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β+ ratio in the decay of 58Co
Physica 28 587-591
Kramer, P. De Beer, A. Rlok, J. 1962
ON THE K/p+ RATIO IN THE DECAY OF 58Co by P. KRAMER, Natuurkundig
A. DE BEER
Laboratorium,
and J. BLOK
Vrije Universiteit,
Amsterdam.
synopsis Using an internal source in a 4n proportional of 58Co was determined to be 4.83 & 0.1.
counter, the K/p+ ratio in the decay
In the last years several authorsi-4) reported experimental values of the of 5sCo. Recently Depommier and Nguyen Khac5) published new theoretical calculations on K//3+ ratios of which the results agree fairly well with accurate experimental values for a large number of nuclides. Since for 5X0 a disagreement occurs between the experimental values and these calculations, it seemed interesting to remeasure the K/B+ ratio of this nuclide.
K//l+ ratio in the decay
71d co5* 2+
1.28~ 0.0006%,~+
(* 0.0001 %E 1
o+ Stable
Fe’*
Fig. 1. Decay scheme of SsCo.
The decay schemea) of 5sCo is shown in fig. 1. Nearly all positron and electron capture decay occurs to the first excited level of s*Fe. Some 2% feeds the 1600 keV level. We tried to determine the K//l+ ratio by counting positrons, K Auger electrons and K X-rays in a 4n proportional counter with an efficiency of nearly lOOo/o. In order to reduce background we measured coincidences of pulses from the proportional counter and pulses from a 3” NaI crystal, caused by 810 keV gamma radiation. -
587 -
588
P. KRAMER,
s*Co was produced
A. DE BEER
AND
J. BLOK
by an (a, n) reaction on Mn.
The manganese was dissolved in diluted hydrochloric acid, a solution of ammonium citrate was added and the pH was made 8.5 with ammonia. Ten micrograms of cobalt were added. The cobalt solution of dithizone in carbontetrachloride.
was extracted
with a
The organic layer was washed by a buffer solution of ammonium citrate (pH 8.5), and evaporated. The organic matter was destroyed by perchloric acid. The energy of the a-beam was 15 MeV, in order to reduce the 55Mn (a, 2~2) 57Co reaction. The small amount of 57Co produced at this a-energy, did not affect our measurements. The carrierfree source was evaporated in vacua on a very thin ( 10 pg/cms) conducting foil, which was placed hereafter in the wall between two adjacent counters, described elsewhere’) 8). The solid angle of the source with regard to the counter was 47~. The double counter was filled with an Ar-CH4 (9 : 1) mixture at a pressure of 7 atm. In this way an 100% efficiency was achieved for the detection of X-rays, Auger electrons and positrons. Only a small correction had to be applied for absorption of some 5,5 keV Auger electron in the foil. The efficiency of 100% for the K peak was proved by the fact that at higher pressures the counting rate did not increase. The efficiency for positrons was calibrated by means of a measurement of ls*Au. The pulsespectrum caused by positrons and the K-peak were separated nearly totally. The 3” NaI crystal was placed at a distance of 10 cm from the counter tube to make the effect of summation of 5 10 keV and 810 keV pulses negligible. In order to take into account the delays in the proportional counter (4,~ sec.) the resolving time of the coincidence circuit was 10 lo sec. 3 measurements were performed. 1. the gammaspectrum coincident with the K-peak (y, K) during 50.000 sec. 2. the gammaspectrum coincident with the fl+ spectrum (y, /I+) during 68.000 sec. 3. the gammaspectrum coincident with the K peak + b+ spectrum. (y - K + /I+) during 35.800 sec. The spectra of the NaI crystal measured in coincidence with the K-peak and with the positron spectrum are shown in figs. 2 and 3. We applied, corrections for dead time of the trigger-circuits, absorption of Auger electrons in the source backing and random coincidences. We have taken into account the 810 keV - K coincidences, caused by the electron capture decay to the 1620 keV level and also corrected for the seeming 810 keV - K coincidences which are caused by p+ pulses under the K-peak.
