共查询到20条相似文献,搜索用时 298 毫秒
1.
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
2.
P. Pawłowski B. Borderie G. Auger Ch.O. Bacri N. Bellaize F. Bocage R. Bougault R. Brou P. Buchet J.L. Charvet A. Chbihi J. Colin D. Cussol R. Dayras A. Demeyer D. Doré D. Durand J.D. Frankland E. Galichet E. Genouin-Duhamel E. Gerlic D. Guinet P. Lautesse J.L. Laville J.F. Lecolley R. Legrain N. Le Neindre O. Lopez M. Louvel A.M. Maskay L. Nalpas A.D. Nguyen M. Pârlog J. Péter E. Plagnol M.F. Rivet E. Rosato F. Saint-Laurent S. Salou J.C. Steckmeyer M. Stern G. Tăbăcaru B. Tamain L. Tassan-Got O. Tirel E. Vient C. Volant J.P. Wieleczko 《The European Physical Journal A - Hadrons and Nuclei》2000,9(3):371-383
The prompt component at intermediate velocity of light charged particles is investigated. An improved coalescence model coupled
to the intra-nuclear cascade code ISABEL is used to obtain light complex particle energy spectra and multiplicities as a function
of impact parameter. The results are compared with experimental data from the 36Ar + 58Ni experiment at 95 MeV/nucleon, performed with the INDRA 4π detection system. The calculated prompt component is found to
rather well reproduce proton spectra. For complex light charged particles the calculated components well populate the high
energy part of spectra. Prompt emission can therefore explain the large transverse energies experimentally observed at mid-rapidity.
Received: 27 July 2000 / Accepted: 20 November 2000 相似文献
3.
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
4.
E. Vardaci G. La Rana A. Brondi R. Moro A. Principe D. Fabris G. Nebbia G. Viesti M. Cinausero E. Fioretto G. Prete F. Lucarelli E.M. Fiore L. Fiore V. Paticchio P.F. Bortignon 《The European Physical Journal A - Hadrons and Nuclei》1998,2(1):55-60
The α-particle emission from the 28Si+170Er fusion-evaporation reaction at 165 and 185 MeV has been measured and compared with published data relative to the pre-scission
emission in the same reaction. The spectra in the two channels exhibit nearly the same shape in the low energy region, whereas
in the high energy region the spectrum for the fusion-evaporation case features a larger apparent temperature. The interpretation
of the difference in shape between the two decay channels is based on statistical model calculations which account for the
effects due to the different length of the decay chain. Statistical model calculations with standard parameters describe well
the gross features of the alpha particle spectra in the fusion-evaporation channel and the proton spectra in the pre-scission
channel. On the contrary, the model predictions seem to overestimate by ≃2 MeV the emission barrier for the alpha particles
in the pre-fission channel. This effect is ascribed to the larger elongation of the nucleus during the fission process. An
average axis ratio b/a∼ 2 for the emitter is suggested.
Received 29 April 1997 / Revised version 10 September 1997 相似文献
5.
C. Signorini M. Mazzocco G.F. Prete F. Soramel L. Stroe A. Andrighetto I.J. Thompson A. Vitturi A. Brondi M. Cinausero D. Fabris E. Fioretto N. Gelli J.Y. Guo G. La Rana Z.H. Liu F. Lucarelli R. Moro G. Nebbia M. Trotta E. Vardaci G. Viesti 《The European Physical Journal A - Hadrons and Nuclei》2001,10(3):249-253
Large cross-section reaction channels were measured in the systems 6Li( 7Li) + 208Pb with high statistical accuracy at 5(3) energies around the Coulomb barrier from 29 to 39 MeV. These channels were assigned
(mainly) to the breakup of 6Li, very loosely bound, into α + d and to the breakup of 5Li, produced by n-transfer to the target, into α + p and to similar processes with 7Li beam. The cross-sections with 6Li, S
α = 1.475 MeV, are systematically larger than the 7Li ones. This reflects, most likely, the higher binding energy of 7Li, S
α = 2.468 MeV. Theoretical predictions for the 6Li + 208Pb system which include for 6Li breakup to continuum states within a continuum discretized coupled-channels approach (CDCC) and resonant breakup plus n-transfer
with DWBA reproduce the angular distribution shapes but still underestimate the cross-sections by a factor ∼ 3.
