Gaseous Medium Physical Concepts - Revision history

Abdehait: /* Diffusion */

2015-06-23T14:54:38Z

Diffusion

Abdehait: /* Diffusion */

2013-09-06T16:07:57Z

Diffusion

Abdehait: /* Diffusion */

2013-09-06T16:07:41Z

Diffusion

Abdehait: /* Multiplication */

2013-09-04T14:07:43Z

Multiplication

Abdehait: /* Boundary Element Method (BEM) */

2013-09-04T14:06:54Z

Boundary Element Method (BEM)

Abdehait: /* ion Diffusion */

2013-09-04T14:05:16Z

ion Diffusion

Abdehait: /* Townsend's Coefficients */

2013-09-04T01:33:07Z

Townsend's Coefficients

Abdehait: /* Diffusion */

2013-08-29T22:41:48Z

Diffusion

Abdehait: /* Ionization in fission chambers */

2013-08-29T22:10:49Z

Ionization in fission chambers

Abdehait: /* Ionization in fission chambers */

2013-08-29T21:56:01Z

Ionization in fission chambers

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 =Diffusion=
-;Main differences between electrons and ions behavior in a gas <ref name="Mason">Mason, Edward A. and Earl W. MacDaniel. 1988. Transport Properties of Ions in Gases. John Wiley & Sons. </ref>
+;Main differences between electrons and ions behavior in a gas <ref name="Mason">Mason, Edward A. and Earl W. MacDaniel. 1988. Transport Properties of Ions in Gases. John Wiley & Sons. QC717.5 I6 M37 </ref>
 Studying diffusion and mobility  of  charged particles in a gas is classified in to two main groups, ion and electron diffusion and mobility. They are conceptually similar, but they have many differences. First, The ratio between the mass of the electrons and the gas atoms is very small, so with a few eV work done by the electric field, the electrons will gain a high velocity compared to that of the ions that are accelerated under the same electric field. Also, the probability of low energy electrons to make an interaction is higher than that of the low energy ions, the electron interactions are a supported with accurate calculations for the electron drift velocity. Electrons at low energy have the ability to produce vibrations and excitations in the gas atoms or molecules which are measured within the lab frame, but low energy ions have very low cross sections for most of the interactions with a gas atoms or molecules. When interactions happen, a complexity appears in measuring the ion interactions' products, but the calculations are simpler for  the velocity distribution for the electrons in many gases, since the ratio between a gas atom or molecule mass to the electron mass is very small. Since Producing electrons is simpler than producing ions in a gas,  many interactions are responsible for producing electrons, such as thermionic emission, photoemission, or radioactive decay. On the other hand,  creating an ion requires electron bombardment, photo-ionization or an electric discharge which requires more sophisticated conditions for the experiment and they are not as sensitive as the electrons for the the non-uniformity of the electric field, electric potential and magnetic field. Finally, the existence of the impurities is always a concern; the ions lose most of their energy in the molecular level, but the electron energy loss  within the atomic level in a pure gas, as a result, the ionic velocity distribution is not affected by the existence of these impurities except for some cases related to a highly accurate ionic studies in gases.

← Older revision		Revision as of 16:07, 6 September 2013
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	;Main differences between electrons and ions behavior in a gas <ref name="Mason">Mason, Edward A. and Earl W. MacDaniel. 1988. Transport Properties of Ions in Gases. John Wiley & Sons. </ref>		;Main differences between electrons and ions behavior in a gas <ref name="Mason">Mason, Edward A. and Earl W. MacDaniel. 1988. Transport Properties of Ions in Gases. John Wiley & Sons. </ref>

