Independent method of Au determination in different materials by applying (γ,γ¹)m-reaction
Represented results are based on using the ¹⁹⁷Au(ƴ,ƴ')¹⁹⁷mAu reaction, the experimental integrated cross sections of the isomer excitation through activation levels and the Monte-Carlo simulation method. It is shown that applying of high-current electron accelerator (EA) with energy 8:7MeV perm...
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irk-123456789-1112642017-01-10T03:02:47Z Independent method of Au determination in different materials by applying (γ,γ¹)m-reaction Afanas'ev, S.N. Kuplennikov, E.L. Krasil'nikov, V.V. Ядернo-физические методы и обработка данных Represented results are based on using the ¹⁹⁷Au(ƴ,ƴ')¹⁹⁷mAu reaction, the experimental integrated cross sections of the isomer excitation through activation levels and the Monte-Carlo simulation method. It is shown that applying of high-current electron accelerator (EA) with energy 8:7MeV permits to determine the threshold of gold definition in nature and technological materials ≥ 0.1 g/t. Представлені результати засновані на використанні ¹⁹⁷Au(ƴ,ƴ')¹⁹⁷mAu-реакції, експериментальних інтегральних перерізів збудження ізомерів через рівні активації і моделювання методом Монте-Карло. Показано, що застосування могутнього прискорювача електронів з енергією 8.7 МеВ забезпечує межу виявлення золота у природних і технологічних матеріалах ≥ 0.1 г/т. Представленные результаты основаны на использовании ¹⁹⁷Au(ƴ,ƴ')¹⁹⁷mAu-реакции, экспериментальных интегральных сечений возбуждения изомеров через уровни активации и моделирования методом Монте-Карло. Показано, что применение мощного ускорителя электронов с энергией 8.7 МэВ обеспечивает предел обнаружения золота в природных и технологических материалах ≥ 0.1 г/т. 2009 Article Independent method of Au determination in different materials by applying (γ,γ¹)m-reaction / S.N. Afanas'ev, E.L. Kuplennikov, V.V. Krasil'nikov // Вопросы атомной науки и техники. — 2009. — № 3. — С. 54-57. — Бібліогр.: 12 назв. — англ. 1562-6016 PACS: 03.65.Pm, 03.65.Ge, 61.80.Mk http://dspace.nbuv.gov.ua/handle/123456789/111264 en Вопросы атомной науки и техники Національний науковий центр «Харківський фізико-технічний інститут» НАН України |
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Ядернo-физические методы и обработка данных Ядернo-физические методы и обработка данных |
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Ядернo-физические методы и обработка данных Ядернo-физические методы и обработка данных Afanas'ev, S.N. Kuplennikov, E.L. Krasil'nikov, V.V. Independent method of Au determination in different materials by applying (γ,γ¹)m-reaction Вопросы атомной науки и техники |
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Represented results are based on using the ¹⁹⁷Au(ƴ,ƴ')¹⁹⁷mAu reaction, the experimental integrated cross sections of the isomer excitation through activation levels and the Monte-Carlo simulation method. It is shown that applying of high-current electron accelerator (EA) with energy 8:7MeV permits to determine the threshold of gold definition in nature and technological materials ≥ 0.1 g/t. |
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Article |
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Afanas'ev, S.N. Kuplennikov, E.L. Krasil'nikov, V.V. |
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Afanas'ev, S.N. Kuplennikov, E.L. Krasil'nikov, V.V. |
| author_sort |
Afanas'ev, S.N. |
| title |
Independent method of Au determination in different materials by applying (γ,γ¹)m-reaction |
| title_short |
Independent method of Au determination in different materials by applying (γ,γ¹)m-reaction |
| title_full |
Independent method of Au determination in different materials by applying (γ,γ¹)m-reaction |
| title_fullStr |
Independent method of Au determination in different materials by applying (γ,γ¹)m-reaction |
