Distribution of naturally occurring radionuclides activity concentration in East Malaysian marine sediment

Studies of naturally occurring radioactive materials (NORM) distribution of ²²⁶Ra, ²²⁸Ra and ⁴⁰K in East Malaysia were carried out as part of a marine coastal environment project. The results of measurements will serve as baseline data and background reference level for Malaysia coastlines. Sediments from 21 coastal locations and 10 near shore locations were collected for analyses. The samples were dried, finely ground, sealed in a container and stored for a minimum of 30 days to establish secular equilibrium between ²²⁶Ra and ²²⁸Ra and their respective radioactive progenies. They were counted using a high-purity germanium (HPGe) spectrometer covering the respective progeny energy peak. For ⁴⁰K, the presence of this was measured directly via its 1460 keV energy peak. The concentration of ²²⁶Ra, ²²⁸Ra and ⁴⁰K in samples obtained from coastal Sarawak ranged between 23 and 41 (mean 30±2) Bq/kg, 27 and 45 (mean 39±4) Bq/kg and 142 and 680 (mean 462±59) Bq/kg, respectively. Meanwhile, the concentration of ²²⁶Ra, ²²⁸Ra and ⁴⁰K for samples obtained from coastal Sabah ranged between 16 and 30 (mean 23±2) Bq/kg, 23 and 45 (mean 35±4) Bq/kg and 402 and 842 (mean 577±75) Bq/kg, respectively. For the Sarawak near shore stations, the concentration of ²²⁶Ra, ²²⁸Ra and ⁴⁰K ranged between 11 and 36 (mean 22±2) Bq/kg, 21 and 65 (mean 39±5) Bq/kg and 149 and 517 (mean 309±41) Bq/kg, respectively. Meanwhile, the concentration of ²²⁶Ra, ²²⁸Ra and ⁴⁰K for samples obtained from Sabah ranged between 9 and 31 (mean 14±2) Bq/kg, 10 and 48 (mean 21±3) Bq/kg and 140 and 580 (mean 269±36) Bq/kg, respectively. The calculated external hazard values of between 0.17 and 0.33 (less than unity) showed that there is little risk of external hazard to the workers handling the sediments.     

Natural radioactivity in underground water from the Outer Carpathians in Poland with the use of nuclear spectrometry techniques

The investigations of natural radioactivity in underground mineral water and spring water in health resorts in the Outer Carpathians were performed. Samples from 40 water springs were collected 3–4 times over a period of 10 years (1997–2007). In order to obtain necessary data, two different nuclear spectrometry techniques were applied: WinSpectral α?β 1414 liquid scintillation counter from Wallac and α-spectrometer 7401 VR from Canberra–Packard, USA with the silicon surface barrier detector. The activity concentrations of ²²²Rn in the investigated samples varied from below 1 to 50 Bq/l. For radium isotopes the concentrations were in a range from below 10 to 490 mBq/l for ²²⁶Ra and from 29 to 397 mBq/l for ²²⁸Ra. The highest concentrations for both radium isotopes were obtained for medicinal water Zuber III from Krynica spa. The activity concentrations for uranium isotopes varied from below 0.5 to 16 mBq/l for ²³⁸U and from below 0.5 to 162 mBq/l for ²³⁴U with the highest values obtained for water Zuber IV. The highest annual effective dose arising from mainly radium isotopes was obtained for Zuber III water and was equal to 75 μSv/yr. Additionally, the annual effective doses due to ²²²Rn consumed with water were also estimated. The isotopic ratios between isotopes originating from the same decay chain (²³⁴U/²³⁸U, ²²⁶Ra/²³⁸U) and from different radioactive decay chains (²²⁶Ra/²²⁸Ra) were determined. The correlations between different isotopes were presented.     

Radium-226 concentration in spring water sampled in high radon regions

Water ²²⁶Ra concentration in springs was measured in regions with high indoor radon: Ural, North Caucasus (Russia), Niska Banja (Serbia), Piestany (Slovakia), and Issyk-Kul (Kyrgyzstan). This paper presents the results for ²²⁶Ra concentration above 0.03 Bq l^–1. Radium in water could indicate indoor radon problem in the region and water investigation is useful at the initial stage of radon survey. Even low ²²⁶Ra concentration in water (0.1–0.6 Bq l^–1) caused high ²²⁶Ra activity in travertine (up to 1500 Bq kg^?1), which resulted in indoor radon concentration above 2000 Bq m^?3 (Niska Banja).     

