P-wave Neutron Strength Functions Research Articles

Neutron resonance spectroscopy of104Pd,105Pd,and110Pd

We have measured neutron resonances in the palladium isotopes 104, 105, and 110 for neutron energies from 1 to 2100 eV. Many new p-wave resonances have been observed. Their neutron widths and, in several cases, the radiative widths were measured. The average level spacings and the s-wave and p-wave neutron strength functions were determined. The time-of-flight method was used for both neutron total cross section measurements and total $(n,\ensuremath{\gamma})$ reaction yield measurements at the pulsed spallation neutron source of Los Alamos Neutron Science Center. Well established resonance spectroscopy for these isotopes is essential for the analysis of parity violation data that were recently measured in palladium.

Parity violation in232Thneutron resonances above 250 eV

The analysis of parity nonconservation (PNC) measurements performed on {sup 232}Th by the TRIPLE Collaboration has been extended to include the neutron energy range of 250 to 1900 eV. Below 250 eV all ten statistically significant parity violations have the same sign. However, at higher energies PNC effects of both signs were observed in the transmission of longitudinally polarized neutrons through a thick thorium target. Although the limited experimental energy resolution precluded analysis in terms of the longitudinal asymmetry, parity violations were observed and the cross section differences for positive and negative neutron helicities were obtained. For comparison, a similar analysis was performed on the data below 250 eV, for which longitudinal asymmetries were obtained previously. For energies below 250 eV, the p-wave neutron strength functions for the J=1/2 and J=3/2 states were extracted: S{sub 1/2}{sup 1}=(1.68{+-}0.61)x10{sup -4} and S{sub 3/2}{sup 1}=(0.75{+-}0.18)x10{sup -4}. The data provide constraints on the properties of local doorway states proposed to explain the PNC sign effect in thorium. (c) 2000 The American Physical Society.

P-Wave Neutron Strength Functions in Nuclear Vibrational Region

P-Wave Neutron Strength Functions in Nuclear Vibrational Region

P-wave neutron strength functions in nuclear vibrational region.

The effect of doorway states on the p-wave neutron strength functions is investigated for even-even target nuclei in the vibrational region. A semi-empirical formula including contributions from both doorway state and coupled channel is derived for the p-wave strength function. The calculated results are compared with experimental data. Overall agreement in the mass region of 40~180 is fairly well except for a few nuclides. In addition, isotopie trends of the p- wave neutron strength functions are studied for Cr, Fe, Ni, Zn, Se, Zr, Mo, Ru, Pd, Cd and Nd.

P-wave neutron strength functions

P-wave neutron strength functions for 20 nuclei have been extracted from the average radiative capture cross sections sigma (n, gamma ) at 24 keV, using the latest available values of ) Gamma gamma 0), (D0), S0, ( Gamma gamma 1) and (D1). The authors' values for the P-wave strength functions are compared on the one hand with previous experimental 'local' values and on the other hand with the theoretical predictions of the optical model of Buck and Perey (1962).

Resonance Neutron Capture in 138Ba and 140Ce and the Prompt Neutron Correction to ?-ray Detectors

The neutron capture cross sections of 138Ba and 140Ce have been measured with high energy resolution between 3 and 100 keY using the capture cross section facility at the 40 m station of the Oak Ridge Electron Linear Accelerator. The average s-wave level spacings are <D)s = 6�3 � 1 �7 and 3�2 � 0�8 keY for 138Ba and 140Ce respectively. The deduced s-wave neutron strength functions are 104So = 1�0�0�4 and 1�54�0�53 respectively, and the average s-wave radiative widths are <r,)s = 55�20 and 35�9meY. The p-wave neutron strength functions are 104S1 ~ 0�03 and 0�32�0�12 respectively. The average 30 keY Maxwellian capture cross sections are 3�9�0�8mb for 138Ba and 7�7 � 0�9 mb for 140Ce. A more rigorous treatment of the prompt neutron correction for l'-ray detectors is described, and it is shown that previously published results for 138Ba have underestimated this correction. The 140Ce data provide excellent corroboration for the calculated magnitude and time dependence of the prompt neutron correction.

Neutron total cross section and resonance parameters ofFe58

Neutron total cross section measurements in the energy range from 30 eV to 500 keV have been made using a pulsed neutron time-of-flight method with a 78.2 m flight path and a nominal resolution of about 0.07 ns/m. From the analysis of the data up to 350 keV we have obtained values of the s- and p-wave neutron strength functions and of the mean level spacings. These are S/sub 0/ = (3.2 +- 1.4), S/sub 1/ = (0.68 +- 0.13) in units of 10/sup -4/ eV/sup -1/2/, /sub l/ = 0 = (32 +- 12) keV and /sub l/ = 1 = (8 +- 1) keV.

Neutron Resonance Spectroscopy on 209Bi

The neutron transmission through 209Bi was measured with high resolution at both the 80 and 200 m stations of the Oak Ridge Electron Linear Accelerator. Resonance parameters for s-wave levels below 270 keY and for p-wave levels below 100 keY bombarding energy were obtained. Approximately 25 % of the expected neutron strength of a particle-vibrator doorway was identified in the energy range analysed for s-wave resonances. The average s-wave level spacing is s = 4�5 � 0�6 ke V after correcting for missed levels. The s- and p-wave neutron strength functions are respectively: 104 So = 0�65 � 0�15 (E < 170 keY); 104 Sl = o� 25 � 0�07 (E < 60 keY). Both strength functions show evidence of energy-dependent structure.

