ITR-21
  CALIBRATION OF 4- INCH LOW BACKGROUND BETA COUNTING

          SYSTEMS FOR COUNTING AIR FILTERS

                         By
                    R. E. Jaquish
     Southwestern Radiological Health Laboratory

  U.S. Department of Health, Education and Welfare
                Public Health Service
Consumer Protection andEnviromnental Health Service
        Environmental Control Administration
           Bureau of Radiological Health
                      May, 1969

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                           ABSTRACT
The 4-inch low background beta counters were recalibrated




and alternate methods of preparing standards were studied.




It was concluded that the placement of a standard solution




directly on a 4-inch stainless steel counting planchet is




an acceptable approximation of activity on the surface of




an air filter.

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                             LIST OF TABLES








TABLE                                                                Page




  I.  Beta Calibration - System 01                                     4




 II.  Beta Calibration - System #2                                     5




III.  Beta Calibration - System #3                                     6
                             LIST OP FIGURES






FIGURE                                                               Page




1.    Efficiency vs. Beta Energy - System #1                          7




2.    Efficiency vs. Beta Energy - System #2                          8




3.    Efficiency va. Beta Energy - System #3                          9




4.    Fission Product Average Maximum Beta Energy  vs.  Time




      After Fission                                                  10




5.    Coated Filters - Efficiency vs. Energy                         11
                                    ii

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In January 1969 a recalibration of the beta systems used for counting
4-inch glass fiber filters from the Air Surveillance Network was
initiated.  The objective was to determine the effect of the resultant
difference, if any, between the current method of calibration by
placing a known anount of activity directly on a 4-iisch stainless steel
planchet and an alternative nothod of depositing the activity on a
filter.  This ^calibration was performed with three types of samples
as follows:

     a.   The standard solution was uniformly distributed directly
          over the surface of a 4-inch stainless steel planchet.

     b.   The standard solution was uniformly distributed over the
          surface of a 4-inch glass fiber filter attached to a
          4-inch stainless steel planchet.

     c.   The standard solution was uniformly distributed on the surface
          of a 4-inch glass fiber filter coated with acrylic lacquer
          attached to a stainless steel planchet.

1.   Sample Preparation

     All samples were prepared by pipetting a standard solution directly
     onto tho planchet and filter, as specified with an Eppendorff
     micro-pipette.  The volume of the solution used was either 500
     or 1000   depending on tho activity of tho standard.  The range
     of activity on the samples at tho time of count was between
     10,000 and 100,000 transforcations/min.  Tho solution was placed
     on the sample in small droplets iron the cento? out to the edge of
     the sample in a spoke-like pattern.

     The samples with a filter on the planchet were prepared by spraying
     the planchet with spray adhesive and placing the glass fiber
     filter directly on the planchot.  Tho filters used were Gelman
     Type E glass fiber filter with an area of 81 en2.

     The coated filters were prepared by spraying the filter with an
     acrylic lacquer frca a pressurized can.  The filters were allowed
     to dry under a heat lamp beforo the solution was pipetted onto
     the coated filter.  Four of tho filters were weighed before and
     after the acrylic coating was applied to determine the weight of
     the acrylic applied.  The average weight of material on the filter
     was 2.7 mg/cm.  This thin film was considered to be essentially
     zero and the added backscattcr material would have practically
     no effect.

     When the standard solution was placed on the coated filter, the
     solution beaded-up on the filter and did not soak into the filter
     during the entire drying time.

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     The standards used for the recalibration were:

                                             Max. Beta
                Nuclide                      Energy (MeV)
                  C                          0.156
                99Tc                         0.229
                185W                         0.429
                J37Cs                        0.559
                36C1                         0.714

                904T190                      °*766
                  Sr                         1.463
                32P                          1.710

                                                           137
     All of these are pure single beta emitters except the    Cs and
     90Sr-Y.  Pure beta enitters were used whenever possible to eliainate
     the problem of conversion electrons.  The beta counter is very
     insensitive to gaoma radiation with less than 1% of the photons
     being detected.

             137
     For the    Cs the value used for conversion electrons was 9.5%;
     therefore, 1.095 betas/transfomation was used.  The energy
     distribution of the betas froa 137Cs is:

                           1.180  HeV    4.8%
                           0.518  K9V   95.2%
                           0.662  HeV    9.5%
                                    137
     The average maximum energy for    Cs is 0.559 MeV.  This average
     is not exact since the beta values for the 1.18 and 0.518 MoV betas
     are maxinun energies with an average energy of about 1/3 the
     maxiouQ.  The 0.662 MeV conversion electrons are monoenergetic.
         90
     For   Sr-Y the energy distribution is:
>-
90y _

0.526
2.27
90_
MeV
MeV

100%
100%
•» .4 «
     The average maximum energy for

2.   Counting

     All samples were counted for five minutes on each of the three beta
     systeas.

