The actinium-uranium ratio in Colorado carnotite

THE ACTINIUM-URANIUM RATIO IN
COLORADO CARNOTITE

KARL H. FUSSLER

A THESIS

Presented to the Faculty of the Graduate School of the

University of Pennsylvania in Partial Fulfilment of

the Requirements for the Degree of

Doctor of Philosophy

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THE ACTINIUM-URANIUM RATIO IN
COLORADO CARNOTITE

BY

KARL H. FUSSLER
///

A THESIS

Presented to the Faculty of the Graduate School of the

University of Pennsylvania in Partial Fulfilment of

the Requirements for the Degree of

Doctor of Philosophy

PRESS OF

THE NEW ERA PRINTING COMPANY

LANCASTER, PA.

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THE ACTINIUM-URANIUM RATIO IN COLORADO
CARNOTITE.

[Reprinted from The Physical Review, N. S., Vol. IX, No. 2, February, 191 7.

THE ACTINIUM-URANIUM RATIO IN COLORADO
CARNOTITE.

By Karl H. Fussler.

IT is generally accepted by investigators in radio-activity that actinium
is a branch product from the uranium transformation series. This
is based on the following facts: (i) Actinium is always found in uranium
minerals; (2) Boltwood^ separated the actinium from North Carolina
uraninite and determined the ratio of its activity, with its products in
radio-active equilibrium, to the activity of the uranium with which it
was associated. The values of this ratio, from the four determinations
which he made, were 0.14, 0.15, 0.24 and 0.36. He gives the value 0.28
as the weighted mean of these results. (3) He^ also measured the total
activity of various uranium minerals and determined what fraction of
this total activity is due to each of the separate radio-elements contained
in the minerals. His results indicate that the activity of a uranium
mineral, containing equilibrium amounts of the various radio-elements,
is about 4.7 times the activity of the -uranium in the mineral. The sum
of the activities of the separate radio-elements, uranium to polonium,
plus 0.28 X uranium for the actinium series, gives 4.64 X uranium as
the total activity of the mineral. If actinium is a branch product of the
uranium series there should be a constant ratio between the activities
of the actinium and of the uranium in all uranium minerals.

Since this ratio has been directly measured for only one uranium
mineral and for only two specimens of that mineraP it was thought
desirable to determine it using another uranium mineral. This paper
describes the experiments carried out using Colorado carnotite.

Through the courtesy of the Cummings Chemical Company, manu-
facturers of radium, of Lansdowne, Pa., I was enabled to select my
specimens from ton lots of mineral. Only large, firm lumps of the
higher grade ores were chosen. The final selection was made at the
laboratory from the bulk of the mineral brought from the factory, and,
as a rule, only the centers of the larger lumps were chosen. The two

^ Boltwood, Amer. Jour. Sci., XXV., p. 269, 1908.

* The specimens used are described by Boltwood as no. 3 and no. 4 uraninite from Spruce
Pine, N. C. Two of the results were obtained from one sample of specimen no. 3, one result
from another sample of the same specimen, and one from a sample of specimen no. 4.

No^2^-^'] COLORADO CARNOTITE. I43

Specimens finally selected represented two different shipments of ore.
Specimen A after pulverizing and passing through a 40-mesh screen
consisted of about 300 grams ©f carnotite. Specimen B was a lower
grade material. There were about 75 grams in this lot.

The radio-active measurements were made in an alpha-ray electroscope
which will not be described as it differed in no essential detail from one
described by Boltwood.^ The gold-leaf was charged by connecting,
through a water resistance, to the negative terminal of a 400-volt battery
of "Spindler and Hoyer" cadmium cells. The guard ring was perma-
nently connected to the negative terminal of the battery. The case of
the electroscope and the positive terminal of the battery were connected
to earth.

A microscope, with a graduated scale in the eye-piece, was rigidly
clamped in front of the electroscope. The readings consisted in timing
the passage of the tip of the gold-leaf over a certain definite portion of
the graduated scale. The sensitiveness of the electroscope was deter-
mined for every series of measurements by taking a reading of the leak
produced by a standard film of uranium oxide. This standard was
made several years ago by Professor D. H. Kabakjian, from a very pure
specimen of uranium oxide. It was deposited in the form of a thin film
on a light brass disc. It has been carefully preserved and from time to
time its activity has been compared with the activity of a primary
uranium standard, which was similarly prepared, and which has been
used only as a comparison specimen for the secondary standards.

The natural leak of the electroscope was determined for every series
of measurements and the corrections made for it. It was fairly low and
has not varied materially during the past one and one half years.

