The bounce resonance heating of low-energy electrons in capacitively coupled discharges

Electron energy distribution functions (EEDFs) were measured with increasing discharge voltages in hydrogen capacitively coupled plasmas by means of radio-frequency compensated Langmuir probe. The results are compared with EEDF in argon plasmas. It was found that, in the hydrogen capacitive discharge, abnormally low-energy electrons became highly populated and the EEDF evolved to a non-Maxwellian distribution as the discharge voltage was increased. This voltage dependence of the EEDF in the hydrogen is contrary to argon capacitively coupled plasma, where at high discharge voltage, low-energy electrons are significantly thermalized due to γ heating and the EEDF evolves to the Maxwellian distribution. The highly populated low-energy electrons at high gas pressure, which was not observed in capacitively coupled argon plasma, show that the γ heating mechanism is somehow inefficient in terms of the molecular gas in capacitive discharges. It appears that this inefficient γ heating seems to be attributed to an efficient vibrational excitation in hydrogen capacitive plasma.

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Transfer optics for high spatial resolution electron spectroscopy

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100105394 ◽

1988 ◽

Vol 46 ◽

pp. 666-667

Author(s):

G. G. Hembree ◽

Luo Chuan Hong ◽

P.A. Bennett ◽

J.A. Venables

Keyword(s):

Magnetic Field ◽

Scanning Transmission Electron Microscope ◽

Low Energy ◽

Objective Lens ◽

State University ◽

Arizona State University ◽

Initial Field ◽

Resolution Electron ◽

Scanning Transmission ◽

Low Energy Electrons

A new field emission scanning transmission electron microscope has been constructed for the NSF HREM facility at Arizona State University. The microscope is to be used for studies of surfaces, and incorporates several surface-related features, including provision for analysis of secondary and Auger electrons; these electrons are collected through the objective lens from either side of the sample, using the parallelizing action of the magnetic field. This collimates all the low energy electrons, which spiral in the high magnetic field. Given an initial field Bi∼1T, and a final (parallelizing) field Bf∼0.01T, all electrons emerge into a cone of semi-angle θf≤6°. The main practical problem in the way of using this well collimated beam of low energy (0-2keV) electrons is that it is travelling along the path of the (100keV) probing electron beam. To collect and analyze them, they must be deflected off the beam path with minimal effect on the probe position.

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Preincubation with Sn-complexes causes intensive intracellular retention of 99mTc in thyroid cells in vitro

Nuklearmedizin ◽

10.3413/nukmed-0450-11-12 ◽

2012 ◽

Vol 51 (05) ◽

pp. 179-185 ◽

Cited By ~ 3

Author(s):

M. Wendisch ◽

D. Aurich ◽

R. Runge ◽

R. Freudenberg ◽

J. Kotzerke ◽

...

Keyword(s):

Cell Model ◽

Low Energy ◽

Thyroid Cells ◽

Low Energy Electrons ◽

A Cell ◽

Vitro Model ◽

Uptake Studies ◽

Radiobiological Effects ◽

Radioactivity Retention

SummaryTechnetium radiopharmaceuticals are well established in nuclear medicine. Besides its well-known gamma radiation, 99mTc emits an average of five Auger and internal conversion electrons per decay. The biological toxicity of these low-energy, high-LET (linear energy transfer) emissions is a controversial subject. One aim of this study was to estimate in a cell model how much 99mTc can be present in exposed cells and which radiobiological effects could be estimated in 99mTc-overloaded cells. Methods: Sodium iodine symporter (NIS)- positive thyroid cells were used. 99mTc-uptake studies were performed after preincubation with a non-radioactive (cold) stannous pyro - phosphate kit solution or as a standard 99mTc pyrophosphate kit preparation or with pure pertechnetate solution. Survival curves were analyzed from colony-forming assays. Results: Preincubation with stannous complexes causes irreversible intracellular radioactivity retention of 99mTc and is followed by further pertechnetate influx to an unexpectedly high 99mTc level. The uptake of 99mTc pertechnetate in NIS-positive cells can be modified using stannous pyrophosphate from 3–5% to >80%. The maximum possible cellular uptake of 99mTc was 90 Bq/cell. Compared with nearly pure extracellular irradiation from routine 99mTc complexes, cell survival was reduced by 3–4 orders of magnitude after preincubation with stannous pyrophosphate. Conclusions: Intra cellular 99mTc retention is related to reduced survival, which is most likely mediated by the emission of low-energy electrons. Our findings show that the described experiments constitute a simple and useful in vitro model for radiobiological investigations in a cell model.

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