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Improvements have been made to the nuclear data standards largely as a result of an IAEA Data Development Project. The work includes the traditional activities related to standards, extending the energy ranges of some standards, and reference data that are not as well known as the standards but can be very useful in the measurements of certain types of cross sections. Also included is an effort to improve evaluations of 235U thermal and 252Cf spontaneous fission neutron spectra., JRC.D.4-Standards for Nuclear Safety, Security and Safeguards

Neutron cross section standards are the basis for the determination of most neutron cross sections. They are used for both measurements and evaluations of neutron cross sections. Not many cross sections can be obtained absolutely – most cross sections are measured relative to the cross section standards and converted using evaluations of the standards. The previous complete evaluation of the neutron cross section standards was finished in 1987 and disseminated as the NEANDC/INDC and ENDF/B-VI standards. R-matrix model fits for the light elements and non-model least-squares fits for all the cross sections in the evaluation were the basis of the combined fits for all of the data. Some important reactions and constants are not standards, but they assist greatly in the determination of the standard cross sections and reduce their uncertainties – these data were also included in the combined fits. The largest experimental database used in the evaluation was prepared by Poenitz and included about 400 sets of experimental data with covariance matrices of uncertainties that account for all cross-energy, cross-reaction and cross-material correlations. For the evaluation GMA, a least-squares code developed by Poenitz, was used to fit all types of cross sections (absolute and shape), their ratios, spectrum-averaged cross sections and thermal constants in one full analysis. But, the uncertainties derived in this manner, and especially those obtained in the R-matrix model fits, have been judged to be too low and unrealistic. These uncertainties were substantially increased prior to their release in the recommended data files of 1987. Modified percentage uncertainties were reassigned by the United States Cross Section Evaluation Working Group's Standards Subcommittee for a wide range of energies, and no covariance (or correlation) matrices were supplied at that time. The need to re-evaluate the cross section standards is based on the appearance of a significant amount of precise experimental data and improved developments in the methodology of analysis and evaluation. Initial efforts to produce a new evaluation were made by the United States Cross Section Evaluation Working Group which formed a Task Force. It was realized that international cooperation would be needed to produce the evaluation. The Working Party on International Evaluation Cooperation of the Nuclear Energy Agency Nuclear Science Committee formed a Subgroup, and the International Atomic Energy Agency formed a Coordinated Research Project (CRP). These groups worked cooperatively to improve the evaluation process. The major effort in producing the evaluation was through the CRP. The evaluations of the neutron cross section standards were finalized in October 2005. Previous difficulties experienced with a data evaluation problem known as “Peelle's Pertinent Puzzle” create biases in the fit of correlated data, and they have been addressed to reduce this phenomenon. The new evaluations of the cross section standards also include covariance matrices of the uncertainties that contain fully justifiable values. The product of this international effort has been adopted as the neutron standards for ENDF/B-VII.0.

New measurements and an improved evaluation process were used to obtain a new evaluation of the neutron cross section standards. Efforts were made to include as much information as possible on the components of the data uncertainties that were then used to obtain the covariance matrices for the experimental data. Evaluations were produced from this process for the 6Li(n,t), 10B(n,α), 10B(n, α 1 γ ), 197Au(n,γ), 235U(n,f), and 238U(n,f) standard cross sections as well as the non-standard 6Li(n,n), 10B(n,n), 238U(n,γ) and 239Pu(n,f) cross sections. There is a general increase in the cross sections for most of the new evaluations, by as much as about 5%, compared with the ENDF/B-VI results. Covariance data were obtained for the 6Li(n,t), 6Li(n,n), 10B(n,α), 10B(n, α 1 γ ), 10B(n,n), 197Au(n,γ), 235U(n,f), 238U(n,f), 238U(n,γ) and 239Pu(n,f) reactions. Also an independent R-Matrix evaluation was produced for the H(n,n) standard cross-section, however, covariance data are not available for this reaction. The evaluations were used in the new ENDF/B-VII library.

A new accurate measurement of the 27Al(n,2n) 26Al excitation function leading to the ground state of 26Al ( t 1/2 = 7.1×105 years) in the near-threshold region ( E th = 13.55 MeV) was performed, with the goal to achieve relative cross-sections with the highest accuracy possible using proven methods. In addition, the measurements were also designed to provide good absolute cross-section values, since absolute cross-sections are important for radioactive waste predictions in future fusion reactor materials. Samples of Al metal were irradiated with neutrons in the energy range near threshold ( E n = 13.5-14.8 MeV) in Vienna and St. Petersburg, and at 14.8 MeV in Tokai-mura. In addition, irradiations with neutrons of higher energies (17 and 19 MeV) were performed in Tubingen, to obtain also cross-section values well above threshold. The amount of 26Al produced during the irradiations was measured via accelerator mass spectrometry (AMS). With this system, a background as low as 3×10-15 for 26Al/ 27Al isotope ratios was obtained, corresponding to a (n,2n) cross-section of 0.04 mb. Utilizing AMS, cross-sections with much higher precision and considerably closer to the threshold than in previous investigations were measured. A substantial improvement in the knowledge of this excitation function was obtained. Its expected strongly non-linear behaviour near threshold makes the production of 26Al sensitive to temperature changes in a deuterium-tritium (D-T) fusion plasma. The prerequisite for such an application as a temperature monitor, namely a very well-known shape of the excitation function, was met. A quantitative prediction of the sensitivity of this method for monitoring the temperature in a D-T fusion plasma was therefore possible.

