Neutron Total Cross Section Measurements Research Articles

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 in Vanadium, Manganese, and Cobalt

High-resolution total neutron cross-section measurements in natural vanadium, manganese, and cobalt were made in the energy range up to a few hundred keV with the Columbia University Nevis neutron velocity spectrometer using a 200-m flight path and a nominal resolution of 0.5 ns/m. These cross-section data were analyzed with an R-matrix multilevel code, and the resonance parameters (E/sub lambda/, GAMMA/sub n/, J/sup ..pi../, S/sub 0/, D) were obtained. In addition, making use of the published thermal energy data, the parameters of the bound levels were determined. From these measurements the values of S/sub 0/ up to 215-keV neutron energy for vanadium, up to 200 keV for manganese, and up to 80 keV for cobalt have been obtained. The value of spin cut-off factor sigma is found to vary from 2.7 to 4 for these nuclei. These results do not show any J dependence on the strength function.

Total neutron cross-section measurements of 236U in the energy range 40 eV to 4.1 keV

Transmission measurements have been performed on 236U using the time-of-flight technique with a 100 m flight path of the 80 MeV electron linear accelerator of CBNM. The Γ n values have been evaluated for 185 resonances in the energy range 40 eV to 4.1 keV. Assuming only s-wave contributions in the analysis range, the average level spacing, the average reduced neutron width and the strength function were determined to be D = 16.2 ± 0.8 eV, Γ n 0 = 1.61 ± 0.18 meV and S 0 = (1.00 ± 0.1) × 10 −4, respectively. The method of Fuketa and Harvey was used to consider missed resonances. Finally, Dyson's Δ 3 and W statistics, including the method of Bollinger et al., were applied to bring the presence of p-wave resonances in the analysis range into evidence.

Neutron resonance spectroscopy:Bi209

Neutron total cross section vs energy measurements were made for several thicknesses of bismuth metal. The results of the resonance parameter evaluation for 30 levels (12 $s$ and 18 $p$) to 75 keV are given. Parameters for the $p$ levels, and for three weak $s$ levels were determined using a transmission area analysis. An $R$-matrix multilevel shape analysis fitting was used to obtain the final choice resonance parameters for the nine dominant $l=0$ levels. The experimental points and $R$-matrix fit curve to 75 keV are shown. The (${E}_{0},J,{\ensuremath{\Gamma}}_{n}$) choices for these nine levels are (0.800, 5, 4.6), (2.312, 4, 19.5), (5.112, 5, 5.4), (12.15, 4, 270), (15.54, 4, 118), (27.08, 4, 24), (33.34, 4, 240), (45.58, 5, 160), and (69.18, 5, 520), where ${E}_{0}$ is in keV and ${\ensuremath{\Gamma}}_{n}$ is in eV. On the basis of these levels, we obtain for the $s$ and $p$ strength functions $10^{4}S_{0}=({0.62}_{\ensuremath{-}0.20}^{+0.36})$ and $10^{4}S_{1}=({0.13}_{\ensuremath{-}0.04}^{+0.06})$. A channel radius of 9 fm was used to calculate ${S}_{1}$ and the evaluation ignores the possibility that some $p$ levels were missed below 75 keV.NUCLEAR REACTIONS $^{209}\mathrm{Bi}$, $E=500 \mathrm{eV}\ensuremath{-}75 \mathrm{keV}$, measured ($n$, total); deduced resonance ${E}_{0}$, $l$, $J$, ${\ensuremath{\Gamma}}_{n}$ or $g{\ensuremath{\Gamma}}_{n}$, ${S}_{0}$, ${S}_{1}$.

