1
LE.1
1
N~&wr Physics A180 (1972) 569486;
@ North-~ofla~
P~iishi~#
Co., Amsterdam
Not to be reproduced by photoprint or microSlm without written permission from the publisher
GAMMA
RAYS FROM
THERMAL-NEUTRON
IN NATURAL AND 39K ENRICHED
CAPTURE
POTASSIUM
A. M. F. OR DEN KAMP and A. M. J. SPITS
Fysisch ~boTatori~~, ~~~sl~n~v~~s~te~t,
Utrecht, Nether~~~s
Received 20 August 1971
Abstract: Gamma rays following thermal-neutron
capture in natural and in jgK enriched
potassium have been investigated with a Ge(Li) and a Ge(Li)-NaI spectrometer. In the
3pK(n,y)40K reaction 222 y-rays were found, of which 187 could be fitted into the level
scheme of 40K. Fifteen y-rays could be ascribed to the 41K(n, y)42K reaction. Excitaticu energies
of 54 levels in 40K and of 9 levels in 42K have been determined with 0.2-1.0 keV errors. The
Q-values of the 3gK(n,y)40K and 41K(n,y)4zK reactions are Q = 7799.740.8 keV and
7533.9h1.2 keV, respectively.
1E
NUCLEAR REACTIONS
3p*4iK, ‘H, 6Li 12C 19F, 4oAr, s6Fe 207Pb(n,y), E =
thermal; 19F, ?!ii(n,n’y),
E = fast; meas;ed
i,
$. K, 39K(n:y), E = thermal;
measured E,, I,., yy-coin; deduced Q. 40*42K deduced levels, y-branching. Ge(Li),
NaI detectors.
1. Introduction
Gamma rays following thermal-neutron capture in natural potassium have been
studied with scintillation spectrometers ‘*2), magnetic pair spectrometers 3s“) and
magnetic Compton spectrometers St6). The resolution of these spectrometers is insufficient for an adequate study of the complex 3gK(n, Y)~‘K y-ray spectrum.
In 1966, Kennett et al. ‘) investigated the 3gK(n, Y)~‘K reaction with a Ge(Li)
detector and examined a possible correlation between (n, y) and (d, p) strengths. This
investigation was incomplete because practically only primary y-rays were studied.
A preliminary decay scheme for 4oK was obtained by Skepps~dt “) with a threecrystal Ge(Li) pair spectrometer, but this investigation did not give more information
than given by Kennett et al. ‘).
To obtain a more detailed picture of the 39K(n, Y)~‘K reaction the present investigation was performed with high-resolution Ge(Li) spectrometers. The results
will be compared with those of Johnson and Kennett 9), who recently reported very
similar data: 252 y-ray transitions and 55 excitation energies. Branching ratios of
bound states and intensity balances for the deduced levels were not reported.
Excitation energies of 40K levels and Z, values, obtained from the 3gK(d, p14’K
reaction, are summarized by Endt and Van der Leun ’ ‘). A partial decay scheme and
some excitation energies have been deduced by Freeman and Gallman 12) from the
39K (d, P~)~‘K reaction. Spins for several levels have been determined by Twin
569
570
A. M. F. OP DEN
KAMP
AND
A. M. J. SPITS
et al. 13) from the 40Ar(d, ny)40K reac tt-0 n. They also pointed out that the 2290 keV
level must be a doublet. The excitation energies of the components
are determined in
the present investigation.
The natural abundances
of 3gK, 40K and 41K are 93.1 %, 0.012 % and 6.9 7;
[ref. “)I, their thermal-neutron
capture cross sections 1.94&O. 15 b, 70 f20 b and
1.24kO.10 b [ref. ‘“)I, respectively. About 5 % of the thermal-neutron
capture thus
will occur in 41K; the contribution
of 40K is negligible. The use of a sample enriched
in 3gK has helped to differentiate
between the 3gK(n, y) and 41K(n, y) reactions.
2. Experimental
The experiment
has been performed at the High Flux Reactor at Petten, Netherlands. The target was placed in a beam of thermal neutrons with a flux of about
lo7 cmm2 - s-l.
The samples used were 400 mg of natural K,CO, and 400 mg K2C0, enriched to
98.3 % in 3gK. The enriched sample was on loan from AERE, Harwell, England.
The samples were encapsulated
in thin-walled
teflon tubes. A detailed description of
the experimental
set-up has been given by van Middelkoop
and Spilling I “).
To facilitate the interpretation
of a peak as a full-energy, single- or double-escape
peak, the y-rays were detected with true-coaxial
Ge(Li) detectors of different volume:
6.5 and 20 cm3. The resolution for the 1.33 MeV 6oCo y-ray was 3.0 and 2.6 keV,
respectively. The overall resolution
(measuring
time 4 d) of the system with the 20
cm3 Ge(Li) detector was 2.9 keV at E,, = 1.27 MeV and 5.9 keV at _!$ = 6.7 MeV.
Gamma rays from the “C(n, y)i’C and 56Fe(n, y)57Fe reactions and from radioactive sources (table 1) together with the y-rays from the 3gK(n, Y)~*K reaction were
investigated
with a 23 cm3 Ge(Li) detector to obtain an accurate energy calibration.
The resolution of this detector was 3.0 keV for the 1.33 MeV 6oCo y-ray. The linearity
of the system with the 23 cm3 detector was tested with a precision pulse generator.
Various runs, covering the E,, = 0.1-2.5 and 0.5-0.7 MeV regions were made with
the different detectors. Separate runs covering the same energy regions were performed
to investigate the background
radiation. Gamma rays from the enriched sample were
only measured with the 20 cm3 Ge(Li) detector. The electronic equipment consisted
of an Ortec FET preamplifier,
an Ortec main amplifier and a Laben 4096-channel
pulse-height
analyser.
Gamma-gamma
coincidence measurements
were performed with a sample of 7 g
natural potassium.
The coincidence
set-up consisted of the 20 cm3 Ge(Li) detector
and a 12.7 cm x 12.7 cm NaI crystal. The time resolution of the coincidence system
was 22 = 80 ns. A digital discriminator
16) with 16 windows routed the subgroups
of the memory. Thirteen windows were placed on the pulse-height
spectrum of the
Ge(Li) detector. About 1 % of the incoming pulses passed the discriminator;
5 % of
the accepted pulses was due to random events. The counting rate after the discriminator was 3.8 s- ‘. The total measuring time was 39 d.
