J.D. MacArthur

A Heavy Water Detector to Resolve the Solar Neutrino Problem

Abstract The observation of the following three reactions: νed→ppe; νxe→νxe; and νxd→νxpn (where νx is any left- handed neutrino) in a heavy water Cerenkov detector which is being designed, allows the solar 8B ve flux, spectrum and direction to be measured. In addition, the total solar 8 Bν c neutrino flux, direction and integral spectrum, independent of neutrino flavor, may be determined to provide several independent methods to resolve the solar neutrino problem.

An improved experimental setup for the simultaneous PIXE analysis of heavy and light elements with a 3 MeV proton external beam

The external beam line of the AGLAE IBA facility at the Laboratoire de Recherche des Musees de France is of particular relevance for the analysis of works of art and archaeological artefacts. In order to reduce both target damage and acquisition time, we perform the simultaneous analysis of light (5 < Z < 30) and heavy elements by PIXE with 3 MeV protons, using two Si(Li) X-ray detectors. To achieve this goal, we have made the following improvements to the experimental setup. (i) To protect the low energy dedicated Si(Li) crystal from the backscattered protons which could markedly alter its resolution, a compact magnetic deflector has been designed and placed along the outgoing X-ray path. (ii) The ultrathin detector window is shielded against visible light by a 100 μg/cm2 carbon foil. (iii) To reduce the angular straggling of the backscattered particles and to keep a good X-ray transmission for elements down to carbon, the whole system is flooded with He or H gas. In this paper, we present different tests and preliminary results obtained with this setup.

The alpha widths of the 5603, 5605 and 5668 keV states in 18F

Abstract A differentially pumped gas target has been used for high resolution studies of the 14 N( α , α ) 14 N differential cross section in the region of 5650 keV excitation energy in 18 F. Interference anomalies in the excitation functions were observed at energies corresponding to levels at 5603, 5605 and 5668 keV in 18 F. The data were analysed using the R -matrix formalism, and the level parameters of the resonances were determined to be Γ α = 42.8 ± 1.6 eV, l α = 0; Γ α = 32.0 ± 2.1 eV , l α = 1 ; and Γ α = 130 ± 5 eV, l α = 1 for the 5603, 5605 and 5668 keV states respectively. The isospin mixing between the 5605 and 5668 keV levels and the possibility of studying the parity mixing between the 5603 and 5605 keV levels are discussed.

Trace element fingerprinting of emeralds by PIXE/PIGE

Abstract Gemologists consider the mineral beryl, beryllium aluminium silicate, to be the gem, emerald, when it contains sufficient chromium, > 0.1%, to colour it a strong green. Emeralds usually contain other trace elements. To investigate the feasibility of distinguishing an emeralds country of origin through its trace content, the trace elements in emeralds and a few beryls from sixteen locations have been determined with a single nondestructive measurement using PIXE and PIGE. From the database established with this limited number of samples, distinguishing trace element patterns were found.

Elemental analysis of algae with PIXE and PIGME

Abstract With an external proton beam, layers of algae a few μm thick produced by the simple procedure of filtering fixed amounts of a colony onto millipore filters have been examined. The biological aspects of the investigation dealt with the influence of F− on the growth of the algae; therefore proton inelastic scattering was used in addition to PIXE for the elemental analysis. Since the samples were thin (∼8 μm), the broad resonance structure in the 19 F( p , p ′γ) 19 F yield curve at Ep=2.03 Me V was used to increase the sensitivity. A sensitivity of 10 ppm was reached for these thin specimens, quite adequate to show that the algae take up fluorine from the environment. With beams of a few nanoamperes, the counting rate for all elements was found to decrease linearly with flux, reaching 70% of the initial value after about 1000 s. The concentration of fluorine in the algae was found to be proportional, up to 150 ppm, to the F− ion concentration in the nutrient. For one species of algae, S. leopoliensis, the presence of fluoride ion in the nutrient caused a marked change in the growth pattern. Furthermore, this change was found to be correlated with the concentration in the algae of one essential element, potassium, which the algae seemed to lose and then recover.

External PIXE and mu-PIXE measurements of elemental concentrations in volcanic rocks

Abstract PIXE measurements have been performed on volcanic rocks, using external 3 MeV proton beams of 50 to 200 μm diameter, at the KN3000 Van de Graaff accelerator of the Physics Department of the Florence University. Two or more Si(Li) detectors are used during each run and the elemental composition is computed from the peak areas obtained in the different detectors with an absolute procedure whose reliability has been checked by analyzing several geological standards. In order to obtain solid-liquid partition coefficients of trace elements, the groundmass composition has been determined by directly bombarding standard polished rock sections mounted on a glass support.

The 18O(p, α)15N cross section at low energies

Abstract The 18 O(p, α) 15 N reaction cross section has been measured over the energy range 661 keV > E c.m > 223 keV. The S -function was extrapolated to energies of astrophysical interest using the R -matrix theory. The S -factor, S 0 , is estimated to be 46 MeV · b which is a factor of 3 larger than the value used in a recent tabulation of nuclear reaction rates. The effects of broad levels near the proton threshold are discussed.

Element concentrations from overlapping X-ray spectra

Abstract Minimum detection limits for elements with Z ∼ 60 using L X-rays are predicted to be ~ 1 ppm for reasonable amounts of charge collected. In practical situations, especially when measuring the rare earth elements, the detection of a particular element is limited by the complexity of the spectrum and the amount of the other elements present. Consequently, a stripping procedure for determining the concentrations of many elements whose X-ray spectra overlap has been developed to test the detection limits for such cases. It is based on an accurate determination of the response function of the system to a single element. The procedure has been applied to the measurement of the REE in artificial and natural minerals. For the dominant elements at the level of a few hundred ppm an accuracy of 10% in the concentration can be achieved, while a detection limit of a few tens of ppm for the heavier elements in a complex spectrum dominated by the light rare earth elements is possible.

Element analysis of algae treated with F− or arsenite

Abstract The multi-element analysis by proton induced X-ray emission and proton induced γ-ray emission has been used to follow the element concentrations in algae when the toxins F− or arsenite were added to their growth medium. The analysis was done in air on cells deposited on thin filters. Both toxins produced a lag phase in the growth curve of the culture. The F concentration rose initially and then decreased, suggesting that the cells adapted by expelling the toxin. Furthermore, with F−, the concentrations of other elements, except K for which there was almost a complete loss in a medium of 150 ppm F, follow the changes observed in an untreated culture. The level of As initially rose and then remained constant. No changes in the concentrations of the other elements caused by this toxin were observed. In an attempt to determine whether As was tightly bound to a large molecule in the cell, the filtered algae were treated with several reagents and the concentration of As left in the algae was determined. The results indicated that As is not immobilized in the cells.

Bulk elemental analysis using γ rays from inelastic scattering of neutrons produced by the 13C(α,n)16O reaction

Abstract The 2H(d, n)3He, 7Li(p, n)7Be, 9 Be(α, n) 12 C and 13 C(α, n) 16 O reactions are compared for suitability as a neutron source for bulk multielement analysis by inelastic neutron scattering. The 13C(α, n)16O reaction at Eα = 3.4 MeV is found to be the most su ble, with minimum detection limits at least a factor of 2 better than the other reactions. Minimum mass detection limits for twenty-nine elements are presented. An example of the application of the technique to non-destructive analysis of a glass archaeological specimen is given.