INVESTIGATION OF THE GAMMA ACTMTIES AND GAMMA SPECTRA OF SNOW SAMPLES

By

�93 T£ T. ZSOLDOS and A. URB�93

~d]~V IIEALTH SERVICE, P]~CS

(Presented by L. P• -- Received 18. I[. 1965)

Ah analysis of the total gamma activities and the gamma spectra of 25 samples of snow and 1 of rainwater-snow collected in Hungary (between 16~ ~ longitude and 460--48 ~ latitude) between 29th January and 22nd February 1963 revealed that a) the 1STCs-equivalent total gamma activity is on the average 5,1 �9 10-7 #c/rol; b) the total beta concentration cal- culated from this is ~ 1,2 �9 10-6 #c/mi; elements detected with great probability: ~~lCe, 144Ce, l~ 7Be, 137Cs, 95Zr and 9aNb. Age of fission products: ranging from 50 to 80 days. ~37Cs and (~£ ~ ~ have been estimated. Our total activity data agree well with those of other authors; the results of our selective determinations ate of the order of the values obtained by other authors, differences being due to losses in collection and sample treatment. Our Szeged sample distinguished itself from the others by its anomalously high (approximately three times higher) radioactivity.

Introduction

Owing to a tomic bomb explosion tests precipi tat ion and falling dust inject fission products into the biosphere. On account of this man ' s external and

internal radiat ion dose increases above the natura l dose, and so does the radio-

ac t iv i ty of the environment . This fact affects geophysical investigations and the deterininat ion of man ' s exposure to na tura l radioact ive elements in the field,

the investi~ations of the contamina t ion of the envi ronment and the measure-

ment of low radioactivit ies. This accounts for the impor tance of analysis of precipi tat ion for the presence of fission products.

In this coun t ry such measurements have been in progress at Debrecen, since 1952 [11, 12, 38, 39, 40]. The purpose of the present paper is to supplement

these and other valuable Hungar ian [37] and the m a n y foreign data with some

results of our own obtained by a prel iminary informatory method. The improve- ment of the method employed is in progress.

Survey of the literature

Many excellent summaries of this problem have been published [10, 25,

28, 39, 51]. Several authors have dealt with the determinat ion of fission product concentra t ion in snow [1, 2, 3, 4, 14, 24], in ra inwater [2, 3, 5, 9, 13, 14, 15,

1 Acta Physica Academiae Scientiarum Hungaricae 20, 1966

306 �93 T‰ T. Z$OLDOS and A, URB~N

17, 20, 24, 26, 27, 30, 31, 36, 37], in aerosols; and in snow, rainwater and in aerosols on the whole [6, 7, 8, 11,, 12, 18, 22, 23, 29, 31, 38, 39, 44], as well as with the detection of the presence of these elements. The determinations are affected by the 7Be [16, 32, 33, 44] and the 212pb [44], isotopes of natural origin and in the case of "ho t" particles [58] by the phenomenon of fractionation [19].

Characteristic data for fission products in fall-out samples [8, 27, 34, 35, 42, 43] and assignments to atomic weapon tests carried out in 1962 have also been published [12, 21, 22, 23, 24].

Results of our investigations

The total gamma activities and gamma spectra of twenty-five snow samples and one rainwater-snow samp]e have been investigated. The samples were colleeted in the arca between 16 ~ and 22 ~ longitude and 46~ ~ lat i tude of this country (10 snow and 1 mixed rainwater-snow samples from P› 2 snow samples from Mar• (Baranya County) and 1 snow sampl› from each of the fo]lowing towns: Szigetv• Szeksz• Szombathe]y, Sopron, Kaposv• Gy£ Tapolea, Debreeen, Somosk£250 (N£225 Connty), Miskole, Szeged, Kecskem› and Budapest) between 29th January and 22nd February 1963. Although the reason for our choosing snow for the analysis was that it was simple to collect snow samples, later on, it appeared that snow was worth eol- lceting also because its radioactivity was higher tllan that of rain[14, 24, 36]. On the other hand, the measurement of gamma activity and spectra is techni- cally, preparationally and even informationally more advantageous than the observation of total beta aetivity detected after radiochemieal t reatmeat , although the disturbing element 7Be eannot be separated from the 500 keV photopeak without radioehemical separation by means of the gamma spectro- metrieal instruments now avilable to us, and if at all, this can only be done b y half-life estimation.

The snow was sampled from approx, lm 2 area, to its full depth, wi thout traces of soil. The melted snow mixed with rainwater was taken from the rain- water pipe. The volume of our samples prior to evaporation to dryness was 5000 mi, with one exception (sample marked F - - 1 8 : 3 0 0 0 mi). As no acids of carriers were added to the vcssels when the snow samples were eolleetcd, melted and transported to the laboratory we did not use polyethylene vessels [14, 17, 19, 24, 26, 27] and did not record how long before collection the snow fell (leaching: [14]). Thus significant losses of fission produets may have oceurred.

After preliminary filtration the samples were boiled with nitrie acid to the volume of 5--10 rol neeessary for the measurement. The filtrate was also washed with nitrie aeid added to the filtered liquid. Thus, at th i ss tage of the

Acta Physica Academia* Scientiarum Htmgaricae 20, 1966

INVESTIGAT/ON OF THE GAMMA ACTIVITIES OF SNOW SAMPLES 30~

�9 the adsorption can be assumed to be smaller [50], al though it can stilI be very considerable [5], for carrier-free iodine, ruthenium and circonium. I t has been shown tha t the adsorption loss can be decreased by rubbing with diatomaceous earth [26]. The solutions evaporated to approximately 9 mi were put into normal test tubes and measured in these with a single-channel recording spectrometer type 1820B, manufactured by Nuclear Chicago [52, 56] having a NaJ(T1) detector of a bore-hole volume of 8,4 mi, and with scalers, types FH--49 and PSZ--20, eonnected to the spectrometer (their input sensi- tivities were 0,5 V and 3,0 V, respectively).

