Nuclear model calculations on proton and deuteron induced reactions on 122Te and 120Te with particular reference to the formation of the isomeric states 120m,gI.

Nuclear model calculations were performed on (p,xn) reactions on 122Te and 120Te, and (d,xn) reactions on 120Te. The computer code used (STAPRE) incorporates statistical and precompound models as well as nuclear structure effects. The total cross-sections of (p,xn) and (d,xn) processes leading to the formation of the radioisotopes 119I, 120gI, 121I and 122I are described well by the calculations. The isomeric cross-section, however, is rather difficult to calculate. The yield of the high spin isomer (120mI) depends on the type of reaction involved and increases with the increasing projectile energy. From an analysis of the energy dependence of the isomeric cross-section ratio, the excitation energy of 120mI was deduced to be 550+/-50 keV and its spin and parity as 4+. The experimental data reported earlier and the theoretical analysis presented in this work allow to define the optimum conditions for the production of the medically important beta+ emitter 120gI with enhanced confidence.     

Some optimisation studies relevant to the production of high-purity 124I and 120gI at a small-sized cyclotron.

Optimisation experiments on the production of the positron emitting radionuclides 124I(T(1/2) = 4.18d) and (120g)I (T(1/2) = 1.35 h) were carried out. The TeO(2)-target technology and dry distillation method of radioiodine separation were used. The removal of radioiodine was studied as a function of time and the loss of TeO(2) from the target as a function of oven temperature and time of distillation. A distillation time of 15 min at 750 degrees C was found to be ideal. Using a very pure source and comparing the intensities of the annihilation and X-ray radiation, a value of 22.0 +/- 0.5% for the beta(+) branching in 124I was obtained. Production of 124I was done using 200 mg/cm(2) targets of 99.8% enriched 124TeO(2) on Pt-backing, 16 MeV proton beam intensities of 10 microA, and irradiation times of about 8 h. The average yield of 124I at EOB was 470 MBq(12.7 mCi). At the time of application (about 70 h after EOB) the radionuclidic impurity 123I (T(1/2) = 13.2 h) was <1%. The levels of other impurities were negligible (126I < 0.0001%;125I = 0.01%). Special care was taken to determine the 125I impurity. For the production of (120g)I only a thin 30 mg target (on 0.5 cm(2) area) of 99.9% enriched 120TeO(2) was available. Irradiations were done with 16 MeV protons for 80 min at beam currents of 7 microA. The 120gI yield achieved at EOB was 700 MBq(19 mCi), and the only impurity detected was the isomeric state 120 mI(T(1/2) = 53 min) at a level of 4.0%. The radiochemical purity of both 124I and 120gI was checked via HPLC and TLC. The radioiodine collected in 0.02 M NaOH solution existed >98% as iodide. The amount of inactive Te found in radioiodine was <1 microg. High purity 124I and 120gI can thus be advantageously produced on a medium scale using the low-energy (p,n) reaction at a small-sized cyclotron.     

Excitation functions of 125Te(p, xn)-reactions from their respective thresholds up to 100 MeV with special reference to the production of 124I.

Excitation functions of the nuclear reactions 125Te(p, xn) (119,120m, 120g, 121,122,123,124,125)I were measured for the first time from their respective thresholds up to 100 MeV using the stacked-foil technique. Thin samples were prepared by electrolytic deposition of 98.3% enriched 125Te on Ti-backing. In addition to experimental studies, excitation functions were calculated by the modified hybrid model code ALICE-IPPE. The experimental and theoretical data generally showed good agreement. From the measured cross section data, integral yields of (123,124,125)I were calculated. The energy range Ep 21 --> 15 MeV appears to be very suitable for the production of the medically interesting radionuclide 124I (T(1/2) = 4.18 d; I(beta)+ = 25%). The thick target yield of 124I amounts to 81 MBq/microA h and the level of 125I-impurity to 0.9%. The 125Te(p,2n)124I reaction gives 124I yield about four times higher than the commonly used 124Te(p,n)124I and 124Te(d,2n)124I reactions. The proposed production energy range is too high for small cyclotrons but large quantities of 124I can be produced with medium-sized commercial machines.     