Received: 15 January 2001 / Accepted: 3 March 2001 相似文献
6.
E. Gadioli G.F. Steyn F. Albertini C. Birattari M. Cavinato S.H. Connell A.A. Cowley E. Fabrici S.V. Förtsch E. Gadioli Erba J.J. Lawrie M. Pigni J.P.F. Sellschop E. Sideras Haddad 《The European Physical Journal A - Hadrons and Nuclei》2003,17(2):195-212
In this paper we study the emission of 8Begs, B and N fragments in the interaction of 16O ions with 59Co, 93Nb and 197Au at incident energies varying from 6 to 25 MeV/nucleon. The spectra of these fragments, as well as those of C fragments
studied in a previous paper, are dominated at forward angles by a component originating from break-up of 16O. At the higher incident energies break-up occurs after quite a sizeable projectile energy loss. Another mechanism which
dominates at large emission angles, favours the emission of low-energy fragments and is attributed to the coalescence of nucleons
during the cascade of nucleon-nucleon interactions by means of which the excited nuclei produced in the primary two-ion interaction
thermalize.
Received: 21 January 2003 / Accepted: 27 March 2003 / Published online: 5 June 2003 相似文献
7.
C. Beck R. Nouicer D. Mahboub B. Djerroud R.M. Freeman A. Hachem T. Matsuse Sl. Cavallaro E. De Filippo G. Lanzanó A. Pagano M.L. Sperduto R. Dayras E. Berthoumieux R. Legrain E. Pollacco 《The European Physical Journal A - Hadrons and Nuclei》1998,2(3):281-293
Fusion-fission and fully energy-damped binary processes of the 35Cl+24Mg reaction were investigated using particle-particle coincidence techniques at a 35Cl bombarding energy of Elab≈ 8 MeV/nucleon. Inclusive data were also taken in order to determine the partial wave distribution of the fusion process.
The fragment-fragment correlation data show that the majority of events arises from a binary-decay process with a relatively
large multiplicity of secondary light-charged particles emitted by the two primary excited fragments in the exit channel.
No evidence is observed for ternary-breakup processes, as expected from the systematics recently established for incident
energies below 15 MeV/nucleon and for a large number of reactions. The binary-process results are compared with predictions
of statistical-model calculations. The calculations were performed using the Hauser-Feshbach method, based on the available
phase space at the scission point of the compound nucleus. This new method uses temperature-dependent level densities and
its predictions are in good agreement with the presented experimental data, thus consistent with the fusion-fission origin
of the binary fully-damped yields.
Received: 12 March 1998 相似文献
8.
R.I. Badran D.J. Parker I.M. Naqib 《The European Physical Journal A - Hadrons and Nuclei》2001,12(3):317-325
Excitation functions for the production of eight radioactive products of the reactions of 7Li on 56Fe have been measured up to E(7
Li) = 89 MeV. Recoil range distributions for these products, together with inclusive proton, deuteron, triton and alpha spectra,
have been measured at energies of 50 and 68 MeV. The α, t and d spectra show characteristic “break-up” components at forward
angles, while the recoil distributions show evidence of complete fusion and incomplete-fusion process 56Fe( 7Li,α) 59Co * . A parallel study on 55Mn shows some evidences of the ( 7Li,t) incomplete-fusion process, but the cross-section for this process is significantly less than for the triton fusion process.
The recoil distributions can be reproduced on the assumption that essentially all the observed break-up fragments are in fact
associated with incomplete fusion, but uncertainties in normalisation leave open the possibility of a significant contribution
of pure break-up. A diffraction model of the ( 7Li,α) transfer process reproduces the observed break-up α spectra with some success.
