14 Search Results

The newest radioisotope for brachytherapy treatment of prostate cancer is ¹³¹Cs (t_1/2 = 9.69 d, 100% EC). Generated via electron capture decay of ¹³¹Ba (t_1/2 = 11.6 d, 100% EC), ¹³¹Cs has been used in brachytherapy for prostate cancer since 2004. The ¹³¹Ba parent is produced through neutron capture of enriched ¹³⁰Ba in a nuclear reactor. For large-scale production of ¹³¹Ba, an accurate knowledge of production and burnup cross sections of ¹³¹Ba are essential. Here, we report two group cross sections (thermal and resonance integrals) for ¹³⁰Ba and ¹³¹Ba and a new measure of the half-life of ¹³¹Ba. Targets consistingmore » of milligram quantities of enriched 130Ba (~35%) were irradiated in Oak Ridge National Laboratory's High Flux Isotope Reactor at thermal and resonance neutron fluxes of (1.9–2.1) × 10¹⁵ and (5.8–7.0) × 10¹³ neutrons·cm^-2 s^-1, respectively, for durations ranging from 3 to 26 days. In addition, cadmium covered samples of ¹³⁰Ba were irradiated for 1 hour at 12.6% full reactor power (10.7 MW). The yield of ¹³¹Ba approaches a saturation value of ~60 GBq (~1.6 Ci) per mg of ¹³⁰Ba for 20 days irradiation at a thermal neutron flux of 1.8 × 10¹⁵ n·s^-1·cm^-2, with a thermal/epithermal ratio of ~30. Under the above experimental conditions, the two group cross sections of ¹³⁰Ba are 6.9 ± 0.5 b (thermal, σ⁰) and 173 ± 7 b (resonance, I⁰). These values represent the sum of cross sections to metastable and ground states of ¹³¹Ba. For ¹³¹Ba, the empirically measured thermal cross section is 200 ± 50 b assuming an I⁰/σ⁰ of 10. This cross section is reported for the first time. Further, the half-life of ¹³¹Ba was remeasured to be 11.657 ± 0.008 d. Lastly, this study also resulted in the co-production of ¹³³Ba (t_1/2 = 10.52 y, 100% EC). The experimental yield of ¹³³Ba is ~370 MBq (~10 mCi) per mg of ¹³²Ba (thin target) for one cycle irradiation in the High Flux Isotope Reactor, and measured two-group ¹³²Ba cross sections are 7.2 ± 0.2 b and 39.9 ± 1.3 b. These values also represent the sum of cross sections to metastable and ground states of ¹³³Ba.« less

Abstract Unwanted targeting of healthy organs caused by the relocation of radionuclides from the target site has been one of the limiting factors in the widespread application of targeted alpha therapy in patient regimens. GdVO ₄ nanoparticles (NPs) were developed as platforms to encapsulate α -emitting radionuclides ²²³ Ra, ²²⁵ Ac, and ²²⁷ Th, and retain their decay daughters at the target site. Polycrystalline GdVO ₄ NPs with different morphologies and a zircon-type tetragonal crystal structure were obtained by precipitation of GdCl ₃ and Na ₃ VO ₄ in aqueous media at room temperature. The ability of GdVO ₄ crystalsmore » to host multivalent ions was initially assessed using La, Cs, Bi, Ba, and Pb as surrogates of the radionuclides under investigation. A decrease in Ba encapsulation was obtained after increasing the concentration of surrogate ions, whereas the encapsulation of La cations in GdVO ₄ NPs was quantitative (∼100%). Retention of radionuclides was assessed in vitro by dialyzing the radioactive GdVO ₄ NPs against deionized water. While ²²⁷ Th was quantitatively encapsulated (100%), a partial encapsulation of ²²³ Ra (∼75%) and ²²⁵ Ac (>60%) was observed in GdVO ₄ NPs. The maximum leakage of ²²¹ Fr (1st decay daughter of ²²⁵ Ac) was 55.4 ± 3.6%, whereas for ²²³ Ra (1st decay daughter of ²²⁷ Th) the maximum leakage was 73.0 ± 4.0%. These results show the potential of GdVO ₄ NPs as platforms of α -emitting radionuclides for their application in targeted alpha therapy.« less

Targeted alpha therapy (TAT) offers great promise for treating recalcitrant tumors and micrometastatic cancers. One drawback of TAT is the potential damage to normal tissues and organs due to the relocation of decay daughters from the treatment site. As such, the present study evaluates La(²²⁷Th)PO₄ core (C) and core +2 shells (C2S) nanoparticles (NPs) as a delivery platform of ²²⁷Th to minimize systemic distribution of decay daughters, ²²³Ra and ²¹¹Pb. In vitro retention of decay daughters within La(²²⁷Th)PO₄ C NPs was influenced by the concentration of reagents used during synthesis, in which the leakage of ²²³Ra was between 0.4 ±more » 0.2% and 20.3 ± 1.1% in deionized water. Deposition of two nonradioactive LaPO₄ shells onto La(²²⁷Th)PO₄ C NPs increased the retention of decay daughters to >99.75%. The toxicity of the nonradioactive LaPO₄ C and C2S NP delivery platforms was examined in a mammalian breast cancer cell line, BT-474. No significant decrease in cell viability was observed for a monolayer of BT-474 cells for NP concentrations below 233.9 μg mL^–1, however cell viability decreased below 60% when BT-474 spheroids were incubated with either LaPO₄ C or C2S NPs at concentrations exceeding 29.2 μg mL^–1. La(²²⁷Th)PO₄ C2S NPs exhibit a high encapsulation and in vitro retention of radionuclides with limited contribution to cellular cytotoxicity for TAT applications.« less

