- Email: [email protected]
The decay scheme of caesium 137
490
Technical notes TABLE 2. Calibration figures for rssI in the NPL standard 1383A ionisation chamber (serial number 14), used without liner, corrected to a pressure of 760 mm of Hg and a temperature of 22% Type of Ampoule
lass
of
Solution 4s
Calibration figure pA/mCi
standard Error Of the mean
Total Randdm O-feXdl uncertainty systamti'o (9% confidenceuncertainty l.Xel)
.IiPL 2cm3
1
5.86
+ 0.5%
2:1.5%
,+1%
BS 2cal3
1
6;76
2 0.6%
,+l,.d
22%
6.34
.-+4.6%
,+l..5%
+29s-
Bs 5m3
3
ampoule wall thickness, it is intended that, in the very near future, all issues of standardised solutions of radionuclides will be issued in British Standard ampoules of the 2 cm3 and 5 ems squat variety (specification BS 795: 1961 Type Q). Calibration figures for these ampoules have also been measured for lz51. Since the BS ampoules, although having stricter dimensional tolerances, do not have a specification for their chemical composition, the NPL is prepared to supply either standardiied solutions of 1251 or BS ampoules from the same batch as that used for the calibration measurement. The results of the calibration measurements are listed in Table 1 and a summary of the calibration factors given in Table 2. Where more than one standardisation was performed on the same stock solution either by different methods or by repeating the same method, the results were tested for consistency and a mean was calculated, weighted or unweighted according to the results of the consistency tests. The total random uncertainties are quoted at a 95% confidence level. The estimated overall systematic uncertainties, quoted in Table 2, include allowances for the possible variation in wall thickness of the respective ampoules and users should add to these a systematic uncertainty of i 1.8% to allow for possible variations in wall thickness of their own chamber. Acknowledgements-This paper is the result of the work of several members of the Division of Radiation Science, and the authors wish to acknowledge their participation, in particular Messrs. GOODIER, KINGHAM, MAKEPEACE,SARA and WILLIAMS. Division of Radiation Science National Physical Laboratory Teddington Middlesex TW11 OLW
M. J. WOODS SYLVrAE. M. LUCAS
References 1. DALE J. W. G., PERRY W. E. and PULFER R. F., Int. J. a@l. Radiat. Isotopes lo,65 (1961). 2. TAYLOR J. G. V. Standardization of Radionuclides,
pp. 341-354. IAEA, Vienna (1967). 3. WILLIAMS A. and BIRD~YE ROSEMARYA. Znt. J. appl. Radiat. Isotopes 18, 202 (1967). 4. CAMPIONP. J., BURNSJ. E. and WILLIAMSA. A code of practice for the Detailed Statement of Accuracy, HMSO (11 480037 5) (1973). International Journal ofApplied Radiition and Isotopes, 1975, Vol. 26, pp. 490-492. Pcrgamon Press. Printed in Northern Ireland
The Decay
Scheme
of Caesium
137
(Received 15 July 1974) THE DECAYof 1srCs (Fig. 1) has been reinvestigated with a view to determining more accurate decay scheme parameters necessary in the absolute standardisation and routine assay of this radionuclide. This necessitated the measurement of the absolute disintegration rate together with the y-quantum emission rate of a 13’Cs solution, and the total internal conversion coefficient of the 662 keV level in 137mBa. Measurements of the total internal conversion coefficient of 137mBa were carried out on separated samples of ls7*Ba solution prepared by the ion exchange elution technique of MERRITTand TAYLOR(~). The y-emission rate of the separated 137mBasolution was measured using a high pressure ionisation chamber having a calibrated response as a function of photon energyt4) while the conversion electron emission rate was measured for weighed sources of this solution counted in a 4rp proportional counter. The efficiency of this counter for the 137mBa conversion electrons was assumed to be 100%(4’. The maximum residual activity of 1s’Cs in the 137mBa sources at the completion of measurement was 0.2%.
491
Technical notes
120 i z
1150 h
L
137
Ba
FIG. 1. The decay scheme of 1s7Cs.