Excitation functions of 124Te(d,xn)124,125I reactions from threshold up to 14 MeV: comparative evaluation of nuclear routes for the production of 124I.

Excitation functions of the nuclear reactions 124Te(d,xn)124-125I were measured from their respective thresholds up to 14.0 MeV via the stacked-foil technique. Thin samples were prepared by electrolytic deposition of 99.8% enriched 124Te on Ti-backing. The excitation function of the 124Te(d,n)125I reaction was measured for the first time. The present data for the 124Te(d,2n)124I reaction are by an order of magnitude higher than the literature experimental data but are in good agreement with the results of a hybrid model calculation. From the measured cross sections, integral yields of 124,125I were calculated. The energy range Ed = 14 --> 10 MeV appears to be the best compromise between 124I-yield and 1251-impurity. The calculated 124I-yield amounts to 17.5 MBq/microA h and the 125I-impurity to 1.7%. A critical evaluation of the three nuclear routes for the production of 124I, viz. 124Te(d,2n)-, 124Te(p,n)- and 125Te(p,2n)-processes, is given. The reaction studied in this work proved to be least suitable. The 124Te(p,n)-reaction gives 124I of the highest radionuclidic purity, and a small-sized cyclotron is adequate for production purposes. The 125Te(p,2n)-reaction is more suitable at a medium-sized cyclotron: the yield of 124I is four times higher than in the other two reactions but the level of 0.9% 125I-impurity is relatively high.     

Excitation functions of proton induced nuclear reactions on natural tellurium and enriched 123Te: Production of 123I via the 123Te(p,n)123I-process at a low-energy cyclotron

Excitation functions were measured by the stacked-foil technique for (p, xn) reactions up to E_p = 20 MeV on natural tellurium and enriched ¹²³Te. Thick target yields were calculated for the formation of ¹²¹I, ¹²³I, ¹²⁴I, ¹²⁶I, ¹²⁸I and ¹³⁰I from natural tellurium, and ¹²²I and ¹²³I from enriched ¹²³Te. The optimum energy range for the production of ¹²³I via the ¹²³Te(p, n)¹²³I reaction is E_p = 14.5 → 11.0 MeV, and the theoretical thick target yield 4 mCi/μAh. The levels of the three major impurities ¹²⁴I, ¹²⁶I and ¹³⁰I are directly dependent on the ¹²⁴Te, ¹²⁶Te and ¹³⁰Te contents, respectively, in enriched ¹²³Te. The levels of impurities determined experimentally under high-current production conditions agree with those calculated from the cross section data. A comparison of the three direct methods of ¹²³I-production, viz. ¹²⁴Te(p, 2n)¹²³I, ¹²³Te(p, n)¹²³I and ¹²²Te(d, n)¹²³I, under optimum conditions for each reaction, is given. The yield and impurity-level data suggest that the ¹²³Te(p, n)¹²³I reaction has a great potential for production in a low-energy cyclotron, if highly enriched ¹²³Te (>91%) is used.     

Nuclear data relevant to the production of I via the Te(p,n)-Process at aSmall-Sized Cyclotron

Excitation functions of the nuclear reactions ¹²⁰Te(p,xn)^119,120m,gI were measured for the first time from their respective thresholds up to 35 MeV. Use was made of the stacked-foil technique. Thin samples were prepared by electrolytic deposition of highly enriched ¹²⁰Te (99.0%) on Ti-backing. Integralyields of ^119,120m,gI were calculated from the measured cross section data. For the production of the medically interesting β⁺-emitting radioisotope ^120gI (T_1/2=1.35 h) the energy range E_p=16→9 MeV appears to be optimum, the thick target yield of ^120gI amounting to 2.3 GBq (62 mCi)/μAh and the ^120mI and ¹¹⁹I impurity levels to 4.8 and 4.4%, respectively. A comparison of the ¹²²Te(p,3n)- and ¹²⁰Te(p,n)-processes for the production of ^120gI is given. Despite the higher cost of the target material, the ¹²⁰Te(p,n)-process is superior since a small-sized cyclotron is adequate and the radionuclidic quality of the product is better.     

