ᵃʳᶜʰPbWO₄ with improved optical parameters from archaeological lead
Technological principles of manufacturing a lead tungstate crystal from archaeological lead for use in low-background experiments to search for rare events are presented. The influence of the conditions for obtaining single crystals of ᵃʳᶜʰPbWO₄ on the photochromic effect in single crystals is inves...
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nasplib_isofts_kiev_ua-123456789-1959302025-02-10T01:05:47Z ᵃʳᶜʰPbWO₄ with improved optical parameters from archaeological lead ᵃʳᶜʰPbWO₄ з покращеними оптичними параметрами з археологічного свинцю ᵃʳᶜʰPbWO₄ с улучшенными оптическими параметрами из археологического свинца Yakubovskaya, A.G. Tupitsyna, I.A. Dubovik, A.M. Physics and technology of structural materials Technological principles of manufacturing a lead tungstate crystal from archaeological lead for use in low-background experiments to search for rare events are presented. The influence of the conditions for obtaining single crystals of ᵃʳᶜʰPbWO₄ on the photochromic effect in single crystals is investigated. By minimizing deviations from the stoichiometric composition, it was possible to improve the optical parameters of the lead tungstate single crystal. Single crystals with improved optical parameters have been obtained using double crystallization and the introduction of an excess of ᵃʳᶜʰPbO, which makes it possible to consistently influence various defects in crystals of ᵃʳᶜʰPbWO₄. Наведено технологічні основи виготовлення кристала вольфрамату свинцю з археологічного свинцю для застосування в низькофонових експериментах із пошуку рідкісних подій. Досліджено вплив умов одержання монокристалів ᵃʳᶜʰPbWO₄ на фотохромний ефект у монокристалах. Шляхом мінімізації відхилень від стехіометричного складу вдалося поліпшити оптичні параметри монокристала вольфрамату свинцю. Одержані монокристали із застосуванням подвійної кристалізації та введенням надлишку ᵃʳᶜʰPbO дозволяють послідовно впливати на різні дефекти в кристалах ᵃʳᶜʰPbWO₄ з покращеними характеристиками. Приведены технологические основы изготовления кристалла вольфрамата свинца из археологического свинца для применения в низкофоновых экспериментах по поиску редких событий. Исследовано влияние условий получения монокристаллов ᵃʳᶜʰPbWO₄ на фотохромный эффект в монокристаллах. Путем минимизации отклонений от стехиометрического состава удалось улучшить оптические параметры монокристалла вольфрамата свинца. Полученные монокристаллы с применением двойной кристаллизации и введением избытка ᵃʳᶜʰPbO позволяют последовательно влиять на различные дефекты в кристаллах ᵃʳᶜʰPbWO₄ с улучшенными характеристиками. 2022 Article ᵃʳᶜʰPbWO₄ with improved optical parameters from archaeological lead / A.G. Yakubovskaya, I.A. Tupitsyna, A.M. Dubovik // Problems of Atomic Science and Technology. — 2022. — № 1. — С. 204-211. — Бібліогр.: 34 назв. — англ. 1562-6016 DOI: https://doi.org/10.46813/2022-137-204 https://nasplib.isofts.kiev.ua/handle/123456789/195930 546.05:548.2:548.4:539.1.074.3:620 en Вопросы атомной науки и техники application/pdf Національний науковий центр «Харківський фізико-технічний інститут» НАН України |
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Physics and technology of structural materials Physics and technology of structural materials |
| spellingShingle |
Physics and technology of structural materials Physics and technology of structural materials Yakubovskaya, A.G. Tupitsyna, I.A. Dubovik, A.M. ᵃʳᶜʰPbWO₄ with improved optical parameters from archaeological lead Вопросы атомной науки и техники |
| description |
Technological principles of manufacturing a lead tungstate crystal from archaeological lead for use in low-background experiments to search for rare events are presented. The influence of the conditions for obtaining single crystals of ᵃʳᶜʰPbWO₄ on the photochromic effect in single crystals is investigated. By minimizing deviations from the stoichiometric composition, it was possible to improve the optical parameters of the lead tungstate single crystal. Single crystals with improved optical parameters have been obtained using double crystallization and the introduction of an excess of ᵃʳᶜʰPbO, which makes it possible to consistently influence various defects in crystals of ᵃʳᶜʰPbWO₄. |
