te rmined with a flow meter. The solution passed

through the column and emerged through side-arm 4 at

the top of the bunker. The mlfocarbon, whose level at

the top of the column was kept eonstant, passed down-~

wards under gravity and its speed was regulated by the rotat ion rate of the screw 5. The spent carbon fel l into bunker 2 and when necessary it was transferred to bunker 6. Analysis samples were withdrawn from four taps along the column.

In the exper iment described, the working 0.0125 N solution of l i th ium chloride was introduced at 0.25 m l / / s e c , counter to the ion-exchange mater ia l , which was moving at 1.9 �9 10 "z m l / s e e .

A stationary state was established after 2-hr opera-

tion and as a result of this the distribution of l i th ium ion concentrat ion along the column remained constant. The stat ionary state was not disrupted for 5 hr. Samples for mass spectrometr ic analysis of the l i th ium isotopes were withdrawn at distances of 70 and 100 em from the beginning of the column. The LiT/Li 6 ratios were 12.6

and 13.3, respect ively, instead of 11.7. The column was operated by the residues method

and therefore only 3% of the starting mater ia l was separated.

We consider it most advantageous to operate the column under the following conditions: Lithium is in-

troduced at the bottom of the column and the eluent moves upward through the column, while the resin moves downward. The result obtained in the stat ionary state on a small section of the column corresponds to the result which could be obtained on a column of in- f in i te length.

From a comparison of exper imenta l data on the

single-state separation factor [9] and the operation of the column, the enrichment of the solution in the heavy

isotope in experiments with l i th ium hydroxide and ben-

zoate may be explained by the inverse concentrat ion dependence of the single-stage separation factor.

In actual fact , in these experiments carried out by the frontal analysis method there was a decrease in the solution concentrat ion with passage through the column due to irreversible reactions with the formation of water and sparingly soluble benzoic acid. This also explains the compara t ive ly low enrichment factors. Data from experiments with l i th ium chloride agree comple te ly .

L I T E R A T U R E C I T E D

1. T. Taylor and H. Urey, J. Chem. Phys. 6__ L, 429 (1938). 2. E. Glueekauf, K. Barker, and G. Kitt, Disc. Faraday

Soe. 7, 199 (1949). 3. J. Grosse, AECD Report No. 295229 (1950). 4. C. Davies and B. Owen, J. Chem. Soc. 6, 1676

(1956). 5. F. Menes, E. Sa'ito, and E. Roth, Proc. Symp. Separ.

(Amsterdam, 1957).

6. S. Mayer and E. Tompkins, J. Amer. Chem. Soc. 69, 2869,(1947).

7. G. Dickel and K. Becker, Chem. Ing-Tech. 28..__~, 529

(1956). 8. G. Dickel , Z. Elektrochem. 54, 353 (1950). 9. G . M . Panchenkov, E. M. Kuznetsova, and O. N.

Kaznadzei , Atomnaya Energ. 7_, 6, 556 (1959).*

* Original Russian paginat ion. See C. B. translation.

SOME ASPECTS OF AERIAL ~-RAY PROSPECTING

OVER FORESTED REGIONS

G. N. Kotel'nikov and N. I. Kalyakin Translated from Atomnaya ~nergiya, Vol. 8, No. 4, pp. 370-372, April , 1960 Original a r t ic le submit ted May 30, 1959

Due at tention is not always given to the screening effect of the forest plant growth when aerial y - ray surveys are carried out. This results in the overlooking of uranium deposits and in mapping of an annoying number of spurious anomalies .

In this let ter , we shall c i te examples of established uranium minera l i za t ion and discuss the effect of the screening capac i ty of the forest cover on the results of airborne y - ray prospecting of the uranium bodies.

1. The deposit is located in ' a region of absolute elevat ions ranging 400-450 m and re la t ive elevations 100'-150 m. The region is covered with dense stands of mixed flora and thick shrub growth. Denuded patches of land are sufficient to f ac i l i t a t e the work.

The airborne y - r a y surveys (using AN-2 airplanes with ASGM-25 equipment) were carried out on a 1 : 25,000 scale at f lying at i tude 60 m. A narrow local anomaly peaking at 17 p r / h r (background: 4 p r / h r ) was detected

321

Absorption of G a m m a Radiation by Forestal Flora

T t e e

species

Spruce . .

