US3831027A - Imaging gas for improved resolution in imaging chamber of electron radiography system - Google Patents

Imaging gas for improved resolution in imaging chamber of electron radiography system Download PDF

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Publication number
US3831027A
US3831027A US00401689A US40168973A US3831027A US 3831027 A US3831027 A US 3831027A US 00401689 A US00401689 A US 00401689A US 40168973 A US40168973 A US 40168973A US 3831027 A US3831027 A US 3831027A
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United States
Prior art keywords
gas
gap
electronegative
anode
electrons
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Expired - Lifetime
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US00401689A
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English (en)
Inventor
A Proudian
P Scott
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ELSCINT IMAGING Inc
Elscint Ltd
Elscint Inc
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Xonics Inc
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Priority to US00401689A priority Critical patent/US3831027A/en
Application filed by Xonics Inc filed Critical Xonics Inc
Priority to CA204,352A priority patent/CA1017788A/en
Priority to DE2434287A priority patent/DE2434287A1/de
Priority to GB3217474A priority patent/GB1435236A/en
Publication of US3831027A publication Critical patent/US3831027A/en
Application granted granted Critical
Priority to FR7428562A priority patent/FR2257932B1/fr
Priority to BE147869A priority patent/BE819148A/xx
Priority to NL7411647A priority patent/NL7411647A/xx
Priority to IT53105/74A priority patent/IT1021649B/it
Priority to JP49107891A priority patent/JPS5062445A/ja
Assigned to ELSCINT, INC., ELSCINT IMAGING, INC., ELSCINT, LIMITED reassignment ELSCINT, INC. ASSIGNORS DO HEREBY QUITCLAIM, ASSIGN AND TRANSFER THEIR ENTIRE RIGHTS, TITLE AND INTEREST THEY MAY HAVE IN SAID INVENTIN TO ASSIGNEES Assignors: XONICS MEDICAL SYSTEMS, INC., XONICS, INC.
Assigned to XONICS INC., A CA. CORP. reassignment XONICS INC., A CA. CORP. RELEASED BY SECURED PARTY (SEE DOCUMENT FOR DETAILS). Assignors: FIRST CHICAGO INVESTMENT CORPORATION, AS AGENT
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    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03G—ELECTROGRAPHY; ELECTROPHOTOGRAPHY; MAGNETOGRAPHY
    • G03G15/00—Apparatus for electrographic processes using a charge pattern
    • G03G15/054—Apparatus for electrographic processes using a charge pattern using X-rays, e.g. electroradiography
    • G03G15/0545—Ionography, i.e. X-rays induced liquid or gas discharge