Applications of statistical tests to proton resonances in 45Sc and 49V

Several statistical tests have been applied to 1 2 − and 1 2 + proton resonances observed in 44Ca(p, p) and to 1 2 + resonances observed in 48Ti(p, p). The energy dependence of the density was unfolded (to a constant density) in order to make comparison with theoretical spacing predictions for single level populations. The functional form for the density does not appear to significantly affect the results: a constant temperature density function was adopted for simplicity. The 44Ca data overall indicate missing and spurious levels. However for a subsection of these data, where the observed total number of resonances of all spins and parities is relatively lower, and where the effects of 1 2 + and 1 2 − analogue states enhance the widths, the data appear nearly complete. For 52 1 2 − levels in 45Sc, Δ 3 exp = 0.39 (〈 Δ 3〉 correlated = 0.35) and ϱ exp( S i , S i + 1 ) = −0.32 (〈 ϱ〉 correlated = −0.27). For 39 1 2 + levels in 45Sc, Δ 3 exp = 0.34 (〈 Δ 3〉 correlated = 0.35) and ϱ exp = −0.35 (〈 ϱ〉 correlated = −0.28). For 48Ti all of the 1 2 + levels were included. For 66 1 2 + levels in 49V, Δ 3 exp = 0.51 (〈 Δ 3〉 correlated = 0.38) and ϱ exp = −0.21 (〈 ϱ〉 correlated = −0.27). Dyson's F-statistic test was applied to all of these data, and the kth nearest spacing distributions were calculated for k = 0 through 10. All of these results appear internally consistent. There is thus strong evidence for both short and long range correlations in the spacings of single level populations observed by proton resonance reactions. These results are consistent with the first experimental demonstration of such correlations by the Columbia group in total neutron cross section measurements.

S- and p-wave neutron spectroscopy Xc. Intermediate structure: 88Sr

Neutron total cross section measurements of natural Sr were made from 50–875 keV using a high resolution proton beam and the 7Li( p, n) reaction as a neutron source. These data were analyzed with the help of an R-Matrix code to extract resonance (energies and other) parameters up to about 850 keV. 2 p-1 h and particle-vibration doorway interpretation of the s-, p- and d-wave resonances is attempted in terms of the sum rule Σ γ n 2 = γ d 2. Predictions based on both of these models agree with the experimental results. As expected the p-wave resonances are stronger than either s- and d-wave structure. Theory accounts for the p-wave strength remarkably well. Possible location of the p-wave s.p. resonance is reproduced with a real potential and its damping due to the imaginary potential is calculated. More fragmentation of the strong p-wave doorways is observed than was expected for a compound nucleus so near 90Zr, but a larger strength function is observed apparently due to the p-wave giant resonance.

Precision Neutron Total Cross Section Measurements Near 24 keV

Neutron total cross section measurements near 24 keV were carried out with the Fe-filtered beam technique at the KUR 46-MeV electron linac laboratory. The cross sections of elemental Be, C and O were determined and found to be (5.903 ± 0.011), (4.684±0.009) and (3.736±0.007)b respectively at a mean neutron energy of 23.5 keV. These data differ between 0.5 and 1.5% from the ENDF/B-III evaluated cross section at 23.5 keV.

Precision Neutron Total Cross Section Measurements Near 24 keV

Neutron total cross section measurements near 24 keV were carried out with the Fe-filtered beam technique at the KUR 46-MeV electron linac laboratory. The cross sections of elemental Be, C and 0 were determined and found to be (5.903±0.011), (4.684±0.009) and (3.736±0.007)b respectively at a mean neutron energy of 23.5 keV. These data differ between 0.5 and 1.5% from the ENDF/B-III evaluated cross section at 23.5 keV.

Neutron resonance spectroscopy: Calcium

Results are presented to 550 keV of high resolution time of flight neutron total cross section measurements using various sample thicknesses of natural calcium. An $R$-matrix analysis was made to fit the results for the nine strong $s$ levels in $^{40}\mathrm{Ca}$ above 100 keV. A transmission area analysis was made for the 22 weaker observed levels which are also mainly due to $^{40}\mathrm{Ca}$, but have $l>0$. We obtain $10^{4}\mathrm{S}_{0}=({2.97}_{\ensuremath{-}1.05}^{+1.95})$ for $^{40}\mathrm{Ca}$.NUCLEAR REACTIONS $^{40}\mathrm{Ca}(n,n)$, ($n,\ensuremath{\gamma}$), $E=0\ensuremath{-}550$ keV; measured ${\ensuremath{\sigma}}_{t}(E)$; deduced ${E}_{0}$, ${\ensuremath{\Gamma}}_{n}$, ag ${\ensuremath{\Gamma}}_{n}$, ${S}_{0}$.

The neutron total cross section measurements on protons and nuclei in the energy range of 28–54 GEV

The results of the total cross section measurements of neutrons on protons, deuterons and nuclei C, O, Al, Cu, Sn, Pb in the energy range of 28–54 GeV are reported.

Precision neutron total cross section measurements on gold and cobalt in the 40 ?eV-5 meV range

The slow neutron absorption cross sections of gold and cobalt have been accurately redetermined by transmission measurements in the neutron wavelength range 4 to 47 A. For the range 4 to 7.6 A a new time-of-flight spectrometer at the FRM reactor was used which involves a system of three synchronized choppers and a 150 m long guide tube as flight path. Utilizing the high wavelength resolution of the spectrometer, the time-of-flight wavelength scale could be accurately calibrated (±2 · 10−3 A) by means of various Bragg cutoff breaks observed in transmission on polycrystalline samples. Supplementary transmission measurements on gold and cobalt were performed in the range 11–47 A using the time-of-flight spectrometer for ultracold neutrons at the FRM reactor.