THERMA~NE~RON
571
CAPTURE
3. Analysis of the measurements
The energy calibration for each spectrum was obtained by fitting a sixth-degree
polynomial to the calibration lines (see below). The y-ray spectra measured with the
23 cm3 Ge(Li) detector were analysed to obtain an accurate set of internal calibration
energies.
The positions of the peaks were determined by fitting Gaussian functions to the
experimental points.
TABLE 1
Energies of prays used for calibration
Isotope “)
57co
(r)
‘9F
annihilation
20F
137cs
s4Mn
88Y
60C0
r:;
::;
Er (keW ?
Ref.
Isotope “1
Er (key) “1
Ref.
122.05f0.05
197.2 f0.2
511.01+0.01
583.5 ho.3
611.59+0.08
834.84kO.08
898.01 ztO.08
1173.2310.04
17
)
18
17
:
1s
19
,’
ZZNa (r)
zz$
(r)
1274.52;tO.O7
1332.48rtrO.05
1633.4 rlzo.3
1836.08hO.08
2223.35kO.05
4945.0 &0.2
7631.0 &IO.5
7645.2 AO.5
20
1-I
;
18
20
20
,'
17
1
82Ry
‘JC
57Fe
57Fe
(rJ
20
:
211
18
1
18
18
;
"f The symbol (r) denotes radioactive source. The 2H, 13C, 20F and 37Fe y-rays originate from
the~ai-neutron capture in ‘H, W, ‘*F and 56Fe, respectively, the ‘*F and z”Ne y-rays from the
‘*F(n, n’y) and ~gF(n,~)zoF(~~)zoNe reactions, respectively.
b, Uncorrected for recoil.
The low-energy spectrum (,!$ = 0.1-2.5 MeV) was calibrated with the lines listed
in table 1. The calibration curve deviates at most AE = 0.2 keV from a linear fit. The
standard deviation between the energies calculated from the calibration curve, and
the calibration energy was c = 0.06 keV. The energies of some prominent y-rays
thus obtained together with the “C(n, y)13C and 56Fe(n, y)“Fe energies listed in
table 1, were used for the energy calibration of the high-energy spectrum (EY =
0.5-7.0 MeV). Moreover, 52 energy relations in the form of 511 or 1022 keV differences between full-energy peaks and escape peaks were used as constraints in the
least-squares fitting problem, leading to BE = 0.7 keV and d = 0.2 keV.
The spectra measured with the 20 cm3 Ge(Li) detector were analysed to resolve
complex parts and to determine the intensities of all y-lines precisely.
Peak positions were determined from a least-squares fitting of a slightly asymmetric
response function to the observed peaks. Isolated peaks were used to determine the
asymmetry and the FWHM as a function of energy. The program allowed the analysis of a group of up to six overlapping peaks. With this detector one finds AE = 0.4
and 0.3 keV and CT= 0.06 and 0.2 keV for the energy calibration of the low- and
high-energy spectra, respectively.
Intensities were calculated by means of efficiency curves for full-energy, single- and
double-escape peaks. These curves were determined as described in ref. 23).
0
0
u3
0
0
v
c
0
0
-3
0
z
-
0
E
.-I$
-iu,
:x
0
0
0”
000 7
009 E
I’
000 &
1
.
574
A. M. F. OP DEN
KAMP
AND
A. M. J. SPITS
TABLE 2
Observed y-rays from the 39K(n,y)40K
EY+E, “)
(keV)
Intensity “)
246.9 &0.3
0.16&0.02
310.7&0.2
330.5kO.2
371.4AO.2
0.1610.02
0.49&0.04
0.23 +0.03
380.2kO.3
459.6hO.2
522.2kl.O
554.9&0.2
612.8f0.3
646.2hO.l
736.8AO.2
741.0*0.2
770.4fO.l
791.2f0.2
799.4f0.2
827.7&0.3
843.6kO.2
870.2f0.3
891.6hO.2
904.5f0.3
939.lkO.2
977.1 kO.3
1023.8hO.3
0.18ztO.02
0.25&-0.03
2.0 f0.9
0.18&0.02
0.13f0.03
2.86kO.09
0.24AO.03
0.32f0.03
56.1 *1.2
0.68 zto.03
0.16&0.02
0.60&0.04
1.5010.18
0.28 +0.06
1.16f0.05
0.15f0.03
0.24f0.03
0.2110.03
0.39 +0.07
1069.1 &to.2
1083.1 ho.3
1086.9f0.2
1123.9f0.3
1131.650.3
1144.9f0.4
1151.8hO.3
1159.0*0.1
1162.8+0.3
0.38f0.03
0.24&0.04
1.43 ztO.06
0.26f0.26
0.32AO.04
0.17kO.04
0.33f0.06
10.0 f0.3
0.5OztO.06
1178.3&0.2
1226.1 ho.3
1233.0+0.3
1247.2 AO.2
1256.OhO.5
1266.1 ho.3
1269.2hO.2
1283.1+0.3
1303.4hO.2
1320.9*0.3
1331.9+0.3
0.3740.03
0.12f0.02
0.19f0.03
4.89+0.12
0.13f0.05
0.38ztO.05
0.3610.10
0.20&0.03
3.50*0.10
0.3650.05
0.29 ho.04
Interpretation
(& in keV) ‘)
4149 -+ 3902
(4396 + 4149)
(3394 -+ 3146)
3797 -+ 3487
2290 --f 1959
3128 -+ 2756
(2419 -+ 2047)
(4908 + 4537)
3110+2731
2419 --f 1959
2626 -+ 2104
3923 -+ 3368
