Photoexcitation of ⁸⁷mSr by (γ,γ') reaction
The photoexcitation of ⁸⁷mSr (energy of isomeric level Eiso = 388.532 keV ) using the gamma rays produced by electron electrostatic accelerator was examined for the bremsstrahlung end-points energy covered the range from 1.4 to 3.1 MeV . Isomer activation yield was measured and intermediate states (...
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| Zitieren: | Photoexcitation of ⁸⁷mSr by (γ,γ') reaction / O.S. Shevchenko, Yu.M. Ranyuk, A.M. Dovbnya, E.L. Kuplennikov, A.A. Nemashkalo, I.G. Goncharov, V.N. Borysenko, V.I. Noga // Вопросы атомной науки и техники. — 2007. — № 5. — С. 48-51. — Бібліогр.: 12 назв. — англ. |
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nasplib_isofts_kiev_ua-123456789-1101652025-02-23T18:55:56Z Photoexcitation of ⁸⁷mSr by (γ,γ') reaction Фотозбудження ⁸⁷mSr в (γ,γ') реакції Фотовозбуждение ⁸⁷mSr в (γ,γ') реакции Shevchenko, O.S. Ranyuk, Y.M. Dovbnya, A.M. Kuplennikov, E.L. Nemashkalo, A.A. Goncharov, I.G. Borysenko, V.N. Noga, V.I. Ядерная физика и элементарные частицы The photoexcitation of ⁸⁷mSr (energy of isomeric level Eiso = 388.532 keV ) using the gamma rays produced by electron electrostatic accelerator was examined for the bremsstrahlung end-points energy covered the range from 1.4 to 3.1 MeV . Isomer activation yield was measured and intermediate states (IS) 1228, 1770, 1920 and 2656 keV contribution were observed. Experimental and published nuclear Resonance Fluorescence data were analyzed and photo-activation intermediate state integral cross section determined, which are: 0.090, 0.009, 0.070 and (1.7 ± 0.5) eV · b. Дослідженно фотозбудження ⁸⁷mSr в (γ,γ') реакції з використанням гама-променів, генерованих електронним пучком електростатичного генератора з граничною енергією гальмового спектра в інтервалі 1.4 - 3.1 МеВ. Визначено вихід ізомерної активності і внесок в нього проміжних станів з енергією 1228, 1770, 1920 і 2656 keВ. Отримані експериментальні дані та табличні дані з резонансної флюоресценції були проаналізовані і визначені інтегральні перерізи фото активаційних проміжних станів. Вони виявилися такими, що дорівнюють: 0.090, 0.009, 0.070 та (1.7 ± 0.5) eВ, відповідно. Исследовано фотовозбуждение ⁸⁷mSr в (γ,γ') реакции с использованием гамма лучей генерируемых электронным пучком, ускоренным электростатическим генератором с граничной энергией тормозного спектра в интервале от 1.4 до 3.1 MэВ. Определен выход изомерной активности и вклад в него промежуточных состояний с энергией 1228, 1770, 1920 и 2656 kэВ. Полученные экспериментальные данные и табличные данные о резонансной флюоресценции были проанализированы и определены интегральные сечения фотоактивационных промежуточных состояний. Они оказались равными 0.090, 0.009, 0.070 и (1.7 ± 0.5) эВ, соответственно. 2007 Article Photoexcitation of ⁸⁷mSr by (γ,γ') reaction / O.S. Shevchenko, Yu.M. Ranyuk, A.M. Dovbnya, E.L. Kuplennikov, A.A. Nemashkalo, I.G. Goncharov, V.N. Borysenko, V.I. Noga // Вопросы атомной науки и техники. — 2007. — № 5. — С. 48-51. — Бібліогр.: 12 назв. — англ. 1562-6016 PACS: 25.20.-x https://nasplib.isofts.kiev.ua/handle/123456789/110165 en Вопросы атомной науки и техники application/pdf Національний науковий центр «Харківський фізико-технічний інститут» НАН України |
