Studies in heavy ion activation analysis

¹¹B induced radioactivation was used to study the trace determination of light elements with 1Z17. 49 nuclear reactions were investigated with ion beam energies ranging from E_lab=10 MeV to E_lab=27 MeV. Five elements were found to be determinable nondestructively, selectively and sensitively: Li, Be, B, Mg and Si. Nuclear interferences have also been defined and quantified. The technique has been applied to simultaneous Li-B trace determinations in glass samples and to Mg determination in Al₂O₃ ceramic material.     

Studies in heavy ion activation analysis

¹⁵N induced radioactivation was used to study the possible trace determination of light elements with 1Z17. 55 nuclear reactions were investigated with ion beam energies ranging from E_1ab=10 MeV to E_1ab=30 MeV. Three elements were found to be determinable non-destructively, selectively and sensitively: Li, Be and Mg. Nuclear interferences have also been defined and quantified. The technique has been tested by analyzing NBS standards. Finally, Li and Be have been determined in glass samples and Mg in various types of alumina.     

Studies in heavy ion activation analysis

A procedure for measuring trace amounts of Li and Be in different types of samples has been studied using a 12.5 MeV¹⁴N beam. At this energy the principal nuclear reactions are⁶Li(¹⁴N, d)¹⁸F,⁷Li(¹⁴N, t)¹⁸F, and⁹Be(¹⁴N, αn)¹⁸F. Detection limit for destructive analysis for either beryllium or lithium has been calculated at 300 ppb with a determination limit of 5 ppm for an irradiation with a beam of 1 μA·h/cm². Destructive analysis was performed on CANMET SY-2 and USGS BCR-1 (rock samples 1–10 ppm Be). Non-destructive analysis for beryllium and lithium was performed on NBS SRM 610 (500 ppm trace element glass), NBS 612 (50 ppm trace element glass), and NBS SRM 181 (Spodumene ore, 6.4% Li₂O). Detection limit of 2 ppm has been calculated for nondestructive analysis of either lithium or beryllium.     

Studies in heavy ion activation analysis

⁷Li induced radioactivation was used for the trace determination of hydrogen via the¹H(⁷Li, n)⁷ Be reaction. At 21 MeV⁷Li, only boron and magnesium present small nuclear interferences. An activation curve has been established by bombarding a stack of thin mylar foils. The comparison of this curve with the excitation function for the forward reaction, namely⁷Li(p, n)⁷ Be, shows that the recoil range from the superficial hydrogen atoms is only 1.7 mg·cm^–2, allowing post-irradiation etching. Hydrogen has been determined in titanium and lead bronze at the 100 ppm level with a relative precision of 6 to 10%. Studies of 32 potential interfering elements suggest the extension of Li activation to the trace determination of Na[²³Na(⁷Li,⁶Li)²⁴Na] and K[³⁹K(⁷Li, d)^44m,⁴⁴Sc].     

Trace determination of silicon by heavy ion activation analysis

The Si(¹¹B, x)^34mCl and Si(¹⁹F, x)^44mSc reactions have been studied in order to work out their capabilities in determining traces of silicon. The first one has been tested with beam energies ranging from 19 to 27 MeV¹¹B; only Mg and Al have shown nuclear interferences and a 30-min 27 MeV¹¹B irradiation yields a 14 ng detection limit. The second reaction, investigated in between 35 and 46 MeV¹⁹F, yields a 16 ng detection limit with a 2 hrs 46 MeV¹⁹F irradiation; at that energy only Al and P present nuclear interferences.     

Studies in heavy ion activation analysis

The use of 7 MeV⁶Li⁺ for heavy ion activation analysis was investigated. A survey of reactions, involving targets of lithium through oxygen inclusive, were studied for production of β⁺ radioactivation products with half-lives of 10¹−10⁵ seconds. Specific activities for all reactions under the experimental conditions are reported and their use for analysis is assessed. Parts I–III: J. Radioanal. Chem. Vols. 53, 54, 57, respectively.     

Studies in heavy ion activation analysis

¹⁸O induced radioactivation may be used for the trace detection of¹H via¹H (¹⁸O, n)¹⁸F. Matrices in which this reaction is interference-free include: Al, Si, S, K, Ti, V, Ni, Cu and Zn. However, due to numerous radioisotopes created at the bombarding energies used (E≥51 MeV), a post-irradiation chemical separation of¹⁸F is required.¹⁸O activation also appears as a promising means for the trace determination of S[S(¹⁸O, x)⁴⁷V], Si[Si(¹⁸O, x)^43–44Sc] and B[B(¹⁸O, x)³⁷Mg]. Part I: in Journal of Radioanalytical Chemistry, 53 (1979) 181.     

