Working, principle and construction of Geiger Muller counter and Ionization chamber

along with GIF representation

1. Working, principle and construction of Geiger Muller counter and ionization chamber Niroj sandha B.Sc. MIT 1 ST YEAR NAMS , BIR HOSPITAL

2. CONTENTS INTRODUCTION TYPES OF RADIATION DETECTOR G a s f i l l e d d e t e c t o r s CONCLUSION REFERENCES

3. W h a t i s r a d i a t i o n R a d i a t i o n i s t h e e m i s s i o n o r t r a n s m i s s i o n o f e n e r g y i n t h e f o r m o f w a v e s o r p a r t i c l e s t h r o u g h a m a t e r i a l m e d i u m . 2 t y p e s I o n i z i n g r a d i a t i o n e l e c t r o m a g n e t i c w a v e s ( x r a y , g a m m a r a y ) P a r t i c l e s ( A l p h a , b e t a , n e u t r o n ) 2 . N o n - i o n i z i n g r a d i a t i o n

4. G e i g e r m u l l e r c o u n t e r I o n i z a t i o n c h a m b e r w o r k s o n p u l s e / r a t e m o d e o r b o t h

5. I m p o r t a n t e f f e c t s o n w h i c h d e t e c t i o n o f r a d i a t i o n a r e b a s e d u p o n ; - I o n i z a t i o n L u m i n i s c e n c e P h o t o g r a p h i c e f f e c t T h e r m o l u m i n e s c e n c e C h e m i c a l B i o l o g i c a l

6. W h y d o w e n e e d t o d e t e c t r a d i a t i o n ? R e s e a r c h a p p l i c a t i o n E n v i r o n m e n t a l s a f e t y P e r o s n a l p r o t e c t i o n o f o c c u p a t i o n a l w o r k e r s E s t i m a t i o n o f r a d i a t i o n d o s e i n t r e a t m e n t o f p a t e i n t s

7. T y p e s o f r a d i a t i o n d e t e c t o r s G a s f i l l e d d e t e c t o r s ( i o n i z a t i o n c h a m b e r , p r o p o r t i o n a l c o u n t e r a n d G M c o u n t e r ) S o l i d s t a t e d e t e c t o r C h a r g e c o u p l e d e t e c t o r s

8. G a s f i l l e d d e t e c t o r s C o n s t r u c t i o n M e t t a l i c c y l i n d e r C e n t r a l e l e c t r o d e B a t t e r y E l e c t r o n i c s G a s e s

9. P r i n c i p l e B a s e d o n i o n i z a t i o n g a s m o l e c u l e g e t s i o n i z e d w h e n e n e r g e t i c p a r t i c l e s p r o p a g a t e t h r o u g h g a s

10. W o r k i n g

11. R e c o m b i n a t i o n r e g i o n W h e n v o l t a g e i s l o w ( a l m o s t z e r o ) i o n p a i r s p r o d u c e d b y t h e r a d i a t i o n r e c o m b i n e a n d n o c u r r e n t f l o w s t h r o u g h t h e c i r c u i t .

12. I o n i z a t i o n r e g i o n W o r k s a t t h e r a n g e o f 2 v - 4 v

13. W o r k i n g

14. T y p e s A c c o a r d i n g t o c o n s t r u c t i o n : 1 . F r e e a i r c h a m b e r f i l l e d w i t h a m b i e n t a i r E x a m p l e : s m o k e d e t e c t o r where a natural flow of air through the chamber is necessary so that smoke particles can be detected by the change in ion current

15. P r e s s u r e c h a m b e r v e n t e d c h a m b e r S e a l e d l o w p r e s s u r e c h a m b e r H i g h p r e s s u r e c h a m b e r V e n t e d c h a m b e r C y l i n d r i c a l i n s h a o e O p e r a t e a t a t m o s p h e r i c p r e s s u r e C o n t a i n d e s s i c a n t t o p r e v e n t m o i s t u r e

16. S e a l e d l o w p r e s s u r e c h a m b e r S i m i l a r t o v e n t e d c h m a b e r B u t a r e s e a l e d H i g h p r e s s u r e c h a m b e r a pressure of 8-10 atmospheres can be used, and various noble gases are employed t o i n c r e a s e e f f i c a c y

17. A c c o r d i n g t o s h a p e o f c h a m b e r T h i m b l e P a r a l l e l p l a t e M o n i t o r T h i m b l e c h a m b e r Most commonly used for radiation therapy measurements A bias voltage applied across the cavity collects ions and produces a current which can be measured with an electrometer.

