Electrofission of238U and232Th

Absolute electrofission cross sections for²³⁸U and²³²Th in the energy regionE _e =7 ?65 MeV and fission fragment angular distributions forE _e =7–30 MeV have been measured. The angular distributions show strong anisotropies for low energies. The relative dipole and quadrupole contributions as a function of excitation energy are discussed in terms of the low lying fission transition states above the fission barriers. The cross sections show significant deviations from the results of some earlier measurements, in particular in the energy region above the giant dipole resonance. From the difficulties of absolute electrofission cross section measurements and the ambiguities in their interpretation it is concluded that by this time the quantitative analysis of electrofission cross sections with respect to the contributions of the giant quadrupole resonances to the fission decay channel should be regarded as rather tentative.     

Observation of orbital magnetic dipole strength in the actinide nuclei 232Th and 238U

Precise experimental information has been obtained on the distribution of orbital M1 strength using high resolution nuclear resonance fluorescence and inelastic electron scattering. We report on the first observation of those J^π = 1⁺ states in actinide nuclei that are excited by the M1 scissors mode. The M1 strength induced through the convection current part of the M1 operator is closely centered around 2 MeV in both nuclei. The observed spreading of strength is again of the same magnitude that has been observed already in rare-earth nuclei.     

Photofission in238U,232Th and209Bi at intermediate energy

Fragment energy correlation measurements have been made for²³⁸U,²³²Th and²⁰⁹Bi with bremsstrahlung of 600 MeV maximum energy. The study was performed with silicon surface barrier detectors. Distributions of kinetic energy as a function of fragment mass are presented. The results are compared with earlier photofission data and, in the case of bismuth, with calculations based on the liquid drop model.     

Radiationless transition probabilities in muonic208Pb,232Th,and238U

The probabilities for non-radiative (n.r.) excitationsP _n.r. in the muonic nuclides²⁰⁸Pb,²³²Th, and²³⁸U have been determined from (μ^?,γγ)-measurements by comparing the intensities of muonic X-ray transitions in single and coincidence spectra. The value ofP _n.r. (3p→1s), measured for the first time, is about 90% for the actinides²³²Th and²³⁸U, but only about 8% for²⁰⁸Pb. The value ofP _n.r. (3d→1s) is found to be 10 % for²³³Th, 13% for²³⁸U, and about 4% for²⁰⁸Pb. For²⁰⁸Pb a vanishing strength of the n.r. decay of the 2p-level is found, while for²³²Th and for²³⁸U n.r. strengths of about 20% and 26%, respectively, are observed. By regarding two subcomplexes of the 2p→1s transitions leading to different mean excitation energies the n.r. transition probabilities were found to be different for²³⁸U only, 21.6% and 31.1.%, respectively.     

Parity violation at neutron p-wave resonances of238U and232Th and related questions

Parity violation effects have been studied at 40 neutron p-wave resonances of the even-even nuclei²³⁸U and²³²Th. Of these 11 show parity violation effects larger than 2 standard deviations, making parity violation a rather common phenomenon. Parity mixing up to 10% has been found. The root-mean squared matrix elements for parity violation derived from these resonances are M=0.58 (+0.50/-0.25) meV for²³⁸U, respectively 1.39 (+0.35/-0.38) meV for²³²Th.     

Symmetric and asymmetric yields in the photofission of232Th,235U,238U and239Pu

Measurements are presented for the mass and energy distributions of fragments from the photofission of²³²Th,²³⁵U,²³⁸U and²³⁹Pu. The experiments were performed for bremsstrahlung endpoint energies between 15 and 55 MeV, using silicon surface barrier detectors. The results are discussed with respect to the competition between the symmetric and asymmetric fission modes.     

Energy Dependence of the Most Stable Nuclei Production in Proton-Induced 238U and 232Th Fission

Using the available experimental data, production cross sections of the most stable nuclei have been calculated for the proton-induced fission of ²³⁸U and ²³²Th at 12, 20, 35, 50, 96 MeV in case of ²³⁸U and at 8, 9.3, 12, 19.55, 32.2, 44.7, 53 MeV for ²³²Th. The analysis has been carried out for the fission fragment mass ranges corresponding to N/Z ratios in the ranges 1.33 ± 0.09 and 1.32 ± 0.08 for ²³⁸U and ²³²Th respectively. Results have been compared with the ones generated indirectly by employing GEF nuclear reaction code, version 2017/1.1. From the production cross sections point of view, for the same energy, ²³²Th is found to be a better target than ²³⁸U for producing nuclei A around the symmetric mass peak, while ²³⁸U comes out to be a better one than ²³²Th for producing the fission fragments around the asymmetric peaks of the mass distribution.

