Absolute Activation Cross-sections Research Articles

Measurement of absolute activation cross sections from carbon and aluminum for proton therapy

This experimental study aims to measure nuclear cross sections from natC and 27Al which serve as reference targets regarding radioactivation in proton therapy. Graphite and aluminum foils were activated in broad, quasi-monochromatic proton fields generated with the pencil-beam scanning technique. The γ-emissions were analyzed subsequently in a nearby γ-ray spectrometry facility designed for low-level radioactivity measurements. The number of incident protons was measured with a Faraday Cup. A detailed evaluation of the uncertainties was performed.The cross section for the natC(p,x)11C reaction at 100 MeV is (70.2 ± 1.6 (sys.) ± 0.2 (stat.)) mb. The production cross sections from 27Al at 100 MeV are (19.9 ± 0.4 ± 0.3) mb for 22Na and (11.5±0.3±0.1) mb for 24Na. The systematic uncertainties contribute 2.0%–2.4% of the quoted uncertainties (k=1) of cross sections. Concluding, radioactivation cross sections were measured with proton fields in a clinically commissioned environment. The measured activation cross sections from aluminum used for monitoring of the proton fluence agree with the averaged values compiled in nuclear reaction data bases. For proton-induced radioactivation from carbon the chemical purity of the target strongly affects the experimental results. The cross section for the production of 11C derived from a measurement with a high-purity graphite target is in line with the largest cross section obtained in prior studies.

Fast neutron capture by vanadium and titanium

Fast neutron capture cross sections of 51IV and 10Ti have been measured by the activation method as a function of neutron energy between about 150 keV and 1·7 MeV. These cross sections were measured relative to both the 235U( n,f) cross section and the 197Au( n, γ) 198Au cross section. Neutrons were produced by the 7Li( p, n) 7Be reaction from a Van de Graaff accelerator. The uncertainties on the absolute activation cross sections are ±8·5 per cent for 51V and ±9·9 per cent for 50Ti and were evaluated with the aid of a computer code which is described. A complete error analysis is given. The data have been compared with calculations based upon the statistical compound nucleus model of nuclear reactions. The significant feature of the measured reactions is the sizeable fluctuations of the cross section about a smooth average which cannot be described by the theoretical calculations. Possible explanations for this observed structure are given.

Half-lives and activation cross-sections of some radio-isotopes of iodine, tellurium and antimony formed in the interactions of iodine with 14·7 MeV neutrons

Accurate half-lives and absolute activation cross-sections have been estimated for some of the isotopes formed in the interactions of iodine with 14·7 MeV neutrons. They are as follows: 128 I:25·5±0.3 min; ρ n,y=7·2±1·2 mb 126 I:13·02±0.07 day; ρ n,2n=1128±120 mb 125 I:58±2 day; ρ n,3n=40±15 mb 127 Te:9·23±0.13 hr; ρ n,p=8·9±1·0 mb 124m Sb:21·3±0.8 min; ρ n,α=1·5±0·2 mb At this particle energy direct interaction processes also contribute. A search for the alleged 2·6 hr isomeric state in 126I showed that this activity probably does not exist.

Cross-sections for the reactions141Pr(n, p)141Ce,141Pr(n, t)139Ce,142Ce(n, 2n)141Ce and140Ce(n, 2n)139Ce

Absolute activation cross-sections for the reactions141Pr(n, p),141Pr(n, t),142Ce(n, 2n),140Ce(n, 2n) were determined at 14.8 MeV neutron energy, using a Ge(Li) spectrometer. The results are in good agreement with the data calculated on the basis of empirical relationships.

Absolute activation cross sections for reactions of niobium with 14·5 MeV neutrons

Absolute neutron activation cross sections at 14·5 MeV have been measured for the mono-isotopic nuclide, 93Nb, by means of γ-scintillation spectroscopy and β-proportional counting as well as by the use of chemical separation techniques. The observed reactions, product half-lives, and cross-sections are as follows: 93Nb ( n, 2 n) 92 g Nb, 10·1 days, 499 ± 91 mbarns; 93Nb ( n, γ) 94 m Nb, 6·6 min, 0·44 ± 0·25 mbarns; 93Nb ( n, α) 90bY, 64 hr, 8·6 ± 2·5 mbarns; 93Nb ( n, α) 90 m Y, 3·0 hr, 5·9 ± 2·0 mbarns; 93Nb ( n, n′ α) 89 m Y, 16 sec, 2·5 ± 1·1 mbarns. No activity was observed in the zirconium fraction, the ( n, p) product, nor was the 13 hr 92 m Nb produced through an ( n, 2 n) reaction. Half-lives of 90 m Y and 89 m Y were determined by least squares analysis to be 3·02 ± 0·09 hr and 16·3 ± 1·3 sec, respectively.

