SOME PROPERTIES OF T H E RADIATION FROM RADIOMANGANESE 54 AND T H E ADSORPTION OF MANGANOUS MANGANESE ON HYDROUS FERRIC OXIDE' DON H . ANDERSON'
Chemistry Department, The University of Idaho, Moscow, Idaho Received March 19, 1947
During the course of an investigation to identify an unknown radio element present in an iron disc,a it was observed that variation in the pII a t which the hydrous ferric oxide was precipitated caused a marked change in the amount of radiation of the precipitate. Subsequent determinations of the half-life and the chemical properties indicated that the material was radiomanganese. There is only one known stable isotope of manganese; this is &InS5. Several art,ificial isotopes (3) have been produced. These are radioactive and all but one have quite short half-lives, so short as to make some experimental work rather difficult. 1sot)opesof mass numbers 51, 52, and 56 have half-lives from 21 min. up to 0.5 days. Radiomanganese 54 has a half-life of about 310 days, which permits experiments to be performed over a period of several days without the need for compensation for decreased activity of the preparation. This isotope \yas the one used in this work. The decomposition of radiomanganese 51 results in the formation of stable chromium 51. Two kinds of radiation are observable, one soft and one hard. The mechanism has been demonstrated to be that of K electron capture. An electron falls into the manganese nucleus, the atomic number decreases by 1, and an outer electron falls in to replace the missing electron in the K shell of the new chromium e.tom and chromium x-radiation results. The absorption data in aluminum foil-corresponds to that of chromium x-radiation excited in the usual manner (3). 1;QUIPAltiST
The Lauritsen quartz-fiber electroscope is suitable for measuring the radiation from the manganese. The electroscope used had an aluminum-foil xindowv and the samples mere placed about 1 cm. below the v-indow. The pH measurements were made by means of a glass electrode and are accurate to + 0.05 pH unit. The colorimetric determinations of iron and manganese were made by means of the thiocyanate complex and the oxidation to permanganate, respectively. The colors were compared vith standards, using a Cenco Photelometer for comparison. 1 Portions of this paper were presented a t the Regional Meeting of the American Chemical Society which was held a t Seattle, Washington, on October 20, 1945. * Present address: Eastman Kodak Company, Color Control Division, Kodak Park Works, Rochester 4, Kew York. The iron disc, source of radiomanganese, was obtained b y Dr. Gerhart Friedlander while he was at the University of Idaho. J
PROPERTIES OF THE RADIATIOK FROM RADIOMAKGANESE
51:
957
EXPERIMENTAL
An iron disc 3 mm. thick with a diameter of 85 mm. was the source of the manganese for this work. Sections cut from the disc possessed a considerable variation in activity; this indicated that the radioactive material might be localized, a conclusion which was confirmed by placing photographic film in contact with the disc. After a 3-day exposure the film was developed and a definite area of intense radioactivity was found. With this record as a guide, drillings were taken from the active area for analysis, and a permanent reference \vas prepared by mounting some drillings on a piece of cardboard. This standard preparation was used to determine the ease of absorption of the radiation. The materials that were used were: aluminum, lead, manganese TABLE 1 Absorption data for aluminum ALUMINUM g. fcm.2
0.0 0.025 0.075 1.7 3.4
0 0.006 0.018
0.43 0.86
0.077* 0.040 0.023 0.020 0.018
* This is the average of ten determinations with an average deviation of 0.004 TABLE 2 Absorption data for lead LEAD
I
LEAD THICKNESS
I
ACTIVITY
p./cm.a
mm ,
diu./min.
1.36 2.32 4.0
1.1 2.0 3.5
6.96
6.0
0.010 0.009 0.008 0.0065
dioxide, hydrous ferric oxide, and cellophane. Aluminum and lead nere chosen to make a comparison with the values in the literature (3) and to assist in identifying the active material. The data for the various materials are readily compared on a plot of activity expressed as divisions per minute against grams of material per square centimeter. The data for aluminum are in table 1. There is a radiation that is extremely soft, and the absorption in the region 0-0.014 g. of aluminum per square centimeter has been shown by Livingood and Seaborg (3) to be the same as that for the chromium K-radiation. The region beyond about 0.02 g./cm.* is best investigated with lead, as the absorption of the hard radiation is more pronounced with this material. The data are given in table 2. They yield a value of 9 g./cm.*of lead as being neces-
938
DOii
H. ANDERSON
sary to reduce the radiation by one-half. The value reported by Livingood and Seaborg (3) is 8.4 g./cm.* The absorption data indicate the need for a careful consideration of the effect of materials present as contaminants or as a matrix to contain the manganese whose activity is to be measured, since small amounts of material can markedly reduce the amount of soft radiation. Aqueous solutions of radio-
.