Age of wood, years

40 60

100

Number trees per hectare

3t 23 t 509 700

I I Total weight of I Tota l thickness wood mass per of screen, hectare , tons g / c m ~

8844 89,7 3996 4t. 2 2934 30.5

Absorption V a l u e of O(~,h) of y - rad ia - at V = 0.04, [ in c m 2 / g I t i~

0.56. t0 -~ 99,5 6 0 . 1 0 -~ 94,0

1 0 . 9 , t 0 -2 89 . t

Pine 40 60

t00

3000 1200

560

3560 2485 t737

36.8 26,0 t8,6

7 ,5 . t0 -2 t 3 . 8 . t 0 -2 22,2.10-2

92.5 86.2 77.8

on one prospecting sortie. Detai led surveying carried out on a 1 : 10,000 scale at 30 m al t i tude on two routes pinpointed an anomaly with peaks at 17-18/l r / h r and

a third at 7 / l r /h r . On the map compi led from the aer ia l survey data,

the anomaly was found to extend 300 m with a width of 30-40 m. Subsequent ground sorties using y - ray equip- ment revealed , on the site of the unique anomaly dis-

~ t_ . . . . t ~

39- o : o o 0 . . . .

38 " W e s t e n ~ o n % / / ' / ~ -~ - ~ / / o e Eastern o o o : L o / / ~ 1

7 / / ~ _ ~ o ~ -

~ ~ p , ~ ~ ~ o

36 1 1

~ - - "X2- -o -o 34 ~ ~ _ - " ~ . . . . . . = - - - ' - - 2 _ % 2 - - _ - ~ ,,"

33 - ~ / ~ ' - . . . . . . . . . . . / o ~ , ~ o o ~ , F ~

32 j o k 0 o ~ / o k o

3 ! /

Scale fO0 0 tOO 2gO 3gO

FtT-qf Cg'qz F~-13 ~-1~ ~ s ~ 6 ~ 7 ~ 8 ~ s

Fig. 1. Base map for anomaly No. 1: 1) ter t iary coarse-grained sandstone; 2) carbonaceous c l ayey shales of Upper Permian; 3) ore zone with contours t raced according to aer ia l survey data; 4) ore zone with contours t raced according to ground sortie data; 5) ore dump zone; 6) deforested zone; 7)softwoods (spruces, pines); 8) aer ia l survey intineraries and anomalies , scale 1 : 25,000; 9) i t ineraries and anomalies in deta i led work, sgale 1 :10 ,000.

covered from the air, three ore zones running para l le l at 300-500 m separation from each other (Fig. 1). The principal ore zone, part of which was exposed as an out- cropping seen from the air, was t raced for 2000 m. Sur- face uranium minera l iza t ion is manifested in the form of discrete patches of surface area ranging from 1 m wide to 1200 m 2 in area, at a y-emiss ion intensity of 50-1500/a r / h r (against the background noise of 6-7 g r / h r from neighboring interfering rocks). The areal

ore-bearing coeff ic ient of the anomaly is about 30%. Aside from the outcropping of bedrock, bodies of ore mate r ia l (blocks up to 10 em 3 with y intensity from 50 to 1500 g r / h r ) extend over an area of about 80,000 m 2 in the principal ore zone. These ore runs, l ike the flanks of the principal ore zone. went unnoticed in the aer ia l survey, and yet were well exposed except that they were hidden in a dense forest stand. The ano- malous sector detected was distinguished by absence of

forest growth, lesser shrubbery, and heightened re l i e f . The fact that areas considerable in extent and of

high radiat ion intensi ty were not spotted in the aer ia l y - ray survey is to be explained by the high screening abi l i ty of the forest wood. This supposition was con-

o ~_ o~ . . . . ~ o

I7

16

I5

[ r

13

/g

o o o o O o 0 o

o o o o o

--~ ~ . . . . . t. o, ....

0 o - ~ o o o 0 0 8so'

Scale 50 Ct 50 tOg tSO

~-~1 W~3 e L-E~ 3

Fig. 2 . Base map for anomaly No. 2: 1) aer ia l survey i t ineraries; 2) contours of ore zones; and dumps; 3) conifers.

322

f i rmed by empi r i ca l data. When the tree height over

the area l = 33 m , the trunk d iameter H = 36 era, the specific weight of the wood t imber is 0.8, the weight

of the crown, brushwood, pine needles in the case of

conifers, is equal to the weight of the trunk, the total

weight of the wood is PI - (vl �9 0.8) �9 2 = (gmHl �9 0.8).2= = 2.705 m [1, 2] (where vl is the trunk volume, gm is the species number of the tree; 2 is the correc t ive factor for the weight of the crown, deadwood, needles or cones). When the density of a forest stand presents us with one tree per 10 m 2, the distributed density is d = 2705/10 = 270.5 k g / m 2 = ~27 g / c m z.

Absorption of the b roadbeam of y radia t ion on its path to the radiat ion detectors aboard the surveying air- plane is expressed by the formula

I = 10el) (~d),

where ~(/1 d) is King's function, and I0 is the radia t ion

intensi ty at ground level . The effect ive mass at tenuat ion coeff ic ient of 7

radia t ion for wood g = 0.04 c m 2 / g [3]; so that ff (g d)= = 0.13 and I = I 0 �9 0.13, i .e . , 13% of the unscreened y radiat ion.