A simultaneous evaluation of all important neutron cross sections for each of the isotopes was performed in the incident neutron energy range from end of the resonance region to 20 MeV. The Bayesian least-squares code GLUCS combined the results of nuclear model calculations („prior”) with the complete existing experimental database to obtain the most accurate description of the cross sections and their covariances within our present knowledge („posterior”). The results of the new evaluations agree with ENDF/B-VI and EFF-2 within the uncertainties of these evaluations. Most of the uncertainties of our evaluated cross sections, however, are considerably smaller than those of ENDF/B-VI and EFF-2.

An accurate determination of the 27 Al(n,2n) 26 Al excitation function near threshold was carried out. The detection of the produced 26 Al was performed with 26 Al/ 27 Al isotope ratio measurements via AMS with the Vienna Environmental Research Accelerator (VERA). To this end systematic investigations of Al-metal and Al-oxide samples were performed and several standards were systematically investigated. No difference in the AMS results were obtained using either Al-metal or Al 2 O 3 samples but inconsistencies of different Al standards were found. An independent Al standard was produced by irradiating Al-metal samples with a high neutron fluence measuring the 26 Al activity with a Ge-diode. The resulting 26 Al/ 27 Al ratio could then be directly compared with the results from an AMS measurement on the same material. A very good agreement between the activity and the AMS measurement was obtained, normalizing the AMS results with Al standards used at Purdue and Munich.

The Vienna Environmental Research Accelerator (VERA) is a 3-MV Pelletron tandem mass spectrometer system. Since July 1996, extensive tests with 26 Al detection were performed. Systematic investigations of reproducibility, transmission, overall efficiency etc. are necessary for a new facility such as VERA in order to come up with reliable results. To this end several different 26 Al standards with an 26 Al/ 27 Al isotopic ratio between 5 × 10 −10 and 1 × 10 −12 were used. The results of these investigations revealed no systematic deviation beyond counting statistics. In order to determine the cross section for the 27 Al(n,2n) 26 Al reaction Al-metal samples with 26 Al produced from neutron irradiation were measured and compared with 26 Al standards.

Neutron-induced reactions producing light charged particles continue to be investigated at the spallation fast-neutron source at the Los Alamos Neutron Science Center (LANSCE). New data on the cross sections for alpha-particle production for neutrons on {sup 58}Ni and {sup 60}Ni are presented from threshold to 50 MeV. Recent changes in the experiment now allow protons, deuterons, tritons, {sup 3}He and alpha particles to be identified.

Intense neutron fluxes within fusion reactors that are currently being designed will lead to the activation of structural components. To assess and minimize this radioactivity, nuclear cross sections are needed for neutrons with energies up to 20 MeV. We describe research performed for the International Atomic Energy Agency (IAEA) Coordinated Research Programme on activation cross sections for fusion reactor technology, which has selected certain high-priority reactions for both experimental and theoretical study. Using statistical model codes, we have investigated: (1) excitation function cross sections for radionuclide production in the reactions 94 Mo(n,p) 95 Nb, 109 Ag(n,2n) 108m Ag, 151 Eu(n,2n) 150 m Eu 153 Eu(n 2n) 152g+m2 Eu, 159 Tb(n,2n) 158 Tb 187 Re(n 2n) 186m Re 179 Hf(n,2n) 178m2 Hf, 193 Ir(n,2n) 192m2 Ir; and (2) the systematical dependence of isomeric ratios on isomer spin and incident-energy. Using our calculated results for the excitation functions, along with calculations by other groups, the theoretical excitation functions have been normalized to experimental values at 14.5 MeV to produce evaluated excitation functions. These evaluations can be used within radiation transport and nuclide inventory codes to design and assess the environmental impact of fusion reactors.