The three groups of our measurements (total gamma activity measure- ment, measurement of spectra by automatic continuous, aud manual step method) ate summarized in Table 1.

Our measurements of total gamma activity were carried out by the integral mode of operation above 80 keV, by scalers. Our equipment was calibrated by a point-like 137Cs source for energy (linearity is fulfilled, see also Fig. 5) and for total efficiency. The values thus obtained: e----5,6-105 cpm/pc and ~t = 25,4~ agree well with the resuhs observed under different conditions (6,1 �9 105 cpm/#c and 27~ , but with a 50 mV input sensitivity scaler [48]) Gr calculated [49] by others.

For a known fission product mixture, ah efficiency of 3 9 ~ was measured for photon energies above 60 keV [26]. This is substantially modified by the difference in the composition from tha t used in [26] and by, the actual condi- tions of the measurement. The counting rates of our solutions with au average volume of 9 mi have been reduced to zero solution height, so tha t the correc- tions obtained hy others [44, 45, 46, 47, 48] for NaJ(T1)-crystals, the bore-hole of which was of a size similar to that of our detector, have been made universal by establishing the (sample/bore hole) -- volume ratio. A eurve has been plot- ted based also on the Operation Manual of our instrument [52].

The laTCs equivalent concentration shown in Table 1 has been calculated on the basis of the background-less counting rates M, the above data and the original volumes. The roughly approximate total beta concentration calculated from the 137Cs equivalent concentration, as can be seen from Table 2, is in good agreement with the values of others for a similar period [37, 38]. As ~~ is also present in the samples [1, 20, 24, 37] our total beta value exceeds the leveI 1,0 - 10 -8 #c/mi fixed by ICPR (1959) by approximately 20~ . This assertion is supported by the presence of 9~ actually detected by other authors in precipitations over the same period of collection, e. g. in Rumania [1], Canada [20], England [24] and even in this eountry [37]. The age of fissio= products on the basis of our total gamma measurements (see Table 1) is approx- imately 50--80 days. To obtain preliminary information as to composition we measured the spectra of our twenty six samples by automatic registration [52], four ofwhich are shown in Figs. 1, 2, 3 and 4. These represent the speetra

| * Acta Physica AvQdemia~ Scientiarum Hungaricae 20, 1966

308 Jk. T‰ T. ZSOLDOS and A. URB�93

of the remaining twenty two samples very well, apart from the 140 keV photopeak of the rainwater -- melted snow sample, marked F--22, which is completely missing, and the 750 keV photopeak, which is scarcely visible

�9

2~0-

180-

120 -

60.

OkeVJ

2~o 5bo 7~o io'oo [,~ev;

F i g . 1. Automat iea l ly recorded gamma speetrum of our P› sample. Sample mark : F - I ' Site of eollection: P› Date of collection: 29.01.1963; Time and date of measurement : 16h;

19.02.1963; Volume of melted snow prior to evapora t ion: 5000 mi

(losses due to collection from the rainwater pipe). The figures in brackets indicate the values concerning the increased counting rate (cpm) -- limits of measurement.

I t is known [41] that the shape of spectra recorded by single-ehannel automatic analyzers with ratemeters is distorted (the photopeaks ate flattened

Acta Physica Academia8 Scientiarum Hungaricae 20, 1966

Table I

S u m m a r y of the resu l t s of the m e a s u r e m e n t s

Type of measurement

I.!

ro t a l g a m m a - eoun t ing r a t e m e a s u r e m e n t s 1 II.

( threshold: 80 keV)

!H. I.

Total number of measurements

and s p e c t r a

taken of 26 samples

26 (1)~

26 (1)2

Arithmetic average of the t ime between

eolleetion and measurement

(reeording of spectra)

At (day)

15 (18h

Arithmetic average and statistieal

% of integral, baekground-free eolmting rates

M (~vm)

1030 -4- 3 % (3600 • 1 ,3%) 2

73 :~ 14% (286 • 3 ,1%) 2

Average, approxi- mate, l~TCs-equi-

valent concentration caleulated from M, not eorrected for 7Be, at the t ime of measurement

c (m/m1)

5,09 �9 10 -7 (14,4 �9 10-7)2

Arithme,ie averages and statistical errors in % of some important, observed photopeak-heights and photopeak area ratios corrected for Compton

scattering [27] and flattening [41]. (For error caleulation see explanatory

~o. of

measure- ments

( 5 0 0 keV~ 140 k•

rernarks 10. and 22.)

N o .

of nleasu- rements

i I _

t 750 keV~ 140 keV/

Average approximate age os fission

produets in the samples

t h (day)

Ideatifieation of elements by eomparing the decay in time of ah identieal photopeak height (area) of a given sample and the Table of eorrections for deq ty

published in [57]

652 (653)2

(0,07 ~: 14,3~243 (0,08 ~ 3 ,4%) 2

No. of ( 500 keV~

measure- \ 750 keV/ ments

50 ~- 203

or

80 • 104

sign of 140 I 500 662

sample keV

750

- - j t i

I

~ a m m a spee t ra t aken for pre l imi- n a r y i n fo rma t ion by a u t o m a t i e recording 5

~ a m m a spec t ra t a k e n by t he s t e p w i s e m e t h o d 15

306 15

22z7

o r

640u,

25=

13,9

0,80

17,5%10

0,92

-4- 53%2~

33

o f

328

920

2,07

o f

1,898

~: 21,8%,0

2,442t

-4- 55%2z

229 0,41

:t: 21,5~ot0

0,45

•

b e t w e e n

45 a n d 65 H

ap p ro x . 45,2

a p p r o x . 5023

F-17,a

i

F-26

I F-172~ I

F-26zs

t44Ce

t4 tCe

~4~Ce?

roCe?

i I l l a C e , 4

7Be;

,03Ru?

