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Патент USA US2405572

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Aug. 13, 1946.
H. FRIEDMAN
2,405,572
RADIOGRAPHIC EXPOSURE METER
Filed Aug. s, 1945
732
Elma/Mm
HERBERT FRIEDMAN
MW
P'aiented Aug. 13, 1946
2,405,572
UNITED STATE S PATENT OFFICE
2,405,572
RADIOGRAPHIC EIQOSURE METER
Herbert Friedman, Arlington, Va.
Application August 3, 1943, Serial No. 497,271
4 Claims. (Cl. 250-835)
(Granted under the act of March 3, 1883, as
amended April 30, 1928; 370 0. G. 757)
1
2
This invention relates to an exposure meter for
the determination of photographic exposures to
penetrating radiations and particularly to a form
of Geiger-Mueller tube for inclusion in a meas
uring circuit to make a radiographic exposure
meter.
It is an object of the invention to provide a
comprising capillary tubes 22 and 23 and spring
member 24, respectively. Electrical connection
is made to the tube by way of the hole in end cap
12 which is aligned with anode cap 25 on the
tube.
use‘
In general, in constructing the tube it is desirable to make it of material highly permeable to
Geiger-Mueller tube for use in an exposure me
the radiation which is to be measured. Inasmuch
ter sensitive to all penetrating radiations harder
as it is contemplated that the speci?c tube will
than about 100 kilovolt X-rays.
10 ?nd its greatest application in radiography of
Another object includes the provision of a
metals and like materials to determine exposure
form of sensitive element having a built-in
times, the parts should be of material permeable
to X-rays of all degrees 05 hardness commonly
standard of calibration to check circuit adjust
ments quickly and to eliminate the need for
used in such practices, gamma rays, and alpha
highly stabilized circuits.
15 particles. Since these radiations are all inher
Other objects and advantages will be apparent
ently very penetrating, such common materials
The invention, accordingly, comprises a radia
as glass or quartz for end caps I‘! and IB, alumi
num, beryllium, copper, brass, or bronze for the
tion intensity measuring and comparing appa
tube body it, and Bakelite, or laminated cloth
from the following description.
4
ratus embodying in a Geiger-Mueller tube the 20 and Bakelite, for the outer casing, ll, I2, I3, are
eminently suitable. Within the tube, the anode
features of construction, combination of ele
2| is preferably of a high grade wire such as
ments, and arrangement of parts, which will be
exempli?ed in the construction hereinafter set
steel piano wire and the spacers I9 and 20 are
preferably of mica.
forth and the scope oi the invention will be in
The gas ?lling of the tube may be any of the
dicated in the claims.
25
gases ordinarily used in Geiger-Mueller tubes,
In order that the invention may be fully un
i. e., the inert gases, hydrogen, argon, neon,
derstood, it is described in detail with reference
krypton. I have found that argon in the tube at
to the accompanying drawing in which,
a pressure of about four centimeters of mercury
Figure 1 is a sectional view of a Geiger-Mueller
counter tube for use in the type of measurement 30 serves well. A mixture of argon and ethyl alco
hol vapor, the partial pressure of the argon being
to be made;
four centimeters and that of the alcohol about
Figure 2 is a diagram of a frequency measuring
four millimeters of mercury, functions well as
circuit which can be employed with the Geiger
gas ?lling for a fast counter.
Mueller tube to form an exposure meter.
The construction of the tube is preferably such
Referring to Figure 1, It! represents a. Geiger 13 MI
that a known “active" or “counting‘ volume is
Mueller tube enclosed in an insulating casing
de?ned by the body I6 and spacers l9 and 20.
which comprises a plurality of sections, ll, l2
This volume is preferably predetermined so that
and I3, the first being a body section and the
its projected area, namely, that identified as the
other two end pieces. Body section II is a sub
stantially cylindrical member open at one end 10 rectangle developed by taking a section through
the body and the spacers and indicated by the
and having an axial hole 14 in the other end.
