GB1558601A - Device for monitoring the centring intensity and uniformity of a beam of ionizing radiation - Google Patents
Device for monitoring the centring intensity and uniformity of a beam of ionizing radiation Download PDFInfo
- Publication number
- GB1558601A GB1558601A GB445776A GB445776A GB1558601A GB 1558601 A GB1558601 A GB 1558601A GB 445776 A GB445776 A GB 445776A GB 445776 A GB445776 A GB 445776A GB 1558601 A GB1558601 A GB 1558601A
- Authority
- GB
- United Kingdom
- Prior art keywords
- electrode
- electrodes
- elements
- safety system
- radiation beam
- 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
Links
Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01T—MEASUREMENT OF NUCLEAR OR X-RADIATION
- G01T1/00—Measuring X-radiation, gamma radiation, corpuscular radiation, or cosmic radiation
- G01T1/29—Measurement performed on radiation beams, e.g. position or section of the beam; Measurement of spatial distribution of radiation
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
- H01J37/00—Discharge tubes with provision for introducing objects or material to be exposed to the discharge, e.g. for the purpose of examination or processing thereof
- H01J37/02—Details
- H01J37/244—Detectors; Associated components or circuits therefor
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
- H01J37/00—Discharge tubes with provision for introducing objects or material to be exposed to the discharge, e.g. for the purpose of examination or processing thereof
- H01J37/30—Electron-beam or ion-beam tubes for localised treatment of objects
- H01J37/304—Controlling tubes by information coming from the objects or from the beam, e.g. correction signals
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
- H01J2237/00—Discharge tubes exposing object to beam, e.g. for analysis treatment, etching, imaging
- H01J2237/244—Detection characterized by the detecting means
- H01J2237/2445—Photon detectors for X-rays, light, e.g. photomultipliers
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
- H01J2237/00—Discharge tubes exposing object to beam, e.g. for analysis treatment, etching, imaging
- H01J2237/244—Detection characterized by the detecting means
- H01J2237/24455—Transmitted particle detectors
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
- H01J2237/00—Discharge tubes exposing object to beam, e.g. for analysis treatment, etching, imaging
- H01J2237/244—Detection characterized by the detecting means
- H01J2237/2446—Position sensitive detectors
- H01J2237/24465—Sectored detectors, e.g. quadrants
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
- H01J2237/00—Discharge tubes exposing object to beam, e.g. for analysis treatment, etching, imaging
- H01J2237/245—Detection characterised by the variable being measured
- H01J2237/24507—Intensity, dose or other characteristics of particle beams or electromagnetic radiation
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
- H01J2237/00—Discharge tubes exposing object to beam, e.g. for analysis treatment, etching, imaging
- H01J2237/245—Detection characterised by the variable being measured
- H01J2237/24571—Measurements of non-electric or non-magnetic variables
- H01J2237/24578—Spatial variables, e.g. position, distance
Landscapes
- Chemical & Material Sciences (AREA)
- Analytical Chemistry (AREA)
- Physics & Mathematics (AREA)
- Health & Medical Sciences (AREA)
- Life Sciences & Earth Sciences (AREA)
- General Physics & Mathematics (AREA)
- High Energy & Nuclear Physics (AREA)
- Molecular Biology (AREA)
- Spectroscopy & Molecular Physics (AREA)
- Measurement Of Radiation (AREA)
- Electron Tubes For Measurement (AREA)
Description
(54) A DEVICE FOR MONITORING THE CENTRING,
INTENSITY AND UNIFORMITY OF A BEAM
OF IONIZING RADIATION
(71) We, C.G.R.-MeV, a French
Body Corporate, of 13, Square Max Hymans, 75015 Paris, France, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- The present Application for a Patent of
Addition relates to an improvement in a device for monitoring the centring, intensity and uniformity of an ionizing radiation beam of the kind described by the present
Applicant in the British Patent No 1,463,891 and relates more particularly to the ioncollecting electrodes arranged in the ionization chambers of the device.
In accordance with the present
Application for a Patent of Addition, a device for monitoring the centring, intensity and uniformity of an ionizing radiation beam issued from a radiation source comprises two ionization chambers respectively provided with two electrodes, one of said electrodes having an area smaller than the area of the other electrode, the area of said other electrode being substantially equal to the cross-sectional area of said radiation beam, at least said other electrode comprising a plurality of electrically conducting elements which are electrically insulated from one another, said electrodes being respectively associated with circuits for processing electrical signals furnished by said electrodes, said processing circuits controlling a safety system and said safety system controlling said source of said radiation beam.
