Neutron Capture Cross Section Measurements Research Articles

Measurement of neutron-capture cross section and capture γ-ray spectrum of 105Pd(n,γ)106Pd reaction

We measured the neutron-capture cross section and the capture γ-ray spectrum of the 105Pd(n,γ)106Pd reaction with about 550 keV neutrons produced from the 7Li(p,n)7Be reaction at a 3-MV Pelletron accelerator. The capture yields of the palladium or gold sample were obtained by applying a pulse-height weighting technique to the corresponding net capture γ-ray pulse-height spectra. The neutron-capture cross section of the 105Pd(n,γ)106Pd reaction was determined with errors less than 5 % by using the standard capture cross sections of 197Au. The neutron-capture γ-ray spectrum was obtained by unfolding the observed capture γ-ray pulse-height spectra. Theoretical calculations of cross sections and γ-ray spectra with the Empire code have been performed by utilizing the Hauser-Feshbach statistical model. The calculated results have a good agreement with present measurements.

Development of an experimental set-up for the measurement of neutron-induced fission and capture cross sections of highly radioactive fissile nuclei

The measurement of neutron-capture cross sections of many actinides is complicated by the difficulty in separating capture γ-rays from the large fission-fragment prompt γ-ray background. For example, current estimates of the capture cross section of 233U show large discrepancies, with differences of more than 20%. To improve the accuracy of data, a new experimental set-up for the simultaneous measurement of the neutron-induced capture and fission cross sections was designed, assembled and optimized. The measurements will be performed at the GEel LINear Accelerator (GELINA) neutron time-of-flight facility in Belgium, where neutron cross sections can be measured over a wide energy range with high energy resolution. The fission detector consists of a dedicated multi-plate high-efficiency ionization chamber (IC). The γ-rays produced in capture reaction are detected by an array of C6D6 scintillators. Fission γ–rays are distinguished from capture γ–rays by the anticoincidence signals from the IC and the C6D6 detectors. For the undetected fission events a correction has to be applied based on the efficiency of the IC that should be high and known with a high accuracy. The performance of the IC during dedicated test experiments is presented, focusing on the determination of the detection efficiency.

Neutron capture cross section measurement for the 174Yb(n,γ)175Yb reaction at 0.0372 eV energy

The neutron capture cross section for the 174Yb(n,γ)175Yb reaction at 0.0372eV energy was measured using the activation of Ytterbium oxide (Yb2O3) target powder pressed in pellet and sandwiched between two thin gold foils used as neutron flux monitor, via the 197Au(n,γ)198Au reference reaction. The neutron irradiations were performed at the horizontal channel of Es-Salam nuclear research reactor and the capture cross section of σ≈(59.07±2.3) b was measured for the first time at this energy after the correction for neutron self-shielding and gamma attenuation effects. The measured value was compared to the evaluated cross section reported in EAF-2010 nuclear data library. The thermal cross section was also determined at 0.0253eV neutron energy and compared to those recommended by Mughabghab (2006) and Simonits et al. (1996).

Neutron transmission and capture cross section measurements for 241Am at the GELINA facility

Resonance parameters for neutron-induced reactions on 241Am below 110 eV have been determined. The parameters result from a resonance shape analysis of transmission and capture data measured at the time-of-flight facility GELINA, with the accelerator operating at a 50 Hz repetition rate. The transmission experiments were carried out at a 25 m station using a Li glass scintillator. The capture experiments were performed at a 12.5 m station by applying the total energy detection principle in combination with the pulse height weighting technique using a pair of C6D6 detectors. The normalization of the capture data was determined by a combined least squares adjustment of the transmission and capture data. From the adjusted resonance parameters a capture cross section of 749 ± 35 b for a neutron energy of 0.0253 eV and an average radiation width of 〈Γ γ 〉 = 42.0 meV for s-wave resonances were obtained. A missing-level analysis for s-wave neutron resonances within the statistical model results in compatible values with previous estimates. The neutron widths obtained in this work are approximately 22% larger compared to other experimental data and evaluated data libraries. Also the thermal capture cross section is larger than most of the recommended values. However, the resonance parameter file presented in this work is consistent with results of both integral experiments and of the experimentally determined resonance integrals.