| title_full_unstemmed |
Independent method of Au determination in different materials by applying (γ,γ¹)m-reaction |
| title_sort |
independent method of au determination in different materials by applying (γ,γ¹)m-reaction |
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Національний науковий центр «Харківський фізико-технічний інститут» НАН України |
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Ядернo-физические методы и обработка данных |
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http://dspace.nbuv.gov.ua/handle/123456789/111264 |
| citation_txt |
Independent method of Au determination in different materials by applying (γ,γ¹)m-reaction / S.N. Afanas'ev, E.L. Kuplennikov, V.V. Krasil'nikov // Вопросы атомной науки и техники. — 2009. — № 3. — С. 54-57. — Бібліогр.: 12 назв. — англ. |
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Вопросы атомной науки и техники |
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| fulltext |
NUCLEAR-PHYSICAL METHODS AND PROCESSING OF DATA
INDEPENDENT METHOD OF Au DETERMINATION IN
DIFFERENT MATERIALS BY APPLYING (γ,γ’)m-REACTION
S.N. Afanas’ev1, E.L. Kuplennikov1∗, V.V. Krasil’nikov2
1National Science Center ”Kharkov Institute of Physics and Technology”, 61108, Kharkov, Ukraine
2Belgorod State University, Belgorod, Russia
(Received April 5, 2008)
Represented results are based on using the 197Au(γ,γ’)197mAu reaction, the experimental integrated cross sections of
the isomer excitation through activation levels and the Monte-Carlo simulation method. It is shown that applying
of high-current electron accelerator (EA) with energy 8.7 MeV permits to determine the threshold of gold definition
in nature and technological materials ≥ 0.1 g/t.
PACS: 03.65.Pm, 03.65.Ge, 61.80.Mk
1. INTRODUCTION
Gold is a less-common metal. So it is necessary to
apply very susceptible methods having a high preci-
sion, efficiency and output for Au concentration to be
found in geological samples at searching, exploration
and mining. As an example of a successful decision of
this problem it can be pointed applying the gamma-
activation techniques for gold presence analysis in dif-
ferent materials. Two the most important reactions
used in these techniques are (γ,n) and (γ,γ’) ones.
For example the reaction 197Au(γ,n)196Au (half-
life of the 196Au T1/2 = 6.8 days) was used to de-
termine Au content in the Ukraine ores [1]. Acti-
vation was realized by bremsstrahlung photons. For
this purpose, it was used the linear EA (LEA) with
an energy range of 16 ... 25 MeV , a mean current
Ie = 0.1 ... 1 mA and an irradiation time (tirr) from
1 hour up to days. The threshold of Au determi-
nation 0.03 ... 0.1 g/t is gotten for the most of ores
researched except the samples having high content of
Mn (≥10%) where the threshold is below than 1-1.5
g/t. A mass of the probes irradiated is Mpr ≤ 500 g.
The cooling time (tc) is generally 5 ... 10 hours. Out-
put of the method is ∼ 50 samples per shift.
First experimental investigations [2-5], using
bremsstruhlung photons and 197Au(γ,γ’)197mAu re-
action for elemental analysis of geological probes,
have showed principal opportunity of using high-
current EA for express-analysis of natural and tech-
nological materials for Au determination. Soon on
a base of the laboratory investigation results was
worked out and introduced into industrial exploita-
tion photonuclear analytical complex ”AURA” [5].
For analysis is used LEA with energy Ee = 8 MeV .
Sample weight is 500 g. Diameter of mixture particles
are 1 mm. Time of irradiation, cooling and measuring
(tm) − 15, 3 and 15 s respectively. Detecting system
consists of two monocrystalls NaJ(Tl) 150×100 mm.
Above mentioned parameters provide the definition
threshold of Au 0.2 ... 0.5 g/t in ores of different com-
position. Project complex productivity is 400 analy-
ses per shift.
