共查询到20条相似文献,搜索用时 0 毫秒
1.
W.J. Triggs A.R. Poletti G.D. Dracoulis C. Fahlander A.P. Byrne 《Nuclear Physics A》1983,395(1):274-300
The yrast decay scheme of 208Rn has been investigated up to spin and an excitation energy of ≈ 6 MeV. Several different γ-ray spectroscopic techniques were used to determine the properties of excited states and transitions in the nucleus. Significant changes to the previously established level scheme are proposed, based on the existence of an unobserved 3.1 keV transition. Simple empirical shell-model calculations of level energies aided in the assignment of shell-model configurations to excited states and the decay scheme is discussed in terms of these configurations. The energy level systematics for the even radon isotopes, from A = 206 to 212 are discussed, as are core polarization effects in the even radon isotopes (A = 204 to 210) and polonium isotopes (A = 202–208). 相似文献
2.
The mechanisms involved in the production of fast α-particles in 12C-induced reactions have been studied for the 12C + 208Pb system at the bombarding energies of E12c = 132, 187 and 230 MeV. Absolute cross sections for the reactions 208Pb(12C. 12C1→α + 8Be), 208Pb(12C, 8Be(g.s.)) and 208Pb(12C, 8Be(2.94 MeV)) have been determined by coincidence measurement of two or three correlated α-particles. Inclusive α-particle production cross sections were also measured at E12c = 187 MeV. It is found that the inelastic process (12C, 12C1→α + 8Be) does not contribute significantly to fast α-particle production but that the production of 8Be by projectile fragmentation is an important source of α-particles. At the highest bombarding energy (230 MeV) it appears that the 12C → 3α fragmentation reaction becomes more prominent at the expense of the 12C→α + 8Be fragmentation channel. 相似文献
3.
Measurements were made of elastic and inelastic proton scattering on 207Pb targets in the energy range from 11.1 to 14.4 MeV. The scattering to the ground state and to the and exciced levels was analyzed in terms of a 0+ analogue resonance interfering with the non-resonant background and with the contribution from the 3? resonance. The resonance parameters were determined together with the magnitude and relative sign of three background components. 相似文献
4.
Angular distributions of photoprotons following the (e, e′p) reaction in 208Pb have been measured at incident energies of 25.0 MeV and 40.0 MeV. The proton energy distributions were measured at several angles and the angular distributions were obtained for several proton energy ranges. Proton groups at around 11.0 MeV and 15.3 MeV are separated for the angular distributions and the results show almost isotropic distributions, which indicate that these proton groups are emitted through IAR. The angular distributions for other slowly varying parts of the proton spectra proved strongly asymmetrical, indicative of interference between E1 and E2 transition. 相似文献
5.
A. Celler Ch. Briançon J.S. Dionisio A. Lefebvre Ch. Vieu J. Żylicz R. Kulessa C. Mittag J. Fernandez-Niello Ch. Lauterbach H. Puchta F. Riess 《Nuclear Physics A》1985,432(2):421-435
Yrast states in the nucleus 220Ra were studied by means of the 208Pb(14C, 2n) reaction at 61 and 64 MeV. A staggering sequence of levels of positive and negative parity has been observed up to spin and parity Iπ = 16+ (18 +) and from Iπ = 5? to Iπ = 17?, respectively. These states are connected by strong E1 transitions competing with the stretched E2 transitions, the ratio being ~ 10 ?6 fm?2. The ratio of the excitation energy of the 4+ state to that of the 2+ state is close to the vibrational limit. The moment of inertia associated with the negative-parity yrast states is slightly increasing with the rotational frequency ω. It is considerably higher than that of the positive-parity states at lower spins, the difference decreasing monotonically with increasing ω. The data are discussed with reference to the octupole vibrational picture as well as to the results of recent models predicting reflection-asymmetric shapes in the Ra-Th region. 相似文献
6.
7.
E.E. Gross J.R. Beene K.A. Erb M.P. Fewell D. Shapira M.J. Rhoades-Brown G.R. Satchler C.E. Thorn 《Nuclear Physics A》1983,401(2):362-396
The elastic and inelastic scattering of 18O ions at 120 MeV from a target of 208Pb have been studied. Cross sections for excitation of the 2+ state at 1.982 MeV in 18O and of the 3? state at 2.61 MeV in 208Pb were measured. In addition, the populations of the m-substates for the 18O excitation were deduced from the Doppler-broadened line shapes. The data were subjected to a coupled-channels analysis using either Woods-Saxon or folding-model potentials. In addition, the 18O excitation was found to be described very well by use of a semi-microscopic model. The analyses consistently indicated the presence of a positive static hexadecapole moment of several e · fm4 for the 2+ state of 18O. The m-substate population distributions were found to be better fitted if a vector spin-orbit coupling was introduced for the 2+ state of 18O with a sign opposite to that for the nucleon-nucleus case. 相似文献
8.