, 0 3 R u

14

137Csl4 I P

' 37Cs,4

95Zr

95Nb

E x p l a n a t o r y r e m a r k s : I: f i r s t series of m e a s u r e m e n t s ; II : s econd series of m e a s u r e m e n t s .

2 Va lues for t he a n o m a l o u s Szeged s a m p l e m a r k e d : F-17. 3 B a s e d on 1030- ' and 73- t. 4 B a s e d on 1030 -~ and 73 -~ [40]. 5 D u r a t i o n of a r u n = 30 m i n u t e s ; s p e c t r u m s c a n n i n g speed - - 0,555 keu record ing

p a p e r speed = 30,5 c m / h o u r ; w i n d o w w i d t h = 2 Vol ts ; c o u n t i n g ra te , r a n g e in genera l : 0 - - 1 5 0 c p m ; ra re ly : b e t w e e n 0 - - 3 0 0 c p m ; cha rg ing t ime c o n s t a n t o f t he r a t e m e t e r for 0 - - 3 0 0 cpIn: of t h e o rder o f 100 /~sec [55]; i n t e g r a t i o n t ime c o n s t a n t of t he r a t e m e t e r : 40 sec [52]; e q u i l i b r i u m t i m e ca l cu la t ed for t he r e co rd i ng pen a d j u s t m e n t to t h e new ave rage c p m w i t h a p r o b a b i l i t y of 5 0 % , as well as for t he d i f ference b e t w e e n t he c p m - s in t he p h o t o p e a k s a n d t he "va l leys ' " be low the p h o t o p e a k s f o r a t i m e c o n s t a n t of 40 sec: app rox . 100 sec [56]; ene rgy r ange : f r o m 0 to 1 MeV.

s Since we h a v e t a k e n four s p e c t r a a l t o g e t h e r for t he s a m p l e F - l , two spec t r a for t he s a m p l e F-2 a n d two spec t r a for t he s a m p l e F-17, t he a u t o m a t i c s p e c t r u m of F-5 was no t record- ed a t all owing to i n s t r m n e n t f a u h .

7 0 w i n g to d i s to r t ion ir was n o t poss ib le to e v a l u a t e t h e 140 keV p h o t o p e a k severa l t imes . s W i t h o u t t he a n o m a l o u s v a l u e of (7,84) o b t a i n e d for F-26. z For t h e F e b r u a r y 1963 m e a s u r e m e n t s wh ich could be e v a l u a t e d . t0 P h o t o p e a k he i gh t s g r a p h i c a l l y cor rec ted for the ave rage , d i s to r t ed , t o t a l b a c k g r o u n d ,

in [cpm/20 k e u - - un i t s , for 140, 500 a n d 750 keV: Ni - - 51, 47 a n d 24. The re la t ive s t a t i s t i c a l errors of t h e o b s e r v a t i o n s of � 9 ( a s s u m i n g an equ i l i b r i um t ime of app rox . 100 sec a n d t h a t t he d i f fe ren t ia l b a c k g r o u n d is zero; we know, however , t h a t t he se a s s u m p t i o n s are no t sa t i s f ied) a te for t h e t i m e c o n s t a n t T 2 = 40 sec on t he bas is of the f o r m u l a s

= • 100 V ~ ) a n d 6 = :~ ( 8 7 / V N i ) [a£

of t he va lues : =~12,2; ~=12,7; -4-17,8~ . T h e errors in t he ra t ios h a v e been c a | c u l a t e d by t he s q u a r e law of t h e p r o p a g a t i o n o f error.

tt F r o m t h e c o m p a r i s o n of t h e s h a p e s o f our spec t r a a n d t hose in [51b]. 12 For t h e ra t io of va lue 0,41, as well as for t he cond i t i ons o f m e a s u r e m e n t g iven in

[51a], a s s u m i n g 2asU-fission p r o d u c t s . ~3 See Fig. 3. t4 Cer ta in ly .

1.5 W i n d o w w i d t h = s tep d i s t ance = 2 Vol t s = 20 keV; e n e r g y - r a u g e : 0 to 1 MeV; o b s e r v a t i o n b y scaler ; d u r a t i o n s of o b s e r v a t i o n s (tt: s a m p l e + b a c k g r o u n d ; t2: b a c k g r o u n d ) : for the s amp le F-17 ea r ly in 1963: t I = 2 ' ; t 2 = o ' ( the t e n t i m e s sma l l e r b a c k g r o u n d - c p m was neg lec ted) ; l a te in 1964: t 1 - - t 2 = 3' . Fo r t h e s a m p l e F-26 ea r ly 1963: t I = t 2 = 2 ' ; la te in 1964: t t = t 2 = 4' . E r ro r s of t h e r e spec t ive o b s e r v a t i o n s : F-17, 1963, in t h e n e i g h b o u r h o o d of 750 keV: • 500 keV: :s 140 keV: ~5~ F-17, 1964, 660 keV: approx . •176243 F-26, 1963, 750 keV: • 500 keV: ~10~ 140 keV: -4-8~ F-26, 1964, 660 keV: app rox , i 3 0 % .