In 1992 the systematic investigation into the pho-
toexcitation of isomers over wide mass ranges, includ-
ing Au, was studied [6] with the bremsstrahlung fa-
cility at the superconducting Darmstadt LEA. Ex-
citation functions were measured for the (γ,γ’)m re-
actions populating the metastable states for energies
of 2 ... 7 MeV and the important intermediate states
were identified. Simultaneously it was defined inte-
grated cross sections (σΓ)j
iso of isomer 197mAu ex-
citation through intermediate (activated) levels Ej .
Obtained experimental data gave the opportunity to
calculate a number of activated Au nuclei by new,
independent method.
In the present work, it is considered the possibil-
ity of applying the high-current EA for the express-
analysis of Au content in nature and technological
materials. Calculations were made taking into ac-
count existing experimental and theoretical investi-
gation results, measured energy of the activated lev-
els and integrated cross sections of isomer excitation
and achievements in optimization region.
2. WORKING PARAMETERS SELECTION
As it is known [5], a yield of the (γ,γ’)m reaction
increase with growing of the endpoint photon energy
(Eγmax). So increasing of activated nuclei number
in (γ,γ’)m reaction can be obtained by increasing of
electron energy. However maximum Ee must be lower
than the neutron emission threshold (εn) of the exit
and dividing foils, converter, target and protection
materials as neutron appearance lead to a formation
of by-products radionuclides. Comparison of the εn
∗Corresponding author. E-mail address: kupl@kipt.kharkov.ua
54 PROBLEMS OF ATOMIC SCIENCE AND TECHNOLOGY, 2009, N3.
Series: Nuclear Physics Investigations (51), p.54-57.
of different materials shows that the energy of elec-
trons can be increased up to 8 (9) MeV, using natural
Ti (Al, Cu) for exit and dividing foils and Au (Cu)
for converter.
A proposed arrangement of activation equipment
on the EA exit is represented by Fig.1. Notations
of Fig. 1: 1, 4 - are Ti foils, every one is of 50 µm;
2 - is two water layers, every is of 1.5 mm; 3 - Au
converter; 5 - air layer of 5 mm; 6 - gold- containing
mixture; 7 - Al container; 8 - polyethylene cover.
Fig.1. Block - scheme of the activation equipment
Whereas the neutron emission threshold of Au is
large as against traditional metals Ta and W, the gold
disk is proposed to use as the converter. Based on
simulation by the GEANT3.21 package, it was found
that an optimal Au converter thickness for proposed
kinematics is 1 mm.
Selectivity that is ability of the analysis to sep-
arate nuclei of a desired element from rest sample
nuclei plays an important role for founding optimal
conditions in carrying out the activation analysis. On
the Fig.2 [7], it is shown the dependence of a specific
selectivity of gold determination in quartz ore on a
endpoint energy Eγmax of a bremsstrahlung spectrum
for four values of irradiation time. Curves 1-4 corre-
spond tirr = T1/2, 3T1/2, 5T1/2, 7T1/2.
It can be seen the most specific selectivity is ob-
served at Eγmax = 8.5 MeV for any tirr and increases
with decreasing irradiation time. So this optimal en-
ergy is taken as the base in this work. However, as
electrons lose ∼ 200 keV passing an EA exit foil and
a water layer, the initial beam energy is increased up
to 8.7 MeV in further estimates.
The container in which broken muck is to be
charged consists of a straight truncated Al cone with
the wall thickness of 1 mm and the polyethylene
cover of 1 mm thickness. The cone height 40 mm,
small r and large R of cone radiuses are equal 20
and 35 mm respectively. Internal volume of the con-
tainer is 97.39 cm3 at the above mentioned parame-
ters. A density of the milled sample is 0.8 g/cm3
(mean value of the gold-bearing ore [8]), the weight
of a container content is 77.92 g and the Au mass
is 0.779×10−4 g under condition that its content in
mixture is 1 ppm. At above conditions number of
Au nuclei per cm2 is NT = 0.979×1016. Required
calculations are carried out with the following pa-
rameters. The electron energy 8.7 MeV, the mean
current is 1 mA, half-live of 197mAu 7.73 s, detected
γ-line Eγ = 279.0 keV. Irradiated time tirr = 16 s,
cooling time tc = 3 s and measuring time tm = 19 s.
