Stephen M. Shafroth

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).

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.

Substantial increase in acceleration potential of pyroelectric crystals

We report on a substantial increase in the acceleration potential achieved with a LiTaO3 pyroelectric crystal. With a single 2.5 cm diameter and 2.5 cm long z-cut crystal without electric field-enhancing nanotip we produced positive ion beams with maximal energies between 300 and 310 keV during the cooling phase when the crystal was exposed to 5 mTorr of deuterium gas. These values are about a factor of 2 larger than previously obtained with single pyroelectric crystals.

High resolution electron spectroscopy at nonzero degree observation angles

Abstract An electron spectrometer has been developed for the study of Auger electrons ejected from fast (MeV) ion beams at nonzero degree observation angles in high resolution. The analyzer is a double pass 30° parallel plate analyzer equipped with a chevron microchannel plate detector with resistive anode readout for position sensitive detection of electrons in the focal plane. High resolution is obtained through second order focusing of projectile electrons at an observation angle of 9.6° and through deceleration of these electrons before energy analysis. Spectra have been acquired for O q + + H 2 , He and Ne ( q = 3, 4 and 6) for ion ener ranging from 6 to 22 MeV. Various processes such as excitation, ionization, capture, capture plus ionization, and capture plus excitation are identified for different incident charge states. Performance of the spectrometer is discussed along with its capabilities and limitations.

Radiative Electron Capture (REC) as an Indicator of the K-Vacancy State of Highly Ionized Projectiles in Solids: Application to Stopping Power

Radiative electron capture (REC) has been studied at the Tandem Accelerator Center,Tsukuba University. The NEC 12 UD tandem and sputter ion source provided na beams of Clq+ ranging from 17+, 16+, 10+, 8+ and 7+ at energies of 120,95 and 80-MeV which were incident on C targets of varying thickness. The object of this work was to extend to higher energies and charge states the REC target thickness studies which had been done at TUNL. In this report the data on REC cross sections, centroid energies and widths vs. target thickness are given and discussed qualitatively. The relevance of such studies to target thickness dependence of stopping power is demonstrated.

Alignment effects in fast ion-atom collisions

Abstract Angular distribution of Auger electrons and X-rays, and X-ray polarization in high energy ion-atom collisions, measured in the last few years, are reviewed. The excitation mechanisms of interest are the resonant and nonresonant transfer and excitation (RTE and NTE respectively), capture, ionization, excitation and transfer ionization. An alignment of the excited states formed through these excitation mechanisms is often observed and seems to be strongly dependent on the excitation mechanism.

Possible two-electron excitations in C3+ following 1 MeV/u collisions with atomic targets; Z=2, 10, 18 and 36

Auger electrons emitted from Li-like Carbon projectiles excited during I MeV/u collisions with atomic targets (Z = 2, 10, 18 and 36) have been measured. As a function of the target Z, we observe the yieldsof singly and doubly excited autoionizing configurations (Al) of C[sup 3+] excited during the collision that decay to the (1s[sup 2]([sup 1]S) + e[sub c][ell][sub c])[sup 2]L ground state. The investigation focuses on Auger electrons emitted with energies between 220 and 260 eV in the projectile reference frame. In addition to the singly excited (1s2s2[ell])[sup 2]L AI configurations expected from projectile 1s electron excitation, doubly excited states to the (1s(2p[sup 2])[sup 1]D)[sup 2]D and (1s(2p[sup 2])[sup 1]S)[sup 2]S are also observed with increasing intensities in going from He to the higher Z targets. If the [sup 2]D and the [sup 2]S peaks are the result of two-electron excitations, it may be possible to investigate this aspect of the collision using some of the recent approaches taken in studying the excitations of the two electrons in He targets.