| format |
Article |
| author |
Yakubovskaya, A.G. Tupitsyna, I.A. Dubovik, A.M. |
| author_facet |
Yakubovskaya, A.G. Tupitsyna, I.A. Dubovik, A.M. |
| author_sort |
Yakubovskaya, A.G. |
| title |
ᵃʳᶜʰPbWO₄ with improved optical parameters from archaeological lead |
| title_short |
ᵃʳᶜʰPbWO₄ with improved optical parameters from archaeological lead |
| title_full |
ᵃʳᶜʰPbWO₄ with improved optical parameters from archaeological lead |
| title_fullStr |
ᵃʳᶜʰPbWO₄ with improved optical parameters from archaeological lead |
| title_full_unstemmed |
ᵃʳᶜʰPbWO₄ with improved optical parameters from archaeological lead |
| title_sort |
ᵃʳᶜʰpbwo₄ with improved optical parameters from archaeological lead |
| publisher |
Національний науковий центр «Харківський фізико-технічний інститут» НАН України |
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2022 |
| topic_facet |
Physics and technology of structural materials |
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https://nasplib.isofts.kiev.ua/handle/123456789/195930 |
| citation_txt |
ᵃʳᶜʰPbWO₄ with improved optical parameters from archaeological lead / A.G. Yakubovskaya, I.A. Tupitsyna, A.M. Dubovik // Problems of Atomic Science and Technology. — 2022. — № 1. — С. 204-211. — Бібліогр.: 34 назв. — англ. |
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Вопросы атомной науки и техники |
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| fulltext |
204 ISSN 1562-6016. ВАНТ. 2022. №1(137)
https://doi.org/10.46813/2022-137-204
UDC 546.05:548.2:548.4:539.1.074.3:620
arch
PbWO4 WITH IMPROVED OPTICAL PARAMETERS FROM
ARCHAEOLOGICAL LEAD
A.G. Yakubovskaya
1,2
, I.A. Tupitsyna
1,2
, A.M. Dubovik
1,2
1
Institute for Scintillation Materials NAS of Ukraine, Kharkiv, Ukraine;
2
V.N. Karazin Kharkiv National University, Kharkiv, Ukraine
E-mail: nikann2007@gmail.com
Technological principles of manufacturing a lead tungstate crystal from archaeological lead for use in low-
background experiments to search for rare events are presented. The influence of the conditions for obtaining single
crystals of
arch
PbWO4 on the photochromic effect in single crystals is investigated. By minimizing deviations from
the stoichiometric composition, it was possible to improve the optical parameters of the lead tungstate single crystal.
Single crystals with improved optical parameters have been obtained using double crystallization and the
introduction of an excess of
arch
PbO, which makes it possible to consistently influence various defects in crystals of
arch
PbWO4.
INTRODUCTION
The search for rare events such as interactions with
non-baryonic “dark matter”, double (without the
participation of neutrinos) beta-decay of nuclei or
radioactive decay of isotopes with a long lifetime is a
very actual problem in modern elementary particle
physics. It is expected that these events will prove the
existence of new fundamental particles, as well as
expand the understanding of the structure of the
Universe [1–4]. Further progress in research in these
areas requires new detectable technologies that are able
to distinguish between weak and rare interaction signals
against the background of significant radioactivity
caused by extraneous factors, namely geological,
cosmogenic or anthropogenic [5–7].
Low-background experiments using the
spectrometric method are carried out in deep
underground laboratories. Radioactive contaminants
with natural, cosmogenic or anthropogenic origin are
present in all of the parts of the experimental apparatus.
The detectors, their components, the nearby
environment and the shields can be source of possible
background, a limiting factor for the achievable
sensitivity of the experiments [1, 5].
The sensitivity of an experiment dedicated to a rare
event search is roughly inversely proportional to the
square root of the background rate. A wide set of
requirements have to be satisfied to achieve the highest
sensitivity in ultralow level detection: primarily, the
choice of a suitable underground laboratory that allows
a reduction of the cosmic rays induced background by
several orders of magnitude, also protecting the
equipment of underground laboratories from the
radioactive environment, mainly from gamma radiation
and gaseous radon, for this purpose, passive or active
screens are used [5].