For a better understanding of the present
Application and to show how the same may be carried into effect, reference will be made, by way of example, to the drawings accompanying the ensuing description and in which:
Figures 1, 2 and 3 schematically illustrate three embodiments of electrodes used in a
device in accordance with the present
Application for a Patent of Addition:
Figure 4 schematically illustrates two
electrodes which can be used when the
radiation beam is previously centred by
known means;
Figure 5 illustrate two ionisation
chambers provided with electrodes shown
in Figure 4;
Figure 6 shows two examples of the
distribution of the radiation beam intensity
along a diametral axis of the electrodes::
Figure 7 schematically illustrates a
comparator circuit associated with
electrodes shown in Figure 4;
Figures 8, 9 and 10 respectively illustrate
a diagram of processing circuits and two
comparators circuits for monitoring the centring, intensity and uniformity of an ionizing radiation beam.
In a first embodiment, the device comprises two ionization chambers respectively equipped with two circular split electrodes E" E2 shown schematically in
Figure 1. Each of these electrodes E" E2 is constituted by a sheet of polyethylene terephthalate known by the trade mark of "Mylar" upon both faces of which there has been deposited by vaporisation under vacuum a thin metallic film which is transparent to the ionizing beam. Two insulating strips 3 and (formed of Mylar not carrying the metallising) diametrically split the electrode E, into two elements e" and e,2 and the electrode E2 into two other elements e2, and e22 these insulating strips 3 and 4 being arranged at 90" to one another.
The electrode E, has an area S, substantially equal to the cross-sectional area of the ionizing beam, whilst the electrode E2 has a smaller area S2.
In operation, the elements e", e,2 and e21, e22 of the electrodes E, and E2 respectively pick up currents lii, i,2 and i21, i22. The ionizing radiation fluxes 01 and 02 respectively intersecting the electrodes E, and E2 are proportional to the currents l,=i"+i,2 and 12=i21+i22, respectively picked off by the electrodes E1 and E2. If the flux is uniform, then the equation:
S1 #1 = #2 (1') S2 corresponding to:
S1
I1 I2 (2')
S2 is satisfied.
In operation, assuming that the beam intensity remains rotationally symmetrical about the beam axis, if we consider the most unfavourable case of a non-uniform radiation beam having an eccentricity Ad in accordance with the axis of the insulating strip 3 of the electrode E1, such that: d,-d,
#d# (5) 2 d, and d2 being the respective diameters of the electrodes E, and E2, then a comparison of the currents I, and I2 which are picked off, provides the following information: S, Ii < 12 (6)
S2 1ii=112 (7)
i21 > i22 (8) The inequalities (6) and (8) then give rise to the operation of an alarm or safety system which stops the radiation beam.
In the case of a uniform beam which is eccentric, then the information: =i12 (9) 121=122 (10) S,
Ii < 12 (11) S2 is obtained. The inequality (11) causes the safety system to halt the emission of the radiation beam.
However, it should be pointed out that a centred, non-uniform beam, produces at the outputs of the monitoring circuits relationships identical to those (9), (10), (11). As in the former case, the inequality ( I 1) produces operation of the safety system and consequent halting of emission of the radiation beam. In the embodiment which has just been described, the reliability of operation of the device is therefore assured, but no indication is given of the defect which has developed in the radiation beam:
In two other preferred embodiments (Figures 2 and 3), the defects which the beam has developed are indicated.
Figure 2 schematically illustrates two electrodes E3 and E4 utilised in the device in accordance with the invention.
The electrode E3 comprises four elements e21, e32, e33 and e34 and the electrode E4 comprises a single element e4.
In operation, measurement of the current
I3=i31+i32+i33+i34 enables the electrode E3 to monitor the flux # that is to say the radiation dose which is proportional to the current 13, this flux # likewise being monitored by the second
ionization chamber furnishing a current S4
14= 13.
S2 Moreover:
centring of the beam is obtained if: i3,=i32=i33=i34 ( I 2) uniformity of the beam is satisfactory if:
S3
I3=k I4 (13)
S4 k being a coefficient close to 1, taking account of the safety standards which are imposed.