3599 -+ 2986
2290 + 1644
4105 4 3368
3869 + 3128
800+
30
3599 + 2808
4537 + 3738
2787 -+ 1959
1644+
800
892
4807
2986
4105
3128
(3599
4807
3840
2731
3414
3888
4744
3110
1959
3738
(4149
2070
3487
3630
2047
+
-+
-+
+
+
-+
-+
-+
-+
4
+
+
+
+
+
--f
+
-+
+
+
0
3902
2047
3128
2104
2575)
3738
2756
1644
2290
2751
3599
1959
800
2575
2986)
892
2261
2397
800
3664 -+ 2397
2070 + 800
2104 -+ 800
3368 --f 2047
reaction
EY+C “)
(keV)
Intensity b,
Interpretation
(E,in keV) ‘)
1354.330.2
1373.1 hO.2
I398.8&0.2
1418.250.2
1424.3hO.2
1438.4*0.3
1466.1 kO.3
1477.5hO.3
1479.950.2
1483.9h0.4
1489.6hO.2
1502.8*0.4
1517.0*0.3
1551.5f0.3
1565.6f0.4
1582.9f0.6
1597.8kO.3
0.45f0.06
1.7810.07
0.27+0.04
0.21*0.10
0.45~0.04
0.35*0.04
0.31 f0.06
0.28f0.05
2.28 ho.09
0.14ztO.02
1.8110.08
0.5110.18
0.23 ho.03
0.23 &0.03
0.25hO.04
0.09 hO.02
0.35+0.03
4465-+3110
3664 + 2291
2291 -+ 892
4149 + 2731
3822 --f 2397
4807 -+ 3368
3110 + 1644
3738 + 2261
3439 -+ 1959
3128 -+ 1644
2290 + 800
3146 -+ 1644
4465 -+ 2947
3599 -+ 2047
1613.7&0.2
1618.910.2
1625.5&0.3
1667.6hO.6
1674.1 f0.4
1694.OhO.6
1702.0&0.4
1704.6f0.3
1718.1 ho.6
7.62*0.19
8.2 +0.2
0.32kO.04
0.22f0.07
0.18&0.04
0.2610.06
0.53f0.08
1.85f0.10
0.27hO.08
1752.0*0.3
1765.OhO.3
1795.3hO.3
1819.5f0.5
1825.7hO.3
1838.3f0.3
0.40&0.04
0.30f0.03
1.8430.06
0.34&0.10
0.83 10.06
0.5110.04
1854.5rtO.4
1858.2kO.3
0.30&-0.07
0.76hO.05
1881.1f0.3
0.63 ho.05
1915.9+0.3
1929.2*0.2
1956.5kO.2
1961.2hO.6
1964.5AO.6
0.42 *0.04
2.8550.12
2.55xtO.10
0.1410.03
0.14f0.03
1972.9&0.3
2007.6f0.3
2017.6&0.3
0.4530.06
3.18f0.10
3.8 10.2
3630 + 2047
3888 -+ 2290
(4744 + 3146)
1644-t
30
2419+
800
3738 + 2070
3797 + 2104
3664 +
3822 +
(4666 -+
3711 -+
3869 +
3439 +
3923 -+
2626 -+
3797 *
(4465 +
3902 +
4149 +
(4666 -+
3840 -+
(4908 +
4020 -+
19.59 +
2756 -+
4587 -+
3923 +
(4254 -+
4020 -+
2808 -+
2047 --f
1959
2104
2947
1959
2104
1644
2104
800
1959
2626
2047
2291
2808)
1959
3027)
2104
30
800
2626
1959
2290)
2047
800
30
THURMAN-NEUTRON
575
CAPTURE
TABLE 2 (continued)
-++-& “)
(keV)
Intensity b,
2022.3hO.6
2032.1 AO.5
2040.1 rtO.3
2047.510.3
2057.2kO.6
2069.7kO.3
2073.710.3
2102.1&0.9
2122.210.5
2143.3f0.4
2150.1kO.4
2153.8kO.3
2175.OrfrO.5
2184.5&0.4
2196.9&0.4
2205.1+0.6
2206.9 kO.6
2230.7hO.3
2234.SkO.9
2260.4hO.4
2290.710.3
2294.9 jO.6
2310.5&0.5
2324.310.8
2330.410.5
2346.OkO.7
2367.450.4
2374.810.5
2389.3f0.3
2397.1+0.5
2418.610.5
2430.5&0.4
2459.3f1.6
2546.2-3-0.6
2577.6jO.6
2593.4f 1.2
2609.9f0.4
2614.0&0.4
2639.610.7
2686.8hO.7
2726.6kO.4
2736.6kO.9
2756.7&0.4
2786.1hl.O
2799.1 f0.4
2806.110.4
2839.1 ho.4
2892.110.6
2917.4kO.4
2926.8 kO.4
0.22kO.04
0.60&0.14
3.5 50.2
3.6OkO.14
0.23 &to.05
2.1610.14
8.7 +0.5
0.10*0.03
0.27&0.03
0.23 &0.03
0.65*0.05
0.95+0.04
0.19f0.02
1.2OkO.07
0.60&0.05
0.61 kO.20
0.9 hO.2
1.29f0.15
0.16f0.05
0.43 10.05
3.6010.14
0.48 AO.06
0.66&0.08
0.21&0.06
0.43 10.06
0.99~0.10
1.9 *0.3
0.40~0.05
1.89sO.19
0.34 &O.OS
0.83 &0.08
0.81~0.11
0.23AO.12
3.0 50.7
0.48 aO.07
0.49f0.13
1.1 +0.2
1.55*0.16
1.05*0.17
0.28&0.05
1.25f0.13
0.56f0.14
1.7 *to.2
0.33&0.09
1.2810.19
1.70*0.17
1.7 10.3
0.36&0.07
0.67rtO.11
0.6510.11
Interpretation
(E, in keV) “)
4789 -+
2070 -+
2047 +
4105 -+
2070 +
2104+
4149 -+
4908 +
2156
30
0
2047
0
30
2047
2787
4254
3797
4465
4254
3840
2104
1644
2290
2070
1644
-+
-+
-+
-+
+
4254 --f 2047
2261 -3
30
2261 -+
0
2291 +
0
4254 --f 1959
31104
800
4744 + 2419
3146
2397
4666
2419
2397
2419
+ 800
+
30
--f 2291
-+
30
+
0
+
0
2575 +
30
4537 -+ 1959
3394 -+ 800
4254 --c 1644
3414+
800
3439 + 800
3487 + 800
2756 +
30
4807 + 2070
2787 -+
30
2787 -+
0
3599 -+- 800
4908 + 2070
C -+ 4908
2947 -+
30
EY+-% “)
(keV)
Intensity b,
Interpretation
(E. in keV) ‘)
2949.310.8
2992.5kO.7
3010.610.6
3055.610.4
3099.3&0.6
3120.5*0.7
3127.OiO.5
3133.010.7
3213.410.9
3262.250.4
3285.811.2
3304.0fO.S
3326.8hO.5
3336.0&0.5
3339.1 &to.6
3349.010.4
3379.3f0.7
3384.511.1
3403.6kO.5
3447.0&0.5
3453.611.0
3518.9*0.5
3526.9i0.4
3545.8&0.4
3569.810.9
3619.710.5
3630.750.6