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Ядерная физика и элементарные частицы Ядерная физика и элементарные частицы |
| spellingShingle |
Ядерная физика и элементарные частицы Ядерная физика и элементарные частицы Shevchenko, O.S. Ranyuk, Y.M. Dovbnya, A.M. Kuplennikov, E.L. Nemashkalo, A.A. Goncharov, I.G. Borysenko, V.N. Noga, V.I. Photoexcitation of ⁸⁷mSr by (γ,γ') reaction Вопросы атомной науки и техники |
| description |
The photoexcitation of ⁸⁷mSr (energy of isomeric level Eiso = 388.532 keV ) using the gamma rays produced by electron electrostatic accelerator was examined for the bremsstrahlung end-points energy covered the range from 1.4 to 3.1 MeV . Isomer activation yield was measured and intermediate states (IS) 1228, 1770, 1920 and 2656 keV contribution were observed. Experimental and published nuclear Resonance Fluorescence data were analyzed and photo-activation intermediate state integral cross section determined, which are: 0.090, 0.009, 0.070 and (1.7 ± 0.5) eV · b. |
| format |
Article |
| author |
Shevchenko, O.S. Ranyuk, Y.M. Dovbnya, A.M. Kuplennikov, E.L. Nemashkalo, A.A. Goncharov, I.G. Borysenko, V.N. Noga, V.I. |
| author_facet |
Shevchenko, O.S. Ranyuk, Y.M. Dovbnya, A.M. Kuplennikov, E.L. Nemashkalo, A.A. Goncharov, I.G. Borysenko, V.N. Noga, V.I. |
| author_sort |
Shevchenko, O.S. |
| title |
Photoexcitation of ⁸⁷mSr by (γ,γ') reaction |
| title_short |
Photoexcitation of ⁸⁷mSr by (γ,γ') reaction |
| title_full |
Photoexcitation of ⁸⁷mSr by (γ,γ') reaction |
| title_fullStr |
Photoexcitation of ⁸⁷mSr by (γ,γ') reaction |
| title_full_unstemmed |
Photoexcitation of ⁸⁷mSr by (γ,γ') reaction |
| title_sort |
photoexcitation of ⁸⁷msr by (γ,γ') reaction |
| publisher |
Національний науковий центр «Харківський фізико-технічний інститут» НАН України |
| publishDate |
2007 |
| topic_facet |
Ядерная физика и элементарные частицы |
| url |
https://nasplib.isofts.kiev.ua/handle/123456789/110165 |
| citation_txt |
Photoexcitation of ⁸⁷mSr by (γ,γ') reaction / O.S. Shevchenko, Yu.M. Ranyuk, A.M. Dovbnya, E.L. Kuplennikov, A.A. Nemashkalo, I.G. Goncharov, V.N. Borysenko, V.I. Noga // Вопросы атомной науки и техники. — 2007. — № 5. — С. 48-51. — Бібліогр.: 12 назв. — англ. |
| series |
Вопросы атомной науки и техники |
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| fulltext |
PHOTOEXCITATION OF 87mSr BY (γ,γ′) REACTION
O.S. Shevchenko, Yu.M. Ranyuk∗, A.M. Dovbnya,
E.L. Kuplennikov, A.A.Nemashkalo, I.G. Goncharov,
V.N. Borysenko, V.I. Noga
National Science Center ”Kharkiv Institute of Physics and Technology”, 61108, Kharkiv, Ukraine
(Received May 15, 2007)
The photoexcitation of 87mSr (energy of isomeric level Eiso = 388.532 keV ) using the gamma rays produced by
electron electrostatic accelerator was examined for the bremsstrahlung end-points energy covered the range from
1.4 to 3.1 MeV . Isomer activation yield was measured and intermediate states (IS) 1228, 1770, 1920 and 2656 keV
contribution were observed. Experimental and published nuclear Resonance Fluorescence data were analyzed and
photo-activation intermediate state integral cross section determined, which are: 0.090, 0.009, 0.070 and (1.7 ±
0.5) eV · b.
