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1.
Differential cross sections for the 38Ar(α, γ0)42Ca, 40Ar(α, γ0, 1)44Ca and48Ti(α, γ0, 1)52Cr reactions were measured at 90° to the beam direction in 50 or 100 keV steps over the bombarding energy ranges 6.0–15.0 MeV, 5.5–11.1 MeV and 6.0–12.0 MeV respectively. Gamma-ray angular distributions were measured at forty bombarding energies. These show that the (α, γ0) reaction proceeds through 1? levels and to a lesser extent 2+ levels, whereas the (α, γ1) reaction most probably proceeds through 1? and 3? levels. It is deduced that 〈Γ〉/〈D〉 ≦ 1 for the 40Ar(α, γ)44Ca. reaction whereas the fine structure observed in the 48Ti(α, γ)52Cr reaction is probably due to fluctuations. From a comparison with other data it is shown that the (α, γ) reaction is most probably statistical in nature. Using Hauser-Feshbach theory it is deduced that the 36Ar(α, γ)40Ca. reaction is inhibited by isospin selection rules and an estimate is made of isospin mixing in the 40Ca giant dipole resonance. The 38Ar(α, γ)242Ca and40Ar(α, γ)44Ca data are considered with respect to theories of isosopin splitting of the giant dipole resonance.  相似文献   

2.
Excitation functions at θ = 90° have been measured for 16O(3He, γ0?2, 3?5, 6)19Ne, 15N(3He, γ0, 1?4)18F, 14N(3He, γ0, 1,2,3)17F, and 20Ne(3He, γ0 + 1)23Mg, in the range E3He = 3–19 MeV. The first reaction has also been studied at θ = 40°. Excitation functions at 90° have also been measured for 40Ca(3He, γ0?2)43Ti for E3He = 4–17 MeV and 4He(3He, γ0 + 1)7Be for E3He = 19–26 MeV. Angular distributions have been measured for the first four reactions.For the most excitation functions, a broad peak is observed, several MeV wide, centred at about Ex≈ 20 MeV. Superimposed on this, in some cases, are narrower peaks, with width ≈ 1 MeV. Energies and widths have been extracted for all resonances.Cluster-model calculations have been carried out, using methods similar to those which have proved successful for low-lying states in A= 18–19 nuclei. No satisfactory correspondence with the present results was found. The shell model has been used to calculate Γ3He and Γγ for 1?ω excitations in the final nuclei. These generally show good agreement with the trends of the experimental data. The results are consistent with the excitation of the giant dipole resonance in 3He capture, but much more weakly than in proton capture.  相似文献   

3.
Angular distributions of γ-rays from the 2H(d, γ)4He reaction have been measured at the deuteron energies Ed = 6.05, 8.96 and 11.67 MeV with a 12.7 cm × 15.2 cm NaI(Tl) crystal enclosed in a Cerenkov anticoincidence shield. A least-square fit of the angular distributions indicates that the differential cross section is proportional to sin2θ cos2θ and that the process proceeds through an E2 transition of the type 1D21S0.  相似文献   

4.
The γ-ray spectra from the reactions 89Y(n, γ)90Y and 140Ce(n, γ)141Ce have been measured in the neutron energy range of 6.2–15.6 MeV. The pulse-height spectra were recorded with NaI(Tl) spectrometers and time-of-flight techniques were used to improve signal-to-background ratio. Capture cross sections were determined for γ-ray transitions to the two 2d52 levels at 0 and 203 keV of 90Y and to the 2f72 ground state of 141Ce as well as integrated cross sections to bound states in these nuclei. The observed γ-ray spectra and partial radiative capture cross sections were compared with predictions of the direct-semidirect capture theory. The resonance behaviour with neutron energy of both the ground-state and integrated partial capture cross sections shows the validity of the semidirect model for 89Y and 140Ce in the region of neutron energy encompassing the giant-dipole resonance. The observed symmetry of the cross sections about the peak of the resonance argues strongly for the complex form of the particle-vibration coupling interaction. A detailed comparison of the predictions of the DSD model using the complex coupling interaction shows that the capture cross sections are relatively insensitive to the real part of the interaction.  相似文献   

5.
We report a measurement of the forward-backward asymmetry in the radiative capture of polarized cold neutrons in the reaction 35Cl(n, γ)36Cl where 36Cl is in the ground state. The measured value of the asymmetry is a = (1.57 ± 0.531) × 10?4. We deduce the mixing between the 2+ capture level and the neighboring 2? levelto be 〈2?¦Hp.v.¦2+〉 = ?0.25 ± 0.08 eV before corrections. A measurement of the integral asymmetry of all γ-rays in the neutron capture by 35Cl leads to agreement with measurements at Leningrad.  相似文献   