Trace determination of beryllium by heavy ion activation analysis

A novel procedure for measuring the concentration of trace beryllium in different samples has been studied using¹¹B heavy ion activation analysis. The specific reaction,⁹Be/¹¹B, 2n/¹⁸F, is sensitive and selective when using a 10 MeV¹¹Be³⁺ bombardment energy. The detection limit for a nondestructive analysis is 0.1 ng for a 2 h irradiation in a A cm^–2 beam current. A precision of 12% was achieved at the 50 g g^–1 level. Beryllium has been determined in a standard beryllium-copper alloy NBS-SRM C1123. Glass samples containing up to 61 trace elements were also analyzed nondestructively. When using a clean vacuum irradiation chamber, the technique might allow ultra-trace determinations, dealing with solid samples of a few milligrams.     

Determination of deuterium in heavy water by secondary deuteron activation

The deuterium concentration of heavy water was determined by utilizing recoiling deuterium nuclei from n-d collisions to induce the reaction (16)O(d, n)(17)F. The internal ratio of 66-sec fluorine-17 to 7.35-sec nitrogen-16 activity, formed by the reaction (16)O(n, p), (16)N, was found to vary linearly with deuterium concentration. When such an internal ratio of activities is measured, the neutron flux and sample weight need not be known. Deuterium was determined over the range from 2.6 to 94.5 atom %, with a relative standard deviation of 2.8%. The effect of sample size was investigated and it was found that the relative amount of fluorine-17 activity formed became less as sample size decreased, due to the loss of recoiling deuterons from the sample. A simple relationship to account for this effect was obtained.     

Studies in heavy ion activation analysis I. on the selection of activation reactions

Among the numerous heavy ion reactions, those of potential interest for chemical analysis can be identified based on their Q values, Coulomb barriers, and threshold energies. A simple computer code has been written for these calculations. The use of the calculated data is illustrated with a survey of the possibilities of HIAA with N⁺, Li⁺, B⁺, Be⁺ and C⁺ beams yielding radioisotopes with half-lives of 10 to 10⁴ sec.     

Nuclear and atomic activation with heavy ion beams

Heavy ion activation has been studied as a method for determining hydrogen. The reactions used [e.g.¹H(⁷Li, n)⁷Be] are the “inverse” of well known reactions [e.g.⁷Li(p, n)⁷Be]. Nuclear activation parameters for the ion beams of interest (⁷Li²⁺,¹⁰B²⁺) have been studied. The analytical feasibility is demonstrated with the determination of hydrogen in titanium at the 100 and 30 ppm levels with relative precisions of 8 to 10%. Detection limits in titanium are in the 0.1 to 0.5 ppm range. Heavy ion bombardment is also accompanied by the emission of characteristic X-rays (“atomic” activation). The parameters governing X-ray emission and background production have been investigated. Experimental K and L X-ray yields from thick targets have been measured for many elements excited by Oⁿ⁺ beams of 0.5 to 7 MeV/amu and Kr⁷⁺ beams of 0.5 to 1 MeV/amu. The simultaneous determination of trace elements at levels of 10 to several 100 ppm in microsamples (∼10⁻⁵ g) is demonstrated on biological specimens. K and L X-ray yields and corresponding detection limits have also been measured with the⁷Li²⁺ and¹⁰B²⁺ beams used for the nuclear activation of hydrogen. With these beams (∼6 MeV/amu) simultaneous nuclear and atomic activation is possible, yielding an unusual multielement trace analysis capability covering hydrogen and medium and high Z elements.     

Hydrogen/deuterium exchange of myoglobin ions in a linear quadrupole ion trap

The hydrogen/deuterium (H/D) exchange of gas-phase ions of holo- and apo-myoglobin has been studied by confining the ions in a linear quadrupole ion trap with D(2)O or CD(3)OD at a pressure of several mTorr. Apo-myoglobin ions were formed by collision-induced dissociation of holo-myoglobin ions between the orifice and skimmer of the ion sampling system. The exchange takes place on a time scale of seconds. Earlier cross section measurements have shown that holo-myoglobin ions can have more compact structures than apo-myoglobin. Despite this, both holo-myoglobin and apo-myoglobin in charge states +8 to +14 are found to exchange nearly the same number of hydrogens (ca. 103) in 4 s. It is possible the ions fold or unfold to new conformations on the much longer time scale of the exchange experiment compared with the cross section measurements.     