16 For t h e s a m p l e s F-17 a n d F-21 t h e n u m b e r of pa r t i a l s p e c t r a r ecorded in t h e ne igh- b o u r h o o d of 660 keV is n o t i nc luded here.

17 For t h e 11 m e a s u r e m e n t s carr ied o u t in M a r c h 1963. ,s For t h e 6 m e a s u r m e n t s ca r r i ed o u t in 1964. t~The 500 keV p h o t o p e a k a l r eady d e c a y e d in t h r ee cases, while for t h e s a m p l e F-22

the 140 keV p h o t o p e a k was miss ing . so The 750 k eV p h o t o p e a k was m i s s i n g in 8 spec t ra . 2, For t h e r e l a t i on t ~ 50 to 60 d ay s , a n d for t h e a s s u m p t i o n s of [18] th is p h o t o p e a k

a t ea ra t io is on ly a p p r o x . : 0,5. Acco rd ing to [42] th i s ra t io for th = 42 d a y s , w h e n ir is j u s t m a x i m u m , is on ly of t h e va lue : 1,33. As t h e ra t ios o b se rv ed b y us a re m u c h larger , t h u s in our case ir is e i ther due to t h e d i s t u r b i n g effect of t h e e l em en t 7Be t h a t t h e a t e a of t h e 500 keV p h o t o p e a k is la rger , of ir is due to losses in col lect ion a n d t r e a t m e n t t h a t t h e a t e a of t h e 750 keV p h o t o p e a k is smal ler , or in our case t h e a s s u m p t i o n in [18] a b o u t t h e f i ss ion of 238U by fa s t n e u t r o n s can no longer be m a i n t a i n e d . As t h e errors of our r a t i o s are a b o u t 209£ and 5 0 0 , t hese can o n ly be used for e s t i m a t i o n .

22 The error o f t h e p h o t o p e a k a rea ra t ios h a s been ca l cu l a t ed in t h e fol lowing way: a) t he own re l a t ive s t a t i s t i ca l er rors of t h e v a l u e s of m e a s u r e m e n t s d e t e r m i n i n g t h e a t ea of the p h o t o p e a k h a v e b een e s t ab l i shed ; b) for s impl i c i ty t h e a r i t h m e t i c av e r ag e of t h e errors so o b t a i n e d h a s been t a k e n for the s ign i f i can t p h o t o p e a k s of each sample : c) f ina l ly t h e a r i th - me t i c ave r age of t h e av e r ag e errors re fe r red to in b) h a s been t a k e n for t h e g iven iden t i ca l p h o t o p e a k e n e r g y of e ach s am p le (i.e. s e p a r a t e l y for t h e 140 keV, 500 k e u a n d 750 keV ener- gies.) For t he e s t i m a b l e 140 keV p eak of 16 we h a v e t h u s o b t a i n e d ah er ror of • for t h e 500 keV of 14 an er ror of ~:42%, an d for t h e 750 keV of 10 an er ror o f -{-35% . Th e er- rors of p h o t o p e a k a rea ra t ios h a v e been ca l cu l a t ed b y t h e s q u a r e l aw of t h e p r o p a g a t i o n of error. These errors , as c an be seen in t h e Tab le , are a p p r o x i m a t e l y 50~o.

23 Accord ing to t h e p h o t o p e a k area ra t io of approx . 0,45 a n d [51a] (see r e m a r k 12). 24 See Fig. 7. 2.5 See Fig. 8.

II~~ESTIGATION OF THE GAMMA ACTIVITIES OF SNOW SAMPLES 309

and shifted, resolving power decreases.) For the conditions of our measurements [55, 52, 56] we have determined the distortions (at 140, 500 and 750 keV: a) flattening of photopeak 27, 16 and 12%, respectively; correction factors 1,27, 1,16 and 1,12; b) decrease of resolving power: at least 28, 11 and 10%, correction factors: 1,28; 1,11 and 1,10; c) photopeak shift towards small energies: 15, 17 and 19 keV), for the automatic spectrum obtained for lZTCs

[cpm 7 L2oee~

I I I ~ J,

C120J. ;

(6o�91 ~so.

z'5o 5'o0 7Do looo [kev]

Fig. 2. Automatically recorded gamma spectrum of our Somosk£250 sample. Sample mark: F-14; Site of colleetion: Somosk£237 (N£225 County); Date of collection: 12.02.1963; Date of measurement: 22.02.1963; Volume of melted snow prior to evaporation: 5000 m

(the resolution is 13,75%; and by dividing this by the correction at least 1,11 for 660 keV, the undistorted resolutiort gives 12,4%, while in the stepwise operation (see later) it is 11,6~o. Thus the correction is good within the 7% error mentioned in [41].)

After graphical Compton correction [27] the rough photopeak heights have been corrected according to [41] and the ratios of the corrected values are given in Table 1. Figs. 1--4 and Table 1 show that expressed photopeaks appear mainly in the neighbourhood of 140, 500 and 750 keV (thus, at places

Acta Physica Academiae Scienliarum Hungaricae 20, 1966

310 •. T‰ T. ZSOLDOS tmd A. "URB.~~N

dis tan t f rom one ano ther in this coun t ry the dis tr ibut ion of fission produc ts is approx imate ly identical) the heights of which, except for the 140 keV peaks, a lways exceed the values of the to ta l background (below them). 0wing to

,li: ~e~,~ (800).; 2z~

(z~oo).;12o.

~I 19.o663.