If the radiation beam is previously centred before entering the two ionization chambers, then the electrode E3 of the first ionization chamber can be changed to an electrode E01 having a single element (this corresponding to the electrode E3 having elements both connected) as shown in
Figure 4. Electrode E01 and electrode Eo2 which is identical to electrode E4 for example, are respectively disposed in two ionization chambers as shown in Figure 5 for example. Electrode E01 has a diameter d, substantially equal to the diameter of the ionizing beam whilst that E02 has a diameter smaller than dl. These areas, respectively S0, and S02 are such that.
Sol > S02 In operation, the ionizing fluxes 0, and 02 respectively intersecting the electrodes E01 and E02 are proportional to the currents Io1 and 102 picked off by the electrodes E01 and Eo2 If the flux is uniform, then the equation: SO,
i #2 (1) S02 corresponding to: Soi
lo1=102 (2) S02 is satisfied.
It is to be noted that the electrodes located within these ionization chambers and having upper and lower metallised transparent walls (not shown in the figures) are suitably biased by a substantially identical bias, which is a negative bias with respect to these walls. A frame C carries the sheets of metallised Mylar forming the electrodes E01 and E02 as illustrated in
Figures 4 and 5.
In Figure 6, graph (a) represents the variation in the current lo1 and therefore in the flux #01, along a diametral axis xx of the electrode E01, for a uniform and properly centred radiation beam, whilst in said same figure the graph (b) illustrates the variation in the current lo1 through said electrode E01 when the centred radiation beam is nonuniform (in the considered case, the ionising beam is denser at its centre than at its periphery).The currents lo1 and 102 are then no longer proportional to the areas S0, and
S02 of the electrodes E01 and E02, and the equation (2) becomes: SO, Ioi < 102 (3)
S02
A circuit (Figure 7) comprising two comparators Cp0, and Cp02 enables the voltages V01 and V02 corresponding to the currents I01 and I02 picked off at the electrodes E01 and E02 to be compared, so that the safety system Ss is triggered if:: Soi vo1 Vo2 > vthreshold (4)
S02 Threshold being a threshold voltage of given value, which depends upon the operating parameters or the characteristics of the irradiation device.
The electrode arrangement of Figure 4 controlling the intensity and uniformity of the centred radiation beam can be associated with means for checking the centring of the radiation beam, for example with probes, or comprising a known type of split electrode enabling the centring of the beam to be monitored.
If the radiation beam is a scanning beam, monitoring of the centring of the beam can be achieved by associating with the ionization chamber equipped for example with the electrode E2 which has four elements e3t, e32, e33, e34, a cent ring device of the kind described in the British Patent
No. 1.488,555 of the present Applicant, which centring device may also be associated with two electrodes such as E1 and E2. each having two elements.
In another embodiment, the monitoring device in accordance with the present application comprises three ionization chambers 5, 6 and 7 respectively provided with three electrodes E5, E6 and E7 as shown in Figure 3. The electrodes E5 and E6 substantially have the same diameter as the radiation beam and each comprise two elements e51, e52 and e61, e82 respectively.
The electrode E7 of smaller diameter, has only a single element, E7.
The elements e51, e52 of the electrode E5, those e61, e62 of the electrode E5 and the element e7 of the electrode E7 respectively pick up the currents i51, i52; i5,; i52 and i7.
In the case of a non-uniform beam, this non-uniformity being due, for example, to the absence of a correcting filter or to some defect in the beam scan function, the relationships: i7 > k(i51+i52) (13) i7 > k(i61+i62) (14)
are obtained. These inequalities lead to trigger a safety system which interrupts the operation of the radiation source, or controls the ionization beam.
Figure 8 schematically illustrates an embodiment of the circuits for processing the signals picked off by the electrodes E5,
E6, E7. Amplifiers Ast, A52 produce voltages proportional to the current i51, i52. The operational amplifier Ass produces the voltage V,55 proportional to the sum of the currents iS1 +iS2. The variable resistor R51 makes it possible to calibrate the measured value so that this sum represents the dose rate measured by the chamber 5, for a given scale.
The operational amplifier AD5 furnishes a voltage VDS proportional to the difference of the currents 15ii52. A variable resistor R52 makes it possible to compensate any slight dissymetry which might exist between the two elements e51, and e52 of the electrode E5.
Similar elements have been indicated by corresponding references in the processing circuit belonging to the electrode E6. The amplifier A07 produces a voltage V7 proportional to the current i7 picked off by electrode E7, and therefore to the dose rate.
