215
TABLE 77.
M? ano C ror Varrovus Gases
Gas
1. Has
2. CF,
Pressurerange,
ure
C
2-11
1.3-11
5.0
10.3
42.2
84.0
9-27
5-20
4-12
3-14
3-10
3-12
2.3-9
1.9-8
1.1-8
1.0-4
1.5-9
1.9-6
1,0-6
2.414
2.4-18
4-12
5.2
6.2
9.9
10.2
11.9
10.6
14.2
18.4
19.6
17.5
22,0
23,0
25.1
8.0
6.8
3.2
|
3. PHs
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
17.
18,
19.
CH,
CH,OH
C.H;OH
(CH3)20
(CH3).CO
eyeloC3H,
(CH;}CH
nC
(CH3)},C
CH,
cyeloCgHis
nCelT is
nC His
Xe
CsHy
H.0
2-12
|
4.6
|
|
45.9
53.8
66.4
97.7
105.2
118.0
106.2
141.9
184.8
182.9
162.4
213.2
223.4
256.2
72.4
68.8
32.3
o(em?) = 1.874 % 1072 (M2xr, + Cx»)
B
I
a=
1
g
ge
1 Bt
—1
lxw=-
Be
(velocity of primaryelectron) /(velocity of light}.
results quoted above to be the most reliable, but the
uncertainty in the absolute values is not indicated.
Limits of error will be discussed in the following section
of this report.
Our previous measurements on Xe and C,H, were less
self-consistent than we would like, so newsets of data
for them were obtained and analyzed. The data for H,O
are reanalyzed. The results, given in the last three lines
of Table 77, supplant the results reported earlier.
LIMITS OF ERROR
Errors maybest be discussed in relation to the Bethe
formula, which has been used as the basis for smoothing
and averaging our observations, On theoretical grounds,
the formula should be expected to describe accurately
the energy dependence of cross sections throughout and
well beyond the range of our measurements; within their
limits, the measurements conform to this expectation.
The formula maybe written
o = (1.874 & 10°" em*)C[(M?/C)a, + 2].
Its form is illustrated in Figure 166, where o/C is plotted
against log £ for the values of M’/C = 0.08, 0.10, and
0.12. Amongourresults, values of C range from 7 to 250,
TABLE78.
entrance windowof a gas-filled counter. Calculations
showed that at 0.1 MeV the average path of primaries
E, MeV
between entrance and exit windows is 114 % greater
than the distance between the windows; the difference
becomesnegilgible for energies above 0.5 MeV. Previ-
200
Theresults for CO, reported previously were obtained
by Geiger Mueller counting. When we learned that proportional counting could be used with this gas, a new
set of measurements with this mode of counting were
carried out to provide a eross check. The results orig-
The same data, reevaluated and reduced according to
our current criteria and method, yield the values
W= 5.754010,
C= 559 +04.
eee fTRU ang SRE
ear
The new data, with proportional counting, give the result
MM = 5754007,
1.0015 + 0.0041
‘ Relative standard deviation, based on counted numbers.
report.
C= 55.7 + 0.6.
0.9960 + 0.0057
1.0075 + 0.0059
Average
by increasing AZ” by 4% and decreasing C by 34%; the
correction has been applied to all values quoted in this
M’ = 6.14 + 04,
otfae
0.77
1.10
ously reported results can be corrected for this effect
inajly reported, corrected for scattering, are
Comparison oF [LONIZATION CROSS SECTIONS OF
ELECTRONS AND PosrTRONS ON ARGON
w
E
S
150
ts
100
4 10
8a
blo
é0
T
PRESENT
EXPERIMENTS
4
60
6
40
4
30
3
Q
C= 579403.
The uncertainties indicated are the standard deviations
as given by the least squares solutions, each involving
about forty data points, and indicate the degree of
internal consistency of the data. We believe the last
20
|
105
|
10¢
L
107
{
108
10?
2
ev
Fic. 166—-Bethe formula ¢/C as a function of primary en-
ergy. &, with 1f°/C as a parameter,