Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms
New cross-sections and intercomparison of deuteron monitor reactions on Al, Ti, Fe, Ni and Cu
Introduction
A systematic study of charged particle induced nuclear reactions on metals has been started years ago among others with the aim to evaluate their potential use for monitoring the energy and/or intensity of particle beams. The use of monitor reactions is a simple, convenient and cheap method for characterisation of the bombarding beam when the required accuracy is not too high or under difficult irradiation conditions. It remains, however, necessary to know precisely the absolute cross-sections of the applied monitor reactions to determine the intensity or the energy of a bombarding charged particle beam with low uncertainty. Reliable data sets of cross-sections for charged particle induced reactions have also to meet the requirements needed for other applications such as charged particle activation analysis, medical isotope production, thin layer activation, estimation of neutron yield and residual activity of accelerator components, calculation of activity for radiation safety and simulation of radiation damage. In these applications, the required bombarding energy is generally below 15 MeV, therefore the irradiation cannot be monitored with 27Al(d,x)22Na or 27Al(d,x)24Na reactions. The aim of this study was hence twofold: (1) to study other reactions and propose them as monitors below 20 MeV and (2) to make an intercomparison between the investigated reactions to increase the reliability of the measured cross-sections and minimise the possible systematic errors of the experiment. The metals used, aluminium, titanium, iron, nickel and copper, are ideal target materials with respect to their availability, physical, mechanical and chemical properties. In a view to enhance our knowledge of the necessary excitation functions, we have measured, compiled and critically evaluated absolute cross-sections of the 27Al(d,x)22Na, 27Al(d,x)24Na, natTi(d,x)48V, natFe(d,x)56Co, natNi(d,x)61Cu and natCu(d,x)65Zn processes.
Cross-sections of the above processes were measured by several authors in the past. In spite of the simple target preparation, irradiation and activation detection technique needed to assess these reactions, surprisingly large disagreements exist between the different experimental results. The cross-sections reported by different authors are considered to be independent experimental results, which in some cases show unacceptable deviations both in the values of cross-sections and in the energy scales. The analysis of available publications led to the conclusion that, only on the basis of the scarce reported experimental circumstances and even after correction for outdated nuclear data and other small mistakes and errors, the selection of a reliable data set is still difficult. Consequently, the collected published cross-sections cannot be used for monitoring of bombarding beams without critical evaluation. In some cases it required precise remeasurement. In the present work, the above six reactions were considered for a detailed study in the low and medium deuteron energy region. We performed new cross-section measurement with improved experimental techniques and accuracy and we have linked the six reactions together by irradiating different types of target foils in one stack. The acquired new experimental data allowed us to solve most of the discrepancies existing among the earlier published data. An attempt was made to calculate the cross-sections for the above reactions by different model codes in order to be able to compare the results of experimental and theoretical calculations. The comparison showed that the prediction capability of the available codes do not provide the precision required in the everyday nuclear technology.
Section snippets
Status of the literature data
The literature survey shows that the main part of the experiments was performed at cyclotrons using a stacked foil technique on natural metallic targets and applying an activation method without chemical separation. The most common procedure to measure the beam intensity was charge collection with a Faraday cup. In a few cases highly enriched targets were irradiated and other techniques as beam current measurements with monitor reactions or back scattering were used. NaI, Ge(Li) or Ge detectors
Model codes and fit calculations
Different versions of the model code ALICE-91 were used to calculate the cross-sections of the investigated processes. The basic physics of the code can be found in [6], [7], [8]. The ALICE-91 code uses a hybrid or geometry dependent pre-compound model and the Weisskopf–Ewing evaporation theory [9] for the equilibrium part. The code uses the Fermi gas level density and has the option of using the shell-dependent level densities from Kataria and Ramamurthy [10]. The ALICE-IPPE code is a version
New results
Excitation functions were measured for the 27Al(d,x)22Na, 27Al(d,x)24Na, natTi(d,x)48V, natFe(d,x)56Co, natNi(d,x)61Cu, natCu(d,x)65Zn processes using the activation method and a stacked foil technique. The presented data are experimental elemental cross-sections. The cross-sections obtained in separate irradiations agree well with each other in the overlapping energy region and allow us to present a consistent data set corresponding to an accurate broad energy range experiment. The numerical
Experimental
All measurements were made using thin, high-purity foils (99.99–99.999% supplied by Goodfellow Metals, England) with natural isotopic composition. The experimental technique used, evaluation of raw data and error analysis were similar to those reported in our earlier publications [1], [2], [17], [18], [19]. Only some of the important features relevant to the present work are discussed here. Several stacks were irradiated in external deuteron beams of the CGR930 cyclotron of Louvain-la-Neuve at E
New results
The excitation function has a special shape. A normal rising part is seen up to 50 MeV followed by a plateau-like continuation, which is the result of the complexity of open reaction channels. In this work, we measured data points up to 50 MeV. The measurements were done several days after the irradiation allowing the complete decay of all short-lived isotopes in the target. All the values given are cumulative elemental cross-sections, i.e. they describe the sum of direct production and decay
Conclusion
In this work, we measured the elemental cross-sections of six processes using deuteron beams with 30 and 50 MeV primary bombarding energy. Detailed measurements were made on the two most frequently used monitor reactions e.i. 27Al(d,x)22Na and 27Al(d,x)24Na. We found excellent agreement among our new data and the selected cross-sections measured by other authors for both reactions over the whole energy region. Since the irradiated stacks contained, apart from the Al foils, also Ti, Fe, Ni or Cu
Acknowledgements
We are pleased to acknowledge the co-operation and help in performing the irradiations of the teams of the Louvain-la-Neuve-Cyclone CGR 930, the VUB-CGR 560 and the Debrecen-MGC 20E cyclotron laboratories.
This work was partly supported in the frame of a Co-ordinated Research Project “Development of Reference Charged Particle Cross-section Data Base for Medical Radioisotope Production” organised by the International Atomic Energy Agency, Vienna, Austria. Financial support was received from the
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