3650.430.4
3664.711.6
3688.910.4
3695.3 kO.4
3737.5&0.6
3779.3&0.6
3791.911.2
3821.410.7
3838.5+0.5
3857.5+0.8
3868.2i1.3
3877.0&0X
3898.511.3
3911.9f0.5
3930.8&0.5
3944.050.5
3959.6fO.S
3978.1 &to.5
3989.550.8
4001.9*0.5
4061.4sO.6
4088.8&0.7
4110.7~0.8
0.54&0.06
0.61 fO.11
0.77f0.18
2.8 10.2
1.11&0.16
0.28 kO.07
0.61&0.10
0.40*0.11
0.26rtO.06
2.8 10.2
0.2510.07
1.11&0.16
0.93kO.19
1.27hO.11
0.60&0.11
1.3 hO.3
0.3O,tO.O8
0.42&0.10
1.08f0.19
0.7510.18
1.5 10.7
1.06&0.13
1.00~0.13
4.5 10.4
0.50+0.08
o.s4+0.13
0.50&0.03
2.6 &to.4
0.40*0.17
l&%&O.18
1.32jzO.17
1.3 10.3
Ct.88&-0.19
0.25f0.08
0.47 +0.04
0.69+0.18
0.4710.12
0.2110.06
0.50~0.11
0.37f0.17
1.2 10.3
1.51*0.18
1.040.17
1.6 ho.3
1.4 hO.2
0.45 h-to.08
1.7 *0.2
1.8 10.3
0.51 hO.17
0.63f0.15
4908 + 1959
C + 4807
C -+ 4789
c-+4744
4744-t 1644
3128-t
0
C -+ 4666
C -+ 4587
c * 4537
4105 +
800
C-+4465
3368 -+
30
4149 -+ 800
3414 -+
30
C -+ 4396
4254 +
800
C --f 4254
3599 -+
30
3630-t
0
c --f 4149
4465 -+ 800
c -+ 4105
4537 -+ 800
c-+4020
3822 -+
30
3822 -+
0
3869 -+
30
3888 +
30
3869 +
0
C + 3923
C -+ 3902
C -+ 3888
C -+ 3869
4744-t
800
C --f 3840
C -+ 3822
4789 -+ 800
c -+ 3797
c + 3738
c -+ 3711
576
A. M. F. OP DEN
KAMP
AND
A. M. J. SPITS
TABLE 2 (continued)
&I-E, “)
(keV)
Intensity “)
4136.OkO.5
4169.810.6
4200.3 50.5
4224.1&0.6
4243.0&0.7
4279.OhO.6
4299.9*1.1
4313.0*0.7
4360.6-&0.5
4385.550.5
4390.1+0.8
4406.0+1.3
4421.3&0.6
4431.1f0.6
4452.6hl.l
4507.9kO.6
4654.5&0.8
4671.4hl.4
3.4 10.4
0.85f0.14
2.5 ho.3
0.84f0.13
0.531fo.10
0.56f0.08
0.24rtO.07
0.38f0.06
5.1 50.5
1.8 10.3
0.5910.16
0.6 +0.3
0.55f0.09
0.79hO.14
0.31 kO.08
1.0 hO.3
0.9 f0.3
0.6 ho.3
Interpretation
(E, in keV) ‘)
C
c
c
4254
+ 3664
+ 3630
-+ 3599
+
30
C + 3487
c -+ 3439
c + 3414
c --f 3394
C + 3368
4537 -+
30
C -+ 3146
C + 3128
EY+E, “)
(keV)
Intensity b,
4769.5fl.2
4851.8kl.O
4908.6fl.3
4992.0f0.6
5013.3f0.6
5043.2hO.6
5069.2 50.6
5173.9f0.6
5223.2fl.4
5380.8rtO.6
5495.9 *2.2
5509.8f0.7
5696.2f0.6
573O.OfO.6
5752.4f0.6
5840.9&1.0
6999.4&0.8
7769.6hO.8
0.38%0.12
0.18&0.04
0.10~0.04
2.5 &0.4
1.58kO.17
2.4 10.3
1.5 10.3
2.9 hO.3
0.37hO.11
9.8 *0.9
0.12&0.06
4.1 *0.4
7.0 hO.7
3.0 hO.3
7.1 hO.5
0.23 ho.08
2.7 &0.3
7.3 *to.7
Interpretation
(E. in keV) ‘)
c -+ 2947
4908 -+
0
C -+ 2808
C -+ 2787
C + 2756
C-+2731
C + 2626
C + 2575
c -+ 2419
c -+ 2290
C -+ 2104
C -+ 2070
C+2047
c + 1959
C -+ 800
c-t
30
“) The recoil correction is denoted by E,.
‘) The total intensity of the primary y-rays has been normalized at 100.
“) Alternative interpretations are given between brackets; C denotes the capturing state.
4. Results
Fig. 1 shows the low-energy y-ray spectrum; fig. 2 shows the y-ray spectrum in the
energy region from 2.5-7.0 MeV. Both spectra were measured with the 20 cm3 Ge(Li)
detector. The background has been subtracted. Peaks originating from incomplete
background subtraction or from impurities in the sample are labelled with “b” or
the symbol of the final nucleus.
Energies and intensities of y-rays from thermal-neutron capture in 39K are given
in table 2. The values listed are the weighted means of those deduced from full-energy,
single-escape and double-escape peaks. All energies are recoil corrected. The errors
in the y-ray energies also contain a systematic part of 100 ppm. It originates from
(i) systematic errors in the calibration energies, especially in the high-energy region,
(ii) the use of extrapolation methods (energy relations) to calculate the energies
for E, > 2.5 MeV and (iii) the use of calibration lines from the 39K(n, Y)~‘K
reaction for the energy calibration of the spectra measured with the 20 cm3 Ge(Li)
detector.
The intensities of the y-rays are normalized such that the sum of the primary intensities equals 100. Errors in the intensities given in table 2 contain in addition to
the statistical errors the estimated errors in the efficiency curves used; the latter amount
to 2 % for Ey S 2 MeV, and increase up to 10 % at Ey = 10MeV.