3.   Data

     The data from the counting of standards are listed in Tables I, II,

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     III.  The activity added is as of the time the sample was counted.

4.   Calibration and Conclusions

     Calibration curves for each systea indicating the three geometries
     are shown in Figures 1, 2, and 3.  For all three systems the
     calibration curves are sinilar.  At the lower energies there is
     greater self-absorption in the filter; therefore, the efficiency
     values show a wider difference.  The calibration with the solution
     placed directly on the stainless steel planchet and the activity
     of the coated filter are very similar.

     Figure 4 shows the average maximum beta energy for mixed fission
     products as a function of tice after fission.  Accordingly an
     average value of 1 KeV could bo assumed at anytime between two and
     100 days after fission.  Also shown is the average maximum beta energy
     for plowshare devices with a predominance of tungsten components.
     Note that the average naximun beta energy is somewhat lowor, being
     constant at 0.5 MeV after 10 days.

     The efficiency used for beta emitter on the three counters is 50%.
     This efficiency is an acceptable value as it lies between efficiency
     for beta emitters from Plowshare devices and pure fission devices.
     The efficiency for 1 HGV beta particle is 54% and for 0.5 MeV botas
     is about 47%.
                                                            36
     For all three counts the calculated efficiency for the   Cl was
     high.  The activity of the solution was checked by having an aliquot
     4i7~ beta counted and the resulting count was less than 3% different
     frost the calibration from the supplier.  On previous calibrations
     the   Cl was also high.  The   T1! is low.  This could be due to
     the fact that there is a disagreement on the half-life of   rri in
     the references and this standard was several years old.

     Figure 5 shows the calibration curves for each system for the
     coated filter geometry.  It is felt that this geometry is most
     representative of a filter sample with activity deposited on its
     surface.  It is noted that all three systems respond nearly
     identically.

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              Table I
Nuclide
14C
11
11
"TC
it .
tt
185
"
137
Cs
•Ck "
it
36ci
11
It
204
Tl
11
tf
9°Sr-Y
IT
8!sr
„
B Energy
(Max.)
.156
II
It
.292
II
tl
.429
tt
tT
.514
tl
tt
.714
It
It
.766
Tl
Tf
1.41
It
II
1.463
ft
ti
Half-life
5730y
Tl
it
2.12xl05y
It
II
75 d
; t
"
30y
rt
3xl06y
tl
tl
3. Sly
tl
1 T
27. 7y
Tt
11
50. 4d
rt
M
dpm
Activity
Added
24,400
It
I r
1.12xl05
it
Tl
5
2.40x10
ri
1 1
23,700
i r
it
16,400
Tl
11
12,500
Tl
tl
25,610
10,250
25,610
31,350
tt
II
1.710      14.28d
32,000
                                      BETA CALIBRATION

                                         System #1

                                      Date of     CPM        CPM
                                      Count       Planchet   Filter
             1-9-69
             1-9-69
                                      1-9-69
                                      3-10-69
             2-12-69
                                                   3,671
                                      2-14-69     40,992
                                      3-27-69    115,800
                                      1-30-69     11,377
            10,356
             6,226
                                                  14,460

                                                  18,340
1-28-69     19,202
                                     514
                                  21,499
                                  71,000
                                    9,326
 8,971



 5,087


 5,185



17,228
                                  CPM
                                  Coated
                                  Filter
                                               2293
35,262



95,900



11,003


 9,592



 5,684


14,580
           17,912


           19,240
                      % Eff.
                      Planchet

                      15.0
                                                         36.6
                                                         48.2
                                                         48.0
                                                                                  63.1
                                                         49.8
           56.5

           58.5



           60.0
                                                                              % Eff.
                                                                     % Eff.    Coated
                                                                     Filter    Filter
                                                                                              2.1
                                                                                              19.1
                                                                                              29.6
                                                                                              39.3
                                                                     54.7
                                                                     40.7
                                                                     50.6
                                                                     55.0
                                                                                                        9.4
                                                                              31.5
                                                                              40.0
                                                                              46.4
                                                                              58.5
                                                                              45.5
                                                                              56.9
                                                                              57.1
                                                                              60.1
                                                            18,873
                                                                     59.0

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                                                  Table II
32
                                               BETA CALIBRATION




                                                   System #2


Nu elide
14
C
it
11
"TC
it
ti
185W
tf
tf
137
Cs
tt
1 1
36ci
II
II
204T1
II
It
90
Sr
ft
tt
89
Sr

B Energy
. (Max.)