letters a, b, c, d, in Figure 1 is relatively small
The open end of section II is closable by a cap
and known. If the body of the tube l0 be cylin
i2 having a hole therein to provide for electrical
drical and the tube oriented with its longitudinal
connection to parts within the case. The closed
axis parallel to a given plane, e. g., the plane of
end of section Ii is made engageable with an in
a photographic ?lm, the area abcd remains
ternally recessed cap 13, the recess l5 in cap l3
constant for all positions of rotation of the tube
being made to match the hole M in the end of
section II in order to permit the insertion of
about its axis, or movements in the Plane of its
a standard radiation source into said recess.
axis. This has the distinct advantage of caus~
The Geiger-Mueller tube proper comprises a
ing the active volume of the tube to intercept
radiation over a constant irradiated area and
radiation permeable body I6, which serves as a
cathode ?tting snugly in section II, radiation
makes relatively simple the scanning of a very
permeable end caps I1 and I8 sealed to body It,
much larger area. Other geometrical con?gura
internal insulating supports l9 and 20, anode 2i,
tions of the tube body can be used, but they have
and anode guide and tension sustaining means
the disadvantage that rotation about the longi
2,405,572
,
3
tudinal or anodic axis of the tube varies the area
used to intercept radiation.
In the internal recess l5 within cap l3 there
current pulses through the counter tube l0 con
trol the magnitude of the current ?owing in the
tube 21 which is indicated by the meter 32. The
is placed a radiation source in the form of a
indication of the meter thus becomes a measure
radioactive button enclosed in container 23.
The button is made of known size and material
of the intensity of the radiation to which the
tube It is exposed.
A variety of sensitivity ranges for the meter
and acts as a constant known source of radia
tion. By ‘making its container 26 of lead, provid
can be obtained by providing a selection of grid
resistors as shown in Figure 2. When the grid
container in place in the recess to align it co 10 resistance is less than one hundred megohms the
axially with the tube, the emanations from the
current flow through the tube In is not appre
button can be collimated and directed through
ciably aifected by the external resistance and the
the end of the tube proper into its active volume
potential developed at the grid 28 is therefore
to initiate discharges therein. In this manner, a
nearly proportional to the magnitude of the ex
direct comparison of the unknown radiation in 15 ternal resistance. By varying the grid resistors
tercepted by the active volume of the tube (or
in the range from one megohm to one hundred
the area indicated by abcd in Fig. 1) with the
megohms a series of sensitivity ranges can be
standard source can be achieved. Knowledge of
established to permit determination in a few
the exposure time required to photograph prop
minutes of exposure times from a few minutes to
erly the emanations from the button gives a di 20 several hundred hours, the ranges commonly en
rect measure of the exposure time needed to pho
countered in gamma ray and X-ray radiography,
tograph any portion of the area scanned.
If the different resistances for the several sen
The manner of using the tube in an exposure
sitivity ranges merely served to alter the scale of
meter can be readily understood by reference to
the ampli?er circuit, it would be simpler to pro
Figure 2 which is a circuit diagram of a simple 25 vide corersponding shunts for meter 29. The
exposure meter employing a Geiger-Mueller tube
grid resistance, however, does more than merely
as a detector in, cooperation with a measuring
determine the current gain of the ampli?er. A
circuit. In the diagram, It! represents diagram
high grid resistance gives a high sensitivity but
matically a Geiger-Mueller tube corresponding to
the response saturates quickly with increasing in
that shown in Figure 1 which has a cathode l6 30 tensity. The lowering of the grid resistance de
and an anode 2|. The Geiger-Mueller tube is
creases the ampli?cation but brings about a lin
ing it with a small hole 26a, and fastening the
connected to an electronic amplifying circuit
which includes tube 21, having a grid 28, plate 29
ear response at high intensities.