THERMAL-NEUTRON
CAPTURE
517
Energies and intensities of y-rays from thermal-neutron capture in 41K are given
in table 3. No peaks could be ascribed to y-rays from capture in 40K.
The decay scheme, the excitation energies of bound states and the reaction energy
for the relevant potassium isotopes have been determined with a computer program.
First the program determines all possible transitions in the decay scheme by comparing
each y-ray energy with the differences between the excitation energies following from the
(d, p) work lo). Th e p ro gram selects those y-ray energies which correspond with
TABLE 3
Observed y-rays from the 41K(n, JJ)~~K reaction
E,, -i-E, “>
Intensity b,
ikeV)
107.110.3
151.4kO.2
268.4kO.3
431.3hO.3
532.012.0
639.OkO.3
682.OkO.2
1861.9kO.4
5672.0&1.1
6155.2&0.9
6278.850.7
6851.7hl.O
6894.211.3
7427.010.8
7533.9kl.2
58 f2
20 f1.4
4.5f0.5
4.6f0.7
9 f3
8.OkO.9
32.Cf1.6
7.0f0.9
9 f3
2.8f1.2
3.9hl.2
10 f4
3.4f1.6
5.9f2
3.4f1.3
Interpretation ‘)
(i?, in keV)
107+
0
258 +
107d)
1113 -+ 845d)
1113 --f 682 d,
639 +
107
639 +
0
682 +
0
1862 +
0
C -+ 1862
c + 1379 d)
C + 1255 d,
C -+ 682
C -+ 639
c+
107
C+
0
“) The recoil correction is denoted by &
b, Intensity in arbitrary units.
“) The capturing state is denoted by C.
d, Interpretation
from ref. 8).
only one possible transition, within the limits set by the standard deviations, and
which were also accepted in a cascade from the capturing state, via known intermediate levels to the ground state. Secondly, the program selects y-rays which were
observed in the coincidence measurements (table 6) and which could easily be fitted
in the decay scheme. Some y-ray assignments were based on intensities. The energies
of the y-rays which thus were positioned in the decay scheme form an over-determined
set of linear equations with the excitation energies and the Q-value as unknowns.
Finally, the program repeats the calculations with excitation energies and Q-value
which follow from the solution of the least-squares problem mentioned.
The measured excitation energies of 40K levels are compared with published values
in table 4. The reaction energy determined as Q = 7799.7kO.8 keV is in agreement
with the values reported in ref. ‘) (Q = 7800.5 f0.2 keV; this error does not contain
a contribution for the error in the calibration procedure) and ref. “) (Q = 7798.6&
578
A. M. F. OP DEN
KAMP
AND
A. M. J. SPITS
TABLE 4
Excitation energies and intensity balances of levels in 40K
Intensity ‘)
E. CkeV)
present
investigation “)
0
29.8 kO.2
800.1 kO.2
891.610.2
1643.710.2
1959.1 *to.3
2047.4AO.3
2069.7kO.3
2103.7kO.3
2260.5kO.3
2289.8hO.3
2290.5kO.3
2397.3 10.4
2419.0*0.3
2575.310.5
2625.8 ho.4
2730.6kO.4
2756.4&0.4
2786.610.4
2807.8hO.4
2947.5&0.5
2986.410.7
3110.4&0.4
3127.6k0.4
3146.210.5
3368.4k0.4
3393.611.0
3413.9&0.6
3439.0*0.5
3486.8&0.6
3599.110.5
3630.3+0.6
3663.610.4
3711.1 AO.5
3737.910.4
3797.510.4
3821.6*0.5
3840.210.5
3868.6*0.4
3887.8kO.5
3902.1 hO.5
3923.3 &to.5
4020.0&0.5
ref. g,
0
29.6hl.O
800.0& 1.O
892.011.0
1643.511.0
1959.2h1.3
2047.3&1.1
2069.3&0.8
2104.3hl.4
2290.4hO.7
2418.8kO.9
2457.5A2.0
2557.9*0.9
2576.7k2.0
2626.5+2.1
2730.1f1.3
2756.2h1.9
2786.2kO.9
2807.7hO.8
2946.5hl.3
2978.6kO.8
3027.lfl.3
3109.111.4
3128.3hl.O
3146.6k1.3
3367.1 rt1.3
3378.3f2.3
3414.4h1.8
3438.7sl.l
3485.711.3
3599.9h1.3
3630.5h2.0
3663.6*0.8
3713.211.3
3738.3hl.2
3767.6+0.8
3797.211.3
3822.3kl.l
3839.Ortl.l
3875.010.8
3887.7+1.3
3897.810.8
4019.8&1.1
refs. 11*12) “)
0
29.6kO.8
799.9kO.8
891.6kO.2
1644
“)
1958.8hO.9
2047.1fl.O
2069.9f1.3
2103.5f0.9
2256 &8
2290 *2
2393
2419
14
12
2569 18
2625.7fl.0
2757
2787
2808
2948
2988
3030
3108
3128
3146
3365
3392
3414
&2
&2
12
&8
18
14
18
&4
*5
&4
14
13
3481
3599
3630
3664
3714
3739
3768
3798
3822
3840
3867
3886
3898
3920
4017
+8
*2
13
12
&5
&2
14
12
&2
&2
52
&2
&8
f8
18
in
out
119.8
106.3
59.0
0.6
10.8
9.3
9.9
6.7
11.6
0.4
4.9
3.0
1.0
10.0
56.1
1.2
9.1
12.9
12.3
6.4
12.2
1.7
5.2
3.1
1.3
11.1
9
0.9
3.0
1.9
3.8
1.8
3.2
0.4
0.1
1.4
3.8
2.6
3.2
0.7
0.2
0.5
1.2
0.9
1.5
0.6
1.8
5.1
0.5
2.7
0.8
3.4
0.5
2.3
1.5
1.4
1.5
1.0
0.5
2.2
5.1
0.4
2.8
0.8
4.0
0.4
1.0
1.7
1.4
1.6
1.5
1.2
0.7
0.5
0.9
1.9
1.4
1.5
1.5
1.1
0.3
0.7
0.9
3
2.9
THERMAL-NEUTRON
TABLE
CAPTURE
579
4 (continued)
Intensity C)
E, (keV)
-present
investigation
ref. g,
refs. ll. I*) b,
in
-
out
“)
-4104.6-fO.5
4148.910.5
4253.9f0.S
4396.laO.7
4464.6&O.S
4537.3 &OS
4586.8 10.8
466X8-+0.7
4743.9hO.S
4788.910.7
4806.9&0.5
4908.510.6
7799.7hO.8 ‘)
4104.0&1.0
4149.3 *to.9
4253.6kO.6
4273.311.5
4281.1+1.1
4397.211.2
4462.821.2
4537.8&-0.7
4579.611.0
4744.7*1.9
4792.7f1.4
4808.5&0.9
4908.6kO.9
7800.5f0.2 ‘)
4102 iS
1.3
2.6
4.5
4253 ~t8
4396
4462
4539
4582
4658
f8
i8
+8
i-8
18
4788 f8
4801 f8
4902 f8
7801.5f2.7
1.1
1.3
2.8
0.3
0.4
2.8
0.8
0.6
0.4
‘)
1.8
2.5
6.7
1.3
2.9
0.1
0.4
2.5
1.0
1.4
2.6
100
“f The results are obtained from least-squares analysis. The errors have been enlarged with 100
ppm to incorporate a possible systematic error.