The voltages VS5, VS6 and V7 are applied respectively to error-detection circuits comprising comparators Cp1, Cp2, Cp3, Cp4, Cp5, Cp6 as Figure 9 shows. The resistors R, to R7 make it possible to adjust the values of the signals applied to the comparators, to take account of mechanical inaccuracies in manufacture.
Since the area of the electrode E5 is larger
than that of the electrode E7, the voltage V65 is higher than the voltage V7 in a ratio
S7
S5
namely the ratio of the areas S7 and S5 of the
electrodes E7 and E5. The resistors R1, R2
and R3 have resistances such that the
voltages V7 satisfies the double inequality:
R, R2+R3 Vs5 < V7 < V55,
R,+R2+ R3 R,+ R2+ R3 If this double inequality is not satisfied,
the comparator Cp, or Cp2 (depending upon
the imbalance) will produce a positive
output voltage triggering the safety system Sss or a signal K.
The comparators Cp and Cp4 trigger the
system Ss if the dose rate exceeds a given value VMax. Whilst the comparators Cp5 and CP6 trigger the safety system if there is any disagreement between the voltages V55 and
Vs6 and therefore between the dose rates measured by the electrodes E5 and E6.
In another embodiment shown in Figure
10, the currents picked off by the elements of the electrodes E5, E6, E7 are applied to a system constituted by a multiplier M and an analogue-digital converter CA associated with a computer C1, this system carrying out checks on the aforesaid conditions and controlling a safety system Ss which makes it possible to stop the radiation beam source if these conditions are not met.
WHAT WE CLAIM IS:- 1. A device for monitoring the centring, intensity and uniformity of an ionizing radiation beam issued from a radiation source, the device comprising two ionization chambers respectively provided with two electrodes, one of said electrodes having an area smaller than the area of the other electrode, said area of said other electrode being substantially equal to the cross-sectional area of said radiation beam, at least said other electrode comprising a plurality of electrically conducting elements which are electrically insulated from one another, said electrodes being respectively associated with processing circuits for processing electrical signals furnished by said electrodes, said processing circuits controlling a safety system and said safety system controlling said source of said radiation beam.
2. A device as claimed in claim 1, wherein said electrodes each comprise two semicircular elements separated from one another by an electrically insulating diametral strip, the insulating strip of said
one electrode being disposed at right angles
to that of said other electrode.
3. A device as claimed in claim 1, wherein said other electrode is split into four elements substantially of quadrantal shape and said one electrode is constituted by a single element.
4. A device as claimed in claim 1, said system comprising three ionization chambers. two of said chambers being respectively provided with electrodes having areas of substantially the same size as the cross-sectional area of said radiation beam, said electrodes being respectively provided with two semi-circular elements separated from one another by an electrically insulating diametral strip, said insulating strips being disposed at right angles to one another, the third chamber having an electrode constituted by a single element which electrode is of smaller size than the electrodes of said two chambers.
5. A device as claimed in claim 2, wherein the elements of each of said electrodes are associated with a processing circuit for processing the signals furnished by said elements of said electrode, said processing circuits comprising:
a comparator circuit making it possible, in respect of each electrode, to compare the sum and the difference of the signals furnished by said elements with predetermined threshold values; and
a safety system making it possible to control the radiation source when the measured signals have values which differ from said threshold values.
6. A device as claimed in claim 4, wherein said electrodes of said two chambers are respectively associated with processing circuits comprising:
a comparator circuit making it possible, in respect of each electrode, to compare the sum and the difference of the signals furnished by the elements of said electrodes with predetermined threshold values:
**WARNING** end of DESC field may overlap start of CLMS **.
Claims (7)
1. A device for monitoring the centring, intensity and uniformity of an ionizing radiation beam issued from a radiation source, the device comprising two ionization chambers respectively provided with two electrodes, one of said electrodes having an area smaller than the area of the other electrode, said area of said other electrode being substantially equal to the cross-sectional area of said radiation beam, at least said other electrode comprising a plurality of electrically conducting elements which are electrically insulated from one another, said electrodes being respectively associated with processing circuits for processing electrical signals furnished by said electrodes, said processing circuits controlling a safety system and said safety system controlling said source of said radiation beam.
2. A device as claimed in claim 1, wherein said electrodes each comprise two semicircular elements separated from one another by an electrically insulating diametral strip, the insulating strip of said
one electrode being disposed at right angles
to that of said other electrode.