The general plan of the experiments was to separate chemically the
ionium, radio-actinium, and actinium, as a group, with the rare earths
as oxalates, from the other radio-elements in a specimen of carnotite,
to determine the weight of the mixture of these elements and the non-
radio-active elements separated with them and to make a very thin
film, of known weight, on a metal plate, from this active material. The
growth of activity of this film was measured at intervals over a period
of about 100 days, at which time the equilibrium value had been attained.
The activity due to ionium and actinium plus its products in equilibrium
in one gram of carnotite was calculated from the equilibrium value of
the activity of this film. A film, of known weight, was also made from
the uranium separated from the same specimen of mineral. The activity
due to the uranium alone in one gram of carnotite was calculated from

1 Loc. cif., p. 272.

144 KARL H. FUSSLER, [j

Second
Series.

the activity of this film. Boltwood^ has shown that the activity of
ionium in a uranium mineral is 34 per cent, of the activity of the uranium
with which it is associated. This result was used in calculating the
activity of the ionium per gram of mineral. Deducting the activity due
to ionium, from the combined activity of ionium and the actinium series,
gives the value of the activity due to actinium and its products in equi-
librium in one gram of the mineral. This latter value divided by the
activity due to the uranium in one gram of the mineral gives the value
of the actinium-uranium activity ratio.

Because of the minute quantities of these radio-elements in a mineral
the usual method used in separating them is to introduce into the solu-
tions other elements, or carriers, which are either isotopic, or chemically
similar to them. The best method of separating ionium from a mineral
is to introduce thorium, if not already present, and then separate the
thorium by the well-known chemical processes. Wishing to avoid the
introduction of another radio-element, cerium was used as a carrier,
the chemical properties of which are not very different from those of
ionium. In the same way lanthanum was used as a carrier for the
actinium.^ As radio-actinium is isotopic with ionium,^ evidently it will
be precipitated with the ionium. The details of the experiments are as
follows :

Experiment i. — Twenty-five grams of specimen A carnotite were de-
composed by heating with dilute nitric acid and the solution evaporated
to dryness. The residue was treated with hot dilute nitric acid. The
insoluble matter was separated by decantation and again treated with
the hot dilute acid. The solutions were combined and the insoluble
matter, consisting largely of silica, after washing, was found to have
negligible activity. The solution was saturated with hydrogen sulphide
to separate the insoluble sulphides after the addition of a small quantity
of bismuth nitrate to ensure complete precipitation of the polonium.
The filtrate was boiled to remove the excess of hydrogen sulphide.
Small amounts of cerium nitrate, and lanthanum nitrate, were added,
and while the solution was still hot, an excess of oxalic acid was added
and allowed to stand for about twenty hours. The precipitated oxalates
were removed, a minute quantity of the cerium and lanthanum salts was
again added, and the precipitation by oxalic acid repeated.'^ The
oxalates were combined, converted into nitrates, and again precipitated

* Loc. cit., p. 289,

2 Auer von Welsbach, Sitzungber. K. Akad. Wiss. Wien, 1910, 119, ii., a, i.
' Fleck, Journ. Chem. Soc, 103', 381, 1913.

* In work preliminary to these experiments it was found that a third oxalate precipitate
had a negligible activity.

}Jo^-2^^] COLORADO CARNOTITE. 1 45

by oxalic acid. The oxalates were converted into oxides by intense

ignition over the blast-lamp. The rare earth oxides obtained in this

manner weighed 1.0230 grams. A film weighing 0.0082 gram was made.

The activity of this film when it had reached equilibrium, was 5.202

,. . . . 1 • . 1.0230

divisions per minute. This gives — — — X 5.202 = 26 divisions

25 X 0.0082

per minute for the activity due to the ionium and the actinium, plus its

products in equilibrium, in one gram of carnotite.

The filtrates, from which the oxalates were separated, were evaporated
to dryness and gently heated to destroy the oxalic acid. The residue
was taken up in dilute hydrochloric acid, a small amount of barium
chloride was added, and the radium precipitated as sulphate with the
barium. The addition and precipitation of the barium was twice
repeated to ensure complete removal of the radium. The filtrate was
boiled with an excess of sodium carbonate, containing some ammonium
sulphide, and the carbonates filtered off. The uranium was precipitated
and weighed as sodium uranate. It weighed 6.6042 grams and the film
made from it weighed 0.0096 gram. The activity of the film was 1.990
divisions per minute. This gives an activity of 55 divisions per minute
for the uranium in one gram of the mineral.