Aktivierungsquerschnitte von Hf 178m(4.3 sec) und Hf 179m (18.6 sec) für thermische neutronen

Using a pulsed neutron beam the formation of Hf 178m and Hf 179m by thermal neutron capture in natural Hafnium was investigated. For the decay of Hf 178m a half-life of 4.3±0.1 sec was found. By comparing the γ-ray intensities from the Hafnium isomers with the prompt γ radiation of a Boron target exposed in the same position to the neutron beam, absolute activation cross sections could be determined. The following values were found: H f 177 ( n , γ ) H f 178 m ( 4.3 sec ) : σ a c t = 1.4 ± 0.6 b , H f 178 ( n , γ ) H f 179 m ( 18.6 sec ) : σ a c t = 50 ± 15 b . The isomeric cross-section ratios σ act/σ abs for Hf 178m and Hf 180m are almost equal. Therefore the compound states of these two nucleides formed by thermal neutron capture have probably the same spin J = 4. The possibility of a strong transition leading directly to the 18.6 sec isomeric state in Hf 179 is discussed.

Absolute Activation Cross Sections for Reactions of Bismuth, Copper, Titanium, and Aluminum with 14.8-Mev Neutrons

Absolute neutron activation cross sections at 14.8 Mev have been measured for bismuth, copper, titanium, and aluminum based on comparison with the ${\mathrm{Cu}}^{63}(n, 2n){\mathrm{Cu}}^{62}$ reaction (556 millibarns) which served as a standard for monitoring the flux. The reactions studied, measured half-lives, and cross sections are: ${\mathrm{Bi}}^{209}(n, \ensuremath{\alpha}){\mathrm{Tl}}^{206}$, 4.29\ifmmode\pm\else\textpm\fi{}0.05 min, 1.1\ifmmode\pm\else\textpm\fi{}0.3 mb; ${\mathrm{Bi}}^{209}(n, p){\mathrm{Pb}}^{209}$, 3.31\ifmmode\pm\else\textpm\fi{}0.03 hours, 0.83\ifmmode\pm\else\textpm\fi{}0.40 mb; ${\mathrm{Bi}}^{209}(n, \ensuremath{\gamma}){\mathrm{Bi}}^{210}$, \ensuremath{\le}1.7 mb; ${\mathrm{Cu}}^{65}(n, 2n){\mathrm{Cu}}^{64}$, 12.85\ifmmode\pm\else\textpm\fi{}0.05 hours, 954\ifmmode\pm\else\textpm\fi{}130 mb; ${\mathrm{Cu}}^{65}(n, p){\mathrm{Ni}}^{65}$, 2.56\ifmmode\pm\else\textpm\fi{}0.20 hours, 27\ifmmode\pm\else\textpm\fi{}11 mb; ${\mathrm{Ti}}^{50}(n, p){\mathrm{Sc}}^{50}$, 1.8\ifmmode\pm\else\textpm\fi{}0.2 min, 27\ifmmode\pm\else\textpm\fi{}6 mb; ${\mathrm{Ti}}^{50}(n, p){\mathrm{Sc}}^{50}$, 22\ifmmode\pm\else\textpm\fi{}3 min, 48\ifmmode\pm\else\textpm\fi{}15 mb; ${\mathrm{Ti}}^{50}(n, \ensuremath{\gamma}){\mathrm{Ti}}^{51}$, \ensuremath{\le}9 mb; ${\mathrm{Ti}}^{49}(n, p){\mathrm{Sc}}^{49}$, 58\ifmmode\pm\else\textpm\fi{}2 min, 29\ifmmode\pm\else\textpm\fi{}5 mb; ${\mathrm{Ti}}^{48}(n, p){\mathrm{Sc}}^{48}$, 44.0\ifmmode\pm\else\textpm\fi{}0.9 hours, 58\ifmmode\pm\else\textpm\fi{}8 mb; ${\mathrm{Ti}}^{47}(n, p){\mathrm{Sc}}^{47}$, 3.45\ifmmode\pm\else\textpm\fi{}0.06 days, 230\ifmmode\pm\else\textpm\fi{}40 mb; ${\mathrm{Ti}}^{46}(n, 2n){\mathrm{Ti}}^{45}$, 3.06\ifmmode\pm\else\textpm\fi{}0.08 hours, 50.4\ifmmode\pm\else\textpm\fi{}8.0 mb; ${\mathrm{Ti}}^{46}(n, p){\mathrm{Sc}}^{46}$, 85\ifmmode\pm\else\textpm\fi{}2 days, \ensuremath{\sim}520 mb; ${\mathrm{Al}}^{27}(n, \ensuremath{\alpha}){\mathrm{Na}}^{24}$, 15.00\ifmmode\pm\else\textpm\fi{}0.06 hours, 114\ifmmode\pm\else\textpm\fi{}7 mb; ${\mathrm{Al}}^{27}(n, p){\mathrm{Mg}}^{27}$, 9.46\ifmmode\pm\else\textpm\fi{}0.02 min, 53\ifmmode\pm\else\textpm\fi{}5 mb.Comparisons of the experimental cross sections with values estimated according to the continuum theory of the compound nucleus outlined by Blatt and Weisskopf are in agreement within an order of magnitude, except in the case of the bismuth results which exhibit large discrepancies.From irradiations of natural titanium and highly enriched ${\mathrm{Ti}}^{50}$, a new activity was observed having a half-life of 22\ifmmode\pm\else\textpm\fi{}3 minutes. This activity is not produced from enriched ${\mathrm{Ti}}^{47}$ or ${\mathrm{Ti}}^{49}$ samples, and it is therefore assigned tentatively to an isomer of ${\mathrm{Sc}}^{50}$. Further work on this activity is in progress.