Intercomparison of Different Instruments That Measure Radon

Chapter 13

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Intercomparison of Different Instruments That Measure R a d o n Concentration i n Air Michikuni Shimo, Takao Iida, and Yukimasa Ikebe Department of Nuclear Engineering, Faculty of Engineering, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464, Japan An intercomparison of different instruments for measurement of radon concentration was carried out. The instruments include an ionization chamber, the charcoal-trap technique, a flow-type ionization chamber (pulse-counting technique), a two-filter method, an electrostatic collection method and a passive integrating radon monitor. All instruments except for the passive radon monitor have been calibrated independently. Measurements were performed over a concentration range from about 3.5 Bq/m (in outdoor air) to 110 Bq/m (in indoor air). The results obtained from these techniques, except the two-filter technique, are comparable. Radon daughter concentration measured using a filter-sampling technique was about 52 % of radon concentration. 3

3

There are various techniques for measuring radon concentration in air (Budnitz, 1974). Needless to say, a value obtained with a given instrument should be the same one with another method. The data from an instrument assured of "exchangeability" is useful. The authors have thought that an intercomparison between devices is necessary and important to ensure exchangability between instruments operating by different principle. From this viewpoint, an intercomparison between various instruments for measuring radon concentrations was planned and carried out in natural concentration levels using outdoor and indoor airs. The measuring techniques are (see Table I): (1) an ionization chamber method — measurement of ionization current obtained from ion ization chamber which was directly filled by sample gases (DSC), (2) a charcoal-trap method — the method for sampling radon gas with a cooled activated charcoal and for measuring activity of alpha particle from radon and its daughters with ionization chamber (ACC), (3) a flow-type ionization chamber method — the method for directly drawn air samples into a pulse-counting flow-type ionization chamber (PFC), (4) a two0097-6156/87/0331-0160$06.00/0 © 1987 American Chemical Society

Hopke; Radon and Its Decay Products ACS Symposium Series; American Chemical Society: Washington, DC, 1987.


Radon

Monitor

Passive Integrating

Monitor

Radon

Method

Ionization

Charcoal

Chamber

Electrostatic

Two-Filter

Chamber

Flow-Type

Method

Activated

Method

Ionization

Instrument/Method

PRM

ERM

TF

PFC

ACC

DSC

o f v a r i o u s radon

rate:

rate:

-73°C, chamber

time:

lhr, filter:

two months

a

measurement

-180 V a p p l i e d , d e h u m i d i f i e d ,

sampling: exposed time:

electrostatic CN-film,

c o n t i n u o u s l y m e a s u r e d , d e t e c t o r : ZnS(Ag)

0.5 &/min, e l e c t r o d e : -3000 V a p p l i e d ,

dehamidified,

rate:

ionization

gross c o u n t i n g or α-spectrometry,

40 &/min, s a m p l i n g

and ot-pulse c o u n t i n g

Rn a n d T n m e a s u r e d

flow

current

s a m p l e d temp.:

into

5 l/min,

chamber,

1-2 &/min, c o n t i n u o u s l y m e a s u r e d , c u r r e n t

membrane f i l t e r ,

flow

rate:

lhr.,transfered

5g, f l o w time:

measurement

flow

sampling

charcoal:

instruments

sampled t o an e v a c u a t e d

measurement

directly

Remarks

Intercomparison

Symbol

Table I.

162

RADON AND ITS DECAY PRODUCTS

f i l t e r method (TF), (5) an e l e c t r o s t a t i c radon monitor — the method for sampling with e l e c t r o s t a t i c c o l l e c t i o n (ERM), and (6) a passive radon monitor — the e l e c t r o s t a t i c integrating radon monitor with c e l l u l o s e n i t r a t e f i l m (PRM). Also, measurements with a i r f i l t e r (namely, f i l t e r - p a c k method, FP) (Harley, 1953; Shimo, 1985) was s i multaneously carried out and the results compared with those obtained by using the other methods.