ON THE
5000 -
1000
K /fi+ RATIO
IN THE DECAY
589
OF 58co
010 keV
_
L I
L--a-_-
1620keV _A -\_
+
.I
CHANNEL
I
250
150
50
NUMBER
Fig. 2. Spectrum of the NaI-crystal measured in coincidence with the K-peak.
5000
610 ke'
;2 s-i g g
3000
fz ii .
is 010 krV
1000
-\ -------
__-_-150
CHANNEL
---
l
250
NUMBER
Fig. 3. Spectrum of the NaI-crystal measured in coincidence with the /?+-spectrum.
To determine the first of these last-mentioned corrections we measured coincidences between 810 keV and 810 keV gamma quanta with two NaI crystals and a fast-slow coincidence circuit. The result of this measurement
590
P.
KRAMER,
A. DE
BEER
AND
J.
BLOK
was that 810-810 coincidences occurred for 1.55 f 0.2% of all 810 keV transitions. We subtracted 3.1% of the (810, K + ,!3+) coincidences neglecting the difference in L capture fractions in the two branches. The amount of fl+ pulses under the K-peak was determined by extrapolating the p+ spectrum in this region. The correction appeared to be 2 & 0.6%. The results of the measurements
are shown in table I. TABLE
Results area of 810 keV photopeak
I
of the measurements coincident
with:
of ttCo
K + fi+ 49860 8320 8’ K
random
.
coincidences:
. .
absorption dead time. 810-810
.
.
. .
coincidences
K peak.
K + 8’
274 88 257
. . 1.5% . . . 0.4% . . . 3.1% . . 2%
result K = 4.83 f 0.1 8’ K + B+ ___ =5.82&0.1 t?+
Table Experimental
. . .
sec.
41640
B’ K of Auger electrons
fi+ pulses under Final
.
counts/50000
and theoretical
II
values
of the K/B+ ratio
In table II the results of our measurements
of Wo
are compared
with other
experimental values and the theoretical predictions of Nguyen K hat. Our value is in good accordance with the results of Depommier and Nguyen Khac. The accuracy of our result is mainly caused by the fact that no separate determination of solid angle and efficiency was needed and the corrections we had to apply, were small. Moreover we did not need to use a value of the K fluorescence yield. It is remarkable that the agreement of the experimental and theoretical values of the K//If ratio is fairly good, as opposed to the value for the L/K capture ratio reported recently by Fink and Molera) which showed a discrepancy of 17% from the theoretical values of Brysk and Rose. Since Depommier and Nguyen Khac used the Brysk-Rose values for
ON THE
the K-capture
probability
K//l+RATIO
IN THE DECAY
591
OF 58c0
it seems that the disagreement
in the
L/K capture
ratio mainly results from an error in the calculated L capture probability. To check this assumption further accurate measurements are needed on nuclides decaying by positron-emission and electron capture. Recently Jo s hi and Lewis la) measured this K/p+ ratio by using a NaI scintillation counting technique. They reported a value can be seen our value is in agreement with this one.
4.92 f
0.09.
As
Received 19-2-62 REFERENCES
1) Konijn, 2) 3) 4) 5) 6) 7) 8) 9) 10)
J., Van Nooyen, B., Hagedoorn, H. L. and Wapstra, A. H., Nucl. Physics B (1959) 296. Ramaswamy, M. K., Bull. Am. phys. Sot. 3 (1958) 357. Cook, C. S. and Tomnovec, F. M., Phys. Rev. 104 (1956) 1407. Grace, M. A., Jones, G. A. and Newton, J. O., Phil. Mag. 1 (1956) 363. Depommier, P., Nguyen-Khac, U., and Bouchez, R., J. Phys. Radium El (1960) 456. Nuclear Data Sheets, National Academy of Sciences, Nat. Research Council, Washington, DC. Kramer, P., Thesis Vrije Universiteit Amsterdam, 1961. Kramer, P., De Ridder, J. and Blok, J., Nucl. Instr. and Methods. 16 (1962) No. 4 or 5. Fink, R. W. and Moler, R. B., Bull. Am. Phys. Sot. 13(1961) 428. Joshi, B. R. and Lewis, G. M., Proc. phys. Sot. 78 (1961) 1056.
