G. L. Molnár

Database of prompt gamma rays from slow neutron capture forelemental analysis

The increasing importance of Prompt Gamma-ray ActivationAnalysis (PGAA) in a broad range of applications is evident, and has beenemphasized at many meetings related to this topic (e.g., TechnicalConsultants Meeting, Use of neutron beams for low- andmedium-fluxresearch reactors: radiography and materialscharacterizations, IAEA Vienna, 4-7 May 1993, IAEA-TECDOC-837, 1993).Furthermore, an Advisory Group Meeting (AGM) for the Coordination of theNuclear Structure and Decay Data Evaluators Network has stated that thereis a need for a complete and consistent library of cold- and thermalneutron capture gammaray and cross-section data (AGM held at Budapest,14-18 October 1996, INDC(NDS)-363); this AGM also recommended theorganization of an IAEA CRP on the subject. The International NuclearData Committee (INDC) is the primary advisory body to the IAEA NuclearData Section on their nuclear data programmes. At a biennial meeting in1997, the INDC strongly recommended that the Nuclear Data Section supportnew measurements andupdate the database on Neutron-induced PromptGamma-ray Activation Analysis (21st INDC meeting, INDC/P(97)-20). As aconsequence of the various recommendations, a CRP on Development of aDatabase for Prompt Gamma-ray Neutron Activation Analysis (PGAA) wasinitiated in 1999. Prior to this project, several consultants had definedthe scope, objectives and tasks, as approved subsequently by the IAEA.Each CRP participant assumed responsibility for the execution of specifictasks. The results of their and other research work were discussed andapproved by the participants in research co-ordination meetings (seeSummary reports: INDC(NDS)-411, 2000; INDC(NDS)-424, 2001; andINDC(NDS)-443, 200). PGAA is a non-destructive radioanalytical method,capable of rapid or simultaneous in-situ multi-element analyses acrossthe entire Periodic Table, from hydrogen to uranium. However, inaccurateand incomplete data were a significant hindrance in the qualitative andquantitative analysis of complicated capture-gamma spectra by means ofPGAA. Therefore, the main goal of the CRP was to improve the quality andquantity of the required data in order to make possible the reliableapplication of PGAA in fields such as materials science, chemistry,geology, mining, archaeology, environment, food analysis and medicine.This aim wasachieved thanks to the dedicated work and effort of theparticipants. The CD-ROM included with this publication contains thedatabase, the retrieval system, the three CRM reports, and otherimportant electronic documents related to the CRP. The IAEA wishes tothanks all CRP participants who contributed to the success of the CRP andthe formulation of this publication. Special thanks are due to R.B.Firestone for his leading roll in the development of this CRP and hiscomprehensive compilation, analysis and provision of the adopteddatabase, and to V. Zerkin for the software developments associatedwiththe retrieval system. An essential component of this data compilation isthe extensive sets of new measurements of capture gamma-ray energies andintensities undertaken at Budapest by Zs. Revay under the direction ofG.L. Molnar. The extensive participation and assistance of H.D. Choi isalso greatly appreciated. Other participants inthis CRP were: R.M.Lindstrom, S.M. Mughabghab, A.V.R. Reddy, V.H. Tan and C.M. Zhou. Thanksare also due to S.C. Frankle and M.A. Lone for their active participationas consultants at some of the meetings. Finally, the participants wish tothank R. Paviotti-Corcuera (Nuclear Data Section, Division of Physicaland Chemical Sciences), who was the IAEA responsible officer for the CRP,this publication and the resulting database. The participants aregrateful to D.L. Muir and A.L. Nichols, successive Heads of the NuclearData Section, for their active and enthusiastic encouragement infurthering the work of the CRP.

Wide energy range efficiency calibration method for Ge detectors

Abstract A new method is proposed for the relative efficiency calibration of HPGe detectors in the energy range from 50xa0keV to 11xa0MeV. By simultaneously fitting all separately measured data sets from calibrated and uncalibrated multigamma sources as well as neutron capture γ-rays with a sum of orthogonal polynomials on a log–log scale, accuracies better than 0.5% between 100 and 3500xa0keV and better than 1% up to 6000xa0keV could be achieved for relative full energy peak efficiencies. Dividing the energy range and fitting piecewise with lower-order polynomials does not offer any advantage. Moreover, none of the popular non-linear empirical functions are able to fit the full range. The polynomial fit is nearly indistinguishable from a semiempirical fit. If at least one calibrated γ-ray source is included, the method can be used for absolute efficiencies as well.

Introducing HYPERMET-PC for automatic analysis of complex gamma-ray spectra

In short time activation analysis prompt gamma-activation analysis and in high rate γ-ray spectroscopy in general, the shape parameters for peaks and back ground usually vary, rendering spectrum evaluation codes based on a fixed shape calibration unsuitable. An interactive version of the well-known, fully automatic γ-ray spectrum analysis code HYPERMET has been developed in C ++ for the IBM-PC. It runs under MS-DOS, in conventional memory, and can handle up to 16k-channel spectra, recorded with CANBERRAs System 100 and AccuSpec and with ORTECs ACE plug-in MCA cards. A Windows-like graphics environment is provided with mouse controlled pull-down menus, pop-up windows and rubber band expansion. All basic features of HYPERMET such as fully automatic peak search, nonlinear fitting of multiplets with automatically adjusted Gaussian peak widths exponential tails and a complex background function have been retained. All details of the fitting procedure are recorded in a data base, hence any fitted region can be retrieved and modified interactively, even after a fully automatic spectrum evaluation. The program also provides an output peak list in SAMPO90 format for further processing. The latter format is widely used in a number of sample analysis programs such as KAYZERO a software package fork0 standardization in neutron activation analysis.

