US3892968A - Electron capture detector systems - Google Patents

Electron capture detector systems Download PDF

Info

Publication number
US3892968A
US3892968A US42161573A US3892968A US 3892968 A US3892968 A US 3892968A US 42161573 A US42161573 A US 42161573A US 3892968 A US3892968 A US 3892968A
Authority
US
United States
Prior art keywords
detector
output signal
electrodes
potential
electron
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired - Lifetime
Application number
Inventor
James Ephraim Lovelock
Original Assignee
James Ephraim Lovelock
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority to GB3702571A priority Critical patent/GB1404754A/en
Priority to US27841172A priority
Application filed by James Ephraim Lovelock filed Critical James Ephraim Lovelock
Priority to US42161573 priority patent/US3892968A/en
Application granted granted Critical
Publication of US3892968A publication Critical patent/US3892968A/en
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

Links

Images

Classifications

    • GPHYSICS
    • G01MEASURING; TESTING
    • G01NINVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N27/00Investigating or analysing materials by the use of electric, electro-chemical, or magnetic means
    • G01N27/62Investigating or analysing materials by the use of electric, electro-chemical, or magnetic means by investigating the ionisation of gases; by investigating electric discharges, e.g. emission of cathode
    • G01N27/64Investigating or analysing materials by the use of electric, electro-chemical, or magnetic means by investigating the ionisation of gases; by investigating electric discharges, e.g. emission of cathode using wave or particle radiation to ionise a gas, e.g. in an ionisation chamber
    • G01N27/66Investigating or analysing materials by the use of electric, electro-chemical, or magnetic means by investigating the ionisation of gases; by investigating electric discharges, e.g. emission of cathode using wave or particle radiation to ionise a gas, e.g. in an ionisation chamber and measuring current or voltage

Abstract

Two electron capture detectors are connected together such that a gas flows through the first detector and then into the second detector. The potential across the first detector is switched regularly between maximum and minimum values and the signal derived from the second detector is modulated by this switching action whenever a strong electron absorber is present in the gas flow.

Description

United States Patent [191 Lov'elock 1 July 1, 1975 [76] Inventor: James Ephraim Lovelock,

Bowerchalke, Salisbury, England [22] Filed: Dec. 4, 1973 [2-1] App]. No.: 421,615 [63] Related US. Application Data Continuation of Ser. No. 278,411, Aug. 7. 1972, abandoned. [30] Foreign Application Priority Data Aug. 6, 1971 United Kingdom 37025/71 52 US. Cl. 250/389; 250/384; 250/385; 1 250/387 [51] Int. Cl. G0lt 1/18 [58] Field of Search 250/389, 385, 432, 356, 250/384; 324/33; 313/54, 93

[56] References Cited UNITED STATES PATENTS 3,009,097 11/1961 Strange 324/33 gas inlet.

3,154,680 10/1964 Greene 324/33 3,573,460 4/1971 Skala 324/33 3,688,106 8/1972 Brain 250/389 Primary Examiner-Harold A. Dixon Attorney, Ag'e'ht, or Firm--Woodhams, Blanchard and Flynn [5 7 ABSTRACT Two electron capture detectors are connected together such that a gas flows through the first detector and then into the second detector. The potential across the first detector is switched regularly between maximum and rriinimum values and the signal derived from the second detector is modulated by this switching action whenever a strong electron absorber is present in the gas flow.

3 Claims, 1 Drawing Figure LOW FREQUENCY GENERATOR l SYNCHRONOU CONVERTOR.

oti fi t. AMPLl'F lER.

SIGNAL.

POLARIZATION FOR DETECTOR B.

LOW FREQUENCY GENERATOR l SIGNAL.

0353i. AMPLIFIER as i nlet.

POLARIZATION FOR DETECTOR B.

1 ELECTRON cA rURir DErEcToig SYSTEMS This is a continuation-of application seiner-278,41 l filed'Au'g. 7, 197-2, and now abandoned;

The present invention relates to electron capture detector systems. n! r An electron capture detector,comprisesanionization chamber having spaced apart; elpctrodesanda:source of ionising radiation located withirtthe chamber. Upon entry of a gas possessing no affini ty for electrons into the chamber, recombination of positive ions and free electrons is unlikely to take place because of the high mobility of the free electrons. Thus by applying a potential across the chamber all ions formed by the ionising radiation can be collected. When the gas contains a substance having an affinity for electrons negative ion formation occurs which is accompanied by an observed decrease in current.

The presence of extraneous weakly absorbing subtances in the gas flow through the detector can interfere with or prevent the correct functioning of the de- 1 the electrodes of the first detector between zero and maximum values and means for detecting an output signal from the second detector.

The invention will be described further, by way of example, with reference to the accompanying diagrammatic drawing of an electron capture detector system.

In the drawing reference letters A and B denote two electron capture detectors coupled together such that gas entering A through an inlet passes through A and enters B before exhausting at an outlet from B. The detectors A and B are electrically insulated the one from K the other as denoted at C. Detector B is connected to an amplifier or other electronic system. The operation of detector B can be by a DC polarising potential, by pulses or by a frequency modulated procedure.

