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CONVENTIONS IN EXPRESSING lSOTGPIC CWF’OSITION OF 9

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URANIUM SAMPLFS, AVIXAGE ATOMIC I,EIGHTS .—— -. PU6UCLYRELEASABLE

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CB14 REPORTC - TK)N

REPRODUC ION

R. W . Dodson

‘ COPY

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The following discussion is written for the convenience of those

handling Yo12 product; it presents some of the conventions used in expressing isotopic composition and suggests an atomic weight scale for use in con.

nection with mixtures,of varying isotopic constitution.

In describing these mixtures it is necessary to speoify the relative amounts of ~,”2b, and 28. At least four different methods of description

--

are in current use. The percentages of the various constituents may be expressed on either an atomic or a mass basis; alternatively two ratios between

the amounts of the three

or mass basis.

different components may be given on either an atomic

These quantities have been used to express the results

at Berkeley and at Site Y.

in a given sample

in a given sample

spectrometer determinations are

The symbols ~ and ~ are proposed

often expressed

for the ratios

No. of atoms of 2t3 in a given sample

No. Of atoms of 25

NO. Of at0m8 Of 25

No. of atoms of ~

in a given sample

APPROVED FOR PUBLIC RELEASE

APPROVED FOR PUBLIC RELEASE
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~. UNCLASSIFIED”

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(,~) Mass ~.ercentDefinitions 100R%= 100 (m#” mi) =

250 28) nrhere mi is the maas of the

(1+) Atomic percent o

mass percent of i.th component (i = 240

ith Conponent in a given mmple.

Definition 100 xi 5 mo (Qqni) = atomic percent of ith component. where

ni iS the mmber of atoms of the ith component (i = 2& 2cj,26) in a given

B8111plC30

RFMTIC)NS IHTKEEN THE ABOVE QUANTITIES —.

R=r

238.48 — = g x 1.0128

- 2jYj.CYj’

s

235.0~

=

‘-

= gx 1.00)43

mtms fraction * =

mI18f3fraction 25 =

imma fraotion 28 =

atomic fraction *

a;omic fraction 25

atomic fraotion 28

●

R

a20 =

l+R+l/S

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= ‘== +-vii

-.btl$i= atomio weight of ith constituent

..

~ = average almmio weight of miimple

APPROVED FOR PUBLIC RELEASE

APPROVED FOR PUBLIC RELEASE
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a.

1=

Xi( Mi/ti ) = Xi(l.!if

‘i=ai*

In mass spectrometer data, the amount of 2&0is often not given.

this case a reasonable assumption for present racetrack m“aterialis that

is ccnstant and equal to 1220 Then,

The

1)

. Mattauch ;

fcllowing packing fractions are given by Hahn, Flf.igge,and

Calculated Atomio Weight

Isotope -(M- A)/.- Chemical Scale

J%:’;6:;:0 ~~) (Normal Oxygen = 16,000.~~~)

—. .

a 5.51x 10-4 234.129

2a 6008 X 10”4 2*0 N45

The fourth column is obtained from the third

234.06

235?07

238.08

by dividing byloOO0275.

From Nier$s mass spectrometer assays of normal material (~ = 139,

s = 17000)0 we obtain

’24 = oooooo5~5 for normal uranium

%5 2 oooo71&2 for normal uranium

—. —.

—,

-—_

_-— — –_

__ :- —. ..: .

..

UNCIASSIFIEO

APPROVED FOR PUBLIC RELEASE

APPROVED FOR PUBLIC RELEASE
’28 =

o4927B for normal uranium

Using these values and tho above atomic weights, the calculated chemical atomic

weight of normal uranium is 23&.o6 (of. 238.07, Mt. Chem. At. ht.).

.

It is fully realized that the above numbers contain a greater.number

of figures then our experimental knowledge justifies. It seems worthwhile,

hovvevcr, purely for the sake of consistency, to adopt a given set of values

for the atomic weights of the uranium iso~opcs and for the composition of normal uranium, especially when etoichiom.gtriccalculations are made for large

sasiples. The above numbers are proposed for this purpose.

The above numbers and relations have been kindly cheoked by Dudley

hilliarnsand Gcrhart Friedlander.

b

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APPROVED FOR PUBLIC RELEASE