deviation of the
multiplicity distribution was estimated to be 4.2±0.4. The variation of the standard deviation of the multiplicity distribution
has also been obtained as a function of kinetic energy of one of the fragments and was found to exhibit a strong zigzag dependence
on the single fragment kinetic energy. The results have been discussed on the basis of the emission mechanism of prompt gamma
rays in fission. 相似文献
9.
The structures in the total kinetic energy (TKE) distributions in cold fission of234U and236U are interpreted in terms of the Coulomb interaction energy (C) between fragments at the scission point. The maximal value ofC, C max, corresponding to the most compact scission configuration, is calculated for several mass fragmentations. It is shown that withQ being constant,C max increases if one increases the charge asymmetry for a given primary fragmentation. This condition produces oscillations with a period of approximately 5 amu ofC max as a function of the light fragment mass which are correlated with the observed oscillations of the maximal value of TKE. Moreover, the enhancement of the yields of the more asymmetric charge fragmentation for a given fragmentation is explained. 相似文献
10.
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
11.
P. David J. Debrus F. Lübke H. Mommsen R. Schoenmackers 《Physics letters. [Part B]》1976,60(5):445-447
The variation in the mass yield distribution of the spontaneous fission of 252Cf as a function of the total kinetic energy (TKE) of the two fragments is investigated. With increasing TKE the peaks of the mass yield distributions become narrower. 相似文献
12.
In order to compare the distributions of the prompt energy release in the fission of a doubly even nucleus into even-Z and odd-Z fragments, the spectra of fragment kinetic energy and the coincident K X-rays were measured in a two-parameter mode with high statistical accuracy for the case of 252Cf spontaneous fission. By means of computer spectrum decomposition techniques data were obtained for average kinetic energies of fragments with even and odd atomic number. The comparison did not show any noticeable correlation of the mean fragment kinetic energy with oddness or evenness of the fragments. 相似文献
13.
The dependence on excitation energy of the mass distribution of the fragments arising from the fission of 240Pu is studied in a statistical model. The level densities needed are calculated on the basis of the single-particle energies obtained from a deformed Woods-Saxon potential. First we investigate when and how the shell effects disappear in 240Pu with increasing excitation energy. Using the transition state method we then calculate some characteristic properties of the fragment mass distributions and compare the results with the experimental observations. Reasonable agreement is obtained. 相似文献
14.
R. Kalpakchieva Yu. Ts. Oganessian Yu. E. Penionzhkevich H. Sodan 《Zeitschrift für Physik A Hadrons and Nuclei》1977,283(3):253-256
The mass distributions and total c.m. kinetic energies of fission fragments formed in the reaction40Ar+243Am at bombarding energies of 214, 222, 240 and 300 MeV have been measured using the angular correlation method. Angular distributions and anisotropy for 222 and 300 MeV have also been obtained. A symmetric mass distribution corresponding to the decay of a highly excited compound nucleus was obtained at 300 MeV bombarding energy. However, with decreasing bombarding energy the fission fragment mass distribution becomes asymmetric, the most probable heavy fragment mass being about 200–210 amu. 相似文献
15.
O. T. Grudzevich 《Physics of Atomic Nuclei》2001,64(9):1564-1580
The properties of neutron emission from fragments formed in the spontaneous fission of 252Cf and in the thermal-neutron-induced fission of 235U are analyzed on the basis of the statistical model of nuclear reactions. Upon extracting the mean excitation energies of fission fragments from experimental data on the mean multiplicities of neutrons, the observables of neutron emission can be described over wide ranges of total kinetic energies and masses. The observed values of mean fragment spins are also reproduced. A method for calculating the isomeric ratios of the independent yields of fission fragments that is based on the cascade-evaporation model of excited-nucleus decay is employed to describe experimental data on 235U fission induced by thermal neutrons and on 238U fission induced by alpha particles. The effect exerted on the isomeric ratios for fission fragments by two different assumptions on the spin distributions of primary-fragment populations—the assumption of the distribution associated with rotational degrees of freedom and the assumption of the distribution associated with the internal degrees of freedom of fully accelerated fragments—is investigated. 相似文献
16.