−	Studying diffusion and mobility of charged particles in a gas is classified in to two main groups, ion and electron diffusion and mobility. They are conceptually similar, but they have many differences. First, The ratio between the mass of the electrons and the gas atoms is very small, so with a few eV work done by the electric field, the electrons will gain a high velocity compared to that of the ions that are accelerated under the same electric field. Also, the probability of low energy electrons to make an interaction is higher than that of the low energy ions, the electron interactions are a supported with accurate calculations for the electron drift velocity. Electrons at low energy have the ability to produce vibrations and excitations in the gas atoms or molecules which are measured within the lab frame, but low energy ions have very low cross sections for most of the interactions with a gas atoms or molecules. When interactions happen, a complexity appears in measuring the ion interactions' products, but the calculations are simpler for the velocity distribution for the electrons in many gases, since the ratio between a gas atom or molecule mass to the electron mass is very small. Since Producing electrons is simpler than producing ions in a gas, many interactions are responsible for producing electrons, such as thermionic emission, photoemission, or radioactive decay. On the other hand, creating an ion requires electron bombardment, photo-ionization or an electric discharge which requires more sophisticated conditions for the experiment and they are not as sensitive as the electrons for the the non-uniformity of the electric field, electric potential and magnetic field. Finally, the existence of the impurities is always a concern; the ions lose most of their energy in the molecular level, but the electron energy loss within the atomic level in a pure gas, as a result, the ionic velocity distribution is not affected by the existence of these impurities except for some cases related to a highly accurate ionic studies in gases.	+	Studying diffusion and mobility of charged particles in a gas is classified in to two main groups, ion and electron diffusion and mobility. They are conceptually similar, but they have many differences. First, The ratio between the mass of the electrons and the gas atoms is very small, so with a few eV work done by the electric field, the electrons will gain a high velocity compared to that of the ions that are accelerated under the same electric field. Also, the probability of low energy electrons to make an interaction is higher than that of the low energy ions, the electron interactions are a supported with accurate calculations for the electron drift velocity. Electrons at low energy have the ability to produce vibrations and excitations in the gas atoms or molecules which are measured within the lab frame, but low energy ions have very low cross sections for most of the interactions with a gas atoms or molecules. When interactions happen, a complexity appears in measuring the ion interactions' products, but the calculations are simpler for the velocity distribution for the electrons in many gases, since the ratio between a gas atom or molecule mass to the electron mass is very small. Since Producing electrons is simpler than producing ions in a gas, many interactions are responsible for producing electrons, such as thermionic emission, photoemission, or radioactive decay. On the other hand, creating an ion requires electron bombardment, photo-ionization or an electric discharge which requires more sophisticated conditions for the experiment and they are not as sensitive as the electrons for the the non-uniformity of the electric field, electric potential and magnetic field. Finally, the existence of the impurities is always a concern; the ions lose most of their energy in the molecular level, but the electron energy loss within the atomic level in a pure gas, as a result, the ionic velocity distribution is not affected by the existence of these impurities except for some cases related to a highly accurate ionic studies in gases.

← Older revision		Revision as of 16:07, 6 September 2013
Line 68:		Line 68:
	;Main differences between electrons and ions behavior in a gas <ref name="Mason">Mason, Edward A. and Earl W. MacDaniel. 1988. Transport Properties of Ions in Gases. John Wiley & Sons. </ref>		;Main differences between electrons and ions behavior in a gas <ref name="Mason">Mason, Edward A. and Earl W. MacDaniel. 1988. Transport Properties of Ions in Gases. John Wiley & Sons. </ref>

