low-lying positive-parity states in 71ge

Nuclear Physics A171 (1971) 435-448; @ North-Holland Publishing Co., Amsterdam

Not to be reproduced by photoprint or microl%n without written permission from the publisher

LOW-LYING POSITIVEPARITY STATES IN “Ge

G. MURRAY, N. E. SANDERSON and J. C. WILLMOTT

Physics Department, University of Manchester, England

Received 29 March 1971

Abstract: The 20 ms “Ge isomeric activity has been positively identified with a 198.4 keV #+ level, by measuring the conversion coefficient of the transition involved. The energies and relative intensities of the y-rays following the decay of “As have been measured, and log ft values calculated. A level scheme for ‘rGe is proposed and compared with the schemes deduced from the (d, p) scattering measurements of Goldman and the (p, ny) measurements of Malan. It is deduced that the first anomalous positive-parity state in ‘rGe is the &+ 525.1 keV level.

E RADIOACTIVITY “rmGe, 71As [from 70Ge(d, p), ‘OGe(d, n)] measured T+, EY, I,, r/-coin; deduced log ft. ‘IGe deduced levels, J, n. Enriched target, Ge(Li) detector.

1. Introduction

A number of anomalous low-lying 3’ and 3’ states have been identified in nuclei with N = 39, 41, 43, 45 and 47 and the available information ‘) on the occurrence of such levels is summarized in fig. 1. The observation ‘) of the 3’ ground state in i$eag led to the present study of the levels of ‘I 32Ge,g in view of the conflicting assignments of 4’ and 3’ for the 198 keV level in ‘lGe arising from previous work as discussed below.

Previous results on the ‘lGe level scheme are summarized in fig. 2. The ‘IGe ground state and 174.8 keV level have been positively identified as having spins of &- and $- respectively and the half-life of the 174.8 keV level has been measured to be 70 ns [ref. “)I. The 198 keV level has been assigned a spin of 3’ by Thulin et al. “)

and 3’ by Graves and Mitchell “). The two assignments arise from conflicting results obtained by the two groups on the conversion electrons following the decay of ‘lAs as summarized in table 1. There is however agreement on the absence of a direct /3- transition from the ‘lAs ground state to the ‘lGe ground state and consequently on a spin of +- for the ‘lAs ground state. Logft values of 7.8 [ref. ‘)I or 8.4 [ref. “)I may be deduced for the transition from the “As ground state to the 198 keV ‘lGe level according to the weight given to the different results in table 1. Graves and Mit- chell “) also reported observing a 23 keV y-ray transition using a NaI(T1) detector although they did not measure its half-life. If this is assumed to be the transition between the 198 keV and 175 keV levels, it lends weight to their assignment of 3’ for the 198 keV level, for reasons discussed in sect. 3.

435

436 G. MURRAY et al.

The ‘IGe 175 keV y-ray has been observed to be associated with a 20 ms half-life in ‘lGa(p, n) [ref. “)I, “Ge(d, p) [ref. ‘)I, 72Ge(p, pn) [ref. *)I and “Ge(n, y) [ref. ‘)I studies. Since the 175 keV level has a half-life of 70 ns, the 20 ms activity has been assumed to be associated with a 23 keV transition from the 198 keV level to the

32 34 36 30

Z Value Fig. 1. The occurrence of low-lying anomalous 4’ and $+ states in the region12 = 32-38, N = 39-47.

f 1.95

1.70

1.55

I.38

” P

1.09

2 I.01

or a41

v2- 71

O Ild

Ge 32 39

Fig. 2. The ‘IGe level scheme based on previous work.

“Ge STATES 437

TABLE 1

Conversion electron data

Intensity ratios ‘) Graves and Mitchell 3, Thulin et al. 4,

K17s/h NN 10 1.5 L/(L+M)2~ M 1 5.490.8 KI.IS/(L+M)~~S 6.3 8.9h1.0 tLYI75 0.095 0.07 (K+L+M+Y/),B W+L+M+y),,s

B 0.01 0.055

“) Subscripts refer to y-ray energies in keV.

175 keV level, although no 20 ms y-ray of this energy has been observed. If this is so it strongly favours an M2 transition and hence a spin of $+ for the 198 keV level. There is however no direct evidence that the transitions in the two types of work are identical, and for this reason the possibility of an anomalous 3’ level at, or close to 198 keV led to this investigation. The higher excited states of “Ge shown in fig. 2 are from the “Ge(d, p) work of Bochin et al. lo) and Goldman ‘I).