‘) Excitation energies with a deviation less than 2 keV are from ref. I*); all other excitation
energies are from ref. rl).
“) The total intensity of the primary y-rays has been normalized at 100.
d, Not observed (see text).
“) No error given.
‘) Reaction Q-value.
1.0 keV). The value reported in the 1965 mass table “) is Q = 7801.5t-2.7 keV.
Some excitation energies in 42K and the 4*K(n, Y)~‘K reaction energy are given in
table 5.
The decay schemes of 40K and 42K are shown in figs. 3 and 4, respectively. The
excitation energies, the intensities of the primary y-rays and the branching ratios for
the bound states are from the present investigation. The l,(d, p) values for levels
in ““K and 42K are from ref. lo) and ref. 31), respectively; spins and parities are
from ref. 13) and ref. 32), respectively.
Table 6 lists the coincidence relations obtained from the coincidence measurements.
In table 7 the y-ray energies of strong background lines as calculated from the
present investigation are compared to the values given by other authors.
Some rather strong y-rays from the 39K ( n, Y)~‘K reaction could not be positioned
between levels known from the (d, p) work I’). They were supposed to correspond to
decay via other levels if both feeding and de-exciting y-rays were observed (with
energies checking within the experimental errors), and if the intensity balance was
satisfactory, This has lead to four additional levels at E, = 2731,3439,4149 and 4744
keV. These levels have also been reported in ref. “).
580
A. M. F. OP DEN KAMP
AND A. M. J. SPITS
3gK + n
J= I,,
h+ (d.p)
Fig. 3. Decay scheme of “OK. The intensities of the primary y-rays are normalized such that the sum
equals 100. Branching ratios of the bound levels are given in percent.
THERMAL-NEUTRON
CAPTURE
Fig. 4. Decay scheme of 42K.
TABLE5
Excitation energies of some levels in 42K
& WV) 9
E, WV) “1
107.110.3
258.5f0.3
639.0f0.5
682.0f0.3
844.9 ho.6
1113.3kO.4
1255.OhO.6
1378.7f0.7
1861.9f0.5
7533.9kO.9 b)
“) The results are obtained from a least-squares
b, Reaction Q-value.
analysis (see text).
TABLE6
Results of yy coincident measurements
Gate *)
(E, in keV)
6999
5752
5730
5696
5510
5381
Coincident y-rays
(I?,, in keV)
770
770,
770,
770,
331,
770,
“) Windows placed on the corresponding
1247,2018,2048
1178, 1269, 2040, 2010
1303, 2074
646, 770, 1159, 1490, 1929
1159, 1619, 1929, 2389, 2419
double-escape
peak in the Ge(Li) spectrum
581
582
A. M. F. OP DEN
KAMP
AND A. M. J. SPITS
TABLE 7
Energies of the strongest background y-rays
Reaction
E, +E, “1 (keV)
present work
other work
110.1~0.2
197.2hO.3
583.5hO.3
656.1 ho.3
109.8 10.2
197.2 kO.2
583.5 &0.2
656.3 10.3
655.9 10.2
983.8 10.3
983.9 AO.3
1261.76~0.07
1261.92f0.06
1293.58&0.06
1633.7 f0.3
1778.70&0.17
1779.1 +0.3
2223.35f0.05
“)
6129.6 10.4
6130.2 +0.4
7250.0 * 1.0
7250.0 *0.5
7278.5 10.7
7367.5 10.7
7630.9 10.6
7645.3 10.6
983.4kO.4
1261.9f0.4
1293.6kO.3
1633.610.3
1778.910.3
2223.3 ho.2 b,
6129.6hO.8
7250.3zhO.9
7278.211.0
7367.8hl.O
7631.1 +I.0
7645311.0
“) The energy of the recoil correction
“) Uncorrected for recoil.
ref.
is denoted by E,.
5. Discussion
Results from the present investigation are generally in agreement with those reported in refs. ‘. rz, 13), though many differences occur especially with the results reported
in ref. g), for the low-energy region. Some of the discrepancies are discussed
below.
5.1. LEVELS NOT REPORTED IN REF. *)
The ii& = 2261 keV level. The 2261 keV state de-excites by the 2231 and 2260 keV
y-rays. The first transition has not been reported in ref. ‘); the second is interpreted
as a 2290 -+ 30 keV transition. This interpretation has to be rejected because the
2260 keV y-ray is not coincident with the 5510 keV y-ray, which feeds the E, = 2290
keV state. The present interpretation for the 2260 keV y-ray, as a ground state transition, is based on intensities and is in agreement with the interpretation reported in
ref. 13).
The E, = 2290-2291 keV doublet. The computer program interprets the 2291 and
1399 keV y-rays as de-exciting the 2290 keV level; the latter feeds the E, = 892 keV
THERMAL-NEUTRON
CAPTURE
5x3
level. However, the two y-rays are not observed in coincidence with the 5510 keV
y-ray feeding the E, = 2290 keV level. Another position in the decay scheme is impossible for either y-ray. This indicates a doublet at E, = 2290 keV. The cascade
y-rays feeding the E, = 2291 keV level have also been observed. The existence of the
doublet is also suggested by Twin et al. 13) on the basis of y-ray angular distributions.
The excitation energies are calculated as E, = 2289.8kO.3 and 2290.5kO.3 keV.
