Evaluation the relative emission probabilities for 56Co and 66Ga

1
Evaluation the relative emission probabilities
for 56Co and 66Ga

• Yu Weixiang Lu Hanlin Huang Xiaolong
• China Nuclear Data Center
• China Institute of Atomic Energy,
  
• P.O. Box 275(41), Beijing 102413,
  China
• e-mail huang_at_ciae.ac.cn

2
Measurement

• A 136cm3 coaxial Ge(Li) detector connected to an
  ORTEC-919 data acquisition system operating on a
  PC is used in present work. Spectra were recorded
  by the front face of the detector 17.5cm far from
  the source

3
Full-energy peak efficiency

• In the energy range from 100 to 2754keV, the
  primary standard radioactive sources with
  well-known activities were used to calibrate the
  absolute efficiencies of Ge(Li) detector. For
  example 24Na, 60Co, 54Mn, 65Zn, 137Cs and 133Ba
  were used to calibrate the efficiency curve in
  this region. At the same time, a mixed
  125Sb154Eu155Eu multi-energy source produced by
  National Institute of Standards Technology
  (NIST) with uncertainties in 0.6-1.3 was used.
• The I? values used in the calibration were taken
  from the Table of Isotopes, Eighth Edition. The
  uncertainties (one standard deviation) of these
  sources are about 0.6-1.3. The uncertainties of
  full-energy peak efficiency curve are about 1-2
  in this region.

4
Full-energy peak efficiency

• Above 2754keV, there are no radioactive sources
  suitable for efficiency calibration. Therefore,
  nuclear reactions are commonly used. In present
  work, the efficiency curve is obtained by the
  calculated results using the EGS4 M-C code above
  2754MeV, and calibrated at 6.13MeV using
  19F(p,??)16O reaction at resonance energy point
  Ep340keV.

5
Full-energy peak efficiency

6
Full-energy peak efficiency
7
Measurement

• By using the efficiency curve measured above,the
  new relative intensities were determined for the
  emitted ?-rays of 56Co and 66Ga. The final
  results are presented in Table 2 and 3,
  respectively.
• Its noted that our measurements are about 2
  lower than other new measurements in high energy
  range.

8
Measured relative ?-ray intensities for 56Co
9
Measured relative ?-ray intensities for 66Ga
10
Standards ?-ray emission probabilities for
14N(n,?)15N reaction

• The main measurements of the ?-ray emission
  probabilities for 14N(n,?)15N reaction are
  T.J.Kennett et al., E.T.Jurney et al., H.Takayama
  and T.Belgya. The main difference among these
  measurements are from the level scheme. For
  example, the levels are 15, 19, 19 and 17,
  respectively and ?-rays are 28, 58, 64 and 55,
  respectively corresponding to these measurements.
  
• Fig. 3 shows the comparison of the ?-ray emission
  probabilities. Its easy to find that the
  measurements of H.Takayama and E.T.Jurney et al.
  are in good agreement in 1.7-6MeV energy region.
  But the ratio of the ?-ray emission probabilities
  for Kennett/Jurney and Belgya/Jurney are exactly
  reverse(see Fig.4).

11
Standards ?-ray emission probabilities for
14N(n,?)15N reaction
12
Standards ?-ray emission probabilities for
14N(n,?)15N reaction
13
Standards ?-ray emission probabilities for
14N(n,?)15N reaction

• From Fig.4 its easy to find that the
  measurements of Kennett are higher about 1.2 to
  3.7 than Jurneys in 2.54MeV and 68MeV range.
  To average of these two measurements simplely is
  not suitable for the standard for detector
  efficiency calibration.
• About 58 ?-rays were observed in the measurements
  of Jurney, but only 30 ?-rays of Kennett. In
  order to keep the intensity balance(?I?(in-out)),
  the measured ?-ray emission probabilities of
  Kennett should be higher than Jurneys.
• We think that the ?-ray emission probabilities of
  Jurney are better than Kennett because the level
  scheme of Jurney is reasonable and complete.

14
Correction

• G.Molnar calibrated the detector efficiency curve
  using 14N(n,?)15N reaction, in which their ?-ray
  emission probabilities were from the measurements
  of T.J.Kennett et al.
• S.Raman calibrated the detector efficiency curve
  using 14N(n,?)15N reaction, in which their ?-ray
  emission probabilities were from the average of
  measurements of T.J.Kennett et al. and E.T.Jurney
  et al.
• So its necessary to correct the measurements of
  S.Raman and G.Molnar using the ?-ray emission
  probabilities of Jurney above 2.5MeV.
• In present work the level scheme suggested by
  Jurney is adopted to correct the ?-rays
  intensities of 56Co and 66Ga.