Studies in heavy ion activation analysis trace determination possibilities with9Be bombardment

⁹Be induced radioactivation was used to study the trace determination of 19 elements at 3 different ion beam energies (E_lab=14, 32 and 63 MeV⁹Be²⁺). Nine nuclear reactions, yielding radionuclides with half-lives longer than 2.5 m, present potential analytical features. Beside the very sensitive detection of B and N, the multielemental determination of Na, Si, Ca, Sc, and Zn is possible with a⁹Be ion beam of appropriate incident energy. Nuclear interferences have also been investigated and quantified.     

Trace analysis of heavy metal ions by ion chromatography

Summary An ion chromatographic separation technique for heavy metal ions is described. Using pressure-stable, silica-based, ion-exchange supports and standard HPLC equipment with post-column reaction detector high resolution is achieved as well as extremely high sensitivity in the parts per trillion (ppt)-range.     

Water and potassium ion absorption by deuterium oxide resistant winter rye seedlings

The concentrations of deuterium oxide (D2O) in the root tissue water of winter rye seedlings equilibrated with the external D2O concentration within 30 min and in the shoot tissue water after 5-6 h. The equilibrated value in the root water was 87% and in the shoot water, 55% of the external concentration. The K+ absorption rate of the seedlings decreased from a value of 39 to 18 mumol g-1 h-1 when the D2O concentration was changed through a range from 0% to 97%. D2O suppressed the absorption of water and K+ by the seedlings. The higher the D2O concentration the greater the suppression, but it was less than with similarly treated rice plants. However, the process of D2O absorption by the seedlings was similar to that of rice seedlings (Envir. exp. Bot., 24, 369).     

Neutron activation analysis of heavy rare earths

A method of nondestructive activation analysis of heavy rare earth elements (Sm−Lu) is described. Intensities of γ-ray peaks are compared to that of an internal reference after irradiations by both thermal and fission spectrum neutrons. Results are obtained from computer comparisons of peak areas. Work was performed at the Ames Laboratory of the U.S. Atomic Energy Commission. Contribution No. 2895.     

Trace analysis of heavy metals in high purity materials by helium-3 activation analysis

A method is described to determine traces of V, Fe, Ni, Zn, Nb and Mo in high purity matrices of niobium, tantalum and tungsten by non-destructive 14 MeV³He activation analysis. The influence of nuclear and γ-ray interferences in the determination of these elements is discussed.     

Trace element analysis via heavy ion induced X-ray fluorescence

Ohne ZusammenfassungWork supported by the National Science Foundation, Grant MPS 75-17746.     

Hydrogen and deuterium atoms in octasilsesquioxanes: experimental and computational studies

The rate of detrapping of atomic hydrogen from several octasilsesquioxanes is the same for dissolved and solid samples and is independent of the presence of other species such as free radicals or oxygen; varying the cage substituents leads to only minor differences in the activation parameters. Hydrogen atoms are found to be more strongly stabilized in homosubstituted octasilsesquioxanes compared with singly Ge-substituted cages. A kinetic isotope effect observed for the detrapping of H and D from MeT(8) is ascribed to the difference in the zero-point energies of the trapped atoms. There is a secondary H/D isotope effect in the temperature dependence of the (29)Si-superhyperfine splitting constants in the range 228-353 K. Cage relaxation has a substantial effect on the detrapping barrier but little influence on the intracage potential. Calculations using a rigid cage approximation give satisfactory agreement with zero-point parameters extracted from experimental data. Different model chemistries yield qualitatively different pictures of the dependence of the hyperfine coupling constant of the trapped H atom upon the detrapping coordinate. Within an isotropic approximation of the vibrational displacements, the B3LYP data give fairly close agreement with the experimental temperature dependence, subject to a shift of the absolute value related to known weaknesses of the method. For the Si(7)Ge cage, it is found that the transition state in which the H atom passes through a Ge-containing face is strongly favored, accounting for the larger detrapping rate parameters observed experimentally for this species.