Calculated 118Te production rates from enriched 122,123Te targets

The ¹¹⁸Te/¹¹⁸Sb generator has potential application for positron emission tomography. In this study, we modelled the production of the ¹¹⁸Te precursor via proton activation of ¹²²Te and ¹²³Te targets. ¹¹⁸Te excitation functions were calculated for the (p, xn) and (p, pxn) production channels using a compound nucleus/statistical evaporation approach. These calculations indicate that ¹¹⁸Te can be produced in GBq (100 mCi) quantities by the irradiation of a thin (0.4 g/cm²) enriched ¹²²Te target with 62 MeV protons. This corresponds to a cumulative ¹¹⁸Te production rate in the 62-60 MeV proton energy region of 16 GBq/C (1.6 mCi/μA-h). In this proton energy range, ¹¹⁸Te production is maximized while the production of such contaminant nuclides as ¹¹⁹Te is relatively low. In view of the sizable ¹¹⁸Te production rate estimate, we are proceeding with the development of optimal Te/Sb separation chemistry applicable to a generator system.     

Cross sections of natSb(p,x) reactions for 30–46 MeV protons

In order to optimize the production of ¹¹⁸Te in thick targets for use in a ¹¹⁸Te/¹¹⁸Sb radionuclide generator, the excitation function for the ¹²¹Sb(p,4n)¹¹⁸Te reaction has been measured for 30–46 MeV protons. The excitation functions for the competing reactions ^natSb(p,xn)^119mTe, ^natSb(p,xn)¹¹⁹Te, ^natSb(p,xn)^121mTe, ^natSb(p,pxn)^120mSb and ¹²³Sb(p,pn)¹²²Sb have also been determined using stacked foil techniques. The ¹²¹Sb(p,4n)¹¹⁸Te reaction cross section maximum was found to be 480 mbarn at 44 MeV. In order to minimize the ^{119m + 119}Te interference a minimum proton beam energy of 40 MeV is required. The cross section results are compared with published data and with calculated excitation functions.     

Study of the 192Os(d,2n) reaction for production of the therapeutic radionuclide 192Ir in no-carrier added form.

In the frame of an IAEA coordinated research project (CRP) on nuclear data for production of therapeutic radionuclides, the production of 192Ir via deuteron-induced reactions on enriched 192Os was investigated up to 21 MeV deuteron energy. Cross sections were measured using the conventional stacked-foil irradiation technique and high-resolution gamma-ray spectroscopy of the activation products. No earlier experimental data were found in the literature. The excitation functions of the 192Os(d,2n)192m1+gIr and 192Os(d,p)193Os reactions were compared with the results of nuclear model calculations using the standard and presently upgraded versions (D-version) of ALICE-IPPE, EMPIRE-II and GNASH codes, while for the (d,2n) channel the GNASH and EMPIRE-II codes reproduced the data in an acceptable way; in both cases for the (d,p) reaction the very large discrepancy observed between the experimental data and standard codes results is vanishing when the upgraded versions of ALICE and EMPIRE-II are used. A comparison of the reactor and cyclotron production routes of 192Ir is given.     

Assessment of the short-lived non-pure positron-emitting nuclide 120I for PET imaging