Definitions

  • ABSTRACT An electron radiography system with improved resolution obtained by incorporating a few per cent of an electro-negative gas with the imaging gas to combine with the electrons forming negative ions for attracting to the anode and depositing on the dielectric sheet.
  • This invention relates to the creation of X-ray images without the use of conventional X-ray film, sometimes referred to as electron radiography, such as is described in the copending application of Muntz et al., Ser. No. 261,927, filed June 12, 1972, entitled RADIO- GRAPl-IIC SYSTEMS WITH XEROGRAPHIC PRINTING, and assigned to the same assignee as the present application.
  • an X-ray opaque gas at high pressure is maintained in a gap between electrodes in an imaging chamber to produce electrons within the gap as a function of X- rays entering the gap.
  • the electrons are collected on a dielectric sheet placed at the anode, resulting in a latent electrostatic charge on the sheet.
  • the latent image is then made visible by xerographic techniques.
  • the gas in the chamber may be maintained at superatmospheric pressure, and the thickness of the X-ray absorbing gas layer may be made as large as two centimeters or more.
  • the electrostatic image formed in the imaging chamber can be blurred or unsharp and exhibit poor resolution, due to two effects which are dependent on gap thickness.
  • the first effect is that of geometric unsharpness due to oblique X-rays, and is handled in a manner not related to the present invention.
  • a second significant source of geometric unsharpness is the diffusive spreading of the charges as they travel from their point of creation to the insulating receptor. Proper orientation of the collective electric fields cannot overcome this problem.
  • the purpose of the present invention is to reduce image blurring due to diffusion and to improve the resolution of the imaging chamber of the electron radiographic system. In order to clarify the basis of the solution proposed in the present invention, it is ncessary to describe the process of charge creation by the X-rays and their transport to the dielectric receptor in some detail.
  • the gas in the imaging chamber consists of a high Z radiopaque gas such as Xenon or Krypton, together possibly with a small amount of a quenching" gas such as methane, which is known experimentally to suppress electrical breakdown sparks in gas discharges.
  • a quenching gas such as methane
  • X-ray photon incident upon a Xenon atom When an X-ray photon incident upon a Xenon atom is absorbed by the latter, it emits an electron, typically from its most tightly bound shell or K-shell, and typically with an energy of ten to a few tens of kilovolts.
  • This ejected photoelectron rather rapidly dissipates its energy by further ionization of Xenon atoms with which it collides, leading to a ball or cloud of ionization around the initial absorbing atom, consisting of typically a thousand or so electron/Xenon-ion pairs, the electrons having energies typically less than the ionization energy of Xenon, and the Xenon ions being in various excited states.
  • the diameter of this ball is typically X to 10 cm at the typical operating pressures.
  • the cloud electrons would eventually be thermalized (i.e., achieve a mean thermal kinetic energy (3/2)k'l", T gas temperature) and would recombine with the Xenon ions, leading to eventual complete neutralization of the gas, although such recombination is slow in gas kinetic terms for a process such as Xe +e' Xe.
  • the electrons drift under the influence of the electric field 'E in the direction of while the ions drift in the direction of E.
  • the electrons gain energy from the applied field by the combined process of acceleration by the field and inefficient collisional energy exchange with the chamber gas atoms.
  • the ions mostly because of their far greater mass (of the order of 200,000 electron masses), transfer energy efficiently with the gas atoms, and remain essentially at the (room) temperature of these neutral atoms (which constitute all but 1 part in about 10 of the gas).
  • the electrons pick up significant energy from the field and achieve energies of several electron volts, compared to 1/40 of an electron volt thermal energy corresponding to the gas and positive ion temperature at 300K (nominal).
  • the electrons and ions respectively drift towards the anode and cathode under the influence of the applied field, and, at the same time, they both undergo random thermal motions due to collisions with neutral atoms, these motions being the underlying source of diffusion.
  • the ions on the other hand, would on their own produce an image much less blurred due to their own diffusion.
  • the positive ions themselves diffuse negligibly, they suffer from the diffusiveeffects of the electrons, because of the recombination/ionization processes in the gas: indeed, the positive ions which reach the image receptor at the cathode are not just those created in the initial ball of ionization. Some of those are neutralized by electron/ion recombinatiomwhile others'are created by electron-atom collision, and the latter are of course created everywhere along the path of the random motion of the electrons, so that their spatial distribution reflects the random diffusive motions of the electrons.
  • the solution to the above problem lies in simultaneously inhibiting both electron diffusion and the recombination/ionization process, so that there is neither loss of sensitivity on the one hand, nor loss of resolution on the other.
  • the source of the carrier ion is an electronegative gas added to the imaging gas.
  • An excellent choice for such a carrier is the negative ion SP of sulfur hexafluoride: sulfur hexafluoride (SP is an extremely active electrophyllic molecule, which attaches electrons by very rapidattachment processes (e.g., SP e third body SP third body), and with a binding energy of approximately 4 electron volts.
  • the working gas rather than being a pure high Z gas such as Xenon, or such a gas with a small fraction of quenchant gas, also contains a few per cent, typically 2 to 10%, of an electronegative attaching gas with a strong affinity, such as SP
  • an electronegative attaching gas with a strong affinity such as SP
  • the attaching gas such as SF forming a stable negative ion, such as SP
  • the latter will then drift towards the collecting anode or receptor (while the positive ions drift toward the cathode), but will neither create new ions nor recombine in any significant amount during the drift time between creation by attachment and collection, because recombination processes of the form SP Xe" SF Xe between a highly stable negative ion such as SP and a relatively weakly electrophyllic ion such as Xe are quite slow.
  • FIG- URE of the drawing illustrates a typical electron radiographic system with imaging chamber and incorporating the presently preferred embodiment of the invention.
  • X-rays are directed from a source 10 past the object 11 being X-rayed to the imaging chamber 12, which may be conventional in design such as set out in the aforementioned copending application.
  • a typical imaging chamber includes a housing 13 carrying a cathode 14 on an insulator 15, with an anode 16 carried on a housing cover 17. Alternatively, the housing cover may serve as the anode.
  • the dielectric sheetreceptor 18 is carried on the anode, with the imaging gas introduced into the chamber at 19 filling the gap between the electrodes. An electric field is produced across the gap by a high voltage supply 22 connected to the electrodes.
  • the imaging gas is a high Z, X-ray opaque gas such as Xenon or Krypton maintained at high pressure, typically 5 to 20 atmospheres.
  • a small amount of a quenchant such as methane may be added but is not normally required. in a system of the invention, a few per gas is also added, typically in the order of 2 to 10%.
  • the system is operated in the conventional manner in making the X-ray exposure.
  • the dielectric sheet is mounted on the anode and the chamber is sealed.
  • the gas is introduced into the chamber at the pressure desired and the high voltage supply is turned on.
  • the X-ray source is turned on to make the exposure, producing the electrostatic charge image on the receptor.
  • the high voltage supply is turned off, the pressure in the chamber is reduced, the chamber is opened and the receptor sheet is removed for developing and fixing of the visual image.
  • An electronegative gas has a lower energy when an electron is added to the molecule forming a negative ion.
  • a preferred electronegative gas has a strong affinity for electrons, a high attachment rate for electrons, and forms a heavy negative ion which is nonrecombining in nature. These various characteristics depend upon the molecular structure of the electronegative gas and can be determined by testing of gases.
  • the halogen compounds are suitable for use as sources of the negative ions.
  • the following gases are suitable: sulfur hexafluoride, carbon tetrachloride, tungsten hexafluoride, uranium hexafluoride, oxygen and perfluorohexene.
  • the gap was 6 mm and the pressure 5 atmospheres (absolute) while in Table Ill, the gap was 12.6 mm and the pressure 8 atmospheres (absolute).
  • first means for supporting said electrodes in spaced relation with a small gap therebetween and for maintaining a superatmospheric pressure in said gap with a dielectric sheet in said gap at said anode
  • an X-ray absorber and electron and positive ion emitter in said gap between said anode and cathode for producing a charge image on' said dielectric sheet, said emitter comprising an X-ray opaque gas at superatmospheric pressure and having an atomic number of at least 36, and
  • the improvement comprising including in said X-ray opaque gas a few percent of an electronegative gas for combining with electrons in the gap forming negative ions for attraction to said anode.
  • said electronegative gas is selected from the group consisting of positioning the dielectric sheet at an electrode in a gap between anode and cathode electrodes positioned adjacent an object to be imaged;
  • absorbing incoming X-rays in the gap by maintaining in the gap an X-ray opaque gas of atomic number at least 36 at superatomspheric pressure and generating electrons and positive ions in the gas; converting electrons in the gap to negative ions by combining electrons with electronegative gas molecules maintained in the gap with said X-ray opaque gas; and attracting negatively charged particles toward the anode by applying a high potential across the elec trodes depositing said charged particles on the dielectric sheet.
  • said electronegative gas is selected from the group consisting of sulfur hexafluoride, carbon tetrachloride, tungsten hexafluoride, uranium hexafluoride, oxygen and perfluorohexene.

