1. Nesamostatné elektrické výboje

2. Nesamostatné elektrické výboje
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3. V slabom elektrickom poli môže atmosférou na zemskom povrchu pretekať len velmi slabý prúd s hustotami až 10-6 A/m2 v dôsledku ionizácie zpôsobenej radioaktivným žiarením Zeme a kozmickým žiarením vesmíru. ,
Týmto spôsobom sa v 1 cm3 zemskej atmosféry vytvára asi iónových párov za 1 s. Rovnovážna koncentrácia náboja je 103 – 104 el. nábojov na cm3. Pre vedenie elektrického proudu väčšej hustoty je treba dodatočné ionizačné činidlo a výboje vyvolané týmto spôsobom nazývame nesamostatné.

4. 5 hlavných zdrojov ionizácie pozadia:
Kozmické (galaktické) žiarenie
Slnečné žiarenie
Rádioaktívne žiarenie zo zemskej kôry
Rádón (v USA je radón po fajčení druhým najdôležitejším dôvodom k vzniku rakoviny pľúc)
Ionizujúce žiarenie v dôsledku ľudskej činnosti

6. Svensmark, H. , T. Bondo, and J
Svensmark, H., T. Bondo, and J. Svensmark (2009), Cosmic ray decreases affect atmospheric aerosols and clouds, Geophys. Res. Lett.,.
Our results show global-scale evidence of conspicuous influences of solar variability on cloudiness and aerosols.
From solar activity to cosmic ray ionization to aerosols and liquid-water clouds, a causal chain appears to operate on a global scale.

7. Volt-ampérová charakteristika nesamostatných výbojov
prúd v dôsledku ionizácie pozadia, Townsendov el. výboj (tmavý el. výboj)

8. Aplikácie nesamostatných el. výbojov
Pri prúdoch menších než saturačný prúd, alebo v oblasti saturčného prúdu – napr. ionizačné detektory dymu
Americium 241

9. Ionizácia nárazom elektrónu – 1. Townsendov koeficient
je počet ionizačných zrážok, ktoré elektrón vykoná na jednotkovej dráhe (1 cm) pri pohybe v smere elektrickéo poľa.
Elektrónová lavína

11. Proporcionálne detektory/počitače
Zachovávajú priamu úmeru medzi počtom elektrónov vzniklých ionizáciou nárazom častice s vysokou energiu a počtom elektrónov vzniklých ionizáciou nárazom elektrónu – t.j. zachovávajú priamu úmeru medzi energiou častice, ktorá sa uvolní medzi elektródami a prúdovým signálom.
Nemeriame prúd vzniklý dopadom nabitých častíc na elektródy, ale indukovaný prúd !
Lama-Shockley teorém

12. Detector theory
In gas-flow and sealed detectors, X-rays produced from the sample ionize an inert detector gas, ejecting an outer shell electron to produce an electron-ion pair (Ar –> Ar+ + e-). The first ionization potentials of the inert gases are small (less than 25 eV); however, the effective ionization potential that is required to produce an electron-ion pair is somewhat higher due to competing processes which absorb incident photon energy without causing ionization.
The average number of electron-ion pairs (n) produced by an X-ray is:
1st Ionization
Potential
Average
Ionization He
24.5 eV
27.8 eV Ar
15.7
26.4 Xe
12.1
20.8

13. Consider: the energy of Cu-Ka is 8
Consider: the energy of Cu-Ka is 8.04 keV, so, using Ar detector gas, n = 8040/26.4 = 304 primary electron-ion pairs. This number is too small to detect, but placing a potential across the gas from wire to tube wall produces amplification. The electrons produced by the incoming X-ray are accelerated towards the anode wire by the detector voltage and can in turn ionize other Ar atoms producing another electron-ion pair and so on (Figure). This "avalanche" effect produces an amplification of the initial signal. The chain of ionizations causes a momentary voltage across the detector producing a pulse.
Figure. Principle of detection of an X-ray photon. Incident X-rays ionize the Ar detector gas losing an average of 26.4 eV, then continue to ionize other atoms. The resulting secondary electrons are accelerated toward the detector wire, gaining sufficient energy to ionize other Ar atoms, producing an electron avalanches. The Ar ions are neutralized by electrons donated by methane molecules in the detector gas mix.

14. The amount of amplification produced by the gas depends on the amount of voltage applied to the detector (Figure). At very low voltages in the region of undersaturation, the detector potential difference is too small to prevent recombination of electron-ion pairs formed by incident X-rays before they reach the collecting wire. At slightly higher voltages in the ionization chamber region, the potential is just sufficient to counter recombination so that the number of electron-ion pairs produced by X-rays equals the number reaching the anode wire, and the gain is 1. Further increases in the detector voltage produce the avalanche effect and significant gains. At voltages in the proportional counter region, the pulse height is proportional to the energy of the incident X-ray. Too high a voltage drives the detector out of the proportional region and into the Geiger region.
Figure. The effect of increasing the applied anode voltage on (a) the gas amplification factor and (b) the observed count rate (ignoring pulse height analysis settings) for a gas proportional counter. Note the rapid increase in observed count rate at the threshold of Geiger breakdown (after Potts 1987).