     

Cranking-HFB calculations of the yrastline for the nuclei232Th,234,236,238U,248Cm

The CHFB method is applied to actinide nuclei. The calculated neutron alignment agrees with the experimental data, but for the proton alignment discrepancies are observed. The reliability of our approach and the information from measured odd-mass-actinide spectra are discussed. It is concluded that the experimental even-even spectra might have to be interpreted as bands in which the lowest excitation of two (651, 3/2) protons is not populated.     

Determination of terrestrial gamma, 238U, 232Th and 40K in soil along fracture zones

²³⁸U, ²³²Th and ⁴⁰K concentrations in 72 soil samples from two major fault systems (North and East Anatolian Active Fault Sytems) in Turkey have been studied. However, terrestrial gamma radiation dose originated by natural radionuclides in soil was measured and compared with other measurements in literature for different countries. This extensive survey regarding U, Th and K radionuclide and terrestrial gamma dose measurement was carried out by means of NaI(TI) gamma spectroscopic system and a dose rate meter, respectively. The mean concentration of ²³⁸U, ²³²Th and ⁴⁰K in soil samples in NAFS is higher than determined in EAFS. The measured and calculated mean gamma dose rates in two fault systems are found to be higher than 57 nGyh⁻¹.     

Elastic and inelastic4He-scattering on208Pb,232Th and234, 236, 238U

The angular distributions of the elastic⁴He-scattering on²⁰⁸Pb and the elastic and inelastic⁴He-scattering on²³²Th and^234,236,238U at \(E_{4_{He} } = 50 MeV\) were measured between 20° and 60°. The⁴He-particles were detected with a position sensitive detector in the focal plane of a split-pole spectrograph. The aim was to get data to determine the deformation parameters of the equilibrium states by coupled channels calculations.     

Heavy-ion potentials for ellipsoidally deformed nuclei and application to the system 238U + 238U

The nuclear potential between deformed nuclei is calculated within the framework of the double-folding model. An analytical expression for the potential is obtained on condition that the two-body interaction is of gaussian type and the nuclear densities have ellipsoidal equidensity surfaces. The computed potential values are used for a least-square fit of the radial potentials in a multipole expansion of the heavy-ion potential. The method is applied for the calculation of the ²³⁸U + ²³⁸U potential.     

Activity concentrations of 238U and 232Th in some soil and fertilizer samples using passive and active techniques

Uranium and thorium concentrations in some soil and fertilizer samples were determined using passive technique with CR-39 and LR-115 polymeric nuclear track detectors, whereas the fertilizer samples were measured using active technique with passive technique. The two different techniques have been used in order to ensure and compare between the obtained results. The main purpose of the present investigation is to assess the activity concentration of ²³⁸U and ²³²Th in soil of particular regions and measure the pollution due to the production plant of complex fertilizers. From the obtained data we can conclude that there is no radioactive healthy hazard for human and living beings in the selected area.     

Structure of high-spin states in 232Th, 234U and 236U

Multiple Coulomb excitation of ²³²Th, ²³⁴U and ²³⁶U by 5.3 $\text{MeV}\text{u}$²⁰⁸Pb ions has been studied using γ-ray spectroscopy. Excitation of ground-band levels is observed up to spin I^π = 26⁺ (tentatively 28 ⁺) in ²³²Th and ²³⁴U and I^π = 28⁺ (tentatively 30⁺)in ²³⁶U. High-spin levels of the K^π = 0^? octupole-vibrational bands are also observed in these nuclei. The measured transition energies between ground-band levels suggest that at $\text{I≈ 28}\text{h}\text{?}$ several units of angular momentum are carried by single particles aligned with the rotation axis.This result can be understood in terms of a super band built on aligned two-quasiparticle configurations which crosses the ground-state rotational band at a rotational frequency of $\text{h}\text{?}\text{ω ? 0.25}\text{MeV}\text{(I ? 28}\text{h}\text{?}\text{)}$. The E2 transition-matrix elements deduced from the experimental γ-yields agree within their errors with the rigid-rotor predictions up to the highest spins observed.The experimental results are discussed using the concept of rotation alignment and are compared with predictions of the rotation-vibration model and the interacting-boson model.     