Measurement Method Ionization Chamber Method (DSC). The ionization chamber i s one of the most common instruments for measuring radon gas. The chmaber was c y l i n d r i c a l l y shaped and had a 1.5 l i t e r volume. A i r samples were drawn through a dryer f i l l e d with CaCl^ and a f i l t e r to remove water vapor, radon daughters and aerosols, so that only the parent radon gas i s admitted to the chamber. The radon gas subsequently decays and reaches equilibrium with i t s daughters i n 3.5 hours after entry into the chamber. The ionization currents are measured with a vibraing reed electrometer. We have made the DSC the standard method f o r the radon measurement. The c a l i b r a t i o n procedures have been described elsewhere (Shimo et a l . , 1983); B r i e f l y , the Rn-222 emanating from a standard Ra-226 hydrochloric acid solution (37 kBq) contained i n a bubbling bottle entered a large stainless steel container (937 it). A small part of radon gas i n the container was transfered into the ionization chamber (1.5 &). The radon concentration i n the container was controlled by varying the storage time of radon i n the bubbling bottle. Therefore, a relationship between the radon concentration Q

e x p

(Bq/m^) and the ionization current I (fA) was experimentally obtained;

3 On the other hand, the radon concentration Q (Bq/m ) can t h e o r e t i c a l l y be calculated as follows:

f - f

x

χ f

2

χ f

3

(3)

where W i s the energy needed for making one ion pair production by alpha p a r t i c l e i n a i r , 35.5 eV; I, measured currents ( f A ) ; e, -19 elementary unit of charge 1.602 χ 10 coul; E, t o t a l alpha energy from Rn, RaA and RaC, 19.17 MeV; V, the e f f e c t i v e volume of the 3 chamber (m ), and f , a correction factor. The factor f i s f^xf^xfy f^: correction for decay during the measurement, correction for the wall loss (loss of ionization due to the wall of chamber) (Tachino et a l . 1974) and f ^ : correction from the columnar


13.

SHIMO ET AL.

163

Instruments That Measure Radon Concentration in Air

r e c o m b i n a t i o n (Boag, 1966)· F o r the DSC u s i n g a 1.5 £ volume chamber, the v a l u e o f f i s 0.46 ( f ^ O . 9 8 7 , f = 0 . 4 7 , and f = 0 . 9 8 5 ) . 2

T h e r e f o r e , the c a l c u l a t e d Q

c a l

= 16.8

3

radon c o n c e n t r a t i o n Q ^ ca

(Bq/m^) i s

I

(4)