In the present work experiments have been carried out to determine the level in 71Ge which has the 20 ms half-life, to measure the c(k of the 23 keV transition and to establish the decay scheme of ‘IGe and hence the logft value of the transition from the ‘IAs ground state to the 198 keV level, in order to resolve the present uncertainty in the spin of this level.

During the course of this work a paper was published by Malan et al. “), who in- vestigated the level structure of 71Ge using the ‘lGa(p, nr) reaction. The results of this paper will be discussed in sects. 5 and 6.

2. The “Ge 20 ms isomeric level

The ‘lGe isomeric activity was produced by the “Ge(d, p) reaction using the Manchester HILAC. Electromagnetically separated “Ge targets of thickness 5 mg/cm’ on 25 mg/cm’ gold backings were used (“Ge - 87.7 %; 72Ge - 5.3 %; 73Ge - 1.2 %; 74Ge - 4.6 %; ’ 6Ge - 1.2 “/o). The beam pulse was 2.0 ms in duration with a repetition rate of 10 per second. The radiation from the target was studied, in between beam pulses, using a 0.4 cm3 Ge(Li) detector which had a resolution of 500 eV at 14.4 keV, and a 0.25 mm thick beryllium window giving an intrinsic detector efficiency for 23 keV y-rays of 90 “4. An Ortec preamplifier (Model series no. 98) and an amplifier built after the design of Goulding 13) were used for pulse amplification. Pulses from the amplifier were fed into a Laben 4K channel A.D.C. and stored in a DEC PDP 9 computer. In order to follow the decay of the isomeric activity, y-ray spectra were recorded at 10 ms intervals between beam pulses. The beam intensity during the pulse was 0.02 PA and the deuteron energy was 8.4 MeV. A typical spectrum is shown in fig. 3. The half-lives of the 174.9kO.l keV and 23.5 +O.l keV y-rays


I a W

AVM -x nv I~c8-----, AVU -X nV b.tL-

AVci-X 01 9 .LS-----+ AVtj-X 01 c.9s -

a9.cs - w

d

I”

“Ge STATES 439

were found to be 22.25 1.0 ms and 23.0 +4.9 ms respectively. No other y-rays were observed to be associated with the 22 ms activity. The ratio of the intensities of the 174.9 keV and 23.5 keV y-rays was 190+37 where the quoted error includes contributions from the counting statistics and the uncertainty in the energy dependence of the counter e5ciency. The efficiency was measured using sources of 241Am, “Co, 13’Cs ‘03Hg of known strength supplied by IAEA Vienna, and a “Se source.

Thd results of the preceeding paragraph, in particular the absence of any y-rays of energy greater than 174.9 keV associated with the 22 ms activity, together with the results on the ‘IGe level structure from the (d, p) scattering work of Goldman II), can only be interpreted on the basis that the isomeric activity is associated with the 198.4 keV level. The results on the y-ray intensities imply an u of 206+40 for the 23.5 keV transition where an a of 0.086 has been assumed for the 174.9 keV E2transition ‘). As discussed in the introduction, previous workers have assigned spins of 3’ and e+ [refs. 3* 4)] to the 198.4 keV level. An El transition and an M2 transition of energy 23.5 keV would be expected to have an u of 4.9 and 214 respectively and a half-life, based on single-particle estimates, of the order lo-l1 s and 10m3 s respectively. We therefore conclude that the ‘lGe 198.4 keV level has a spin and parity of 3’.

3. The 23 keV transition following the “As /I-decay

The work of the preceding section has established that the ‘IGe 198.4 keV level is 2+, but the possibility of a )’ state close to this level must also be considered in view of the fact that Graves and Mitchell 3), using NaI(T1) crystals, observed a 23 keV y-ray following the decay of ‘IAs. The intensity of this 23 keV y-ray was not quoted, but from considerations of the likely logft values and internal conversion coeffi- cients such an observation would appear to favour an interpretation based on a first- forbidden B-decay followed by an El transition rather than the unique first-forbidden b-decay followed by an M2 transition which would be the case if the positon decay went to the 198.4 keV 8’ level. This part of the experiment of Graves and Mitchell has therefore been repeated.

