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.     

Operator Ranges in Banach Spaces,I

Let X be a Banach space. A subspace L of X is called an operator range if there exists a continuous linear operator T defined on some Banach space Y and such that TY = L. If Y = X then L is called an endomorphism range. The paper investigates operator ranges under the following perspectives: (1) Existence (Section 3), (2) Inclusion (Section 4), and (3) Decomposition (Section 5). Section 3 considers the existence in X of operator ranges satisfying certain conditions. The main result is the following: if X and Fare separable Banach spaces and T : Y → X is a continuous operator with nonclosed range, then there exists a nuclear operator R:Y→X such that T + R is injective and has nonclosed dense range (Theorem 3.2). Section 4 seeks to determine conditions under which every nonclosed operator range in a Banach space is contained in the range of some injective endomorphism with nonclosed dense range. Theorem 4.3 contains a sufficient condition for this. Examples of spaces satisfying this condition are c₀, l_p (1 < p < ∞), L_q (1 < q < 2) and their quotients. In particular, this answers a question posed by W. E. Longstaff and P. Rosenthal (Integral Equations and Operator Theory 9 , (1986), 820-830. Section 5 discusses the possibility of representing a given dense nonclosed operator range as the sum of a pair L_1, L₂ of operator ranges with zero intersection in the cases where (a) L₁ and L₂ are dense, (b) L₁ and L₂ are closed. The results generalize corresponding results, for endomorphisms in Hilbert space, of J. Dixmier (Bull. Soc. Math. France 77 (1949), 11-101 and P. A. Fillmore and J. P. Williams (Adv. Math. 7 (1971), 254-281. A final section is devoted to open problems.     

Megawatt, 330 Hz PRF tunable gyrotron experiments

Repetitively pulsed and cw gyrotrons have hitherto used thermionic cathodes, whereas cold cathode gyrotrons have normally operated as single shot devices. The novel results presented here show that cold cathode gyrotrons can be successfully pulsed repetitively. A tunable gyrotron with a pulse repetition frequency (PRF) of 150Hz is demonstrated. This system developed >4MW mm-wave output pulses at 100GHz. The gyrotron is based on a two-electrode configuration comprising a field-immersed, field emission, cold cathode and a shaped anode cavity. A superconducting magnet was used to produce the homogeneous intra-cavity magnetic field and a cable pulser was used to drive the electron beam. This pulser produced up to a (200±20)kV pulse with 10ns rise time, a 100ns flat top, a 10ns decay with a characteristic impedance of 200. The energy storage capacity of the cable pulser was 35J. The charging unit limited the maximum PRF to 330Hz. Due to spark gap switching limitations 330Hz was only obtainable in 5 to 10 pulse bursts. For substantial periods of the order of 30 seconds, 100Hz PRF was achieved over an oscillating range of 28 to 100GHz and 150Hz PRF was achieved at 80GHz. No degradation effects on the mm-wave output pulse was evident due to diode recovery time throughout this series of results. A subsequent conclusion is that the diode recovery time in our cold cathode gyrotron is less than 3ms.     

Density-functional theory structures of 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid complexes for ions across the lanthanide series

The use of organically chelated lanthanides in diagnosis and treatment is a rapidly growing field in medicine. In order to gain a deeper understanding into the properties of these chelates, particularly spectroscopic, density-functional calculations have been performed on a series of lanthanide ions chelated with 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid. Based on the results of these calculations, it has been concluded that the local symmetry experienced by the chelated lanthanide ion may be treated as being axial, which will make the interpretation of their spectroscopic properties greatly simplified. It has also been suggested that the so-called "capping" water molecule at the ninth coordination position of the lanthanide is hydrogen bonded to the acetate oxygens of the sidearms, rather than coordinated as the ninth ligand of the lanthanide.     

Separation of Dihydrofolate Reductase Inhibitors by RP-HPLC and Comparison with Capillary Zone Electrophoresis

The dihydrofolate reductase inhibitors (DHFRIs) are a group of antibiotic compounds with closely related chemical structures. A previous attempt to separate the eight compounds by CZE was successful, but only at low pH (2.1) and high buffer concentration (250mM phosphate). As a result, baseline noise was high. Additionally, baseline resolution was not quite achieved and the separation took 25 minutes. However, the size-based separation indicated that reversed-phase HPLC might be a good alternative. A three-dimensional overlapping resolution mapping (OR_sM) scheme utilised pH, flow rate and percentage organic modifier (for both methanol and acetonitrile). Clear generalised outcomes were observed under isocratic conditions. At higher pHs, where the analytes were largely unionised, retention was excessive. At higher percentages of MeOH or ACN, the more-difficult-to-separate components were poorly resolved. On the other hand, low pHs (2.5 in 50mM phosphate) with low percentages of the organic modifiers (7% ACN or 11% MeOH) but high flow rates (2.3mLmin^–1) yielded better than baseline resolution in 17 minutes. A partially optimised gradient run (at pH 6.5) again yielded far better than baseline resolution in 12 minutes, but required 4 minutes re-equilibration. Hence, the HPLC separations are superior to the CZE separation in all of runtime (40%), resolution and limit of detection (down by 6).     

Salt effects in capillary zone electrophoresis. V. Adsorption and retention of electrically neutral analytes

Two electrically neutral analytes previously observed to be separated from the neutral marker in capillary zone electrophoresis (CZE) experiments [sulphanilamide (SAA) and sulphaguanidine (SGW)] have been examined to determine the basis for separation. The degree of separation increases markedly with buffer concentration and improves with increasing field strength. On the basis of the apparent electrophoretic mobilities in conventional CZE, migration times in a zero EOF environment were calculated for SAA, SGW and six other sulphonamides that were known to be ionized. These six markers were used to test the legitimacy of our predictions and to correct for small discrepancies between the predicted and observed migration times. It was concluded that SAA and SGW have negligible electrophoretic mobilities and that they are retained in the electrical double layer close to the capillary wall. A mechanism for adsorption is proposed and the generality of the phenomenon is discussed.     

Surface-enhanced Raman scattering from ordered Ag nanocluster arrays

We have examined the effect of ordered silver nanocluster substrates on the surface-enhanced Raman spectrum of rhodamine 6G (R6G). Triangular shaped silver nanocluster arrays with order on the approximately 100 mum range were prepared using nanosphere lithography. Direct comparisons of R6G surface-enhanced Raman spectroscopy (SERS) signals between ordered nanocluster regions and amorphous Ag regions prepared under identical deposition conditions provide strong evidence of an electromagnetic field enhancement attributed to the unique nanocluster morphology. We have obtained order of magnitude enhancement factors for both 200 and 90 nm Ag nanocluster SERS substrates relative to Ag films.     

2,-5-diselena-3,3,4,4-tetrafluorohexane and 2,5-diselena-1,1,1,6,6,6-hexafluorohexane and their platinum and palladium chloride complexes

The diselenoethers, CH₃SeCF₂CF₂SeCH₃ and CF₃SeCH₂CH₂ SeCF₃ are described. 1:1 Complexes are formed between these ligands and platinum(II) and palladium(II) chloride.