The absolute disintegration rate of a stock solution of 1srCswas measured by a conventional 4-&y efficiency tracer technique(rmslusing the &branches in ls4Cs decaying via the 1.4 MeV nuclear level as a /I efficiency monitor. The choice of a y-gate setting on the 1a4MeV sum peak obviated any contribution from rs7Cs y-rays in the measurement of the ls4Cs p-efficiency. Nine homogeneous sources of ls’Cs and l”Cs were prepared and the total B count rate was measured as a function of the rs4Cs p-efficiency [e#s4Cs)]. Knowing the latter and the activity of r%s in each source the b-count rate of the rs7Cs [N,#37Cs)] was obtained over a wide range of p-efficiencies. The p efficiency was varied by the addition of thin plastic or aluminium absorbers to the sources. For each of the nine sources the values N#srCs) were fitted as a function of 1 - e#‘%s) (Fig. 2) and in all cases a second order polynomial was found to be the best fit to the experimental data. Extrapolation to 1 - ~s(~~Cls) = 0 gave the absolute activity of the 13’Cs plus the contributions arising from the detection of conversion electrons and 662 keVy quanta, emitted in the decay of ls7*Ba in the /l counter. The contribution from the conversion electrons was determined from Table
coefficient or Berl37ln
Brmohingratio in the &O&y of cs-137 vi.?.
Be.437~1
0.1100
(Rwmt work) x:::2
0.0%
I 0.2
I 0.1
I-q
I\ 0.4
[cs-1343
I. W. GOODIER J. L. MAKEPEACE L. E. H. STUART
National Physical Laboratov TeaUington Middlesex TWI 1 OLW 1 Systsmatiounoertainty
Combined vnoertainties
?: 0;5 + 0,5% z l.ok
0.3s
?r r.* +, 0.5% f bd
0.3%
f l.o;c t m% 2 18
Cdibration figure for
the 1303A Ionisation
Chembrused without liner
0.3%
I 0.5
the y quantum emission rate of the r3’Cs stock solution and the knowledge of the 1371nBatotal internal conversion coefficient. The y quantum emission rates were measured using the calibrated high pressureionisation chamber.t4) It was estimated that the interpolated response at 662 keV was known to within j~0.37~. The detection efficiency of y quantum in the j.l counter had been determined in previous work.t5) The values obtained for the total internal conversion coefficient of ls7”‘Ba and the branching ratio in the decay of rsrCsvia ls’*Ba are compared with the most recent values reported by HANSEN et al.@) and by LECRAND et al.(‘) in Table 1.
!:I
0.860 (Presentwork)
1 0.3
FIG. 2. Graph of Nb (ls7Cs) against 1 - ES (r”Cs).
{;I
0.955 (Preasntwork) z$
Intensity of 662 keV 7 ray emission
0
Random uncertainty (StandardError of &an)
Qmtity Total 1ntenw.lConversion
1050
: 1.3
492
Technical notes References
1. CAMPION P. J., TAYLOR J. G. V., MERRITT J. S. and KENNEDYJ. M. Int. J. a#. Radiat. Isotopes 8, 8 (1960). 2. GOODIERI. W. and WILLIAMSA. Standardisation of Radionuclides p. 153. IAEA, Vienna (1967). 3. MERRITT J. S. and TAYLOR J. G. V. Am&. Chem. 37, 351 (1965). 4. GOODIER I. W., HUGHES F. H. and WOODS M. J. Int. J. appl. Radiat. Isotopes 19, 795 (1968). 5. CA~~PIONP. J. and WILLIAMSA. Int. J. a#. Rudiat. Isotopes 14, 553 (1963). 6. HANSEN H. H., LOWENTHALG., SPERNOLA. VAN DER EYK W. and V ANINBROUX R. 2. Physik 218,25 (1969).
7. LEGRANDJ., BRETHANJ. P. and LAGOUTINE F. Report C.E.A. R-4428 (1973). International Journal ofA plied Radiation and Isotopes, 1975,Vol. 26. Ip-. pp. 4924%. Pergamon Printed in NorthernIreland
An Empirical
Equation for the Photoelectric Cross-Section
(Receiued 10 February 1974) THEORETICALproblems of radiation transport involve considerations of the interactions of radiation with matter, and their probabilities of occurrence.
TABLE 1. Fifth degree polynomial coefficients for the evaluation of photoelectric cross-sections HmaIAL
iEi7.
A0
4
A2
A3
‘4
A5
I*v
m-150
11.43465
-4.56316
#J#473
-#.%723
6.74#32
2.3919
1.34944 -2.$1679
4.56553
lo-l 50
d.22785
#.#14@
#L%a%
10-2w
i7.43126
-9.27213
2.55999
#.%6#4
IWW
13.21627
-3.853%
l.#w5
-#.41#8# -5.45427
#.%277 -P a63
lo-400
13.79474
-3.27874
lo-q00
7.72738
lo-400
14.#8555
5.685#1 -2.7#516
#.169## -4.69165 -#.25116
10300 IO-600
11.67155 14.28851
-6.22298 -3.25176
IO-600
11.65619
lo-Boo
13.84136
1.47791 -l/$3%4:
10-8m
17.44735
-7.#8126
lo-lea
15.37685
-2.15149
lO-loo0
14.25951 39.38734 21.6#21?