From e q u a t i o n s (1) and ( 4 ) , i t i s c l e a r t h a t t h e r e s u l t s o f c a l i b r a t i o n agreed w i t h the t h e o r e t i c a l c a l c u l a t i o n w i t h i n 8.4 p e r c e n t . F i n a l l y , we have used the e x p e r i m e n t a l r e s u l t s f o r the r e l a t i o n s h i p between radon c o n c e n t r a t i o n and i o n i z a t i o n c u r r e n t . 3 The s e n s i t i v i t y of the DSC i s about 40 Bq/m . C h a r c o a l - T r a p Method (ACC). The C h a r c o a l - T r a p Method has been used f o r s a m p l i n g radon gas i n t h e a t m o s p h e r i c a i r and f o r measuring radon emanation r a t e from the s o i l s u r f a c e by some r e s e a r c h e r s ( e . g. Kawano and N a k a t a n i , 1964; Megumi and Mamuro, 1972). The t r a p c o n t a i n e d about 5 grams o f a c t i v a t e d g r a n u l a r c h a r c o a l i n a b r a s s tube. The c o o l a n t system c o n s i s t e d o f a m i x t u r e o f d r y - i c e and e t h a n o l to keep the temperature a t -73°C d u r i n g a i r s a m p l i n g a t 5 &/min. The absorbed radon gas was purged u s i n g argon gas a t 800°C and t h e n t r a n s f e r e d i n t o an i o n i z a t i o n chamber. The radon a c t i v i t y i n the chamber was measured a t about 4 hours a f t e r t r a n s f e r e n c e i n the same manner as the DSC (Shimo e t a l . , 1983). The c o l l e c t i o n c o e f f i c i e n t o f the ACC was e v a l u a t e d t o be 0.88+0.05. Flow-Type I o n i z a t i o n Chamber ( P F C ) . The Flow-Type I o n i z a t i o n Chamber Method (PFC) has been developed f o r c o n t i n u o u s l y measuring radon gas i n the a t m o s p h e r i c a i r . The d e t a i l o f the d e v i c e has been d e s c r i b e d elsewhere (Shimo, 1985). B r i e f l y , measurements a r e c o n t i n u o u s l y c a r r i e d out by drawing a i r t h r o u g h t h e d e t e c t o r a t 1.0 ~ 2.0 &/min. The i o n i z a t i o n c u r r e n t d u e t o a l p h a p a r t i c l e s from radon and i t s daughters i s d e t e c t e d w i t h a v i b r a t i n g r e e d e l e c t r o m e t e r (VRE) i n the same manner as the DSC. The s e n s i t i v i t y 3 of the c u r r e n t method o f t h i s d e v i c e was about 10 Bq/m . Thus t o d e t e c t a lower c o n c e n t r a t i o n o f radon, a p u l s e - c o u n t i n g t e c h n i q u e was used; The output s i g n a l o f the VRE was d e t e c t e d i n t o a d i f f e r e n t i a l a m p l i f i e r , and a s i g n a l from an a l p h a p a r t i c l e i s d i s t i n g u i s h e d from background c u r r e n t s due t o gamma-radiation and cosmic r a y s and counted. The a l p h a - c o u n t s i n an hour, C i s o b t a i n e d by the f o l l o w i n g f o r m u l a : C = QTVf

(5)

3 where Q i s the radon c o n c e n t r a t i o n (Bq/m ); T, the c o u n t i n g time 3 —3 3 ( s e c ) ; V, the volume o f chamber (m ) (12.72 χ 10 m ) and f , a correction factor. The c u r r e n t measurement was c a l i b r a t e d u s i n g the same way as the DSC, and good agreement between t h e expreiment and t h e o r e t i c a l c a l c u l a t i o n was o b t a i n e d . The PFC was s i m u l t a n e o u s l y a b l e t o d e t e c t 3 over the range o f 10 ~ 100 Bq/cm o f radon c o n c e n t r a t i o n u s i n g the c u r r e n t and p u l s e - c o u n t i n g methods. T h e r f o r e , the c a l i b r a t i o n o f the p u l s e - c o u n t i n g t e c h n i q u e was performed by u s i n g the r e s u l t o f


164


the c u r r e n t measurement c a r r i e d out s i m u l t a n e o u s l y w i t h c o n v i e n i e n t radon c o n c e n t r a t i o n ; T h i s gave the r e l a t i o n s h i p between the radon 3 c o n c e n t r a t i o n Q (Bg/cm ) and counts C ( c o u n t s / h r ) : Q = 0.0418 C

Bq/m

^The .

(6)

s e n s i t i v i t y o f the p u l s e - c o u n t i n g method i s about 0.2

T w o - F i l t e r Method ( T F ) . The Two F i l t e r Method was f i r s t i n t r o d u c e d by Thomas and L e C l a r e (Thomas and L e C l a r e , 1970). A m o d i f i e d 66.3 l i t e r decay chamber was used w i t h a f i l t e r on each end. A i r was sampled a t 40 Z/min. The i n l e t f i l t e r removed a l l o f the radon daughters and a e r o s o l p a r t i c l e s but a l l o w e d radon gas t o pass. D u r i n g the t r a n s p o r t i n the chamber, radon atoms decay t o form RaA atoms. The RaA atoms except those d i f f u s e d t o the w a l l o f the chamber a r e c o l l e c t e d on the e x i t f i l t e r . The sample c o l l e c t e d on the e x i t f i l t e r i s removed and counted. The p r e s e n t method i s a b l e to s i m u l t a n e o u s l y measure radon and t h o r o n c o n c e n t r a t i o n s by a l p h a s p e c t r o s c o p i c t e c h n i q u e (Ikebe e t a l . , 1979). 3 The radon c o n c e n t r a t i o n i n a i r , Q (Bq/m ) , i s o b t a i n e d from the equation