A time-of-flight spectrometer for ultracold neutrons

A time-of-flight spectrometer for ultracold neutrons was developed and installed at the FRM Swimming-pool reactor Munich. The spectrometer consisting of a vertical curved neutron guide tube and a special chopper allows neutron total cross-section measurements in the energy range 10 −7 − 5 × 10 −4eV with an energy resolution of about 20%. The neutron spectrum of the spectrometer was measured and found to be consistent with the theoretical expectation. A value of 0.97 was obtained for the reflectivity of the guide tube material (electrolytically polished copper tube).

Evidence for Doorway States inPb207,Pb208, andFe57from Threshold Photoneutron Cross-Section Measurements

The proposed doorway state in $^{207}\mathrm{Pb}$ seen by neutron total cross-section measurements on $^{206}\mathrm{Pb}$ also has been observed in the ($\ensuremath{\gamma},n$) reaction. Both the envelope of the strength and the correlation between fine structure in the two channels support the doorway-state interpretation. The width for $\ensuremath{\gamma}$-ray decay of the doorway state to the ground state ${\ensuremath{\Gamma}}_{\ensuremath{\gamma}0}^{D}$ is found to be 36.5 \ifmmode\pm\else\textpm\fi{} 3.5 eV. Other possible doorway states in the $\ensuremath{\gamma}$-ray channel in $^{208}\mathrm{Pb}$ at 500 keV, $^{207}\mathrm{Pb}$ at 125 keV, and $^{57}\mathrm{Fe}$ at 50 and 250 keV above threshold are discussed. An attempt is made to produce a correlation between neutron and $\ensuremath{\gamma}$-ray widths; no significant correlation was observed for these nuclei.

Neutron Resonance Spectroscopy. VII. Ti, Fe, and Ni

High-resolution neutron total cross-section measurements were performed on natural samples of titanium, iron, and nickel from 200 eV to a few MeV using the Nevis synchrocyclotron neutron velocity spectrometer with a 200-m flight path. The energy resolution was adequate only up to 200 keV to perform a detailed $R$-matrix multilevel analysis of the data. The resonance energies, isotopic and $l$-value assignment, neutron widths, etc., up to this energy have been determined. From these the mean level spacings $〈D〉$ and the $s$-wave strength functions (${S}_{0}$) have been calculated. Information about the resonance parameters of the bound level in iron and nickel has been also obtained. Values of ${\ensuremath{\Gamma}}_{\ensuremath{\gamma}}=8.2$ eV for the ${\mathrm{Ti}}^{48}$ (17.8 keV) resonance, ${\ensuremath{\Gamma}}_{\ensuremath{\gamma}}=0.64$ for the bound level at -2 keV in ${\mathrm{Fe}}^{56}$, and ${\ensuremath{\Gamma}}_{\ensuremath{\gamma}}=9.0$ eV for the bound level at -28.5 keV in ${\mathrm{Ni}}^{58}$ have been determined by requiring an agreement with the measured thermal-neutron-capture cross section in these nuclei.

High resolution inelastic proton scattering near A = 50

The yield of the deexcitation gamma ray following inelastic proton scattering to the first excited states of 46Ti, 48Ti, 50Cr, 54Fe, and 56Fe has been studied for proton energies between 2.5 and 3 MeV with energy resolution of approximately 1700 eV. For all targets except 54Fe, angular distributions of the gamma-ray yield have been measured as a means of assigning spins and parities to resonances observed in the excitation functions. A total of approximately 160 resonances have been observed and assigned in this way. This work has shown the first excited state of 50Cr to have spin 2. In addition, the spacings of 5 2 + levels in the compound nuclei 47V, 51Mn, and 57Co are consistent with the dependences on neutron excess and shell structure observed in neutron total cross section measurements. There are also indications in the data of a maximum in the D-wave proton strength function in the neighborhood of mass number 47.

Total neutron cross-section measurements in the 10 μ eV range

Total neutron cross-sections of Cd near λ = 10 nm ( E n = 8 μeV) have been measured with the “Doppler chopper” method, in which a moving sample is attached to the rotor which simultaneously performs the neutron velocity selection.