Cross sections for 209Bi, 232Th, 235U, 238U, and 237Np fission induced by intermediate-energy protons and deuterons

The cross sections for ²⁰⁹Bi, ²³²Th, ²³⁵U, ²³⁸U, and ²³⁷Np fission induced by protons of energy in the range 1.0–3.7 GeV and by deuterons of energy 1.0 GeV were measured. The results are compared with data from other experiments, with available estimates, and with the predictions of theoretical models.     

The low-energy dipole structure of <Superscript>232</Superscript>Th , <Superscript>236</Superscript>U and <Superscript>238</Superscript>U actinide nuclei

In this study, I^p = 1⁺\ensuremath I^{\pi} = 1^{+} and I^p = 1^-\ensuremath I^{\pi} = 1^{-} dipole mode excitations are systematically investigated within the rotational and translational + Galilean invariant quasiparticle random-phase approximation for ²³²Th , ²³⁶U , and ²³⁸U actinide nuclei. It is shown that the investigated nuclei reach a B(M1) strength structure, which corresponds to the scissors mode. The calculated mean excitation energies as well as the summed B(M1) value of the scissors mode excitations are consistent with the available experimental data. The results of calculations indicate large differences to the rare-earth nuclei as is the case for the experiment: a doubling of the observed dipole strengths and a shift of the energy centroid to the lower energies by about 800keV. The calculations indicate the presence of a few prominent negative-parity K^p = 1^-\ensuremath K^{\pi} = 1^{-} states in the 2.0-4.0MeV energy interval. The occurrence of the negative-parity dipole states with the rather high B(E1) value less than 4MeV shows the necessity of explicit parity measurements for the correct determination of the scissors mode strength in ²³²Th , ²³⁶U , and ²³⁸U isotopes.     

Fission of 232Th, 238U, 244Pu, 248Cm induced by Xe and Kr ions at coulomb barrier energies

Excitation functions and angular distributions have been measured for the fission of ²³²Th, ²³⁸U, ²⁴⁴Pu and ²⁴⁸Cm induced by ⁸⁶Kr and ¹³⁶Xe ions at energies in the vicinity of the Coulomb barrier. No large differences as a function of either target or projectile were found. These results suggest that the main process occuring is not Coulomb fission.     

Investigation of the <Superscript>232</Superscript>Th and <Superscript>238</Superscript>U photofission

The average angular momenta of the ⁸⁴Br, ¹³²Sb, ¹³³Te, and ¹³⁵Xe fission fragments, produced as a result of ²³²Th and ²³⁸U photofission by bremmsstrahlung γ photons with an endpoint energy of 8.5 MeV, have been determined by measuring the isomeric yield ratios. The experimental isomeric yield ratios have been calculated taking into account the contribution from β decay of isobaric nuclei to the yields of isotopes studied.     

Possible observation of light neutron nuclei in the alpha-particle-induced fission of 238U

Searches for nuclear-stable multineutrons among products originating from the fission of ²³⁸U nuclei that is induced by 62-MeV alpha particles were performed by the activation method. The reaction involving the transfer of four neutrons and occurring on the isotope ⁸⁸Sr, ⁸⁸Sr( ^x n, (x ? 4) n)⁹²Sr??⁹²Y, was used to identify nuclear-stable multineutrons. A line at the energy of E = 1384 keV was found in the measured gamma-ray spectra of irradiated samples. This line, together with the measured time dependence of the decrease in its activity, is indicative of the formation of the beta-active nucleus ⁹²Sr. This result was reproduced in repeated measurements. It suggests the possible existence of nuclear-stable multineutrons ( ^x n) for x ?? 6. The differential cross section for the ^x n yield at an angle of 30° in the alpha-particle-induced fission of ²³⁸U was about 6 × 10^?2 mb/sr.