Half-life measurements of the 86.6 keV level in233Pa and 59.6 keV level in237Np

The half-lives of the 86.6 keV level in²³³Pa and the 59.6 keV level in²³⁷Np have been measured. A silicon surface barrier alpha detector and a NaI(Tl) gammadetector were used. The decay time spectrum of alpha-gamma coincidences obtained from a start-stop type of time-to-pulse height converter was recorded on a 2048-channel analyser. Analysis of the data gave the following half-life values: $$\begin{gathered} T_{\frac{1}{2}} :^{233} Pa (86.6 keV level) = (37.4 \pm 0.4) ns \hfill \\ T_{\frac{1}{2}} :^{237} Np (59.6 keV level) = (66.7 \pm 0.7) ns \hfill \\ \end{gathered}$$ . Using the experimental levelT _1/2's, partial gamma-ray half-lives have been calculated for the 86.6- and the 29.6-keV transitions (from the 86.6 keV level) in²³³Pa and the 59.6- and the 26.36-keV transitions (from the 59.6 keV level) in²³⁷Np. The results are compared with the single particle and the Nilsson estimates.     

Muon attachment in prompt fission of237Np

The probabilities of muon attachment to fission fragments in the prompt fission of²³⁷Np have been determined as a function of fragment mass and total kinetic energy release in a ( ^–,f ₁ f ₂ e ^–)-coincidence measurement. A strong dependence of the attachment probability on the fragment mass is observed. The experimental results are compared with theoretical predictions.It is a pleasure to thank Professor T. Mayer-Kuckuk for his co-operation in performing the project. We gratefully acknowledge the permanent support of Professor J.P. Blaser and his staff at PSI. We thank Professor R. Engfer, Dr. A.v.d. Schaaf, and Dr. H.C. Walter for their support in using the electron spectrometer SIN-DRUM I. We are thankful to Professor S. Polikanov (GSI) and to Dr. T. Krogulski (University of Warsaw, Bialystok) for intensive and fruitful discussions. We appreciate the collaboration of Professor W. Müller and Dr. J. Pauwels (CBNM-Mol) in the target preparation. This work has been funded by the German Federal Minister for Research and Technology (BMFT) under the contract number 06BN271 (PD, HH, FR, ChR, WS). We thank the following institutions and organisations for financial support: Foundation for Fundamental Research on Matter (FOM), the Netherlands Organisation of the Advancement of Pure Research (NWO) (JK, CdL, AT), and the Swiss National Foundation (SNF) (WB, EH; HP, DV). One of the authors is grateful for a fellowship granted by the Studienstiftung des deutschen Volkes (FR).     

Investigating 237Np and 241Am photofission

Average angular momenta of the fission fragments ⁹⁰Rb, ¹³⁰Sb, ¹³³Te, ¹³⁴I, and ¹³⁵Xe resulting from ²³⁷Np photofission induced by Bremsstrahlung ??-ray quanta with endpoint energies of 9.8 and 17 MeV, and from ²⁴¹Am photofission induced by ??-ray quanta with an endpoint energy of 17 MeV, are found by measuring the isomeric yield ratios. The experimental values of the isomeric ratios are calculated with allowance for the contribution from the beta decay of isobaric nuclei to the yields of the investigated isotopes.     

237Np separation from environmental matrices by extraction chromatography method

Aliquat-336 anchored on hydrophobized silica gel was used for effective separation of ²³⁷Np from soil matrices and from model solutions. Alpha spectrometry for ²³⁷Np determination was used. The interfering radionuclides present in environmental samples such as ²³⁴U, ²³²Th, ²³¹Pa and ^239+240Pu were removed by separation with nitric acid solutions containing formic acid and ferrous sulfamate as reducing agents. Spiking samples with ^238,234U, ²³²Th and ²³⁸Pu were used to check separation effectiveness. A separation yield of ²³⁷Np from soil matrices was checked by measuring of added known amount activity and was found to be about 15%. The yield of separation for model solutions was about 56%. Different parameters of eluant on recovery of ²³⁷Np from column were studied.     

237Np Mössbauer spectroscopy on neptunium doped borosilicate glasses

Mössbauer and magnetization measurements have been carried out on borosilicate glasses containing neptunium. Different melting and annealing times, in various crucibles have been investigated. Using the 59.5 keV Mössbauer resonance in²³⁷Np we have characterized valency states of neptunium ions in glasses and studied hyperfine interactions. Roughly, absorption spectra show two sites easily differenciated above 50 K by two lines. Isomer shifts (relative to NpAl₂) are respectively: – 10.0 (1.0) and + 32.5(.5) mm/s. These resonance lines can be assigned, the first at Np⁴⁺, the second at Np³⁺ species. The intensity ratio Np⁴⁺/Np³⁺ varies with elaboration conditions. At 4.2 K, Np⁴⁺ ions exhibit a hyperfine splitting arising from relaxation phenomenon. Magnetization measurements do not show any magnetic ordering.     

The probability of prompt and delayed fission of muonic237Np

Fission fragments from the reaction²³⁷Np(μ ^?,γ,f) have been measured in coincidence with muonic X-rays. The efficiency of the fission fragment detector is determined from (μ ^?,γ,f)-data of the same experiment. The total fission probability perμ-stopP _t has been measured as well as the fission probabilities P_f of the non-radiative muonic (3d→1s)- and (2p→1s)-transitions; the latter has been divided into two parts leading to different mean excitation energiesE:P _t =(54±17)%,P _f (3d→1s)=(41±21)%,P _f (2p→1s,E=6.218 MeV)=(61±19)%, andP _f (2p→1s,E=6.525 MeV)=(57±18)%. The influence of the muon on the fission barrier is discussed. The fission probability after muon capture is compared with a calculated value using a distribution of nuclear excitation energies following muon capture and the fission probability as measured in a²³⁸U(³He,αf)-reaction.     