Scintillation single crystals are the main material
used in detectors. The sensitivity of the experiment
depends on their properties.
The uniqueness of the properties of the lead
tungstate crystal makes it possible to use it not only as
an element in a cryogenic scintillation-bolometric
detector for searching for dark matter, rare events,
studying coherent neutrino scattering on the nuclei of
heavy elements, but also in spectrometric experiments
as an active protection of photomultiplier tube (PMT)
radioactivity [1, 5]. But lead tungstate crystals have a
fairly high intrinsic radiation background due to the
presence of
210
Po and
210
Pb isotopes, which are always
present in modern lead. The idea of using
archaeological lead with a low content of these isotopes
was realized in the work.
Recently, the RES-NOVA project aimed to search
neutrinos from core-collapse supernovae (SN) via
coherent elastic neutrino-nucleus scattering (CEνNS)
using an array of archaeological lead (Pb) based
massive cryogenic detectors. This project proposes the
development and application of new neutrino telescopes
based on lead tungstate and lead molybdate crystals [8].
In this work, we have developed a technique for
obtaining raw materials, as well as the technological
methods for growing low-background optically high-
quality crystals of
arch
PbWO4 with improved functional
parameters.
1. EXPERIMENTAL
We used Teflon glassware (this material does not
contain its own radioactive isotopes) and reagents:
ammonia solution (32%) Extra pure from Merck, nitric
acid (65%) Extra pure from Merck for
arch
PbO·nH2O
synthesis from
arch
Pb.
The synthesis of the charge
arch
PbWO4 was carried
out in a chamber furnace of the SNOL-40/1300 type
with intermediate stirring.
The growing of single crystals was carried out by
Czochralski method in “Donets-1” and “Kristall-607A”
type modified induction installations from a platinum
crucible. Heat treatment of each crystal was carried out
in SNOL 7.2/1300 type muffle furnace with heating
speed and temperature automatic control.
X-ray phase analysis (XRD) of the mixture and
single crystals was carried out on a Siemens D 500
powder diffractometer (Cu Kα, nickel filter, Bragg-
Brentano geometry). The identification of powder X-ray
ISSN 1562-6016. ВАНТ. 2022. №1(137) 205
diffraction patterns was carried out on the basis of the
card index of the International Center for Diffraction
Data (JCPDS-IC).
The content of the main impurity elements in PbO
and WO3 oxides was determined by inductively coupled
plasma atomic mass spectrometry (ICP MS).
Transmission spectra were measured by Shimadzu
UV mini-1240 single-beam spectrophotometer with an
operating range of 190…1100 nm. UV irradiation of the
samples was carried out with two LUFCH-6 lamps
(365 nm, power 2 × 6 W).
2. RESULTS AND DISCUSSION
2.1. PURIFICATION OF RAW MATERIALS
Ordinary lead contains the radioactive isotope
210
Pb,
the activity of which can be tens or even thousands of
Bq/kg, which is unacceptable for the creation of low-
background scintillation devices. The half-life of
210
Pb
is 22.3 years. In archaeological lead (Fig. 1), made after
tens of half-lives,
210
Pb is almost completely absent
(Table 1) [9–11]. Lead tungstate, obtained from
ordinary lead, contained much more radionuclides,
especially
210
Pb (Table 2).
Fig. 1.