Screening
TABLE 3 effect of varaous materials
SCREENING MATERIAL
QCANTII)
1
ACTIVITY
dru /mtn
MnO? MnOI MnOI MnO. IInO? MnO. MI102
Cellophane Cellophane Cellophane Cellophane Silver
I
~
~
1
1 I
I ~
-
0.012 0 026 0 059 0.066 0 085 0.160 0 296 0 006 0.012 0.030 0060 0.ooo12
I
I
I
0 077 0 040 0 031 0 024 0.022 0 026 0 023 0 025 0.043 0 033 0 024 0.023 0.074
ocellophmr P silver d alumiwm m n g m u diordc
M I J I ~ ~ D ~ N M C ~ J ~ . I2 . Y 3 ~ B )
FIG.1 , Absorption of radiation by various materials. Ordinate relative activity espressed as divisions per minute discharge race of the electroscope. Abscissa, grams per square centimeter of absorbing material. The scale is compressed a t the right.
manganese did not produce a significant discharge rate, so all samples used were dried a t 110°C. The data for a number of materials are included in table 3 and figure I , The manganese dioxide was dusted uniformly over a cellophane carrier, and these values of grams per square centimeter include the cellophane. It is apparent that if a quantitative analysis for manganese is to be undertaken, it, R i imperative that the conditions be very reproducible with respect to the
PItOPERTIES OF THE RADIATIOX FROM RADIOMAXGANESE 54
959
presence of foreign material that may exert a screening effect on the radiation. This last imposes some serious limitations on the electroscopic method for determining the absolute amount of manganese present. However, there is a definite advantage in that the electroscope is capable of detecting very small amounts of manganese. Measurements have been made readily on amounts of manganese as small as O.oooO11 g. of manganese,giving an activity of 0.015 div./min. which is readily detectable in the presence of a background radiation of 0.010 div./min. The smallest amount detected was 4 y with an activity of 0.007 div./min., which is still not the lowest limit detectable. This amount \\as measured in the presence of 0.010 g. of iron, a 10,000-fold excess present ab Iivtlrous ferric ouide. Hydrous ferric oxide appears to be a useful agent for TABLE 4 Screening effect of hydrous ferric ozzde lPON
1
0.023 0.035 0.051 0.081 0.168 0:260
ACTIVITY
dsr fnin
grams
~
0.065 0.056 0.034 0.034 0.026 0.020
FIG.2. Absorption of radiation by hydrous ferric oxide, the amount of manganese being constant. Ordinate, relative activity of the preparation. Abscissa, g r a m of iron present as hydrous ferric oxide times 100. carrying small amounts of manganese, and it is quite easy to compensate for any screening action. During the initial phases of the isolation of the manganese, it was observed that the ferric hydroxide would carry down varying amounts of manganese. It seemed desirable to know how complete a separation could be effected. This investigation involved two series of measurements: one on the screening effect of ferric hydroxide, and one on the effect of the Hf concentration on the adsorption of the manganese. The screening effect was determined by analyzing a series of hydrous ferric oxide precipitates containing known amounts of iron and identical amounts of manganese. These data are in table 4 and figure 2.
This information may be used t o convert the activity readings to a definite amount of iron hydroxide if desired, and it indicates the need for working with as small an amount of carrier as possible when making measurements on the activity of the manganese. To investigate the adsorption of manganese by hydrous ferric oxide, a series of identical solutions was prepared. These solutions contained about, 0.03 g. of iron added as ferric sulfate, 90 y of manganese, 4 g. of ammonium nitrate, and sufficient ammonia in 100 ml. of solution to bring the pH to the indicated value for each solution. The ammonium nitrate was added to maintain the concentration of the ammonium ion nearly const,ant. .lbout. a third of each preparation was withdraum an hour after the hydrous ferric oxide was precipitated. This \vas filtered with mild suction, washed with three changes of water, about 25 ml. of water in all, rinsed with alcohol, and dried overnight a t 110°C. A second portion was removed from each solution about one month Iatei. mid t,reatrci in the same manner. The activity of each portion was drterTABLE 5 h.fsorptioiL of manganese by hydrous f e r r i c oxide ~
INIT'*L
~..
PI1
4.0
4.9 6.0 6.8 7.3 s.0
~
__
.
OSE MONTH LAIER
DATA
...
