l
l
'
18—8.
TYPES OF _COUNTER TUBES
423
is applied
in such a manner as to make the metal tube
'
negat1ve With respect to the wire. The voltage (V) is greater
than a certain critical or threrhold value but less than that whiçh
would cause a discharge of electricity to occur through the gas
A slight ionization produced in the gas by the entrance of even a
single particle will initiate a process of cumulative ionization
between the two electrodes and a comparatively large current will
ow through the external resistance (R). The potential drop
across _R rises quickly, the net voltage across the tube falls below
the extinction voltage (in many cases equal, approximately, to
the threshold voltage) and the current ceases to ow.
_
An inherent and valuable characteristic of counter tubes is
the large internal a772plcation due to the cumulative ionization
_
’
initiàted by each ionizing particle. The currents in ionization
chambers_ are usually of the order of magnitude of 10—10-to 10—15
.
ampere and require sensitive instruments or high gain ampliers -
for their detection.
With counter tubes,
the other hand, the
currents
(through R of güre 18—5) are sometimes as great as
10”5 amperes.
A two stage amplier connected across R isofte
suicient to operate a countèr-meter.
_
»
_
The number of voltage impuls'es produced across the load
resistance (R) each second is directly proportionalto the number
-
of particles incident on the tube in nit time, provided
the individual ionizing events do not occur so rapidly that the discharge
in the tube can not ceaSe in the brief
between SHCC€SSIVC
—
Çvents.
'
.
_
‘
18—8.
Types of Counter
; types of counter
_
‘
tubes are used for the detection‘of
kinds Of particles.
‘
When constructed in“ the
With com—
"
paratively thick walle‘d.»cath0dés‘,th€îYafeusell
more
.
penetrating radiations,“ s‘u‘çhasxandgammarays Inthese
cases, secondary particlesejectedfmmthecath0de
,
t°
'
-
‘
the thickness and surfacecondltlfm0fth€cath‘3demuSt be‘°,‘Γ-Î
,
*
l
'
18—8.
TYPES OF _COUNTER TUBES
423
is applied
in such a manner as to make the metal tube
'
negat1ve With respect to the wire. The voltage (V) is greater
than a certain critical or threrhold value but less than that whiçh
would cause a discharge of electricity to occur through the gas
A slight ionization produced in the gas by the entrance of even a
single particle will initiate a process of cumulative ionization
between the two electrodes and a comparatively large current will
ow through the external resistance (R). The potential drop
across _R rises quickly, the net voltage across the tube falls below
the extinction voltage (in many cases equal, approximately, to
the threshold voltage) and the current ceases to ow.
_
An inherent and valuable characteristic of counter tubes is
the large internal a772plcation due to the cumulative ionization
_
’
initiàted by each ionizing particle. The currents in ionization
chambers_ are usually of the order of magnitude of 10—10-to 10—15
.
ampere and require sensitive instruments or high gain ampliers -
for their detection.
With counter tubes,
the other hand, the
currents
(through R of güre 18—5) are sometimes as great as
10”5 amperes.
A two stage amplier connected across R isofte
suicient to operate a countèr-meter.
_
»
_
The number of voltage impuls'es produced across the load
resistance (R) each second is directly proportionalto the number
-
of particles incident on the tube in nit time, provided
the individual ionizing events do not occur so rapidly that the discharge
in the tube can not ceaSe in the brief
between SHCC€SSIVC
—
Çvents.
'
.
_
‘
18—8.
Types of Counter
; types of counter
_
‘
tubes are used for the detection‘of
kinds Of particles.
‘
When constructed in“ the
With com—
"
paratively thick walle‘d.»cath0dés‘,th€îYafeusell
more
.
penetrating radiations,“ s‘u‘çhasxandgammarays Inthese
cases, secondary particlesejectedfmmthecath0de
,
t°
'
-
‘
the thickness and surfacecondltlfm0fth€cath‘3demuSt be‘°,‘Γ-Î
,
*