Proportional Detector Absorption and Transmission Characteristics

Contents

Formula for X-ray Transmission

where:
is approximately 2.71828
is the mass absorption coefficient in cm2 per gm
is the density in gm/ cm3
is the thickness in cm

or

where:
is approximately 2.71828
is the mass absorption coefficient in 103 cm2 per gm
is the mass thickness in ug per cm2 times 10-6

X-ray Absorption @ 1 atmosphere in 2.25 cm (approximate detector absorption path length)

l (angs.) Propane P-10 Ne Ar Kr Xe  
1.0       .11   .73  
1.5       .30   .97  
2.0       .59 .76 .99  
2.5 .063 .78   .78 .93 .95  
2.78 .086 .86          
3.0       .91 .98 .98  
3.36 .15 .96          
4.0       .43 .99 .99  
4.16 .26 .45          
4.73 .36 .58          
5.0     .64 .66      
5.41 .49 .71          
6.0     .82 .81      
6.07 .61 .82          
7.0     .92 .92      
7.13 .78 .93          
8.0     .97 .98      
8.34 .91 .98          
9.89 .98 .99          
10.4 .99 .999          
               
               

Note that Cameca microprobes use 2 atmospheres of P-10 gas for x-ray detection down to approximately one angstrom (~12 KeV). For example, in the case of attempting to detect Zn Ka (~10 KeV) x-rays, the resulting loss due to transmission in 30 PSIA of P-10 gas is over 50%.

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X-ray transmission of Be and Al windows

l (angs.) Be MAC 103 cm2/g Be trans. .001" (4699 ug/cm2) Be trans. .0005" (2350 ug/cm2) Al MAC 103 cm2/g Al trans. .00025" (1714 ug/cm2)    
1.0 0.57 .99 .999        
1.5 1.55 .99 .996        
2.0 3.38 .98 .992        
2.5 6.2 .97 .986 190 .72    
3 10.3 .95 .976        
4 22.7 .90 .95        
5 43.7 .81 .90        
6 74 .71 .84 2250 .021    
7 118 .57 .76 3300 .003    
8 174 .44 .66        
8.34 179 .43 .66 403 .50    
9.89 300 .24   639 .33    
10.4         .    
11.9 530 .08   1068 .16    
12.3 578 .07   1152      
13.3 745     1453      
14.6 963     1848      
16.0 1268     2379      

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Transmission of Polypropylene and Mylar

l (angs.) eV Polypro. MAC 103 cm2/g Polypro. trans. .22u (20 ug/cm2) Polypro. trans. .33u (.30 ug/cm2) Polypro. trans. .99u (.90 ug/cm2) Mylar. MAC 103 cm2/g Mylar. trans. (350 ug/cm2)
               
               
               
2.29           19.8  
2.78              
4.16           133 .95
5.73              
6.07           400 .87
7.13 (Si)           629 .80
8.01 1550 550     .95    
8.34 (Al) 1487 615   .98   980 .71
9.89 (Mg) 1254 1006 .98 .97 .92 1578 .58
10.01 1240 1040     .91    
11.9 (Na) 1041 1700 .97 .95 .86    
12.0 1033 1740   .95 .85    
12.3 1012 1839          
14.03 885 2660   .92 .79    
16.02 775 3830   .89 .70    
18.05 688 5200   .86 .62    
18.3 (F) 679 5455 .90 .85 .61    
22.0 654 8800   .76 .45    
22.3 556 9161          
23.6 (O) 525 10610 .81 .73 .38    
31.4 395 21450          
31.6 (N) 392 21850 .65 .52 .14    
34.02 365 25900   .46 .10    
42.08 295 42200          
44.7 (C) 277 2100 .96 .94 .82    
67.6 (B) 183 5784 .89 .84 .59    
109 114 17280          
114 (Be) 109 19120 .68 .56 .18    
230 (Li) 54.2 87300 .17 .07 .0004    
               

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Transmission of Detector Window Coatings

l (angs.) C MAC 103 cm2/g C trans. 5 ug/cm2 Al MAC 103 cm2/g Al trans. 12 ug/cm2 Ag MAC 103 cm2/g Ag trans. 12 ug/cm2
             
6.155 (P)            
7.126 (Si)            
8.339 (Al) 718 .996 403 .995 2887  
9.889 (Mg) 1174 .994 639 .992 4254  
11.91 (Na) 1984 .990 1068 .987 6497  
18.31 (F) 6366 .967 3407 .960 14730  
23.71 (O) 12380 .940 6715 .923 19260 .793
31.60 (N) 25490 .880 13830 .847 3900 .954
44.7 (C) 2373 .988 30160 .696 5507 .936
67.6 (B) 6456 .968 65170 .457 6462 .925
114.0 (Be) 20810 .901 107000 .277 5880 .932
             

 

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