−	~~Haitham, here is a chance to get help with writing from the help center.~~	+	Studying diffusion and mobility of charged particles in a gas is classified in to two main groups, ion and electron diffusion and mobility. They are conceptually similar, but they have many differences. First, The ratio between the mass of the electrons and the gas atoms is very small, so with a few eV work done by the electric field, the electrons will gain a high velocity compared to that of the ions that are accelerated under the same electric field. Also, the probability of low energy electrons to make an interaction is higher than that of the low energy ions, the electron interactions are a supported with accurate calculations for the electron drift velocity. Electrons at low energy have the ability to produce vibrations and excitations in the gas atoms or molecules which are measured within the lab frame, but low energy ions have very low cross sections for most of the interactions with a gas atoms or molecules. When interactions happen, a complexity appears in measuring the ion interactions' products, but the calculations are simpler for the velocity distribution for the electrons in many gases, since the ratio between a gas atom or molecule mass to the electron mass is very small. Since Producing electrons is simpler than producing ions in a gas, many interactions are responsible for producing electrons, such as thermionic emission, photoemission, or radioactive decay. On the other hand, creating an ion requires electron bombardment, photo-ionization or an electric discharge which requires more sophisticated conditions for the experiment and they are not as sensitive as the electrons for the the non-uniformity of the electric field, electric potential and magnetic field. Finally, the existence of the impurities is always a concern; the ions lose most of their energy in the molecular level, but the electron energy loss within the atomic level in a pure gas, as a result, the ionic velocity distribution is not affected by the existence of these impurities except for some cases related to a highly accurate ionic studies in gases.
−	~~Take the paragraph below to them and learn how to correct it.~~
−
−	~~H: Sure, but I need to add and edit some more to complete the idea then I will go there.~~
−
−	Studying diffusion and mobility of charged particles in a gas is classified in to two main groups, ion and electron diffusion and mobility. They are conceptually similar, but they have many differences. First, The ratio between the mass of the electrons and the gas atoms is very small, so with a few eV work done by the electric field, the electrons will gain a high velocity compared to that of the ions that are accelerated under the same electric field. Also, the probability of low energy electrons to make an interaction is higher than that of the low energy ions, the electron interactions are a supported with accurate calculations for the electron drift velocity. Electrons at low energy have the ability to produce vibrations and excitations in the gas atoms or molecules which are measured within the lab frame, but low energy ions have very low cross sections for most of the interactions with a gas atoms or molecules. When interactions happen, a complexity appears in measuring the ion interactions' products, but the calculations are simpler for the velocity distribution for the electrons in many gases, since the ratio between a gas atom or molecule mass to the electron mass is very small. Since Producing electrons is simpler than producing ions in a gas, many interactions are responsible for producing electrons, such as thermionic emission, photoemission, or radioactive decay. On the other hand, creating an ion requires electron bombardment, photo-ionization or an electric discharge which requires more sophisticated conditions for the experiment and they are not as sensitive as the electrons for the the non-uniformity of the electric field, electric potential and magnetic field. Finally, the existence of the impurities is always a concern; the ions lose most of their energy in the molecular level, but the electron energy loss within the atomic level in a pure gas, as a result, the ionic velocity distribution is not affected by the existence of these impurities except for some cases related to a highly accurate ionic studies in gases.