Q =

Iuïa7

k

( 7 )

where C i s the t o t a l a l p h a counts i n the measured t i m e ; ε, t h e c o u n t i n g e f f i c i e n c y ; ζ, the emerging e f f i c i e n c y o f the a l p h a p a r t i c l e s from the f i l t e r ; η, the c o l l e c t i o n e f f i c i e n c y ; q , the f l o w r a t e ; F, a c o n s t a n t d e c i d e d from the decay c o n s t a n t s o f radon o r t h o r o n and progeny, the f l o w r a t e and sampling and c o u n t i n g t i m e s , and k, a c a l i b r a t i o n f a c t o r . The c a l i b r a t i o n o f t h i s method was performed w i t h Rn-222 and Rn-220 emanating from s t a n d a r d Ra-226 and Th-228 s o l u t i o n s , respectively. I t i s d e f i n e d t h a t the c a l i b r a t i o n f a c t o r i s the r a t i o o f e x p e r i m e n t a l counts t o one expected from used radon and/or t h o r o n gases by u s i n g E q u a t i o n ( 7 ) ; The c a l i b r a t i o n f a c t o r s o f radon and t h o r o n were e v a l u a t e d t o be 0.81 and 0.51, respectively. E l e c t r o s t a t i c Radon M o n i t o r (ERM). The Flow-Type E l e c t r o s t a t i c Sampling Instrument ( t h e e l e c t r o s t a t i c radon m o n i t o r ) was f i r s t developed by D a l u and D a l u , 1971 ( D a l u and D a l u , 1971). I n the p r e s e n t study a m o d i f i e d v e r s i o n developed by I i d a (1985) was used. A 15 l i t e r , s e m i s p h e r i c a l sampling v e s s e l w i t h a f l o w r a t e o f 0.5 &/min was used. The e l e c t r o d e (38 mm d i a m e t e r ) i n f r o n t o f the ZnS(Ag) s c i n t i l l a t o r was p l a c e d i n the c e n t e r o f the bottom and was set a t -3,000 V r e l a t i v e t o the v e s s e l w a l l . S i n c e the ERM i s s e n s i t i v e t o water vapor ( P o r s t e n d o r f e r e t a l , 1980; D a l u e t a l . , 1983), the a i r sample was passed through a d e h u m i d e f i e r t o m a i n t a i n the r e l a t i v e h u m i d i t y i n the chamber l e s s than 2.9 %. 3 The radon c o n c e n t r a t i o n i n a i r Q (Bq/m ) i s e s t i m a t e d from the following equation:


13.


SHIMO ET AL.

CCD g

- A

C'(l-i)

VÏTÏ5

m

χ

165

( 8 )

k

where C ( I ) i s the t o t a l a l p h a counts i n the measured time i n t e r v a l I ; C ( I - i ) , the expected a l p h a counts from p r e v i o u s s a m p l i n g p e r i o d i ; V, the volume o f sampling v e s s e l (m) ; F ( ( I ) , a c o n s t a n t determined from the decay c o n s t a n t s o f radon progeny, the f l o w r a t e and s a m p l i n g and c o u n t i n g t i m e s , and k, the c a l i b r a t i o n f a c t o r . The i n s t r u m e n t was c a l i b r a t e d u s i n g a 1.5 l i t e r f l o w - t y p e i o n i z a t i o n chamber: The c a l i b r a t i o n f a c t o r was e v a l u a t e d t o be 0.318. f