18. Parallel plate chamber shaped like a small disc with circular collecting electrodes separated by a small gap, typically 2mm or less.  Monitor chambers Monitor chambers are typically parallel plate ion chambers which are placed in radiation beams to continuously measure the beam's intensity.

19. A dvantages Uniform response to gamma radiation capable of measuring very high radiation rates Disadvantages sophisticated electrometer circuit Operation accuracy easily affected by moisture

20. P r o p o r t i o n a l c o u n t e r r e g i o n I n t e r m e d i a t e r e g i o n w h e r e c u r r e n t p u l s e s i z e i s p r o p o r t i o n a l t o v o l t a g e a p p l i e d

21. G M c o u n t e r

22. G m c o u n t e r

23. H i s t o r y named after Hans Geiger I nvented i n 1908 w i t h c o l l a b o r a t i o n w i t h walther muller used for measuring ionization radiation It detects ionizing radiation such as alpha particles ,beta particles and gamma rays using the ionization effect produced in a Geiger-muller tube It is perhaps one of the world’s best known radiation detection elements

24. C o n s t r u c t i o n H o l l o w m e t t a l i c c y l i n d e r f i l l e d w i t h n o b l e g a s ( A r g o n + a l c o h o l ) B a t t e r y ( 9 v - 1 2 v ) M e t t a l i c e l e c t r o d e ( t u n g s t e n ) E l e c t r o n i c s ( A m p l i f i e r s , p u l s e c o u n t e r )

25. W o r k i n g E x t e r n a l p a r t i c l e i o n i z e s t h e g a s p r e s e n t i n s i d e t h e c h a m b e r

26. P r i n c i p l e b a s e d o n t o w n s e n d o r a v a l a n c e e f f e c t , f r e e e l e c t r o n s i n s t r o n g e l e c t r i c f e i l d g e t s a c c e l e r a t e d r e s u l t i n g i n c o l l i s i o n w i t h o t h e r a t o m s t h e r b y i o n i z i n g t h e m

27. D e a d t i m e T i m e d u r i n g c o u n t e r i s c o m p l e t e l y i n s e n s i t i v e R e c o v e r t i m e T i m e a f t e r w h i c h o r i g i n a l p u l s e l e v e l i s r e s t o r e d

28. Q u e n c h i n g P r o c e s s o f d e - i o n i z i n g a f t e r t h e p a r t i c l e h a s b e e n d e t e c t e d 2 m e t h o d s C h e m i c a l q u e n c h i n g A c h i e v e d b y u s i n g a l c o h o l c o m p o u n d s 2 . E x t e r n a l q u e n c h i n g A c h i e v e d b y s w i t c h i n g t h e G M c o u n t e r o f f

29. T y p e s End window type Pancake tube Windowless type Thick walled Thin walled

30. E n d w i n d o w t y p e P A N C A K E T Y P E variant o f the end of window tube D e t e c t i o n of beta and gamma r a d i a t i o n Mica is commonly used window material due to its low mass per unit area

31. Windowless tube Thick walled Used for gamma radiation detection above energies of about 25 kev wall thickness of about 1-2 mm of chrome steel. I t is attenuated at low energy below 20 kev Thin walled Used for high energy beta detection attenuated at high energy about 300-400 kev

32. A p p l i c a t i o n detection of alpha and beta particles To detect radioactive rocks and minerals To check for environmental levels of radioactivity.

33. Advantages Cheap detector a n d e a s i l y a v i a l a b l e i n t h e m a r k e t Disadvantages Cannot measure high radiation rates due to dead time

34. C o n c l u s i o n

35. T h a n k y o u

36. R e f e r e n c e s R a d i o l o g i c s c i e n c e f o r t e c h n o l o g i s t s 1 t h e d i t i o n , s t e w a r t c a r l y l e b u s h o n g t h e p h y s i c s o f r a d i o l o g y a n d i m a g i n g , k t h a y a l a n G o o g l e

37. Q u e s t i o n s D e f i n e r e c o m b i n a t i o n r e g i o n ? R a n g e o f v o l t a g e a t w h i c h i o n i z a t i o n c h a m b e r w o r k s ? T y p e s o f i o n i z a t i o n c h a m b e r ? W h a t d o y o u m e a n b y a v a l a n c e e f f e c t ? W h a t i s d e a d t i m e a n d r e c o v e r y t i m e ? D e s c r i b e q u e n c h i n g ? T y p e s o f g m c o u n t e r ? w h y d e a d t i m e o f G m c o u n t e r i f g r e a t e r t h a n i o n i z a t i o n c h a m b e r ?