PACS: 25.20.-x
Isomers in atomic nuclei are the levels with the
total angular momentum Jiso significantly different
from the one of the ground state Jg.s.. They appear in
the spectra due to the shell structure of a mean field
and their excitation energy in the the odd-mass nuclei
does not exceed a few hundred keV . For these reason,
decay of isomers into the ground state is strongly hin-
dered and their lifetime vary for milliseconds to days
depending on the spin difference ∆J = |Jg.s. − Jiso|
[1]. Isomers are populated after decay of intermedi-
ate state(s) with the energy of (2−4) MeV and finite
branching to the isomeric level. IS are excited by
bremsstrahlung radiation with the end-point energy
of (2− 5) MeV .
The previous experiments [2 − 5] have already
shown that the number of such IS which are linked to
both the ground and isomeric states, is very small, i.e.
one-two states per MeV in spherical nuclei. There
was also a set of experiments in which the isomeric
states were populated in the (γ, n) reaction via excita-
tion and cascade decay of the giant dipole resonance
[6]. In this paper we report our results on the isomer
photoproduction in 87Sr (the isotopic abundance is
7.00%). It has the stable ground state with the spin
and parity Jπ
g.s. = 9/2+. The isomeric state in this
nucleus has the excitation energy Eiso = 388.532 keV
and Jπ
iso = 1/2−. Thus, the spin difference ∆J = 4
and at least the E2−E3 sequence is need to populate
the isomer from the ground state. The T1/2 value is
equal 2.81 hours.
The decay scheme of the isomer in 87Sr is pre-
sented in Fig.1. The isomer decays to ground states
by M4 transition with the relative γ - line intensity
of Iγ = 82.1. An early work [7] examined the pro-
duction of 87mSr by bremsstrahlung with end points
which could be varied up to 3MeV . The tunability
of that device allowed three distinct gateways to be
identified at 1.22, 1.88 and 2.66 MeV , and their in-
tegrated cross sections to be measured.
Fig.1. Decay scheme of the isomeric Jπ
iso = 1/2−
state in 87mSr [9]. See text for the details
They are 0.085+0.040
−0.030, 0.16+0.08
−0.05 and 3.8+2
−1 eV ·b
respectively [8]. The next experiment have been per-
formed for the bremsstrahlung end-point energy 4
and 6 MeV [8]. The obtained integrated cross section
(σΓ) are (3.90± 0.13) and (8.70± 0.18) eV ·b, respec-
tively. The low experimental resolution did not allow
the IS determination. It is seen that attempts at
quantitative IS integrated cross sections still do not
converge. Subsequently we reexamined the reaction
∗Corresponding author. E-mail address: ranyuk@kipt.kharkov.ua
48 PROBLEMS OF ATOMIC SCIENCE AND TECHNOLOGY, 2007, N5.
Series: Nuclear Physics Investigations (48), p.48-51.
87Sr(γ,γ′)87mSr used precious electrostatic electron
accelerator and spectroscopic nuclear resonance fluo-
rescent data.
The experiment have been carried out in the Na-
tional Science Center ”Kharkiv Institute of Physics
and Technology” at the 3MV electrostatic elec-
tron accelerator ELIAS having an voltage instabil-
ity 50 kV and a beam intensity up to 500 µA. The
investigation have been performed using activation
technique. Bremsstrahlung spectra have been gener-
ated by electrons irradiating of 0.5 mm thickness Ta
converter. Samples of natural Sr (0.2 mm thick and
15 mm in diameter) have been placed in the photon
beam behind the converter. The photo activities have
been measured with Ge(Li) detector by observing the
388.532 keV γ -rays. The detector sensitive volume
is 50 cm3 and the energy resolution is about 2.5 keV
for 1332 keV of 60Co source. The schematic layout
of photo activation experiment and standard pro-
cedure for activation data development is described
elsewhere [10].
The principal results of the study and details
are discussed below. A part of the pulse height γ-
spectrum seen in the detector when bremsstrahlung
of end-point energy of 2.7 MeV irradiates a stron-
tium scatterer is depicted in Fig.2. It is a typ-
ical activated spectrum of our experiment. The
388.532 keV γ-line is seen in all other runs.