-#.&6%
-5.52255
#.#7W
1.24525
-#.%7#5 -#.16498
#.1271#
-#.63112
#.%871#
#*%135
#.*I8 #.##864 #.%259 a##47 -P.%159
d.5887# -2.2#248
-#.23495
$.#3368
d.55658
-#.#7346
#.#Wl 2.92265
-#.1#641 lam22
-# .%641
-6.36149
-#.17253 -3 .#8872
-26.9378#
18.42722
d.25379 -2.16#66
-#.#33@ d.21414
-5.65W
d.83663
+L#5447
-#.#lW
21.95746
-5.79897
5.65435
-3.17393
l.#W
-#.#117# -#.24879
70-looo
2$.2398# 11.62455
#.8697# -1.6523.1 -#.d9186 5.24417
6.13563
#.#1892
#.4##73
-6.12775
-#.%#6# #.#1126
-#.##82l P.17487
#.%742 -#.d491#
+.###24 #.%413
20-loo0
29-lcoo 33-too0 12-70
#.7441#
14-79
21.96629
-5.83376
79-loOa
11.51#49
1.83449
+.6925#
15-86 86-1000
19.22544
-3.42#98 2.33%9 Il.87679
-#.#77#6
356.44915
as -3.99752 -1.63##3
-#BP788
#.%396 -#.%l#P -#.##631 #a’##61 #.%183 -#.%811 #.%129 $.%lU #.#1975
-# .#4#59
P.61296
-#.#%n
-#.#51#3
d.16494
hPl759
#.;raM d.11369
-# .%931
#.###l#
#.%727 -%.#2155
-$.%15#
16-88
2.724d9
88-1000
14.39648
2.54474
22-116
15.2#416
116-looo
21.383##
#.7#917 -2 .a7458
X-200
17.4312d
-9.27213
33-loo0
22.#6939
-5.91558
d.14997 -d.45@3 2.55999 +.41#8# -#.%)86 d&563
lo-1ouJ
15.43521
-I’.83584
-0.169% -#.#3413
-1 .12282
#.#2#21 Ib.22881
#.%%4 -#.#1#71
P.%W
#.%122 P.%277 #.#a29 -#.%#39
Technical notes TABLE 2. Calibration figures for rssI in the NPL standard 1383A ionisation chamber (serial number 14), used without liner, corrected to a pressure of 760 mm of Hg and a temperature of 22% Type of Ampoule
lass
of
Solution 4s
Calibration figure pA/mCi
standard Error Of the mean
Total Randdm O-feXdl uncertainty systamti'o (9% confidenceuncertainty l.Xel)
.IiPL 2cm3
1
5.86
+ 0.5%
2:1.5%
,+1%
BS 2cal3
1
6;76
2 0.6%
,+l,.d
22%
6.34
.-+4.6%
,+l..5%
+29s-
Bs 5m3
3
ampoule wall thickness, it is intended that, in the very near future, all issues of standardised solutions of radionuclides will be issued in British Standard ampoules of the 2 cm3 and 5 ems squat variety (specification BS 795: 1961 Type Q). Calibration figures for these ampoules have also been measured for lz51. Since the BS ampoules, although having stricter dimensional tolerances, do not have a specification for their chemical composition, the NPL is prepared to supply either standardiied solutions of 1251 or BS ampoules from the same batch as that used for the calibration measurement. The results of the calibration measurements are listed in Table 1 and a summary of the calibration factors given in Table 2. Where more than one standardisation was performed on the same stock solution either by different methods or by repeating the same method, the results were tested for consistency and a mean was calculated, weighted or unweighted according to the results of the consistency tests. The total random uncertainties are quoted at a 95% confidence level. The estimated overall systematic uncertainties, quoted in Table 2, include allowances for the possible variation in wall thickness of the respective ampoules and users should add to these a systematic uncertainty of i 1.8% to allow for possible variations in wall thickness of their own chamber. Acknowledgements-This paper is the result of the work of several members of the Division of Radiation Science, and the authors wish to acknowledge their participation, in particular Messrs. GOODIER, KINGHAM, MAKEPEACE,SARA and WILLIAMS. Division of Radiation Science National Physical Laboratory Teddington Middlesex TW11 OLW
M. J. WOODS SYLVrAE. M. LUCAS
References 1. DALE J. W. G., PERRY W. E. and PULFER R. F., Int. J. a@l. Radiat. Isotopes lo,65 (1961). 2. TAYLOR J. G. V. Standardization of Radionuclides,
pp. 341-354. IAEA, Vienna (1967). 3. WILLIAMS A. and BIRD~YE ROSEMARYA. Znt. J. appl. Radiat. Isotopes 18, 202 (1967). 4. CAMPIONP. J., BURNSJ. E. and WILLIAMSA. A code of practice for the Detailed Statement of Accuracy, HMSO (11 480037 5) (1973). International Journal ofApplied Radiition and Isotopes, 1975, Vol. 26, pp. 490-492. Pcrgamon Press. Printed in Northern Ireland
