A high efficiency gamma-ray set-up for hydrogen profile studies

A multitarget reaction chamber and a gamma-ray detector system have been installed at the LNL for profile studies by means of nuclear reactions. In particular the system has been applied to hydrogen profiling via the ¹⁵N(p, αγ)¹²C reaction. Several modifications to the 7 MV CN Van de Graaff of the LNL have been performed to allow ¹⁵N beam acceleration.     

Measurement of activation yields for platinum group elements using Bremsstrahlung radiation with end-point energies in the range 11-14 MeV

Activation yields have been measured for (γ,n) reactions of the elements Ru, Rh, Pd, Ir and Pt. Metallic foils of natural isotopic composition were irradiated using Bremsstrahlung radiation produced from an electron linear accelerator operated with electron beam energies in the range 11-14 MeV. Activation products, including both unstable ground states and metastates were measured using a high-purity germanium detector. Cross-sections were estimated from the yield data by assuming a simple two-parameter model for the shape of the cross-section with energy.     

Measurement of thermal neutron cross-section and resonance integral for the Yb(n,γ)Yb reaction by the cadmium ratio method

The thermal-neutron cross-section and the resonance integral for the ¹⁷⁴Yb(n,γ)¹⁷⁵Yb reaction were measured by the activation method using a ⁵⁵Mn monitor as single comparator. Analytical grade MnO₂ and Yb₂O₃ powder samples with and without a cylindrical 1 mm Cd shield box were irradiated in an isotropic neutron field obtained from three ²⁴¹Am-Be neutron sources. The gamma-ray spectra from the activated samples were measured with a calibrated n-type high-purity Ge detector. The experimental results were corrected for the correction factors calculated for thermal and epithermal neutron self-shielding effects, epithermal neutron spectrum shape and gamma-ray self attenuation. Thus, the thermal neutron cross-section for the ¹⁷⁴Yb(n,γ)¹⁷⁵Yb reaction is found to be 126.5 ± 6.6 b, relative to that of the ⁵⁵Mn monitor. The resonance integral value for the ¹⁷⁴Yb(n,γ)¹⁷⁵Yb reaction is found to be 59.6 ± 8.5 b, at cadmium cut-off energy of a 0.55 eV. Using the measured cadmium ratios of ⁵⁵Mn and ¹⁷⁴Yb, the result for resonance integral of the ¹⁷⁴Yb(n,γ)¹⁷⁵Yb reaction has also been obtained relative to the reference value of the ⁵⁵Mn monitor. The present results for the ¹⁷⁴Yb(n,γ)¹⁷⁵Yb reaction agree well only with the recent experimental ones obtained by Kafala et al. [1] and De Corte and Simonits [2] within uncertainty limits. However, the previously reported experimental data for the thermal neutron cross-section for this reaction are distributed between 24 and 141 b, and similarly the experimental values for the resonance integral value also show a large scatter in the range of 30-69 b.     

Carrier-free production of Tc at an electron accelerator

We report on the results of studies of the ⁹⁵Tc isotope production conditions in a poorly investigated ⁹⁶Ru(γ,N)⁹⁵Tc reaction at a relatively inexpensive electron accelerator. Based on the analytical model it is demonstrated the possibility for estimating the effective and peak cross-sections and the isotope yield for a given reaction in a thick production target without preliminary determination of its excitation function. For this purpose we compared specific activities of two small samples that were activated under the same conditions using the reference reaction ⁶⁸Zn(γ,p)⁶⁷Cu and the one under investigation. The experiment on simultaneous photo-activation of natural zinc and ruthenium targets was performed followed by the investigation of their isotope composition. The specific activity of the radionuclide was measured and cross-sections for the ⁹⁶Ru(γ,N)^95g,mTc reactions were determined. The yields of desired isomers and admixtures in the natural ruthenium targets of different size were estimated. It is shown, in particular, that the operating conditions of the NSC KIPT accelerator KUT-30 can provide ^95gTc yields up to 120 mCi/h.     