arch
Pb samples [11]
Table 1
Radioactive impurities in
arch
Pb samples [11]
Chain Nuclide
Activity,
mBq/kg
232
Th
40
K
60
Co
137
Cs
226
Ra
228
Th
< 7
< 0.2
< 0.5
< 0.4
< 1.2
238
U
234m
Pa
226
Ra
210
Pb
210
Po ()
< 21
< 10
< 30
< 0.3
Table 2
Radioactive impurities in PbWO4 from ordinary lead
(data obtained using γ-spectroscopy at LNGS [12])
Chain Nuclide
Activity,
mBq/kg
232
Th
226
Ra ≤13
238
U
226
Ra
210
Pb
≤10
(53…79)∙10
3
It is clear that for the production of high-quality
scintillation crystals of
arch
PbWO4, the initial lead and
the lead oxide obtained from it must have not only a
high degree of radioactive purity, but also a high degree
of purity for other chemical impurities. In this work, we
used archaeological lead, a complex method of refining
which by distillation in a vacuum was developed and
implemented at the National Science Center “Kharkov
Institute of Physics and Technology” [13]. Purified
archaeological lead oxide (
arch
PbO) was obtained by a
series of chemical transformations:
arch
Pb+4HNO3 →
arch
Pb(NO3)2 + 2NO2 + 2H2O;
arch
Pb(NO3)2 + 2NH4OH →
arch
PbO·nH2O +
+2NH4NO3;
arch
PbO·nH2O →
arch
PbO + nH2O.
Initially, the lead samples were dissolved in nitric
acid solution (3.54 M) of at 250 °C. Thereafter, the lead
nitrate solution was treated with ammonia vapor. Lead
oxide hydrate PbO·nH2O precipitated at a pH of the
mother liquor of 9…11 units. The precipitate was
washed with distilled water several times, centrifuged
and dried at 150 °C for 3 h. Thereafter, PbO·nH2O was
annealed at 600 °C for 12 h to obtain stoichiometric lead
oxide PbO. The resulting sample had an inhomogeneous
color from yellow to orange, which indicates the
presence of several multi-colored phases.
It is known that the PbO system includes six
compounds [14]. There are two stable modifications of
PbO: the tetragonal form α-PbO (red litharge) and the
rhombic form β-PbO (yellow massicot). Their
compositions may deviate from stoichiometric ones
[14, 15].
The β → α polymorphic transition proceeds more
slowly than α → β; therefore, β-PbO can exist at room
temperature in metastable states, but upon rubbing it
transforms into α-PbO. The main properties of lead
oxides are presented in Table 3 [14].
Table 3
Lead oxides properties [14]
Characteristic α-PbO β-РbО α-Pb3O4 β-Рb3О4 α-PbO2 β-РbО2
Color Red Yellow – Red Brown Black
Syngonia Tetragonal Rhombic Rhombic Tetragonal Tetragonal Rhombic
Phase
transformation
temperature
550…590
a
887
b
-90
a
– – –
a
polymorphic transformation α → β temperature;
b
melting point.
206 ISSN 1562-6016. ВАНТ. 2022. №1(137)
β-PbO (mascot) is used for the synthesis of the
PbWO4 charge. β-PbO (JCPDS No. 38-1477) was
obtained by annealing PbO according to the following
scheme: β-PbO (yellow powder I) → α-PbO (red
powder II) → Pb3O4 (orange powder III) → β-PbO
(yellow powder IV).
The phase composition of PbO was determined by
X-ray diffraction. Data of stepwise transformations of
PbO showing in Table 4. Yellow β-PbO powder was
obtained after stepwise calcinations of the original
sample with intermediate mechanical homogenization.
High-purity tungsten oxide WO3 was manufactured
at the Nikolaev Institute of Inorganic Chemistry of the
Siberian Branch of the RAS (Novosibirsk). The content
of basic impurity elements in oxides (Table 5),
measured by atomic mass spectrometry with induction-
coupled plasma, meets the requirements for the purity of
the source components for the production of
scintillators.
Table 4
PbO stepwise transformations data
No
Source substance: color and X-ray
data
Processing
temperature and
duration
Final product: color and X-ray
data
1
Yellow powder I:
23-1159 Pb(NO3)25 PbO
28-0536 Pb5O3(OH)4
28-0537 3Pb(NO3)27H2O
22-0661 Pb(NO3)23 Pb(OH)2
350 °С
5 h
Red powder II:
23-1159 Pb(NO3)25 PbO
36-1462 Pb(NO3)2
27-1201 PbO1,37
2
Red powder II
420 °С
5 h
Orange powder III:
38-1477 β-PbO Massicot
5-0561 α-PbO Litharge
8-0019 Pb3O4
3 Orange powder III
600 °С
12 h
Yellow powder IV:
38-1477 β-PbO Massicot
Table 5
The basic impurity elements content in the initial oxides
Element
ppm
Element
ppm
арх
PbO WO3
арх
PbO WO3
Mg < 5 15 Co < 0.02 < 0.05
Al < 1 1 Ni < 0.1 < 0.05
K < 10 2 Cu < 0.2 < 0.05
Ca < 5 0.5 Zn < 0.3 –
Ti < 0.5 – Ag < 0.2 < 0.05
V < 0.01 – Cd < 0.05 –
Cr < 0,1 < 0.1 Ba – < 0.1
Mn 0.1 < 0.5 Th < 1 < 0.2
Fe < 10 1 U < 1 < 0.2
The charge for growing crystals of
arch
PbWO4 was
obtained by high-temperature solid-phase synthesis
method with
arch
PbO and WO3 by the reaction:
arch
PbO + WO3 →
arch
PbWO4 .