F. Saint-Laurent M. Conjeaud S. Harar J.M. Loiseaux J. Menet J.B. Viano 《Nuclear Physics A》1979,327(2):517-532
Reaction-product cross sections following 20Ne+12C and 16O + 16O collisions at several incident energies have been measured with a E-ΔE counter telescope. They are compared to statistical model predictions. Fair agreement is obtained for the high-Z evaporation residue cross sections, but a strong discrepancy is observed for the lower-Z reaction products. Possible explanations are discussed. It is shown that the compound nucleus formation does not depend on the structure of the colliding ions in the entrance channel and also that it is not limited by the 32S yrast line. 相似文献
9.
Low-lying proton-emitting states of 16F have been investigated through the sequential particle decay reactions 14N(3He, n)16F(p)15O. Excitation energies were determined by measuring outgoing proton energies. Estimations of proton decay widths and spin limitations were made from proton spectra and angular correlation data which were obtained by detecting the protons in time coincidence with the associated neutrons at θn = 0°. To date, the ground-state spin of 16F has been considered to be J = 0; however, the present work suggests J = 1 to be preferable. 相似文献
10.
P.B. Vold J.O. Andreassen J.R. Lien A. Graue E.R. Cosman W. Dünnweber D. Schmitt F. Nüsslin 《Nuclear Physics A》1973,215(1):61-78
The reaction 207Pb(d, p)208Pb has been studied at Ed = 18.0 MeV using the MPI Heidelberg Emperor tandem accelerator and multiple-gap spectrograph. The average resolution of 18 keV was better than previous measurements, and this, combined with the long beam exposure, allowed many finer details of the neutron particle-hole structure of 208Pb to be examined. In all, 45 levels were seen up to Ex = 6.3 MeV, many of which had never been seen before. A DWBA analysis of the stripping transitions angular distributions is made, and values of (2J + 1)Sij, energy centroids, and summed strengths are given. An interesting cluster of 1i and 2g levels at Ex ≈ 4.2 MeV are resolved and are compared to recent isobaric analog state data. A search for weak stripping strength to known pairing vibrations in 208Pb gave essentially negative results and points to the need for improved ultra-resolution measurements. 相似文献
11.
S. Joly G. Grenier D.M. Drake I. Bergqvist D.K. McDaniels A. Lindholm L. Nilsson N. Olsson A. Waheed R. Zorro F. Rigaud 《Nuclear Physics A》1982,382(1):71-78
The reaction 208Pb(n, γ0)209Pb was studied from 0.8 to 7.7 MeV to investigate relative contributions of the compound-nucleus and direct and semidirect processes in this energy range. Compound-nucleus reactions dominate below about 5 MeV and semidirect processes above 6 MeV. The direct-semidirect (DSD) model with a complex particle-vibration coupling describes the experimental data in the giant resonance region. A relatively large imaginary term is necessary to obtain a good fit to the data indicating either that the reactions proceed to a large extent in more complicated ways than the simple two-step semidirect reaction or that the model has a serious defect in its present formulation. A second objective was to search for a possible excitation of the isoscalar E2 and the M1 giant resonances by measuring asymmetries around 90° in the angular distribution of the γ-rays. The results indicate no (or very weak) asymmetry effects. 相似文献
12.
Energy spectra and differential cross sections of nitrogen products formed in the reaction 28 MeV 11B + 12C have been measured using a ΔE?E counter telescope. The energy spectra are smooth and therefore indicate that the nitrogen products were formed by a compound nucleus mechanism, via the formation and decay of the compound nucleus 23Na. The experimental results are compared with statistical model calculations and good agreement is obtained. This result provides further evidence for the importance of the compound nucleus mechanism in heavy ion reactions with light nuclei and also gives added validity to the statistical model for light compound systems. 相似文献
13.
The tensor analysing powers T20 and T22 of(d, p) reactions leading to several states of the final nuclei 29Si, 68Zn, 91Zr and 209Pb were measured at 12.3 MeV deuteron beam energy. The measured tensor analysing powers together with the vector analysing power and cross-section data are compared with DWBA calculations with and without the deuteron D-state. The D-state effects and j-dependence of the tensor analysing powers are discussed. The spin transfers involved in populating the 1.08, 1.88 and 3.30 MeV states in 68Zn in the 67Zn(d, p)68Zn reaction are deduced to be predominantly . This implies an assignment for the 3.287 MeV level of 68Zn of Jπ = 2+. 相似文献
14.
R.C. Weiss R.E. Anderson J.J. Kraushaar R.A. Ristinen E. Rost S. Shastry 《Nuclear Physics A》1981,355(1):45-65
The 205Tl(p, t)203Tl reaction has been used at 26.2 MeV to obtain additional information on the particle-vibration multiplets in 203Tl. Enhancement factors for the L = 0 and L = 2 transitions to the lower excited states of 203Tl were well accounted for by using enhancement factors from the 206Pb(p, t)204Pb reaction and the wave functions from the intermediate coupling calculations of Covello and Sartoris. Additional data on the 208Pb(p, t)206Pb reaction at 26.2 MeV were used along with data at other energies to examine the energy dependence of the zero-range enhancement factors. 相似文献
15.