15
Previous evaluation I? for 56Co

• The decay data of 56Co were evaluated based on 33
  measured data sets from 1965 to 2002 years by
  C.M.Baglin et al. in 2004.
• Firstly several measured values are statistical
  outliers(about 11) according to the Chauvenet
  criterion. Secondly the measured data relied on
  linear extrapolations of the efficiency on a
  log-log plot above 3MeV were excluded. The rest
  measured data were processed by several
  evaluation methods weight average(WM),
  limitation of relative statistical weight
  average(LWM), normalized residuals method(NR) and
  Rajeval method(RA). At the same time, the whole
  measured data, the whole measured data except the
  exceed Chauvenet criterion value, were also
  processed by these evaluation methods.
• The recommended values are obtained from one of
  these processed values according to authors
  judgments. Its easy to find that the final
  recommended data are evaluated based on the whole
  measured data below 2598keV and 8 data sets above
  2598keV.

16
Present evaluation I? for 56Co

• Fig.5 shows the comparison of the ratio of newly
  measurements of S.Raman et al.,G.Molnar et al.
  and present work above 2.5MeV, present evaluation
  below 2.5MeV to the evaluations of C.M.Baglin for
  the relative ?-ray emission probabilities of
  56Co. Below 2.5MeV the present evaluation is in
  good agreement with Baglins within 0.4. But
  above 2.5MeV, the evaluation of Baglin is larger
  than the newly three measurements.
• The similar trend can be found for 66Ga (see the
  next section in detail). We think that the
  different detector efficiency curve may cause
  this discrepancy.

17
Present evaluation I? for 56Co
18
Present evaluation I? for 56Co

• The modified values of S.Raman and G.Molnar using
  the ?-ray emission probabilities of Jurney for
  56Co are listed in table 2. Its noted from table
  2 that the systematic deviation among the
  measurements of S.Raman, G.Molnar and present
  work is not existed. Present measurements are in
  good agreement with the modified values of
  S.Raman and G.Molnar within 1. Fig. 6 shows the
  comparison of present evaluations to the modified
  measurements of S.Raman and G.Molnar, and
  evaluations of C.M.Baglin.
• The present evaluation is obtained from the
  average of 11 measured data sets including
  present measurements using LWM below 2.5MeV
  energy region. Above 2.5MeV energy region, the
  present evaluation is obtained from the
  unweighted average of the measurements of S.Raman
  et al.,G.Molnar et al. and present work(the
  measurements before 2000 are rejected when
  evaluated due to present knowledge of detector
  efficiency curve).

19
Present evaluation I? for 56Co

• Table2

20
Present evaluation I? for 56Co
21
Temporary evaluation I? for 66Ga

• The newly recommended relative ?-ray emission
  probabilities for 66Ga were evaluated by E.Browne
  et al. based on the measurements of S.Raman et
  al.(quoted data from Budapest), G.Molnar et
  al.(Budapest) and C.M.Baglin et al.(Berkeley) in
  2004. Weve finished the measurements of relative
  ?-ray emission probabilities for 66Ga. A
  temporary evaluation of the relative ?-ray
  emission probabilities for 66Ga was given based
  on the measurements of S.Raman et al., G.Molnar
  et al.(Budapest), C.M.Baglin et al.(Berkeley) and
  present work.
• This two evaluations are in agreement with each
  other within 1, but the deviation between the
  evaluations and newly measurements is up to 2.5,
  which is shown in Fig. 7.

22
Temporary evaluation I? for 66Ga
23
Present evaluation I? for 66Ga

• We corrected the measurements of S.Raman and
  G.Molnar using the ?-ray emission probabilities
  of 14N(n,?)15N reaction from Jurney above 2.5MeV.
  We also corrected the measurements of C.M.Baglin
  using present evaluated ?-ray emission
  probabilities of 56Co. The modified values are
  given in table 3 and shown in Fig.8.

24
Present evaluation I? for 66Ga
25
Present evaluation I? for 66Ga

• Present final evaluations are recommended based
  on present measurements and modified measurements
  of S.Raman, G.Molnar and C.M.Baglin shown in
  Fig.9. The present evaluations are in good
  agreement with the modified measured values
  within 1.3.

26
Present evaluation I? for 66Ga
27
Present evaluation I? for 66Ga
28
Conclusion

• The newly recommended relative ?-ray emission
  probabilities for 56Co and 66Ga evaluated by
  C.M.Baglin et al., E.Browne et al. and present
  work show that the old standard for detector
  efficiency calibration existes systematic errors
  (up to 30) in high energies range. But present
  evaluation is lower than the evaluation of Browne
  and Baglin above 2.5MeV. The deviation at 3.4MeV
  is up to 2.7 and this deviation is consistent
  with the difference shown in Fig.6. The
  rationality of present evaluation and corrected
  method will be dependent upon new measurements,
  and more precise standard data are desirable in
  further.