The Decay
Scheme
of Caesium
137
(Received 15 July 1974) THE DECAYof 1srCs (Fig. 1) has been reinvestigated with a view to determining more accurate decay scheme parameters necessary in the absolute standardisation and routine assay of this radionuclide. This necessitated the measurement of the absolute disintegration rate together with the y-quantum emission rate of a 13’Cs solution, and the total internal conversion coefficient of the 662 keV level in 137mBa. Measurements of the total internal conversion coefficient of 137mBa were carried out on separated samples of ls7*Ba solution prepared by the ion exchange elution technique of MERRITTand TAYLOR(~). The y-emission rate of the separated 137mBasolution was measured using a high pressure ionisation chamber having a calibrated response as a function of photon energyt4) while the conversion electron emission rate was measured for weighed sources of this solution counted in a 4rp proportional counter. The efficiency of this counter for the 137mBa conversion electrons was assumed to be 100%(4’. The maximum residual activity of 1s’Cs in the 137mBa sources at the completion of measurement was 0.2%.
491
Technical notes
120 i z
1150 h
L
137
Ba
FIG. 1. The decay scheme of 1s7Cs.
The absolute disintegration rate of a stock solution of 1srCswas measured by a conventional 4-&y efficiency tracer technique(rmslusing the &branches in ls4Cs decaying via the 1.4 MeV nuclear level as a /I efficiency monitor. The choice of a y-gate setting on the 1a4MeV sum peak obviated any contribution from rs7Cs y-rays in the measurement of the ls4Cs p-efficiency. Nine homogeneous sources of ls’Cs and l”Cs were prepared and the total B count rate was measured as a function of the rs4Cs p-efficiency [e#s4Cs)]. Knowing the latter and the activity of r%s in each source the b-count rate of the rs7Cs [N,#37Cs)] was obtained over a wide range of p-efficiencies. The p efficiency was varied by the addition of thin plastic or aluminium absorbers to the sources. For each of the nine sources the values N#srCs) were fitted as a function of 1 - e#‘%s) (Fig. 2) and in all cases a second order polynomial was found to be the best fit to the experimental data. Extrapolation to 1 - ~s(~~Cls) = 0 gave the absolute activity of the 13’Cs plus the contributions arising from the detection of conversion electrons and 662 keVy quanta, emitted in the decay of ls7*Ba in the /l counter. The contribution from the conversion electrons was determined from Table
coefficient or Berl37ln
Brmohingratio in the &O&y of cs-137 vi.?.
Be.437~1
0.1100
(Rwmt work) x:::2
0.0%
I 0.2
I 0.1
I-q
I\ 0.4
[cs-1343
I. W. GOODIER J. L. MAKEPEACE L. E. H. STUART
National Physical Laboratov TeaUington Middlesex TWI 1 OLW 1 Systsmatiounoertainty
Combined vnoertainties
?: 0;5 + 0,5% z l.ok
0.3s
?r r.* +, 0.5% f bd
0.3%
f l.o;c t m% 2 18
Cdibration figure for
the 1303A Ionisation
Chembrused without liner
0.3%
I 0.5
the y quantum emission rate of the r3’Cs stock solution and the knowledge of the 1371nBatotal internal conversion coefficient. The y quantum emission rates were measured using the calibrated high pressureionisation chamber.t4) It was estimated that the interpolated response at 662 keV was known to within j~0.37~. The detection efficiency of y quantum in the j.l counter had been determined in previous work.t5) The values obtained for the total internal conversion coefficient of ls7”‘Ba and the branching ratio in the decay of rsrCsvia ls’*Ba are compared with the most recent values reported by HANSEN et al.@) and by LECRAND et al.(‘) in Table 1.
!:I
0.860 (Presentwork)
1 0.3
FIG. 2. Graph of Nb (ls7Cs) against 1 - ES (r”Cs).