The E, = 2397 keV level. The decay of the E, = 2397 keV level has also been
observed in the 40Ar(p, ny)40K reaction 13). The decay of this level is not reported
in ref. ‘3, although the 2367 keV y-ray, which must be interpreted as a transition to
the Ex = 30 keV level, was observed. Of the three y-rays at Ey = 1233, 1266 and
1424 keV feeding the E, = 2397 keV level, only the first has been reported in ref. “).
The E, = 3923 keV level. None of the y-rays (E, = 555, 1820 and 1965 keV) deexciting the E, = 3923 keV level has been reported in ref. “). They appear clearly in
the single spectrum (see fig. 1). The E,, = 3877.O-tO.8 keV y-ray which feeds the
E, = 3923 keV level has been reported in ref. “) with slightly different energy:
E, = 3875.2kO.8 keV.
The E, = 4666 keV level. The 3133 and 2375 keV y-rays feeding and de-exciting
the Ex = 4666 keV level, respectively, have also been reported in ref. “>. Another
interpretation has been given because the E, = 2290 keV level was not recognized
as a doublet.
5.2. LEVELS REPORTED IN REF. p, BUT NOT FOUND IN THE PRESENT
INVESTIGATION
The E, = 2458,2558,4273 and 4281 keV levels. None of these levels has been
reported [ref. ‘“)I f rom the (d, p) reaction. A 5341 keV y-ray, ZY= 0.10+0.03,
reported “) to feed the E, = 2458 keV level has not been observed in the present investigation. An upper limit for the intensity of this y-ray should be Z, = 0.03. The
intensity balance for the reported E, = 2458 keV level is poor: Zi,/ZoUt= 0.14kO.12.
Two y-rays, E, = 1695 and 2558 keV, feeding and de-exciting the E, = 2558 keV
level, respectively, have been reported in ref. “). The 1695 keV y-ray should be interpreted as de-exciting the E, = 3797 keV level. A peak at 2558 keV has not been observed (Z, 5 0.06) in the present investigation. The reported intensity of the 2558 keV
y-ray is Z, = 0.60t0.13.
From the five y-rays at E, = 1646, 2629, 3382, 3473 and 4254 keV, with I7 =
0.2OI):O.O5,0.40+0.10, 0.3050.07, 0.20+_0.05 and 0.20+0.05, respectively, reported
[ref. “)I to de-excite the E, = 4273 keV level, only one y-ray (3414 -+ 30 keV) has
been observed in the present work (ZY= 0.42f0.10). The upper limits for the intensities of the other y-rays are 0.03,0.08,0.03 and 0.10, respectively. The reported y-rays
are transitions to levels with .Z” = O-, O+, 2-, 3- and 5-. Consequently, whatever
the J” value of the 4273 keV level, one or more transitions should at least have octupole character, which also makes the given interpretation, and therefore the existence
of the E, = 4273 keY level, doubtful.
584
A. M. F. OP DEN KAMP
AND
A. M. J. SPITS
The 297 keV y-ray, observed in the present investigation and which has been reported “) to feed the E, = 4281 keV level must be ascribed to thermal-neutron capture
in 72Ge. The three y-rays reported “) to de-excite this level have also been observed
in the present experiment but the energies are such that they cannot originate from
one level.
The E, = 3027 and 3768 keV levels. Levels at E, = 3030f4 and 3768+4 keV
are given in the review article of Endt and Van der Leun 1‘). From the three y-rays
which are reported “) to de-excite the E, = 3027keV level, the 609 keV y-ray, also
observed in the present investigation, must be ascribed to the 73Ge(n, y)74Ge reaction, while the 973 and 2136 keV y-rays with ZY= 0.10 +0.03 and 0.20&0.05, respectively, have not been observed in the present experiment (Z, 5 0.01 and 6 0.01,
respectively).
From the two y-rays, which are reported “) to de-excite the E, = 3768keV level,
the 1173 keV y-ray must be ascribed to background radiation, while the peak at 3768
keV must be interpreted as the single-escape peak of the 4279 keV y-ray.
5.3. THE DECAY
OF SOME LOW-ENERGY
LEVELS
The ground state transition of the first excited state is not observed in the present
experiment because of the strong low-energy background radiation near the reactor.
The excitation energy calculated from energy differences, E, = 29.8kO.2keV, is in
reasonable agreement with the value reported in ref. “) (E, = 29.52fO.10keV).
The decay of the E, = 800keV second excited state proceeds entirely via a 770 keV
y-ray to the E, = 30 keV state. The E, = 799.4f0.2keV y-ray cannot be interpreted
as a ground state transition of the E, = 800.1
f0.2 keV state as suggested by Johnson
and Kennett ‘). This y-ray has not been reported by Bass and Wechsung 24), Freeman
and Gallman r2) or Twin et al.13),
which also indicates that this is a transition between two high-energy levels (4537 -+ 3738 keV).
The branching ratios of the next five levels at E, = 892,1644, 1959, 2047 and
2070 keV are in good agreement with the results reported in refs. 9*13). The decay
of the E, = 2047 and 2070 keV levels is confirmed by coincidence measurements
(table 6).
A 2105 keV ground state transition (Z, = 0.80+0.15) from the E, = 2104 keV
level as reported in ref. ‘) is less probable because (i) this transition is not reported
in refs. r2, 13*24)) (ii) a 2104 keV y-ray has not been observed in the present single
spectrum (ZY5 0.06),
(iii) the present coincidence measurements which confirm the
other decay branches from the 2104 keV state do not give any evidence for the existence of a 2104 keV y-ray.
One of the y-rays de-exciting the E, = 2419keV level, E, = 459 keV (feeding the
E, = 1959keV level, has not been reported in ref. 13). Alternatively it can be interpreted as a transition between the E, = 2104 and 1644 keV levels. Observed coincidences between the 5381 keV y-ray, which feeds the E, = 2419 keV level, and the
1929 and 1159 keV y-rays de-exciting the E, = 1959keV level make the interpretation
THERMAL-NEUTRON
CAPTURE
585
given here more probable. In the coincidence spectrum the 459 keV peak is obscured
by the strong 511 keV annihilation peak.
The intensity of the y-rays feeding the E, = 2575 keV level is found to be too low
(table 4). The decay of this level entirely proceeds by the 2546 keV y-ray. This interpretation is supported by the 40Ar(p, ny)40K data 13).
Different branchings have been found for the E, = 2626 keV level. The present
result is in good agreement with that reported in ref. “).