Kramer, P. De Beer, A. Rlok, J. 1962
ON THE K/p+ RATIO IN THE DECAY OF 58Co by P. KRAMER, Natuurkundig
A. DE BEER
Laboratorium,
and J. BLOK
Vrije Universiteit,
Amsterdam.
synopsis Using an internal source in a 4n proportional of 58Co was determined to be 4.83 & 0.1.
counter, the K/p+ ratio in the decay
In the last years several authorsi-4) reported experimental values of the of 5sCo. Recently Depommier and Nguyen Khac5) published new theoretical calculations on K//3+ ratios of which the results agree fairly well with accurate experimental values for a large number of nuclides. Since for 5X0 a disagreement occurs between the experimental values and these calculations, it seemed interesting to remeasure the K/B+ ratio of this nuclide.
K//l+ ratio in the decay
71d co5* 2+
1.28~ 0.0006%,~+
(* 0.0001 %E 1
o+ Stable
Fe’*
Fig. 1. Decay scheme of SsCo.
The decay schemea) of 5sCo is shown in fig. 1. Nearly all positron and electron capture decay occurs to the first excited level of s*Fe. Some 2% feeds the 1600 keV level. We tried to determine the K//l+ ratio by counting positrons, K Auger electrons and K X-rays in a 4n proportional counter with an efficiency of nearly lOOo/o. In order to reduce background we measured coincidences of pulses from the proportional counter and pulses from a 3” NaI crystal, caused by 810 keV gamma radiation. -
587 -
588
P. KRAMER,
s*Co was produced
A. DE BEER
AND
J. BLOK
by an (a, n) reaction on Mn.
The manganese was dissolved in diluted hydrochloric acid, a solution of ammonium citrate was added and the pH was made 8.5 with ammonia. Ten micrograms of cobalt were added. The cobalt solution of dithizone in carbontetrachloride.
was extracted
with a
The organic layer was washed by a buffer solution of ammonium citrate (pH 8.5), and evaporated. The organic matter was destroyed by perchloric acid. The energy of the a-beam was 15 MeV, in order to reduce the 55Mn (a, 2~2) 57Co reaction. The small amount of 57Co produced at this a-energy, did not affect our measurements. The carrierfree source was evaporated in vacua on a very thin ( 10 pg/cms) conducting foil, which was placed hereafter in the wall between two adjacent counters, described elsewhere’) 8). The solid angle of the source with regard to the counter was 47~. The double counter was filled with an Ar-CH4 (9 : 1) mixture at a pressure of 7 atm. In this way an 100% efficiency was achieved for the detection of X-rays, Auger electrons and positrons. Only a small correction had to be applied for absorption of some 5,5 keV Auger electron in the foil. The efficiency of 100% for the K peak was proved by the fact that at higher pressures the counting rate did not increase. The efficiency for positrons was calibrated by means of a measurement of ls*Au. The pulsespectrum caused by positrons and the K-peak were separated nearly totally. The 3” NaI crystal was placed at a distance of 10 cm from the counter tube to make the effect of summation of 5 10 keV and 810 keV pulses negligible. In order to take into account the delays in the proportional counter (4,~ sec.) the resolving time of the coincidence circuit was 10 lo sec. 3 measurements were performed. 1. the gammaspectrum coincident with the K-peak (y, K) during 50.000 sec. 2. the gammaspectrum coincident with the fl+ spectrum (y, /I+) during 68.000 sec. 3. the gammaspectrum coincident with the K peak + b+ spectrum. (y - K + /I+) during 35.800 sec. The spectra of the NaI crystal measured in coincidence with the K-peak and with the positron spectrum are shown in figs. 2 and 3. We applied, corrections for dead time of the trigger-circuits, absorption of Auger electrons in the source backing and random coincidences. We have taken into account the 810 keV - K coincidences, caused by the electron capture decay to the 1620 keV level and also corrected for the seeming 810 keV - K coincidences which are caused by p+ pulses under the K-peak.