%e-,,t/'l t j '~

' ' ' - E } ,

2'50 5'00 7'50 lO00 [keV]

Fig. 3. Automatically reeorded gamma spectra of our Szeged sampIe showing an aetivity mueh higher than the average. The second spectrum was recorded approx, four months later. Sample mark: F-17; Site of collection: Szeged; Date of collection: 07.02.1963; Volume of melted

snow prior to evaporation: 5000 rol

errors [41] it would be unreasonable to regard smaller protrusions a s " p h o t o - peaks" of to assign t hem to specific elements.

Based on au tomat ic recordings, Table 1 also contains age and element- ident i f icat ion est imations (45- -60 days, z41Ce, la4Ce, 7Be, l~ 95Zr and 95Nb).

Acta Physica Academiae Scimtiarum Hungaricae 20, 1966

INVESTIGATION OF THE GAMMA ACTIVITIES OF $NOW $AMPLES 31 ]

The presenee of z44Ce is eonfirmed b y the faet t ha t af ter more than one and a ha l l years i t can stiU be de tec ted in the stepwise spectra (see Figs. 7 and 8). On the o ther hand, the presence of the other elements (except for 7Be) is sug-

�91 20 keVJ C2~,o# ;mo-

.(~8o). ;90.

(12o).; 6o-

(6o). ;3o-

r

i

t 1

250 500 750 lO00.,/keVJ

Fig. 4. Automatically recorded gamma spectrum of our Kecskem› sample. Sample mark: F-21; SŸ of collection: Kecskem› Date of collection: 14.02.1963; Date of measurement:

26.02. 1963; Volume of melted snow prior to evaporation: 5000 rol

gested b y the fact t ha t t hey were also de tee ted in ne ighbour ing countries during the period of our collections (see Table 2).

The manua l stepwise speetra of a few samples (measurements with scalers) were t aken direct ly af ter the au tomat ic recordings, and (to de tec t 13~Cs) again much later , in order to decrease stat is t ical and distort ion errors. (Unfor tuna te ly , owing to the res t r ic ted durat ion of the measurements we failed to obta in a smaller stat is t ical error).

.dcia Physiva Academias Scientiarrtrn tIungarir 20, 1966

Tab

le

2 oz

Pre

sen

ce a

nd

co

nce

ntr

atio

n o

f fi

ssio

n p

rod

uct

s in

pre

cl f

itat

ion

s

�9

Iso

top

e

144C

e

Med

ium

(r +

s) ~

r

Dat

e an

d si

te o

f co

llec

tion

21.1

2.19

62--

10.0

1.19

63

Bu

char

est,

R

um

ania

30.0

4.19

62--

01.0

1.19

63

Vie

nn

a, A

ust

ria

Dat

e of

mea

sure

men

t

12.1

962

1 01

.196

3 ~

Lo

nd

on

02

.196

3 |

En

gla

nd

03

.196

3 J

11.0

5.19

62--

04

.01.

1963

s 29

.01.

1963

--22

.02.

1963

A

fter

~

15

and

64

0 H

un

gar

y

day

s

141C

e r

?

Co

nce

ntr

atio

n C

(gc

/ml)

?;

ce

.9;

ce

2,5

�9

10

-7;

CO

7,0

�9 1

0-7

; CO

3,

5 �9

1

0-7

; C

o 3,

0 �9

10

-v;

CO

Tre

nd

in t

ime

of

C

--_-

---

LX

Lite

ratv

Lre

[1]

[51

[241

16.0

7.19

62--

15.0

8.19

62

Sy

dn

ey,

Au

stra

lia

l~

s 17

.02.

1963

28

.02.

1963

an

d

?;

ce

Bu

dap

est,

H

un

gar

y

19.0

6.19

63

(Tab

le

1)

? o

21--

22.0

3.19

62

<

0,68

�9 1

0-7

; co

?

[2]

S r

11--

13.0

3.19

62

Sei

ber

sdo

rf,

Au

stri

a

05--

07.1

1.19

61

Sei

ber

sdo

rf,

Au

stri

a

11--

13.0

3.19

62

Sei

ber

sdo

rf,

Au

stri

a

27--

28.1

1.19

61

21

--2

2.0

3.1

96

2

?;

ce

? (T

able

1)

o

2,7

�9 10

-7

i [1

3]

9;

ce

?;

ce

30.0

4.19

62--

01.0

1.19

63

11.0

5.19

62--

V

ien

na,

A

ust

ria

04.0

1.19

63

?;

ce

11.1

961

and

03

.196

2 11

.196

1 an

d

Sei

ber

sdo

rf,

Au

stri

a 03

.196

2 ?;

ce

lO6

Ru

+

1O6R

h

lO6

Ru

14O

Ba

S

[21

[51

[2]

O

p~

i z

~40B

a (~

+

~)~

r

12.1

962

I 01

.196

3 ~

Lo

nd

on

02

.196

3 |

En

gla

nd

O

3.19

63 1

1,1

�9 10

-7;

CO

5,5

�9 1

0-7

; CO

1,

2 �9

10

-7;

CO

1,2

' 10

-S;

CO

i m

ax d d

[241

14~

s 2

1.1

2.1

96

2--

10

.01

.19

63

9

9 B

uch

ares

t,

Ru

man

ia

" ?;

pr

. .

[1]

r 05

.11.

1961

--07

.11.

1961

2

7--

28

.11

.19

61

0,

8 �9

10

-7;

co

? [2

] S

eibe

rsdo

rf,

Au

stri

a

16.0

7.19

62--

15.0

8.19

62

? 9,

3 �9

10 -

s ~

[13]

S

yd

ney

, A

ust

rali

a

13

7C

s 21

.12.

1962

--10

.01.