Decay of the first excited state at 13.3 keV in73Ge

Singles and coincidence measurements of the 13.3 keV transition of⁷³Ge are reported. The total andK conversion coefficients of this gamma-ray and the half-life of this level have been determined. The results are: α _T =1095±55; α _K =312±30;T _1/2=2.98±0.05 μs.     

Fission of237Np+n through a double humped fission barrier

The subthreshold fission cross section of neutron induced fission of²³⁷Np has been measured between 20 and 60 eV with the CBNM time-of-flight spectrometer. The resonances in this energy range have been analysed with a single level shape fitting computer program. The result is interpreted in the frame of Strutinsky's theory of nuclear deformation.     

237Np and 57Fe Mössbauer study of NpFeGa5

⁵⁷Fe and ²³⁷Np Mössbauer ōmeasurements have been performed for NpFeGa₅, which is one of the so-called neptunium 1-1-5 compounds. The ⁵⁷Fe Mössbauer spectra below T _N = 118 K show the magnetically ordered state. The magnitude of the hyperfine magnetic field at the ⁵⁷Fe nucleus is determined to be 1.98 ± 0.05 T at 10 K. From the ²³⁷Np Mössbauer spectrum at 10 K, the hyperfine magnetic field at the ²³⁷Np nucleus is 203 T and the hyperfine coupling constant is determined to be 237 T/μ_B using the Np atomic magnetic moment of 0.86 μ_B determined by the neutron diffraction study.     

Monte Carlo simulation of fast neutron-induced fission of ~(237)Np

The potential-driving model is used to describe the driving potential distribution and to calculate the preneutron emission mass distributions for different incident energies in the ~(237) Np(n, f)reaction. The potential-driving model is implemented in Geant4 and used to calculate the fission-fragment yield distributions, kinetic energy distributions, fission neutron spectrum and the total nubar for the ~(237) Np(n, f)reaction. Compared with the built-in G4 ParaFissionModel, the calculated results from the potential-driving model are in better agreement with the experimental data and evaluated data. Given the good agreement with the experimental data, the potential-driving model in Geant4 can describe well the neutron-induced fission of actinide nuclei, which is very important for the study of neutron transmutation physics and the design of a transmutation system.     

Multimodal analysis of prompt neutron spectra for 237Np(n,f)

An attempt was made to analyzed the systematic variation of the prompt neutron spectra of ²³⁷Np(n,f) on the basis of the multimodal analysis of mass and kinetic energy distributions. The spectra of neutrons emitted from fragments of each mode (standard I, II, III, superlong) were calculated independently and the total spectra were synthesized. It was found that the partial spectrum for standard I mode is the softest, getting harder in ascending order for standard II, standard III and superlong modes. The calculated total spectra well represented the experimental data and were found to be more sensitive to the variation of the incident energy than the conventional treatment of the Madland-Nix model.     

Multimode approach to 241Am and 237Np fission induced by 660-MeV protons

The results obtained by measuring cross sections for the formation of fragments originating from ²⁴¹Am and ²³⁷Np fission induced by 660-MeV protons are presented. The charge and mass distributions of fragments are analyzed within the multimode-fission model, symmetric and asymmetric fission channels being separated. The contributions of various fission components are estimated, and the fission cross sections for the ²⁴¹Am and ²³⁷Np nuclei are calculated along with the fissilities of these nuclei.     

Nuclearg-factors of the 328 keV state in194Pt,the 240 keV state in195Pt,and the 356 keV state in196Pt determined by recoil-implantation into iron and cobalt hosts

The iron-implantation-perturbed-angular-correlation technique (IMPACT) has been used to measure the Larmor precessions of the 328, 240, and 356 keV states of¹⁹⁴Pt,¹⁹⁵Pt, and¹⁹⁶Pt nuclei, respectively, in ferromagnetic iron and cobalt hosts. The observed angular precessions in iron, corrected for the transient field effect, wereω τ ₁₉₄(328)=0.103±0.006 rad,ω τ ₁₉₅ (240)=0.142±0.012, andω τ ₁₉₆(356)=0.084±0.010. For cobalt hosts, the observed Larmor precessions were ω τ₁₉₄(328)=0.068±0.006, ω τ₁₉₅(240)=0.096±0.012, andω τ ₁₉₆(356)=0.057±0.013. Agreement between theg-factors obtained from the measurements in iron hosts and the measurements in cobalt hosts is very good, and a weighted average of the two measurements givesg ₁₉₄(328)=0.349±0.031,g ₁₉₅ (240)=0.136±0.013, andg ₁₉₆(356)=0.329±0.039.     

Magnetic moment of the 1,307 keV state in69As

The Larmor precession of the 1,307 keV 2 ns state in⁶⁹As in an external magnetic field of 2 T has been observed in a time integral perturbed angular distribution experiment. The deducedg-factor ofg=1.05±0.13 confirms the rather pureg _9/2 proton structure of this state on which a triaxial rotational aligned band is built.     

Magnetic moment of the 308 keV state in48V

The g-factor of the 308 keV 2⁺ state in⁴⁸V has been measured by means of the time differential perturbed angular correlation technique, following the implantation of⁴⁸Cr activity into ferromagnetic iron in the reaction⁴⁶Ti(,2n)⁴⁸Cr. We obtained g = 0.222(8) and a substitutional fraction of f₁>80%.     

Isomeric ratios in photon-induced spallation reactions at intermediate energies

Available experimental isomeric cross-section ratios in photon-induced spallation reactions at intermediate energies are compiled. The experimental data are compared to calculations based on the statistical model formalism.