Neutron total cross-section measurements of S and Fe near 2 MeV

The neutron total cross sections of sulfur and iron were measured from 1.8 to 2.6 MeV with energy resolution of a few keV. The cross sections of both elements show fluctuations with widths of the order of 10 keV. For sulfur, the properties of the fluctuations are in good agreement with predictions based on the statistical variations of the compound nuclear levels. For iron, the measured amplitudes are somewhat lower than the predictions.

Neutron Resonance Spectroscopy. V. Nb, Ag, I, and Cs

Total neutron cross-section measurements for niobium, natural silver, iodine, and cesium have been made using a neutron velocity spectrometer with a resolution of about 0.5 nsec/m near the highest energy. The measurements were performed in the energy interval of 35 eV to 8 keV for niobium and 100 eV to about 4 keV for the other elements. The energies and neutron widths of about one thousand levels observed in these nuclei have been determined. The level-spacing distributions of these nuclei were investigated and found to be compatible with the random-matrix model of Wigner. These elements have $A$ values in the neighborhood of an expected peak in the $p$-wave strength function and relative minimum in the $s$-wave strength function. Histograms of the distribution of values for $y={〈g{{\ensuremath{\Gamma}}_{n}}^{0}〉}^{\frac{1}{2}}$ show a considerable excess of small widths over the number expected from the Porter-Thomas $\ensuremath{\nu}=1$ distribution. This excess is interpreted as being due to the observation of many $p$-wave levels. In the case of Nb, about $\frac{2}{3}$ of the observed levels are probably $p$ wave, while the percentages were much smaller for the other elements. The numerical values of the correlation coefficients between level spacings, neutron reduced widths, and local spacing have been determined for all these nuclei. The correlation coefficients, except for the spacing correlation coefficients, are found to be consistent with zero within the statistical accuracy of the measurements. The $l=0$ strength-function values averaged over spin states and isotopes of Nb, Ag, I, and Cs have been determined as (0.36\ifmmode\pm\else\textpm\fi{}0.06)\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}4}$, (0.48\ifmmode\pm\else\textpm\fi{}0.04)\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}4}$, (0.69\ifmmode\pm\else\textpm\fi{}0.08)\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}4}$, and (0.70\ifmmode\pm\else\textpm\fi{}0.10)\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}4}$, respectively.

Angular distributions of neutrons elastically scattered from O 18

The angular distributions of neutrons elastically scattered from O 18 were measured for neutron energies between 405 and 2702 keV by the recoil-particle method. For these measurements, a proportional counter filled with carbon dioxide enriched to 97.2% in O 18 was irradiated with neutrons, and the recoil spectra were recorded by a 256-channel pulse-height analyser. Subtraction of the carbon recoil spectra yielded the O 18 spectra. The results were analysed in conjunction with the total neutron cross-section measurements of Vaughn et al., using one- and two-level nuclear dispersion theory. New states in O 19 have been located at excitation energies of 5.097, 6.13, and 6.20 MeV. Definite spin and parity assignments of 3 2− , 1 2− , and 5 2+ , have been made to the states at excitation energies of 4.587, 5.097, and 5.43 MeV respectively. In addition, probable spin and parity assignments of 3 2+ , 1 2− , and 7 2− , have been made to the states at excitation energies of 6.13, 6.20 and 6.271 MeV respectively. In the excitation energy region near 5.5. MeV, there is definite evidence for an additional level, for which a probable assignment of 1 2− has been made.

Total Slow Neutron Cross Section Measurements of Titanium, Zirconium, and Hafnium

Total neutron cross section measurements have been made on metallic samples of Ti, Zr, and Hf with the MTR crystal spectrometer. The Ti cross section was measured in the energy region 0.025 to 45 ev and values of 4.19 ± 0.04 b and 6.09 ± 0.13 b were obtained for the bound atom scattering and 2200 meters/sec absorption cross sections. The Zr cross section was measured in the energy region 0.02 to 78 ev and a value of 6.40 ± 0.07 b was obtained for the bound atom scattering cross section. The Hf cross section was measured from 0.04 to 3.5 ev and a value of 102 ± 3 b for the 2200 m/sec absorption cross section is reported. Energy values of 1.095 ± 0.005 ev and 2.378 ± 0.016 ev were determined for the peak cross sections of the first two Hf resonances. Values of σ0 = 6030 ± 80 b, Γ = 0.068 ± 0.001 ev and gΓn = 0.163 ± 0.003 mv were obtained for the 1.095 ev resonance.