A Survey of New Methods for Production of Some Radionuclides, at Laboratory Scale, through Secondary Reactions in Nuclear Reactors


The studies performed in the frame of a project destined for the search of new (t,n) and (p,n) reactions of interest in nuclear reactors are described. Experimental evidences of the observations of the reactions: 46Ti(t,n)48V, 48Ti(p,n)48V, 52Cr(t,n)54Mn, 56Fe(p,n)56Co, 72Ge(t,n)74As and 74Ge(p,n)74As, are presented. Additional data on some secondary reactions, already characterised for the production of 7Be, 56Co, 58Co, 65Zn and 88Y, were also obtained. The significance of these data is discussed.

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Cohen, I. , Siri, S. and Iljadica, M. (2014) A Survey of New Methods for Production of Some Radionuclides, at Laboratory Scale, through Secondary Reactions in Nuclear Reactors. Advances in Chemical Engineering and Science, 4, 300-307. doi: 10.4236/aces.2014.43033.

2. Experimental

2.1. Irradiations

All the irradiations were carried out in the RA-3 reactor (Ezeiza Atomic Centre). The reactor is of the MTR pool type, with fuel elements of 20% enriched uranium. At nominal 10 MW thermal power, the thermal flux of the most favourable positions reach 1014 n∙cm2∙s1.

Two irradiation positions were preferentially used for the different experiments, one of them predominantly thermal, with an intermediate thermal flux (2.72 × 1013 n∙cm2∙s1) and other one characterised not only by a relatively high thermal flux (3.43 × 1013 n∙cm2∙s1) but also by a significant fast flux (1.04 × 1013 n∙cm2∙s1, as measured by the 54Fe(n,p)54Mn reaction). Although the fast flux was not fully characterized, some preliminary experiments tend to demonstrate that it is similar to an undisturbed 235U fission flux.

Spectrographically pure chemicals, whenever possible, or analytical grade reagents, were irradiated in masses smaller than 100 mg, sealed in quartz ampoules or wrapped in small aluminium envelopes, and placed in aluminium cans. Pure compounds having in their molecular composition both the precursor of the particles (lithium or hydrogen) and the target isotope, solutions (for proton-induced reactions) and intimate samples between precursor and target compounds were alternatively used. The irradiation times depended on the half-lives of the investigated radionuclides; calculations of the major activities that could be generated in each of the matrixes were also contemplated. These factors were considered, as well, in the definition of the decay times.

2.2. Radiochemical Separations

After irradiations, direct measurements were performed in many cases. When radiochemical separations became necessary, the purpose was to reach favourable conditions for identification and characterization of the product, rather than to accomplish a complete purification. The priority was, for all the experiments, to define the prospective possibilities of the use of the searched radionuclide.

2.3. Measurement and Data Treatment

Both the solutions resulting from the radiochemical separations or the irradiated powders were placed in measurement polyethylene vials of specific size and measured by high resolution gamma spectrometry in a system comprised of an EG&G Ortec HPGe detector, having 1.97 keV (FWHM) resolution for the 1332.5 keV 60Co peak, and associated electronics. The data treatment was carried out with the GammaVision Software [21] . For all peaks in a spectrum, the programme of this software analyses the information and generates as output data a list of background, net area, counting uncertainty, FWHM, and net count rate.

3. Radionuclides and Reactions

The list of radionuclides investigated and the corresponding reactions were:

