US3792278A - Electron radiographic imaging chamber with current enhancement - Google Patents

Electron radiographic imaging chamber with current enhancement Download PDF

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Publication number
US3792278A
US3792278A US00305339A US3792278DA US3792278A US 3792278 A US3792278 A US 3792278A US 00305339 A US00305339 A US 00305339A US 3792278D A US3792278D A US 3792278DA US 3792278 A US3792278 A US 3792278A
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United States
Prior art keywords
potential
electron
imaging chamber
field
current
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Expired - Lifetime
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US00305339A
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English (en)
Inventor
A Proudian
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
ELSCINT IMAGING Inc
Elscint Ltd
Elscint Inc
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Xonics Inc
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Publication of US3792278A publication Critical patent/US3792278A/en
Assigned to ELSCINT, LIMITED, ELSCINT IMAGING, INC., ELSCINT, INC. reassignment ELSCINT, LIMITED 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
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

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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

  • an X-ray opaque gas at high pressure e.g. 2O atmospheres
  • a photoelec'tric current within that chamber as a function of X- rays entering the chamber.
  • the current is collected on a dielectric sheet placed on one or the other of the electrodes, resulting in a latent electrostatic image on the sheet.
  • the latent image is then made visible by xero graphic techniques Collection of the primary photo electrons created by the X-rays absorbed in the interelectrode gas filled gap and of the secondary electrons created by collisions of the primaries with the gas atoms is achieved by use of an accelerating potential difference, typically of the order of 5,000 volts, applied between the electrodes.
  • the value of the applied d.c. potential between the anode and cathode is selected in the above system so as to satisfy two constraints.
  • the applied accelerating field or potential should be as high as possible so as to maximize the current or total electron count produced per absorbed X-ray quantum.
  • the controlling quantity, which determines the collected current is the accelerating field divided by the pressure p, i.e., the quantity E/p, rather than the voltage V (E/p) pd,
  • This new and improved performance is achieved by augmenting the appliedsteady or do. accelerating or current collecting electric field in the imaging chamber with an a.c. field which does not itself collect current but does increase the number of electrons collected by the dc. field, at any given value of the latter, above the number that would result in the absence of the a.c. field.
  • 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 another insulator 17.
  • the dielectric sheet receptor 18 may be carried on the anode, with gas introduced into the chamber at 19 filling the gap between the electrodes.
  • a d.c. field is produced across the gap by a d.c. supply connected at terminal 25 and coupled to the anode 16 through an RF choke coil 26 and a coupling inductance 27, with the cathode 14 connected to system ground.
  • the a.c. field is provided by a radio frequency oscillator 30 connected to the grid of a power amplifier triode 31, with the amplifier energized from the B+ supply I and with the RF output coupled through the inductance 27 to the anode 16, with a variable capacitor 32 connected across the triode for RF tuning.
  • the drift velocity of the electrons is approximately proportional to the applied field. In their drift, the electrons gain energy from the field, and lose energy in elastic and inelastic collisions with the gas molecules. The electrons can also recombine with the ions present in the gas, either directly or more frequently by attachment to a neutral molecule followed by negative ion-positive ion recombination. Re-
  • the electron (and negative ion) drift velocity is low, and the energy gained by the electrons from the field per unit length of travel in the direction of the field is low, so that a majority of the secondary electrons produced in the swarm are lost by recombination before they reach the collecting electrode.
  • the electron drift velocity increases while the probability of recombination (and attachment), which is strongly dependent on electron energy, decreases because of the increased energy gained from the field by the electrons between collisions.
  • the above description is an oversimplification in that it omits another process which occurs in the gas, namely the increase in the number of electrons in a swarm due to inelastic collisions of the electrons with neutral molecules in the gas, which result in the creation of additional ion pairs.
  • the ionization and recombination are competing processes, and the former increases with applied field (and therefore field strength)just as the latter decreases with increasing applied field. Ionization becomes significant well before recombination is reduced essentially to zero, and indeed there is no true plateau in collected current, but rather a very slow increase with increasd voltage.
  • the rate of ionization exceeds the rate of recombination and there is a net gain in collected current. This is the so-called avalanche regime in which each initial secondary electron leads to collection of more than one electron at the receptor.
  • the applied a.c. field would act much as an addition to the steady field, with respect to breakdowns, since the formation of breakdown avalanches have characteristic times of the order of microseconds.
  • I0 Hz which corresponds to a wavelength of 30 cm
  • field nonuniformities over the dimensions of the imaging chamber would become significant.
  • the criteria for selecting frequencies are, at the lower end, that the imposed fields should not appear as d.c. fields with respect to the breakdown phenomenon, and at the upper end that uniform enhancement, and therefore uniform fields, and effective coupling to the free electron gas be achieved.
  • the effective a.c. field strength E required for an applied a.c. field E is simply achieved. Note that by use of ac; fields, itbecomes possible to operate the imaging chamber somewhat into the avalanche region (i.e., to induce electron multiplication in the ac. field) and thereby achieve gains in current beyond the full collection current. However, the ac. field must be kept to values below those at which it would itself induce gas breakdown. It is interesting that the threshold for ac. breakdown will in fact be raised by the presence of the dc. field which inhibits local electron breakdown. Thus the do. and ac. fields aid each other in terms of permitting full current collection and possibly amplification without breakdown.
  • Typical values for the tandem fields would be, in terms of the applied potential differences around 3,000 volts for the dc. potential, and around 3,000 volts (r.m.s.) for the ac. potential.
  • the dc. potential may be reduced to as low as 1,000 volts, or
  • ac. potentials may also range as low as 1,000 volts and as high as 10,000volts.
  • an imaging chamber having spaced electrodes with a gas filled gap there between;
  • a system as defined in claim 1 including means for generating said a.c. potential in the range of about 10 Hz to about 10 Hz.
  • a system as defined in claim 1 including means for generating said a.c. potential in the range of about 10 Hz to about 10 Hz.
  • a system as defined in claim 1 including:
  • a radio frequency amplifier energized from said do.

