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1.
The energy dependence of the 12C(16O, α) reaction was measured at incident energies of Elab=112−191 MeV. In the range ofEx(24Mg)=30−56 MeV, the excitation energies of the structures in the inclusive α spectrum were found to vary continuously as a function of incident energy in this region. This fact indicates that these structures do not represent excitations in 24Mg, but rather that they originate from a different process such as a sequential ejectile decay.  相似文献   

2.
The 40Ca(p,p′ α) reaction has been studied at an incident proton energy Ep = 99.5 MeV for proton laboratory scattering angles Θplab = 17°, 23° and 27°. Emission of α particles coincident with the scattered proton has been measured for an angular range Θα 0° − 180° relative to the recoil axis. A multipole decomposition for the α0-decay channel to the 36Ar ground state has been performed from the angular-correlation functions. The energy distribution of the dominating E2 strength deduced in the excitation energy range Ex = 11–21 MeV agrees reasonably well with the results from electron and α-induced α0-decay investigations. The exhaustion of the E2 energy-weighted sum rule in this channel up to an energy of 17 MeV is 16.1(4.0)%, in accord with the study of the (α, α′ α0) reaction. However, this value is twice what is found in the (e,e′ α0) experiment in the same energy region. Thus, the puzzling discrepancy in the E2 strengths derived from electromagnetic and hadronic probes remains unsolved.  相似文献   

3.
Energy spectra and multiplicities of neutrons from the reaction system 838 MeV32S projectiles on197Au have been measured in coincidence with binary fragmentations. Neutron detection was performed simultaneously in a 4 scintillator sphere and by time-of-flight. The linear momentum transfer (LMT) and the excitation energyE CN * are deduced with the folding angle technique. Neutron multiplicities are compared for consistency and discussed as a measure of LMT andE CN * . The saturation ofM 4 (E CN * ) beyondE CN * 400 MeV seen for several systems of high fissility (x0.8) is attributed to the spreading of the folding angle distribution and the increasing competition of charged particle evaporation.  相似文献   

4.
5.
The reaction γd↦π0 X has been measured with TAPS at MAMI in the energy range E γ = 140-300 MeV. Using the Glasgow tagging spectrometer a photon energy resolution of 0.8 MeV was achieved. The energy excitation functions of integral and differential total cross-sections show no structures of statistical significance > 2σ. Upper limits for the production of narrow isoscalar or isovector dibaryons with masses m? 2100 MeV/c2 were deduced. They are in the range 2-5 μb averaged over the 0.8 MeV energy resolution. Received: 25 October 2000 / Accepted: 24 November 2000  相似文献   

6.
Radiative decay of 21 resonances in the 55Mn(p, )56Fe reaction was studied in the proton beam energy region E p = (1.3–1.8) MeV. Branching of decay to many low lying bound states up to excitation energy E x 8 MeV was measured. Exact energy of all resonances has been established, what pointed out that five of the resonances are very close doublets. For all studied resonances their spin-parity characteristics were determined. Assignment of some resonances as isobaric analogues of the states in the 56Mn nucleus was discussed and short note about energy systematics of isobaric analogue resonances was given.  相似文献   

7.
Excitation functions for the 56Fe(α, γ0)60Ni and 56Fe(α, γ1)60Ni reactions have been measured at 90° to the beam direction over the bombarding energy range 8.0–17.6 MeV. Gamma-ray angular distributions were measured at ten bombarding energies. Excitation functions for the 59Co(p, γ0)60Ni and 59Co(p, γ1)60Ni reactions were measured over the range Ex = 16.58–16.92 MeV and compared with the (α, γ) data. The angular distribution data indicate that the (α, γ0) and (α,γ1) reactions proceed through 1, and 1 and 3 states, respectively. The (α, γ) excitation functions are discussed with respect to isospin splitting of the 60Ni giant dipole resonance. The fine structure observed in the excitation functions is shown to be most probably due to Ericson fluctuations. The gross (α, γ) cross sections are shown to be in reasonable agreement with the results of calculations made using the theory of Hauser and Feshbach assuming excitation of the giant dipole resonance.  相似文献   

8.
The reaction 30Si + 238U → 268Sg* was studied at beam energies close to the Coulomb barrier. At a center-of-mass energy of E c.m. = 144.0MeV for reactions at half thickness of the target we measured three decay chains of 263Sg produced by evaporation of five neutrons. The cross-section was ( 67+67 -37) pb. At E c.m. = 133.0MeV we measured three spontaneously fissioning nuclei which we assigned to the isotope 264Sg. The production cross-section was ( 10+10 -6) pb and a half-life of ( 120+126 -44) ms was determined. This half-life is a factor of twenty shorter than theoretical predictions. At E c.m. = 128.0MeV an upper cross-section limit of 15pb was measured. The cross-section data reveal a strong influence of the orientation of the deformed target nucleus on the production yield. Compared to excitation functions measured for the lighter system 16O + 238U → 254Fm*, a reduction of the fusion probability was observed at low beam energies indicating increasing competition from quasifission processes.  相似文献   