The synthesis of the charge
arch
PbWO4 was carried
out by stepwise heating and holding the mixture of
starting oxides in air at temperature range 250…800 °C
with mixture grinding in a ball mill (rotation speed
70…80 rpm) for 20…30 min.
2.2. GROWING A SINGLE CRYSTAL
BY THE CZOCHRALSKI METHOD
Since single crystals of lead tungstate melt
congruently, the Czochralski method with induction
heating of a crucible was applied to grow them, which
made it possible to dynamically control thermal
conditions.
It was necessary to minimize the temperature
fluctuation of the melt in the longitudinal and cross-
sections of crystals in the growth process and cooling
taking into account the specific properties of the
compounds (complex disordered low-symmetry
structure, violation of stoichiometry, increased viscosity
and low thermal conductivity of melts) for growing
single crystals suitable for the manufacture of large-
sized samples with specified parameters. For this
purpose, well-known measures were tested and
improved: placement of additional heaters over the
crucible in the form of a platinum cylindrical screen and
symmetric blowing of a crystal with a gas flow near the
crystallization front.
The most technologically advanced was the method
of placing a platinum cylindrical and ceramic screens
over the crucible (Fig. 2). Improvement made it possible
to regulate the axial temperature gradient in the growth
zone in the range of 30…100 deg/cm and create
ISSN 1562-6016. ВАНТ. 2022. №1(137) 207
relatively autonomous thermal conditions with a
monotonic temperature distribution in the cooling
chamber in the same crystallization unit. The
dimensions of the screens and rings in the crystallization
unit were correlated in a certain proportion to the
diameter of the crucible. However, in the absence of
melt feeding while growing large-sized single crystals
by an automated method a programmed change in the
rotation and displacement speeds of the single crystal
was used in a Kristall-607A installation to ensure the
stability of crystallization conditions.
Fig. 2. Crystallization unit for
arch
PbWO4 crystals
growing: 1 – additional platinum diaphragm;
2 – fire-resistant ceramics;
3 – platinum screen with a crucible; 4 – crystal
An analysis of the experimental results showed that
monophase and optically uniform lengthwise crystals of
arch
PbWO4 can be obtained only in the case of a
monotonic and smooth change in the heating capacity
required to maintain a constant radius of the growing
crystal within a certain region. This type of capacity
change corresponds to a monotonic change in thermal
conditions during the extraction of the crystal and
guarantees high quality of the crystal. In this case, the
crystal growth occurs from the melt, the
thermochemical stability of which is not violated.
In our case, experiments have shown that the most
preferable conditions for growing colorless single
crystals of
arch
PbWO4 with a diameter of about 45 mm
and a mass of 1300 g (Fig. 3) were:
• gaseous medium – argon;
• gradient in the crystallization zone Тz ≤ 20 deg/cm;
• gradient in the cooling zone Тz ≤ 40…45 deg/cm;
• extraction speed ν = 2.0 mm/h;
• mass increment dm/dt = 40 g/h;
• rotation speed ω = 10 → 20 rpm;
• the ratio of the crystal diameter dk to the crucible
diameter dt: dk/dt = 0.50.
Obtaining scintillators consists of two main stages:
growing crystals (in our case, the traditional Czochralski
method) and thermal treatment of crystals before and
during their mechanical treatment. Moreover, the
second stage was the most difficult and important,
because such tasks as maintaining the integrity of the
crystals during mechanical processing were solved, and
the spectral-luminescent properties of the
arch
PbWO4
scintillators were corrected. To improve the optical
characteristics and reduce impurities, including
radioactive ones, double crystallization was applied.