Radioactive sources of 61 h ‘IAs were prepared by bombarding “Ge targets (see sect. 2) for 7 h with a 2.5 PA, 8.4 MeV deuteron beam from the Manchester HILAC. The sources were left for several hours to permit the short-lived activities, produced by reactions other than “Ge(d, n)‘lAs, to decay. The radiation from the targets was then studied using the Ge(Li) detector described in sect. 2 and those sections of the spectrum in the region of 23 keV and 175 keV are shown in fig. 4. Other y-rays following the decay of ‘IAs will be discussed in sect. 4. The energies of the two lines were measured to be 23.5 kO.1 keV and 174.9 fO.l keV using y-rays and X-rays of known energy in 241Am, 5 ‘Co, ‘03Hg, 13’Cs and “Se sources, calibration and ‘I As source runs being alternated to minimize the effect of any time-dependent gain changes in the amplifiers. The relative intensity of the 174.9 keV and 23.5 keV y-rays is 4430 + 886 where the quoted uncertainty includes contributions from counting statistics and the


energy dependence of the counter efficiency. The associated half-lives of the 174.9 keV and 23.5 keV y-rays were measured to be 61 f2 h and 65If: 10 h by recording a series of spectra at 10 h intervals for several days after the irradiation.

We can compute the conversion coefficient ~1, of the 23.5 keV transition following

GAMMA SINGLE

TARGET “Ge

BEAM 8.4 MeV

ENERGIES IN ke

COUNTS

PER

CHANNE L

d

i

174.9

I

i t I

930 850 900 CHANNEL

Fig. 4. The 23.5 keV and 174.9 keV y-rays following the &decay of “As observed with a Ge(Li) detector.

the “As p-decay by combining the results of the preceding paragraph with the previous work on the conversion electron intensities summarized in table 1. On the as- sumption that the 174.9 keV transition is E2 with an a of 0.086, the results of Thulin et al. “) on the relative intensities of conversion electrons from the 23.5 keV and 174.9 keV transitions together with the present data on the corresponding y-ray intensities lead to a value of 270* 54 for the conversion co~~cient of the 23.5 keV transition as

“Ge STATES 441

compared with the value of 206240 found from the “Ge(d, ~)~lGe reaction in the previous section. On the other hand the results of Graves and Mitchell “) lead to a much lower value of 43 + 9.

In the next section we show that the 198.4 keV level is indirectly fed by y-rays of 326.8 keV and 391.4 keV. From the measured intensities of these and the 23.5 keV y-rays we can obtain a minimum value of the conversion coefficient for the 23.5 keV transition of 157 +32 by assuming there is no direct j-decay to the 198.4 keV level. This minimum value is again compatible with the value obtained using the results of Thulin, but not with that using theresultsof Graves. Thelow valueof the (K/(L+ M))23 ratio given by Graves in table 1 compared with the theoretical M2 value of 4.2 could be the result of an underestimation of the effect of the counter window cut-off on the low-energy K, a conversion electrons.

The conversion coefficient of the 23.5 keV transition may also be deduced from our y-ray data and the value of 0.055 for the (K+L+M+~),J(K+L+M-I-~)~~~ ratio given by Thulin et al. This leads to a conversion coefficient of 264 2 53.

From the results in the above paragraphs we conclude that the 71As /?-decay pop- ulates a level at 198.4 keV which decays by an M2 transition to the 3_- level at 174.9 keV and therefore that this 198.4 keV level is identical to the 20 ms, 198.4 keV level discussed in sect. 2. There is therefore no evidence from the present work to support the possibility of a closely spaced pair of levels around 198 keV with spins of 8’ and

3’.

4. The “Ge level scheme

In order to calculate the logff value of the unique first-forbidden B-transition from the “As _5- transition to the ‘IGe 8’ 198 keV level, a knowledge of the relative intensities of the P-branches to the ‘lGe levels is required. For this purpose sources of 71As were produce d in the way described in the preceding section.

Singles y-ray spectra were studied using a 25 cm3 Ge(Li) detector with a resolution of 2.2 keV at 1.3 MeV. A typical spectrum is shown in fig. 5 and the energies, intensities and associated half-lives were obtained by the methods described in the preceding sections, using standard y-ray sources of 241Am, ‘03Hg, 57Co, 137Cs, 54Mn, 22Na and 6oCo. Su~ciently strong sources of ‘IAs were produced so that y-rays of intensity < 0.1 y0 that of the 174.9 keV line could be observed. Gamma rays following reactions on the other germanium isotopes, present in reduced abundance in the target, and on the gold backings were also observed and identified by their energies and associated half-lives (see fig. 4).