Received: 29 March 2001 / Accepted: 12 November 2001 相似文献
9.
J. Benlliure P. Armbruster M. Bernas C. Böckstiegel S. Czajkowski C. Donzaud H. Geissel A. Heinz C. Kozhuharov P. Dessagne G. Münzenberg M. Pfützner C. Stéphan K.-H. Schmidt K. Sümmerer W. Schwab L. Tassan-Got B. Voss 《The European Physical Journal A - Hadrons and Nuclei》1998,2(2):193-198
Projectile fragmentation of 238U in a lead target was investigated at a bombarding energy of 750 A MeV. Isotopic production cross sections of about 250 different projectile fragments in the element range Z= 30–53 were measured with the FRagment Separator (FRS). The magnetic selection and the kinematical analysis of the measured
isotopes allowed to disentangle fission and fragmentation residues. The mass loss of these residues indicates a violent collision
where a large amount of energy is dissipated. The position of the fragmentation corridor defined by the measured residues
was used to determine an effective proton-evaporation barrier.
Received: 3 October 1997 / Revised version: 27 February 1998 相似文献
10.
G. Casini M. Bini S. Calamai R. Laforest P.R. Maurenzig A. Olmi G. Pasquali S. Piantelli G. Poggi F. Saint-Laurent J.C. Steckmeyer A.A. Stefanini N. Taccetti 《The European Physical Journal A - Hadrons and Nuclei》2000,9(4):491-513
Primary and secondary masses of heavy reaction products have been deduced from kinematics and E-ToF measurements, respectively,
for the direct and reverse collisions of 93Nb and 116Sn at 25 AMeV. Light charged particles have also been measured in coincidence with the heavy fragments. Direct experimental
evidence of the correlation of energy-sharing with net mass transfer has been found using information from both the heavy
fragments and the light charged particles. The ratio of hydrogen and helium multiplicities points to a further correlation
of angular momentum sharing with net mass transfer.
Received: 18 September 2000 / Accepted: 2 December 2000 相似文献
11.
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
12.
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
13.
High resolution measurements of prompt γ-rays emitted from fission fragments accompanied by light charged particles (LCP) and those emitted from normal binary fission fragments in 252Cf fission were simultaneously carried out using a 30 cm3 Ge(Li) detector. A “sandwich” type of arrangement in the source-detector assembly was used to eliminate Doppler broadening of the γ-ray lines in both cases. About thirty γ-ray lines were assigned to specific fission fragments by comparison with the published results for binary fission, and the ratios of intensities of these γ-ray lines in LCP fission and binary fission were determined. Assuming that 2+ → 0+ transition intensities of doubly even isotopes are a measure of their yields, the yields of several such isotopes in LCP accompanied fission relative to that in binary fission were obtained. 相似文献
14.
E. Gadioli G.F. Steyn C. Birattari M. Cavinato S.H. Connell A.A. Cowley E. Fabrici S.V. Förtsch E. Gadioli Erba J.J. Lawrie F.M. Nortier J.P.F. Sellschop E. Sideras Haddad 《The European Physical Journal A - Hadrons and Nuclei》2001,11(2):161-173
The spectra of 8Begs fragments emitted in the interaction of 100, 200, 300 and 400 MeV 12C with 59Co, 93Nb and 197Au have been measured and analysed. Our analysis suggests that, before breaking up, 12C may suffer a considerable energy loss which increases with increasing incident energy. The amount of excitation energy provided
to the target nucleus in this process increases with decreasing charge of the target nucleus.
Received: 3 May 2001 / Accepted: 5 June 2001 相似文献
15.
M. Kmiecik A. Maj B. Herskind A. Bracco R.A. Bark M. Bergström F. Camera G. Hagemann N. Hashimoto A. Holm S. Leoni T. Saitoh T.S. Tveter 《The European Physical Journal A - Hadrons and Nuclei》1998,1(1):11-13
The decay of 170W* formed in reactions with two different projectile - target combinations was studied. The observed differences in the average
number of emitted neutrons suggest an entrance channel effect at the highest excitation energy and angular momentum. It may
be explained by different excitation energies of the equilibrated system, resulting from the emission of pre-equilibrium α-particles
during a longer fusion time, in the more symmetric reaction.