From the crystals of the first crystallization, cylindrical
parts were cut out, which were used as raw materials for
the melt. Were grown two single crystals were double
crystallization, from which samples of sizes
40…83 mm were made. The samples of
arch
PbWO4 of
the second crystallization were transparent, had no
visible gas inclusions and other phases creating
scattering centers (Fig. 4).
Fig. 3. Single crystal
arch
PbWO4 of the first
crystallization
Fig. 4. The samples of
arch
PbWO4 of the second
crystallization
2.3. OPTICAL CHARACTERISTICS
OF
arch
PbWO4 CRYSTALS
2.3.1. Photochromic effect investigation
It is known that high-quality pure PbWO4 crystals
are transparent to light with a wavelength of more than
330 nm [16]. Structural defects and most impurities lead
to a narrowing of the transparency band due to the shift
of the absorption edge to longer wavelengths. It would
seem that the best purity of the raw material for crystal
growth is the key to obtaining crystals with the best
optical parameters. However, crystals with low impurity
content exhibit very high sensitivity to ionizing
radiation, which leads to the appearance of induced
absorption (IА). A cylindrical element made from a
crystalline boule of
arch
PbWO4 of the first crystallization
acquired a noticeable green color, which was later found
to be caused by irradiation with ultraviolet light during
mechanical processing under the light of mercury
discharge lamps.
In [17–19], a significant effect of stoichiometric
defects was found for very transparent crystals with a
low content of impurities in the charge under conditions
of radiation coloration. It has been established that the
spectrum of IA, caused by light, is equivalent to the
spectrum of IA after ionizing irradiation. Thus, the use
of UV irradiation gives qualitatively the same effect as
gamma irradiation [17].
Under the influence of visible or ultraviolet
radiation, the color of the crystal and, accordingly, its
transparency, undergo significant changes. The induced
color is sometimes restored after some time in the dark,
either under the influence of radiation of a different
frequency, or when heated. Studies have shown that
under the action of visible light, crystals of
arch
PbWO4
restore transparency [20].
Detailed studies of the spectral properties of
arch
PbWO4 of the first crystallization under different
conditions were carried out on a crystal sample
10 × 10 × 7 mm in size. Studies of the effect of UV
irradiation have confirmed our assumption that the color
of the crystal during mechanical processing is due to
208 ISSN 1562-6016. ВАНТ. 2022. №1(137)
UV irradiation. UV irradiation for 1 h led to a
significant color (Fig. 5, curve 2), which was reflected
in the intensity of the absorption bands.
The colored crystal sample was annealed in air at
900 °C for 12 h, after which it lost its color (see Fig. 5,
curve 3).
Fig. 5. Optical transmission spectrum of a 7 mm thick
arch
PbWO4 crystal sample: 1 – before treatment;
2 – after UV irradiation; 3 – after heat treatment
(750 °С for 24 h)
During UV irradiation, defects capture charge
carriers, and color centers (CC) are formed, which can
represent not only point defects, but also associates of
CC or clusters such as those arising under radiation
exposure and give a broad absorption band. Annealing
leads to the release of charge carriers from the traps, but
does not destroy them, because after annealing in any
atmosphere and subsequent UV irradiation, the color
reappears. As indicated in [21], heat treatment and
irradiation in any atmosphere do not significantly affect
the regular crystal lattice. We see the same thing with
our crystals.
After growing, many PbWO4 crystals exhibit broad
absorption bands with maxima at 330…370, 420, or
550…600 nm. The 420 nm band imparts a characteristic
yellow color to the PbWO4 crystals and negatively
affects the light yield, since the spectrum of this band
overlaps the spectrum of the scintillation pulse [22].
There were different opinions on the nature of the
optical absorption bands in PbWO4. In [23], the
absorption band at 420 nm was assigned to 3-valent
impurity ions in place of Pb. The 350 nm band was
associated with cation vacancies, since it disappears
upon doping of niobium samples [24].