Proton elastic scattering and proton induced γ-ray emission cross-sections on Na from 2 to 5 MeV

Differential cross-sections for proton elastic scattering on sodium and for γ-ray emission from the reactions ²³Na(p,p′γ)²³Na (E_γ = 440 keV and E_γ = 1636 keV) and ²³Na(p,α′γ)²⁰Ne (E_γ = 1634 keV) were measured for proton energies from 2.2 to 5.2 MeV using a 63 μg/cm² NaBr target evaporated on a self-supporting thin C film.The γ-rays were detected by a 38% relative efficiency Ge detector placed at an angle of 135° with respect to the beam direction, while the backscattered protons were collected by a Si surface barrier detector placed at a scattering angle of 150°. Absolute differential cross-sections were obtained with an overall uncertainty estimated to be better than ±6.0% for elastic scattering and ±12% for γ-ray emission, at all the beam energies.To provide a convincing test of the overall validity of the measured elastic scattering cross-section, thick target benchmark experiments at several proton energies are presented.     

Photo-neutron Cross Section Calculations of Several Structural Fusion Materials

In this study, the theoretical photo-neutron cross-sections produced by (γ,n) reactions for several structural fusion materials such as ⁵¹V, ⁵⁵Mn, ⁵⁸Ni, ^90,91,92,94Zr, and ¹⁸¹Ta have been investigated in the incident energy range of 7–40 MeV. Reaction cross-sections as a function of photon energy have been calculated theoretically using the PCROSS and TALYS 1.2 computer codes. TALYS 1.2 default and pre-equilibrium models have been used to calculate the pre-equilibrium photo-neutron cross-sections. For the reaction equilibrium component, PCROSS Weisskopf-Ewing model calculations have been preferred. The calculated results have been compared with each other and against the experimental data in the existing databases EXFOR and TENDL-2011. PCROSS Weisskopf-Ewing model calculations show a similar structure with experimental data but they are higher than the experimental values for all reactions except for ⁹⁰Zr(γ,n)⁸⁹Zr reaction. Generally, TALYS 1.2 default and pre-equilibrium model cross-section calculations are the best agreement with the experimental data for all reactions except for ⁵⁸Ni(γ,n)⁵⁷Ni reaction along the incident photon energy in this study. The TALYS 1.2 curves fit the TENDL-2011 data the best. If photo-neutron cross-section data is needed for an isotope where there is no experimental data available for comparison, TALYS 1.2 pre-equilibrium option has been recommended.     

Thermal neutron cross section determination of short-to-medium lived nuclides using a 20 Ci Am–Be neutron source

While there are growing demands for the nuclear data at higher energy regions than keV for up-to-date scientific and technological development, accurate capture cross sections at thermal energy are still needed. The thermal neutron capture cross sections for the reactions ¹²⁷I(n,γ)¹²⁸I, ¹⁵²Sm(n,γ)¹⁵³Sm,¹⁵⁴Sm(n,γ)¹⁵⁵Sm, and ²³⁸U(n,γ)²³⁹U were determined by the method of foil activation using ⁵⁵Mn(n,γ)⁵⁶Mn as a reference reaction. The experimental samples with and without a Cd cover were irradiated in an isotropic neutron field of a 20 Ci ²⁴¹Am–Be neutron source facility. A high purity Ge detector was used to measure the induced gamma-rays from the samples and the monitor. The thermal neutron capture cross sections of the reactions ¹²⁷I(n,γ)¹²⁸I, ¹⁵²Sm(n,γ)¹⁵³Sm, ¹⁵⁴Sm(n,γ)¹⁵⁵Sm, and ²³⁸U(n,γ)²³⁹U were deduced from the analysis of obtained gamma-ray spectra. The thermal neutron capture cross section values for ¹²⁷I(n,γ)¹²⁸I, ¹⁵²Sm(n,γ)¹⁵³Sm, ¹⁵⁴Sm(n,γ)¹⁵⁵Sm, and ²³⁸U(n,γ)²³⁹U reactions are (5.93 ± 0.52), (207.3 ± 9.4), (7.7 ± 0.3), and (2.79 ± 0.09) barns respectively. The obtained results have been discussed and compared with the available experimental data and were found to be in agreement with each other.     