Measurement of thermal neutron capture cross-section and resonance integral for the 165Ho(n,γ)166gHo reaction by the activation method

The thermal neutron capture cross-section and resonance integral for the 165Ho(n,γ)166Ho reaction were measured experimentally by the activation method. Holmium oxide, manganese oxide and cobalt oxide powders, all dissolved in a mixture of hydrochloric acid and nitric acid, were irradiated within and without cadmium covers in the Tehran Research Reactor. The measured value of the thermal neutron cross-section relative to the 55Mn(n,γ)56Mn and 59Co(n,γ)60Co monitor reactions (with thermal neutron cross-section of 13.3±0.1b and 37.18±0.06b) was 58.6±1.8b. The result was in a good agreement with the most previously reported values. Also the resonance integral was determined relative to the 55Mn(n,γ)56Mn and 59Co(n,γ)60Co monitor reactions with the reference value of 14.0±0.3 and 75.9±2.0, respectively. The measured resonance integral of the 165Ho(n,γ)166Ho reaction at the cadmium cut-off energy of 0.55eV was 650±31. The result was measured with high precision and compared with other measurements in the literature.

Production of double-sided targets by electrodeposition: initial evaluation and optimization of performance

The Detector for Advanced Neutron Capture Experiments (DANCE) located at the Los Alamos Neutron Science Center is used to perform neutron capture cross-section measurements on radioactive and non-radioactive isotopes. Thin actinide targets for the DANCE detector are typically prepared by molecular deposition on thin titanium foils. For the preparation of double-sided deposits, a Teflon electrodeposition cell was constructed with two liquid chambers with a foil substrate in between, allowing electrodeposition on both sides of the foil. We have been studying the electrodeposition of uranium from isopropyl alcohol solutions using this cell. Effects of acid composition, uranium concentration, current, and deposition time will be described.

Recent developments in the manufacture of 173lutetium targets

To better model nuclear processes there is an interest in measuring neutron capture cross sections of lanthanide radioisotopes. A natural hafnium target was irradiated with 100 meV protons at the Los Alamos Isotope Production Facility at the Los Alamos Neutron Science Center (LANSCE) to produce neutron poor lutetium radioisotopes. After irradiation, the target was allowed to cool to allow shorter lived lutetium isotopes to decay. This left predominately 173Lu with small amounts of 174Lu. The hafnium target was then chemically processed to isolate the lanthanide fraction through ion exchange techniques. Recent efforts have focused on the separation of lanthanide species to produce an elementally pure lutetium product, the manufacture of small high density lutetium targets, and neutron capture cross section measurements.

Temperature-tuned Maxwell–Boltzmann neutron spectra for kT ranging from 30 up to 50 keV for nuclear astrophysics studies

The need of neutron capture cross section measurements for astrophysics motivates present work, where calculations to generate stellar neutron spectra at different temperatures are performed. The accelerator-based 7Li(p,n)7Be reaction is used. Shaping the proton beam energy and the sample covering a specific solid angle, neutron activation for measuring stellar-averaged capture cross section can be done. High-quality Maxwell–Boltzmann neutron spectra are predicted. Assuming a general behavior of the neutron capture cross section a weighted fit of the spectrum to Maxwell–Boltzmann distributions is successfully introduced.

An Innovative Method to Measure the Gamma-Ray Emission Probabilities in the Decay of 238Np and 233Pa

The absolute emission probabilities of gamma rays from the decay of 238Np and 233Pa have been measured by an innovative method combining pile oscillation and neutron activation techniques. We obtained values of (24.99 ± 0.34)% and (37.79 ± 0.64)% for the 984.5- and 311.9-keV gamma rays from 238Np and 233Pa, respectively, in good agreement with the recommended values proposed by the Decay Data Evaluation Project (DDEP): (25.18 ± 0.13)% and (38.3 ± 0.5)%. The influence of gamma-ray emission probabilities from 238Np and 233Pa on neutron capture cross-section measurements of 237Np and 232Th, respectively, are discussed and tend to confirm the recommended values from the DDEP. A patent has been granted for this method.