6.
The 102Mo activity was obtained by photofission of natural U and thermal-neutron induced fission of 235U, with subsequent chemical separation of the molybdenum fraction. In addition, nuclei with mass 102 were separated from fission products of 235U(nth, f) using the mass separator LOHENGRIN. A decay scheme and absolute γ-intensities are deduced from measured γ-ray, X-ray and γ-coincidence spectra. Logftvalues are calculated. Shell-model calculations for a (πlg92)3(νlg72)3 multiplet have been carried out using effective nucleon-nucleon interactions. The γ-decay between low-lying, low-spin members of this multiplet was studied in detail and compared with the experimental data.  相似文献   

7.
The 48K, 49K and 50K nuclides have been produced in high energy fragmentation and analyzed by mass spectroscopy techniques. Their half-lives have been measured as 6 ± 1 s, 1.1 ± 0.3 s and and 0.7 ± 0.3 s, respectively. The γ-rays from their radioactive decay have been observed and the corresponding γ-intensities measured. The nuclide 50K is shown to be a delayed neutron emitter. The antianalog states in the daughter Ca nuclei with a (1d32)? neutron configuration, preferentially populated in the β-decay, have been located. The corresponding 1d32 neutron single-particle energy is found to remain approximately constant for these neutron-rich Ca isotopes.  相似文献   

8.
Energy levels in 42Ca up to 7.8 MeV have been studied in the neutron capture reaction 41Ca(d, p)42Ca with 12 MeV bombarding energy. Ninety-four excited states have been identified and angular distributions have been measured in the interval from 5° to 110° by means of a broad-range magnetic spectrograph. The angular distributions together with DW calculations have been used to determine In values and spectroscopic factors. The f72 strength sum agrees with shell-model expectations if the f72 spectroscopic factors are renormalized by 10.75, in line with other f72. transfer experiments on 40Ca and 41Ca. A similar renormalization of the ln = 1 spectroscopic factors brings this strength sum in accordance with the shell-model calculations. The effective (f722) matrix elements for 42Ca are compared with the corresponding matrix elements of 42Sc and 48Sc. The differences between the three sets of matrix elements are of the order of a few hundred keV or less. The monopole centroid energy of the (f72)2 multiplet is shifted downwards in the mass-42 nuclei compared to 48Sc, possibly indicating the importance of the monopole pairing force near 40Ca.  相似文献   

9.
The nucleus 11B has been studied over the excitation energy range from 8.5 MeV to 21.5 MeV with the 9Be(3He, p)11B / reaction at / E3He = 38 MeV. The analogs of the parent states in 11Be have been located at 12.56, 12.92, 14.40, 16.44, 17.69, 18.0, 19.15 and 21.27 MeV. A complementary measurement with the 9Be(α, d)11B reaction at Eα = 48 MeV demonstrates that the 16.44, 17.69, 18.0 and 19.15 MeV resonances have rather pure isospin Tf = 32. The 14.40 MeV state is a strongly isospin-mixed analog of the 52+1.78 MeV state in 11Be. It is argued that spin S = 1 transfer is involved in the excitation of the 16.44 MeV state and its 3.887 MeV parent in 11Be in a two-step stripping process. The Tf = 12 states and the lowest three Tf = 32 states are compared with the predictions of DWBA utilizing shell-model form factors. It is concluded that the Tf = 12 strength is more strongly fragmented than is implied by the calculations of Teeters and Kurath.  相似文献   