Spallation of ${}^{27}\mathrm{Al}$ and ${}^{56}\mathrm{Fe}$ by 800 MeV protons was investigated at the WNR facility of the Los Alamos National Laboratory. Production cross sections for a considerable number of residual nuclei were determined for both targets by use of three different methods. Because of the specific time structure of the WNR beams it was possible to observe both the prompt \ensuremath{\gamma} radiation resulting from the final stage of the spallation reaction and the \ensuremath{\gamma} radiation due to the decay of short-lived residual nuclei by delayed \ensuremath{\gamma}-ray spectroscopy. The activity of long-lived residual nuclei was measured several weeks after the irradiation with a calibrated high-purity Ge \ensuremath{\gamma}-ray detector. In the prompt \ensuremath{\gamma}-ray spectrum it was possible to observe the transitions from the first excited ${2}^{+}$ state to the ground state for all even-even nuclei strongly populated in the spallation reactions and, from these data, to deduce the production cross sections of these mostly stable nuclei in addition to the short- and long-lived residual nuclei mentioned before. In this way production cross sections for 36 nuclides from the proton interactions with ${}^{56}\mathrm{Fe}$ and for 12 nuclides in the case of ${}^{27}\mathrm{Al}$ could be measured; in addition, meaningful upper limits were obtained for a number of further nuclides in both cases. The results are in reasonable agreement with previous measurements obtained by different methods; for a number of nuclides, production cross sections were determined for the first time. The present data as well as the results of all previous measurements are compared with the predictions of the semiempirical systematics and with quantum molecular dynamics calculations.

The gamma radiation from the interaction of 14.6-MeV neutrons with aluminum has been investigated by high-resolution germanium-detector gamma-ray spectroscopy. Cross sections for gamma lines from the {sup 27}A(n,n{prime}{gamma}), (n,p{gamma}), and (n,np{gamma}) reactions have been measured at an emission angle of 125 deg. The results are compared with previous measurements and with predictions based on the statistical theory of nuclear reactions (including direct and precompound contributions). The current results are within the range of values reported in the widely discrepant previous measurements and thus allow the resolution of these discrepancies. The relative intensities of the gamma lines analyzed in this work are in good agreement with the results of a white neutron source measurement performed by two of the authors at Los Alamos National Laboratory. The measure gamma-ray production cross sections were compared with the results of nuclear model calculations using the GNASH code. The agreement with the calculated cross sections is unsatisfactory. The results of the statistical calculations are an average {approximately}20% below the measured cross sections, and there are also some discrepancies between the calculated and measured relative intensities for the different lines from the (n,n{prime}{gamma}) reaction.

Intense neutron fluxes within fusion reactors that are currently being designed will lead to the activation of structural components, and to assess and minimize this radioactivity, nuclear cross sections are needed for neutrons with energies up to 20 MeV. We describe research performed for the International Atomic Energy Agency (IAEA) Coordinated Research Programme on activation cross sections for fusion reactor technology, which has selected certain high-priority reactions for both experimental and theoretical study. Using statistical model codes, we have investigated excitation function cross sections for radionuclide production in the reactions {sup 94}Mo(n,p){sup 94}Nb, {sup 109}Ag(n,2n){sup 108m}Ag, {sup 151}Eu(n,2n){sup 150m} Eu, {sup 153}Eu(n,2n){sup 152g+m2}Eu, {sup 159}Tb(n,2n){sup 158}Tb, {sup 187}Re(n,2n){sup 186m}Re, {sup 179}Hf(n,2n){sup 178m2}Hf, {sup 193}Ir(n,2n){sup 192m2}Ir. Using our calculated results for the excitation functions, along with calculations by other groups, the theoretical excitation functions have been normalized to experimental values at 14.5 MeV to produce evaluated excitation functions. These evaluations can be used within radiation transport and nuclide inventory codes to design, and assess the environmental impact of, fusion reactors. 23 refs., 4 figs., 1 tab.

Neutron-induced helium production, which can contribute substantially to radiation damage, is an important parameter in the choice of structural materials and other component materials for both fusion and fission reactors. Here, helium production cross sections for the elements iron, nickel, and copper and for the isotopes {sup 56}Fe, {sup 58}Ni, {sup 60}Ni, and {sup 61}Ni for 9.85-MeV neutrons have been measured by irradiation with an intense, quasi-monoenergetic neutron source followed by helium analysis with isotope dilution gas mass spectrometry. The results are in fair agreement with (n, {alpha}) cross sections measured by alpha-particle detection and integration over the alpha-particle energies and angular distributions.

Alpha-particle production cross sections and spectra produced by neutron bombardment of 59Co are measured at 30, 60, 90, and 135 deg over the neutron energy range from 5 to 50 MeV. A source of neut...

The $^{103}\mathrm{Rh}$(n,${\mathit{n}}^{\ensuremath{'}}$${)}^{103}$${\mathrm{Rh}}^{\mathit{m}}$ cross section was measured by the activation method in the neutron energy range 5.7--12 MeV with an uncertainty of \ensuremath{\approxeq}5%. Monoenergetic neutrons produced by the D(d,n${)}^{3}$He reaction were used to irradiate metallic Rh samples at 0\ifmmode^\circ\else\textdegree\fi{} relative to the deuteron beam. The K x rays from $^{103}\mathrm{Rh}^{\mathit{m}}$ were measured with a calibrated Si detector, and the neutron fluence was determined by means of a $^{238}\mathrm{U}$ fission chamber. The measured cross sections resolve the discrepancies in previous data and agree with the results of recent statistical model calculations of the fast-neutron cross sections of rhodium. \textcopyright{} 1996 The American Physical Society.