3.1. Beryllium-7

This nuclide (t½ 53.6 d) is the only practicable radiotracer of beryllium; 7Be sources is often employed in high resolution gamma spectrometry for the determination of energy calibration curves, because the gamma transition associated with its electron capture decay (477.6 keV) corresponds to a region with scarce availability of adequate standards. As it was mentioned, the production of 7Be by secondary reactions in nuclear reactors was described by Roy et al. [13] . On the basis of the irradiation of several lithium, boron and 6Li enriched compounds for 5 d at a fast flux of 2.0 × 1011 n∙cm2∙s1, they concluded that none of the reactions studied led to the production of large amounts of 7Be, and that the 7Li(p,n)7Be reaction on LiHO offered the most promising possibilities. At the authors’ laboratory, different experiments destined to improve the yield of 7Be production were performed [22] . Samples of LiHO∙H2O powder and solutions of lithium carbonate were irradiated at a fast flux about 1.04 × 1013 n∙cm2∙s1; 7Be was easily identified by both direct measurement and after a radiochemical separation. Although 7Be activity per unit of lithium mass obtained by irradiation of lithium in solution is significantly higher than that induced in solid lithium hydroxide (ratio = 4.3) a production based on long irradiations could imply, as undesirable effect, the evolution of gaseous radiolysis products in the aqueous media. Therefore, the estimation of the prospective yield was calculated on the basis of the irradiation of powders.

For a routine of two irradiation cycles of five days, with two days elapsed in between, the activities obtained could reach 22.3 µg per gram of lithium (It should be taken into account that several tens of grams can be placed in an irradiation can).

3.2. Vanadium-48

Because of its relatively long half-life (15.97 d) and their gamma rays (983.5 keV and 1312.1 keV, among the most intense) 48V is the only practicable vanadium tracer; 49V, in spite of its favourable half-life (330 d) is of very restricted potentiality, since no gamma emissions are associated to its decay. All the remaining radioisotopes are very short-lived.

48V is, typically, a cyclotron-produced radionuclide. Since no direct reactions exist in nuclear reactors leading to 48V, the authors successfully attempted a novel method for its production by irradiation of Li2TiO3, through the sequence: 6Li(n,a)3H;46Ti(t,n)48V [23] [24] ; 47Ti(t,2n)48V should also be considered, but with a priori less probability, due to its less favourable Q. Prospectively, the yield for a five days irradiation cycle is 4 µCi per gram of lithium titanate.

In view of the promising results obtained by tritons as bombarding particles, the possibilities of the 48Ti(p,n)48V reaction with recoil protons were investigated. Samples of (NH4)2TiF6 were irradiated for 24 h and measured after 20 d. Although 48V was identified without the need of radiochemical separation, the yields were, somewhat surprisingly, considerably less that those obtained for tritons.

3.3. Manganese-54

The investigation was oriented to search for the possible existence of the 52Cr(t,n)54Mn reaction, taking into account that the precursor is the most abundant chromium isotope (q = 83.879%). Samples of K2CrO4, K2Cr2O7, 6Li2CO3, and mixtures: K2Cr2O7-6Li2CO3 (1.4:1 mass ratio) and K2CrO4-6Li2CO3 (1.8:1 mass ratio) were irradiated for 24 h, in a predominantly thermal position. The samples were directly measured without chemical separation, after the decay of the 51Cr formed by capture reaction (90 and 130 days).

Peaks at 834.8 keV were observed in the samples of pure K2CrO4 and K2Cr2O7, attributable to iron impurities, which led to the formation of 54Mn through (n,p) reaction on 54Fe, whereas 6Li2CO3 showed a clean spectrum. The presence of 54Mn was also confirmed in the K2Cr2O7-6Li2CO3 and K2CrO4-6Li2CO3 mixtures; since the activity per gram of the compounds was higher in the mixtures by a factor approximately equal to 5, the conclusion was that the (t,n) reaction had effectively taken place. However, the low yields obtained do not allow envisaging future applications.