The activity of the ionium per one gram of the mineral, using Bolt-
wood's value, should be (0.34 X 55) 18.6 divisions per minute. De-
ducting this value from the activity calculated from the ionium-actinium
film (26 divisions per minute per one gram of mineral) gives 7.4 divisions
per minute as the activity due to actinium and its products in equilibrium.
This is 0.135 times the activity of the uranium.

Experiment 2. — Fifty grams of specimen B carnotite were taken for
this experiment. The material was treated in the same manner as that
of experiment i. The activity of the ionium-actinium film 100 days
after separation was 2.1 16 divisions per minute which gave 18.2 divisions
per minute as the total activity of the ionium and actinium per one gram
of mineral. The sodium uranate separated weighed 8.5234 grams, and
the film weighed 0.0041 gram, which showed an activity of 0.849 divi-
sion per minute. This gave an activity of 35.2 divisions per minute
for the uranium in one gram of carnotite. The activity of the ionium,
calculated as before, is (0.34 X 35-3) 12.0 divisions per minute. Sub-
tracting this from the combined ionium-actinium activity gives 6.2
divisions per minute as the activity of the actinium series. This divided
by the activity of the uranium (35.3 divisions per minute) gives 0.176
as the value found for the ratio of the activity of the actinium and its
products to that of the uranium with which it is associated.

146

KARL H. FUSSLER.

[Second
[series.

Experiment J. — Twenty-five grams of specimen A carnotite were treated
in the same manner as in experiment i. The activity of the uranium
per gram of carnotite was 51.5 divisions per minute. The combined
activity of the ionium and the actinium series per gram of carnotite
was 23 divisions per minute. The calculated activity due to the ionium
(0.34 X 51-5) is 17.5 divisions per minute which leaves 5.5 divisions per
minute as the activity due to actinium and its products in equilibrium.
This divided by the activity of the uranium gives 0.107 as the actinium-
uranium ratio.

The values for the relative activity of the actinium series obtained in
these experiments were, therefore, 0.135, 0.176, and 0.107 X Ur.

A theoretical curve was plotted on the assumption that an equilibrium
amount of radio-actinium was precipitated with the actinium. This
curve was obtained by adding the ordinates of curves I and //, Fig. i.

•

3

'i

>

5 ^

X.

^

^

2 60

y^

9

**

y^

"Ty^

u

y^

y^^

^^

/

y^

«

y

/

•

/

y ^

/

^ ~~/

I

/

^^"^-^5

Ex^i»«.t No.a

10

--

> —

To So — 30 ^ — :

ro <o 7« eo *«

K

DW

Fig. 1.

Curve / is the recovery curve of actinium freed from all its active pro-
ducts.^ The ordinates represent the activity and the abscissae the time
in days from separation. The equilibrium value of the activity is taken
as 100. McCoy and Leman^ have shown that the equilibrium activity
of radio-actinium is 17.6 per cent, of the total activity of the actinium
series. This value is used as the initial value of the radio-actinium
curve (Curve 77). The crosses give the experimental values of the
growth with time of the activity of the film of experiment no. 2. The
curves for experiments no. i and no. 3 were similar in shape, but with
initial activities somewhat lower. (13.9 per cent, for no. i and 11.7
per cent, for no. 3.) The agreement is well within the limits of experi-
mental error. This, I believe, indicates that the film did not contain

1 Hahn, Phil. Mag., XIII., 165. 1907-
' Phys. Rev., 4 Ser. 2, 1914, p. 409.

Na2!'^'] COLORADO CARNOTITE. 1 47

other radio-active elements in quantities sufficient to appreciably alter
the shape of the actinium plus radio-actinium curve. The disagree-
ment between the experimental and the theoretical curves may be
accounted for by an incomplete precipitation of the ionium in the speci-
mens. A computation shows that if 1.5 per cent, (for film of experiment
no. 2) of the ionium remained in the solution the starting point of the
two curves would agree. This would make the actinium ratio larger by
about 2.8 per cent.

Conclusions.

1 . The ratio of the activity of the actinium series to the activity of the
uranium associated with it in Colorado carnotite has been determined.

2. The results indicate that the quantity of actinium in carnotite is
proportional to the quantity of uranium.

3. The value of the ratio is of the same order of magnitude, but some-
what lower than that obtained by Boltwood using North Carolina
uraninite.

4. The results are in agreement with the theory that actinium is a
branch product of the uranium series.

In conclusion I wish to acknowledge my indebtedness to Professor
Arthur W. Goodspeed for kindly placing at my disposal all the facilities
of the Randal Morgan Laboratory, and to Professor D. H. Kabakjian
for suggesting the subject of this research and for his continued co-
operation and valuable criticisms during the course of the investigation.

Randal Morgan Laboratory of Physics,
University of Pennsylvania.

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