3. A device as claimed in claim 1, wherein said other electrode is split into four elements substantially of quadrantal shape and said one electrode is constituted by a single element.
4. A device as claimed in claim 1, said system comprising three ionization chambers. two of said chambers being respectively provided with electrodes having areas of substantially the same size as the cross-sectional area of said radiation beam, said electrodes being respectively provided with two semi-circular elements separated from one another by an electrically insulating diametral strip, said insulating strips being disposed at right angles to one another, the third chamber having an electrode constituted by a single element which electrode is of smaller size than the electrodes of said two chambers.
5. A device as claimed in claim 2, wherein the elements of each of said electrodes are associated with a processing circuit for processing the signals furnished by said elements of said electrode, said processing circuits comprising:
a comparator circuit making it possible, in respect of each electrode, to compare the sum and the difference of the signals furnished by said elements with predetermined threshold values; and
a safety system making it possible to control the radiation source when the measured signals have values which differ from said threshold values.
6. A device as claimed in claim 4, wherein said electrodes of said two chambers are respectively associated with processing circuits comprising:
a comparator circuit making it possible, in respect of each electrode, to compare the sum and the difference of the signals furnished by the elements of said electrodes with predetermined threshold values:
another comparator making it possible to simultaneously compare the signal furnished by the electrode of said third chamber with the sum of the signals furnished by the elements of said two chambers; and
a safety system making it possible to control the radiation source when the measured signals have values which differ from threshold values.
7. A device substantially as hereinbefore described with reference to the accompanying drawings.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| FR7503798A FR2300414A2 (en) | 1975-02-07 | 1975-02-07 | DEVICE FOR MONITORING THE P |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| GB1558601A true GB1558601A (en) | 1980-01-09 |
Family
ID=9150889
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB445776A Expired GB1558601A (en) | 1975-02-07 | 1976-02-04 | Device for monitoring the centring intensity and uniformity of a beam of ionizing radiation |
Country Status (7)
| Country | Link |
|---|---|
| JP (1) | JPS5823704B2 (en) |
| CA (1) | CA1067624A (en) |
| CH (1) | CH588086A5 (en) |
| DE (1) | DE2604672C2 (en) |
| FR (1) | FR2300414A2 (en) |
| GB (1) | GB1558601A (en) |
| NL (1) | NL7601175A (en) |
Families Citing this family (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| NL7804037A (en) * | 1978-04-17 | 1979-10-19 | Philips Nv | ELECTRONIC MICROSKOP WITH UNDIFFERENTIATED PHASE IMAGE. |
| US4347547A (en) * | 1980-05-22 | 1982-08-31 | Siemens Medical Laboratories, Inc. | Energy interlock system for a linear accelerator |
| GB8415709D0 (en) * | 1984-06-20 | 1984-07-25 | Dubilier Scient Ltd | Scanning microscope |
| JPH0610001U (en) * | 1992-07-14 | 1994-02-08 | 正雄 宮前 | Trolley |
Family Cites Families (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FR2133318A5 (en) * | 1971-04-16 | 1972-11-24 | Thomson Csf | |
| FR2215701B1 (en) * | 1973-01-26 | 1978-10-27 | Cgr Mev |
-
1975
- 1975-02-07 FR FR7503798A patent/FR2300414A2/en active Granted
-
1976
- 1976-02-04 GB GB445776A patent/GB1558601A/en not_active Expired
- 1976-02-05 NL NL7601175A patent/NL7601175A/en not_active Application Discontinuation
- 1976-02-06 CA CA245,763A patent/CA1067624A/en not_active Expired
- 1976-02-06 CH CH149276A patent/CH588086A5/xx not_active IP Right Cessation
- 1976-02-06 DE DE19762604672 patent/DE2604672C2/en not_active Expired
- 1976-02-07 JP JP1186076A patent/JPS5823704B2/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| NL7601175A (en) | 1976-08-10 |
| JPS51102800A (en) | 1976-09-10 |
| FR2300414A2 (en) | 1976-09-03 |
| CA1067624A (en) | 1979-12-04 |
| CH588086A5 (en) | 1977-05-31 |
| DE2604672A1 (en) | 1976-08-19 |
| JPS5823704B2 (en) | 1983-05-17 |
| FR2300414B2 (en) | 1978-12-01 |
| DE2604672C2 (en) | 1984-09-27 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| PS | Patent sealed |