1963

[1

] B

uch

ares

t,

Ru

man

ia

?;

ce

[241

12

.196

2 |

01.1

963

~ L

on

do

n

02.1

963

| E

ng

lan

d

03.1

963

•

8,0

�9 1

0-a

; co

5,

0 �9

10-8

~ co

4,

0 �9

10

-s;

co

3,5

�9 1

0-s

; co

i m

ax d d

9nZ

r

03,

14

and

17

.02.

1963

af

ter

~ 67

0 d

ays

> (6

,0 �

9 10-

9);

a;

j ?

o H

un

gar

y

07.0

2.19

63

afte

r 69

0 d

ays

> (1

,1

�9 1

0-s

);

a;

I ?

o S

zege

d,

Hu

ng

ary

30

.04

.19

62

--0

1.0

1.1

96

3

11

.05

.19

62

--

~;

ce

? [5

] V

ien

na,

A

ust

ria

04.0

1.19

63

'

1,0

�9 1

0-e;

co

5,0

�9 1

0-7

; co

2,

7 �9

10

-7;

co

r s

(r +

s)

~

r $ s

---T

-

,~$

ce

12.1

962

} 01

.196

3 L

on

do

n

02.1

963

En

gla

nd

03

,196

3)

nla

x.

(d)

d d

(r +

sp

r

[24]

95Z

r ~-

a£

s 2

1.1

2.1

96

2--

10

.01

.19

63

9

~ [1

] B

uch

ares

t,

Ru

man

ia

" ?;

p

r "

s 1

1--

13

.03

.19

62

S

eibe

rsdo

rf,

Au

stri

a 2

1--

22

.03

.19

62

?

[2]

r~

Tab

le

2 (c

onti

nued

)

3 P

m

Iso

top

e

9x

y

14

7p

m

90

St

r r s

(r +

s)

r r

(r -

~ s)

x

r r

Dat

e an

d si

te o

f co

llee

tion

16.0

7--1

5.08

.196

2 S

ydne

y,

Aus

tral

ia

Dat

e o

f m

easu

rem

ent

Con

cent

rati

on C

(/~

c/nd

)

2,1

�9 10

-7

02.0

3.11

, 12

, 17

, 22

. af

ter

~-~

12 d

ays

> (3

,0 �

9 10-

s);

a; p

02

.196

3,

Hun

gary

07.0

2.19

63,

afte

r 18

day

s >

(1,3

�9 1

0-7)

; a;

1

Sze

ged,

H

unga

ry

05.1

963

Lon

don,

E

ngla

nd

? 2,

0 �9

10-7

; co

07.1

963

Lon

don,

E

ngla

nd

? 2,

0 �9

10-7

; co

21.1

2.19

62--

10.0

1.19

63

? ?;

ce

Buc

hare

st,

Rum

ania

1955

--19

62,

Dee

p l~

iver

, C

anad

a S

prin

g 19

62

Dee

p R

iver

, C

anad

a L

ate

1962

D

eep

Riv

er,

Can

ada

4,2

�9 10

-9

3,0

�9 10

-s

5,0

�9 1

0 -

9

12.1

962}

01

.196

3 L

ondo

n 02

.196

3 E

ngla

nd

03.1

963

12.1

962}

01

.196

3 B

udap

est

02.1

963

Hun

gary

03

.196

3

03,

14,

and

17.0

2.19

63

Hun

gary

afte

r 3

wee

ks

calc

ulat

ed

from

C

s-13

7 va

lue;

e

6,0

�9 10

-9;

co

3,0

�9 10

-s;

co

2,0

�9 10

-9;

co

2,0

�9 10

-s;

co

3,2

�9 10

-9

4,8

�9 10

-9

1,2

�9 10

-9

1,1

�9 10

-s

> (3

,6 �

9 10-

9);

a; j

Tre

nd i

n

time

of C

i?

o [131

?

Lit

erat

ure

M

e~u

m

o [241

[24]

[11

[201

[24]

[371

.=

o t~

7Be;

n

480

keV

pea

k

7Be

+ 1~

dedu

ctin

g lg

~lt

Tot

al

beta

07.0

2.19

63

Szeg

ed,

Hun

gary

19.0

2.19

56

} 01

.03.

1956

U

ppsa

la

03,0

3.19

56

Sw

eden

20.0

6.19

58

/ B

omba

y 11

.09.

1958

In

dia

14.0

7.19

58

16.0

7.19

62--

15.

08.1

962

Syd

ney,

A

ustr

alia

calc

ulat

ed

from

18

7Cs

vldu

e; e

>

(6,6

�9 1

0-9)

; a;

1

1,31

�9 1

0 -s

1,

61

�9 10

-s

2,64

- 1

0 -s

1,87

�9 1

0 -s

(a

vera

ge

of

19

sam

ples

) 4,

3 �9

10 -s

4,00

�9

10 -7

01.1

963

} B

udap

est

02.1

963

Hun

gary

03

,196

3

afte

r 3

wee

ks?

2,6

�9 10

-e

1,1

�9 1

0 -e

1,7

. I0

-~

--

m

r +

s +

01,1

963

] D

ebre

cen

afte

r 2

days

at

le

ast

0,88

�9 1

0 -8

+ y

02.1

963

J H

unga

ry

0,67

�9

10 -e

03

.196

3 0,

82

�9 10

-6

s 29

,01.

1963

--22

.02.

1963

--

~ 15

da

ys

< (1

,17

�9 10

-6)

? H

unga

ry

f;

i i i na

x,

na

x.

i'd i c d i

[32]

[3

31

[16]

[33]

[13]

[37]

[38]

o

~ _+yS

+

05--

12.0

2.19

63

,-~ 2

da

ys

0,56

�9

10 -8

[3

8]

s 11

.02.