Optical and X-Ray proximity printing systems are resolution limited by diffraction and beam dispersion. Parallel dispersion free ion beam systems are therefore ideal to transfer stencil mask patterns onto all sorts of nonideal substrates. A feasibility study was performed with the existing Alpha ion projector of the Society for the Advancements of Microelectronics in Austria operated in the MIBL (Masked Ion Beam Lithography) mode with ≈ 10×10 mm2 exposure field. Structures as small as 0.2 μm in diameter could be transfered even with a gap of 1 mm between stencil mask and substrate. The widening of resist lines with 10% increase in dose was evaluated to be 14 nm for 2800 μm gap and 4 nm for 300 μm gap. This excellent exposure latitude favourably compares with synchrotron based X-ray lithography, where a widening of 20 nm with 10% overexposure has been reported for a 40 μm gap, and 10 nm for 10 μm gap. Promising applications of the MIBL technique include the fabrication of flat panel displays based on vacuum electronics (field emitter displays), surface acoustic wave and microoptic devices and - in combination with reactive ion etching - the fabrication of micro electro mechanical systems (MEMS). Prospects for MIBL steppers of printing fields > 100×100 mm2 are discussed.

The gamma radiation from the interaction of 14.7-MeV neutrons with {sup 208}Pb is investigated by high-resolution germanium-detector gamma-ray spectroscopy by using an enriched {sup 208}Pb sample. Cross sections for 14 gamma-ray lines from the {sup 208}Pb(n,n{prime}{gamma}) and {sup 208}Pb(n,2n{gamma}) reactions are measured at an emission angle of 124 deg. The results are compared with measurements from previous studies and with predictions based on the statistical theory of nuclear reactions (including direct and precompound contributions). The current results, especially for the {sup 208}Pb(n,n{prime}{gamma}) reaction, are considerably smaller than the results of most of the measurements of the previous studies probably because of the neglect of important sources of background, e.g., gamma-ray production in lead shielding, in the previous studies. Agreement with theory is adequate for the strong transitions between the lowest levels in {sup 207}Pb and {sup 208}Pb, but large discrepancies exist for the weaker transitions, especially for gamma-ray transitions from levels where experimental knowledge of branching ratios is missing. The study of the gamma radiation from the interaction of 14-MeV neutrons with lead is essential for accurate prediction of the gamma-ray heating in such devices. In addition, the nucleus {sup 208}Pb is especially studied as a test case for detailedmore » comparison of the predictions of nuclear reaction theory with experiments.« less

Neutron reactions that produce $\ensuremath{\alpha}$ particles have been investigated experimentally and analyzed by reaction model calculations for incident neutron energies from threshold to 150 MeV on elemental chromium and iron. The cross sections were measured at the Los Alamos Neutron Science Center by direct observation of $\ensuremath{\alpha}$ particles. Previous data on isotopes ${}^{59}$Co and ${}^{58,60}$Ni were also included in the analysis. The model calculations are made for both statistical decay and pre-equilibrium processes. This study particularly focuses on the pre-equilibrium cluster emission, which is described by the clustering exciton model of Iwamoto and Harada. We calculate the $\ensuremath{\alpha}$-particle formation factors numerically without any of the approximations that appeared in the original model. The model parameter $\ensuremath{\Delta}R$, the nuclear surface area where the pickup reaction may occur, is determined by fitting the calculated $\ensuremath{\alpha}$-particle energy spectra to experimental data. The calculated $\ensuremath{\alpha}$-particle-production cross sections agree well with the measured data, except for the Cr case. With a simple sensitivity study for the level density parameters, it is reported that relatively small changes in the level density parameters improve the reproduction of experimental data significantly. Our realistic model calculations for the pre-equilibrium process shed light on uncertainties in the nuclear level densities in statistical decay calculation.

High-resolution \ensuremath{\gamma}-ray spectra from the interaction of neutrons in the energy range from 3 to 200 MeV with $^{207,208}\mathrm{Pb}$ were measured with the white neutron source at the weapons neutron research (WNR) facility at Los Alamos National Laboratory. From these data, excitation functions for prominent \ensuremath{\gamma} transitions in $^{200,202,204,206,207,208}\mathrm{Pb}$ were derived from threshold to 200 MeV incident neutron energy. These \ensuremath{\gamma}-production cross sections reflect the excitation cross sections for the respective residual nuclei. The results are compared with the predictions of nuclear reaction calculations based on the exciton model for precompound emission, the Hauser-Feshbach theory for compound nucleus decay, and coupled channels calculations to account for direct excitation of collective levels. Good agreement was obtained over the entire energy range covered in the experiment with reasonable model parameters. The results of this work clearly demonstrate that multiple preequilibrium emission has to be taken into account above about 40 MeV, and that the level density model of Ignatyuk, which accounts for the gradual disappearance of shell effects with increasing excitation energy, should be used instead of the Gilbert-Cameron and backshifted Fermi-gas models if excitation energies exceed about 30 MeV. No indication for a reduction of the nuclear moment of inertia below the rigid body value was found.