Study on reduction of gamma-ray noise for a pixel-type position-sensitive Li-glass neutron detector

Abstract A pixel-type position-sensitive Li-glass neutron detector has been developed in the Hokkaido University and applied to neutron transmission measurements for obtaining wavelength-dependent neutron images due to its high counting rate. This detector will be applied to monitor the time spectrum of the pulsed neutron beam for the neutron capture cross-section measurements at the Japan Spallation Neutron Source (JSNS). It turned out that the gamma-rays which were accompanied by neutron transmission measurements may be also detected by this detector and may affect wavelength-dependent neutron intensity. We have therefore studied experimentally and numerically the detector efficiency for gamma-rays as a function of photon energy. We have also investigated some practical methods to reduce the effects of gamma-rays on the position-sensitive Li-glass neutron detector by using the Hokkaido University 45MeV LINAC neutron source.

Design of a 4?ðLaBr3(Ce) Spectrometer for Neutron Capture Cross Section Measurements

Design of a 4?ðLaBr3(Ce) Spectrometer for Neutron Capture Cross Section Measurements

Measurements of Neutron-Capture Cross Sections of Palladium Isotopes at the J-PARC/MLF/ANNRI

Measurements of Neutron-Capture Cross Sections of Palladium Isotopes at the J-PARC/MLF/ANNRI

Measurements of Neutron-Capture Cross Sections of 244Cm and 246Cm at J-PARC/MLF/ANNRI

Measurements of Neutron-Capture Cross Sections of 244Cm and 246Cm at J-PARC/MLF/ANNRI

Improved Neutron Capture Cross Section Measurements with the n_TOF Total Absorption Calorimeter

The n TOF collaboration operates a Total Absorption Calorimeter (TAC) [1] for measuring neu- tron capture cross-sections of low-mass and/or radioactive samples. The results obtained with the TAC have led to a substantial improvement of the capture cross sections of 237Np and 240Pu [2]. The experience acquired during the rst measurements has allowed us to optimize the performance of the TAC and to improve the capture signal to background ratio, thus opening the way to more complex and demanding measurements on rare radioactive materials. The new design has been reached by a series of detailed Monte Carlo simulations of complete experiments and dedicated test measurements. The new capture setup will be presented and the main achievements highlighted.

Measurement of the 238U Neutron-capture Cross Section and Gamma-emission Spectra from 10 eV to 100 keV Using the DANCE Detector at LANSCE

A careful new measurement of the {sup 238}U(n,{gamma}) cross section from 10 eV to 100 keV has been made using the DANCE detector at LANSCE. DANCE is a 4{pi} calorimetric scintillator array consisting of 160 BaF{sub 2} crystals. Measurements were made on a 48 mg/cm{sup 2} depleted uranium target. The cross sections are in general good agreement with previous measurements. The gamma-ray emission spectra, as a function of gamma multiplicity, were also measured and compared to model calculations.

Astrophysical reaction rates forNi58,60(n,γ) from new neutron capture cross section measurements

New neutron capture cross sections of $^{58,60}\mathrm{Ni}$ were measured in the energy range from 100 eV to 600 keV using the Oak Ridge Electron Linear Accelerator. The combination of these new neutron capture data with previous transmission data allowed a resonance analysis up to 900 keV using $\mathcal{R}$-matrix theory. The theoretically determined direct capture cross sections were included in the analyses. From these resonance parameters and the direct capture contribution, new ($n$,$\ensuremath{\gamma}$) astrophysical reaction rates were determined over the entire energy range needed by the latest stellar models describing the so-called weak $s$ process.