3.4. Cobalt-56, Cobalt-57, Cobalt-58 and Cobalt-60

All these radionuclides are long-lived gamma emitters, well suited for their use as tracers (half-lives: 77.26 d; 271.79 d; 70.86 d and 5.27 y). Their gamma transitions differ significantly with respect to their energies, ranging from low-energies (57Co, 122.1 keV, 136.5 keV); medium energies (58Co, 810.8 keV); high energies (60Co, 1173.2 keV, 1332.5 kev); medium and high energies (56Co, 846.8 keV, 977.4 keV, 1037.8 keV, 1175.1 keV, 1238.3 keV, 1360.2 keV, 1771.3 keV, 1810.7 keV, 1963.7 keV, 2015.2 keV, 2034.8 keV, 2113.1 keV, 2212.9 keV, 2598.4 keV, 3009.6 keV, 3201.9 keV, 3228.8 keV, 3253.4 keV, 3273.0 keV, 3451.1 keV). Since all these energies have been precisely measured, they can be used as calibration standard; 56Co constitutes a special case, because it is the only long-lived radionuclide, in condition of being employed as calibration standard, which shows such variety of transitions with very high energies.

The production of both 56Co and 58Co by (t,n) reactions in a nuclear reactor has been already reported [18] , in the first case making use of 54Fe enriched targets. At the authors’ laboratory, an investigation was performed [25] with the twofold objective of a): to verify if all the potential reactions induced with tritons on iron targets, i.e. 54Fe(t,n)56Co, 56Fe(t,n)58Co and 58Fe(t,n)60Co, could be produced in samples of natural isotopic composition, and b): to characterise new (p,n) reactions, so far not studied, induced on iron by recoil protons; specifically, these reactions were: 56Fe(p,n)56Co, 57Fe(p,n)57Co and 58Fe(p,n)58Co.

Intimate mixtures: Fe(powder)-6Li2CO3 (1:2 mass ratio) and Fe(powder)-LiHO (1:3 mass ratio) were irradiated for 12 h and 24 h, respectively, in a position having 3.4×1013 n∙cm2∙s1 thermal flux and 1.0 × 1013 n∙cm2∙s1 fast flux. A simple method, based on the use of strong anionic resin in hydrochloric medium, was developed in order to separate the cobalt radioisotopes from the major activities generated on the iron matrix trough (n,g) and (n,p) reactions, i.e. 59Fe and 54Mn.

Traces of 60Co, probably due to cobalt impurities in the matrixes, were observed in the gamma spectra of the irradiated samples. The only significant activities detected correspond to 58Co and 56Co, in the mixtures irradiated with tritons and protons, respectively. These results seem to reflect the influence of the isotopic abundance of the precursors of the searched reactions: 54Fe, 5.8%; 56Fe, 91.72%; 57Fe, 2.2%; 58Fe, 0.28%. In both cases, the identified products were originated by 56Fe, the most abundant iron isotope. The calculated yields were 1 µCi for 58Co and 0.1 µCi for 56Co.

3.5. Zinc-65

The production of 65Zn with good yields via recoil protons in a nuclear reactor has been already reported [20] . The experiments at the authors’ laboratory dealt with the possibility of obtaining this radionuclide from the 63Cu(t,n)65Zn reaction.

Samples of 6Li2CO3, CuO and CuO-6Li2CO3 intimate mixture (1:0.7 mass ratio) were irradiated for 12 h in a predominantly thermal position and in a less thermalized one. Different measurements were accomplished with decays between 24 and 50 days. Since small impurities of zinc are frequently found in many analytical chemicals, and considering that 65Zn can be formed by neutron capture, its presence was checked both in the mixture that acted as target and also in the isolated compounds. The peak at 1115.5 keV was identified in the mixture and also in the pure copper oxide. The statistical differences between counting rates do not permit to conclude that 65Zn could have been produced by (t,n) reaction.

3.6. Arsenic-74

Only 73As and 74As, among arsenic radioisotopes, have half-lives sufficiently high for their use as tracers in studies of long duration (t½: 80.3 d and 17.77 d). Due to the fact that 74As is a gamma emitter of medium energies (595.8 keV and 634.8 keV) it is probably more suitable for measurement, in comparison with 73As, which emits a low-energy gamma radiation (53.4 keV).