Gamma-gamma coincidence measurements on a similar source were made using two 35 cm3 Ge(Li) detectors of resolution 2.2 keV at 1.3 MeV, positioned at 90” to each other. A standard fast-slow coincidence system with a resolution of about 40 ns was used, and coincidences were recorded over a 48 h period in the PDP 9 computer using an on-line programme. In view of the very large number of low-energy transi-


:_

I

i

C’LLS -

71Ge STATES

I


TABLE 2

y-rays associated with the decay of 7iAs

Energy (keV) Half-life (h) Intensity Measured in coincidence with detector 1

23.5kO.l 174.9ztO.l 247.3 10.2 279.250.2 305.9f0.4 326.810.2 348.3f0.4 350.1 kO.2 373.7hO.2 391.410.2 392.0f0.4 431.110.4 46X3&0,2 500.0&0.2

503.9hO.4 526.710.2 570.3f0.4 572.3 SO.2 59.5.4rto.4 615.4f0.2 639.5 f0.2 658.5kO.4 679.7kO.4 698.0+0.4 708.210.2 712.6f0.2 747.2rt0.2 s31.4*0.4 851.7hO.2 906.950.2 920.7f0.2 964.510.2

1006.7f0.2 1026.8f0.2 1033.8f0.2 1037.7f0.2 1059.1 kO.4 1095.7+0.2 1098.6+0.4 1139.5f0.2 1212.710.2 1231.8f0.2 1274.7kO.2 1298.810.2 1331.8f0.2

65flO 61& 2 601 7 54* 4

65f 3

54* 5 49415 604 3

59*14 59* 2

561 3

55% 6

56Ifi 3 70+15

551 4 76i- 9 64L- 8

65& 8 6OL-15 6Ok 6 77121 74f20 55& 4 55f 4 61&- 4

62+ 2

61f 2 581 3 73f16 55+10 69f 7 501 9

0.023 f0.005 100 & 350.1, 511.0, 572.3, 851.7, 920.7, 1037.7

0.16 +0.02 279.2, 348.3, 392.0, 465.3, 500.0, 511.0, 658.5 0.21 +0.02 247.3, 500.0, 511.0, 572.3, 747.2 0.02 *0.005 3.2 10.3 305.9, 373.7, 511.0, 570.3, 679.7, 1033.8 0.04 fO.O1 174.9, 247.3, 500.0, 511.0, 572.3, 747.2 0.26 kO.03 511.0, 570.3, 679.7, 1033.8 0.09 ho.01 305.9, 326.8, 511.0, 831.4 0.60 f0.06 511.0, 615.4 0.07 +O.Ol 247.3, 500.0, 511.0, 572.3, 747.2 0.03 40.007 0.10 *to.01 247.3, 500.0, 511.0, 572.3, 747.2 3.4 50.3 247.3, 279.2, 465.3, 511.0, 595.4, 639.5, 712.6, 906.9,

1006.7, 1059.1, 1098.6 0.18 rtO.02 0.80 10.08 500.0, 511.0 0.03 fO.007 326.8, 350.1, 511.0 0.20 &to.02 279.2, 348.3, 392.0, 511.0, 658.5 0.10 30.01 0.50 10.05 391.4, 511.0 0.04 I-to.05 0.07 *0.01 0.08 10.02 0.03 &0.007 0.26 10.03 387.1, 431.1, 503.9, 511.0, 698.0 0.34 kO.3 500.0, 511.0 0.16 kO.02 279.2, 348.3, 392.0, 511.0, 658.5 0.06 kO.01 373.7, 511.0 0.20 kO.02 0.04 10.005 0.30 f0.03 0.08 *0.01 0.06 kO.01 0.40 f0.04 0.22 f0.02 0.21 f0.02 0.03 &0.007 5.0 f0.5 0.11 fO.O1 0.95 fO.O1 0.40 +0.04 0.07 fO.01 0.10 +0.01 0.24 +0.02 0.08 50.01

tions (175 keV), detector I was set for a dynamic range of 160-1400 keV and detector

II for a range of 240-1400 keV. Each event, consisting of one time pulse and two y-ray

71Ge STATES

?bJ

-

- -

-

!