← Older revision		Revision as of 14:07, 4 September 2013
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	== Multiplication ==		== Multiplication ==
		+
		+	[[GEM pre-amplification]]

	==Decreasing the discharge in THGEM==		==Decreasing the discharge in THGEM==

← Older revision		Revision as of 14:06, 4 September 2013
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		+	GO BACK [https://wiki.iac.isu.edu/index.php/Performance_of_THGEM_as_a_Neutron_Detector]

← Older revision		Revision as of 14:05, 4 September 2013
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	[[Ion Diffusion]]		[[Ion Diffusion]]
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		+	== Multiplication ==

	==Decreasing the discharge in THGEM==		==Decreasing the discharge in THGEM==

← Older revision		Revision as of 01:33, 4 September 2013
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	[[Ion Diffusion]]		[[Ion Diffusion]]
−
−	~~==Townsend's Coefficients==~~
−
−
−	~~===Townsend's First Coefficient===~~
−
−	~~Townsend's first Coefficient is defined as "the number of produced by an electron per unit length in the direction of the electric field"<ref name="Kuffel"/>.~~
−
−
−	*Townsend started his investigations about discharge after fundamental studies were known around 1899 about:
−
−	~~1- Conductivity production by x-rays.~~
−
−	~~2- Diffusion coefficients, mobility of ions and ion-electron~~
−	~~recombinations.~~
−
−	* It was observed for an increment in Electric filed E and pressure P beyond the saturation current value, at some critical value of E and p, the current increases rapidly which will lead to a breakdown of the gap in the form of a spark <ref name="loeb"> L.B.Loeb, basics processes of gaseous electronics, University of California Press, 2nd edition, 1955. call number QC711 .L67 1955a </ref>.
−
−	*Townsend studied the relationship between E/p as a function of x, where x is the separation distance between the plates. His study was based on the photoelectron emission from the cathode by ultraviolet light at high uniform electric field up to 30kV/cm and 1 atm pressure.
−
−
−	*He plotted different values for E/p, he found that the slope of the line is <math>\alpha</math> which is "the number of the new electrons created by single electron in 1 cm path in the filed direction in a gas at appropriately high E/p" <ref name="loeb"/> . Townsend plotted <math> \frac{i}{i_0} </math> against the distance of separation x, he concluded the following equation
−
−	~~<math> ln (\frac{i}{i_o}) = \alpha x </math>~~
−
−	~~to calculate <math>\alpha</math> (the slope) for different values of E/p as shown in the figure:~~
−
−
−	~~[[Image:alpha_town1st_coff_1.png \|thumb\| Fig. relationship between <math>ln{i}/{i_o}</math> and the distance x for different values of E/p <ref name="loeb"/>]]~~
−
−	* Townsend studied <math>\alpha</math> as a function of E/p for a given gas, he founded ,for different values of p,
−	<math>\alpha</math> experimentally is different from expected value calculated, but the plots met in values when it represented the relationship between <math>\alpha</math>/p as a function of E/p as shwon in the figure below.
−
−	~~[[Image:alpha_p_E_p_rations.png \|thumb\| Fig. shows alpha p ratio coincides with E p ratio <ref name="loeb"/>]]~~
−
−
−	*The relationship between <math>\alpha</math>/p and E/p is shown below. However, the equation can not predict all the values of <math>\alpha</math>/p accurately for different values of E/p, i.e having a single analytical function to fit the experimental results for a gas does not exist, because <math>\alpha</math>/p is dependent on the number of electrons produced which changes as the average energy distribution of the ionizing electrons changes <ref name="loeb"/>.
−
−	~~<math> \frac {\alpha}{P}= Ae^{(\frac{-BP}{E})} </math>~~
−
−	~~;Theoretical evaluation of <math>\alpha/p</math> as a function of E/p~~
−
−	* The first attempt was done by Townsend when the experimental data were limited by the to the high E/p.
−
−	~~=== Gas Quenching===~~
−
−	~~Rewrite the first two sentences so quenching is more clearly described.~~
−
−	Gas quenching is a non-ionizing process occurs when a gas molecules with large cross sections for excitation and vibration states decreases a charged particle energy to create any ionization when the charged particle passes through. Usually, the gas mixture ,contains the ionization event, consists mostly of gas atoms as a main source of electrons and the quenching gas, when the free electrons are scattered after the ionization, their energy is decreased by quenching so the number of secondary electrons becomes less, Consequently, a higher voltage is required to get a gain from this mixture than a medium only has a non-quenching gas<ref name="Sharma"> A.Sharma,F. Sauli, first Townsend coefficients measurements for argon gas european organization for nuclear research (1993) </ref >.
−
−	Not only does the quenching process decreases the electron energy, but also decreases the positive ions energy (produced by ionization) when the ions collide with these gas molecules and emits a photon or more from these positive ions. These photons represent the energy loss in a form other than the ionization which is called argon escape peak in case of using Argon gas.
−
−	Gas quenching experimentally can be measured by evaluating Townsend first coefficients A,B for different gas mixtures. The following table represents the Townsend first coefficients' values for different ratio of Ar/CO2 gas mixtures<ref name="Sharma"/>:
−
−
−	~~{\| border="1" cellpadding="4"~~
−	\|-
−	~~\|Percentage of CO2 \|\| 3.7 \|\| 22.8 \|\| 87.2 \|\| 100~~
−	\|-
−	~~\| A <math> cm^{-1}Torr^{-1} </math> \|\| 5.04 \|\| 221.1 \|\| 158.3 \|\| 145.1~~
−	\|-
−	~~\|B <math> Vcm^{-1}Torr^{-1} </math> \|\| 90.82 \|\| 207.6 \|\| 291.8 \|\| 318.2~~
−	\|-
−	~~\| <math> \frac{E}{p} \,\,\, Vcm^{-1}Torr^{-1} </math> \|\| 16.2 \|\| 21.6 \|\| 32.9 \|\| 36.4~~
−	\|}
−
−	~~The electric field pressure ratio in the last row is the upper limit of the reduced electric field which Townsend's equation fits considering E as a uniform electric field.~~
−
−
−	~~===Why 90/10 Ar/CO2 Mixture and why Garfield <ref name="Veenhof"/>===~~
−	~~[[why Garfield]]~~