Fig.2. The dependence of a specific selectivity on a
endpoint energy Eγmax
3. ISOMER PHOTOACTIVATION
Different investigations (see cites in [9]) have con-
firmed that direct resonant excitation of the isomeric
levels is negligible because of very small width. The
population of isomers by (γ,γ’)-reactions at excita-
tion energies below the photoneutron threshold pro-
ceeds by the process depicted schematically in Fig.3.
The figure identifies the relevant parameters in-
cluding the natural width of the intermediate level Γ,
which is the sum of all partial widths for transitions
on all levels, lying between the excited and ground
state and the branching ratios b0 and biso for decay
from the intermediate state directly to the ground
state and by unknown cascade to the isomer.
Number of activated Au nuclei Nf is found by the
expression of a normalized reaction (γ,γ’)m yield [9]:
Y =
Nf
NT Ne
=
∑
j
(σΓ)j
isoN(Ej , Eγmax), (1)
where Ne is a number of electrons passed through
the converter, (σΓ)j
iso is an integrated cross sec-
tion of isomer excitation by the intermediate j level,
N(Ej ,Eγmax) is the photon field spectral inten-
sity in solitary energy interval at energy Eγmax.
55
Ej - denote the activation level energy. The
quantity N(Ej ,Eγmax) is calculated for individ-
ual geometry of irradiation by code GEANT3.21.
Fig.3. Resonant photoexcitation mechanism by
which an isomer at energy of Eiso is populated
through the hatched states
Estimation of Nf is fulfilled with the statistics of
106, step size 10 keV and the experimental integrated
cross sections [6] given by Table. These cross sections
give the most contribution to gold isomer population.
According to Eq. (1), number of activated nuclei in
studied reaction 197Au(γ,γ’)197mAu is 7822.
Intermediate levels and integrated cross sections
Ej , MeV (σΓ)j
iso, (10−29 cm2 · keV )
1.70±0.30 70±30
2.50±0.10 500±50
3.20±0.15 4500±500
4.20±0.20 20000±4000
4. DETECTOR EFFICIENCY
To estimate number of γ-quanta with Eγ =
279.0 keV registered really by the γ-spectrometer it is
need to introduce corrections for efficiency of the sys-
tem. The crystal NaJ(Tl) 150×100 mm is considered
as the detector system. In the case, when only events
with total energy absorption are taken into account,
total efficiency is [10]:
εtot = εgeom · εabsorp · εsample · εevent . (2)
εgeom is fraction of total number of photons, fly-
ing out in 4π angle, reaching a detector. εgeom is
calculated by the Monte-Carlo simulation method.
The surface of crystal NaJ(Tl) is at 3 mm distance
from the probe surface. According to the calcula-
tion, 34.7% of γ-quanta with Eγ = 279.0 keV reach
the crystal of 150 mm diameter.
εabsorp takes into account of influence of interme-
diate materials that absorb a part of irradiation be-
fore photons reach the detector.
εabsorp = exp(−
∑
µi · ρi · xi), (3)
where µi-, ρi- and xi are the mass absorption coeffi-
cient, density and thickness of i-th intermediate ma-
terial, respectively. To reach the detector a photon
with energy of 279.0 keV is to go through the Al foil
of 1 mm thickness, 1 mm polyethylene and 1mm air
layer. Coefficients of mass weakening and materials
density were found in [11].
εsample is a part of γ-quanta irradiated by the
sample. According to [10]:
εsample =
1− exp(−µ · ρ · x)
µ · ρ · x , (4)
where µ-, ρ- and x are the mass absorption coefficient,
density and thickness of material, respectively.
In this work, it is considered that the mixture
of γ-emitting element with sample matrix elements
is uniform and homogeneous enough with respect to
composition and density. Besides particles emitting
photons are small, so self-attenuation inside a sin-
gle particle is negligibly small. These requirements
secure the linear attenuation coefficient has a single
value in a large enough range and it can be used for
calculation. Estimation of εsample is fulfilled with the
mass absorption coefficient and density taken for the
SiO2 chemical compound [11].