An enriched 58 Ni sample has been irradiated with thermal neutrons together with an enriched 54 Fe target. After chemical purification of the nickel sample, the produced radioactivities of 59 Ni and 55 Fe were measured with a silicon detector. The half-life of 59 Ni has been deduced to be 108,000 ± 13,000 years. This halflife is larger than the commonly adopted half-life value of 76,000 ± 5000 years but is in full agreement with 59 Ni concentration and activity measurements of the meteorite Admire. With accelerator mass spectrometry, the cross-section of the reaction 60 Ni(n,2n) 59 Ni for 14.8 MeV neutrons has been measured to be 410 ± 100 mb.

The cross section for the production of the 30 keV isomer in 93 Nb by neutron inelastic scattering was measured by means of foil activation in the energy range 5.93–8.94 MeV relative to the cross section for the reaction 58 Ni(n,p) 58 Co. Thin Nb foils attached to Ni monitor foils were exposed to a high flux of quasi-monoenergetic neutrons produced by the H( t , n ) 3 He source reaction at incident triton energies between 11.5 and 15.1 MeV. The effect of secondary neutrons on the activation of both the Nb and Ni samples was corrected for at each energy by carrying out irradiation runs with the hydrogen gas-cell evacuated. The induced 93 m Nb activities were assessed by measuring the K-shell X-rays from the 30.7 keV isomeric transition by means of a calibrated Si(Li) X-ray detector; the 58 Co activity in the monitor foils were measured by means of standard γ-ray counting techniques using a calibrated high-purity Ge detector. The 58 Ni(n,p) 58 Co cross section, employed as a secondary reference, had been determined in a previous experiment relative to the 238 U(n,f) cross section which was taken from the ENDF/B-VI file. Within the experimental uncertainties the results of this work confirm the recommended cross sections contained in the IRDF-90.

Three experiments with accelerator mass spectrometry (AMS) are described. (1) The cross section of the reaction 60N(n,2n)59Ni with 14.8 MeV neutrons was measured with AMS to be 410+or-100 mb in agreement with the predictions of calculations. On the basis of a radioactivity measurement of 59Ni performed for the same reaction by another group, a half-life of 290000+or-100000 y was deduced for 59Ni. (2) Tests of the Pauli exclusion principle were performed by looking for non-Paulian atoms with three electrons in the K shell and for non-Paulian nuclei with three protons or three neutrons in the nuclear 1 s1/2 shell.

The properties of the triplet of low-lying states in101Mo have been studied through spectroscopy of theγ radiation following thermal neutron capture in100Mo and β− decay of101Nb and through a measurement of the proton angular distributions in the100Mo(d,p) reaction with 14 MeV deuteron energy. The half-lives of the 13.5 keV state and the 57.0 keV 5/2+ state have been measured as 226(7) and 133(7)ns, respectively. These values and the quadrupole/dipole mixing ratios of the 13.5 keV and 43.5 keV transitions yield spin and parity 3/2+ for the 13.5 keV level. The E2 components in the 13.5 (3/2+ →1/2+) and 43.5 keV (5/2+→3/2+) transitions are ≦ 8·10−4 and 54(9)%, respectively. The possibility of an additional state near to the 57.0 keV level is discussed. IBFM/PTQM calculations, taking into consideration the transitional character of the100Mo boson core, account for the electromagnetic-transition and transfer-reaction pattern of the triplet of states.

It is demonstrated that (n,2n) cross sections for many medium-mass and heavy nuclei can be determined with high accuracy (≈3%) from existing data on nonelastic cross sections and energy-differentia...

We have measured the branching ratios for\(\bar pp\) annihilation at rest intoπ+π−η andπ+π−η′ in hydrogen gas in two data samples that have different fractions ofS-wave andP-wave initial states. The branching ratios are derived from a comparison with the topological branching ratio for\(\bar pp\) annihilations into four charged pions of (49±4)% and the branching ratio intoπ+π−π+π−π0 of (18.7±1.6)%. We find a significant reduction of the branching ratios fromP-states for\(\bar pp \to \pi ^ + \pi ^ - \eta \) andπ+π−η′ in comparison toS-state annihilation. $$\begin{gathered} BR(S - wave \to \pi ^ + \pi ^ - \eta ) = (13.7 \pm 1.46) \cdot 10^{ - 3} \hfill \\ BR(P - wave \to \pi ^ + \pi ^ - \eta ) = (3.35 \pm 0.84) \cdot 10^{ - 3} \hfill \\ BR(S - wave \to \pi ^ + \pi ^ - \eta ') = (3.46 \pm 0.67) \cdot 10^{ - 3} \hfill \\ BR(P - wave \to \pi ^ + \pi ^ - \eta ') = (0.61 \pm 0.33) \cdot 10^{ - 3} . \hfill \\ \end{gathered} $$