.156
ri
it
.292
f f
rt
.429
II
:t

.514
i i
tt
.714
tt
tt
.766
II
1 1

1.41
If
f I
1.463


Half-life

5730y
II
If
2.12xl05y
It
;t
75d
It
11

30y
1 1
II
3xl06y
r t
it
3. Sly
tl
•'

27. 7y
II
tl
II

Activity
Added

24 , 400
1 1
i r
1.12xl05
1 1
It
2.40xl05
! 1
f r

23,700
rt
If
16,400
i f
1 1
12,500
ft
II

25,610
10,750
25,610
31,350

Date of
Count

1-9-69
IT
"
2-14-69
tf
rt
3-27-69
1 1
It

1-30-69
It
i I
1-9-69
11
1 1
1-9-69
f ;'
II

3-10-69
f 1
If
2-12-69

CPM
Planchet

3,157
-
-
40,273
-
-
119,100
-
-

11,460
-
-
9,805
-
-
6,173
-
-

-
-
14,764
17,481

CPM
Filter

-
-
476
_
21,414
-
_
73,000
-

-
9,368
-
_
-
8,649
—
-
5,074

-
5,422
-
_
CPM
Coated
Filter

-
2409
-
_
-
34,710
_
-
98,800

-
-
10,786
_
9,855
-
-
5,818
-

14,888
-
-
_
% Eff.
% Eff. % Eff. Coated
Planchet .Filter Filter

12.9
9.9
2.0
40.0
19.1
31.0
49.6
30.4
41.2

48.4
- -
39.5 45.5
59.8
60.0
52.7
49.4
46.5
40.6

58.1
52.8
57.6
55.8
            1.710
14.28d
32,000
1-28-69     19,096
                                                                      17,358
                                                                       18,949
18,097







 19,390
                                                                                             59.7
                                                                                  55-. 3
                                                                                  59.2
                                                                                                                  57.7

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Table III
  BETA CALIBRATION
     System #3


Nuclide
14c
ft
It
"TC
it
it
185
iB w
It
II
137Cs
It
It
36
Cl
tt
ii
204
Tl
It
II
90
Sr
ft
It
89
Sr
tl
II
32P
II
If

B Energy
(Max.)
.156
II
tl
.292
II
II

.429
"
r:
.514
ti
ii

.714
11
tl

.766
"
tt

1.41
11
11
1.463
tl
If
1.710
It
tr


Half-life
5730y
ti
M
2ol2xl05y
1 I
1 1

75d
"
"
30y
ir
1 1
6
3x10 y
II
II

3. Sly
it
"

27. 7h
II
tl
5014d
It
f 1
14.28d
II
II

Activity
Added
24,000
It
1 1
1.12xl05y
"
"
5
2.40x10
i r
H
23,700
if
11

16 , 400
i r
it

12,500
M
"

25,610
10,250
25,610
31 , 350
it
11
32,000
ti

Date of
Count
1-09-69
It
fl
2-14-69
1 1
1 1

3-27-69
i t
II
1-30-69
f 1
11

1-9-69
!f
II

1-09-69
II
ft

3-10-69
i:
n
2-12-69
f 1
ft
1-28-69
f|
CPM
CPM CPM Coated % Eff.
Planchet Filter Filter Planchet
4,568 - - 18.7
3,445
636
47,984 - - 42.8
24,310
41,530

137,600 - - 57.3
80,100
112,300
12,296 - - 51.9
9,853
11,830

10,244 - - 62.5
10,421
8,867

6,655 - - 53.2
6,454
5,319

15,223
5,295
15,036 r
17,826 - - 56*9
17,670
18,504
18,936 - - 59.2
19,161
1O CUT
% Eff.
% Eff. Coated
Filter Filter
_ _
-
2.6
. _
21.7
37.1

-
33.4
46.8
_ «-
41.6 49.9
-

-
63.5
54.1

-
51.6
42.6

59.4
51.7
-
_ _
56.2
59.0
_ _
59.9
KO r»

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