A new low-level γ-ray spectrometry system for environmental radioactivity at the underground laboratory Felsenkeller

A low-level γ-ray spectrometry system, based on an HPGe-detector with 92% relative efficiency recently installed in the underground laboratory Felsenkeller at 110 m water equivalent (w.e.) depth, is described. The integral background count rate normalised to the Ge-crystal mass in the energy range from 40 keV until 2.7 MeV of 0.034 s⁻¹ kg⁻¹ has been achieved by careful material selection of the detector construction material, a graded shielding construction and effective radon suppression. The detector is highly suitable for the effective surveillance of water for human consumption with decision thresholds for ²²⁶Ra and ²²⁸Ra in the order of some mBq L⁻¹.     

Low-level γ-ray spectrometry at the underground laboratory Garching

Two low-background setups for material screening based on HPGe detectors were built in the Garching Underground Laboratory with an overburden of ~10 m.w.e. They include several layers of passive shielding as well as an active muon veto. The first setup (GEM) comprises a 150% efficiency HPGe detector which can optionally be surrounded by a NaI(Tl) scintillation detector that serves as anti-Compton veto. The second setup (LoAx) consists of two smaller HPGe detectors which are arranged face-to-face to cover a larger solid angle around the sample and to allow coincidence measurements.For a 5.6 kg piece of copper after 11 days of measurement we have reached a sensitivity for ²²⁶Ra and ²²⁸Ra/²²⁸Th of ~5 mBq kg⁻¹ with the GEM setup. In the LoAx setup we have achieved limits of less than 100 mBq kg⁻¹ for ²³⁴Th and ²¹⁰Pb with a 156 g sample of PPO wavelength shifter after 18 days of measurement.     

Assessment of natural radioactivity levels and radiation hazards due to cement industry

The cement industry is considered as one of the basic industries that plays an important role in the national economy of developing countries. Activity concentrations of ²²⁶Ra, ²³²Th and ⁴⁰K in Assiut cement and other local cement types from different Egyptian factories has been measured by using γ-ray spectrometry. From the measured γ-ray spectra, specific activities were determined. The measured activity concentrations for these natural radionuclides were compared with the reported data for other countries. The average values obtained for ²²⁶Ra, ²³²Th and ⁴⁰K activity concentration in different types of cement are lower than the corresponding global values reported in UNSCEAR publications. The obtained results show that the averages of radiation hazard parameters for Assiut cement factory are lower than the acceptable level of 370 Bq kg^?1 for radium equivalent Ra_eq, 1 for level index Iγr, the external hazard index Hex ≤1 and 59 (nGy h^?1) for absorbed dose rate. The manufacturing operation reduces the radiation hazard parameters. Cement does not pose a significant radiological hazard when used for construction of buildings.     

Radium content in ground water from a granitic batholith of the metamorphic basement,eastern São Paulo State,Brazil

The radon emanation method was applied to measure the activity of ²²⁶Ra, dissolved and associated with suspended solids, in the ground waters from two wells drilled in the Morungaba Batholith fractured granites, intruded in the metamorphic basement, eastern border of the Paraná basin in São Paulo State, Brazil. The water samples were collected from March 2003,to April 2004, with a time interval of about one month between sampling campaigns. The mean observed dissolved ²²⁶Ra activity concentrations in the two wells were 47.9±7.1 and 51.6±8.8 mBq/L. No systematic time dependence of the ²²⁶Ra activity concentration was clearly identified. The activity of ²²⁶Ra associated with suspended solids contained in 1 L of ground water fell, during the sampling period, from 13±1 to 0.8±0.1 mBq in one well and from 4.9±0.3 to 0.6±0.1 mBq in the second well.     

EC comparison on the determination of 226Ra, 228Ra, 234U and 238U in water among European monitoring laboratories

In anticipation of new European requirements for monitoring radioactivity concentration in drinking water, IRMM organized an interlaboratory comparison on the determination of low levels of activity concentrations (about 10–100 mBq L^?1) of the naturally occurring radionuclides ²²⁶Ra, ²²⁸Ra, ²³⁴U and ²³⁸U in three commercially available mineral waters. Using two or three different methods with traceability to the International System of Reference (SIR), the reference values of the water samples were determined prior to the proficiency test within combined standard uncertainties of the order of 3%–10%. An overview of radiochemical separation and measurement methods used by the 45 participating laboratories are given. The results of the participants are evaluated versus the reference values. Several of the participants’ results deviate by more than a factor of two from the reference values, in particular for the radium isotopes. Such erroneous analysis results may lead to a crucial omission of remedial actions on drinking water supplies or to economic loss by an unjustified action.     