Antiproton-proton annihilation at rest into π+ π− π0 has been studied by stopping antiprotons from LEAR in a H2 gas target at normal temperature and pressure. The reaction is observed in coincidence withL X-rays which are emitted in the cascade of\(\bar pp\) atoms. The X-rays populate one of the angular momentumL=1 states of a\(\bar pp\) atom which then annihilates. A spinparity analysis of the π+ π− π0 Dalitz plot gives contributions from the threeP states from which annihilation into three pions is allowed. The most striking features of the Dalitz plot are production of charged and neutral ϱ(770) and off2(1270) mesons. Production of ϱ(770) mesons proceeds via the isoscalar part of the1P1 state and the isovector part of the3P1 state.f2(1270) mesons are produced abundantly fromP states while their production fromS states is very weak. The π+ π− invariant mass spectrum shows a third strong peak at a mass of 1565±20 MeV/c2 and a width of 170±40 MeV/c2, which we call AX(1565). No reasonable description of the Dalitz plot is obtained without introducing the AX(1565) as a new isoscalar particle. A phase shift analysis shows a phase movement which is fully compatible with a resonance withJPC=2++. The most likely interpretation of the new resonance is a multiquark\((qq\overline {qq} or N\bar N)\) state.

We have observed an isoscalar tensor meson at a mass of 1565 ± 10 MeV/c2 and a width of 170 ± 20 MeV/c2. The resonance is seen in pp annihilation at rest into π+π−π0 from P states of antiprotonic hydrogen atoms.

Proc on line; International audience; The status of the Joint Evaluated Fission and Fusion file (JEFF) is described. JEFF-3.1 comprises a significant update of actinide evaluations, materials evaluations that have emerged from various European nuclear data projects, the activation library JEFF-3.1/A, the decay data and fission yield sub-libraries, and fusion-related data files from the EFF project. The revisions were motivated by the availability of new measurements, modelling capabilities and trends from integral experiments. Validations have been performed, mainly for criticality, reactivity temperature coefficients, fuel inventory and shielding of thermal and fast systems. Compared with earlier releases, JEFF-3.1 provides improved performance with respect to a variety of scientific and industrial applications. Following on from the public release of JEFF-3.1, the French nuclear power industry has selected this suite of nuclear applications libraries for inclusion in their production codes.

A new evaluation of the neutron cross section standards was recently completed. The results of this work became the standards for the new ENDF/B-VII library. This evaluation was performed to include new experiments on the standards that have been made since the ENDF/B-VI standards evaluation was completed and to improve the evaluation process. The evaluations include the H(n,n), 6 Li(n,t), 10 B(n,α), 10 B(n,α1γ), 197 Au(n,γ), 235 U(n,f), and 238 U(n,f) standard reactions. Evaluations were not done for the 3 He(n,p) and C(n,n) standards which were carried over from ENDF/B-VI. The need for standards above 20MeV led to the extension of the 235 U(n,f) and 238 U(n,f) cross sections to 200MeV. In addition evaluations were produced for the non-standard 238 U(n,γ )a nd 239 Pu(n,f) reactions. Results of this work and comparisons with previous evaluations are presented.

New evaluations of all important neutron cross sections of 182,183,184,186 Wa nd 181 Ta were performed from the upper end of the resonance region (2.2-12keV) up to 20MeV. The evaluation combines the results of recent nuclear model calculations (prior) and the complete existing experimental data base by means of the Bayesian code GLUCS06 in order to obtain the most accurate description of the cross section (posterior) within our present knowledge. As result of this work we obtained improved file 3 (cross sections) and file 33 (covariances) data for all important reactions of fast neutrons with the mentioned nuclides. Whenever necessary and possible fine structure of cross sections (at low neutron energies) was superimposed on the GLUCS results for the cross sections in a final evaluation step. For the isotopes of W complete new evaluated general purpose files in ENDF-format were produced by combining our evaluation results (files 3 and 33) with existing resonance data from JENDL 3.3 and file 4 and 6 data (energy-angle distributions for secondary particles) from our prior. These evaluations have been accepted for the Joint European Fission and Fusion File JEFF-3. For Ta a complete new evaluated file based on the described evaluation of cross sections and covariances will be produced in near future and submitted to JEFF-3.

A report is given of the progress achieved in an IAEA Co‐ordinated Research Project (CRP) to improve the cross‐section standards. The objectives of the CRP, started in 2002, were initially the understanding of the origin of the strong uncertainty reduction in R‐matrix model fits and the improvement of the evaluation methodology. These aims were extended in 2003 to the preparation of new evaluations for the standard 6Li(n,t), 10B(n,α), 10B(n,α1), 197Au(n,γ), 235U(n,f), and 238U(n,f) reactions. The methodology, codes, and experimental database developed by Poenitz and Hale for the ENDF/B‐VI standards evaluation were taken as the basis for the new evaluation. The major results achieved by the CRP participants include the testing and intercomparison of a number of codes that can be used in the standards evaluation, updating the database of experimental results, analysis of the reasons leading to the strong uncertainty reduction in model fits, and a study of the bias in evaluated data caused by the Peelles’s Pertinent Puzzle (PPP) effect, which has been widely discussed in the nuclear data community since the ENDF/B‐VI standards evaluation was completed. Preliminary results of the new standards evaluation are shown. The use of the new 235U(n,f) cross section leads to better consistency in calculations of some important integral experiments.