1963

D

ebre

cen,

H

unga

ry

11

days

<

(0,8

5 �9

10

-e)

g;

o

.<

O o M

O ~e

oo

m

3 1 6 �93 T‰ I". ZSOLDOS and A. URBAN

Explanatory remarks to Table 2

r = r a i n s = melted snow r + s = melted snow mixed with rainwater co = corrected for the date of collection i = increasin d = decreasin g max = maximum min = minimum c = approximately constant ce = certainly present pr = probably present ? = not published, undeterminable value of C given in cpm/ml only x = between 11.01.1963 and 08.02.1963 only snow, for [24] o = our investigations a = approximate, neglecting sampling and concentrat ion losses, calculating in a rough approx- imation for the volume-dependence of photopeak-efficiency, taking (95Zr -4- 9aNb) with the efficiency of [27] at the date of measurement (not corrected for decay l) e = obtaindd from eight pairs of data [24, 14], converted with the average value (9~ = = 0,6 y = " d r y " fall-out on preeipitation-free days f = calculated for our conditions by a multiplying factor of N (2,3) [26] from the approximate total gamma concentration in Table 1, determined in ~zrCs-equivalent and not corrected for 7Be, neglecting losses and with a rough eorrection for the volume-dependence of the 137Cs total-efficiency; average value applicable to all 26 samples. The multiplying factor N(2 ,3) can be applied under the following assumptions [26]: a) the fission products in our samples are due to the fission of ~35U by slow neutrons; b) the measurement was made not earlier than 100 days after the fission. With a known fission product mixture [26] and with ah unknown geo- metry the mean integral counting cfficiency is 0,39 and 0,33 for 60 keV and 140 keV threshold, respectively. For 80 keV and ah unknown geometry of measurement approximately 0,38 can be taken. The authors ealculated for point-like Cs-137, for 80 keV and other, known conditions of measurement with ah integral counting efficiency of

[ i m p u l s e ] ~t = 0,254 [impulse/t3rCs disintegration] - - 0,31 661keV-pho ton "

The deviation is in pereentage of the value 0,38: --18,4~o, appropriate for estimation, still acceptable. n = element of natural origin, affecting the determinat ion of fission produets g = see f, but only for our sample, marked: F-15. j = for the samples marked: F-5, 6, 9, 21 and 26 1 = for the sample marked: F-17 p = for the samples marked- F-4, 10, 15, 16, 18, 24, 25 and 26 > = greater than < = ~maller than

.4c~a Physica Academiae Scientiarum Hungaricae 20, 1966

INVESTIGATION OF THE GAMMA ACTIVITIES OF SNOW SAMPLES 317

As shown in Fig. 5 the energy l inear i ty of our appara tus is satisfied between ~ 140 and 1280 keV. Below 100 keV l inear i ty is not guaranteed for our ins t rument by the manufac tu re r [52]. The energy-dependence of energy

~�91

oo

@

1300-

1200 ilO0-

I000

900

800

?00.

600 500.

4,00.

300.

200.

100.

0

No22(i276 keV)

E~ - f (b)

/_M"'~ § Cs '~7(662 eev)

q N+',vo e2(511 keV, ª rodiotion)

200 4,00 600 800 lO00 1200" 1#00" b bese leve/d/v/s/on

Fig. 5. Energy linearity of our gamma-spectrometer

6q 2

9 x102 observed

~ i I c~Iculoted 5 ~ J "

4 +~.~/

3 j � 9 3

Fig. 6. Energy-dependence of the energy reso]ution of our gamma-spectrometer

resolution is shown approx imate ly in Fig. 6, where the ex t rapo la ted s t ra ight line obta ined f rom observat ion - - apparen t ly owing to equal izat ion errors - - does not in tersect the ordinate [54].

Energy cal ibrat ion measurements were carried out wi th non-point l ike sources (solutions). For pointl ike 137Cs in the stepwise mode of operat ion the

Acta Physica Academiae Seientiarum Hungarir 20, 1966

318 •. T‰ T. ZSOLDOS aad A. URB�93

half value width is 76 keV (in au tomat ic recording 91 keV), the resolut ion is 11,6%, and the pho topeak efficiency calculated f rom the atea of the photo- peak: P~62 = 13,8~o. The l a t t e r value is in good agreement with values ob ta ined b y o ther authors: 14% and 1 5 ~ [2, 53].

N 300.

200

100-

6O 5O

30-

20-

7O 8 6 3 4 3

2

0

/ c,o_rn w/:thout bockground 7 20 ke V j

II 03.1963.

18.11.196~ ~ E7

200 .~00 600 800 lOOO [kel/.7

Fig. 7. Gamma spectra recorded by the stepwise method, by scaler, of our Szeged sample. The second speetrum, in which the peak appearing in the vicinity of 660 keV refers to the existence of laTCs, was recorded 20 months later. Sample mark: F-17; Site of collection: Szeged;

Date of colleetion: 07.02.1963; Volume of melted snow prior to evaporation: 5000 mi

Table 1 as well as Figs. 7 and 8 show the results of our stepwise spectra obta ined at two subsequent t ime-intervals for the samples F - - 1 7 and F - -2 6 . At this t ime too, ou t s tand ing peaks appear a t 140, 500 and 750 keV, except for two samples of the remaining twen ty two ( F - - 2 2 : peak appears only a t 500 keV; F - - 2 3 : the 750 keV peak is missing; b u t when observed automat ica l ly ,

Ac.la Physica .4cademiae Scientiart~m Hungaricae 20, 1966

I N V E S T I G A T I O N O F T H E G A M M A A C T I V I T I E S O F $ N O W S A M P L E S 319

soon af ter collection, i t was bare ly visible). For at least one and a half year af ter eolleetion the 140 keV Q~4Ce) peak can still be found in t h e s pectra , the 500 keV peak can scarcely be observed and since the 750 keV peak and its Compton con t inuum have a l ready deeayed, the 662 keV peak of 137Cs also

#

200-

lO0-

80 ~

60- 5 0

60 -

30-

20

8

G 5

6

3

o

cprn without bakkground_~ 2EEs -_/

j 05. 03.1963.