	==Decreasing the discharge in THGEM==		==Decreasing the discharge in THGEM==

@@ Line 73: / Line 73: @@
   H: Sure, but I need to add and edit some more to complete the idea then I will go there.
+Studying diffusion and mobility  of  charged particles in a gas is classified in to two main groups, ion and electron diffusion and mobility. They are conceptually similar, but they have many differences. First, The ratio between the mass of the electrons and the gas atoms is very small, so with a few eV work done by the electric field, the electrons will gain a high velocity compared to that of the ions that are accelerated under the same electric field. Also, the probability of low energy electrons to make an interaction is higher than that of the low energy ions, the electron interactions are a supported with accurate calculations for the electron drift velocity. Electrons at low energy have the ability to produce vibrations and excitations in the gas atoms or molecules which are measured within the lab frame, but low energy ions have very low cross sections for most of the interactions with a gas atoms or molecules. When interactions happen, a complexity appears in measuring the ion interactions' products, but the calculations are simpler for  the velocity distribution for the electrons in many gases, since the ratio between a gas atom or molecule mass to the electron mass is very small. Since Producing electrons is simpler than producing ions in a gas,  many interactions are responsible for producing electrons, such as thermionic emission, photoemission, or radioactive decay. On the other hand,  creating an ion requires electron bombardment, photo-ionization or an electric discharge which requires more sophisticated conditions for the experiment and they are not as sensitive as the electrons for the the non-uniformity of the electric field, electric potential and magnetic field. Finally, the existence of the impurities is always a concern; the ions lose most of their energy in the molecular level, but the electron energy loss  within the atomic level in a pure gas, as a result, the ionic velocity distribution is not affected by the existence of these impurities except for some cases related to a highly accurate ionic studies in gases.
-Studying diffusion and mobility  of  charged particles in a gas is classified in to two main groups, ion and electron diffusion and mobility. They are conceptually similar, but they have many differences. First, The ratio between the mass of the electrons and the gas atoms is very small, so with a few eV work done by the electric field, the electrons will gain a high velocity compared to that of the ions when are accelerated under the same electric field. Also, the probability of low energy electrons to make an interaction is higher than that of the low energy ions, the electron interactions are a supported with accurate calculations for the electron drift velocity. Electrons at low energy have the ability to produce vibrations and excitations  in the gas atoms or molecules which are measured within the lab frame, but the low energy ions have very low cross sections for the most of the interactions with the gas atoms or molecules. When interactions happen, a complexity appears in measuring their products. Furthermore, calculations are simple for  the velocity distribution for the electrons in many gases, since the ratio between a gas atom or molecule mass to the electron mass is very small. Producing electrons is simpler than producing ions in a gas; a number of interactions are resposible for producing electrons in gas, such as thermionic emission, photoemission, or a radioactive decay, on the other hand,  creating an ion requires electron bombardment, photo-ionization or an electric discharge which requires more sophisticated conditions for the experiment, for instance , ions are not as sensitive as the electrons for the the non-uniformity of the electric field, electric potential and magnetic field. Finally, the existence of the impurities is always a concern; the ions lose most of their energy in the molecular level, but the electron energy loss  within the atomic level in a pure gas, so the ionic velocity distribution is not affected by the existence of these impurities except for some cases related to a highly accurate ionic studies in gases.
 ==Electron Diffusion==

@@ Line 57: / Line 57: @@
 |}
-To count the free electrons produced by the fission fragments demands some modifications in the detector design which will be mentioned in details in the detector construction section .
+To count the free electrons produced by the fission fragments demands some modifications in the detector design which mentioned in details in detector construction section .
-They are other  physical processes occur in the medium which are related to the gas mixture properties such as: photoionization, thermal ionization, deionization by attachment (negative ion formation) , photoelectric emission, electron emission by excited atoms or positive ion,penning ,and field emission <ref name="Kuffel"/>. The previos processes probably share in decreasing or increasing the number of free electrons in the medium, so evaluating the number of free electrons before amplification becomes sophisticated processes without a computer simulation.
+They are other  physical processes occur in the medium which are related to the gas mixture properties such as: photoionization, thermal ionization, deionization by attachment (negative ion formation) , photoelectric emission, electron emission by excited atoms or positive ion,penning ,and field emission <ref name="Kuffel"/>. The previous processes may share in decreasing or increasing the number of free electrons in the medium, so evaluating the number of free electrons before preamplification becomes sophisticated without a computer simulation.

@@ Line 20: / Line 20: @@
 ===Ionization in fission chambers===
-Ionization by a fission fragment is not  the only source for free electrons and it  is not the only ionization process in fission chamber. Fission chambers usually contain  neutoron fissinable materials, they are heavy radioisotopes that decay and emit more than one type of the ionizing radiation or  by their daughters after decay. For instance, when the fission chamber contains U-233, free electrons are detected because of escaping fission fragments, alpha particles, beta particles, or gamma rays, more specific details about U-233 decay products is shown by the following tables.
+Ionization by a fission fragment is not  the only source for free electrons and it  is not the only ionization process in fission chamber. Fission chambers usually contain  neutoron fissinable materials, they are heavy radioisotopes that decay and emit more than one type of the ionizing radiation or  by their daughters after decay. For instance, when the fission chamber contains U-233, free electrons are detected because of escaping fission fragments, alpha particles, beta particles, or gamma rays. More specific details about U-233 decay products is shown by the following tables:
 {| border="1" cellpadding="4"