The effect of uranium migration on radionuclide distributions for soil samples at the El-Gor area,Sinai, Egypt

The concentrations and distributions of the activity of natural radionuclides in soil samples were investigated in fifteen soil samples at El-Gor area representing two profiles (A and B) using a HP–Ge detector and alpha counting by SSNTD (CR-39), respectively. The average concentrations of the radionuclides ²³⁸U, ²²⁶Ra, ²³⁵U, ²³²Th and ⁴⁰K are 203.4, 177.23, 9.77, 43.33 and 386.22 Bq kg⁻¹ (dry weight), respectively, and profile A and ²³⁸U, ²²⁶Ra, ²³⁵U, ²³²Th and ⁴⁰K have average concentrations of 232.58, 246, 11.7, 31.7, and 277.07 Bq kg⁻¹ for profile B, respectively. The eTh and eU were estimated to detect the migration process of uranium into or out of an area or uranium to or from the studied profiles. The results indicate a migration of uranium by 29% for profile A and 65.37% for profile B. The activity ratio (²³⁸U/²²⁶Ra) was found to be 0.9 in profile A and 1.15 in profile B. These ratios coincide with the uranium migration processes. The responsible mass corresponding to the measured ²²⁶Ra activity was also calculated. The radon activity concentrations for the two profiles are nearly 300 Bq m⁻³. The emanation coefficient (η) was calculated from the ratio of the expected radon activity to the measured radon for the studied soil samples. The value of η was found to depend only on the radium activity regardless to soil formation.     

Relationship between radioactivity of radium and concentrations of barium and lead in hokutolite

Hokutolite consists of barite (BaSO₄) and anglesite (PbSO₄), and contains significant amounts of radium isotopes as a radioactive mineral. Photon activation and gamma-ray spectrometry were employed to determine Ba, Pb and ²²⁶Ra contents in hokutolite samples and to investigate the correlation between ²²⁶Ra activity and both Ba and Pb content. ²²⁶Ra activity in 30 hokutolite samples were estimated in the range of 40–65 Bq/g and was positively related to Ba content (r=0.859, p<0.001), but independent of Pb content (r=−0.236, p=0.217). Experimental results implied that ²²⁶Ra preferably precipitated with Ba over Pb. The ²²⁶Ra activity in hokutolite from the Peitou Hot Spring was experimentally estimated based on the Ba/Pb ratio and expressed as ²²⁶Ra (Bq/g)=14.67 (Ba/Pb)_molar+14.13.     

Simultaneous determination of Ra and Th nuclides, 238U and 227Ac in uranium mining waters by γ-ray spectrometry

For the investigation of flooding processes in uranium mines, Ra and Th nuclides as well as ²³⁸U and ²²⁷Ac activities in waters were simultaneous analyzed by γ-ray spectrometry. The activities of ²²⁷Ac and ²²⁸Th, not directly determinable by γ-ray spectrometry, can be calculated from two consecutive measurements (≈25 d delay) of the progeny ²²⁷Th and ²²⁴Ra. For the short-lived radionuclides ²³⁴Th, ²²⁷Th, ²²³Ra and ²²⁴Ra a correction of the results to the sampling date is necessary.     

Methodology for labeling proteins and peptides with lead-212 (212Pb)

IntroductionAlpha particles possess an exquisite degree of cytotoxicity when employed for targeted α-particle therapy (TAT) or radioimmunotherapy (RIT). ²¹²Pb, which acts as an in vivo generator of the α-emitting nuclide ²¹²Bi has shown great promise in pre-clinical studies when used to label the HER2 binding antibody, trastuzumab. Currently, the first RIT clinical trial employing ²¹²Pb radiolabeled trastuzumab is in progress. This report provides detailed current protocol operations and steps that were generated for use in the clinical trial as well as the relevant pre-clinical experimentation, and describes in detail the labeling of proteins or peptides with ²¹²Pb as provided via a ²²⁴Ra based generator system.Methods²¹²Pb was eluted from the ²²⁴Ra/²¹²Pb generator using hydrochloric acid (2 M). The generator eluate was evaporated and digested with nitric acid (8 M) followed by extraction of the ²¹²Pb with dilute nitric acid (0.1 M). The dilute nitric acid solution of ²¹²Pb was used to label the immunoconjugate Trastuzumab-TCMC (2-(4-isothiocyanatobenzyl-1,4,7,10-tetraaza-1,4,7,10,tetra-(2-carbamonylmethyl)-cyclododecane) at pH 5.5.ResultsElution of ²¹²Pb from the generator was efficient yielding > 90% of available ²¹²Pb. Trastuzumab-TCMC was efficiently labeled with a radiochemical yield of 94% ± 4% (n = 7) by ITLC and an isolated yield of 73% ± 3% (n = 7).ConclusionsThe results show the feasibility of generating radioimmunoconjugates and peptide conjugates for use as in vivo α generator systems in the clinic. The technology holds promise in applications involving the treatment of minimal disease such as micrometastases and residual tumor after surgical debulking, hematological cancers, infections, and compartmental cancers, such as ovarian cancer.     