9.
The tensor analyzing power fzz has been measured for the 3He( , p)4He reaction at 0 = 0° over an incident deuteron energy range Ed = 6.6–15.8 MeV in steps of 0.5 MeV. The present results agree with and extend the previous measurements of Grüebler et al. The present results indicate that this reaction is a very good tensor analyzer for polarized deuteron beams with energies up to 15.8 MeV.  相似文献   

10.
The energy spectra of photo protons from highly enriched N15 were investigated with the bremsstrahlung from the Heidelberg betatron running at six different endpoint energies between 19 and 30.5 MeV. The protons were detected at 90° to theγ-beam by means of a CsJ-spectrometer with pulse shape discrimination. The energy spectra show pronounced maxima atE p =3.2; 4.6; 9.5 and 13.3 MeV. Proton yields are given as a function of endpoint energy, the yield value atE 0=30.5 MeV being (7.0±0.8) μb/MeV · ster. Because the first excited state in the daughter nucleus C14 lies 6.09 MeV above the groundstate, the cross section for groundstate transitions of the process N15(γ, p)C14 could be derived from the upper 6 MeV of the single proton spectra. The main contribution to the cross section comes from the region between 18 and 26 MeV excitation energy with maxima at 19.5; 20.4; 22.7 and 24.5 MeV. A “pygmy resonance” occurs at 15.2 MeV with further less pronounced structures at 13.6 and 17.0 MeV. The integrated cross section for groundstate transitions up to 30.5 MeV is (22±3) MeVmb assuming isotropic angular distribution. The ratios of protons from transitions to excited states and from the (γ, n p)-reaction to those of groundstate transitions rise from 0.45 atE 0=24.5 MeV to 0.70 atE 0=30.5 MeV.  相似文献   

11.
In a series of experiments, 48Ca induced cold fusion reactions on Pb targets were employed to populate states in 253,254No isotopes. The groundstate band of 254No is identified up to spin 20+. The deduced quadrupole deformation is β=0.27(2). Evidence for decays from a rotational band built on a 7/2[624] configuration was obtained in 253No. The initial angular momentum and excitation energy of 253,254No residues, after neutron emission, was determined. States up to spin 22 ? and excitation energy of E *=8.5 MeV were observed. The data provide direct information on the fission barrier at high spins B f ≥5 MeV, and on the shell-correction energy E shell exp ≥4.1 MeV.  相似文献   

12.
Distributions of the (J =0+, 1+, 2+, 3+, 4+) isoscalar and isovector strength in16O have been calculated in then particle —n hole (n=0, 1, 2) shell model. The isoscalar quadrupole giant resonance comes out fragmentated over eight peaks which exhaust 33% of the EWSR betweenE *=17 and 25 MeV. This result agrees nicely with the recent3He and alpha inelastic scattering experiments. Giant monopole isoscalar (isovector) resonance appears to exhaust more than 50% of the EWSR nearE *=30 MeV (E *=40 MeV). Several collective states of other multipolarities are predicted either near to 30 MeV or between 50 and 60 MeV. The ground state correlations of the 2p2h type give rise to a considerable strength redistributions as compared with the case of the closed shell ground state.On leave fromInstitute of Nuclear Physics, Czechosl. Acad. Sci., 250 68 e, Czechoslovakia.  相似文献   

13.
Calorimetry     
Methods for determining the heat content E */A of hot nuclei formed in energetic nuclear reactions are discussed. The primary factors involved in converting raw data into thermal physics distributions include: 1) design of the detector array, 2) constraints imposed by the physics of the reaction mechanism, and 3) assumptions involved in converting the filtered data into E */A. The two primary sources of uncertainty in the calorimetry are the elimination of nonequilibrium emissions from the event components and accounting for the contribution of neutron emission to the excitation energy sum.  相似文献   

14.
The total kinetic energy release (TKE) of the fissioning nucleus 230Th is measured as a function of the excitation energy Ex, for various mass splittings. A small rise in the TKE(Ex) of 0.2 ± 0.1 MeV per 1 MeV rise in Ex is observed. The mass-yield distributions show fine structure for Ex around 6.7 MeV. The mass yield is presented as function of the TKE.  相似文献   

15.
On the basis of data obtained by the incomplete fusion reactions 7Li(43A MeV)+232Th and 14N(34A MeV)+197Au, the energy dependence of the variance (σ M 2 ) of the fragment mass in fission of highly heated nuclei has been investigated for total excitation energies E tot * ranging from 50 up to 350 MeV. The dependence σ M 2 E tot * shows some unexpected features when E tot * exceeds a value of about 70 MeV. After this value, the steady increase of σ M 2 expected from its temperature dependence changes to some kind of plateau between 100 and 200 MeV. Further on, at E tot * in excess of about 250 MeV, the variance is found to increase again sharply. In order to analyze this behavior quantitatively, a dynamical stochastic model has been developed. The model employs the one-body dissipation mechanism and describes the decay of highly excited and rotating nuclei by fission and light-particle evaporation. It satisfactorily explains the measured prior-to-scission neutron multiplicities and the experimental mass variances up to E tot * ?250 MeV, but the stochastic treatment does not reveal any increase in σ M 2 at higher excitation energies in contradiction with the data.  相似文献   