446 G. MURRAY et af.

pulses, was coded in two 1 &bit words and stored on IBM compatible tape. An off-line programme enabled the data to be recalled and y-rays in coincidence with any transition could be selected by setting a suitable “window” over the peak of interest. Allowances for background contributions were made by setting further “windows” above and below the peak. Typical spectra obtained in this way are shown in fig. 6.

Table 2 contains the information from these two experiments. All the y-rays be- lieved to be associated with the decay of ‘IAs are listed with their relative intensities and, where appropriate, associated half-life and coincidence measurements. It can be seen that transitions of energy 350.1 keV, 391.4 keV and 572.3 keV found in the singles spectra are in fact closely spaced doublets. The remaining transitions observed only in

TABLE 3

Energy sums relevant to the “Ge level scheme

Direct y-ray energy measurement = 174.9 &O. 1 1212.7&0.2-1037.7kO.Z = 175.0z+z0.3 1139.5f0.2- 964.5f0.2 = 175.Oz!zO.3 1095.7&0.2- 920.710.2 = 175.OhO.3 1026.8&0.2- 851.710.2 = 175.110.3 747.2;,0.2- 572.3i0.2 = 174.950.3

Direct y-ray energy measnrement = 23.5fO.l 350.1 -&O.t- 326.8iO.2 = 23.3+0.3

1331.8f0.2-1006.710.2 = 325.110.3 1231.8&0.2- 906.9-&0.2 = 324.9hO.3 1037.7IfrO.2- 712.6kO.2 = 325.1&0.3 964.5&0.2- 639.5f0.2 = 325050.3 920.7&0.2- 595.4&0.4 = 325.3k0.4 851.7&0.2- 526.7*0.2 = 325.OhO.3 572.3+0.2- 247.3f0.2 = 325.OkO.3

Direct y-ray energy measurement = 500.0&0.2 1212.7&0.2- 712.610.2 = 500.110.3 1139.5&0.2- 639.5rtO.2 = 500.0k0.3 109.5.7~0.2- 595.410.4 = 500.3iO.4 1026.8&0.2- 526.710.2 = 500.1 -CO.3 747.2&0.2- 247.310.2 = 499.9f0.3

1095.7-&0.2- 570.3kO.4 = 525.4&0.4 831.4-&0.4- 305.9kO.4 = 525.530.6

Direct y-ray energy measurement = 708.2kO.2 1212.7&0.2- 503.9f0.4 = 708.8+0.4 1139.Sf0.2- 431.1f0.4 = 708.4f0.4 1095.7&0.2- 387.1 f0.4 = 708.6f0.4

Direct y-ray energy measurement = 747.2kO.2 1212.7&0.2- 465310.2 = 747.410.3 1139.5&0.2- 392.010.4 = 747.5f0.4 1095.7f0.2- 348.310.4 = 747.4f0.4 1026.8&0.2- 279.210.2 = 747.6kO.3

‘IGe STATES 447

the yy coincidence work *dere obscured by impurities or background in the singles spectra. Gamma rays of 1231.8 keV, 1274.7 keV and 1332.0 keV were of too low intensity to be observed in the coincidence work.

The ‘IGe level scheme shown in fig. 7 has been established from the coincidence data and from a consideration of the relevant crossover sums. These are shown in table 3. The 1274.7 keV y-ray of intensity 0.1 % has not been included in the scheme.

Comparison with the scheme proposed by Malan et al. 12) using (p, ny) measurements shows complete agreement with the levels selected by our B-activity work. In addition we have confirmed the existence of levels at 1406.7 keV and 1559.0 keV, and uniquely assigned several transitions which were previously left in doubt. Gamma-ray energies and branching ratios are in good agreement.

On the basis of the present scheme 0.89 +0.81 % of the ‘IAs decays feed the 198.4 keV directly. This results in a logft value of 7.6&l: for the unique first-forbidden p-decay from ‘lAs to the 198.4 keV z 9+ level which is camp atible with the empirical range of values 8.5kO.5 published by Wapstra 14). The logft values for the other /3- transitions to ‘lGe levels are shown in fig. 7.