Standardization of radium-223 by liquid scintillation counting

Liquid scintillation (LS) counting was undertaken as part of the primary standardization of ²²³Ra. Radium-223 decays with a half life of 11.43 d through a chain of shorter-lived daughter radionuclides, resulting in five alpha decays and three beta decays. The CIEMAT/NIST method of tritium efficiency tracing was employed, with the beta efficiencies being calculated using the program CN2004, developed by the Physikalisch-Technische Bundesanstalt (PTB). The total calculated LS efficiency, considering all daughter radionuclides, was approximately 598%. Separate experiments were performed to rule out loss of the 3.96 s ²¹⁹Ra daughter from the cocktail and possible counting loss of the 1.78 ms ²¹⁵Po daughter due to LS counter dead-time. No loss was observed in either experiment. In the final experiment an expanded uncertainty (k=2) of 0.55% was achieved. Results were in excellent agreement with confirmatory measurements performed by 2πα proportional counting. However, results are not in agreement with methods based on gamma ray measurements.     

222Rn, 226Ra and hydrochemistry in the Bauru Aquifer System,São José do Rio Preto (SP), Brazil

In this paper, the ²²²Rn and ²²⁶Ra activity concentration was measured in groundwater samples collected from the Bauru Aquifer System, São José do Rio Preto city, São Paulo State, Brazil. The site has been selected for a detailed radiometric survey due to the large number of tubular wells drilled in the aquifer there, which provide water for ~70% of the local population. Despite the importance of groundwater for the local water-supply system, there is a lack of both ²²²Rn and ²²⁶Ra data in the municipality. Establishment of these data is relevant to assure that the water quality from a radiological point of view, is not health threat. São José do Rio Preto city is geologically situated in Bauru Group that is located within the Paraná sedimentary basin. The monitoring program involved the collection of 50 groundwater samples from deep tubular wells during three field campaigns held from 17th to 19th January 2011, from 2nd to 3rd August 2011 and in 30th November 2011. Temperature and pH readings were realized in the field, whereas ²²²Rn and ²²⁶Ra analysis were performed at the laboratory using the Alpha Guard-Aquakit analytical protocol, which allowed us to obtain ²²²Rn activity concentration ranging from 0.69 to 14.95 Bq/L. These data indicate that the abundances of ²²²Rn and ²²⁶Ra in the groundwater system of Bauru Group is below the WHO guideline limit of 100 Bq/L. Chemical analysis has been also realized for major cations and anions in order to better understand the water features in the municipality.     

Gamma-spectrometric analysis of high salinity fluids – how to analyze radionuclides of the thorium decay chain far from radioactive equilibrium?

Highly saline brines from a geothermal plant in Neustadt-Glewe, Germany, were investigated with respect to their radionuclide concentrations. The natural decay series in these fluids are far from radioactive equilibrium with main activity contributions from the radium isotopes ²²⁶Ra, ²²⁸Ra and ²²⁴Ra. A general mathematical formulation for the coupled radionuclide activities within one decay chain is applied on the system ²²⁸Ra…²¹²Pb and tested on real samples in order to evaluate several radionuclide concentrations at the moment of sampling.     

