Reactor Production of Thorium-229
Rose A. Boll1,2, Marc Garland1,3, and Saed Mirzadeh1
1
Nuclear Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, TN, 37831-6229
2
Department of Chemistry, University of Tennessee, Knoxville, TN
3
Department of Mechanical Engineering, University of South Carolina, Columbia, SC
The rapidly increasing interest in the clinical
applications of bismuth-213 [1] coupled with the
limited availability of thorium-229 necessitate
investigation of alternative production routes for 229Th,
225
Ra, and 225Ac. Currently, 233U is the only viable
source for high-purity 229Th; however, the anticipated
growth in demand for 225Ac may soon exceed the
levels of 229Th present in the aged 233U stockpile. It is
estimated that only ~38 g or ~8 Ci of 229Th can be
extracted from entire 233U stockpile, which is only ~80
times the current ORNL 229Th stock. Considering the
rather low annual production rate of 229Th from 233U
(0.92 mCi/kg) and increasing difficulties associated
with the 233U safeguard, routine processing of 233U is
presently unfeasible. The alternative routes for the
production of 229Th, 225Ra, and 225Ac include both
reactor and accelerator approaches. Th-229 can be
produced from neutron transmutation of 226Ra and
228
Ra targets; see Fig. 1 [2].
prediction (Table 1, Column 5, and Fig. 2), whereas,
the experimental to the theoretical yields for 228Th and
227
Ac were 1.4 and 1.0, respectively. The theoretical
calculations, however, are hampered by the lack of
neutron capture cross-section data of the intermediate
radionuclides, 227Ra and 228Ac. Based on the results
from our measurement, it would be possible to
produce ~300 mCi of 229Th by irradiating one gram of
226
Ra at the Target Position of HFIR for one year.
Recycling the 226Ra target will theoretically result in
an increase in the yield of 229Th due to the formation
of 228Ra. Theoretical calculations were performed
using code LAURA [3].
ACKNOWLEDGMENTS
Oak Ridge National Laboratory is managed by
UT-Battelle for the U.S. DOE under Contract
DE-AC05-00OR22725.
The results of a single irradiation at the ORNL
High Flux Isotope Reactor (HFIR), Peripheral Target
Position (PTP) Facility is shown in Table 1. In this
experiment, the target was 43.5 µg of 226Ra as nitrate
and was irradiated for one reactor cycle (~24 d) at a
thermal neutron flux of 1x1015 n.s-1.cm-2, with a
thermal to epithermal ratio of ~20. As shown, the yield
of 229Th is 31 µCi per mg of 226Ra per reactor cycle. As
expected, at the end of bombardment, the activity of
228
Th and 227Ac contaminants, which are co-produced
with 229Th, are 990 and 56 times larger, respectively
(Table 1, Column 6). Nevertheless, even from a
mixture of 228Th and 229Th, high-purity 225Ac can be
obtained from the mixture by initially extracting Ra
from Th and then extracting 225Ac from the Ra mixture
(224Ra, the daughter of 228Th, α-decays to 220Rn with
no ß–decay to 224Ac). Under the above condition, the
229
Th experimental yield is ~50 times larger than
REFERENCES
1. Jurcic, J.G., Larson, S.M., Sgouros, G., McDevitt, M.R.,
Finn, R.D., Divgi, C.R., Ballangrud, A.M., Hamacher,
K.A., Ma, D., Humm, J.L., Brechbiel, M.W., Molinet,
R., Scheinberg, D.A., “Targeted alpha-particle
immunotherapy for myeloid leukemia,” Blood 100(4),
1233-1239 (2002).
2. Mirzadeh, S., “Generator-produced alpha-emitters,” in
Proceedings of CIRMS Medical Subcommittee Workshop
on Radionuclides Used in Bone Pain Palliation Therapy,
NIST, Gaithersburg, Washington September 27, 1996,
Appl. Rad. Isot. 49(4), 345-349 (1998).
3. Mirzadeh, S., Walsh, P., “Numerical evaluation of the
production of radionuclides in a nuclear reactor -- Parts I
& II,” Appl. Rad. Isot. 49(4), 379-382 and 383-395
(1997).
CP769, International Conference on Nuclear Data for Science and Technology,
edited by R. C. Haight, M. B. Chadwick, T. Kawano, and P. Talou
© 2005 American Institute of Physics 0-7354-0254-X/05/$22.50
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FIGURE 1. Reactor production of 229Th via 226Ra[3n,γ](2β-) reactions.
TABLE 1. Experimental yields of
Position of HFIR1.
Half-Life
(y)
Radionuclide
Th-229
Th-228
Ac-227
Ra-228
Pa-233
Zr-95
Cs-137
Ce-141
Ce144
1
2
7,340
1.913
21.77
5.75
0.074
0.175
30.1
0.089
0.68
229
Th,
228
Th, and
227
Ac from neutron irradiation of a
226
Ra target at the Peripheral Target
Experimental Ratio of
Others/229Th
Activity
Mass
1.0
1.0
990
0.26
56
0.16
2.5
1.9x10-3
6.3
6.2x10-5
0.37
9.1x10-4
58
4.3x10-4
19
1.3x10-3
Yield at EOB (Ci/g)
Experimental
0.031
30.7
1.74
0.077
Detected2
0.20
0.012
1.79
0.61
Theoretical
6.8x10-4
21
1.7
~3x10-4
-
Exp/Theo
46
1.4
1.0
~257
-
Target mass: 43.5 µg., Irradiation period: 24 d, Irradiation position: HFIR-PTP, Neutron flux: 1x1015 n.s-1.cm-2.
Source unknown, possibly presence of 232Th impurity in the Ra target.
103
228
Activity (mCi/mg of
226
Ra)
102
101
10
Th
227
Ac
0
1 0 -1
229
10
Th
-2
1 0 -3
1 0 -4
1 0 -5
0
25
50
75
100
Irra d ia tio n T im e (d )
FIGURE 2. Yields of 228Th, 227Ac and 229Th as a function of irradiation time. Solid curves are theoretical and points are
experimental values. Neutron flux: 1x1015 n.s-1 cm-2.
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