Fig.2. γ-ray spectrum measured after
bremsstrahlung irradiation of Sr target with end
-point energy of 2.7 MeV
The reaction yield is defined as the number of ac-
tivated nuclei Niso normalized to the number of tar-
get nuclei NT per cm2 and the number of incident
electrons Ne:
Y (Eγmax) = Niso/NeNT . (1)
The experimental 87Sr(γ,γ′)87mSr reaction yield ver-
sus end point photon energy is shown in Fig.3 by cir-
cles. Full uncertainty values of excitation function
were determined as a sum of systematic and statisti-
cal errors and on average consists of 10-15%.
The isomer yield can be calculated as:
Y (Eγmax) =
∫ Eγmax
Ec
σ(Eγ)Nγ(Eγ , Eγmax)dEγ ,
(2)
where Ec is cutoff energy, σ(Eγ) is the total reac-
tion cross-section as a function of the excitation en-
ergy Eγ and Nγ(Eγ , Eγmax) represents the contin-
uous bremsstrahlung spectral density with the end-
point energy Eγmax.
The typical widths of resonant intermediate states
are small enough to assume that Nγ(Eγ , Eγmax) is
constant over each resonance. Than, equation (2)
can be simplified to
Yi =
∑
(σΓ)j
isoN
j
i (EIS , Eγmax), (3)
where (σΓ)j
iso is the isomer excitation integrated
cross section through the j − IS.
Integrated cross sections of an IS can be deter-
mined by solution of equation system (3). From the
other side those integrated cross sections is related to
its level properties by equation [11]:
(σΓ)iso = π2
(
hc
EIS
)2 2JIS + 1
2J0 + 1
α0 αiso Γ. (4)
J0,IS , are the spins of the g.s. and the intermedi-
ate state, Γ describes the total width and α0, αiso
denote the branching ratios for decay into the g.s.,
isomeric state respectively. If the relevant level prop-
erties Γ, α0, αiso, EIS and J of all intermediate levels
are known, and Eq.(2) can be inverted and informa-
tion on the spectral intensities at the resonance en-
ergies can be extracted [11,12]. For 87Sr the avail-
able data base [9] provides a complete characteriza-
tion of all levels contribution to the isomer yield up
to bremsstrahlung edge 3.1 MeV . The adopted data
and derived integrated cross section are summarized
in Table.
Fig.3. The 87Sr isomer yield as a function of the
bremsstrahlung end-point energy
49
The number of photons N j
i (EIS , Eγmax) in Eq.(3)
with the IS energy EIS for each bremsstrahlung end-
point energy in Fig. 3 has been calculated by mathe-
matical modeling of the bremsstrahlung spectra with
GEANT 3.21 program. The number of launches was
107 and used Ec = 0.5 MeV and the interval of
grouping of 0.01 MeV .
A theoretical yield function can be constructed
from the Geant photon spectra and tested against
the measured result. This method was used in ref.
[10] to determine the contribution of low-lying levels
and to extract information on previously unknown
IS at higher excitation energies. Here, we are con-
cerned with the quality of reproduction of the exper-
imental yield curve for 1228, 1770 and 1920 keV IS
using Monte Carlo Geant generated photon spectra.
Fig.3 clearly shows that the experimental yield varia-
tion for the bremsstrahlung edge less than 2.6 MeV is
agree with the calculation including 1228, 1770 and
1920 keV IS. It is seen sharp increasing of experi-
mental yield above 2.6 MeV . Nuclear tables [9] con-
tain no information about IS in 87mSr for this energy
range. More suitable is level 2656 keV IS integrated
cross section for EIS = 2656 keV was calculated from
difference between experimental and calculated yield.
