18—16.
DESIGN OF EXPANSION CHAMBERS
437
This requires approximately one minute, but may be reduced20
to one—quarter of a minute if, after an expansion, the gas is
tially compressed, then slightly expanded, then fully compressed.
It is left in each of these three conditions for about 5 seconds.
-
With a particular counter—controlled chamber, a particle
passed through the chamber, the electric eld was removed, and
°
the expansion took place in 0.015 second. The light was turned
on 0.035 second later and a photograph of the tracks was secured
during the following 0.1 second. The electric eld was turned on
and, 30—60 seconds later, the gas was compressed. After 30—60
seconds more, the chamber was in thermal equilibrium, ready
for the next expansion.
,
Extraneour Droplets.—Dust particles must be rem0ved by
repeated expansions when the chamber is rst assèmbled. Even
_
then, a general fog results from over—expansion; (never from
__
under-expansion). With the optimum expansion ratio, extraneous
‘
droplets may appear if there is too much liquid, above that needed
_
_
to saturate the gas.
It is thought21 that the impact-of the piston
at the end of an expansion may also cause undesired droplets.
Leakage currents set up by the sweep eld may
alcohol
'
and give general fogging. Photo-ionization of the vapor
(water, —
but not alcohol) by the intense light-may give undes1redtra‘cks.
The photo-nuclei are mostly unchargedand
be«removed
-
with an electric eld, but must
to the bottomof
the
.
‘
chamber.
Photo-electrons from'th‘e metal part—s» o_fthe Chamber
.
_
may be eliminated by painting with
This
reduces the number of alpha part1Cles€mlttedbYC0ntamlnatlons
-
in the walls.
The chamberWalls,‘gasallC111<ä111dmuStbeanree
=
from radioactive
‘
‘maY be used to PfèV€ttheCondensatmn°fdmSOntheWäS Ï ,and window.
.
_
-
__
;
Divaioñ Of the
«l:
Ï, rents of the gas—in
’_
'
…of small leaks, otherw1sethetraCk3WlbeadlYd18t Îted
_? ff
_
;” “&
'
»leak «badly and8h0uldbevam“hed@rœatÔdmta
<
:
,
ΑfÏfâ ï=‘1i»tew ….The latter— is not€fl@ct€dhYal°°h@1Wh‘levarnlShlS
.
f
DESIGN OF EXPANSION CHAMBERS
437
This requires approximately one minute, but may be reduced20
to one—quarter of a minute if, after an expansion, the gas is
tially compressed, then slightly expanded, then fully compressed.
It is left in each of these three conditions for about 5 seconds.
-
With a particular counter—controlled chamber, a particle
passed through the chamber, the electric eld was removed, and
°
the expansion took place in 0.015 second. The light was turned
on 0.035 second later and a photograph of the tracks was secured
during the following 0.1 second. The electric eld was turned on
and, 30—60 seconds later, the gas was compressed. After 30—60
seconds more, the chamber was in thermal equilibrium, ready
for the next expansion.
,
Extraneour Droplets.—Dust particles must be rem0ved by
repeated expansions when the chamber is rst assèmbled. Even
_
then, a general fog results from over—expansion; (never from
__
under-expansion). With the optimum expansion ratio, extraneous
‘
droplets may appear if there is too much liquid, above that needed
_
_
to saturate the gas.
It is thought21 that the impact-of the piston
at the end of an expansion may also cause undesired droplets.
Leakage currents set up by the sweep eld may
alcohol
'
and give general fogging. Photo-ionization of the vapor
(water, —
but not alcohol) by the intense light-may give undes1redtra‘cks.
The photo-nuclei are mostly unchargedand
be«removed
-
with an electric eld, but must
to the bottomof
the
.
‘
chamber.
Photo-electrons from'th‘e metal part—s» o_fthe Chamber
.
_
may be eliminated by painting with
This
reduces the number of alpha part1Cles€mlttedbYC0ntamlnatlons
-
in the walls.
The chamberWalls,‘gasallC111<ä111dmuStbeanree
=
from radioactive
‘
‘maY be used to PfèV€ttheCondensatmn°fdmSOntheWäS Ï ,and window.
.
_
-
__
;
Divaioñ Of the
«l:
Ï, rents of the gas—in
’_
'
…of small leaks, otherw1sethetraCk3WlbeadlYd18t Îted
_? ff
_
;” “&
'
»leak «badly and8h0uldbevam“hed@rœatÔdmta
<
:
,
ΑfÏfâ ï=‘1i»tew ….The latter— is not€fl@ct€dhYal°°h@1Wh‘levarnlShlS
.
f