εevent is a probability that γ-quant reaching de-
tector contributes a pulse to a total absorption peak.
This correction was obtained from expression (41)
[12] for a spot radiation source, disposed at the axis
of crystal.
5. DISCUSSION
Known number of activated nuclei Nf per-
mits to estimate number of real photons regis-
tered by the γ-spectrometer within a photopeak
area (Sγ). Upon that it is need to introduce cor-
rections [7] taking account of nuclei decay dur-
ing irradiation time 1− exp(−λ · tirr) = 0.76, cool-
ing time exp(−λ · tc) = 0.76 and measuring time
1− exp(−λ · tm) = 0.82. Besides, it is necessary to
introduce a correction connected with intensity of γ-
line Iγ = 0.71, to take into account the detector total
efficiency εtot = 0.144 and the dependence on the de-
cay constant λ = 0.693/T1/2 = 0.0897.
Thus, in above mentioned geometry of equipment
arrangement and EA parameters, number of photons
with energy 279.0 keV , registered by the detector
after finishing irradiation of sample with gold con-
centration 1 ppm, is equal 4740. Obtained number
of γ-quanta indicates that applying EA with energy
8.7 MeV permits for one exposure of 16 s duration
at 1 mA current to determine the threshold of gold
definition ≥ 0.1 g/t (Sγ ∼ 474). If it is need one can
extract the Au concentration ∼ 1 g/t in sample re-
ducing current up to 50 µA (Sγ ∼ 237). Obtained
results are in agreement with data [4,5].
The threshold of Au definition can be made bet-
ter if to increase a probe mass up to 500 g, set up
two NaJ(Tl) detectors on the opposite sides of sam-
ple or apply semiconductor detector from high purity
germanium with a large sensitive volume.
56
6. CONCLUSIONS
The represented results are based on using the
197Au(γ,γ’)197mAu reaction, the experimental inte-
grated cross sections of the isomer excitation through
activated levels and the Monte-Carlo simulation
method. It is shown that applying of high-current
EA with energy 8.7 MeV permits for one exposure
of 16 s duration to determine the threshold of gold
definition ≥ 0.1 g/t. Simulation results can be usefull
for elaboration and creation of an Industrial Photonu-
clear Activation Complex in Ukraine.
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”Atomizdat”, 1961, 430 p.
НЕЗАВИСИМЫЙ МЕТОД ОПРЕДЕЛЕНИЯ Au В РАЗЛИЧНЫХ МАТЕРИАЛАХ С
ПРИМЕНЕНИЕМ (γ, γ′)m- РЕАКЦИИ
С.Н. Афанасьев, Э.Л. Купленников, В.В. Красильников
Представленные результаты основаны на использовании 197Au(γ,γ’)197mAu-реакции, эксперименталь-
ных интегральных сечений возбуждения изомеров через уровни активации и моделирования методом
Монте-Карло. Показано, что применение мощного ускорителя электронов с энергией 8.7 МэВ обеспе-
чивает предел обнаружения золота в природных и технологических материалах ≥ 0.1 г/т.
НЕЗАЛЕЖНИЙ МЕТОД ВИЗНАЧЕННЯ Au У РIЗНИХ МАТЕРIАЛАХ З
ВИКОРИСТАННЯМ (γ, γ′)m- РЕАКЦIЇ
С.М. Афанасьєв, Е.Л. Купленников, В.В. Красильников
Представленi результати заснованi на використаннi 197Au(γ,γ’)197mAu-реакцiї, експериментальних iн-
тегральних перерiзiв збудження iзомерiв через рiвнi активацiї i моделювання методом Монте-Карло.
Показано, що застосування могутнього прискорювача електронiв з енергiєю 8.7 МеВ забезпечує межу
виявлення золота у природних i технологiчних матерiалах ≥ 0.1 г/т.
57
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