The ways of 74As production in a nuclear reactor are the 75As(n,2n)74As and 74Se(n,p)74As reactions. The unavoidable low specific activity of the 74As formed form the first reaction, due to the presence of the stable isotope, precludes its use as tracer. The (n,p) reaction on 74Se allows radiochemical separation between 74As and its precursor, making it possible to obtain better specific activities; the product must be separated from very high levels of 75Se activity generated by neutron capture. The experiments carried out at the authors’ laboratory [26] [27] showed a ratio of activities: 75Se/74As equal to 5100 at the end of a 13 h irradiation in a less thermalized position of the RA-3 reactor. Since 75Se is longer-lived (t½: 119.64 d) than 74As, the situation worsens with the decay.

The authors have investigated the possibilities of producing 74As in a nuclear reactor via 72Ge(t,n)74As and 74Ge(p,n)74As. For the study of (t,n) reaction, several irradiations of samples of GeO2 and 6Li2CO3 pure compounds and intimate mixtures: GeO2-6Li2CO3 (mass ratios between 1:1 and 1:1.15), weighing less than 100 mg, were performed for 12 h in both a predominantly thermal position and another one, less thermalized. Identical irradiations of GeO2, NH4NO3 and mixtures: GeO2-NH4NO3 (1:3 mass ratio) were accomplished for the (p,n) reaction.

All the samples were repeatedly measured after decays between 7 and 45 days. Peaks at 595.8 keV and 634.8 keV, reasonably attributable to 74As, were identified in the mixtures: GeO2-6Li2CO3 and GeO2-NH4NO3. The calculated yields were very similar, about 4 µg per gram of germanium.

3.7. Ytrium-88

The interest in this radionuclide (t½: 106.6 d) rest on its use as standard for calibration in energy, due to the gamma emissions of 898.0 keV and, especially, 1836.1 keV. The production of 88Y via recoil protons on strontium oxide targets have been reported several years ago [15] . The authors intended another way of production, on the basis of the reaction: 86Sr(t,n)88Y.

Samples of SrCl2∙6H2O, anhydrous SrCl2, 6Li2CO3 and intimate mixtures SrCl2-6Li2CO3 (mass ratio 1:1.6) were irradiated for 12 h in two different positions of the reactor. Several measurements were performed after 24 - 50 days decay. Whereas 88Y was identified in the SrCl2∙6H2O samples, thus confirming the results of the literature [15] , it was not detected in any other samples.

4. General Discussion and Concluding Remarks

As far as the authors know, the observation of the reactions: 46Ti(t,n)48V, 48Ti(p,n)48V, 52Cr(t,n)54Mn, 56Fe(p,n)56Co, 72Ge(t,n)74As and 74Ge(p,n)74As in nuclear reactors had not been previously informed in the literature. Three of them lead to radionuclides (48V and 56Co) that cannot be produced by direct reactions in nuclear reactors, and the reactions leading to 74As can be reasonably options with respect to the (n,p) and (n,2n) reactions, taking into account the drawbacks already discussed in connection with these modes of production. On the other hand, although the demonstration of the triton induced production of 54Mn contributes to enhance the knowledge about these reactions, no advantages were observed for its practical application, since this radionuclide is easily obtained with good yields by the 54Fe(n,p)54Mn reaction. Similar consideration can be formulated with respect to the production of 58Co by (t,n) reaction on 56Fe, in comparison with the reaction: 58Ni(n,p)58Co.

Negative results were obtained in connection with other reactions investigated on iron, namely 54Fe(t,n)56Co, 58Fe(t,n)60Co, 57Fe(p,n)57Co and 58Fe(p,n)58Co, possibly due to the low isotopic abundances of the precursors.

In spite of the good yields reported for the production of 65Zn through recoil protons [20] no significant results were obtained using tritons as the bombarding particles; the hypothetical activities produced are indistinguishable from those induced by neutron capture on the zinc impurities of the copper compound, which reveals a very low yield.