P a s s i v e I n t e g r a t i n g Radon M o n i t o r ( P R M ) . Many t y p e s o f p a s s i v e i n t e g r a t i n g radon m o n i t o r s have been developed (Urban and P i e s c h , 1981; A l t e r and F l e i s c h e r , 1981; I i d a , 1985). The a u t h o r s developed a s e n s i t i v e d e v i c e , PRM, f o r measuring n a t u r a l radon c o n c e n t r a t i o n l e v e l s by e l e c t r i c a l l y c o l l e c t i n g Rn-222 progeny on an e l e c t r o d e b e h i n d w h i c h a c e l l u l o s e n i t r a t e (CN) f i l m s was s e t (Ikebe e t a l . , 1985). A window f o r v e n t i l a t i n g a i r was p r o v i d e d i n t h e bottom w a l l . The PRM d e t e c t s a l p h a p a r t i c l e s o n l y from Po-218 and does not d e t e c t those from Po-214 because o f an a l u m i n i z e d m y l a r sheet i n f r o n t o f the e l e c t r o d e , the g e o m e t r i c a l arrangement between the a l u m i n i z e d m y l a r sheet and CN f i l m s , and e c h i n g t i m e . An e l e c t r o d e a t the c e n t e r o f the c y l i n d r i c a l v e s s e l (140 mm d i a m e t e r , 100 mm h e i g h t ) i s s e t a t -180 V r e l a t i v e t o the v e s s e l w a l l . The PRM i s a l s o s e n s i t i v e t o water vapor f o r the same r e a s o n i n as the case o f the ERM (Negro and W a t n i c k , 1978; K o t r a p p a e t a l . , 1982; Annanmaki et a l . , 1983). T h e r e f o r e , approximate 150 g o f d r y i n g agent (P °5 2

powder) was put on the bottom o f the v e s s e l f o r remeving water vapor from the sampled a i r . ^ The radon c o n c e n t r a t i o n i n a i r Q(Bq/m ) i s o b t a i n e d from the equation

«> -2 —2 where D (cm ) i s e t c h e d p i t d e n s i t y ; Β (cm ) , background d e n s i t y ; K, the c o n v e r s i o n f a c t o r , and T ( h ) , exposure t i m e . The c o n v e r s i o n —2 —2 —3 f a c t o r was e s t i m a t e d t o be (4.75 ± 0.41) χ 10 (cm /(Bg mm hr)) from comparing w i t h the v a l u e by u s i n g the DSC. D e t e c t i o n L i m i t s o f I n s t r u m e n t s . The measuring range o f those s i x i n s t r u m e n t s a r e shown i n F i g u r e 1. A l l o f the i n s t r u m e n t s except f o r the DSC a r e a b l e t o d e t e c t the minimum radon c o n c e n t r a t i o n a t 1 3 Bq/m . S i n c e the radon c o n c e n t r a t i o n i n outdoor a i r i s s e v e r a l 3 Bq/m ( e . g . Shimo and I k e b e , 1979), f i v e out o f s i x t e c h n i q u e s ( e x c l u d i n g the DSC) a r e comparable o f d e t e c t i n g radon i n the outdoor a i r . The DSC can o n l y be used when t h e radon c o n c e n t r a t i o n i s 3 h i g h e r t h a n 40 Bg/m .