Purpose The non-pure positron-emitting iodine isotope ¹²⁰I (T _1/2=81 min) is a short-lived alternative to ¹²⁴I. ¹²⁰I has a positron abundance more than twice that of ¹²⁴I and a maximum positron energy of 4 MeV. This study was undertaken to evaluate and characterise the qualitative and quantitative PET imaging of ¹²⁰I.Methods ¹²⁰I was produced via the ¹²⁰Te(p,n) reaction on highly enriched ¹²⁰Te. The measurements were done with the Siemens scanner HR+ and the 2D PET scanner GE PC4096+. A cylinder containing three cold inserts and a phantom resembling a human brain slice were used to evaluate half-life, positron abundance and background correction. To analyse the image resolution, a 1-mm tube placed in water was filled with ¹²⁰I and ¹⁸F. Comparisons with ¹⁸F, ¹²⁴I and ¹²³I (measured with SPECT) were made using the Hoffman 3D brain phantom.Results The half-life of 81.1 min was reproduced by the PET measurements. The PET-based positron abundance ranged from 47.9% to 55.0%. The reconstructed image resolution found with the HR+ was 5.4 mm FWHM (12.3 mm FWTM), in contrast to 4.6 mm (8.6 mm) when using ¹⁸F. Erroneous positive and negative numbers of radioactivity found in the cold inserts became nearly zero when the background of γ-coincidences was corrected for. Images of the Hoffman phantom were inferior to those obtained when ¹⁸F or ¹²⁴I was applied but superior to the ¹²³I-SPECT images.Conclusion Our data show that ¹²⁰I of high radionuclidic purity can be regarded as a suitable nuclide for the PET imaging of radioiodine-labelled pharmaceuticals.     

Production of the therapeutic radionuclides 193mPt and 195mPt with high specific activity via alpha-particle-induced reactions on 192Os.

For the production of therapy-relevant radionuclides (193m)Pt (T(1/2)=4.33 d) and (195m)Pt (T(1/2)=4.03 d) with a high specific activity, the (192)Os(alpha,n)(195m)Pt and (192)Os(alpha,3n)(193m)Pt nuclear reactions were investigated for the first time from their respective thresholds up to 28 MeV. Thin samples of enriched (192)Os were prepared by electrodeposition on Ni, and the conventional stacked-foil technique was used for cross-section measurements. The calculated thick target yields were found to be 0.013 MBq/microA h for the (192)Os(alpha,n)(195m)Pt reaction in the energy range of E(alpha)=24-->18 MeV, and 0.25 MBq/microA h for the (192)Os(alpha,3n)(193m)Pt reaction in the energy range of E(alpha)=28-->24 MeV. The two radionuclides could not be detected in the interactions of (3)He particles with (192)Os. A production method involving high-current alpha-particle irradiation of enriched (192)Os and efficient chemical separation of radioplatinum was developed. Batch yields of about 1 MBq (195m)Pt and 8.7 MBq (193m)Pt were achieved. Compared to the reactor production these batch yields are very low, but the (192)Os(alpha,n)(195m)Pt and (192)Os(alpha,3n)(193m)Pt reactions are superior with respect to the specific activity of the products which is higher by two orders of magnitude.     

Evaluation of excitation functions of proton and deuteron induced reactions on enriched tellurium isotopes with special relevance to the production of iodine-124

Cross-section data for the production of medically important radionuclide ¹²⁴I via five proton and deuteron induced reactions on enriched tellurium isotopes were evaluated. The nuclear model codes, STAPRE, EMPIRE and TALYS, were used for consistency checks of the experimental data. Recommended excitation functions were derived using a well-defined statistical procedure. Therefrom integral yields were calculated. The various production routes of ¹²⁴I were compared. Presently the ¹²⁴Te(p,n)¹²⁴I reaction is the method of choice; however, the ¹²⁵Te(p,2n)¹²⁴I reaction also appears to have great potential.     

Cross-section measurements of the nuclear reactions Zn(d,x)Cu, Zn(d,α)Cu and Zn(p,αn)Cu for production of Cu and technical developments for small-scale production of Cu via the Zn(p,α)Cu process

The radionuclides 64Cu (T1/2=12.7h) and 67Cu (T1/2=61.9h) are useful in internal therapy. In connection with production of 64Cu, excitation functions of the reactions natZn(d,x)64Cu, 66Zn(d,alpha)64Cu and 68Zn(p,alphan)64Cu were measured radiochemically using the stacked-foil technique. From the measured data, the thick target yields of 64Cu were calculated and compared with experimental data available in the literature. The three investigated processes are discussed in comparison to the commonly used 64Ni(p,n)64Cu reaction for the production of 64Cu. As regards 67Cu production, the technical feasibility of the 70Zn(p,alpha)67Cu process was investigated. An electroplated isotopically enriched 70Zn target was developed which can withstand slanting beams of 20MeV protons of currents up to 20 microA. Methods for chemical separation of 67Cu and efficient recovery of the enriched target material were worked out. The method is suitable only for small-scale production of 67Cu.     

