New cross-sections and intercomparison of proton monitor reactions on Ti, Ni and Cu

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Abstract

The excitation functions of proton induced reactions on Ti, Ni and Cu were studied using activation method on stacks made of thin metallic foil targets with natural isotopic composition. Since titanium, nickel and copper are ideal target material with respect to their availability, physical, mechanical and chemical properties the use of the natTi(p,x)48V, natNi(p,x)57Ni, natCu(p,x)62Zn, natCu(p,x)63Zn and natCu(p,x)65Zn processes are suitable for monitoring the intensity and/or energy of charged particle beams. These processes are recommended under 40 MeV bombarding proton energy as monitor reaction. The new data sets of these five processes were cross-checked with each other to provide reliable consistent numerical cross-sections. Results were compared to the recommended cross-section values reported recently by the International Atomic Energy Agency [IAEA TECDOC-1211, 2001].

Introduction

In charged particle irradiations, both for basic research and in practical applications, the knowledge of the energy and intensity of the bombarding particles are required. Faraday cup measurements of beam current are sometimes not possible or not accurate enough. On the other hand direct energy measurement requires complicated techniques. The use of monitor reactions can be a solution. It is a simple, convenient and cheap method to determine the energy and intensity of the bombarding beam. Several reactions induced by energetic charged particles on metal targets were studied with among other aims to evaluate their potential use for monitoring the energy and intensity of charged particle beams. Monitoring of beam parameters is also essential in numerous applications, such as isotope production under optimised circumstances, charged particle activation analysis, thin layer activation, estimation of neutron yield and residual activity of accelerator components, calculation of activity for radiation safety and simulation of radiation damage etc. When using monitor reactions to characterise charged particle bombarding beams reliable and accurate cross-section data are required.

The availability of multiple induced radionuclides in the same monitor foil and the use of different metals in one experiment, leading to different reactions, will improve the internal consistency of the cross-section database.

Several authors measured cross-sections of the natTi(p,x)48V, natNi(p,x)57Ni, natCu(p,x)62Zn, natCu(p,x)63Zn and natCu(p,x)65Zn processes 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 excitation function reported by different authors shows unacceptable deviations both in the values of cross-sections and in the energy scales in some cases. A good summary of the available experimental data is given for the above reactions among others in the IAEA TECDOC-1211 [1].

The aim of a recent study was to investigate several frequently used proton monitor reactions and to make an inter-comparison between them to increase the reliability of the measured cross-sections and minimise the possible systematic errors in the experiments. In the present work the above five reactions were considered for a detailed study. We performed new cross-section measurements with improved experimental techniques and accuracy and we have linked the five reactions together by irradiating different types of target foils in the same stack. The acquired new experimental data were compared to the recommended data given in [1].

Section snippets

Experimental

Measurements were made using high purity Ti, Ni and Cu foils with natural isotopic composition (99.99–99.999% supplied by Goodfellow Metals, England). Two stacks were irradiated at the extracted proton beam of the CGR 560 cyclotron of the Vrije Universiteit Brussel (VUB). Stacks were placed in a Faraday type irradiation chamber equipped by long collimator and electron suppresser. Beam current was measured by a digital charge integrator, while the estimated incident beam energy was calculated

Data evaluation

The cross-section for the reaction studied was computed for each foil from the counts measured in the total energy peaks of the nuclide involved, combined with detector efficiency, nuclear data, the number of target atoms and the estimated number of bombarding particles. Possible loss of activity through recoil effects was evaluated and was always less than 1%.

Nuclear decay data used in these experiments (see Table 1) are the same as considered in determining the recommended cross-section

The natTi(p,x)48V process

Four reactions contribute to the formation of 48V by proton bombardment below 35 MeV on a natural Ti target. These are the 47Ti(p,γ)48V, 48Ti(p,n)48V, 49Ti(p,2n)48V and 50Ti(p,3n)48V reactions having Q value of +5.8, −4.8, −12.9 and −23.9 MeV, respectively. The nuclear data (half-life, gamma energy and intensity) were taken from [2] and are collected in Table 1. Foils were measured one to two days after EOB in a well-calibrated geometry of a HpGe detector. The two sets of experimental points

Conclusion

In the Co-ordinated Research Project (CRP) [1] of the International Atomic Energy Agency a detailed analysis were made on the most frequently used monitor reactions for proton beams. Among them are the natTi(p,x)48V, natNi(p,x)57Ni, natCu(p,x)62Zn, natCu(p,x)63Zn and natCu(p,x)65Zn processes. The data evaluation in [1] was made independently for each of the reactions, even in those cases when the reactions take place on the same target material. Recommended cross-section values were given by

Acknowledgements

We are pleased to acknowledge the co-operation and help in performing the irradiations of the team of the VUB-CGR 560 cyclotron laboratory. This work was partly supported by the Hungarian OTKA Fund (contract no. 26556). Financial support was also received from the Fund for Scientific Research (FWO-Vlaanderen) from the Hungarian Academy of Sciences, and from OZR-VUB.

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