As it was mentioned above, the search for the 86Sr(t,n)88Y reaction failed; this fact leads to the question if the upper limit for the (t,n) reactions in nuclear reactors has been already reached, considering the low energy of the tritons. It is worthwhile mentioning that the reaction: 72Ge(t,n)74As, reported in the present work, refers to a precursor having the highest atomic number so far known. Instead, the reasonably expectation is that new radionuclides, with higher Z, can be obtained through reactions induced by recoil protons, and more work will be performed along these lines.

The results allow concluding that some radionuclides can be produced, at laboratory scale, with reasonably good yields; this is the case, for example, of 7Be and 48V. The yields for 56Co and 74As could improve by irradiation of the samples in positions of highest fluxes and with more favourable ratios of the precursor particle compounds to the target compounds. In connection with the proton-induced reactions, the hydrogenous compounds, because of their variety, open a rich field to future studies.

Conflicts of Interest

The authors declare no conflicts of interest.


[1] Knapp Jr., F.F. (2001) Future Prospects for Medical Radionuclide Production in the High Flux Isotope Reactor (HFIR) at the Oak Ridge National Laboratory (ORNL). Annals of Nuclear Medicine Science, 14, 109-118.
[2] Roy, J.C. and Hawton, J.J. (1961) The B10(α,n)N13 and B10(t,2n)C11 Reactions in a Nuclear Reactor. Canadian Journal of Physics, 39, 1528-1534. http://dx.doi.org/10.1139/p61-183
[3] Sher, R. and Floyd, J.J. (1956) Triton-Induced Reactions. Physical Review, 102, 242. http://dx.doi.org/10.1103/PhysRev.102.242
[4] Knight, J.D., Novey, T.B., Cannon, C.V. and Turkevich, A. (1949) Activities from Tritium Bombardment in Neutron Irradiation of Lithium Salts: (t,n) Reaction on Oxygen and Sulfur. Radiochemical Studies, The Fission Products, Book 3, McGraw-Hill, New York, 1916-1923.
[5] Iwersen, E., Koski, W.S. and Rasetti, F. (1953) Triton-Induced Activities in Magnesium and Aluminum. Physical Review, 91, 1229-1231. http://dx.doi.org/10.1103/PhysRev.91.1229
[6] Cook, L.G. and Shafer, K.D. (1954) The Production of 22Na by (3H,n) Reaction in a Nuclear Reactor. Canadian Journal of Chemistry, 32, 94-97. http://dx.doi.org/10.1139/v54-016
[7] Robson, J. and Sorby, P.J. (1974) The Preparation of Mg-28 by the Irradiation in HIFAR of Mixtures Containing Compounds of Li-6 and Mg-26. Australian Atomic Energy Commission Report AAEC-E310. Australian Atomic Energy Commission, Lucas Heights, Sidney.
[8] Wessels, B.W., Yusoff, W.R. and Ercegovic, D. (1985) Reactor Production of Anhydrous 18F Ion. Journal of Radio-analytical and Nuclear Chemistry, Articles, 92, 27-35.
[9] Cohen, I.M., Magnavacca, C. and Baró, G.B. (1987) Determination of Lithium by Reactor Activation Analysis Using the Reaction Chain: 6Li(n,t)4He; 32S(t,n)34mCl. Journal of Radioanalytical Chemistry, 112, 387-394. http://dx.doi.org/10.1007/BF02132371
[10] Absattarova, A., Kist, A.A. and Mukhammedov, S. (1988) Triton Activation in Oxygen Determination. Soviet Atomic Energy, 65, 934-936 (Translated from Atomnaya énergiya, 65, 361-362).
[11] de Goeij, J.J.M. (2003) Triton Activation Analysis of Oxygen in a Nuclear Reactor. 6th International Conference on Methods and Applications of Radioanalytical Chemistry (MARC VI), Kailua-Kona, 7-11 April 2003, 136.