Desferrioxamine as an appropriate chelator for 90Nb: Comparison of its complexation properties for M-Df-Octreotide (M = Nb,Fe, Ga,Zr)

The niobium-90 radioisotope (90Nb) holds considerable promise for use in immuno-PET, due to its decay parameters (t½ = 14.6 h, positron yield = 53%, Eß+mean = 0.35 MeV and Eß+max = 1.5 MeV). In particular, 90Nb appears well suited to detect in vivo the pharmacokinetics of large targeting vectors (50–150 kDa). In order to be useful for immuno-PET chelators are required to both stabilize the radionuclide in terms of coordination chemistry and to facilitate the covalent attachment to the targeting vector. Different chelators were evaluated for this purpose in terms of radiolabelling efficiency and stability of the radiolabelled Nb(V) complex and in order to determine the most suitable candidate for conjugation to a biologically relevant targeting vector. For the purpose of studying the complexation properties the niobium radioisotope 95Nb was used as an analogue of 90Nb, by virtue of its longer half-life (35 days) and lower cost (reactor-based production). Acyclic and cyclic chelators were investigated, with desferroxamine [Df: (N'-{5-[acetyl(hydroxy)amino]pentyl}-N-[5-({4-[(5-aminopentyl) (hydroxy)amino]-4-oxobutanoyl} amino)pentyl]-N-hydroxysuccinamide)] emerging as the best candidate. Greater than 99% radiolabelling was achieved at room temperature over a wide pH range. The 95Nb-Df complex is sufficiently stable for immuno-PET (< 7% degradation over 7 days in vitro). As a proof-of-principle, a Df conjugate featuring a well-established targeting vector, (D)-Phe1-octreotide, was evaluated. The fast labelling kinetics of the unconjugated chelator (Df) were retained for Df-succinyl-(D)Phe1-octreotide (Df-OC), with > 90% labelling after 1 h at room temperature over the pH range 5–7. Stability studies, performed in vitro in serum at physiological temperature (37 °C), revealed that 87 ± 2% of the radiolabelled molecule remained intact after 7 days. Competition studies with relevant metal ions (zirconium(IV), gallium(III) and iron(III)) have been performed with Df-OC to gain insight to the relative stability [Nb-Df]-OC complex to transmetallation. At equimolar metal ion concentrations the [Nb-Df]-OC complex showed the greatest overall stability. The favourable radiolabelling characteristics of Df-OC and its stability indicate that Df is a potentially very useful chelator for the development of radiopharmaceuticals for 90Nb-PET.     

Effect of thermal treatment on TL response of CaSO4:Dy obtained using a new preparation method

We report the effect of thermal treatment on thermoluminescent (TL) sensitivity property of CaSO₄:Dy obtained by a new preparation method at Instituto Nacional de Investigaciones Nucleares (ININ) of Mexico. Samples of phosphor powder were subjected to different thermal treatments respectively at 773, 873, 973 and 1173 K for 1 h and then irradiated from 0.1 to 1000 Gy gamma doses. Low energy dependence was analyzed too by irradiating with X-rays in the range of 16–145 keV. The results were normalized to the energy (1252 keV) of ⁶⁰Co and they were compared with those obtained using the commercial dosimeters TLD-100. Also the kinetic parameters were determined by deconvolution of glow curve.     

Factors influencing hydration status during a National Collegiate Athletics Association division 1 soccer preseason

ObjectivesTo investigate the roles that training load and environmental conditions have on fluid balance during a collegiate men’s soccer preseason.DesignObservational study.MethodsTwenty-eight male collegiate soccer players (mean ± SD; age, 20 ± 1.7 y; body mass (BM), 79.9 ± 7.3 kg; height, 180.9 ± 6.8 cm; body fat, 12.7 ± 3.1%; VO_2max, 50.7 ± 4.3 ml·kg⁻¹·min⁻¹) participated in this study. Prior to (PRE) and following (POST) each team session, BM, percent BM loss (%BML) and hydration status was measured. Participants donned a heart rate and GPS enabled monitor to measure training load. For all team activities, ambient temperature (T_AMB) and relative humidity (RH) were obtained from the nearest local weather station. Participants consumed 500 mL of water as part of the team-based hydration strategy before and after training session. Stepwise linear regression was used to identify the variables that predicted %BML. Significance was set a-priori p < 0.05.ResultsTotal distance covered predicted %BML during all preseason activities (r² = 0.253, p < 0.001), with T_AMB and RH further adding to the model (r² = 0.302, p < 0.001). %BML never exceeded 2% of BM during any one session and daily variation in BM was <1% from baseline measures. Urine specific gravity was greater than 1.020 on 12/15 days and U_COL was above 4 on 13/15 days, indicating a state of hypohydration.ConclusionsTotal distance covered was the best predictor for the extent of body water losses during a collegiate preseason. While the team-based hydration strategy during preseason was successful in minimizing fluid losses during activity, participants arrived hypohydrated 80% of the time, necessitating a greater focus on daily fluid needs.     