IA in the 620 nm region and the absorption band at
350 nm were associated in [24] with a tungsten ion with
an uncompensated charge associated with a 3-valence
ion at the Pb site (420 nm) or with a hole O
–
-center in
the lead vacancy region (35 nm). It was believed that
the absorption band at 420 nm is due to hole centers, the
ion O
–
, while the 350…370 nm band is due to the ion
Pb
3+
[25].
The need for local compensation of excess charge
allows the localization of charge carriers at defective
lattice sites. Evaporation of lead at different growth
phases of a long crystal is compensated by anionic
vacancies (Vo) and F-centers, either by trapping a hole
on a single oxygen (type O
–
defect), or by molecular
oxygen with two antiparallel electron spins (O-Vс-O)
2-
.
The last two defects can be easily recharged by trapping
free charge carriers during irradiation, which is the main
source of the CC in PbWO4 crystals.
When developing a lead tungstate crystal for collider
experiments, a lot of research was carried out aimed at
obtaining radiation-resistant crystals. Pure PbWO4
crystals, even of very high quality, are not used in
experiments in high-energy physics, they do not meet
the requirements of the CMS project on radiation
resistance, since the effect of radiation coloration turns
out to be more significant for crystals with a low content
of impurities in the batch (1 ppm or less) [17–19]. For
this reason, crystals doped with rare earth elements were
used. The production of undoped radiation-resistant
PbWO4 crystals is currently an unresolved problem.
The effects of radiation damage are caused by pre-
radiation defects and defects formed under the influence
of ionizing radiation. Under UV irradiation, the crystal
is exposed only to primary pre-radiation defects,
capturing free charge carriers. Under ionizing
irradiation, additional IA appears in a wide wavelength
band in PbWO4 crystals, which reduces the light yield
due to reabsorption.
In accordance with this, the effect of radiation
bleaching is possible only in crystals with a large initial
absorption in the region of 420 nm. This conclusion is
confirmed in [27], where radiation bleaching was
observed only in the region of 420 nm in crystals doped
with Gd and La. In the latter case, the crystal was grown
in a gas atmosphere with the presence of oxygen. The
bleaching of yttrium-doped PbWO4 samples is
described in [28]. In [26, 27], the effect of radiation
clearing of PbWO4 after γ-irradiation was observed,
which the authors associate with the radiation
transformation of the charge state of 3-valent lead
present in such crystals, that is, with the Pb
3+
Pb
2+
transition It was found that the radiation dose of
PbWO4, corresponding to the saturation IA, is very
small (units of krad). Further irradiation up to doses of
10
7
rad leads to a slight increase in IA, possibly
associated with the formation of structural defects [29].
This means that IA in PbWO4 is associated with the
recharge of impurity or intrinsic defects, and similar
processes are observed under UV irradiation. It is
noticed that crystals with high radiation resistance have
a higher initial transparency in the region of
350…370 nm. The authors of [30] found that the
radiation sensitivity and the shape of the optical
transmission spectrum in the 360 nm region have a clear
relationship. Crystals with high radiation resistance
have a sharp drop in transmission in the short-
wavelength region (350 nm). Crystals with low
radiation resistance have an absorption band in the
region of 350…370 nm, which overlaps the short-
wavelength absorption edge. The light yield of the best
samples is reduced by 70% after a dose of 2 krad, then
by another 50…60% after a dose of 1 Mrad. All
characteristics of the samples were self-healing at room
temperature.
The IA reduction rate differs significantly for
different samples and has no significant relationship
ISSN 1562-6016. ВАНТ. 2022. №1(137) 209
with the initial optical absorption spectra. The
restoration of optical transmission occurs very quickly
(in 10 min by 30…40%) if the samples are exposed to
sunlight. When held in the dark, self-healing is
insignificant in the first 10…60 min. This is due to the
photochromic effect in PbWO4 crystals [30].
At present, two ways have been proposed for
discoloration of a lead tungstate crystal, in which a
photochromic effect is observed. This is annealing at a
temperature of more than 500 °C in any of the
atmospheres: in argon or oxygen, or in air. In this case,
thermal emptying of charge carrier traps occurs. Or the
required activation energy to empty the traps is achieved
by irradiating the crystal with visible light with a
wavelength of more than 450 nm.