M. Sowiński M. Lewitowicz R. Kupczak A. Jankowski N. K. Skobelev S. Chojnacki 《Zeitschrift für Physik A Hadrons and Nuclei》1986,324(1):87-95
The results of coincidence measurements of4He emission with fission fragments in reactions of12C(108 MeV) ions with a197Au target and of16O(144 MeV) ions with a232Th target are presented. On the basis of a Monte Carlo kinematic simulation of nuclear reactions the experimental energy spectra and velocity distributions of alpha particles have been analyzed. A conclusion has been drawn that the main source of4 He emission is evaporation from the fissioning compound nucleus. Substantial part of alpha particles was emitted from fully accelerated fission fragments. Some of4He nuclei with an average energy of about 16 MeV (in the CM system) emitted mainly perpendicular to the fission axis were identified as being similar long-range alpha particles produced in ternary fission of heavy nuclei at a low excitation energy. The emission multiplicities of these particles are considerably higher than those observed at a low excitation energy. The experimental results are compared with the statistical model predictions. 相似文献
17.
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
18.
Zhi Yong He Gen Ming Jin Zu Yu Li Li Min Duan Guang Xi Dai Bao Guo Zhang He Yu Wu Wan Xin Wen Yu Jin Qi Qing Zheng Luo Su Fang Wang 《The European Physical Journal A - Hadrons and Nuclei》1998,1(1):61-64
Emission orders of light charged particles and Li fragments from highly excited fissioning nuclei in the reaction of 40Ar+197Au at E
beam
/A=25 MeV have been studied by measuring difference velocity distributions of two correlated particles at small relative angles
in coincidence with two fission fragments. By comparing the data with three-body trajectory calculations, we found that high
velocity deuterons are emitted prior to high velocity Li fragments but low velocity deuterons are emitted after low velocity
Li fragments. On the other hand, no preferential emission was observed among light particles, such as protons and deuterons.
Furthermore, the emission orders are found to depend only weakly on the mass asymmetry of fission fragments.
Received: 3 June 1997 / Revised version: 23 July 1997 相似文献
19.
《Nuclear Physics A》1997,617(3):331-346
The results of a systematic study of the mass and energy of fission fragments emitted in the spontaneous fission of 236,238,240,242,244Pu are reported. A comparison of the fragments' mass and energy distributions demonstrates the occurrence of different fission modes with varying relative probability. These results are discussed in terms of the random neck rupture model as well as in terms of the scission point model, showing the influence of the neutron number of the fissioning system. Finally an improved method of analysis allows the investigation of the cold fission region. 相似文献
20.
《Nuclear Physics A》1998,644(4):289-305
In the course of an experimental study of the fragment characteristics after neutron-induced fission of 238U with incident neutron energies between 1.2 and 5.8 MeV fission-mode calculations in the frame of the multi-modal random neck-rupture model have been performed. During these calculations some technical parts of the model have been revised. The identification of fission modes is now based on unequivocal and reproducible criteria. The Rayleigh criterion has consequently been applied to determine each possible scission configuration. The most remarkable new results are that all physically relevant fission modes branch off in the second potential minimum exhibiting different outer barriers, and that the total kinetic energy distribution of the fission fragments is a direct consequence of the Rayleigh criterion. The fragment characteristics as the mean mass, the mean total kinetic energy and the corresponding width obtained from the fission-mode calculations compare reasonably well with the experimental findings.For the first time the weighted fission cross sections through each particular fission mode have been analyzed simultaneously using a Hill-Wheeler type expression for the transmission through a double-humped fission barrier. The results support the picture of individual outer barriers with slightly different penetrabilities and a slightly lower inner barrier. 相似文献