Detector A is arranged to be polarised either with a high DC potential, for example 100 volts, which is sufficient to remove all electrons present in an incoming gas, or with zero potential whereby the free electron concentration in the gas can be the maximum possible.

If a strong electron absorber is present in the incoming The system can be used to distinguish a weak from a strong electron absorbing substance. The system can thus be used in the identification of such substances. If I the potential on detector A is switched regularly between zero and high potential, at for example one or more cycles per second, then the signal at the second detector B will be modulated by this switching cycle whenever a strong electron absorber is present in the The system" pr gas-zentering detector A. The drawing s hows ,a.,circuit iarrangement; of the two; detectors .andiincludis'ia synchronous coriverter' tov rectify alternating "signal "tration's of weakly absorbing sub stai,1e,s' can interfere with or even prevent analysis; l The preisent' system incorporati'ng tw'o'detectors -is riot sensitive to weakly absorbing substances provided that the electron concentration in the two detectors is not so far reduced by the presence of the weak absorber as to prevent the detection of the strong electron absorber. Subject to this condition the presence of weakly absorbing substances, such as oxygen, give no detectable or adverse effect.

The synchronous production, amplification and rectification of the signal results in an improvement in stability and a reduction in noise level.

Alpha emitting radio-active sources, such as Am 241, give intense ionisation with only a small amount of radio-active material. However the resulting increase in noise level prevents the use of such sources in conventional electron capture systems. This restriction is avoided by the present system.

I claim:

1. An electron capture detector system, for detecting the presence of an electron absorber in a gas sample, comprising in combination:

first and second electron capture detectors electrically insulated the one from the other, said first and second detectors being coupled together in series such that the gas sample flows through the first detector and then through the second detector, said first detector including electrodes for receiving a potential, said second detector including means for producing an output signal, means periodically switching the potential applied across the electrodes of the first detector between minimum and maximum values for modulating the output signal of the second detector in response to presence of an electron absorber in the gas sample, and means for detecting the output signal from the second detector, said second detector including electrodes, said means for producing an output signal including means applying a polarizing potential to said second detector electrodes, said output signal of said second detector being an alternating signal, said means for detectingthe output signal including a synchronous converter for rectifying said alternating signal from said second detector.

2. An electron capture detector system, for detecting the presence of an electron absorber in a gas sample, comprising in combination:

first and second electron capture detectors electrically insulated the one from the other, said first and second detectors being coupled together in series such that the gas sample flows through the first detector and then through the second detector, said first detector including electrodes for receiving a potential, said second detector including means for producing an output signal, means periodically switching the potential applied across the electrodes of the first detector between minimum and maximum values for modulating the output signal further electrodes, said synchronous converter being coupled further to one of said second detec- 4 tor electrodes for rectifying the alternating output signal from the second detector 3 The system of claim 2 in which said minimum and maximum values correspond, respectively, to a first p0- tenti'al wherein the free electron concentration in the io ized gas sample is maximized and to a second potential wherein substantially all free electrons present in the ionized gas sample are removed therefrom by said first detector electrodes.

Claims (3)

1. An electron capture detector system, for detecting the presence of an electron absorber in a gas sample, comprising in combination: first and second electron capture detectors electrically insulated the one from the other, said first and second detectors being coupled together in series such that the gas sample flows through the first detector and then through the second detector, said first detector including electrodes for receiving a potential, said second detector including means for producing an output signal, means periodically switching the potential applied across the electrodes of the first detector between minimum and maximum values for modulating the output signal of the second detector in response to presence of an electron absorber in the gas sample, and means for detecting the output signal from the second detector, said second detector including electrodes, said means for producing an output signal including means applying a polarizing potential to said second detector electrodes, said output signal of said second detector being an alternating signal, said means for detecting the output signal including a synchronous converter for rectifying said alternating signal from said second detector.
2. An electron capture detector system, for detecting the presence of an electron absorber in a gas sample, comprising in combination: first and second electron capture detectors electrically insulated the one from the other, said first and second detectors being coupled together in series such that the gas sample flows through the first detector and then through the second detector, said first detector including electrodes for receiving a potential, said second detector including means for producing an output signal, means periodically switching the potential applied across the electrodes of the first detector between minimum and maximum values for modulating the output signal of the second detector in response to presence of an electron absorber in the gas sample, and means for detecting the output signal from the second detector, said periodically switching means comprising a low frequency generator and means coupling same across the electrodes of said first detector, said means for detecting the output signal including a synchrOnous converter coupled to said low frequency generator, said second detector including further electrodes, said synchronous converter being coupled further to one of said second detector electrodes for rectifying the alternating output signal from the second detector.
3. The system of claim 2 in which said minimum and maximum values correspond, respectively, to a first potential wherein the free electron concentration in the ionized gas sample is maximized and to a second potential wherein substantially all free electrons present in the ionized gas sample are removed therefrom by said first detector electrodes.
US42161573 1971-08-06 1973-12-04 Electron capture detector systems Expired - Lifetime US3892968A (en)

