90
60
h=4cm, FWHM =8.5cm
50
RELATIVE ACTIVITY
——— Cc UNKNOWN
Cc KNOWN
—-— REAL DISTRIBUTION
DISTANCE (cm)
Fie, 72.—Variations in f(z) caused by previous knowledge of C, A = 4 em
Integrated Activity on fix) - FWHM = 8.5 cm
interval
an fix)
(cm)
C Unknown
Experimental
Value of the
Activity + 3%
c= 85
th-3
/h-z4
(wc)
0-44
helfth=«=2];h*3Jhr4-helth=2
0.9
0.85
1.0
0.7
0.9
09
1.0
ll
0.9
14-44
3.0
2,85
2.9
2.6
3.0
3.0
2.9
3.1
2.9
44-54
45
4.6
4.6
42
46
4.6
4.6
43
47
0-54
&4
8.3
85
7.5
8.5
8.5
8.5
85
&5
Fic. 73—Integrated
f(x) for various h’s.
activities over various intervals
the integrated quantities and the percentage err«
the three previously chosen intervals. The tot:
grated activity C is practically independent
FWHMof K(z,x). (See above for dependenc
on A.)
The results of Figures 74 and 76 suggest th
choice of the “best”? collimator must be based
following :*
(a)
of
Integrated Activity
on fix)
interval
on f(x)
(cm)
oi
FWHM = 15,0 cm
h=2em
i
4-44
3.2
tas
42
~22
~10
Percent Error
FWHM = iL0cm
h=2cm
1.0
2.7
~
7
4.8
~10
FWHM= 85cm
h=2cm
0.9
3
~0
-35
4.6
~2
Experimental
Vaiue of the
Activity +3%
(b)
{uci}
Fic. 74—~Integrated activity with three different point response functions.
the smallest interval Az, where the net
grated) activity
/
f(z) dx = C;
should have acceptable error. (If Avg >
29
47
curacy in the location of the peaks and
magnitude of their slope; in our case Av, ~
FWHM;
ttAXgs
09
~2
the smallest interval Ax, (larger than A) in
the shape of the computed f(z) should re
the actual distribution, namely acceptal
(ce)
this condition is automatically satisfied.) ;
the efficiency of the collimator should be
enough to minimize the statistical errors \
feasible time intervals of measurement.
* These requirements are similar to those needed to i
and measure radioactivity in various organs of the body.