Cross-Section Calculations on Several Structural Fusion Materials for (γ,3n) Reactions in the Photon Energy Range of 20–110 MeV

In this study, photo-neutron cross-sections of (γ,3n) reactions for several structural fusion materials such as ⁵⁵Mn, ⁶⁵Cu, ⁹⁴Zr, ^98,100Mo, ¹⁸¹Ta and ¹⁸⁶W have been investigated in the incident photon energy range of 20–110 MeV. Theoretical cross-section calculations, based on theoretical nuclear reaction models, have been carried out using the PCROSS, EMPIRE 3.1 and TALYS 1.6 codes. EMPIRE 3.1 exciton, TALYS 1.6 two component exciton and TALYS 1.6 pre-equilibrium models have been used to calculate the pre-equilibrium photo-neutron cross-sections. For the equilibrium cross-section calculations, PCROSS Weisskopf–Ewing model has been preferred. The calculated results have been compared with each other and against the experimental nuclear reaction data (EXFOR). Except the ⁶⁵Cu(γ,3n)⁶²Cu reaction, all model equilibrium and pre-equilibrium cross-section calculations exhibit generally good agreement with the experimental values for all reactions used in this study. TALYS 1.6 two component exciton model can be recommended, if experimental photo-neutron cross-section data are not available or are unlikely to be produced because of the experimental difficulties.     

KeV-Neutron Capture in Cesium-133, Gold-197 and Tantalum-181

The keV-neutron capture in ¹³³Cs, ¹⁹⁷Au and ¹⁸¹Ta was studied by measuring the cross section and the emitted gamma-ray spectrum. The neutron was produced with the KUR linear accelerator and a photoneutron target, and the samples were placed at 11.7 m from the neutron source. The gamma-rays following the keV-neutron capture were detected with a pair of C₆D₆ scintillators. The relative capture cross section between 3.2 and 270 keV was normalized to the absolute cross section at 24 keV obtained with an iron-filtered neutron beam. The results of ¹³³Cs and ¹⁹⁷Au are in good agreement with the recently measured and evaluated capture cross sections.

The capture gamma-ray spectrum was obtained by unfolding the observed spectrum with the response functions of the detector. The gamma-ray strength function, which represents the average gamma-ray transition probability, was derived with the spectrum fitting method. The level density distributions used in the calculation of spectrum fitting were investigated and it is found that the constant temperature level density is preferable. The gamma-ray strength functions for ¹⁹⁸Au and ¹³⁴Cs show the 5.5-MeV bump and the deficiency of strength compared with the tail of giant dipole resonance, and that for ¹⁸²Ta does not give the bump but shows the similarity to the tail of giant resonance. The results were compared with other data.     

Nuclear data sheets for A = 179

Nuclear data for the 10 known members of the A = 179 mass chain are compiled. Included in the compilation are drawings presenting most of the experimental data, Summary Sheets showing adopted level and gamma-ray properties, and Data Sheets tabulating the experimental data. Also included are data on the alpha decay of members of the A = 183 mass chain. For brevity, gamma-gamma-coincidence data and some reaction results are presented only on the drawings. This compilation is based on references received before June 1975.Substantial detail is known for the level structures of ¹⁷⁹Hf, ¹⁷⁹Ta, ¹⁷⁹W, and, to a lesser extent ¹⁷⁹Re. The levels of ¹⁷⁹Hf are well studied by beta decay, (n,γ) reactions, and isomer decay. The charged-particle reactions leading to levels in ¹⁷⁹Hf lack definitive ?-transfer values. Beta decay and in-beam gamma-ray spectroscopy studies which populate levels in ¹⁷⁹Ta and ¹⁷⁹W are reported. Levels in ¹⁷⁹Re have been studied by in-beam gamma-ray spectroscopy. Beta decay of ¹⁷⁹Os to levels in ¹⁷⁹Re is now being studied. Nothing is known about excited levels in ¹⁷⁹Lu, ¹⁷⁹Os, ¹⁷⁹Ir, ¹⁷⁹Pt, ¹⁷⁹Au, or ¹⁷⁹Hg.     

Measurement of 3H(d,n)4He neutron spectrum by means of time-of-flight technique for a fast neutron generator

The energy spectrum of neutrons produced from the ³H(d,n) ⁴He reactions has been determined by using the double scintillator time-of-flight technique. Although the technique has limitations in determining the energy and its spread, due to the short flight path of the experimental setup, it has been shown that the determination of primary neutron energy spectrum down to 0.5 MeV, with the expected structures caused by multiple scattering and deuteron build-up effects, is easily achievable for a low energy accelerator operated in continues mode.     