T. Fukuda M. Ishihara H. Ogata I. Miura T. Shimoda K. Katori S. Shimoura M.-K. Tanaka E. Takada T. Otsuka 《Nuclear Physics A》1984,425(3):548-572
Nonequilibrium light-particle emissions have been investigated in the reaction 93Nb + 14N at 132, 159 and 208 MeV by measuring inclusive differential cross sections of p, d, t, 3He and α. The experimental data were analyzed in terms of three models: (i) an extended exciton model, (ii) a coalescence model, and (iii) a moving thermal source model. The angle-integrated energy spectra of the protons were well described by the extended exciton model in which projectile nucleons were assumed to be transferred to the target one by one, but those of composite particles were not. On the other hand, the composite particle spectra (except for α at forward angles) were successfully described by the coalescence model using spectra consistent with those for the protons. Extracted coalescence radii P0 were about 140 MeV/c for d and t, and about 220 MeV/c for α. The light-particle spectra were also fitted by the moving-source model assuming isotropic emission from a source moving with approximately half of the beam velocity and with much higher temperature than that of the compound nucleus. Extracted temperatures followed the systematics of a recent compilation for the various reactions. A discussion of these analyses is given. 相似文献
16.
The 208Pb(p,d)207Pb reaction has been studied at 26.3 MeV and data at 121 MeV reanalyzed. These data, along with the data of others at 22, 35, 41 and 55 MeV, have been compared with zero- and exact-finite-range DWBA calculations carried out in a consistent fashion to determine the energy dependence of the spectroscopic factors for the six strong single-neutron-hole states in 207Pb. Strong energy dependencies were noted for the spectroscopic factors, particularly for the and states. Variations in the calculations provided no satisfactory understanding of the problem. 相似文献
17.
J.A. Pinston R. Bengtsson E. Monnand F. Schussler D. Barneoud 《Nuclear Physics A》1981,361(2):464-482
The 150Nd(7Li, 5n) reaction has been used to study the high-spin states in the odd-odd nucleus 152Eu. Two rotational bands of different behaviour have been identified: a rather regular band based on the Iπ = 8? isomeric state of configuration and a strongly decoupled system belonging to the configuration .It is shown in this work that the aligned angular momentum carried by each two-quasiparticle configuration in 152Eu is the sum of the alignment of the odd neutron and odd proton, which indicates a negligible influence of the neutron-proton residual interaction. Particular attention has been focused on the strong deviations of the moment of inertia of the core when different quasiparticle configurations are involved. 相似文献
18.
The (12C, 10Be) and (12C, 9Be) reactions on 58Ni were studied at 77 MeV. New levels were determined for both residual nuclei, 60Zn and 61Zn. For 61Zn, levels and a new ground state mass were also measured with the 64Zn(3He, 6He) reaction. A mass excess for 61Zn of ?56333±23 keV was obtained. Angular distributions for the 12C induced reactions are compared with finite range DWBA calculations and found to be insensitive to L? and J-transfer. 相似文献
19.
L.-E. De Geer A. Kerek Z. Haratym J. Kownacki J. Ludziejewski 《Nuclear Physics A》1975,246(1):104-116
The excited states of 14260Nd82 have been studied using the 140Ce(α, 2nγ)142Nd and 142Ce(α, 4γ)142Nd reactions. Singles γ-ray, γ-γ coincidence spectra and angular distributions of γ-rays with respect to the beam direction have been measured. Excited states up to 6.7 MeV with spin values up to 14 are populated. The energy spacings between the lower excited states with spin values up to 8 are similar to those found in the lighter N = 82, even-Z isotones. The majority of the observed states with spin values up to 10 can be explained as two-quasiparticle states. Several of the highest-spin states can be explained qualitatively as fourquasiparticle states. Strong population of the highest excited states (at about 5.7 MeV) is noted, like in other N = 82 isotones. The observed levels in 142Nd are compared with the shell model predictions using a simple δ-force interaction between two nucleons. 相似文献
20.
Y. El Masri J.M. Ferté R. Janssens C. Michel P. Monseu J. Steyaert J. Vervier 《Nuclear Physics A》1976,271(1):133-161
Using the 159Tb(p, 4nγ)156Dy reaction at Ep = 27 to 51 MeV and standard on-line γ-ray spectroscopy methods, the energies and decay properties of members of various rotational bands in the nucleus 156Dy have been investigated, i.e. the ground-state band up to 14g+, the β-vibrational band up to 14β+,the γ-vibrational band up to 11γ+,and two other bands, one with odd-spin levels up to 11, the other with even-spin levels up to 10. The results are compared with various calculations in the framework of the collective model, and no satisfactory fit is obtained; possible improvements of the model to remove these discrepancies are suggested. 相似文献