Consequently, 87%of the y radia t ion is absorbed ent i re ly on account of the screening abi l i ty of the forest cover. Taking into account the decl ine in intensity of y radiat ion, at an a l t i tude of 50 m and for an area of 1200 m 2, to 4% of the ground-level intensity, and in-

troducing an ore-bearing coeff ic ient of 30%, we ob- tained the min imum intensi ty value required to ensure

recording, viz. 1540 p r / h r . The intensity of g a m m a radiat ion at ground level did not ac tua l ly exceed 1500 p r / h r for the flanks of the zone and the ore dumps, and the fact that they went unnoticed in the aer ia l survey is to be expected.

2. y-Surveying on the ground, scale 1 : 25,000, and aer ia l ~ surveying at scale 1 : 10,000 with sub- sequent crowding-in of flights over promising areas were carried out over a region of absotute e levat ion 1100- 1600 m and re la t ive e l eva t ion 300-500 m. The region

is covered with dense softwood stands. Because the conifers are grouped together in clumps, the re la t ive amount of barren exposed land is favorable.

A hydrothermal uraniferous deposit consisting of four patches 500 by 300 m in area was detected in ground sorties. Over three of these patches, minera l i za - tion was in the form of veins, the fourth being a bedded structure. The area of the ac t ive patches was found to be 150, 800, and 4,000 m z according to an i sogamma of 300 p r / h r (outcroppings and ore dumps). The ac t i - vi ty of discrete ore blocks and ore lumps exceeded 10,000 /1 r / h r .

In the surveying fl ight carried out crosswise (AN-2 aircraft with SGM-10 equipment , at f l ight a l t i tude 70- 80 m) over the breadth of the ore structures, not one

of these patches was loca ted by air. Several flights

coming in from different directions d i rec t ly over the centers of the ore sectors also yie lded negat ive results.

Calculat ions by R. M. Kogan (using a transparent

over lay with divisions by squares), where the screening abi l i ty of spruce wood was taken into account, indica te

that the mean intensity required for a confident loca- tion of ore zones No. I and No. 3 (in Fig. 2) from the air comes to 1450 and 8000 g r / h r , respect ively. Since the intensity ac tua l ly ranged 300-500 p r / h r , i t is understandable that the anomaly escaped detect ion.

3. In aer ia l y - r ay surveys on a 1 : 25,000 scale over a wooden region structured of Preeambrian gneisses and pa leozo ic intrusives with an increased c larke of uranium (background of 15-40/l r / h r at ground level , 6-7 g r / h r from the air), a grouping of narrow loca l anomal ies of 12-15 p r / h r intensity was de tec ted . Photographs of the anomalous areas were used to in- terpret the phenomenon. All of the anomal ies were

located near forest clearings and cuttings or thinnings with 200-400 m drift on the course (due to instrument inertia), and were due to absence of the forest screen. Verif icat ion by a ground sortie proved the anomaly to be barren of ores.

As an example , we furnish in the accompanying table the results of the ca lcula t ion of ) , - radiat ion ab- sorption by the forestal f lora present. Reference data character iz ing the volume and weight of the t imber mass, the number of trees per hec tare , etc. were used in the calcula t ions [1, 2, 4]. The screening effect of

deadwood, windfallen trees, and shrub undergrowth is left out of account. The pronounced an i so t ropyof the medium, due to the distribution pattern of the tree

trunks, is also neglec ted . In ca lcula t ing the distributed density of the t imber for several regions, the wood mass of the trunks may even be ignored, preference being

given to ca lcula t ions of the more evenly distributed mass of tree crowns, needles and cones, and forest floor, which contribute 30-60% of the total mass.

Even when the correc t ive factors mentioned above (0.3-0.6) are introduced, the density of the t imber screen remains high for par t icular t imber age groups, and

and the percentage absorption of y radia t ion will f luctu- ate from 25% to 60%, which may lead in the case of airborne surveys over wooded regions to the fai lure to loca te ore bodies of industrial interest.

L I T E R A T U R E C I T E D 1. N .F . Lyashenko, Lumber and Logging Handbook

[in Russian] (Izd. Akad. Arkhitektury Ukr SSSR, Kiev, 1955)pp. 32, 68.

2. Forester 's Handbook [in Russian] (Izd. AN Belorus. SSR, Minsk, 1954)p. 180.

3. Radiometry Handbook, edi ted by V. I. Baranov (Gosgeol tekhizdat , Moscow, 1957)pp. 111, 184.

4. G . F . Morozov, Lectures on the Forest [in Russian] Izd. Goslesbumizdat , Moscow-Leningrad, 1949) Vol. 7.

323