Letter - H. Tracy Hall Foundation

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Letter - H. Tracy Hall Foundation
.r
REIN-AJ -51-0117
JOURNAL
OF
APPLIED
PHYSICS
VOLUME
Letter£"<
FR(
I
c.,I
The Size of Latex Particles
No .
I
J
B. R.
X-Ray Scattering*
LEONARD, JR . , J. W. A
EREGG , PAUl. KAESU E RG,t
AND W. " . BlmMAN
D,,/UJrtmrlll
0/ Physics,
Ullivcr . y oj
( Receiv
~Vis,olls':n.
Madisol'z , Wisco1lsi1'Z
October 17, 1951)
HE discovery of e ext remely uniform size of the spher.· al
T
Jot
has
particles of
ystyrene Dow latex S80
caused considerab interest in the possible use of these par cles as
G,
358'
a calibration
ndard for electron microscopes. l A
rvey of
determinati s of the size of these particles has been esented by
eterminations which depend on a mea rement with
on microscope have led to an accepte value of 2590A
particle diameter. Kern and Kern,' hower, have reported
shadowed particles
ue of 2590A for the diameter of the
t a value of 2840A for obliquely shado ed particles. Recently,.
investigators using other methods hav obtained diameters be·
tween these two. Dandliker' has rep ted a value of 2720A as
determined by light scattering an Yudowitch& has reported a
value of 2740A by small angle x- ay scattering. Our result is in
close agreement with these later alues.
We have used the method
small angle x-ray scattering 6 to
. determine the particle dia eter from the secondary diffracted
maxima characteristic of heres. The experimental arrangement
used was similar to that f Ritland, Kaesberg, and Beeman.
The angular distrib ion of scattered intensity from spheri I
particles of uniform ectron density is given by the well-k own
function
0::
J
)
M
23,
ing,
s the x-ray wavelength, and R i the particle radius. The
pos' IOns of the secondary maxima Cl minima of this function
aT. known and are used to determ' e the particle radius.
The scattered x-ray intensit depends on the square of the
difference of the electron del ty between the particle and the
surrounding medium. Sinc the electron density of the latex is
very nearly that of wa ,the scattering from a suspension of
all that its measurement is not feasible.
latex in water is s
Hence our sampl were run dry or in a suspension of methyl
alcohol. The samples were dried over phosphorous pentoxide at
oow
The Effect of Pressure on Scintillation Phosphors'
A. J .
REINSCH ANU
II. G .
DR1 CKAMER
Department oj Chemistry. Uui'l.lers ity oj llli" ois, Urbulln, IllilloiJ
(Received October 19. 1951)
I
N the course of development of high lJreSSUre tracer techniques,
a study has been made of the pressure coefficient of cadmium
tungstate and anthracene phosphors in the range from atmospheric
pressure to 10,000 atmospheres. The windows used were synthetic
sapphire with the" e" axis oriented perpendicular to the fiats.
1.0,.....--..,---....,.---,---,..---,
.. \
LATEX
8 . THIN
~
.----.~
ORY SAMPLE
0.8
.......
-
-~
-.
-~-.--
C. LATEX IN CH,OH
,..
Z
1.0
z
o
"'a:
..."'
•
\
•
,,
10
o
,
•
II>
..
19l,
• Research su pp ted in pa rt by the ONR a~d in p
Alumni Rcscarcl oundation.
t Departme of Biometry and Physics, Univer . y of Wisconsin.
1 R. C . Ba
us and R. C. Williams, J. App!. P s. 19, 1186 (1948); R.C
Backus an R. C . Williams, J. App!. Phys.
,224 (1949); G . D. ScOti'
J. App!. lYS. 20, 417 (1949).
.
'C, . Gerould. J. App!. Phys. 21, 183 950).
'S . Kern and R. A. Kern, J. Appl. hys . 21, 705 (1950).
• . B. Dandliker, J , Am. Chern. So .72,5110 (1950).