Priority Applications (3)

Application Number Priority Date Filing Date Title
GB3702571A GB1404754A (en) 1971-08-06 1971-08-06 Electron capture detector systems
US27841172A true 1972-08-07 1972-08-07
US42161573 US3892968A (en) 1971-08-06 1973-12-04 Electron capture detector systems

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
US42161573 US3892968A (en) 1971-08-06 1973-12-04 Electron capture detector systems

Publications (1)

Publication Number Publication Date
US3892968A true US3892968A (en) 1975-07-01

Family

ID=27259404

Family Applications (1)

Application Number Title Priority Date Filing Date
US42161573 Expired - Lifetime US3892968A (en) 1971-08-06 1973-12-04 Electron capture detector systems

Country Status (1)

Country Link
US (1) US3892968A (en)

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4019863A (en) * 1974-04-08 1977-04-26 Anthony Jenkins Selective detection of a constituent in an atmosphere
US4028549A (en) * 1974-12-06 1977-06-07 Shigeo Baba Synchronized accumulating radiodetector
US4119851A (en) * 1977-06-23 1978-10-10 Honeywell Inc. Apparatus and a method for detecting and measuring trace gases in air or other gas backgrounds
US4567368A (en) * 1984-01-19 1986-01-28 Varian Associates, Inc. Bipolar pulsed electron capture detectors

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3009097A (en) * 1958-02-19 1961-11-14 Mine Safety Appliances Co Method of oxygen detection
US3154680A (en) * 1956-10-18 1964-10-27 Air Reduction Gas analysis by measuring negative ions resulting from captured electrons
US3573460A (en) * 1966-09-12 1971-04-06 Gen Electric Ion chamber detector for submicron particles
US3688106A (en) * 1969-03-28 1972-08-29 Nat Res Dev Measuring the density, velocity and mass flow of gases

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3154680A (en) * 1956-10-18 1964-10-27 Air Reduction Gas analysis by measuring negative ions resulting from captured electrons
US3009097A (en) * 1958-02-19 1961-11-14 Mine Safety Appliances Co Method of oxygen detection
US3573460A (en) * 1966-09-12 1971-04-06 Gen Electric Ion chamber detector for submicron particles
US3688106A (en) * 1969-03-28 1972-08-29 Nat Res Dev Measuring the density, velocity and mass flow of gases

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4019863A (en) * 1974-04-08 1977-04-26 Anthony Jenkins Selective detection of a constituent in an atmosphere
US4028549A (en) * 1974-12-06 1977-06-07 Shigeo Baba Synchronized accumulating radiodetector
US4119851A (en) * 1977-06-23 1978-10-10 Honeywell Inc. Apparatus and a method for detecting and measuring trace gases in air or other gas backgrounds
US4567368A (en) * 1984-01-19 1986-01-28 Varian Associates, Inc. Bipolar pulsed electron capture detectors

Similar Documents

Publication Publication Date Title
Segre et al. Experiments on the Effect of Atomic Electrons on the Decay Constant of Be 7
Bondoux et al. New approach to the analysis of low levels of anions in water
JP4550802B2 (en) Obstacle substance detection method and obstacle substance detection system
US5491337A (en) Ion trap mobility spectrometer and method of operation for enhanced detection of narcotics
US5393979A (en) Photo-ionization detector for detecting volatile organic gases
Bortner et al. Ionization of pure gases and mixtures of gases by 5-MeV alpha particles
Lovelock Ionization methods for the analysis of gases and vapors
US5032721A (en) Acid gas monitor based on ion mobility spectrometry
CA2161924C (en) Radon gas measurement apparatus having alpha particle-detecting photovoltaic photodiode surrounded by porous pressed metal daughter filter electrically charged as po-218 ion accelerator
US4019863A (en) Selective detection of a constituent in an atmosphere
Lubman et al. Plasma chromatography with laser-produced ions
US3997297A (en) Method and apparatus for detecting a constituent in an atmosphere
US2469460A (en) Radioactivity measurement
Karasek et al. Qualitative studies of trace constituents by plasma chromatography
WO1993022033A1 (en) Photoionization ion mobility spectrometer
US5059803A (en) Rugged alpha particle counter
US6924479B2 (en) Ion detecting apparatus and methods
GB828121A (en) Apparatus responsive to the composition of a gaseous medium
JPS62172257A (en) Proton conductor gas sensor
Aue et al. Application of the alkali-flame detector to nitrogen containing compounds
SU1627984A2 (en) Method of gas analysis for impurities
US3920987A (en) Method and system for detecting explosives
US3668383A (en) Apparatus and methods for separating, detecting, and measuring trace gases
CN101504388A (en) Miniature optical ionization sensor
US6727504B1 (en) Boron nitride solid state neutron detector