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  • Health & Medical Sciences (AREA)
  • Pathology (AREA)
  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Analysing Materials By The Use Of Radiation (AREA)
  • Combination Of More Than One Step In Electrophotography (AREA)
  • Apparatus For Radiation Diagnosis (AREA)
  • Radiography Using Non-Light Waves (AREA)
US00401689A 1973-09-28 1973-09-28 Imaging gas for improved resolution in imaging chamber of electron radiography system Expired - Lifetime US3831027A (en)

Priority Applications (9)

Application Number Priority Date Filing Date Title
US00401689A US3831027A (en) 1973-09-28 1973-09-28 Imaging gas for improved resolution in imaging chamber of electron radiography system
CA204,352A CA1017788A (en) 1973-09-28 1974-07-08 Imaging gas for improved resolution in imaging chamber of electron radiography system
DE2434287A DE2434287A1 (de) 1973-09-28 1974-07-17 Abbildungsgas fuer eine verbesserte aufloesung in einer abbildungskammer einer elektronenradiographischen anordnung
GB3217474A GB1435236A (en) 1973-09-28 1974-07-19 Radiographic system for operation with a source of x-rays
FR7428562A FR2257932B1 (xx) 1973-09-28 1974-08-20
BE147869A BE819148A (fr) 1973-09-28 1974-08-23 Procede et dispositif de formation de radiographies par electrographie
NL7411647A NL7411647A (nl) 1973-09-28 1974-09-03 Gas voor het vormen van een beeld met een hoge utie in een beeldvormingskamer van een ronen-radiografisch stelsel.
IT53105/74A IT1021649B (it) 1973-09-28 1974-09-19 Dispositivo radiografico e metodo per produrre immagini elettrostati che
JP49107891A JPS5062445A (xx) 1973-09-28 1974-09-20