Landscapes

  • Health & Medical Sciences (AREA)
  • Pathology (AREA)
  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Measurement Of Radiation (AREA)
  • Analysing Materials By The Use Of Radiation (AREA)
  • Photoreceptors In Electrophotography (AREA)
  • Combination Of More Than One Step In Electrophotography (AREA)
US00305339A 1972-11-10 1972-11-10 Electron radiographic imaging chamber with current enhancement Expired - Lifetime US3792278A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
US30533972A 1972-11-10 1972-11-10

Publications (1)

Publication Number Publication Date
US3792278A true US3792278A (en) 1974-02-12

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US00305339A Expired - Lifetime US3792278A (en) 1972-11-10 1972-11-10 Electron radiographic imaging chamber with current enhancement

Country Status (9)

Country Link
US (1) US3792278A (ja)
JP (1) JPS50841A (ja)
BE (1) BE807096A (ja)
CA (1) CA986237A (ja)
DE (1) DE2356938A1 (ja)
FR (1) FR2206651B1 (ja)
GB (1) GB1403507A (ja)
IT (1) IT996423B (ja)
NL (1) NL7315416A (ja)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3892964A (en) * 1973-06-01 1975-07-01 Xonics Inc Insulating electrode for breakdown inhibition in electronradiography imaging chamber

Families Citing this family (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4704734A (en) * 1986-02-18 1987-11-03 Motorola, Inc. Method and apparatus for signal strength measurement and antenna selection in cellular radiotelephone systems
EP1034557A4 (en) * 1997-11-24 2007-01-17 Gerasimos Daniel Danilatos HIGH FREQUENCY GAS DETECTION DEVICE

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3443097A (en) * 1968-01-05 1969-05-06 Atomic Energy Commission Pocket radiation dosimeter utilizing capacitor integrator
US3594162A (en) * 1967-11-22 1971-07-20 Agfa Gevaert Ag Electrographic recording process with charging deflection

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3594162A (en) * 1967-11-22 1971-07-20 Agfa Gevaert Ag Electrographic recording process with charging deflection
US3443097A (en) * 1968-01-05 1969-05-06 Atomic Energy Commission Pocket radiation dosimeter utilizing capacitor integrator

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3892964A (en) * 1973-06-01 1975-07-01 Xonics Inc Insulating electrode for breakdown inhibition in electronradiography imaging chamber

Also Published As

Publication number Publication date
CA986237A (en) 1976-03-23
DE2356938A1 (de) 1974-05-22
GB1403507A (en) 1975-08-28
FR2206651B1 (ja) 1977-03-11
BE807096A (fr) 1974-05-09
FR2206651A1 (ja) 1974-06-07
IT996423B (it) 1975-12-10
NL7315416A (ja) 1974-05-14
JPS50841A (ja) 1975-01-07

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AS Assignment

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

AS Assignment

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