Excitation functions of Se(d,xn)Br reactions: Comparative evaluation of possible routes for the production of Br at a small cyclotron

Excitation functions were measured for the first time for ⁷⁴Se(d,n)⁷⁵Br and ⁷⁴Se(d,2n)^74mBr reactions from threshold to 23 MeV. Use was made of the stacked-foil technique, and thin samples were prepared by electrolytic deposition of 31.4% enriched ⁷⁴Se on Al-backing. Differential and integral yields of ^74mBr and ⁷⁵Br were calculated from the measured excitation functions. The optimum energy range for the production of ⁷⁵Br via the ⁷⁴Se(d,n)-process was found to be E_d = 12 → 8 MeV, with ⁷⁵Br-yield amounting to 509 MBq (13.75 mCi)/μAh and the ^74mBr impurity to 78Kr(p,)⁷⁵Br and ⁷⁴Se(d,n)⁷⁵Br, suggested for the production of ⁷⁵Br at a small cyclotron is given. The (d,n) reaction gives higher yield than the (p,) process and is preferable at cyclotrons with E_d 10 MeV. In general, at a small cyclotron the achievable batch yields of ⁷⁵Br via both the processes are limited.     

A new binary compound for the production of 124I via the 124Te(p,n)124I reaction.

The binary compound, aluminum telluride (Al(2)Te(3)), was investigated as a target material for the production of (124)I by way of the (124)Te(p,n)(124)I reaction on a low-energy cyclotron. The high melting point and formation of a glassy matrix upon heating provided a stable target material at irradiations up to 20 microA of 11 MeV protons. The 87% tellurium mass fraction and 95% iodine separation yield led to significantly higher quantities of iodine compared to traditional TeO(2)/6%Al(2)O(3) admixtures. Radiochemical analysis of distilled samples using ion chromatography showed that the product remained in the iodide form while supported in weak buffer solutions. Stable Te impurities in the radioiodine product were less than 0.5 microg following purification by ion exchange chromatography. Average thick target yields of 229+/-18 microCi/microAh were achieved, and typical production runs at 18 microA for three hours yielded 12 mCi at the end-of-bombardment. Total losses of the target material after each irradiation and distillation cycle were approximately 2%.     

Excitation function of 122Te(d,n)123I nuclear reaction: production of 123I at a low energy cyclotron

The excitation function of the ¹²²Te(d, n)¹²³I nuclear reaction has been measured from threshold up to 21 MeV by the stacked foil irradiation technique. Good agreement was obtained with the results of the recent model calculations but an energy shift of 2 MeV to lower energy can be seen when comparing with cross section measured earlier. Integral yields have been deduced from the measured excitation function and have been compared with experimental thick target yields found in the literature. A comparison of the yields of the proton and deuteron induced reactions for production of ¹²³I is given.     

Excitation functions of 85Rb(p,xn)(85m,g,83,82,81)Sr reactions up to 100 MeV: integral tests of cross section data, comparison of production routes of 83Sr and thick target yield of 82Sr.

The beta+ emitter 83Sr (T(1/2) = 32.4 h, Ebeta+ = 1.23 MeV, Ibeta+ = 24%) is a potentially useful radionuclide for therapy planning prior to the use of the beta+ emitter 89Sr (T(1/2) = 50.5 d). In order to investigate its production possibility, cross section measurements on the 85Rb(p,xn)-reactions, leading to the formation of the isotopes (85m,g)Sr, 83Sr, 82Sr and 81Sr, were carried out using the stacked-foil technique. In a few cases, the products were separated via high-performance liquid chromatography. For 82Sr, both gamma-ray and X-ray spectrometry were applied; in other cases only gamma-ray spectrometry was used. From the measured excitation functions, the expected yields were calculated. For the energy range Ep = 37 --> 30 MeV the 83Sr yield amounts to 160 MBq/microA h and the level of the 85gSr (T(1,2) = 64.9 d) and 82Sr (T(1/2) = 25.5 d) impurities to <0.25%. In integral tests involving yield measurements radiostrontium was chemically separated and its radioactivity determined. The experimental production data agreed within 10% with those deduced from the excitation functions. The results of the 85Rb(p,3n)83Sr reaction were compared with the data on the production of 83Sr via the 82Kr(3He,2n)-process. In the energy range E3Hc = 18 --> 10 MeV the theoretical yield of 83Sr amounts to 5 MBq/microA h and the 82Sr impurity to about 0.2%. The method of choice for the production of 83Sr is thus the 85Rb(p,3n)-process, provided a 40 MeV cyclotron is available. During this study some supplementary information on the yield and purity of 82Sr was also obtained.     