5.4. SOME J?INAL REMARKS
ON THE 3gK(n,y)40K
DECAY
Discrepancies exist with the results obtained by Johnson and Kennett ‘) also for
some high-energy levels (see table 4). These differences can mainly be explained by
(i) different interpretations of the observed y-rays in the decay scheme, (ii) differences
in the energies of the observed y-rays, (iii) differences in the interpretation of some
peaks as full-energy, single- or double-escape peaks and (iv) a number of y-rays which
have been reported in ref. ‘) as originating from the 39K(n, Y)~‘K reaction could be
ascribed to background radiation or have not been observed in the present investigation. The intensities of these latter y-rays are such that they would have been observed in the present investigation if they would originate from the 39K(n, Y)~‘K
reaction. Some examples have been given in subsect. 5.2.
It was not possible to assign spins unambiguously on the basis of the present experiment, though for some levels spin restrictions may be possible.
5.5. REMARKS
ON THE 41K(n,y)42K
DECAY
Energies and intensities of y-rays from the 41K(n, Y)~‘K reaction have been reported by Skeppstedt s) who used a sample enriched to 99.2 y0 in 41K. Some y-rays from
the 41K(n, Y)~‘K reaction (investigated with a natural potassium target) have also
been reported by Johnson and Kennett ‘).
Three y-rays at 433,532 and 640 keV, reported ‘) as originating from the 39K(n, y)
40K reaction must be ascribed to the 41K(n, Y)~‘K reaction, according to the present
investigation. This interpretation is in agreement with that reported in ref. “). The
532 and 640 keV y-rays de-excite the E, = 639keV level; the first feeds the E, = 107
keV level. A capture y-ray at 6894 keV feeds the E, = 639 keV level. This y-ray has
also been reported in ref. *), but not in ref. ‘).
By Johnson and Kennett “) a 6915 keV capture y-ray has been reported, leading to
E, = 619keV, but y-rays de-exciting this level have not been observed. In the present
investigation this y-ray has been observed, but could be ascribed to background radiation.
It is a pleasure to thank Professor P. M. Endt and Drs. C. van der Leun and H.
Gruppelaar for their interest in this work. We like to thank V. Haase from the Kernforschungszentrum Karlsruhe for the Gauss-fit program and C. J. Zwakhals, T. van
Ittersum and J. Akkermans for their help in the analysis of the spectra. This investi-
586
A. M. F. OP DEN KAMP AND A. M. J. SPITS
g&ion was performed as part of the research program of the Stichting voor Fundamenteel Onderzoek der Materie (FOM) with financial support from the Nederlandse
Organisatie voor Zuiver Wetenschappelijk Onderzoek (ZWO).
References
1)
2)
3)
4)
5)
6)
7)
8)
9)
10)
11)
12)
13)
14)
15)
16)
17)
18)
19)
20)
21)
22)
23)
24)
25)
26)
27)
28)
29)
30)
31)
32)
T. H. Braid, Phys. Rev. 102 (1965) 1109
J. Urbanec, J. Kopeckg and J. Kajfosz, Czech. J. Phys. 9 (1959) 544
B. B. Kinsey, G. A. Bartholomew and W. H. Walker, Phys. Rev. 85 (1952) 1012
G. A. Bartholomew and B. B. Kinsey, Can. J. Phys. 31 (1953) 927
B. P. Adyasevich el al., Atom. Energ. 1 (1956) 28; J. Nucl. Energ. 3 (1956) 325
W. Rudolph and H. U. Gersch, Nucl. Phys. 71 (1965) 221
T. J. Kennett, L. B. Hughes and W. V. Prestwich, Nucl. Phys. 89 (1966) 254
0. Skeppstedt, Proc. of the Int. Symp. on neutron capture gamma ray spectroscopy,
Studsvik, 1969, p. 217
L. V. Johnson and T. J. Kennett, Can. J. Phys. 48 (1970) 1109
H. A. Enge, E. J. Irwin and D. H. Weaner, Phys. Rev. 115 (1959) 949
P. M. Endt and C. van der Leun, Nucl. Phys. A105 (1967) 1
R. M. Freeman and A. Gallmann, Nucl. Phys. Al56 (1970) 305
P. J. Twin, W. C. Olsen and D. M. Sheppard, Nucl. Phys. Al43 (1970) 481
G. A. Ba~holome~v et al., Nucl, Data A3 (1967) 367
G. van Middelkoop and P. Spilling, Nucl. Phys. 72 (1965) 1
P. Spilling, H. Gruppelaar and P. C. van den Berg, Int. Symp. on Nucl. Electronics, Versailles, 1968, Part II, Contr. 140
C. M. Lederer, J. M. Hollander and I. Perlman, Table of isotopes, 6th ed., appendix II (Wiley,
New York, 1967)
P. Spilling, H. Gruppelaar, II. F. de Vries and A. M. J. Spits, Nucl. Phys. All3 (1968) 395
R. L. Graham, Nucl. Instr. 9 (1960) 245
W. W. Black and R. L. Heath, Nucl. Phys. A90 (1967) 650
H. W. Taylor, N. Neff and J. D. King, Phys. Lett. 24B (1967) 659
J. H. E. Mattauch, W. Thiele and A. H. Wapstra, Nucl. Phys. 67 (1965) 32
H. Gruppelaar, A. M. F. Op den Kamp and A. M. J. Spits, Nucl. Phys. A131 (1969) 180
R. Bass and R. Wechsung, Phys. Lett. 32B (1970) 602
T. M. Young et al., Bull. Am. Phys. Sot. 15 (1970) 1329
T. Holtebekk, S. Tryti and G. Vamraak, Nucl. Phys. Al34 (1969) 353
W. V. Prestwich, R. E. Cot6 and G. E. Thomas, Phys. Rev. 161 (1967) 1080
D. H. White and D. J. Groves, Nucl. Phys. AQl (1967) 453
A. M. J. Spits, A. M. F. Op den Kamp and H. Gruppelaar, Nucl. Phys. Al45 (1970) 449
R. C. Greenwood, Phys. Lett. 23 (1966) 482
U. Lynen, H. Oeschler, R. Santo and R. Stock, Nucl. Phys. Al27 (1969) 343
W. H. Moore, J. W. Kelley and II. A. Enge, MIT Lab. Nucl. Sci. Ptogr. Rept. May 1958, p. 114