Results for five sets of forensic genetic markers studied in a Greek population sample

A population sample of 223 Greek individuals was typed for five sets of forensic genetic markers with the kits NGM SElect™, SNPforID 49plex, DIPplex^®, Argus X-12 and PowerPlex^® Y23. No significant deviation from Hardy–Weinberg expectations was observed for any of the studied markers after Holm–Šidák correction. Statistically significant (P < 0.05) levels of linkage disequilibrium were observed between markers within two of the studied X-chromosome linkage groups. AMOVA analyses of the five sets of markers did not show population structure when the individuals were grouped according to their geographic origin. The Greek population grouped closely to the other European populations measured by F_ST^* distances. The match probability ranged from a value of 1 in 2 × 10⁷ males by using haplotype frequencies of four X-chromosome haplogroups in males to 1 in 1.73 × 10²¹ individuals for 16 autosomal STRs.     

Assessment of radionuclidic impurities in cyclotron produced 99mTc

IntroductionThe commercial viability of cyclotron-produced ^99mTc as an alternative to generator-produced ^99mTc depends on several factors. These include: production yield, ease of target processing and recycling of ¹⁰⁰Mo, radiochemical purity, specific activity as well as the presence of other radionuclides, particularly various Tc radioisotopes that cannot be separated chemically and will remain in the final clinical preparation. These Tc radionuclidic impurities are derived from nuclear interactions of the accelerated protons with other stable Mo isotopes present in the enriched ¹⁰⁰Mo target. The aim of our study was to determine experimentally the yields of Tc radioisotopes produced from these stable Mo isotopes as a function of incident beam energy in order to predict radionuclidic purity of ^99mTc produced in highly enriched ¹⁰⁰Mo targets of known isotopic composition.MethodsEnriched molybdenum targets of ⁹⁵Mo, ⁹⁶Mo, ⁹⁷Mo, ⁹⁸Mo and ¹⁰⁰Mo were prepared by pressing powdered metal into an aluminum target support. The thick targets were bombarded with 10 to 24 MeV protons using the external beam line of the U-120 M cyclotron of the Nuclear Physics Institute, ?e?. The thick target yields of ⁹⁴Tc, ^94mTc, ⁹⁵Tc, ^95mTc, ^96m + gTc and ^97mTc were derived from their activities measured by γ spectrometry using a high purity Ge detector. These data were then used to assess the effect of isotopic composition of highly enriched ¹⁰⁰Mo targets on the radionuclidic purity of ^99mTc as a function of proton beam energy. Estimates were validated by comparison to measured activities of Tc radioisotopes in proton irradiated, highly enriched ¹⁰⁰Mo targets of known isotopic composition.ResultsThe measured thick target yields of ⁹⁴Tc, ^94mTc, ⁹⁵Tc, ^95mTc, ^96m + gTc and ^97mTc correspond well with recently published values calculated via the EMPIRE-3 code. However, the measured yields are more favourable with regard to achievable radionuclidic purity of ^99mTc. Reliability of the measured thick target yields was demonstrated by comparison of the estimated and measured activities of ⁹⁴Tc, ⁹⁵Tc, ^95mTc, and ^96m + gTc in highly enriched ¹⁰⁰Mo (99%) targets that showed good agreement, with maximum differences within estimated uncertainties. Radioisotopes ^94mTc and ^97mTc were not detected in the irradiated ¹⁰⁰Mo targets due to their low activities and measurement conditions; on the other hand we detected small amounts of the short-lived positron emitter ⁹³Tc (T_½ = 2.75 h). In addition to ^99mTc and trace amounts of the various Tc isotopes, significant activities of ⁹⁶Nb, ⁹⁷Nb and ⁹⁹Mo were detected in the irradiated ¹⁰⁰Mo targets.ConclusionsRadioisotope formation during the proton irradiation of Mo targets prepared from different, enriched stable Mo isotopes provides a useful data base to predict the presence of Tc radionuclidic impurities in ^99mTc derived from proton irradiated ¹⁰⁰Mo targets of known isotopic composition. The longer-lived Tc isotopes including ⁹⁴Tc (T_½ = 4.883 h), ⁹⁵Tc (T_½ = 20.0 h), ^95mTc (T_½ = 61 d), ^96m + gTc (T_½ = 4.24 d) and ^97mTc (T_½ = 90 d) are of particular concern since they may affect the dosimetry in clinical applications. Our data demonstrate that cyclotron production of ^99mTc, using highly enriched ¹⁰⁰Mo targets and 19–24 MeV incident proton energy, will result in a product of acceptable radionuclidic purity for applications in nuclear medicine.