When using the device as an exposure meter,
and cathode 30, The tube 21 is shown as a tri
the specimen which is to be photographed is in
ode for the sake of simplicity but actually can be 35 terposed between a radiation source such as radi
a tetrode or pentode or, like multi-grid tube
um or an X-ray source and the detector tube held
The cathode i5 of the Geiger-Mueller tube I0 is
in the position which would be occupied by the
photographic ?lm. The entire area correspond
ing to the area of the ?lm can easily be scanned
held at a high positive d1rect potential by con 40 in a few minutes for the sensitivity of the de
nection to a potentiometer 3i which voltage
tector is such that a. reading which will indicate
should be from about 600-1200 volts and should
an exposure time of 100 hours can be made in a
be regulated well enough to keep the tube in its
few minutes.
range of constant operating or counting char
Since certain changes may be made in the
acteristics. The regulation can be readily ac
above construction and different embodiments
complished by means of a series of gas regulator
of the invention could be made without depart
tubes connected across the high voltage source in
ing from the scope thereof, it is intended that all
connected to the grid of the amplifying tube
The anode ‘M of the Geiger-Mueller tube is
conventional manner.
matter contained in the above description or
In the amplifying and measuring circuit com
shown in the accompanying drawing shall be in
prising tube 21 and meter 32, cathode 30 of the 50 terpreted as illustrative and not in a limiting
tube is grounded and a positive potential is ap
sense.
plied to plate 29 through the meter 32. The
The invention described herein may be manu
ground return of the grid 28 includes any one of
factured and used by or for the Government of
several resistance-capacitance circuits 33, 34, 35,
the United states of America for governmental
36, or 31, the particular one desired being selected 55 purposes without the payment of any royalties
by means of switch 38. In order to maintain the
thereon or therefor.
current in tube 2'! at a minimum, or zero, when
I claim:
the tube in is not being activated by received
1. A Geiger-Mueller tube for comparing hard
penetrating radiation, a suitable negative bias is
radiation of unknown intensity with hard radia
applied to the grid 28 by means of potentiometer 60 tion of a known intensity comprising, a radia
39, the positive end of which is at ground poten
tion-permeable tubular member forming a cath
tial.
ode, an anode extending axially therethrough,
In operation, when hard radiation impinges
insulating disks closing the ends of said cathode
on tube to and penetrates the active volume, a
thereby de?ning an active tube volume, a radia
pulsating current is initiated and flows in the cir 65 tion permeable envelope for said anode, cathode,
cuit comprising tube ill, the high potential source
and disks, and means for exposing the active
and one of the resistance capacitance circuits.
volume de?ned by the cathode of said tube to
The capacitance in the circuit serves to average
a source of constant radiation impinging on said
out the irregularities in the current flow so that
tube from a direction substantially coaxial with
a substantially constant potential will be applied 70 the tube axis.
to the grid 28 of tube 27, which potential will in
2. A Geiger-Mueller tube for measuring the
turn depend upon the ?xed bias applied to the
intensity of hard radiation comprising, a radia
grid and the potential drop across the resistance
tion-permeable tubular member forming a cath
of the said resistance-capacitance circuit. In
ode, said cathode having its ends closed by in
this manner the frequency and intensity of the 75 sulating disks thereby de?ning a ?xed active vol
2,405,:72
ume, an anode extending axially therethrough
and means for exposing said tube to a source of
constant radiation impinging on said tube from
a direction substantially coaxial with the tube.
3. A Geiger-Mueller tube for measuring the 5
intensity of penetrating radiation comprising, a .
radiation-permeable tubular member forming a
cathode, mica disks closing the ends of said
cathode thereby de?ning a ?xed active counting
volume, an anode wire extending axially there'
through, and means comprising a recessed con
tainer associated with said tube having a known
quantity of radioactive material therein and a
radiation-collimating aperture for directing radi
ation into the tube for exposing said active vol
ume to a collimated constant known source of”
radiation impinging’ on said tube from a_ direc
tion substantially parallel to the axis of said tube.
4. A Geiger-Mueller tube for comparing the
intensity of-penetrating radiation of unknown
intensity with penetrating radiation of known in
tensity comprising, a radiation-permeable me
tallic tubular member forming a cathode, said
cathode being closed at its ends by mica disks to
de?ne a ?xed active volume having a constant
projected area in a plane parallel to its longi
tudinal axis, an anode extending axially there-h
through and means comprising radioactive ma
terial in a recessed container associated with said
tube for exposing said active volume to radiation
collimated by the exit from said container in a
direction substantially parallel to the longitudi
nal axis of the tube.
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