Cross sections for (n, 2n), (n, p) and (n, alpha) reactions on osmium isotopes in the neutron energy range of 13.5-14.8MeV.

Cross sections for (n, 2n), (n, p) and (n, alpha) reactions on the osmium isotopes were measured in the neutron energies 13.5-14.8MeV by the activation technique with the monitor reaction (93)Nb(n, 2n)(92m)Nb. Our measurements were carried out by gamma-detection using a coaxial high-purity germanium (HPGe) detector. Natural high-purity osmium powder (99.9%) was fabricated as the samples. The neutron energies were determined by the cross-section ratios for (93)Nb(n, 2n)(92m)Nb and (90)Zr(n, 2n)(89m+g)Zr reactions. The fast neutrons were produced by the T(d, n)(4)He reaction. The results obtained were compared with previous data.     

Relationship between run times to exhaustion at 90, 100, 120, and 140% of vVO2max and velocity expressed relatively to critical velocity and maximal velocity

The aim of the present study was to explain the inter-individual variability in running time to exhaustion (tlim) when running speed was expressed as a percentage of the velocity, associated with maximal oxygen uptake (vVO2max). Indeed for the same percentage of vVO2max the anaerobic contribution to energy supply is different and could be dependent on the critical velocity (Cv) and also on the maximal running velocity (vmax). Ten subjects ran four tlim at 90, 100, 120, and 140% of vVO2max; mean and standard deviation for tlim were 839 +/- 236 s, 357 +/- 110 s, 122 +/- 27 s, and 65 +/- 17s, respectively. Each velocity was then expressed 1) as a percentage of the difference between vVO2max and Cv (%AeSR); 2) as a percentage of the difference between vmax and Cv (%MSR); 3) as a percentage of the difference between vmax and vVO2max (%AnSR). Highest correlations were found between tlim90 and tlim100 and velocity expressed as %MSR (r = -0.82, p < 0.01 and r = -0.75, p < 0.01), and between tlim120 and tlim140 and velocity expressed as %AnSR (r = -0.83, p < 0.01 and r = -0.94, p < 0.001). These results show that the same intensity relative to aerobic contribution did not represent the same absolute intensity for all and could partly explain variability in tlim. Therefore expressing intensity as a percentage of MSR for sub-maximal and maximal velocities and as a percentage of AnSR for supra-maximal velocities allows individual differences in anaerobic work capacity to be taken into account and running times to exhaustion to be predicted accurately.     

Averaged cross sections for the reactions (68)Zn(n,p)(68g)Cu and (68)Zn(n,p)(68m)Cu for a (235)U fission neutron spectrum.

Making use of the method developed in our laboratory for the simultaneous determination of cross sections leading to both the ground and metastable states, we have measured the (68)Zn(n,p)(68g)Cu and (68)Zn(n,p)(68m)Cu reactions, using Zn enriched to 99.4% in its isotope (68)Zn. The measured cross sections are (15.04+/-0.35) and (3.69+/-0.30)microb for the ground and metastable state, respectively. However, a direct determination of the cross section leading to the metastable state gives a value of (4.75+/-0.38)microb. A possible reason for this discrepancy-which is outside experimental uncertainties-is that some tabulated values used in our calculations for the decay parameters of (68g)Cu and (68m)Cu, have either larger than quoted, or unknown systematic, uncertainties.