Received: 30 October 1997 相似文献
16.
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
17.
C. Gautherin M. Houry W. Korten Y. Le Coz R. Lucas X.H. Phan C. Theisen C. Badimon G. Barreau T.P. Doan G. Pedemay G. Bélier M. Girod V. Méot S. Peru A. Astier L. Ducroux M. Meyer N. Redon 《The European Physical Journal A - Hadrons and Nuclei》1998,1(4):391-397
Isomeric states have been observed in fission-fragments produced by spontaneous fission of 252Cf. These states are found in neutron rich nuclei of different structure and deformations. About 50 isomeric nuclei have been
observed using coincidences between γ-rays identified in EUROGAM II and fission fragments detected in photovoltaic cells (SAPhIR).
Lifetimes in the range from 20 ns to 2μs have been measured. Presented calculations based on HFB +D1S force on new measured
isomeric states in the 152,154,156Nd show evidence for K-isomers.
Received: 3 November 1997 / Revised version: 15 December 1997 相似文献
18.
Z. Sosin R. Płaneta T. Ciszek J. Brzychczyk W. Gawlikowicz K. Grotowski S. Micek P. Pawłowski A. Wieloch A.J. Cole D. Benchekroun E. Bisquer A. Chabane M. Charvet B. Cheynis A. Demeyer P. Désesquelles E. Gerlic A. Giorni D. Guinet D. Heuer P. Lautesse L. Lebreton A. Lléres M. Stern L. Vagneron J.B. Viano 《The European Physical Journal A - Hadrons and Nuclei》2001,11(3):305-310
The shape of the velocity distributions of charged particles projected on the beam direction can be explained if emissions
from the hot projectile-like fragment and the target-like fragment are supplemented by an emission from an intermediate velocity
source located between them. The creation of this source is predicted by a two-stage reaction model where, in the second stage,
some of the nucleons identified in the first stage as participants form a group of clusters located in the region between
the colliding nuclei. The cluster coalescence process is governed on the average by the maximum value of entropy, although
its fluctuations are also significant. The properties of the intermediate velocity source are precisely described, including
the isotopic composition of the emitted particles.
Received: 12 March 2001 / Accepted: 20 June 2001 相似文献
19.
D. Pierroutsakou M. Di Toro F. Amorini V. Baran A. Boiano A. De Rosa A. D'Onofrio G. Inglima M. La Commara A. Ordine N. Pellegriti F. Rizzo V. Roca M. Romoli M. Sandoli M. Trotta S. Tudisco 《The European Physical Journal A - Hadrons and Nuclei》2003,16(3):423-435
We report on the results obtained from the study of the 32S + 64Ni and 32S + 58Ni peripheral reactions at incident energies E
lab = 288 MeV and E
lab = 320 MeV, respectively. High-energy γ-rays were detected in an array of 8 seven-pack BaF2 clusters. Coincidence with complex fragments detected in 12 three-stage telescopes ensured the selection of peripheral reaction
events. All of the relevant reaction parameters were kept constant with the exception of the different initial dipole moment
caused by the different entrance channel charge asymmetry. While for quasi-elastic events no N/Z effect was observed in the differential γ-ray multiplicities of the two reactions, for deep-inelastic events a larger dipole
γ-ray emission occurs during the more N/Z asymmetric reaction. A theoretical interpretation based on a collective Bremsstrahlung analysis of the reaction dynamics
is presented.
Received: 26 September 2002 / Accepted: 13 November 2002 / Published online: 6 March 2003
RID="a"
ID="a"e-mail: pierroutsakou@na.infn.it
RID="b"
ID="b"Present address: INFN, Laboratori Nazionali di Legnaro, Padova, Italy.
Communicated by C. Signorini 相似文献
20.
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