16.
The decay of 24Na levels below 4.3 MeV excitation was studied by means of the 23Na(d, pγ)24Na reaction at Ed = 2.45 MeV. Gamma-ray spectra were measured at three angles, in coincidence with proton groups detected around 180°. Excitation energies, branching ratios and Doppler shifts were determined. Mean lives were obtained for the levels at 1341 keV (62±15 fs), and 1846 keV (200±50 fs). The 1347 keV level has τ >3 ps. For other levels above 1 MeV upper limits of ≈ 60 fs are set. In some cases spin restrictions follow. In particular J = 2 is assigned to the 1341 keV level.  相似文献   

17.
Inclusive and coincident spectra of alpha particles and fission fragments were measured for the232Th+12C (85 MeV) reaction to study the influence of the excitation energy and the angular momentum on the fission of the compound nucleus and to separate different alpha particle emission mechanisms. At backward angles α emission can be accounted for by the evaporation processes. At forward angles the most important contribution is given by the break-up fusion process. Mass distributions for compound nuclei244Cm (E*=58 MeV,ff coincidences), and240Pu (E*=37 MeV,ff α coincidences) were obtained. In the case of240Pu mass distribution has a shape different from those obtained in light ion reactions at the same excitation energy, indicating the strong influence of the entrance channel. The dependence of the mass distribution shape on the α particle energy is also examined.  相似文献   

18.
We studied the region of giant resonances with positive pions of 226 MeV scattered inelastically on90Zr. Two groups of resonances were seen: the first structure between 12 and 19 MeV excitation energy is explained as a sum of the isoscalar quadrupole resonance at 14 MeV, the isovector dipole resonance at 16.5 MeV and possibly some E0 strength. The second group between 24 and 34 MeV excitation energy also corresponds to more than a simple multipolarity and may be described as a sum of a monopole and a quadrupole isovector resonance.  相似文献   

19.
The inelastic α-scattering reaction at Eα = 120 MeV with an energy resolution of 90–150 keV has been used to investigate isoscalar strength distributions in 24, 26Mg, 28Si and 40Ca. For 24, 26Mg and 28Si the E2 strength between Ex = 14 and 27 MeV is strongly fragmented. In 40Ca the E2 strength is mainly concentrated near Ex ~ 65 A13 MeV, although here the onset of fragmentation can be observed. The sum rule strength for the different multipolarities was obtained by applying for each nucleus an L-dependent normalization procedure. In this way we observed in total in 24, 26Mg, 28Si and 40Ca for excitation energies up to 27 MeV an amount of (61+8?6), (50+9?8), (38+8?6) and (94 ± 14)%, respectively, of the isoscalar E2 energy weighted sum rule (EWSR) of which (36+7?5), (28+8?7), (24+7?5) and (74 ± 12)% was found between Ex = 14 and 27 MeV. In addition isoscalar E0, E3 and E4 strength was observed in this excitation energy region. A detailed comparison has been made between the isoscalar quadrupole strength distribution observed in the 24, 26Mg(α, α') reaction and the E2 strength excitation function obtained from radiative α-capture measurements. In the low excitation energy region coupled channel effects have been observed, especially for the excitation of the 3+ states. Moreover, a considerable percentage of the 1?ω isoscalar dipole and octupole strength has been observed for excitations below 14 MeV.  相似文献   

20.
Spatial distributions of energetic charged particles, neutrons and gamma rays at altitude 500 km (below the radiation belts of the Earth), obtained by the measurements of two apparatuses on board the Intercosmos-17 satellite, are presented. The latitudinal dependences, [i.e. the variation of flux with vertical cut-off rigidity of the measurement point], for neutrons (E n = 1 –30 MeV), gamma rays (E =0·15–6 MeV), secondary electrons (E e > 100 MeV) and for primary protons coming from the west and the east, respectively, are given. The main characteristic, the ratioN p/N e of the counting rate of the particles in the polar regionN p(Rvert< <0·1 GeV/c) and on the equatorN e(Rvert > 16 GeV/c), is obtained for the various types of particles. This value is 10 for neutrons, 3.7 for gamma rays, 1·8 for electrons, 11 for protons in westward direction, 10 for protons in eastward direction. The latitude profile of neutrons and gamma rays is in a good agreement with calculations assuming their production by nuclear reactions of primary cosmic rays with nuclei of the atmosphere. The weakening of rigidity dependence of protons coming from east in comparison with those coming from the west, is interpreted as the cause of additional proton albedo flux. The equality of albedo electron fluxes (Ee = 100–3500 MeV) from these directions is observed. With the use of the shadowing effect the obtained data on electron-positron component are consistent with the flux of albedo positrons (Ee + > 3·5 GeV) of the value (0·5±0·2) m–2. s–1. ster–1. The possibility of abundance of albedo positrons above electrons at these altitudes for the energy intervalE=0·2÷0·3 GeV is indicated.  相似文献   

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