Cold neutron PGAA facility at Budapest

The new cold neutron prompt gamma activation analysis (PGAA) facility provides improved capabilities for routine prompt gamma analysis and for the investigation of radiative neutron capture. The versatile beam chopper makes possible time-of-flight measurements and the acquisition of prompt and decay spectra simultaneously. The chopped beam PGAA technique combines the advantages of the in-beam measurement and the greater simplicity of decay gamma spectra.

Standardisation of the prompt gamma activation analysis method

Summary A complete series of measurements was performed at the Budapest prompt gamma neutron activation analysis (PGAA) facility in order to determine the partial production cross sections of the most suitable neutron capture gamma rays for all naturally occurring elements, excluding noble gases. The values were determined directly, with internal standardisation using stoichiometric compounds and homogeneous mixtures (mainly water solutions) of known composition. A comparison with a recent measurement for 20 elements shows good agreement except for a few non-1/v cross sections. The new data are sufficiently accurate for quantitative multielement determinations in PGAA without the necessity of elemental standards.

Recent developments in HYPERMET PC

HYPERMET PC is a user-friendly γ-ray spectrum analysis software package developed at Budapest, mainly for the purpose of prompt-γ neutron activation analysis (PGAA). The peak fitting algorithm is an improved version of the well-known HYPERMET code, and contains a partial peak-parameter calibration to describe peak shapes more accurately in the wide energy range typical for prompt-γ spectra. A nuclide identification routine has also been developed using a new PGAA library, shown in a parallel paper. The new module for quantitative PGAA includes all the features necessary to obtain concentration values for elements.

The new prompt gamma-activation analysis facility at Budapest

Prompt gamma-activation analysis (PGAA) is an important complementary technique to conventional instrumental activation analysis that can be successfully used in a number of cases when INAA is not applicable. Therefore, a PGAA facility has been constructed at the recently refurbished and upgraded Budapest Research Reactor. It occupies the end position of a new curved themal guide of 30 m length and 2.5×10 cm2 cross section which provides a clean beam of low energy neutrons. The sophisticated HPGe-BGO γ-ray spectrometer system can be operated in Compton-suppression and pair-spectrometer modes simultaneously. The octal splitting of the main BGO improves efficient pair mode operation when coincidences between pairs of opposite segments and the HPGe detector are required separately. Gamma-gamma coincidence measurements will also be possible when the new multiparameter data acquisition system is completed. One of the main tasks at the new facility will be the accumulation of new spectroscopic data for detector calibration and standardisation, as well as for the construction of a more accurate prompt γ-ray library for the chemical elements. Various applications are planned, such as the determination of hydrogen in fullerenes and of toxic trace elements in environmental samples.

66Ga: a standard for high-energy calibration of Ge detectors

Abstract Two independent measurements of the relative emission probabilities for the strongest transitions in 66Ga electron capture decay are reported here. The results of these measurements are in excellent agreement with each other and with those from another recent measurement. Consequently, 66Ga emission probabilities for 18 strong lines, from 834 to 4806xa0keV, are now known to better than 1% accuracy. Thus, 66Ga can now be considered a suitable radionuclide for Ge detector efficiency calibration up to an energy of 4806xa0keV, the highest energy attainable with radioactive calibration sources. We have also provided an empirical function for correcting earlier incorrect emission probability results for Eγ greater than about 3xa0MeV which were produced using an inappropriate efficiency curve extrapolation.

The new prompt gamma-ray catalogue for PGAA

A new catalogue of subthermal neutron-induced prompt gamma rays has been created for 79 elements, from hydrogen to uranium (including fission), on the basis of recent measurements at the Budapest guided-neutron PGAA facility. New energy values have been measured using 35Cl neutron-capture gamma rays, while the gamma-ray production cross-sections have been determined with respect to the 1H thermal capture cross-section. The elemental data have been compared with thermal neutron-capture data for individual nuclides from the Evaluated Nuclear Structure Data File, ENSDF, hence isotope identifications could be made. The catalogue contains elemental spectra and a table with nearly 7000 gamma rays with relative intensity over 1% of the strongest line. The average accuracy is about 0.08 keV for energies and about 5% for cross-sections in the whole energy range, from about 40 keV to 11 MeV.

Revisiting the 238U thermal capture cross section and gamma-ray emission probabilities from 239Np decay

Abstract The precise value of the thermal capture cross section of 238U is uncertain, and evaluated cross sections from various sources differ by more than their assigned uncertainties. A number of the original publications have been reviewed to assess the discrepant data, corrections were made for more recent standard cross sections and other constants, and one new measurement was analyzed. Because of the strong correlations in activation measurements, the gamma-ray emission probabilities from the β– decay of 239Np were also analyzed. As a result of the analysis, a value of 2.683 ± 0.012 b was derived for the thermal capture cross section of 238U. A new evaluation of the gamma-ray emission probabilities from 239Np decay was also undertaken.