166 Experimental

Procedure

S e v e r a l measurements were s i m u l t a n e o u s l y c a r r i e d o u t w i t h f o u r i n s t r u m e n t s , e x c l u d i n g t h e ERM and t h e PRM. The e x p e r i m e n t a l arrangement i s shown i n F i g u r e 2. The pathways 1 and 2 were used f o r sampling outdoor and i n d o o r a i r , r e s p e c t i v e l y . A i r sampled from 3 a 66.3 m room was exhaused back t o i n d o o r s t o keep i n d o o r radon concentration r e l a t i v e l y constant. The i n d o o r radon c o n c e n t r a t i o n 3 3 ranged from 5 Bq/m t o 110 Bq/m (pathway 2 i n F i g u r e 2 ) . The sampling time o f t h e DSC was v e r y s h o r t because t h e a i r was sampled i n t o an evacuated chamber (1.5 l i t e r volume); However, t h e ACC and t h e TF were sampled d u r i n g 1 hour a t t h e f l o w r a t e o f 5 £/min and 40 £/min, r e s p e c t i v e l y . The c u r r e n t measurements o f t h e DSC and t h e ACC were made b e g i n n i n g a t 3 hours a f t e r end o f sampling; The measurement o f t h e TF was performed d u r i n g t h e 4096 seconds immediately a f t e r t h e end o f sampling. The PFC was o p e r a t e d c o n t i n u o u s l y i n t h i s work and t h e radon c o n c e n t r a t i o n has been e s t i m a t e d from t h e counts p e r hour. The FP was o p e r a t e d w i t h a 15 min s a m p l i n g - t i m e and a 40 m i n c o u n t i n g - t i m e , so t h a t a v a l u e was o b t a i n e d once an hour. The simultaneous measurements were performed i n 5 rounds w i t h more t h a n 8 measurements f o r t h e f o u r i n s t r u m e n t s except t h e DSC (one measurement) made i n each round. The i n d o o r measurement w i t h the ERM was c o n t i n u o u s l y made i n t h e l a b o r a t o r y t o g e t h e r w i t h t h e PFC f o r s e v e r a l months a f e r making simultaneous measurements u s i n g the f i v e d e v i c e s . These r e s u l t s were compared w i t h each o t h e r . The measurements w i t h t h e PRM was performed over t h e two years f o l l o w i n g t h e p e r i o d mentioned above. The PRM was exposed f o r two months f o r each measurement. T h i s approach gave an average c o n c e n t r a t i o n i n two months. The r e s u l t s o b t a i n e d i n outdoor and i n d o o r a i r were compared w i t h t h e c o r r e s p o n d i n g d a t a from t h e PFC and t h e ERM. R e s u l t s and D i s c u s s i o n F i g u r e 3 i s an example o f simultaneous measurements o f radon c o n c e n t r a t i o n i n i n d o o r a i r . The measurements shown i n t h i s f i g u r e were made under changing c o n d i t i o n ; t h e i n d o o r radon c o n c e n t r a t i o n i n c r e a s e d a f t e r t h e room had been c l o s e d t i g h t l y . T a b l e 2 i s a summary o f t h e e x p e r i m e n t a l r e s u l t s from a l l methods; T h i s t a b l e g i v e s t h e r a t i o o f each c o n c e n t r a t i o n o b t a i n e d from t h e DSC, t h e PFC, t h e TF, and t h e FP t o t h a t from t h e ACC, and the r a t i o o f each v a l u e from t h e ERM and t h e PRM t o t h a t from t h e PFC. The r e s u l t s i n T a b l e 2 show t h a t good agreement was o b t a i n e d between t h e DSC and t h e ACC. However, t h e r a t i o o f t h e r e s u l t s from the PFC t o t h a t o f t h e ACC was 1.15 ± 0.33. F u r t h e r e m o r e , t h e v a l u e o b t a i n e d from t h e TF was u s u a l l y s m a l l e r than t h a t from t h e ACC, and the mean v a l u e was 0.68 ± 0.18. The v a l u e o b t a i n e d from t h e FP was s m a l l e r t h a n t h a t o b t a i n e d from t h e ACC. T h i s r e s u l t s i s because radon and i t s daughters a r e u s u a l l y a t n o n - e q u i l i b r i u m s t a t e i n t h e atmosphere. On t h e o t h e r hand, a good agreement between t h e ERM and t h e PFC was o b t a i n e d . A l s o , t h e v a l u e from t h e PRM agreed w i t h t h a t from the PFC, whereas t h e simultaneous measurements between t h e ERM and


SHIMO ET AL.