K. L. Yudowilch. J. App!. Phys.
,214 (1951). The value reported by
r. Yudowtich in this article was 27 A. However. Dr. Yudowitch inrormt :
the authors by private comm i tion prior to tillS experiment th.. t li~
had revised his result to 2740A
• Ritland, Kaesbcrg, and B a n, J. Chem. Phys. 18, 1237 (1950); A.
Guinier, Ann. phys. 12, 161 (1939); O. Kratky, J. Polyme( Sci. 3, 195 (19481.
A. THICK DRY SAMPLE
II>
A R Y,
atmospheric pressure, and the wet samples were obtained
resuspending in methyl alcohol.
The accompanying figure shows representative curves of I'
scattered intensity vs angle obtained from two different thir'.
nesses of dry sample and a wet sample. The curves all sholl' I)
smea . g elTect resulting from finite slit dimensions. The I.,
sal lie curve also shows the elTcct of multiple scatlerin" SJ1l~a '
i g the peaks. We have observed the first seventeen axima frr,the thick sample and the first eight maxima fT n t.he thim:"
samples and the wet samples. The accurac with which If,
particle diameter can be determined is di ctly proportional :'"
the scattering angle, and in the analysi of the data the vaL
obtained are weighted in proportior 0 the angle. A weighl,
average of 133 separate values 0 maxima and minima yicl,;.
2731A for the particle diameter. he weighted average devialir·
of the individual measureme s from the mean is 34A, and tho
statistical accuracy of the
. n is about ±3A. The results fro1:1
the wet and dry s,lmples, e in agreement. We have also measure.1
a sample of the latex u d by Yudowitch in his determina ' anQ
this gives a result c sistent with our value.
A
.
.."'
1
N2{Sin(kR)-(kR) COS(kR)}2
(kR )'
'
where },[ is le number of irradiated spheres, N s the number of
sinO .
er sphere, k=4,.. T' 0 IS one-ha
10'
NUMBI!:I(
o
o
..
0.&
..
~----~~---~~---~------7----~~~.~~~ ~~
o
SCATTERING ANGLE
4000
6000
PRBSUR£ ON CRYSTAL.
FIG. I. Representative Curves of scattered x·ray intensil)'
as a function of angle for nolystyrene Dow latex.
FIG. 1.
152
8000
lopoo
A TM •
The effect of pressure on counting rate for _a CdWO.
crystal on a sapphire window.
.J
tl
Jl
II
f
LETTERS
1 cfs 1
V.
TO
TH E
153
EDITOR
I
1.0~
..
7fo
vcs of Ihe
ent thid"
I show Ihe
The lhit ~
~
•
'.0 •
; in srllt>:H.
,,~.
xima froll1
he thinnrr
which th e
)r tional t, )
the valu, ..
, weightt·o\ .
ima yield,
: deviation
-\, and Ihf
!sults frum
) measure,l
nation nn,l
l- ---~ - - - -: --~-;-.- - .
6000
4000
2000
PRES5URE ON
CRYSTAL.
8000
,opoo
A TV
was no noticeable effect of pressure except on the fouling of the
windows.
An explanation of the phenomena can be obtained from Fig. 3,
which shows the absorption cu rve for cadmium tungstate and the
response curve of the photomultiplier tube. The strongest emission
band for CdWO, is at 5200A, that for anthracene is at 4400A.
From the absorption curve for CdWO" it is clear that no reasonable
shift of the emission or absorption band combined would alone be
sufficient to give the measured efTect. However, if th e emission
band for CdWO, would shift 100A toward higher wavelengths, the
relative response of the photomultiplier tube would decrease by
14 percent. A similar shift in the emission band for anthracene
would result in a 3 percent decrease in relative tube response.
The.authors are ind ebted to Dr. R. J. Maurer and his coJleagues
of the Physics Department of the University of Illinois for running
the absorption curve on CdWO., and for helpful conversations
concerning the interpretation of the results.
* This work was supported in pa rt by the AEC.