Precise measurement of the neutron capture reaction 54Fe(n,γ)55Fe via AMS

The measurement of cross sections relevant to nuclear astrophysics has become one main research topic at the VERA (Vienna Environmental Research Accelerator) facility. The technique applied, accelerator mass spectrometry (AMS), offers excellent sensitivity for the detection of long-lived radionuclides through ultra-low isotope ratio measurements. We discuss the potential and preliminary results of ongoing precision measurements of neutron-capture cross sections of 54Fe. Such measurements might help to clarify the recently found discrepancy of s-process nucleosynthesis at lower-mass nuclei (A<120), which might be attributed to a systematic offset in previous experimental data. Samples were irradiated with neutrons from thermal to MeV energies. After the irradiations, the amount of produced long-lived 55Fe (t1/2 = 2.72 yr) was analyzed using AMS. At VERA, detection of 55Fe was developed with a reproducibility of about 1%, which makes the 54Fe(n,γ)55Fe reaction a precise and unique laboratory measurement, which can serve as a reference to complementary techniques. In this regard a new 55Fe standard for AMS measurements was produced. The final cross-section data are expected to be accurate to better than 3%. We report a preliminary, however, already significantly improved thermal neutron cross section value of (2.32 ± 0.10) barn, and a value of (6.3 ± 0.6) mbarn for En = (520 ± 50) keV.

Neutron-induced capture cross sections of short-lived actinides with the surrogate reaction method

Determination of neutron-capture cross sections of short-lived nuclei is opening the way to understand and clarify the properties of many nuclei of interest for nuclear structure physics, nuclear astrophysics and particularly for transmutation of nuclear wastes. The surrogate approach is well-recognized as a potentially very useful method to extract neutron cross sections for low-energy compound-nuclear reactions and to overcome the difficulties related to the target radioactivity. In this work we will assess where we stand on these neutron-capture cross section measurements and how we can achieve the short-lived Minor Actinides nuclei involved in the nuclear fuel cycle. The CENBG collaboration applied the surrogate method to determine the neutron-capture cross section of 233Pa (T1/2 = 27 d). The 233Pa (n,γ) cross section is then deduced from the measured gamma decay probability of 234Pa compound nucleus formed via the surrogate 232Th(3He,p) reaction channel. The obtained cross section data, covering the neutron energy range 0.1 to 1 MeV, have been compared with the predictions of the Hauser-Feshbach statistical model. The importance of establishing benchmarks is stressed for the minor actinides region. However, the lack of desired targets led us to propose recently the 174Yb (3He,pγ) reaction as a surrogate reaction for the (n,γ) predetermined benchmark cross section of 175Lu. An overview of the experimental setup combining gamma ray detectors such as Ge and C6D6 in coincidence with light charged particles ΔE-E Telescopes will be presented and preliminary results will be discussed.

Neutron-induced fission cross sections of short-lived actinides with the surrogate reaction method

Determination of neutron-capture cross sections of short-lived nuclei is opening the way to understand and clarify the properties of many nuclei of interest for nuclear structure physics, nuclear astrophysics and particularly for transmutation of nuclear wastes. The surrogate approach is well-recognized as a potentially very useful method to extract neutron cross sections for low-energy compound-nuclear reactions and to overcome the difficulties related to the target radioactivity. In this work we will assess where we stand on these neutron-capture cross section measurements and how we can achieve the short-lived Minor Actinides nuclei involved in the nuclear fuel cycle. The CENBG collaboration applied the surrogate method to determine the neutron-capture cross section of 233 Pa (T 1/2 = 27 d). The 233 Pa (n,γ ) cross section is then deduced from the measured gamma decay probability of 234 Pa compound nucleus formed via the surrogate 232 Th (3 He ,p) reaction channel. The obtained cross section data, covering the neutron energy range 0.1 to 1 MeV, have been compared with the predictions of the Hauser-Feshbach statistical model. The importance of establishing benchmarks is stressed for the minor actinides region. However, the lack of desired targets led us to propose recently the 174 Yb (3 He ,pγ ) reaction as a surrogate reaction for the (n,γ ) predetermined benchmark cross section of 175 Lu. An overview of the experimental setup combining gamma ray detectors such as Ge and C6D6 in coincidence with light charged particles Δ E-E Telescopes will be presented and preliminary results will be discussed.

Ge検出器及び金箔を用いたJ-PARC MLF BL04ビームラインにおける中性子捕獲断面積の試験測定

Ge検出器及び金箔を用いたJ-PARC MLF BL04ビームラインにおける中性子捕獲断面積の試験測定