15MV医用电子直线加速器光核中子剂量分布的MC模拟及测量

医用电子直线加速器产生的X射线已广泛应用于放射治疗过程,X射线与机头中的高Z物质(铅、钨、铜和铁)发生(γ,n),(γ,2n)反应产生一定量的中子,引起与治疗无关的中子剂量。本文对工作在15MV能量档的Prim μs-M型医用电子直线加速器在标准照射野10cm×10cm内治疗平面的光中子剂量分布,进行了Monte-Carlo模拟,并使用CR39固体核径迹探测器和中子气泡探测器(NBD)进行了实验测量。研究发现,测量与模拟的中子剂量之间最大偏差约±30%,其最主要的原因是由于"加速器产生的光核中子与物质发生非弹性散射反应"而逐步降低能量,产生了低于上述两种探测器阈能(100keV)的中子,使测量值比模拟值偏低。研究结果为X射线放射治疗中减低污染中子剂量的优化设计提供了基础数据。     

Measurement of isomeric yield ratios for 90Zr(γ, n)89m,gZr, natZr(γ, xn1p)86m,gY, and 89Y(γ, xn)87m,g,86m,gY reactions with 50-, 60-, and 70-MeV bremsstrahlung

We measured the isomeric yield ratios in the photonuclear reactions of ^natZr(γ, n)^89m,gZr, ^natZr(γ, xn1p)^86m,gY, and ⁸⁹Y(γ, xn)^87m,g,86m,gY by the activation method. The high-purity natural Zr and Y metallic foils in disc shape were irradiated with uncollimated bremsstrahlung beams of 50-, 60-, and 70-MeV generated from an electron linear accelerator at Pohang Accelerator Laboratory. The induced activities in the irradiated foils were measured by the high-resolution γ-ray spectrometric system consisting of a high-purity germanium detector and a multichannel analyzer. The obtained isomeric yield ratios in the formation of ^89m,gZr, ^87m,gY, and ^86m,gY are compared with the corresponding values found in the literature. The measured isomeric yield ratios at the bremsstrahlung energies of 50-, 60-, and 70-MeV are the first measurement except ⁸⁷Y at 50-MeV bremsstrahlung.     

Application of a 6LiF Small Neutron Detector with an Optical Fiber to Tritium Production Rate Measurement in D-T Neutron Fields

⁶LiF small neutron detectors with an optical fiber have been used to measure ⁶Li(n,α)T reaction rate distributions at thermal research reactors and accelerator facilities. In the present study, we developed an experimental method for the measurement of tritium production rate (TPR) of ⁶Li using this small detector in deuterium-tritium (D-T) neutron fields. Reaction rate measurements with the detector were conducted in the D-T neutron fields at the Fusion Neutronics Source (FNS) facility. From the results, we determined that this detector can be used to measure the TPR distribution in soft neutron spectrum fields such as in a Be assembly. It is difficult to obtain ⁶Li(n,α)T reaction rate separately in hard neutron spectrum fields such as in a Li₂O assembly, because many kinds of charged particle production reactions need to be taken into consideration. However, a time-dependent reaction rate measurement method combined with the ⁶LiF detector and the ZnS detector is effective to separate the ⁶Li(n,α)T reaction from other reactions even in a hard spectrum field, and it can be applied to the measurement of the TPR distribution accurately.     

Measurements of activation cross-sections for the F(n, α)N reaction for neutrons with energies between 13 and 15 MeV

In this study, activation cross-sections were measured for the ¹⁹F(n, α)¹⁶N reaction at six different neutron energies from 13.5 and 14.9 MeV. The fast neutrons were produced via the ³H(d,n)⁴He reaction on SAMES T-400 neutron generator. The cyclic activation technique was used. Induced gamma activities were measured by a high-resolution gamma-ray spectrometer with high-purity germanium (HpGe) detector. Measurements were corrected for gamma-ray attenuations, random coincidence (pile-up), dead time and fluctuation of neutron flux. Results were compared with the previous works.     