DSC ACC PFC

(pulse) (current):

TF Ε RM PRM 10'

10

1

1

10

100 3

Radon Concentration (Efy-m )

Figure 1. The detection range of various instruments, NL: Natural radon concentration l e v e l . 3

Room 66.1m

(1) Outdoor, 2-6 Bq-m'

3

it

(2)

V= Valve Figure 2. system.

Exhaust

Schematic diagram of the simultaneous sampling

-200

door open

door closed

Indoor. Run 5

I

5

10 15 20 25 30 Time from start of experiment

35 (hr)

40

45

Figure 3. Radon and daughter concentrations obtained from various instruments. Hopke; Radon and Its Decay Products ACS Symposium Series; American Chemical Society: Washington, DC, 1987.


Indoors Indoors Indoors Outdoors

12 10 45 8

0.52±0.15

RC

0.92

1.04±0.21

0.30

1.15±0.36

1.15±0.36

Outdoors 12

0.43±0.09

1.04±0.21

Indoors

10

0.52±0.09

0.62+0.20

Indoors

8

PRM/PFC

Remarks

ERM/PFC

No. o f m e a s .

FP/ACC

coefficient

0.68±0.18

0.70±0.09

0.78±0.21

0.54±0.44

0.72±0.08

TF/ACC

SD: s t a n d a r d d e v i a t i o n , RC: R e l a t i v e

0.97

1.15±0.33

0.82±0.19

1.19±0.20

1.30±0.27

PFC/ACC

0.97

1.03

1.03

DSC/ACC

0.91

± SD

mean

7

6

5

4

3

2

1

Round

T a b l e I I . The r a t i o o f r a d o n c o n c e n t r a t i o n o b t a i n e d from v a r i o u s i n s t r u m e n t s

169 in Air 13. SHIMO ET AL. Instruments That Measure Radon Concentration the PFC and between the PRM and the PFC were independently performed from other devices. One can indirectly compare values obtained from these two methods to those from other methods through the PFC. Finally, it was concluded that the values obtained by the DSC, the ACC, the PFC, the ERM and the PRM except fro the TF agreed with each other. Conclusion An intercomparison between different instruments for measurement of radon concentration was carried out using indoor and outdoor air as sampling gas. Consequently, the values obtained by using the PFC, the ACC, the ERM and the PRM based on the DSC agreed with each other. However, the value obtained with the TF was smaller than those obtained with other methods. The availability and suitability of those devices are briefly descrived as follows; In high radon concentration, greater than 10 times outdoor levels, the DSC is suitable because air can simply be sampled in a short time. On the other hand, the ACC is useful for very low concentration but the operation is troublesome. For continuously measurement of the radon concentration over long period, the PFC and the ERM are available. The TF can be used for obtaing the radon and thoron concentrations. The PRM is useful for simultaneously obtaining many radon values at various locations. The FP may be used to estimate a rough radon concentration. References Alter, H. W. and R. L. Fleischer, Passive integrating radon monitor for environmental monitoring, Health Physics, 40: 693-702 (1981). Annanmaki, M., H. Koskela, M. Koponen, and O. Parviainen, RADOK: An Integrating, Passive Radon Monitor, Health Physics, 44: 413-416 (1983). Boag, J. W., Ionization Chamber, in Radiation Dosimetry (F. H. Attix, W. C. Roesch, and E. Tochilin ed) vol. II, pp. 30-36, Academic Press, New York (1966). Budnitz, R. J . , Radon-222 and its daughters --- A Review of Instrumentation for Occupational and Environmental Monitoring, Health Physics, 26: 145-163 (1974). Dalu, G. and G. A. Dalu, An Automatic Counter for Direct Measurements of Radon Concentration, Aerosol Science, 2: 247-255 (1971). Dua, S. Κ., P. Kotrappa, and P. C. Gupta, Infuluence of Relative Humidity on the Charged Fraction of Decay Products of Radon and Thoron, Health Physics, 45: 152-157 (1983). Herley, J. Η., Sampling and Measurement of Airborne Daughter Products of Radon, Nucleonics, 11: 12-15 (July) (1953).