Gadolinium vanadate (GdVO₄) core and core +2 shell nanocrystals (NCs) were evaluated for in vitro retention of ²²⁵Ac, ²²⁷Th, and their first decay daughters, ²²¹Fr and ²²³Ra, respectively. GdVO₄ NCs with a tetragonal crystal system (zircon-type) and spherical morphology were obtained by precipitation of GdCl₃ and Na₃VO₄ using sodium citrate as a complexing agent. The growth of two nonradioactive GdVO₄ shells on both Gd(²²⁵Ac)VO₄ and Gd(²²⁷Th)VO₄ core NCs was demonstrated by an increase of 0.7 nm and 2 nm in the crystallite size, respectively. The maximum leakage of ²²⁵Ac was 15% and 2.4% from core and core + 2 shells,more » whereas the leakage of ²²⁷Th was 3% and 1.5%, respectively. The presence of two nonradioactive GdVO₄ shells increased the retention of ²²¹Fr and ²²³Ra by 20% and 15% with respect to core NCs. Furthermore, a longitudinal proton relaxivity, r₁ = 0.9289 s^–1 mM^–1, confirmed their potential application as contrast agents for magnetic resonance imaging. In summary, GdVO₄ NCs show promising capabilities as radionuclide carriers with partial retention of decay daughters and as contrast agents for theranostic applications.« less

Separation of ²²⁵Ra (t_1/2 = 15 d) from its daughter isotope ²²⁵Ac (t_1/2 = 10 d) is necessary to obtain pure ²²⁵Ac for cancer alpha-therapy. In this study, microscale separation of ²²⁵Ra from its daughter ²²⁵Ac using BioRad AG50X4 cation exchange resin was achieved with good reproducibility across microdevices, and ≥90% purity was achieved for ²²⁵Ac, which is comparable to conventional chromatography. These results indicate the potential for greater use of microfluidics for biomedical radiochemistry. The modularity of the system and its compatibility with different resins allows for quick and easy adaptation to the various needs of a separation campaign.

Tungsten-188 (t_1/2 = 69.4 d) is routinely produced by double neutron capture using highly enriched ¹⁸⁶W target, ¹⁸⁶W(n,γ)¹⁸⁷W(n,γ)¹⁸⁸W reaction, at the ORNL 85 MWt High Flux Isotope Reactor. Here, while the thermal neutron cross section for the first reaction, ¹⁸⁶W(n,γ)¹⁸⁷W, is well known, the single reported 64 b cross-section for the second reaction, ¹⁸⁷W(n,γ)¹⁸⁸W, cannot be validated by experimental results that yield lower than expected activities of ¹⁸⁸W. In this study, we report a new value for the thermal neutron capture cross section of ¹⁸⁷W. After confirming the neutron capture cross section of ¹⁸⁶W (σ⁰ = 37.8 ± 1.8 bmore » for thermal and I⁰ = 476 ± 25 b for resonance integrals with σ⁰/I⁰ = 12.6 ± 0.4) in two short irradiations, longer irradiations (1–10 d) were performed to obtain a value of 6.5 ± 0.8 b for the σ⁰ of ¹⁸⁷W, which is lower than the adopted value by a factor of 10. Due to the short half-life of ¹⁸⁷W (t_1/2 = 23.7 d), the σ⁰ for ¹⁸⁷W was obtained empirically by comparing the ¹⁸⁸W experimental yields with the theoretical yields generated by code IsoChain and varying the ¹⁸⁷W cross section while keeping all other parameters constant.« less

Gadolinium vanadate nanoparticles (NPs) doped with europium, in concentrations between 5–40%, were synthesized via an aqueous route to prove their multimodal imaging functionalities and their performance as radionuclide carriers for targeted alpha therapy. Core–shell Gd_0.8Eu_0.2VO₄ NPs were doped with the α-emitting actinium-225 to assess the in vitro retention of ²²⁵Ac and its decay daughters; francium-221 and bismuth-213. Gd_0.8Eu_0.2VO₄ core–shell NPs were obtained using a precipitation synthesis route having a tetragonal system, a spherical morphology, and a uniform particle size distribution. Gd_0.8Eu_0.2VO₄ core–shell NPs displayed the characteristic intense emission at 618 nm (red) and paramagnetic behavior of Eu and Gd cations,more » respectively. Partial retention of radionuclides was obtained with Gd_0.8Eu_0.2VO₄ core NPs, while deposition of two nonradioactive Gd_0.8Eu_0.2VO₄ shells significantly decreased the leakage of both ²²⁵Ac and ²²¹Fr. As a result, the luminescence and magnetic functionalities as well as radionuclide retention capabilities of Gd_0.8Eu_0.2VO₄ core–shell NPs demonstrate their potential for biomedical applications.« less