Computer codes for shielding calculations — 1969

An extensive library of computer codes useful for radiation transport or shielding calculations is available from the Radiation Shielding Information Center at Oak Ridge National Laboratory. In addition to the point kernel, Monte Carlo, and discrete ordinates codes used for neutron and gamma-ray transport calculations, the collection includes cross-section libraries and codes for processing cross sections, calculating fission product inventories, proton penetration of spacecraft, electron-photon transport, and analyzing neutron activation detector data to determine spectra. A list of the most current codes is given and essential information for each is included.     

Elaboration and characterization of hydrogen standard stable under heavy ion irradiation: Application to nuclear astrophysics

A hydrogen standard has been carried out by ion implantation in silicon. The silicon wafer was implanted with hydrogen at different energies and fluences to provide a ∼100 nm flat distribution to the specimen. The samples obtained were characterized by mean of elastic recoil detection analysis (ERDA) and resonant nuclear reaction analysis (RNRA). All important properties of the hydrogen standard have been controlled: isotopic purity, depth profile, stability under ion irradiation and reproducibility. The standards were validated by the measurement of the resonant cross-section of the ¹³C(p,γ)¹⁴N reaction. The similarity of the resonance energy, the resonance width and the resonance strength measurements with those reported in literature confirms the validity of the proposed procedure for hydrogen standards. Therefore, this kind of target could be used to investigate all nuclear reactions in which a proton is involved, from reactions with astrophysical interest to the ones with concern in material analysis.     

Measurement of thermal neutron cross-sections and resonance integrals for Hf(n,γ)Hf and Hf(n,γ)Hf reactions at the Pohang neutron facility

The thermal-neutron cross-sections and the resonance integrals for the ¹⁷⁹Hf(n,γ)^180mHf and the ¹⁸⁰Hf(n,γ)¹⁸¹Hf reactions have been measured by the activation method. The high purity Hf and Au metallic foils within and without a Cd shield case were irradiated in a neutron field of the Pohang neutron facility. The gamma-ray spectra from the activated foils were measured with a calibrated p-type high-purity Ge detector.In the experimental procedure, the thermal neutron cross-sections, σ₀, and resonance integrals, I₀, for the ¹⁷⁹Hf(n,γ)^180mHf and the ¹⁸⁰Hf(n,γ)¹⁸¹Hf reactions have been determined relative to the reference values of the ¹⁹⁷Au(n,γ)¹⁹⁸Au reaction, with σ₀ = 98.65 ± 0.09 barn and I₀ = 1550 ± 28 barn. In order to improve the accuracy of the experimental results, the interfering reactions and necessary correction factors were taken into account in the determinations. The obtained thermal neutron cross-sections and resonance integrals were σ₀ = 0.424 ± 0.018 barn and I₀ = 6.35 ± 0.45 barn for the ¹⁷⁹Hf(n,γ)^180mHf reaction, and σ₀ = 12.87 ± 0.52 barn and I₀ = 32.91 ± 2.38 barn for the ¹⁸⁰Hf(n,γ)¹⁸¹Hf reaction. The present results are in good agreement with recent measurements.     

Measurements of the Y(n,γ)Y cross-section in the neutron energy range of 13.5-14.6 MeV

The ⁸⁹Y(n,γ)^90mY cross-section has been measured at three neutron energy points between 13.5 and 14.6 MeV using the activation technique and a coaxial HPGe γ-ray detector. The data for the ⁸⁹Y(n,γ)^90mY cross-sections are reported to be 0.39 ± 0.02, 0.43 ± 0.02, and 0.38 ± 0.02 mb at 13.5 ± 0.2, 14.1 ± 0.1, and 14.6 ± 0.2 MeV incident neutron energies, respectively. The first data for the ⁸⁹Y(n,γ)^90mY reaction at neutron energy points of 13.5 and 14.1 MeV are presented. The natural high-purity Y₂O₃ powder was used as target material. The fast neutrons were produced by the T(d,n)⁴He reaction. Neutron energies were determined by the method of making cross-section ratios of ⁹⁰Zr(n,2n)^89m+gZr and ⁹³Nb(n,2n)^92mNb reactions, and the neutron fluencies were determined using the monitor reaction ⁹³Nb(n,2n)^92mNb. The results obtained are compared with existing data.