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James Brownridge

Nuclear Instruction Specialist and
Radiation Safety Officer
Office: S2-506
Phone: 607-777-4370



 Conference on Physics, Chemistry and Biology of water- Poster presentation on thermal oscillations in columns of supercooled water ( .pdf, 250 Kb)

Summary of Recent Work:

Pyroelectric Crystal focused Electron Beams and X-Ray Production:

Self-focusing stable electron beams are produced by cylindrical crystal of LiNbO3 and LiTaO3 in dilute gases on warming and cooling. Beam energies up to 170 keV have been observed. A 4mm diameter X 10 mm crystal heated to ~160oC give rise to a stable beam with a focal length of ~22mm. [ pdf file B ] (.pdf, 12KB).  A 5mm X 5 mm crystal give rise to a stable beam with a focal length of ~16mm.       [ pdf file A ] (.pdf, 44KB)

Below the Curie temperature pyroelectric crystals are spontaneously polarized. Under most conditions the polarization is masked by a collection of charge on the surface of the crystal. However, it is possible to create an environment where the polarization is not masked, when this is done the polarization is manifested by the present of a very strong electric field external to the crystal. Changing the temperature of the crystal in a controlled manner will change this field. When this is done in optimum environments, electrons will be accelerated away from the crystal at energies up to 170 keV in a focused beam. [ pdf file C ] (.pdf, 208KB)

Several x-ray fluorescence spectrometers have been designed and built for use in teaching and research. [ pdf file D ] (.pdf, 48KB)

Nearly Monoenergenic Electron Production:

Multiple production of nearly monoenergetic electron at a given pyroelectric crystal surface charge density is observed on cooling or heating the crystal in ambient gas. Typically, the +z base of 4 mm diam X 10 mm crystal of LiNbO3 is heated to 160oC and then let cool to about 23oC at any pressure less than about 8 mtorr. The electron spectrum consists of a series of peaks equally spaced in energy and having decreasing intensity with order superimposed on a continuously decreasing background. The higher order-peaks and the high-energy continuum are due to two or more electrons hitting the surface barrier detector within its resolving time. [ pdf file E ] (.pdf, 16KB)

Profiling Elements in Tree Leaves:

A study of the nutrient elements Mg, Al, Si, P, Ca, S, Cl, Fe and Mn in leaves is in progress. The objective of this study is to develop a week-by-week profile of these elements in leaves. The profile includes the following information: (1) The elements that each tree collects in its leaves. (2) The location in the leaf with the highest concentration, i. e., whether it is on the top, under side or interior of the leaf. (3) The week during the growing season when each element first appears in the leaves of each tree. (4) The change in the relative concentration from week to week. (5) The source of the element i. e., deposition from the atmosphere or the root system of the tree. This profile information for each year will be correlated with environmental conditions for that year. The leaves are collected weekly from first unfolding in early spring until leaf drop in the fall. Five to seven leaves are collected from each tree and immediately dried in vacuum in order to stabilize and preserve the leaves. Leaves are collected from the same tree year after year and for most tree the same branch. These leaves are from 31 trees and 21 species in Broome County, NY. In addition, leaves from most of the 21 species are randomly collected from trees growing throughout the northeastern US from time to time.

A small sample of each leaf is irradiated with low energy electrons provided conveniently and cheaply by a pyroelectric crystal undergoing temperature changes, as was developed in this laboratory. The low energy electrons incident on the surface of the leaf will excite some of the atoms of the trace elements which in turn will emit characteristic x rays upon de-excitation. The energy of the electrons is sufficiently low so that there is not much penetration of the leaf beyond the first surface, certainly to the opposite surface. After collecting data of the characteristic x-rays emitted by the trace elements of the first surface the leaf is turned over and the process is repeated for the second surface. Then the leaf is pulverized and the powder is irradiated with the electrons followed by the emission of the characteristic x-rays of the elements in the interior of the leaf. The x rays are detected by a Si(Li) x-ray detector. [ pdf file F ] (.pdf, 184KB)

Last Updated: 10/6/16