The result is (σΓ) = (1.7± 0.5) eV · b
Properties of 87Sr levels contribution to the population of
the 388.53 keV isomer for EIS < 3.1 MeV [11]
EIS , keV Jπ t, ps L α0,% αiso,% (σΓ)t, eV ·b (σΓ)e, eV ·b [7] (σΓ)iso, eV ·b
this work
1228 5/2+ 1.0 E2 84.82 15.18 0.090 0.085+0.040
−0.030 -
1770 5/2+ 6.0 E2 78.51 21.49 0.0094 - -
1920 7/2+ 0.133 M1+E2 97.5 2.53 0.070 - -
2656 5/2−, 7/2− - E1, M1 - - - 3.8+2
−1 1.7± 0.5
REFERENCES
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et al. Excitation of low-lying state by E3 transi-
tion in reaction with real photons // Proceedings
of XI International Seminar on Electromagnetic
Interactions of Nuclei. Moscow, September 21-
24, 2006.
2. D. Bohle, A. Richter, W. Steffen et al. New mag-
netic dipole mode // Phys. Lett. 1984, v.B137,
p.27-31.
3. A. Richter. Electron Scattering and elementary
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onant excitation of the 180mTa( γ, γ‘ )180Ta //
Phys.Rev. 1990, v.42, N5, p.1813-1816.
6. Yu.P. Gangrskij, A.P. Tonchev, N.P. Balabanov.
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7. E.C. Booth end J. Browson. Electron and pho-
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8. J. Carrol, M.J. Byrd, D.G. Richmond et. all. Pho-
toexcitation of nuclear isomers by (γ, γ‘) // Phys.
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9. Firestone R.B. Table of Isotops // Eight edition:
1998.
10. O.S. Shevchenko, A.N. Dovbnya, E.L. Kuplen-
nikov et al. Excitation of isomers in 115In( γ, γ‘
)115mIn reaction // PAST. 2005, N6, (45), p.30-
34.
11. P. von Neumann-Cosel, N. Huxel, A. Richtrs et
al. Absolute calibration of low energy, thick tar-
get bremsstrahlung // Nucl. Instr. Meth. in Nucl.
Phys. v.A338, 1994, p.425-431.
12. D. Belic, J. Besserer, C. Arlandini at al. The
new photoactivation facility at the Stuttgart
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50
ФОТОВОЗБУЖДЕНИЕ 87mSr В (γ,γ′)- РЕАКЦИИ
О.С. Шевченко, Ю.Н. Ранюк, А.Н. Довбня, Э.Л. Купленников, А.А. Немашкало,
И.Г. Гончаров, В.Н. Борисенко, В.И. Нога
Исследовано фотовозбуждение 87mSr в (γ,γ′)- реакции с использованием гамма лучей генерируемых
электронным пучком, ускоренным электростатическим генератором с граничной энергией тормозного
спектра в интервале от 1.4 до 3.1 MэВ. Определен выход изомерной активности и вклад в него проме-
жуточных состояний с энергией 1228, 1770, 1920 и 2656 kэВ. Полученные экспериментальные данные и
табличные данные о резонансной флюоресценции были проанализированы и определены интегральные
сечения фотоактивационных промежуточных состояний. Они оказались равными 0.090, 0.009, 0.070 и
(1.7± 0.5) эВ, соответственно.
ФОТОЗБУДЖЕННЯ 87mSr В (γ,γ′)- РЕАКЦIЇ
О.С. Шевченко, Ю.М. Ранюк, А.М. Довбня, Е.Л. Купленнiков, А.А. Немашкало,
I.Г. Гончаров, В.Н. Борисенко, В.I. Нога
Дослiдженно фотозбудження 87mSr в (γ,γ′)- реакцiї з використанням гама-променiв, генерованих
електронним пучком електростатичного генератора з граничною енергiєю гальмового спектра в iнтер-
валi 1.4 - 3.1 МеВ. Визначено вихiд iзомерної активностi i внесок в нього промiжних станiв з енергiєю
1228, 1770, 1920 i 2656 keВ. Отриманi експериментальнi данi та табличнi данi з резонансної флюорес-
ценцiї були проаналiзованi i визначенi iнтегральнi перерiзи фото активацiйних промiжних станiв. Вони
виявилися такими, що дорiвнюють: 0.090, 0.009, 0.070 та (1.7± 0.5) eВ, вiдповiдно.
51
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