10.
Excitation functions of the capture reaction 12C(p, γ0)13N have been obtained at θγ = 0° and 90° and Ep = 150–2500 keV. The results can be explained if a direct radiative capture process, E1(s and d → p), to the ground state in 13N is included in the analysis in addition to the two well-known resonances in this beam energy range [Ep = 457(12+) and 1699 (32?) keV]. The direct capture component is enhanced through interference effects with the two resonance amplitudes. From the observed direct capture cross section, a spectroscopic factor of C2S(l = 1) = 0.49 ± 0.15 has been deduced for the 12? ground state in 13N. Excitation functions for the reaction 12C(p,γ1p1)12C have been obtained at θγ = 0° and 90° and Ep = 610–2700 keV. Away from the 1699 keV resonance the capture γ-ray yield is dominated by the direct capture process E1 (p → s) to the 2366 (12+) keV unbound state. Above Ep = 1 MeV, the observed excitation functions are well reproduced by the direct capture theory to unbound states (bremsstrahlung theory). Below Ep = 1 MeV, i.e., Ep → 457 keV, the theory diverges in contrast to observation. This discrepancy is well known in bremsstrahlung theory as the “infrared problem”. From the observed direct capture cross sections at Ep ? 1 MeV, a spectroscopic factor of C2S(l = 0) = 1.02 ± 0.15 has been found for the 2366 (12+) keV unbound state. A search for direct capture transitions to the 3512 (32?)and 3547 (52+) keV unbound states resulted in upper limits of C2S(l = 1) ≦ 0.5 and C2S(l = 2) ? 1.0, respectively. The results are compared with available stripping data as well as shell-model calculations. The astrophysical aspect of the 12C(p, γ0)13N reaction also is discussed.  相似文献   

11.
The 91Zr(d, 3He) reaction was studied at a deuteron energy of 28 MeV. Angular distributions were measured from 13° to 47°; lp values were extracted for the prominent lines of 90Y. The lp values and transition strengths were determined by DWBA analysis. The angular distributions for the p12)(νd52) doublet (g.s. and 0.20 MeV state) exhibit the characteristic l = 1 shape. States at 1.42, 1.57, 1.64 and 1.81 MeV were also populated strongly in the (d, 3He) reaction; the 1.42, 1.57 and 1.81 MeV levels contain l= 1 transition strength and are most likely members of the p32?1)(νd52) multiplet. The 2.03 MeV state has a characteristic l = 3 angular distribution and is suggested to be the only member of the f32?1)(νd52) sextet to be unambiguously observed in this study, most probably the 5? or 4? member. The members of the g52)(νd92) sextet were populated weakly (less than 100 μb/sr) in this reaction.  相似文献   

12.
The g-factors of the 10+ isomeric states in 194Hg and 196Hg have been measured using the in beam IPAD method. The results g(194Hg) = ?0.24(4) and g(196Hg) = ?0.18(9) are in agreement with the value expected for an (i132?2) neutron satructure and clearly contradict the previous assignment as (h112?2) proton configurations. Cranking model calculations show that the neutron excitation energies in the rotating frame agree satisfactorily with the experimental energies and that the proton excitations are expected ≈2 MeV above the experimental yrast line  相似文献   

13.
The excitation function of the 12C(α, γ0) reaction at θ = 90° has been remeasured for bombarding energies between 6.5 and 8.5 MeV. The measurement was made to resolve discrepancies apparent in earlier measurements relating to the absolute cross section, the location of the lower 1? resonance near 7.05 MeV (16O excitation energy 12.44 MeV) and to the relative peak cross sections of this resonance and a second 1? resonance at 7.88 MeV.  相似文献   

14.
States in 92Tc have been studied by means of the 92Mo(3He, t) reaction at 27.5 MeV. The Q-value for this reaction and the excitation energy of the isobaric ground state analogue of 92Mo were determined to be ?7.882 ± 0.030 MeV and 3.813 ± 0.030 MeV respectively. Strongly populated levels in 92Tc appear to belong to configurations arising from the (1g92)π(1g92)ν?1 multiplet.  相似文献   

15.
Neutron capture and transmission measurements have been carried out on the separated isotopes of 147Sm (98.34 %) and 149Sm (97.72 %) at the 55 m time-of-flight station of the Japan Atomic Energy Research Institute electron linear accelerator. Resonance energies and neutron widths for a large number of resolved resonances were determined up to 2 keV for 147Sm and 520 eV for 149Sm. Radiation widths for 5 resonances in 147Sm + n and 7 resonances in 149Sm + n were derived. The s-wave strength functions, average level spacings and average radiation widths were obtained to be: 104S0 = 4.8 ± 0.5, D = 5.7 ± 0.5 eV and Γγ = 69 ± 2 meV for147Sm; a 104S0 = 4.6 ± 0.6, D = 2.2 ± 0.2 eV and Γγ = 62 ± 2 meV for149Sm. The average capture cr sections were deduced from 3.3 to 300 keV with an estimated accuracy of 5 to 15 %. The measured capture cross sections for 149Sm are largely different from the evaluated data, which are obtained based on the statistical model calculation. Possible reasons for this disagreement are discussed.  相似文献   