[12] Stewart, L. (1979) Hydrogen Scattering Cross Section, H(n,n)H. University of California, Los Alamos Scientific Laboratory Report LA-7899-MS, Informal Report. Los Alamos Scientific Laboratory, New Mexico, 1-15.
[13] Roy, J.C., Hawton, J.J. and Bresesti, M. (1960) On the Production of Be7 in the NRX Reactor by the B10(p,α)Be7, Li7(p,n)Be7, and Li6(d,n)Be7 Reactions. Canadian Journal of Physics, 38, 1428-1435. http://dx.doi.org/10.1139/p60-148
[14] Glickstein, S.S. and Winter, R.G. (1960) Nuclear Reactions from Recoil Protons in a Reactor. Nuclear Instruments and Methods, 9, 226-228. http://dx.doi.org/10.1016/0029-554X(60)90105-1
[15] Levin, V.I., Malinin, A.B., Novoselov, V.S., Petrina, R.V. and Zav’yalova, L.V. (1968) Radioactive Isotopes from Recoil Protons in a Reactor. Soviet Atomic Energy, 24, 323-326 (Translated from Atomnaya énergiya, 24, 265-267).
[16] Hunt, L.H. and Miller, W.W. (1965) Activation Analysis for Oxygen-18 Isotope Abundance Utilizing Recoil Protons. Analytical Chemistry, 37, 1269-1272. http://dx.doi.org/10.1021/ac60229a025
[17] Takahashi, M. and Iijima, S. (1989) Activation of Structural Materials Due to Recoil Protons in Light Water Reactor. Journal of Nuclear Science and Technology, 26, 874-880.
[18] Kiefer, R.L. and Hillman, M. (1969) Relative Yields of 58gCo, 58mCo, and 56Co Produced by Low-Energy Tritons. Journal of Inorganic and Nuclear Chemistry, 31, 915-917.
[19] Mukhammedov, S., Khaidarov, A. and Barsukova, E.G. (2008) 7Be Yield Produced in Secondary Reactions in a Nuclear Reactor. Atomic Energy, 104, 82-84. http://dx.doi.org/10.1007/s10512-008-0012-z
[20] Mukhammedov, S., Khaidarov, A. and Akramov, F. (2012) Nuclear Reactions Induced by Secondary Protons Formed under the Influence of Fast Neutrons. International Conference “Nuclear Science and its Application”, Samarkand, 25-28 September 2012, 338-339.
[21] Ortec (2003) GammaVision-32 Software User’s Manual. 6th Edition, Printed in USA.
[22] Fornaciari Iljadica, M.C. and Cohen, I.M. (2008) The Production of 7Be in a Nuclear Reactor. Book of Abstracts, NRC7—Seventh International Conference on Nuclear and Radiochemistry, Budapest, 24-29 August 2008, 54.
[23] Siri, S. and Cohen, I.M. (2008) The Triton-Induced Production of 48V in a Nuclear Reactor. Book of Abstracts, NRC7— 7th International Conference on Nuclear and Radiochemistry, Budapest, 24-29 August 2008, 235.
[24] Siri, S. and Cohen, I.M. (2009) Production of 48V in a Nuclear Reactor via Secondary Tritons. Radiochimica Acta, 97, 543-546. http://dx.doi.org/10.1524/ract.2009.1676
[25] Fornaciari Iljadica, M.C., Siri, S., Alí Santoro, M.C. and Cohen, I.M. (2012) Las Reacciones Secundarias Inducidas sobre Hierro por Tritones y Protones de Retroceso en Reactores Nucleares. Abstracts, XXIX Argentine Conference of Chemistry, “Centenary of the Argentine Chemical Association”, Mar del Plata, 23. http://aqa.org.ar/pdf99/cd/Qca%20Inorganica,%20Bio,%20radio.nucl/23.pdf
[26] Siri, S. and Cohen, I.M. Unpublished Results.
[27] Siri, S., Fornaciari Iljadica, M.C. and Cohen, I.M. (2012) La Producción de 74As en Reactores Nucleares. Abstracts, XXIX Argentine Conference of Chemistry, “Centenary of the Argentine Chemical Association”, Mar del Plata, 20.

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