In this paper, we describe the ¹⁴⁷Pm production yields and level of impurities from several targets that consisted of milligram quantities of highly enriched ¹⁴⁶Nd oxide irradiated at the High Flux Isotope Reactor (HFIR) at Oak Ridge National Laboratory for durations ranging from 24 to180 h. A comparison between theoretical and experimental data are also presented, and attempts were made to empirically evaluate the neutron capture cross-sections of 41.3-d ^148mPm and 5.4-d ^148gPm. For a one-cycle irradiation (~24 days), ¹⁴⁷Pm yield reaches a maximum value of 101.8 MBq/mg (2.75 mCi/mg) at 60 days after the end of bombardment. Because ofmore » large neutron capture cross-sections of ¹⁴⁷Pm, the yield of ¹⁴⁷Pm does not significantly increase with longer irradiation. Our estimates of the thermal neutron capture cross-section and resonance integral for ¹⁴⁶Nd at 1.48 ± 0.05 b and 2.56 ± 0.25 b, respectively, were consistent with the reported values. The effective neutron capture cross-section of ¹⁴⁷Pm to ^148mPm was 53.3 ± 2.7 b - a factor of 2 lower than the 98.7 ± 6.5 b calculated from reported cross-sections. The measured σ_eff to the ground state (5.37-d ^148gPm) was 82.0 ± 4.1 b; ~34 % lower than the value of 139 ± 0 b calculated from reported cross-sections. In this work, we also describe the development of a chemical process based on extraction and ion-exchange chromatography for separation of ¹⁴⁷Pm from milligram quantities of ¹⁴⁶Nd and other impurities. Sequential separation of Pm from the Nd target and from other radioisotopic impurities (¹⁵³Gd and ^154&155Eu, ¹⁹²Ir, and ⁶⁰Co) was achieved using a LN extraction resin in HCl media followed by further purification of Pm from ⁶⁰Co and ¹⁹²Ir using a low cross-linking cation exchange resin. Based on these data, we estimated that two rounds of purification under our experimental conditions can provide a mass separation factor of > 104 between Pm and Nd. Our data indicate that curie quantities of ¹⁴⁷Pm with suitable chemical and radioisotopic purity for applications in beta voltaic batteries can be produced by irradiating gram quantities of highly enriched ¹⁴⁶Nd in the flux trap of HFIR for one cycle.« less

As a part of a general program to evaluate production routes for ²²⁹Th, we studied production of ²²⁹Th via proton-induced reactions on ²³²Th targets bombarded with low-energy protons, E_p ≤ 40MeV. The reported excitation functions include those for proton-induced reactions on natural thorium yielding to ^{228,229,230&232}Pa isotopes; ²³²Th(p,xn) reactions, where x=1, 3, 4, and 5, at proton energy ranges of 12–40 MeV. Although the data for ²³²Th(p,n)²²⁸Pa, ²³²Th(p,3n)²³⁰Pa, and ²³²Th(p,5n)²³²Pa reactions were deduced by direct analysis of the thorium foils after irradiation, the data for ²³²Th(p,4n)²²⁹Pa were obtained by radiochemical techniques. The half-life of ²²⁹Pa was evaluated and determined tomore » be 1.55 ± 0.01 d. Further, the α-branching ratio, α/(α + EC) of ²²⁹Pa was evaluated to be 0.53 ± 0.10% by allowing ²²⁹Pa to decay for ~7d, then chemically extracting and quantifying the ²²⁵Ac (t_1/2 = 10.0±0.1d) from ²²⁹Pa samples. In addition, we report the effective production cross section of ²²⁹Th in a thick ²³²Th target in the proton energy range of 23–33 MeV. The peak of the excitation function for the ²³²Th(p,4n)²²⁹Pa reaction occurs at 162 ± 14 mb and E_p=29.7±0.5MeV. This is only slightly larger than the effective cross section for the ²³²Th(p,x)²²⁹Th reaction (obtained from a thick target experiment). This data indicates that the ²³²Th(p,4n)²²⁹Pa reaction is the major reaction pathway for the cumulative ²³²Th(p,x)²²⁹Th reaction cross section in this energy range. The measured cross sections were compared with theoretical cross sections using the simulation codes Particle and Heavy Ion Transport code System (PHITS) and Monte Carlo Neutral Particle 6 (MCNP6). Furthermore, at proton energy ranges of 12–33 MeV, the cumulative excitation function predicted by PHITS for the reactions leading to ²²⁹Th was in close agreement with the experimental function, whereas the function predicted by MCNP6 was a factor of two higher at the peak of the excitation function.« less