Iron
icriwtv
ilrami
dir i n i n
0.0097 0.0118 0.0116 0.011s 0,0126 0.0136
0 M)5 0 011 0 010 0 046 0 060 0 066
\In Fe -
h i \ It,
gram,
1
0 51
0.00il
93 38 90 76
0.0073 0.0110 0.0108 0.0095 0.0097
0 1 3 4 1
89
,In,re
4Serwe \iin/ki
0 71 0 63 1 35 4 45 4.42 4 85
0 61 0 78
drr imtn
0.005 0 005 0 015 0 048 0.042 0 047
1 4 4 4
37
1s 50
87
mined; the data are in table 5. The data indicate that no significant aging took place during one month and that the amount adsorbed was dependent on the H+ concentration. Completeness of adsorption a t the high pH values \vas checked by adding a small amount of iron to the filtrate from the sample having a pH of 8.0 and determining thc activity of the resulting precipitate. So activity could be detected. The manganese concentration was determined in the stork solution before this \vas added to the system. The iron content of each portion was determined colorimetrically, using ammonium thiocyanate, after the activity of each had been checked. In table 6 the values have been calculated for the amount, adsorbed and the amount in solut,ion. The percentage adsorbed is plotted in figure 3 as a function of the pH. The amount adsorbed is equal t,o t.he amount in solution a t about pH 6.3. Iiolthoff and Overholser (2) in their extensive work on adsorption have reported that the amount of manganese adsorbed increases with an increase in the ammonia concentration and decreases with increasing concentration of ammonium chloride. They did not report the
961
PROPERTIES O F THE RADIATIOK FROM RADIONASGAKESE 54
TABLE 6 Ratio of adsorbed manganese to manganese in solution
1
PH
[
AXOVNT ADSORBED
11 14 25
4.0 4.9 6.0 6.8 7.3 8.0
IRON PRESENT
prm1
0.010
il
85 90
ADllED
~
PEECENTAGE ADSORBED
79 76 65 13 5
1
--
("4)rSOd
AMOUNI IN SOLUIION
gamma
gammas
12 16 28 86
95
I
100
YATGANESE
PH
PXESENI
MANGAh2SE
PERCENTAGE ADSORPTION
rami
4.9
'
5.1
8
962
DON E. ANDELSON
hydrogen-ion concentrations or point out whether or not this is due to a buffering action. In order to investigate this and to see if the same type of adsorption curve would be obtained with higher concentrations of manganese, the experiment was repeated using sufficient manganese to permit making an accurate colorimetric determination of manganese. Solutions were prepared as indicated in table 7 , with sufficient ammonia to bring the pH to the values indicated. These data are shown graphically in figure 3 ; the curves are all of the same general form. From the results it is evident that the ammonium salts actually interfere with the adsorption of the manganese. Apparently a preferential adsorption is taking place. When there is a large excess of manganese the limiting fact.or is the amount of iron, and up to pH 10 no appreciable precipitation of the manganese takes place. It is possible to state definitely that manganese can be separated from iron by repeated pre:ipitation at a pH in the neighborhood of 4 or 5 , at which pH the precipitation of the iron is complete, as reported by Gilchrist ( 1 ) . Radiomanganese has been separated from the iron by adding a small amount of a manganese salt and then oxidizing to form manganese dioxide. This reduces the activity of the preparation considerably. Whenever possible, no manganese should be added to the radiomanganese to serve as a carrier. Rather, the manganese should be separated from iron by one or more precipitations a t .as low a pH as possible. The presence of ammonium sulfate interferes with the adsorption of the manganese and does so even though the hydrogen-ion concentration is maintained constant, as was indicated by Kolthoff and Overholser. SUMMARY
The adsorption of manganous manganese by hydrous ferric oxide has been studied, using radiomanganese 54 and non-radioactive manganese. The data obtained indicate that a t a pH value of 4, which permits the precipitate of hydrous ferric oxide to form, less than 12 per cent of the manganese is precipitated. This relationship holds for ratios of 10 mg. of iron to 5 mg. of manganese and 10 mg. of iron to 0.03 mg. of manganese, in the presence of ammonium nitrate. The effect of ammonium salts has been demonstrated to be related to the adsorption phenomenon and not to a buffer effect that changes the hydrogenon concentration of the system and so the solubility of a coprecipitated manganous hydroxide. The effect of hydrous ferric oxide, manganese dioxide, cellophane, aluminum, and lead on the radiation from radiomanganese has been indicated. The data for aluminum and lead agree with the values in the literature. REFERENCES (1) GILCHRIST, R . : J. Research Natl. Bur. Standards 30, 95 (1943). (2) KOLTHOFF, I.M.,A N D OVERHOLSER, L.G.:J. Phya. Chem. 43,767 (1939) (3) LIVINGOOD, J. J., A N D QEABORG, G.T.:Phys. Rev. 64,391-7 (1938).
