James D. Brownridge

INVESTIGATIONS OF PYROELECTRIC GENERATION OF X RAYS

Experiments to study the influences of the environment, external to pyroelectric crystals, on certain measurements to discern the properties of crystals, such as LiTaO3, LiNbO3, and CsNO3, are discussed. During increasing temperature and at appropriate pressures electrons in the vacuum system are accelerated to the −z base of the pyroelectric crystal and are repelled from the +z base of the crystal. The electrons striking the crystal may have sufficient energy to excite x-ray absorption edges of the elements in the crystal and the electrons repelled to a target may have sufficient energy to excite x-ray absorption edges in the elements of the target. During decreasing temperature electrons in the vacuum system are repelled from the −z base whereas the electrons are accelerated to the +z base. The light produced, associated with the pyroelectric effect, appears to come from recombination processes in the gases in the vacuum chamber. The polarization charge produced during the change of temperature of the c...

Self-focused electron beams produced by pyroelectric crystals on heating or cooling in dilute gases

Self-focusing, spatially stable, electron beams are produced by cylindrical pyroelectric crystals such as LiNbO3 in dilute gases on cooling provided that heating is done from the +z base. Beam energies up to 170 keV have been observed. A 4 mm diameter×10 mm crystal heated to 160 °C gives rise to spatially stable beams with a focal length of 22 mm and a 1 mm spot size. Here we present photographic as well as electronic proof of the existence of these electron beams.

Pressure dependence of energetic (≤160 KeV) focused electron beams arising from heated or cooled (LiNbO3) pyroelectric crystals

An interesting effect, “gas amplification of electron energy” is reported here; namely when a cylindrical pyroelectric crystal such as (LiNbO3) is contained in a concentric cylindrical chamber and is heated and then allowed to cool in a dilute gas the maximum energy of the resultant focused electron beam more than doubles as the pressure increases from 0.05 to 4 mTorr for seven different gases.

Observation of multiple nearly monoenergetic electron production by heated pyroelectric crystals in ambient gas

Multiple production of nearly monoenergetic electrons at a given pyroelectric crystal surface charge density is observed on cooling or heating the crystal in ambient gas. Typically, the +z base of a 5 mm diam×5 mm crystal of LiNbO3 is heated to 100 °C and then let cool to 23 °C in dry N2 at 10−2–10−6 Torr. 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 (∼1 μs).

Generation of focused electron beam by pyroelectric and photogalvanic crystals

We have developed a model to explain the phenomena of electron focusing by pyroelectric crystals. The pyroelectric crystals used to compare the experiments with theory were the Fe-doped and undoped LiNbO3. The crystals were either heated from the +z end or illuminated with a laser. Heating the crystals by passing a current through a resistor attached to the +z end produced the pyroelectric effect, a change in polarization in response to a change in temperature. The crystal illumination with a cw solid-state diode-pumped laser (532 nm and 100 mW) produces the photogalvanic current, which creates charges on polar surface of the LiNbO3:Fe. In both cases, the polar ends of the crystal becomes electrically charged and produced self-focusing electron beams that were imaged on a ZnS screen. In addition, we have demonstrated x-ray imaging using the pyroelectric effect.

The radial distribution of 137CS and 40K in tree stems

Abstract Analysis of phloem and successive xylem rings from five trees (American beech, Bitternut hickory, Black locust, Red Oak, Sugar maple) for 137Cs and 40K by gamma‐ray spectrometry showed a positive correlation between the concentration of 137Cs and the sapwood/heartwood boundary in the American beech. There was, however, no correlation between the advent of nuclear weapon testing and the concentration of 137Cs in the xylem of any of the trees studied.

Evidence for neutron production in deuterium gas with a pyroelectric crystal without tip

We present evidence for the production of H2(d,n)3He neutrons in gaseous deuterium by using a pyroelectric crystal as positive ion accelerator. In contrast to previous studies, neutrons were generated without a tip attached to the crystal and without using a solid deuterated target. The deuterium gas provided both the projectile and target nuclei. On the average, 1 neutron/s was obtained in our “hot fusion” experimental setup. No neutrons were detected when a tip was used.

X-ray fluoresced high-Z (up to Z=82) K x rays produced by LiNbO3 and LiTaO3 pyroelectric crystal electron accelerators

High-energy bremsstrahlung and K x rays were used to produce nearly background-free K x-ray spectra of up to 87keV (Pb) via x-ray fluorescence. The fluorescing radiation was produced by electron accelerators, consisting of heated and cooled cylindrical LiTaO3 and LiNbO3 crystals at mTorr pressures. The process of gas amplification whereby the ambient gas pressure is optimized to maximize the electron energy was used to produce energetic electrons which when incident on a W∕Bi target, gave rise to a radiation field consisting of high-energy bremsstrahlung as well as W and Bi K x rays. These photons were used to fluoresce Ta and Pb K x rays.

Use of Tree Bark to Monitor Radionuclide Pollution

The outer surface bark of many trees is an excellent monitoring source of fallout radionuclides. The accumulation and retention of these pollutants is evident by the presence of /sup 106/Ru, /sup 125/Sb, /sup 144/Ce and /sup 155/Eu in the outer layer of bark from many trees surveyed during this study. The accumulation and retention of these and other radionuclides suggest that tree bark is an ecosystem monitoring resource that should be exploited for these and possible other environmental pollutants. Therefore, the emphasis of this study was a broad survey of the detectability of gamma-ray emitting radionuclides in and on tree bark rather than a narrow quantitative study.

Reduced heat flow in light water (H2O) due to heavy water (D2O)

The flow of heat, from top to bottom, in a column of light water can be decreased by over 1000% with the addition of heavy water. A column of light water cools from 25to0°C in 11h, however, with the addition of heavy water it takes more than 100h. There is a concentration dependence where the cooling time increases as the concentration of added D2O increases, with a near maximum being reached with as little as 2% of D2O added. This phenomenon will not occur if the water is mixed after the heavy water is added.