biodex ATOMLAB 960 - Determining MDA Formula

ATOMLAB 960 MEDICAL SPECTROMETER APPENDIX F F-3
Determining MDA For Radiation Measurements
U.S. Government formula for MDA (Minimum Detectable Activity)
MDA!=!
!
(2.71!/!T
S
)!+!3.29!(R
b
/T
b
!+!R
b
/T
s
)!
1/2!
!!!!!!!!!!!!!!!!E!(A!/!10 0cm
2
)!!
MDA!=!
!
(2.71!/!T
S
)!+!3.29!(R
b
/T
b
!+!R
b
/T
s
)!
1/2!
Det!efficiency!x!Geometric!efficiency!x!(area/100!cm
2
)!!
NOTE: System assumes a 100 cm
2
wipe
R
B
= count rate of the natural background
T
B
= time of the background count
T
S
= time of the sample count
E = detection efficiency of the counter
A = area monitored or wiped
NOTE: E = Detector efficiency x Geometric efficiency
NOTE: Wipe area program assumes 100 cm
2
/ 100 cm
2
MDA Examples
Geometric!eff!96.82%!
Wipe!Count!10!sec!=!T
S
!=!.166667!
Bkgnd!Count!30!sec!=!T
B!=!
.5!
!
MDA!=!
(2.71/!T
S
!)!+!3.29!(R
B
!/!T
B
!!+!R
B
!/!T
S
!)
1/2
!
!!!!!Det!eff!x!Geo!eff!x!(A/100!cm
2
)!
Example!a)!!CoP57!
MDA!=!
!
(2.71/.166667)!+!3.29!(70/.5!+!70/.166667)
!1/2
!
!!!!!!!!!!!!!!!!!!!!.909!x!.968 2!x !1!
!
!
MDA!=!
!
16.26!+!3.29!(140!+!420)
!1/2
!
!!!!!!!!!!.880093 8!
!
!
MDA!=!
16.26!+!77.85561!
!!!!!!.88009 38 !
=!106.93!dpm!
!
!
!!!!!!!!!!!!!!!!System!Displays!As!106.9!dpm
Example!b)!TlP201!
MDA!=!
!
!!(2.71/.166667)!+!3.29!(46/.5!+!46/.166667)
!1/2
!
!!!!!!!!!!!!!!!!!!!!!!!.505!x!.968 2!x !1!
!
!
!
MDA!=!
!
16.26!+!3.29!(92!+!276)!
½
!
.488941 !
!
!
MDA!=!
!
16.26!+!63.113!
!!!!.488941 !
!
=!162.33685!dpm!
!
!
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!System!Displays!As!162.3!dpm