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
US00401689A US3831027A (en) 1973-09-28 1973-09-28 Imaging gas for improved resolution in imaging chamber of electron radiography system

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US3831027A true US3831027A (en) 1974-08-20

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US (1) US3831027A (xx)
JP (1) JPS5062445A (xx)
BE (1) BE819148A (xx)
CA (1) CA1017788A (xx)
DE (1) DE2434287A1 (xx)
FR (1) FR2257932B1 (xx)
GB (1) GB1435236A (xx)
IT (1) IT1021649B (xx)
NL (1) NL7411647A (xx)

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE2548461A1 (de) * 1974-10-30 1976-05-13 Oki Electric Ind Co Ltd Schnelldrucker
FR2364485A1 (fr) * 1976-09-11 1978-04-07 Philips Nv Dispositif d'enregistrement electroradiographique

Families Citing this family (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS50125694A (xx) * 1974-03-19 1975-10-02
DE2420902A1 (de) * 1974-04-30 1975-11-13 Philips Patentverwaltung Elektroradiographische vorrichtung

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2922911A (en) * 1956-08-31 1960-01-26 Friedman Herbert Apparatus for gas analysis
US2936388A (en) * 1958-12-15 1960-05-10 Talbot A Chubb Counters with a negative-ion-forming vapor additive
US3526767A (en) * 1967-10-18 1970-09-01 Xerox Corp Image amplification in ionography by avalanche method
US3774029A (en) * 1972-06-12 1973-11-20 Xonics Inc Radiographic system with xerographic printing

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2922911A (en) * 1956-08-31 1960-01-26 Friedman Herbert Apparatus for gas analysis
US2936388A (en) * 1958-12-15 1960-05-10 Talbot A Chubb Counters with a negative-ion-forming vapor additive
US3526767A (en) * 1967-10-18 1970-09-01 Xerox Corp Image amplification in ionography by avalanche method
US3774029A (en) * 1972-06-12 1973-11-20 Xonics Inc Radiographic system with xerographic printing

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE2548461A1 (de) * 1974-10-30 1976-05-13 Oki Electric Ind Co Ltd Schnelldrucker
FR2364485A1 (fr) * 1976-09-11 1978-04-07 Philips Nv Dispositif d'enregistrement electroradiographique

Also Published As

Publication number Publication date
BE819148A (fr) 1974-12-16
FR2257932B1 (xx) 1980-03-28
CA1017788A (en) 1977-09-20
IT1021649B (it) 1978-02-20
FR2257932A1 (xx) 1975-08-08
DE2434287A1 (de) 1975-04-03
JPS5062445A (xx) 1975-05-28
GB1435236A (en) 1976-05-12
NL7411647A (nl) 1975-04-02

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Owner name: ELSCINT IMAGING, INC., MASSACHUSETTS

Free format text: ASSIGNORS DO HEREBY QUITCLAIM, ASSIGN AND TRANSFER THEIR ENTIRE RIGHTS, TITLE AND INTEREST THEY MAYHAVE IN SAID INVENTIN TO ASSIGNEES;ASSIGNORS:XONICS, INC.;XONICS MEDICAL SYSTEMS, INC.;REEL/FRAME:005029/0007

Effective date: 19880718

Owner name: ELSCINT, INC., MASSACHUSETTS

Free format text: ASSIGNORS DO HEREBY QUITCLAIM, ASSIGN AND TRANSFER THEIR ENTIRE RIGHTS, TITLE AND INTEREST THEY MAYHAVE IN SAID INVENTIN TO ASSIGNEES;ASSIGNORS:XONICS, INC.;XONICS MEDICAL SYSTEMS, INC.;REEL/FRAME:005029/0007

Effective date: 19880718

Owner name: ELSCINT, LIMITED, ILLINOIS

Free format text: ASSIGNORS DO HEREBY QUITCLAIM, ASSIGN AND TRANSFER THEIR ENTIRE RIGHTS, TITLE AND INTEREST THEY MAYHAVE IN SAID INVENTIN TO ASSIGNEES;ASSIGNORS:XONICS, INC.;XONICS MEDICAL SYSTEMS, INC.;REEL/FRAME:005029/0007

Effective date: 19880718

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Owner name: XONICS INC., A CA. CORP., ILLINOIS

Free format text: RELEASED BY SECURED PARTY;ASSIGNOR:FIRST CHICAGO INVESTMENT CORPORATION, AS AGENT;REEL/FRAME:005013/0715

Effective date: 19881207