Accelerator mass spectrometry (AMS) represents a powerful technique for the detection of long‐lived radionuclides through ultra‐low isotope ratio measurements. In many cases, counting atoms rather than decays yields much higher sensitivities. The potential of AMS will be demonstrated on typical radionuclides of interest with half‐lives between some tens of years up to a hundred million years. The precise measurement of the 27Al(n,2n)26Al excitation function will be exemplified. Lack of information exists for a list of nuclides as pointed out by nuclear data requests. A brief overview on detection limits and some applications for selected long‐lived radionuclides is given.

A new evaluation of all‐important neutron cross sections of the stable isotopes of Ti was performed in the neutron energy range 0.2–20 MeV, which is the whole energy range above the resonance region. The evaluation combines the results of recent nuclear model calculations (prior) and the complete existing experimental database by means of the Bayesian code GLUCS03 in order to obtain the most accurate description of the cross sections (posterior) within our present knowledge. The evaluation of the total cross section is completely based on the accurate experimental database for natural Ti. The results of the evaluation, files 3 (cross sections) and files 33 (cross‐section covariances) for all stable isotopes of Ti will be part of the new isotopic evaluations for Ti for the Joint European Fission and Fusion (JEFF) file.

Starting with a discussion of the requirements and goals for high quality general‐purpose evaluations the paper will describe the procedures chosen in our evaluation work for JEFF for producing new general evaluations with complete covariance information for all cross sections (file 3 data). Key problems essential for the goal of making the best possible use of the existing theoretical and experimental knowledge on neutron interactions with the respective nuclide will be addressed, especially the problem of assigning covariances to calculated cross sections, necessary checking procedures for all experimental data and various possibilities to amend the experimental database beyond the obvious use of EXFOR data for the respective cross sections. In this respect both, the use of elemental cross sections in isotopic evaluations and the use of implicit cross‐section data (that is data which can be converted into cross sections by simple methods) will be discussed in some detail.

A new evaluation of the neutron cross‐section standards is now underway. This evaluation has been supported by the Working Party on International Evaluation Cooperation (WPEC), the Cross Section Evaluation Working Group (CSEWG), and an International Atomic Energy Agency Coordinated Research Program (CRP). The CRP has had the dominant role in producing these evaluations. An important goal is to produce the standards needed for the upcoming new ENDF/B‐VII library. Since most neutron cross‐section measurements are made relative to neutron cross‐section standards, the standards evaluation is of crucial importance. The standard reactions to be evaluated are: H(n,n), 3He(n,p), 6Li(n,t), 10B(n,α), 10B(n,α1γ), C(n,n), Au(n,γ), 235U(n,f), and 238U(n,f). These standards should receive international acceptance to ensure that all evaluation projects use the same set of standards. The last complete evaluation of the standards dates back almost 20 years. In the meantime quite a number of new and improved measurements have occurred for the cross‐section standards. International efforts are presently underway to update the experimental database and to improve the evaluation process. Due to the need for high‐energy standards, the energy range is being extended to 200 MeV for some of the cross‐section standards.

Inclusive light charged-particle emission spectra and cross sections from neutron bombardment of silicon were measured at $30\ifmmode^\circ\else\textdegree\fi{},$ $60\ifmmode^\circ\else\textdegree\fi{},$ $90\ifmmode^\circ\else\textdegree\fi{},$ and $135\ifmmode^\circ\else\textdegree\fi{}$ over the neutron energy range from threshold to approximately 60 MeV. Source neutrons, continuous in energy, were provided by the spallation neutron source of the Los Alamos Weapons Neutron Research facility. Comparisons of our alpha-particle data with Hauser-Feshbach calculations, which include multistage emission processes and preequilibrium particle emission, indicate that the majority of alpha particles result from compound nuclear reactions. For proton and deuteron emission, direct and preequilibrium processes contribute significantly to the emission cross section. These data provide rigorous tests for the calculations while helping to guide the selection of input parameters such as nuclear level densities. The effects of assuming partial or complete isospin conservation are shown to be important for these reactions.

Neutron-induced reactions producing light charged particles continue to be investigated at the spallation fast-neutron source at the Los Alamos Neutron Science Center (LANSCE). New data on the cross sections for alpha-particle production for neutrons on {sup 58}Ni and {sup 60}Ni are presented from threshold to 50 MeV. Recent changes in the experiment now allow protons, deuterons, tritons, {sup 3}He and alpha particles to be identified.