ON THE
5000 -
1000
K /fi+ RATIO
IN THE DECAY
589
OF 58co
010 keV
_
L I
L--a-_-
1620keV _A -\_
+
.I
CHANNEL
I
250
150
50
NUMBER
Fig. 2. Spectrum of the NaI-crystal measured in coincidence with the K-peak.
5000
610 ke'
;2 s-i g g
3000
fz ii .
is 010 krV
1000
-\ -------
__-_-150
CHANNEL
---
l
250
NUMBER
Fig. 3. Spectrum of the NaI-crystal measured in coincidence with the /?+-spectrum.
To determine the first of these last-mentioned corrections we measured coincidences between 810 keV and 810 keV gamma quanta with two NaI crystals and a fast-slow coincidence circuit. The result of this measurement
590
P.
KRAMER,
A. DE
BEER
AND
J.
BLOK
was that 810-810 coincidences occurred for 1.55 f 0.2% of all 810 keV transitions. We subtracted 3.1% of the (810, K + ,!3+) coincidences neglecting the difference in L capture fractions in the two branches. The amount of fl+ pulses under the K-peak was determined by extrapolating the p+ spectrum in this region. The correction appeared to be 2 & 0.6%. The results of the measurements
are shown in table I. TABLE
Results area of 810 keV photopeak
I
of the measurements coincident
with:
of ttCo
K + fi+ 49860 8320 8’ K
random
.
coincidences:
. .
absorption dead time. 810-810
.
.
. .
coincidences
K peak.
K + 8’
274 88 257
. . 1.5% . . . 0.4% . . . 3.1% . . 2%
result K = 4.83 f 0.1 8’ K + B+ ___ =5.82&0.1 t?+
Table Experimental
. . .
sec.
41640
B’ K of Auger electrons
fi+ pulses under Final
.
counts/50000
and theoretical
II
values
of the K/B+ ratio
In table II the results of our measurements
of Wo
are compared
with other
experimental values and the theoretical predictions of Nguyen K hat. Our value is in good accordance with the results of Depommier and Nguyen Khac. The accuracy of our result is mainly caused by the fact that no separate determination of solid angle and efficiency was needed and the corrections we had to apply, were small. Moreover we did not need to use a value of the K fluorescence yield. It is remarkable that the agreement of the experimental and theoretical values of the K//If ratio is fairly good, as opposed to the value for the L/K capture ratio reported recently by Fink and Molera) which showed a discrepancy of 17% from the theoretical values of Brysk and Rose. Since Depommier and Nguyen Khac used the Brysk-Rose values for
ON THE
the K-capture
probability
K//l+RATIO
IN THE DECAY
591
OF 58c0
it seems that the disagreement
in the
L/K capture
ratio mainly results from an error in the calculated L capture probability. To check this assumption further accurate measurements are needed on nuclides decaying by positron-emission and electron capture. Recently Jo s hi and Lewis la) measured this K/p+ ratio by using a NaI scintillation counting technique. They reported a value can be seen our value is in agreement with this one.
4.92 f
0.09.
As
Received 19-2-62 REFERENCES
1) Konijn, 2) 3) 4) 5) 6) 7) 8) 9) 10)
J., Van Nooyen, B., Hagedoorn, H. L. and Wapstra, A. H., Nucl. Physics B (1959) 296. Ramaswamy, M. K., Bull. Am. phys. Sot. 3 (1958) 357. Cook, C. S. and Tomnovec, F. M., Phys. Rev. 104 (1956) 1407. Grace, M. A., Jones, G. A. and Newton, J. O., Phil. Mag. 1 (1956) 363. Depommier, P., Nguyen-Khac, U., and Bouchez, R., J. Phys. Radium El (1960) 456. Nuclear Data Sheets, National Academy of Sciences, Nat. Research Council, Washington, DC. Kramer, P., Thesis Vrije Universiteit Amsterdam, 1961. Kramer, P., De Ridder, J. and Blok, J., Nucl. Instr. and Methods. 16 (1962) No. 4 or 5. Fink, R. W. and Moler, R. B., Bull. Am. Phys. Sot. 13(1961) 428. Joshi, B. R. and Lewis, G. M., Proc. phys. Sot. 78 (1961) 1056.