New cross-section data for the 66Zn(p,n)66Ga, 68Zn(p,3n)66Ga, natZn(p,x)66Ga, 68Zn(p,2n)67Ga and natZn(p,x)67Ga nuclear reactions up to 100 MeV

doi:10.1016/j.nimb.2005.02.011

Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms

Volume 234, Issue 4, July 2005, Pages 375-386

https://doi.org/10.1016/j.nimb.2005.02.011 Get rights and content

Abstract

Excitation functions were measured for the ⁶⁶Zn(p,n)⁶⁶Ga, ⁶⁸Zn(p,3n)⁶⁶Ga, ^natZn(p,x)⁶⁶Ga, ⁶⁸Zn(p,2n)⁶⁷Ga and ^natZn(p,x)⁶⁷Ga nuclear processes up to 100 MeV. These results were compared to the available cross-section values from previous studies. A detailed compilation of the earlier works was also performed.

Introduction

Nowadays, numerous research groups are involved in systematic investigations of alternative production routes for several copper radioisotopes used for PET studies and radiotherapy. Among the processes studied, the Zn + p routes have proved to be very promising for the production of ⁶¹Cu, ⁶²Zn/⁶²Cu, ⁶⁴Cu and ⁶⁷Cu (cf. [1], [2], [3]). In some cases, however, higher incident proton energies (above 30 MeV) are needed to form enough copper radioisotopes for the medical studies. Unfortunately, during the activation of zinc targets, significant amount of ⁶⁶Ga and ⁶⁷Ga are “co-formed” – even at higher energies – causing this way relatively high “radio-gallium” contamination of the irradiated material. To develop a proper radiochemical separation of the Cu radioisotopes from Zn and Ga, and to estimate the radiation doses during the chemistry steps, one has to know also the excitation functions of those Zn + p nuclear reactions which form ⁶⁶Ga and ⁶⁷Ga up to 100 MeV.

The excitation function of Zn + p reactions resulting ⁶⁶Ga and ⁶⁷Ga has been extensively studied in the past since these radioisotopes are also important for nuclear medicine. Due to the large number of the low energy (<30 MeV) proton accelerators, the commercial production of the above radioisotopes are predominantly based on (p,n) and (p,2n) nuclear reactions on highly enriched ⁶⁶Zn, ⁶⁷Zn and ⁶⁸Zn targets. The excitation function of those reactions is therefore well measured and has already been compiled up to around 30 MeV (cf. [4], [5]). Since from practical point of view the knowledge of these cross-sections is less important beyond this energy, it is not surprising that less efforts was done in the past to extend (and to compile) their databases up to higher energies (around 100 MeV). The available cross-section works above 30 MeV therefore are rather scanty or discrepant (cf. [4], [5]) and cannot be used to calculate the contamination levels at copper production.

Recently we have also investigated the merit of Zn + p reactions for the production of ⁶¹Cu [2], ⁶²Cu (via the ⁶²Zn/⁶²Cu generator) [1] and ⁶⁴Cu [3]. Natural and highly enriched zinc targets (⁶⁶Zn and ⁶⁸Zn) were activated up to 100 MeV to study the formation of ⁶¹Cu (on ⁶⁶Zn and ⁶⁸Zn), ⁶²Zn(⁶²Cu) (on ^natZn, ⁶⁶Zn and ⁶⁸Zn), and ⁶⁴Cu (on ⁶⁶Zn and ⁶⁸Zn). We could also observe the presence ⁶⁶Ga and ⁶⁷Ga in our spectra. Using the measured activities of these gallium radioisotopes, we have also calculated the cross-sections of the appropriate nuclear reactions and processes.

To check the reliability of our results, we have also compared our cross-section values with the available literature. Although our data showed acceptable agreement with the recommended values in the lower energy region, our values at higher energies – in some cases – differed even from those data reported most recently. It was especially significant in the case of the ⁶⁸Zn(p,2n)⁶⁷Ga and ⁶⁸Zn(p,3n)⁶⁶Ga reactions [6], [7].

In an attempt to clarify the discrepancies found among the various reported cross-section values and to extend the database of those Zn + p reactions which form ⁶⁶Ga and ⁶⁷Ga up to 100 MeV, we present here the results of our measurements for the following nuclear processes: ⁶⁶Zn(p,n)⁶⁶Ga, ⁶⁸Zn(p,3n)⁶⁶Ga, ^natZn(p,x)⁶⁶Ga, ⁶⁸Zn(p,2n)⁶⁷Ga and ^natZn(p,x)⁶⁷Ga.