11

200 4,00 600 800 v~vvvV. ,

1ooo f keV]

Fig. 8. Gamma spectra recorded by the stepwise method of our Budapest sample. The peak appearing in the vicinity of 660 keV in the spectrum recorded approx. 21 months later refers to the presente of 137Cs. Sample mark: F-26; Site of collection: Budapest; Date of collection:

17.02.1963; u of melted snow prior to evaporation: 5000 mi

appears. The areas of the significant photopeaks have been de termined f rom linear scale graphs by means of the graphical correct ion a l ready ment ioned [27]. The rat ios of the areas ate shown in Table 1. Al though wi th a large error ( ~ 82, 68, 88, 23, 74, 4 6 ~ ) 137Cs has been detec ted in the samples marked F - - 5 , F - - 6 , F - - 9 , F - -17 , F - - 2 1 and F - - 2 6 one a n d a hal f year af ter collection, with the greatest probabi l i ty in the F - - 1 7 sample ( ~ 23% statist ical error).

~4eta Physica Academiae Scientiarum Hungarica~ 20, 1966

320 A. T‰ T. ZS0LDOS and A. URBAN

From the resulting 137Cs concentrations, 9~ concentrat ion for the above six samples has also been es t imated by means of the conversion fac tor ment ioned in remark d) to Table 2 (see Table 2).

The 137Cs concentrat ions (see Table 2) have been calculated on the basis of zero solution height corrections and the P662 = 13,8~o photopeak efficiency. As the value of P6~2 agrees with the one in [27] a n d a s in [27] the 750 keV photo- peak efficiency (for 95Zr q- 95Nb) is P750 = 1 2 ~ , based on the la t ter we have es t imated (95Zr q- 95Nb)-concentration from the 750 keV photopeak areas. This is relat ively simple, a s a single gamma photon of given energy is emi t ted in the decay of each of these elements. As for 137Cs, calculations have also been made for point source geometry assuming a 100~o recovery of the element, ahhough we know tha t this is not true. Table 2 shows the est imated (95Zr q-95Nb)- concentra tion, jus t as the 137Cs concentration, marked by the "grea ter t h a n " sign before the bracket .

According to Table 2 our approximate values agree quite well with those of other authors (for to ta l beta activity) or are of the same order of magni tude (owing to loss of material).

Owing to the dependence of fall-out concentrat ion on la t i tude and season [24, 28, 29] and to possible fract ionation [10, 19, 22] it is difficult to assign the fission product age of approximately 2 months obtained from the three types of measurements (see Table 1) to any part icular nuclear explosion test , a l though snow normal ly contains younger fission products t han does rain[36].

Our prel iminary investigations have revealed tha t the surface of this coun t ry is also contamina ted by fissiort products in snow and tha t some local anomalies occur (F--17 sample collected at Szeged, being approximate ly 3- t imes higher than the average). Improvements in our techniques are in progress.

Acknowledgements

Thanks are due to Prof. D�93 VSDI~6S, for his valuable comments , to the County KOJ �93 Organizations, for collecting and dispatching some of the samples, and to Mrs. K. FILus, Mr. and Mrs. J. P• for t reat ing and measur- ing the samples.

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Acta Physica Acaderniae Scientiarurn Hungaricae 20, 1966

INVESTIGATION OF THE GAMMA ACTIVITIES OF SDIOW SAMPLES 321

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kiad£ Budapest, p. 776, 1959. 51. "Radioaktyivnª csaszticª v Atmoszfere", Szbornyik sztatyej, Goszatomizdat, Moszkva,

1963. a) II. D. SCHULZ and W. KOLB, p. 75, Fig. 3. b) R. MAY and H. SCHr~HDER, p. 56, Figs. 2, 6, 7.

52. Operation and Maintenance Manual of Model 1820 B Recording Spectrometer, Nuclear Chicago Corporation, p. 21.

53. D. REDON et al., Nucl. Intr. and Meth., 26, 18, 1964.

2 Acta Physica .4cademiae Scientiarum Hungaricae 20, 1966

322 .�93 TOTH, T. ZSOLDOS and A. URB�93

54. L. KESZTHELYI, "Scintillation Counters" (in Hungarian), Mª K6nyvkiad£ �8 teehnika sorozat, Budapest, 1964, p. 82.

55. E. V�93243 private communieation (11. I. 1965.). 56. Operation and Maintenance Manual of Model 1620 B Analytical Counting Ratemeter ,

Nuclear Chicago Corporation, pp. 11--19. 57. G. J . HU~TEa and V. F. MITCrtELL, "Tables of Factors for Correcting for Radioactive Decay,

A E R E " - - R 4237, p. 3, Table 27, 1963. 58. J . A. SCr~EDLINg and W. A. M• Zur Frage der Grtisse und des Aufbaus der heissen

Teilchen. Strahlenschutz, 1963. XII. (Bundesministerium fª Atomkernenergie und Wasserwirtschaft).

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Acta Physica Academiae Scienliarum Hungaricae 20, 1966