15. Gain may be defined as:
Detector gains are typically on the order of 104 to 105. With a gain of 104, the 304 EI pairs formed by a Cu-K X-ray produce 3.04 x 106 electrons that reach the anode wire. The size of the resulting pulse can be calculated from:
The charge on a single electron is x coulomb, and a typical detector has a capacitance of farad. Thus, our Cu-K photon will generate a voltage of:
Recall that we've assumed a gain of 10,000! The resulting pulse is still very small and needs further electronic amplification.

16. Nobelova cena za fyziku 1992
Observing the interior of matter
In order to explore the remarkable processes in the interior of matter, detectors of very high precision and performance are needed. Georges Charpak's invention of a new particle detector – the multiwire proportional chamber – has dramatically changed the exploration of the world of particles.
Georges Charpak CERN, Geneva, Switzerland

17. Charpak's invention
With the multiwire chamber it became possible to determine the tracks of charged particles – the smallest constituents of matter – with great precision. However, the success of Charpak's multiwire chamber depended mainly on the enormous increase in data-taking rate.
Every single wire in the multiwire chamber acts as a detector. A wire can detect thousands of particles per second. This makes it possible to study even very rare processes in the world of particles.

18. The electron avalanche in the detector
A charged particle passing through a gas ionises the atoms of the gas. The atoms split into a negatively charged electron and a positively charged ion. In an electrical field the electrons will move towards the anode and the ions towards the cathode. At the anode an avalanche of electrons is produced indicating the passage of the original particle.
The particle ionises the gas In Charpak's invention the anode consists of a large number of parallel wires, normally a hundredth of a millimetre in diameter and one or a few millimetres apart. The cathode consists of an electrically conductive plane on each side of the densely packed anode wires.
The charges move In the electrical field the liberated electrons rapidly move towards the anode wire and the ions move towards the cathode planes. The electrons are accelerated in the strong field near the anode wire.
The electron avalanche More electrons are liberated which in their turn ionise the gas – an avalanche of charges is produced, giving rise to an electric pulse on the anode wire. The proportional chamber is so called because the pulse is proportional to the original amount of ions. .

19. Each anode wire can handle several hundred thousand signals per second
Each anode wire can handle several hundred thousand signals per second. This is of great importance when rare particle collisions are studied. Sometimes only one particle collision in a million is particularly interesting.

20. The multiwire chamber
Charpak realised from the beginning that there were several ways to further develop the multiwire chamber. The most important development was the drift chamber. This is used to measure the time taken for liberated electrons to drift to the anode. In this way precision was further improved.     The multiwire chamber – both the proportional chamber and the drift chamber – is now in use in practically every experiment in particle physics laboratories. These detectors are also used in medicine as a complement to X rays.

21. Six quarks and six leptons
Charpak's principle has been used in the DELPHI detector at CERN. The barrelshaped detector is 10 m long and 10 m in diameter. The tracks of the many charged particles created when an electron collides with its antiparticle, the positron, appear on the computer reconstructed picture. By studying such particle collisions, research groups at CERN and SLAC, USA have shown that the fundamental constituents of matter are six types of quark and six types of lepton, one of which is the electron.

22. The J/Yparticle
W and Z
At the same time as Burton Richter discovered the Y (psi) particle, Samuel C.C. Ting, USA discovered the J particle. They were shown to be the same particle, now called the particle. For this discovery Richter and Ting received the Nobel Prize in Physics 1976.
The observed mass of the particle of 3.1 GeV corresponds to the mass of slightly more than three protons. The necessary precision was obtained thanks to the proportional chamber.
The discovery of the W and the Z particles was rewarded with the Nobel Prize in Physics in 1984 (Carlo Rubbia and Simon van der Meer, CERN). The particle collision in which the Z particle is created and then rapidly decays into an electron and its antiparticle, the positron, can be seen in the middle of the picture. The tracks of all the charged particles are detected in the central drift chamber. The Z particle is only created in one particle collision in a thousand million.

23. Y (epsilon) particle A rat brain
The Y (epsilon) particle was discovered in 1977 by Leon Lederman and his research group. The 22 proportional chambers played a very important role in the experiment. In the two 'arms' muons, into which the very short-lived particle decays, were detected.
A five-thousandth-of-a-millimetre-thick slice of a rat brain. The colours illustrate the concentration of molecules sensitive to radiation. With Charpak's detectors this picture could be produced in a day compared to three months with traditional methods.

24. Lavínový tranzistor

25. TOWNSENDOW VZTAH - uvažujeme nízke tlaky plynu, kde výboj prebieha podľa Townsendovho ionizačného mechanizmu

26. d.c. voltage current characteristic at an electrical discharge with
A B
Townsend dark
Abnormal
Glow
Transition from
Glow to Arc
Dark to Glow
discharge
CURRENT (AMP)
APPLIED
VOLTAGE
(VOLTS) C D E F G
Arc
10-15
10-12
10-9
10-6
10-3 1
103
250
500
d.c. voltage current characteristic at an electrical discharge with
electrodes having no sharp points or edges