18—12.
THE SENSlTIVITY OF COUNTERS
429
depends (among other factors to be discussed later) in an approximately linear manner with the load resistance (R of gure 18—5)
and may amount to 300 volts, although it is usually only a few
score of volts.
The ”l7W/ZOZ6Ï 00/mge
where impulses are rst obtained,
varies from 300 to 2000 volts, as discussed in the section on the
manufacture of a tube.
The difference between the operating and
300
‘
290
240
_
N
lu
_
_
‘s 200
_
È
-
_
/50
_
<:
_
lu
"‘
/20
V
°)
_
Ë 80
'
_
Ë
p
p
5
40
îlt
1020
/040
[060
mao
//00
//20
//40
060
_
,
.
VOLTAGE
__
'
F1G. 18—11.
A typical Counting rate-voltage curve.
_
the threshold voltages (V0 = V
Vi) is called the
_
.
and varies in practice from ten to several hundred volts.
18—12.
The Sensitivity of
instrument
has a
lower limit; it cannot be used to
measure quant1t1es of lesser
-
amount.
In the case of counter tubes, this sens1t1vrty is set l }31y
_
the background or residual
rate.
Further,
when t e
,
'
source is so weak as to add comparat1vely few additional counts
above the background, it becomes necessary
to conmder StÎÎSÜ— _
'callÿ the uctuations which occur around the average or
_0ng.
time ” value.
_
,
.
.
_
—
Now read Section 11—1L
_
_
—_
_
_
»
_
(1
The relative __sensitiv‘ity,as dened by equation 11—26,f ËâÏ1e
from 0 6 to 1.8 for a tube designed for the
detection O_
d
12 centimeters by 2 centimeters
gamma rays.13 The catho __e
was
_
_
_
_
THE SENSlTIVITY OF COUNTERS
429
depends (among other factors to be discussed later) in an approximately linear manner with the load resistance (R of gure 18—5)
and may amount to 300 volts, although it is usually only a few
score of volts.
The ”l7W/ZOZ6Ï 00/mge
where impulses are rst obtained,
varies from 300 to 2000 volts, as discussed in the section on the
manufacture of a tube.
The difference between the operating and
300
‘
290
240
_
N
lu
_
_
‘s 200
_
È
-
_
/50
_
<:
_
lu
"‘
/20
V
°)
_
Ë 80
'
_
Ë
p
p
5
40
îlt
1020
/040
[060
mao
//00
//20
//40
060
_
,
.
VOLTAGE
__
'
F1G. 18—11.
A typical Counting rate-voltage curve.
_
the threshold voltages (V0 = V
Vi) is called the
_
.
and varies in practice from ten to several hundred volts.
18—12.
The Sensitivity of
instrument
has a
lower limit; it cannot be used to
measure quant1t1es of lesser
-
amount.
In the case of counter tubes, this sens1t1vrty is set l }31y
_
the background or residual
rate.
Further,
when t e
,
'
source is so weak as to add comparat1vely few additional counts
above the background, it becomes necessary
to conmder StÎÎSÜ— _
'callÿ the uctuations which occur around the average or
_0ng.
time ” value.
_
,
.
.
_
—
Now read Section 11—1L
_
_
—_
_
_
»
_
(1
The relative __sensitiv‘ity,as dened by equation 11—26,f ËâÏ1e
from 0 6 to 1.8 for a tube designed for the
detection O_
d
12 centimeters by 2 centimeters
gamma rays.13 The catho __e
was
_
_
_
_