Activation Analysis 
Determines Sodium Content 
of Aluminum Alloys 
Precision better than 1%, a limiting accuracy of 0.0001 %, and an average 
standard deviation of 0.00024% are obtained in the range 0.01-0.04% sodium 
when neutron-activation analysis is applied to aluminum alloys 
By ROBERT C. PLUMB and 
RALPH H. SILVERMAN 
Aluminum Research Laboratories 
Aluminum Company of America 
New Kensington, Pa. 
NEUTRON-ACTIVATION-ANALYSIS princi- 
ples and techniques, as applied to 
determining the sodium content of alu- 
minum alloys, are presented by this ar- 
ticle. After outlining the procedure, 
details of the irradiation, chemical 
separation, and measurement steps are 
given. The precision and accuracy 
obtained and the problems overcome 
are presented. 
Analysis Principles 
Analysis by neutron activation has 
been described by many authors (1-4). 
In its simplest form, it consists of ex- 
posing samples containing an unknown 
amount of an element together with 
standards containing a known amount 
of that element to a neutron flux and 
comparing the activity produced in 
each. In the general case a variety of 
radioisotopes could be produced from 
196 
elements in the samples. Therefore, 
the radioisotopes being determined 
must be separated chemically. A 
salient feature of activation analysis is 
that the separation need not be quan- 
titative but must yield a product of 
radiochemical purity, 7.e., free from 
other radioisotopes. A large quantity 
of nonradioactive carrier may be added 
to the irradiated material to facili- 
tate the separation. The comparison 
method of activation analysis de- 
scribed here has a distinct advantage 
over many other comparison methods 
in that primary standards, such-as pure 
salts, can be used. 
There are several possible shortcom- 
ings in activation analysis. It is gen- 
erally assumed that neutron flux 
through reasonably sized samples is 
constant. However, in detailed con- 
sideration, there may be variations in 
neutron flux over the irradiation con- 
tainer dimensions from inhomogeneities 
in the neutron source and from attenu- 
ation of neutrons by the samples them- 
Chemical Analysis Method 
Determination of sodium in aluminum is customarily made by a spectro- 
chemical comparison of samples with standards whose sodium content has been 
determined by a sinter-leach method (5). 
Completeness of sodium removal from aluminum by the sinter-leach method 
has been open to question. 
There has been no direct proof of the validity of the 
chemical determination because of the difficulty of preparing synthetic metal 
standards of known sodium concentration and the prohibitively large blanks 
encountered in complete sample dissolution procedures. 
Neutron activation 
analysis appears to have sufficient sensitivity and inherent accuracy to be 
applied as an independent method of analysis. 
