Supersaturation necessary for condensation of a vapor upon ions is maintained continuously by the diffusion of an initially warm saturated vapor through a noncondensing gas into a refrigerated region. Convection is avoided by diffusion vertically downward between a horizontal heated roof and refrigerated floor. Calculations show what flux of vapor and what roof and floor temperatures are necessary. Experiment shows that this diffusion cloud chamber operates as expected, and with reasonable precautions it is quite stable against turbulence. Successful operation depends on avoiding production of condensation nuclei which will make a diffuse rain of condensation in the chamber. Vapor from liquid in a glass flask heated by radiation from above has been found to be practically free of aggregates. The chamber cannot produce satisfactory ion tracks in the presence of too great an average ion load. In the steady‐state operation of the present apparatus the normal background ionization without shielding loads the chamber so close to its limit that most tracks are diffuse. When first applying refrigeration there is a transient condition in which many more tracks are well defined. There are several possible ways of improving the steady‐state ion load capacity of the apparatus.

1.
F. N. D.
Kurie
,
Phys. Rev.
53
,
215
(
1938
). Sensitive time 5 seconds in each minute.
2.
J. A.
Bearden
,
Phys. Rev.
45
,
758A
(
1934
). Sensitive time over 1 second per expansion.
3.
H.
Brinkman
,
Proc. Roy. Acad. Amsterdam
39
,
1185
(
1936
).
4.
T.
Shimizu
,
Proc. Roy. Soc.
99
,
425
(
1921
).
5.
L. G. Hoxton, “A Continuously Operating Cloud Chamber,” Proc. Virginia Acad. Sci., Abst. 9, p. 23 (1933–34).
6.
R. E.
Vollrath
,
Rev. Sci. Inst.
7
,
409
(
1936
).
7.
A.
Langsdorf
,Jr.
,
Phys. Rev.
49
,
492
(
1936
);
A.
Langsdorf
, Jr.
,
51
,
1026
(
1937
).,
Phys. Rev.
8.
K.
Kuusinen
,
Ann. d. Physik
24
,
445
,
447
(
1935
).
9.
The curve is calculated by the equation ln Scr = k(M/d)(σ4/3/T) as suggested by calculations of
Powell
in the
Proc. Roy. Soc.
119
,
553
(
1928
). Taking Scr = 2.9 at −6 °C evaluates the constant k, where M is the molecular weight of methanol, d its density, σ its surface tension, and T the absolute temperature.
10.
Experiments have not been performed to determine the real necessity of a polished reflecting top.
11.
In a chamber as large as D this sealed space must aspirate so pressure changes from cooling and warming will not break the glass.
12.
Air can be used. Nitrogen decreases fire hazard.
13.
Another type of system capable of being free of convection may be worth mentioning in passing, as illustrated by the specific combination of materials that was used. Butyl alcohol vapor was diffused upward through hydrogen from a warm surface to a refrigerated plate. The gas volume appeared to be free of convection. However, there was a great deal of condensation which started so very close to the top refrigerated plate that one might conclude that the liquid surface on this top plate acted as a source of condensation nuclei. This observation should be of value in an investigation of processes of aggregate formation.
14.
If condensation persists without the chamber floor being cooled, there is strong reason to presume aggregates are present in the vapor supply before it reaches the chamber.
15.
The most promising materials appear to be some combination of water, ammonia, methane, and nitrogen. Ammonia and water are particularly interesting because of the large reduction of the saturation vapor pressure of water by dissolved ammonia, so that a cloud chamber operating with these materials would combine the operating principles of the diffusion cloud chamber and Vollrath’s chemical cloud chamber.
16.
A similar effect has been observed in expansion cloud chambers. See reference 1.
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