The extended database of the above reactions can be used not only to calculate the amount of the gallium contamination during copper production via Zn + p reactions, but to check the predicting capabilities of the different nuclear codes, (cf. ALICE-IPPE, STAPRE etc.) as well.

Section snippets

Experimental

As mentioned above, the results presented in this study were achieved simultaneously with those of primary interest in other studies [1], [2], [3] as these radioisotopes were co-produced in the same experimental irradiations. The experimental techniques and the data evaluation method used, therefore, are the same (or similar) to those reported in these previous articles [1], [2], [3]. We refer the reader to those papers for details (e.g. target preparation, composition of stacks, monitoring,

Results and discussions

The excitation functions for the ⁶⁶Zn(p,n)⁶⁶Ga, ⁶⁸Zn(p,3n)⁶⁶Ga, ^natZn(p,x)⁶⁶Ga, ⁶⁸Zn(p,2n)⁶⁷Ga and ^natZn(p,x)⁶⁷Ga nuclear processes are shown by the closed circles in Fig. 1, Fig. 2, Fig. 3, Fig. 4, Fig. 5, respectively. Table 2 contains the numerical values of the measured cross-sections.

Conclusions

Our detailed measurements extend the database of the ⁶⁶Zn(p,n)⁶⁶Ga, ⁶⁸Zn(p,3n)⁶⁶Ga, ^natZn(p,x)⁶⁶Ga, ⁶⁸Zn(p,2n)⁶⁷Ga and ^natZn(p,x)⁶⁷Ga nuclear processes up to 100 MeV. We have compared and reviewed the available results above 30 MeV in an attempt to get a reliable database for the above processes. It was found that the most recent study reported dubious cross-sections especially at higher energies for the ⁶⁸Zn(p,3n)⁶⁶Ga and ⁶⁸Zn(p,2n)⁶⁷Ga nuclear reactions. On the basis of the present results, the

Acknowledgments

We thank the operators of the cyclotrons at iThemba LABS, Faure, Somerset West and NIRS, Chiba, for performing many irradiations. This work was financially supported by the Hungarian Research Found (OTKA: T037219), the Japanese Society for Promotion of Sciences (Tokyo) and the Hungarian Academy of Sciences (Budapest), the Research and Development Division of Ministry of Education (Budapest) and the National Research Found (Pretoria) [DAK 2/00 and 1/03].

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We present the cross sections for the $^{nat} Zn$ ( $p, x$ ) $^{67} Cu$ and $^{nat} Zn$ ( $p, x$ ) $^{67} Ga$ reactions within a proton energy range of 47.5–99.2 MeV. We efficiently separated the overlapping gamma-ray spectra of the two isotopes $^{67} Cu$ and $^{67} Ga$ , using an analytical method without radiochemical separation. The present data were compared with previous data from the literature, typically obtained by radiochemical separation before measuring the gamma-ray spectra of the two isotopes. Our results for the two isotopes generally showed greater or smaller values than those reported in the literature, except for some data concerning partial energy ranges, which were in agreement with the literature data. The present data were also compared with the TENDL-2017 library based on the TALYS code.
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Citation Excerpt :
Fig. 4 reported the measurements of the 68Zn(p,3n)66Ga cross section: as in case of 67Ga reaction, results obtained in this work described the decreasing part of the nuclear reaction. There was an excellent agreement with latest values by Szelecsényi et al. (2005) [35] in the entire energy range (35–70 MeV); measurements by Stoll et al. (2002) [30] were in good agreement for energies higher than 43 MeV, while at lower energies these previous data seemed to underestimate the nuclear reaction. Hermanne et al. (1991) [36] measured a very high peak value (around 290 mb at 34 MeV), but the same authors repeated the experiment in 1999 [37] and these later data are in good agreement with results obtained in this work.
The cross sections of the ⁶⁸Zn(p,2p)⁶⁷Cu, ⁶⁸Zn(p,2n)⁶⁷Ga and ⁶⁸Zn(p,3n)⁶⁶Ga reactions were measured at the ARRONAX facility by using the 70 MeV cyclotron, with particular attention to the production of the theranostic radionuclide ⁶⁷Cu. Enriched ⁶⁸Zn material was electroplated on silver backing and exposed to a low-intensity proton beam by using the stacked-foils target method. Since ⁶⁷Cu and ⁶⁷Ga radionuclides have similar half-lives and same γ-lines (they both decay to ⁶⁷Zn), a radiochemical process aimed at Cu/Ga separation was mandatory to avoid interferences in γ-spectrometry measurements. A simple chemical procedure having a high separation efficiency (>99%) was developed and monitored during each foil processing, thanks to the tracer isotopes ⁶¹Cu and ⁶⁶Ga. Nuclear cross sections were measured in the energy range 35–70 MeV by using reference reactions recommended by the International Atomic Energy Agency (IAEA) to monitor beam flux. In comparison with literature data a general good agreement on the trend of the nuclear reactions was noted, especially with latest measurements, but slightly lower values were obtained in case of ⁶⁷Cu. Experimental results of the ⁶⁸Zn(p,2p)⁶⁷Cu, ⁶⁸Zn(p,2n)⁶⁷Ga and ⁶⁸Zn(p,3n)⁶⁶Ga reactions were also compared with the theoretical values estimated by using the software TALYS. The production yield of the theranostic radionuclide ⁶⁷Cu was estimated considering the results obtained in this work.
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The experimental production cross section for the reaction ^natZn(p,x)⁶⁷Ga has been measured in the energy range from 1.678 to 2.444 MeV. The methodology used in this work is based on characteristic X-ray emitted after irradiation by the daughter nuclei that decays by electron capture (EC) and the use of a complementary PIXE experiment. By doing so, expressions needed to determine cross section values are simplified since experimental factors such as geometric setup and an detector efficiency are avoided. ⁶⁷Ga is a radionuclide particularly suited for this method since it decays by electron capture in 100% and the subsequent characteristic X-ray emission is easily detected.
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Citation Excerpt :
The cross section data for this reaction have been determined several times. The measurements by Szelecsényi et al. (2003, 2005) exist above 25 MeV, so those data are not relevant. However the earlier data by Szelecsényi et al. (1998) in the energy range of 6–26 MeV describe the trend of the excitation function quite well.
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Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms

Abstract

Introduction

Section snippets

Experimental

Results and discussions

Conclusions

Acknowledgments

References (19)

Investigation of ^natZn(p,x)⁶²Zn nuclear process up to 70 MeV: a new ⁶²Zn/⁶²Cu generator

Appl. Radiat. Isot.

Compilation of cross sections/thick target yields for ⁶⁶Ga, ⁶⁷Ga and ⁶⁸Ga production using Zn targets up to 30 MeV proton energy

Appl. Radiat. Isot.

Evaluated cross section and thick target yield data of Zn + p processes for practical applications

Appl. Radiat. Isot.

Nuclear interactions of ⁴⁵Sc and ⁶⁸Zn with protons of medium energy

Nucl. Phys. A

Cross sections and production yields of ⁶⁶Ga and ⁶⁷Ga for proton reactions in natural zinc

Appl. Radiat. Isot.

Excitation functions and yields of relevance to the production of ⁶⁷Ga by proton bombardment of ^natZn and ^natGe up to 100 MeV

Appl. Radiat. Isot.

Activation cross-section of long-lived products of proton induced nuclear reactions on zinc

Appl. Radiat. Isot.

Study of production possibility of ⁶¹Cu using proton induced nuclear reactions on zinc for use in PET studies

J. Radioanal. Nucl. Chem.

Cited by (21)

Assessment of production of <sup>66</sup>Ga via <sup>66</sup>Zn(d,2n)<sup>66</sup>Ga reaction as a medical radioisotope using GEANT4, MCNPX and TALYS computer nuclear codes

Radionuclide candidates for β+γ coincidence PET: An overview

Measurement of cross sections for proton-induced reactions on natural Zn

New production cross sections for the theranostic radionuclide <sup>67</sup>Cu

Measurements of <sup>67</sup>Ga production cross section induced by protons on <sup>nat</sup>Zn in the low energy range from 1.678 to 2.444 MeV

New cross-section data for the 66Zn(p,n)66Ga, 68Zn(p,3n)66Ga, natZn(p,x)66Ga, 68Zn(p,2n)67Ga and natZn(p,x)67Ga nuclear reactions up to 100 MeV

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Introduction

Section snippets

Experimental

Results and discussions

Conclusions

Acknowledgments

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New cross-section data for the ⁶⁶Zn(p,n)⁶⁶Ga, ⁶⁸Zn(p,3n)⁶⁶Ga, ^natZn(p,x)⁶⁶Ga, ⁶⁸Zn(p,2n)⁶⁷Ga and ^natZn(p,x)⁶⁷Ga nuclear reactions up to 100 MeV

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