16.
The hole-hole structure of 94Y was studied via the reaction 96Zr(d, α)94Y and compared to the particle-hole structure of 90Y, which was populated by the reaction 92Zr(d, α)90Y. The deuteron beam energy was 28 MeV. Angular distributions of both reactions were obtained for the prominent lines. New states of 94Y were observed at 0.44, 1.17, 1.39, 1.53, 1.82, 1.90, 2.17, 2.33, 2.46 and 2.77 MeV. Our data are consistent with the previously reported 2? assignment of the ground state, and we suggest Jπ = 3? for the 0.44 MeV state, these being members of the (π2p12, ν2d32?1) doublet. The 1.17 state is suggested to be a member of the (πp32?1, νd52?1) multiplet. The Q-value of the 96Zr(d, α)94Y reaction was measured to be 7.609 ± 0.020 MeV. The reaction 94Zr(d, α) was performed at two angles. Several new states of 92Y were observed at 0.31, 0.78, 1.03, 1.31, 1.49, 1.69 and 1.89 MeV.  相似文献   

17.
The γ-decay of deep-hole states in 101, 105, 107Pd was studied via the (3He, αγ) reaction at E3he = 70 MeV and supplemented by data from 112, 118Sn targets to investigate the deep-hole spreading mechanism. The γ-decay pattern for the g92 deep-hole state shows a strong dependence on the spreading width: if the deep-hole state is observed as a sharp peak, it mainly decays to the low-lying 72+ state by a spin-flip M1 transition with a large M1-E2 mixing ratio; if the deep-hole state is observed as a broad bump, it decays statistically indicating the complete spreading of the hole strength over the underlying states; if the deep-hole state is observed with a structure intermediate between a sharp peak and broad bump, its γ-decay shows both decay patterns.A sharp peak at Ex = 2.396 MeV in 101Pd which carries a large fraction of the g92 hole strength (C2S = 2.0) was found to be a single state having a width of less than 2.5 keV.For the spin-flip M1 transition the destructive interference between the g92 component and the coupled components of the deep-hole state was found in heavily spread states.A quasiparticle-plus-rotor (QPR) model was applied to calculate the fragmentation in the doorway stage for the g92 neutron deep-hole state in the Pd isotopes. A reasonable agreement between the calculation and the experimental results was obtained for the strength fragmentation, for the nucleus 101Pd. However, the large M1-E2 mixing ratio experimentally observed was not reproduced.  相似文献   

18.
The cross sections for proton capture by 11B to the ground and excited states of 12C have been measured in the proton energy interval between 18 and 43 MeV. The ground-state cross section shows good agreement with theoretical calculations including correlations. Capture photons have also been observed to all the residual 1p-1h states of 12C having a dominant 1p?132 hole: the corresponding cross sections systematically show a giant resonance whose energy increases with the increasing excitation energy of the “background” level. The resonances at 27.4, 31, 33.2, 37 and 43 MeV, seem to show observable interference effects.  相似文献   

19.
Accurate lifetimes have been measured for low-lying levels in 22Ne, 28Si and 31P by bombarding 4He implanted targets with beams of 19F and 28Si ions. Mean lifetimes determined by fitting Doppler-broadened γ-ray lineshapes were (Exin MeV, τ in ps): 22Ne (1.275, 5.15 ± 0.31; 3.357, 0.324 ± 0.009), 28Si (1.779, 0.667 ± 0.035), 31P (1.266, 0.70 ± 0.07; 2.234, 0.363 ± 0.024). The lifetime values for the 3.357 MeV level in 22Ne and the 2.234 MeV level in 31P are used to calibrate low velocity DSAM lifetime data for these two levels and to obtain scaling factors to theoretical electronic stopping powers for Ne and P ions.  相似文献   

20.
Levels of 48Sc up to 3.33 MeV excitation were studied by the reaction 48Ca(p,nγ)48Sc employing a variety of experimental techniques. A level scheme of 48Sc comprising 29 excited states and 54 transitions were determined from the measurements of γ-γ coincidences and γ-ray excitation functions. Within the framework of the statistical compound nucleus model spins and parities of the 48Sc levels were assigned from the angular distributions and linear polarizations of the de-excitation γ-rays as well as the excitation functions of the residual levels. From the present experimental results and other available data we tentatively identified some of the levels of the (1f729, 1d32?1), (1f729, 2s12?1), (1f727, 2p32) and (1f727, 1f52) configurations in addition to the well-known (πf72, vf72?1) multiplet.  相似文献   

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