{;I
0.955 (Preasntwork) z$
Intensity of 662 keV 7 ray emission
0
Random uncertainty (StandardError of &an)
Qmtity Total 1ntenw.lConversion
1050
: 1.3
492
Technical notes References
1. CAMPION P. J., TAYLOR J. G. V., MERRITT J. S. and KENNEDYJ. M. Int. J. a#. Radiat. Isotopes 8, 8 (1960). 2. GOODIERI. W. and WILLIAMSA. Standardisation of Radionuclides p. 153. IAEA, Vienna (1967). 3. MERRITT J. S. and TAYLOR J. G. V. Am&. Chem. 37, 351 (1965). 4. GOODIER I. W., HUGHES F. H. and WOODS M. J. Int. J. appl. Radiat. Isotopes 19, 795 (1968). 5. CA~~PIONP. J. and WILLIAMSA. Int. J. a#. Rudiat. Isotopes 14, 553 (1963). 6. HANSEN H. H., LOWENTHALG., SPERNOLA. VAN DER EYK W. and V ANINBROUX R. 2. Physik 218,25 (1969).
7. LEGRANDJ., BRETHANJ. P. and LAGOUTINE F. Report C.E.A. R-4428 (1973). International Journal ofA plied Radiation and Isotopes, 1975,Vol. 26. Ip-. pp. 4924%. Pergamon Printed in NorthernIreland
An Empirical
Equation for the Photoelectric Cross-Section
(Receiued 10 February 1974) THEORETICALproblems of radiation transport involve considerations of the interactions of radiation with matter, and their probabilities of occurrence.
TABLE 1. Fifth degree polynomial coefficients for the evaluation of photoelectric cross-sections HmaIAL
iEi7.
A0
4
A2
A3
‘4
A5
I*v
m-150
11.43465
-4.56316
#J#473
-#.%723
6.74#32
2.3919
1.34944 -2.$1679
4.56553
lo-l 50
d.22785
#.#14@
#L%a%
10-2w
i7.43126
-9.27213
2.55999
#.%6#4
IWW
13.21627
-3.853%
l.#w5
-#.41#8# -5.45427
#.%277 -P a63
lo-400
13.79474
-3.27874
lo-q00
7.72738
lo-400
14.#8555
5.685#1 -2.7#516
#.169## -4.69165 -#.25116
10300 IO-600
11.67155 14.28851
-6.22298 -3.25176
IO-600
11.65619
lo-Boo
13.84136
1.47791 -l/$3%4:
10-8m
17.44735
-7.#8126
lo-lea
15.37685
-2.15149
lO-loo0
14.25951 39.38734 21.6#21?
-#.&6%
-5.52255
#.#7W
1.24525
-#.%7#5 -#.16498
#.1271#
-#.63112
#.%871#
#*%135
#.*I8 #.##864 #.%259 a##47 -P.%159
d.5887# -2.2#248
-#.23495
$.#3368
d.55658
-#.#7346
#.#Wl 2.92265
-#.1#641 lam22
-# .%641
-6.36149
-#.17253 -3 .#8872
-26.9378#
18.42722
d.25379 -2.16#66
-#.#33@ d.21414
-5.65W
d.83663
+L#5447
-#.#lW
21.95746
-5.79897
5.65435
-3.17393
l.#W
-#.#117# -#.24879
70-looo
2$.2398# 11.62455
#.8697# -1.6523.1 -#.d9186 5.24417
6.13563
#.#1892
#.4##73
-6.12775
-#.%#6# #.#1126
-#.##82l P.17487
#.%742 -#.d491#
+.###24 #.%413
20-loo0
29-lcoo 33-too0 12-70
#.7441#
14-79
21.96629
-5.83376
79-loOa
11.51#49
1.83449
+.6925#
15-86 86-1000
19.22544
-3.42#98 2.33%9 Il.87679
-#.#77#6
356.44915
as -3.99752 -1.63##3
-#BP788
#.%396 -#.%l#P -#.##631 #a’##61 #.%183 -#.%811 #.%129 $.%lU #.#1975
-# .#4#59
P.61296
-#.#%n
-#.#51#3
d.16494
hPl759
#.;raM d.11369
-# .%931
#.###l#
#.%727 -%.#2155
-$.%15#
16-88
2.724d9
88-1000
14.39648
2.54474
22-116
15.2#416
116-looo
21.383##
#.7#917 -2 .a7458
X-200
17.4312d
-9.27213
33-loo0
22.#6939
-5.91558
d.14997 -d.45@3 2.55999 +.41#8# -#.%)86 d&563
lo-1ouJ
15.43521
-I’.83584
-0.169% -#.#3413
-1 .12282
#.#2#21 Ib.22881
#.%%4 -#.#1#71
P.%W
#.%122 P.%277 #.#a29 -#.%#39