Semi-microscopic calculation of the neutron strength functions of spherical nuclei

The fragmentation of single-particle states in odd-A spherical nuclei is studied and the s- and p-wave neutron strength functions are calculated in the framework of the model based on the quasiparticle-phonon interaction. The calculations have no free parameters. The theoretical values of the s- and p-wave strength functions for the compound nuclei 117-123Sn, 125-131Te are approximately equal to S0=(0.1-0.2)*10-4, S1=(2-4)*10-4. They are in satisfactory agreement with experiment.

Neutron strength functions of nuclei in the deformed region

P-wave neutron strength functions of 21 nuclei, in the rare-earth and deformed region 138 < A < 202, have been extracted from the average capture cross sections measured using SbBe photoneutrons and activation technique. S-wave neutron contribution is computed using the s-wave resonance parameters available in literature and subtracted out from the measured total capture cross section to yield the p-wave neutron capture contribution from which the p-wave neutron strength functions are extracted. Present results are found to be in general agreement with the values reported in literature. The experimental p-wave neutron strength functions are also compared with the theoretical predictions based on the different versions of the optical model potential, and qualitative agreement is observed with the deformed optical model theory of Buck and Perey. Strong evidence for shell structure effects is also noticed.

Structure of 3P size resonance in neutron strength functions

Neutron capture cross sections of 21 nuclei have been determined using the activation technique and an antimony-beryllium photoneutron source. The nuclei have been selected in the mass range 60 < A < 140 so as to cover the 3P size resonance region of neutron strength functions. Using the latest available data on the low energy resonance parameters, the P-wave neutron strength functions of the 21 isotopes are extracted, and found to be in general agreement with similar isotopic values reported in literature. The values of experimental P-wave neutron strength functions in the 3P resonance region (60 < A < 140) are compared on the one hand with the theoretical predictions of Fiedeldey and Frahn and on the other with those of Buck and Perey. The shape and structure of the 3P size resonance, as revealed experimentally, are found to agree better with the predictions of Fiedeldey and Frahn, who assumed twice the normal spin-orbit force in their calculations.

Author index

Neutron capture cross sections of 21 nuclei have been determined using the activation technique and an antimony-beryllium photoneutron source. The nuclei have been selected in the mass range 60 < A < 140 so as to cover the 3P size resonance region of neutron strength functions. Using the latest available data on the low energy resonance parameters, the P-wave neutron strength functions of the 21 isotopes are extracted, and found to be in general agreement with similar isotopic values reported in literature. The values of experimental P-wave neutron strength functions in the 3P resonance region (60 < A < 140) are compared on the one hand with the theoretical predictions of Fiedeldey and Frahn and on the other with those of Buck and Perey. The shape and structure of the 3P size resonance, as revealed experimentally, are found to agree better with the predictions of Fiedeldey and Frahn, who assumed twice the normal spin-orbit force in their calculations.

Average s- and p-Wave Resonance Parameters of 115In and 127I

A study of the average s- and p-wave resonance parameters of 115In and 127I has been carried out by activation of samples in a 10B filtered beam of epithermal neutrons from a reactor. Neutron strength functions were obtained that are comparable to recent values obtained by total-cross-section studies but somewhat lower than earlier capture measurements. The s- and p-wave neutron strength functions for 115In were found to be 0.09 ± 0.03 × 10−4 and 3.9 ± 1.4 × 10−4, respectively, and for 127I, the corresponding values were found to be 0.42 × 10−4 and 0.83 ± 0.20 × 10−4. The average energy-dependent neutron cross sections from 1 to 100 keV were computed for both isotopes from the experimentally determined resonance parameters.

Average Neutron Transmission in the keV Region

The theory of averaging neutron transmission over an energy interval in which the nuclear cross section contains many resonances is outlined. Particular consideration is given to the validity of assuming the single-level Breit-Wigner formula for the resonances in carrying out the averaging. Hibdon's data on the average transmission of neutrons through slabs of 238U and 232Th are analysed in order to extract the p-wave neutron strength functions. The values for Tn(1)/D are (2 5 ± 0 4) × 10-4 and (2.40 ± 0 36) × 10-4, respectively.

The s-wave and p-wave strength functions

The s-wave and p-wave neutron strength functions, calculated with an optical model, are compared with experiment for spherical nuclei. The real potential is diffuse and has a spin-orbit term. The imaginary potential is surface-peaked. This surface-peaking produces experimentally required low strength functions between resonances. A detailed fit to the p-wave strength functions required parameters considerably different from those required to explain other data.

The s-wave and p-wave strength functions

The s-wave and p-wave neutron strength functions, calculated with an optical model, are compared with experiment for spherical nuclei. The real potential is diffuse and has a spin-orbit term. The imaginary potential is surface-peaked. This surface-peaking produces experimentally required low strength functions between resonances. A detailed fit to the p-wave strength functions required parameters considerably different from those required to explain other data.