Neutron-production spectra from ([ital p],[ital n]) reactions on [sup 204,206,207,208]Pb and [sup 209]Bi measured previously by a Russian group were analyzed to extract numerical values for the level densities of the residual nuclei up to excitation energies of 5--6 MeV with uncertainties of 20--50%. Comparisons with the Gilbert-Cameron form and various parametrizations of the Ignatyuk formulation indicate that the Ignatyuk model with original parameters describes the results well whereas the other forms yield lower level densities. The agreement with the results of the first analysis by the experimenters themselves varies over the range of nuclei considered, being poorest for [sup 204,206]Bi.

An IAEA Data Development Project was initiated to provide a mechanism for allowing new experimental data and improvements in evaluation procedure to be incorporated into new evaluations of the standards. The work on this project is ongoing. In the past very long periods sometimes occurred between evaluations of the standards. Through the use of this Project, such long periods should not occur. Work on the cross section standards through this Project has included an update of the experimental data to be used in the cross section standards evaluations, a study of the uncertainties obtained in the international standards evaluation; and improvements in the smoothing procedure for capture cross sections. It was decided that this Project should have a broader range of activities than just the cross section standards and thus encompass standards related activities. The following are being investigated: improvements in the gold cross section at energies below where it is considered a standard; work on certain cross sections which are not as well known as the cross section standards but could be very useful as reference cross sections relative to which certain types of cross section measurements can be made. This work includes prompt gamma-ray production in fast neutron-induced reactions; and work on the 252Cf spontaneous fission neutron spectrum and the 235U thermal neutron fission spectrum. Most of the data investigated through this Project are used in dosimetry applications., JRC.D.4-Standards for Nuclear Safety, Security and Safeguards

High-resolution {gamma}-ray spectra from the interaction of neutrons in the energy range from 3 to 200 MeV with {sup 207,208}Pb were measured with the white neutron source at the WNR facility at Los Alamos National Laboratory. From these data, excitation functions for prominent {gamma} transitions in {sup 200,202,204,206,207,208}Pb were derived from threshold to 200 MeV incident neutron energy. These {gamma}-production cross sections represent formation cross sections for excited states of the residual nuclei. The results are compared with the predictions of nuclear reaction calculations based on the exciton model for precompound emission, the Hauser-Feshbach theory for compound nuclear decay, and coupled channels calculations to account for direct excitation of collective levels. Good agreement was obtained over the entire energy range covered in the experiment with reasonable model parameters. The results demonstrate that multiple preequilibrium emission has to be taken into account above about 40 MeV, and that the level density model of Ignatyuk should be used instead of the Gilbert-Cameron and back-shifted Fermi-gas models if excitation energies exceed about 30 MeV.

Evaluated data including uncertainty estimates were derived for the following quantities: σtot’ σnon’ σel’ σine1’ σn,p’ σn,np’ σn,α’ σn,nl’ σn,2n’ σn-em’ σp-em σ∝-em and the reduced Legendre coefficients of the P1, P2 and P3 components of the elastic angular distribution at E = 14.0 MeV. For the purpose of evaluation all measurements in the neutron energy range 13.5n – 14.8 MeV were critically reviewed, reduced to the nominal energy of 14.0 MeV and the evaluation results derived as weighted averages from the accepted and — if necessary — properly renormalized data. The results of this evaluation (with few exceptions) lie within the range of predictions of the new evaluated data files BROND, EFF-2, ENDF/B-VI and JENDL-3 and thus confirm the assumption that comparison of different evaluated files may be used for uncertainty estimates.

The cross sections and energy and angular distributions in the JENDL-3, JEF-2/EFF-2, and ENDF/B-VI evaluations for 52Cr, 56Fe, and 58Ni are compared graphically. The purpose is to understand the reasons for observed discrepancies among the evaluations, and to suggest recommendations for improvements. The accomplishments to date are presented.

On recommendation of the Nuclear Energy Agency (NEANDC) an international working group on activation cross-sections was formed in 1989, which, at its first meeting, initiated an intercomparison of activation cross-section measurements using the D(d,n)3He and H(t,n)3He reactions. For this purpose excitation functions for the 58Ni(n,p)58Co and 93Nb(n,2n)92mNb reactions have been measured at the Argonne National Laboratory and the Physikalisch-Technische Bundesanstalt, Braunschweig (PTB) using neutrons produced by means of the D(d,n)3He reaction and in a collaboration Los Alamos National Laboratory — Institut fur Radiumforschung, Vienna (IRK) by means of neutrons produced by the H(t,n)3He reaction in order to test the different corrections needed to account for the deficiencies of the respective source reactions. Measurements at Argonne were performed in the neutron energy range En = 5–10 MeV, at PTB in the range En = 8–14 MeV and at Los Alamos for 5–13 MeV neutrons. Reasonable agreement was obtained between the results of the three groups for most of the investigated neutron energy range, there are however also some small discrepancies, both in the gamma-efficiency calibration and some cross-section values which need further study. The data obtained in this intercomparison substantially improve our knowledge on the excitation function of the two important dosimetry reactions.