170


Iida, T., An Electrostatic Radon Monotor for the Continuous Measurement of Environmental Radon, in Atmospheric Radon Families and Environmental Radioactivity (S. Okabe, ed) pp. 65-73, Atomic Energy Society of Japan, Tokyo (1985) (in Japanese). Iida, T., Passive Integrating Radon Monitor, Hoken-butsuri, 20: 407-415 (1985). Ikebe. Y., M. Shimo, and T. Iida, A study on the Behavior of Atmospheric Radioactive Aerosols in Facilities, Department of Nuclear Engineering, Faculty of Engineering, Nagoya University, Nagoya(1979) (in Japanese). Ikebe, Υ., T. Iida, M. Shimo, H. Ogawa, J. Maeda, T. Hattori, S. Minato, and S. Abe, Evaluation by alpha track Detectors of Rn Concentrations and f Values in the Natural Environment, Health Physics, 49: 992-995 (1985). Kawano, M. and S. Nakatani, Some properties of Natural Radioactivity in the Atnmosphere, in The natural Radiation Evviroment, (J. A. S. Adams and W. M. Lowder, ed) pp. 291-312, Univ. Chicago Press, Chicago (1964). Kotrappa, P., S. K. Dua, N. S. Pimpal, P. C. Gupta,K. S. V. Nambi, A. M. Bhagwat, and S. D. Soman, Passive Measurement of Radon and Thoron Using TLD of SSNTD on Electrets, Health Physics, 43: 399-404 (1982) . Megumi, K. and T. Mamuro, A Method for Measuring Radon and Thoron Exhalation from the Ground, J. Geophysical Redsearch, 77: 3051-3056 (1972). Negro, V. C. and S. Watnick, "FUNGI" A Radon Measuring Instrument with Fast Response, IEEE Trans. Nuclear Science, 25: 757-761 (1975). Porstendörfer, J. , A. Wicke, and A. Schraub, Method for a Continuous Registration of Radon, Thoron, and Their Decay Products Indoors and Outdoors, in The Natural Radiation Environment III, (T. F. Gesell and W. M. Lowder, ed) pp. 1293-1307, Technical Information Center/U.S. DOE, Springfield (1980). Shimo, M. and Y. Ikebe, Radon-222, Radon-220 and Their Short-Lived Daughter Concentrations in the Atmosphere, Hoken-Butsuri, 14: 251-259 (1979) (in Japanese). Shimo, Μ., Y. Ikebe, J. Maeda, R. Kamimura, K. Hayashi, and A. Ishiguro, Experimental Study of Charcoal Adsorptive Technique for Measurement of Radon in Air, J. Atomic Energy of Japan, 25: 562-570 (1983) (in Japanese). Shimo, M., A Continuous Measuring Apparatus using Filter-Sampling Technique for Environmental Radon Daughters, Research Letters on Atmospheric Electricity, 4: 63-70 (9184).


171 in Air 13. SHIMO ET AL. Instruments That Measure Radon Concentration Shimo, M., A Flow-Type Ionization Chamber for Measuring Radon Concentration in the Atmospheric Air, in Atmospheric Radon Familiers and Environmental Radioactivity (S. Okada, ed) pp. 37-42, Atomic Energy Society of Japan, Tokyo (1985) (in Japanese). Tachino, T., Y. Ikebe and M. Shimo, Wall Effect of Ionization Chambers in Measurement of Ionization Current due to Several Gaseous Alpha Radioactive Sources --- Monte Carlo Calculation, J. Atomic Energy Society of Japan, 16: 626-631 (1974) (in Japanese). Thomas, J. W. and P. C. LeClare, A Study of the Two-Filter Method for Radon-222, Health Physics, 18: 113-122 (1970). Urban, M. and E. Piesch, Low Level Environmental Radon Dosimetry with a Passive Trach Etch Detector Device, Radiat. Prot. Dosim., 1: 97-109 (1981). RECEIVED August 20, 1986


Intercomparison of Different Instruments That Measure Radon

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