1 T. C. Poulter. Phys. Rev. 35. 297 (1930).
'Timmerhaus. Giller. Duffield. and Drickamer. Nucleonics 6. 37 (1950).
Flc. 2. The effect of pressu re
011 counting rate for an
anthracene crystal on a sapph ire window.
ons il\.
1(48) ; R . C
G. D.
~
ScUll.
re por ted Iw
itch inforl1U"11
Ilent that Ii,.
17 (1950); A
l. 195 (194 ~J
losphors'
I1liu o;,f
. techniqu l".
of cadmiu m
atmospher ic
:re synthct k
to the ilal .
lh windows were one-half inch in diameter and one-half inch
and covered a quarter-inch opening. The sapphire and the
f:';r tll wcre ground and lapped Bat, and a Poulter' type seal was
c«' 1. The bomb design and the other seals were standard of the
\·.pc commonly used by P. W. Bridgman. In one test a plate glass
>:ndo'" of approximately the same dimensions was used.
III cach case the crystal was fastened to the window wi th Canada
1I.0I<'1 m, solid sulfur containing S" was piled on the crystal, and
;.n-reel with dissolved Lucite to protect it from the pressure!'.trI,rnilling fluid (heplane). The Lucite was permitted to harden
. Hr night. The light was conducted from the window to a photo-liitil'li{'r tuhe hy a Lucite rod. The tu be was cooled to dry icc
!'"'pcra ture. The tuhe circuit and general setup was only slighLiy
.Iif,ed from that previously descrihed.'
The pressure was ll1e;~sured by a manga nin gauge, calibraled
rrtlm Ihe freezing point of mercury at O°C (7394 atm os).
The rcsults for cadmium tungstate are shown in Fig. 1, those
"'r ant hracene in Fig. 2. In each case there was an irreversihle
' ,(lel~e in cou nting rate, larger on the first run than on later runs,
":r to' the fou ling of the window. This effect was not large enough
:.) mask t he distinct difi'erences in the behavior of the crystals.
1"- the case of cadmium tungstate there was a reversible pressure
c:1<"\:1 on the scintillation efficiency, amounting to 15 to 20 percent
;"rcase ill efficiency at 10,000 atmospheres. For anthracene, there
!~ic k.
Direct Printing of Shadowed Electron Micrographs
R. M. FlsrmR
R esearch Laboratory. UlIiled Slates Sleel C01llpallY. Kearny. New Jer sey
(Received November 5. 195t)
S
HADOWCASTINGI of electron microscope specimens is one
of the most useful and often used techniq ues of electron
microscopy. As is well known, shadowi ng, besides giving a threedimensional aspect to micrographs, improves the contrast of
'organic replicas and v'e ry fine particulate matter .
Unfortunately, to obtain " black" shadows on prints a photographic reversal is required. This is done hy making a positive
transparency from th e original neg.ttive and then making prinls
fro m the posi tive. This extra slep increases the chance of scra tches,
pin-holes, and loss of sharpness in the print and takes considerahle
time, especially when many routine pictures are taken. For these
reasons many laboratories make direct prints from the negatives
and as a result the shadows on such prints arc white. The" shadow'
cap" on heavily shadowed replicas is often mistaken for the
shadow, leading to confusion as to the relief of detail on the surface.
.c.
'OO;---'---::;;..,..."'<::~--r---'----'----,
-.
_I.... . .-.-.".,.....
........., /
,
... . ...., 7·
~ CO~
20 _
~.
I(
I
E,,'SS'ON SPECTRU"
COW04 TRANS ....
RESPONSE
or
,ssrON
TUBE
/
IPZI./'
~'~~-~--4~OOO~--~--~
so~o~o---L--'6~OOO
WAVELENCTH.
CdWO.
ANCSTROloAS
f·'G. J. CdWO. emission and transmission characteristics compared
with r~sponse of photomultiplier tube I P21.
Frc. 1.
Cementit~
lamellae extracted from steel. Direct printed
reversing paper. 16.000X.
011

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