5. Discussion

As stated in the introduction, the ground state of ‘lGe and the 174.9 keV level have spins of $- and 3- respectively. In the present work we have shown that the 198.4 keV level has spin 4’. It is clear that the 160 keV (3-) and 190 keV (3’) levels reported in the (d, p) scattering work of Goldman 11) correspond to these levels. Goldman also reported the possible existence of a 60 keV level in ‘IGe, but we have found no evidence for the existence of such a level, and the isomeric nature of the 198.4 keV 4’ level rules out the possibility of this being the lowest-lying anomalous 3’ or 3’ state. Levels at 480 keV, 700 keV and 1090 keV found in the (d, p) work with Z,, = 1 were assigned a spin of $- on the basis of the Lee-Schiffer effect. These levels could well correspond to the levels at 500.0 keV, 708.2 keV and 1095.6 keV found by Malan et al. 12) and by ourselves. However Malan et al. report that although the levels were fed directly from the “Ge $+(n, 7) capture state, allowing spins of 3, 3 or 3+, the states were strongly populated in the (p, n) reaction from the +- ‘lGa ground state implying spins of $3 or 3. In the present work we find that the logft values for the B-transitions from the 3- ” As ground state are compatible with Z-forbidden allowed transitions 14), leading to 3- states, but not with second-forbidden /?-transitions leading to $- states. We conclude that the spin of these levels is +-.

Goldman reported a level at 510 keV with a transferred orbital angular momentum of 2, and this could well correspond to the level at 525.1 keV. Neither of the two possible spin assignments of 4’ or 3’ can be ruled out by the measured logft value (6.9). However using Weisskopf estimates and mean enhancement and retardation factors [ref. ’ “)I for y-ray transition probabilities it can be shown that only El, Ml and E2 transitions are likely to be competitive, with M2 transitions already a factor 10 5 down,


and higher multipoles even less probable. Using this fact, the observation of a 326.8 keV transition to the 3’ 198.4 keV level excludes a 3’ spin assignment.

The 589.8 keV level decays only to the 9” 198.4 keV level implying a spin of 2 3. The 1205.1 keV level decays only to the 589.8 keV and 831.2 keV levels, and has a logft value of 7.0 implying spins of 5 or J-. The 747.2 keV and 831.2 keV levels were both strongly excited in the (p, n) reaction, both decay to the +- ground state and have logft values > 8.2. Spins off- or possibly 3’ are indicated. All the remanning levels have logfr values between 6.2-7.3 and similar y-decay properties. Spins of 3 are again indicated.

We conclude that the lowest-lying anomalous positive-parity state in “Ge would appear to be a 5’ state at 525.1 keV. In this case the occurrence and energy separation of the positive parity states in 71Ge would resemble more closely the situation in the odd isotopes of Ga and As, discussed most recently by Scholtz and Malik 1 “) rather than in the other odd Ge isotopes.

References

I) Nucl. Data 13, 4, 6 (1966) 2) G. Murray, W. J. K. White, J. C. Wiilmott and R. F. Et-&whistle, Phys. Lett. 28B (1968) 35 3) W. E. Graves and A. C. G. Mitchell, Phys. Rev. 97 (1955) 1033 4) S. Thulin, 3. Moreau and H. Atterling, Ark. Fys. 8 (1954) 219 5) C. M. Lederer, J. M. Hollander and 1. Perlman, Table of isotopes, 6th ed. (Wiley, New York,

1967) 6) A. M. Morozov, JETP (Sov. Phys.) 13 (1961) 72 7) A. W. Chardt and A. Goodman, Phys. Rev. 123 (1961) 893 8) A. M. Morozov and V. V. Remaev, JETP (Sov. Phys.) 16 (1963) 314 9) K. F. Alexander and H. F. Brinckmann, Ann. of Phys. 12 (1963) 225

10) V. P. Bochin er al. as reported in Nucl. Data lB-6-22 11) L. H. Goldman, Phys. Rev. 165 (1968) 1203 12) J. G. Malan, J. W. Tepel and J. A. M. de Vilhers, Nucl. Phys. Al43 (1970) 53 13) F. Goulding, private communication 14) Nuclear spectroscopy tables, A. H. Wapstra, G. J. Nijgh and R. Van Lieshout, p. 58 15) Nuclear spectroscopy tables, A. H. Wapstra, G. J. Nijgh and R. Van Lieshout, p. 71 16) W. Scholz and F. B. Malik, Phys. Rev. 176 (1968) 1355

low-lying positive-parity states in 71ge

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