The 9.2 keV nuclear transition in 227Th was studied in the β−-decay of 227Ac by means of the internal conversion electron spectroscopy to clarify the spin-parity assignment of the ground state and ...the two lowest excited states of 227Th. The transition multipolarity was proved to be of mixed character M1 + E2 and the spectroscopic admixture parameter δ2(E2/M1)=0.695±0.248 (|δ(E2/M1)|=0.834±0.149) was determined. Nonzero value of δ(E2/M1) questioned the present theoretical interpretation of low-lying levels of 227Th. Calculations performed prefer the 1/2+, 3/2+, and 3/2+ sequence instead of the adopted 1/2+, 5/2+ and 3/2+ one for the 0.0, 9.2, and 24.3 keV levels, respectively.
The 9.2 and 24.3 keV nuclear transitions in
227
Th were studied in the
β
-
decay of
227
Ac employing the internal conversion electron spectroscopy. Values of
(
9244.6
±
0.8
)
and
(
24343.1
±
1.1
)
eV ...were determined for their energies. The 24.3 keV transition was found to be of the mixed (M1
+
E2) multipolarity with the spectroscopic admixture parameter
δ
2
(
E
2
/
M
1
)
=
(
0.0116
±
0.0004
)
. Energies of
(
24342.9
±
1.2
)
,
(
28613.3
±
1.7
)
, and
(
37860.2
±
2.0
)
eV were obtained respectively for the 24.3, 28.6, and 37.8 keV transitions in
227
Th by means of the gamma-ray spectroscopy. Natural atomic-level widths of
(
14.1
±
0.5
)
,
(
11.4
±
0.5
)
,
(
6.9
±
0.4
)
,
(
11.4
±
1.4
)
,
(
8.6
±
1.2
)
, and
(
6.0
±
0.7
)
eV for the M
1
-, M
2
-, M
3
-, N
1
-, N
2
-, and N
3
-subshells of thorium, respectively, were derived from conversion electron lines. The cross checking of the energy values of the 9.2, 15.1, and 24.3 keV nuclear transitions obtained by the ICES method is also given.
.
Using the internal conversion electron spectroscopy, the energy of the 15.1 keV
M
1
+
E
2
nuclear transition in
227
Th populated in the
β
-
decay of
227
Ac was determined to be
15098
.
6
±
1
.
0
...eV. This value is more accurate than the present accepted one by a factor of 200. The present uncertainty in the transition multipolarity was removed and it was found to be
M
1
+
E
2
with the admixture
|
δ
(
E
2
/
M
1
)
|
=
0
.
035
±
0
.
006
.
•The thulium L, M, N, O, and P subshell electron binding energies determined.•Five different matrices of the radioactive 169Yb atoms used in the investigation.•The greatest difference of 4.5±0.1eV in ...the average observed between the matrices.•The published N1, N3, and O2,3 values found to be higher by about 3eV.•Natural widths of the thulium K, L, M, N, and O subshells also determined.
The L1, L2, L3, M1, M2, N1, N3, O1, O2, O3, and P1 subshell electron binding energies (related to the Fermi level) in thulium generated by the electron capture decay of radioactive 169Yb atoms implanted at 30keV into polycrystalline platinum and aluminum foils and deposited by vacuum evaporation on surfaces of polycrystalline platinum, carbon, and aluminum foils were determined by the internal conversion electron spectroscopy. The greatest differences in the electron binding energies (4.5±0.1eV in the average without the P1 shell and 7.0±0.5eV for the P1 shell alone) were found between the matrices of the evaporated ytterbium layer on the aluminum foil and the bulk of the high purity polycrystalline platinum. The thulium electron binding energies in the matrices of the evaporated ytterbium layers on both the platinum and carbon foils and in the aluminum bulk were observed to be the same within the experimental uncertainties. The N1, N3, and O2,3 electron binding energies most frequently presented in data compilations were found to be higher by about 3eV. Natural widths of most of the K, L1, L2, L3, M1, M2, M3, N1, N3, and O1 subshells in Tm in the investigated matrices were also determined. No significant differences in the natural widths were found among the matrices. The results obtained demonstrate that the physicochemical surrounding of the radioactive atoms should be well defined and understandable for any type of electron calibration source particularly in the case of the super stable calibration 83Rb/83mKr electron sources for the KATRIN neutrino mass experiment.
The energy scale of the main spectrometer in the KATRIN tritium project is required to remain stable within ±60 meV at an electron energy of 18.6 keV for two months in order to reach the intended ...sensitivity of 0.2 eV for the rest mass of the electron antineutrino. A natural source of reference electrons with an energy of 17824.3 ± 0.5 eV based on
K
-conversion electrons of the 32-keV nuclear γ-transition in
83m
Kr from the decay of parent
83
Rb was developed for this purpose using precision low-energy nuclear electron spectrometry. The spectroscopic parameters of
83m
Kr/
83
Rb sources fabricated by ion implantation into polycrystalline platinum foils were significantly better than the parameters of vacuum-deposited sources. A large-scale study of the influence of the physicochemical environment of atoms of different radioisotopes in various matrices of vacuum-deposited and implanted radioactive sources on the energy of emitted conversion and Auger electrons and on the structure of the corresponding energy spectra was conducted in the process. The possibility of application of photoelectron sources with a metallic converter as sources of reference electrons for the KATRIN project was also considered.
•Eight different matrices (evaporated and implanted at 30keV) used.•The greatest average difference in the binding energies amounted to 3.1±0.1eV.•The presence of trivalent and divalent Sm ions found ...in some implanted samples.•No significant differences in Sm natural atomic level widths were observed.
Effects of the atomic environment on the L1, L2, L3, M1, M2, M3, and N1 electron binding energies in samarium generated in the electron capture decay of radioactive 149Eu were investigated by means of the internal conversion electron spectroscopy using the conversion electron spectrum of the 22.5keV M1+E2 nuclear transition in the daughter 149Sm. In this investigation, four pairs of 149Eu sources prepared by vacuum evaporation deposition and by ion implantation at 30keV with the use of four different source backing materials, namely polycrystalline carbon, aluminium, gadolinium and platinum foils, were employed. The greatest average difference of (3.1±0.1)eV in the L1, L2, L3, and M1 subshell electron binding energies was observed between the 149Eu sources prepared by ion implantation into the aluminium and platinum substrates. On the other hand, minimal differences in the electron binding energies were generally found between samarium generated in the evaporated layer and in the bulk for the individual investigated source backings with the exception of the gadolinium foil. A doublet structure of all investigated conversion electron lines with the average values of 8.1±0.2eV and 1.5±0.1 for the separation energy and the intensity ratio of the low-energy to high-energy components, respectively, was observed for the 149Eu sources prepared by ion implantation into the aluminium and carbon foils. This structure was presumably caused by the presence of both the trivalent and divalent Sm ions in the sources. No significant differences in natural widths of the L1, L2, L3, M1, M2, and M3 samarium atomic levels among the investigated matrices were observed with the exception of the source prepared by the implantation of the 149Eu ions into the platinum foil for which the determined values for all investigated subshells were apparently higher.
PDF