After annealing the
arch
PbWO4 crystal for 24 h in air
at a temperature of 750 °С, its color decreased
significantly (Fig. 6, curves 2), which improved the
crystal transmission. The inset to Fig. 6 shows the
difference (Т2-Т1) of the absorption bands for curves 2
and 1. This difference spectrum is an intense broad band
with a maximum at about 420 nm, which is typical for
PbWO4, as described above. A sufficiently large half-
width of the strip and a complex shape indicate that it is
not elementary.
Fig. 6. Transmission spectra of
arch
PbWO4 crystals
( 4083 mm): 1 – colored crystal of the first
crystallization before heat treatment; 2 crystals of the
first crystallization after heat treatment;
3 and 4 – crystals obtained by the method of double
crystallization. Insert: difference of absorption bands
for samples 2 and 1
As shown by the study [31, 32], cluster defects are
formed in lead tungstate crystals, which include reduced
tungsten. The same defects are formed when exposed to
high-energy radiation. In the IA spectra, broad bands are
observed [21]. When grown in a crystal, similar
inclusions can also form, which is associated with redox
processes. Their number can be changed by irradiation
(see increase, Fig. 5, curve 2) or heat treatment (see
decrease, Fig. 5, curve 3; Fig. 6, curve 2), which we
observe in our samples.
In [1], the energy spectra of
137
Cs and
207
Bi γ-quanta
were investigated, measured with a CdWO4 scintillation
crystal ( 2020 mm) mounted directly on the PMT
and mounted on a fiber made of an
arch
PbWO4 crystal
(( 40×83 mm) after its bleaching. The relative pulse
amplitude of the detector with the fiber was 65% with
respect to the crystal mounted directly on the PMT. The
quality of this fiber met the requirements of a low-
background experiment to study the double neutrinoless
beta decay of
106
Cd, measured using a
106
CdWO4
scintillation crystal. Under the conditions of this low-
background experiment, the parameters of the crystals
did not change [33].
2.3.2. Methods for improving the optical
characteristics of
arch
PbWO4
For collider experiments, the optical quality and
radiation resistance were improved by alloying with rare
earth elements. For low-background nuclear
spectrometry, this method is unacceptable, since rare-
earth elements contaminate the crystal with radiation
isotopes. To improve the optical characteristics of the
crystal and reduce the number of stoichiometric defects,
we added an excess of
arch
PbO to the stoichiometric
mixture of the starting oxides in an amount of
0.05 wt.%. During crystal growth,
arch
PbO evaporates
more intensively than tungsten oxide, which leads to the
appearance of a deposit of this substance inside the
growth chamber. This process leads to a violation of the
stoichiometry of the melt and the appearance of a
photochromic effect in the crystal, as shown by
experiments. The introduction of an excess of
arch
PbO
prevents the formation of intrinsic defects associated
with deviations from stoichiometry, namely, Pb
2+
and
О
2–
vacancies, as well as hole centers of O-centers. In
Fig. 7 shows the transmission spectrum of a crystal
sample of
arch
PbWO4 from a charge with an excess of
arch
PbO of 0.05 wt.%. A crystal grown from a charge
with an excess of
arch
PbO 0.05 wt.% did not exhibit a
photochromic effect (see Fig. 7).
Fig. 7. Transmission spectrum of a crystal sample of
arch
PbWO4 (d = 1 cm) with an excess
of
arch
PbO 0.05 wt.%: 1 – before UV irradiation;
2 – after UV irradiation
We applied the double crystallization method in
order to further improve the optical characteristics of
lead tungstate single crystals. The positive effect of
double crystallization (recrystallization) on the level of
radioactive contamination of crystalline scintillators was
demonstrated by the example of CaWO4: the level of
radio purity of the crystal increased by an order of
magnitude (for example,
238
U was rejected by the crystal
nm
210 ISSN 1562-6016. ВАНТ. 2022. №1(137)
with a segregation coefficient of ≈ 0.3), which made it
possible to improve the energy resolution of the
scintillators [34].
The transmission of crystals obtained using the
double crystallization method (see Fig. 6, curves 3, 4) in
the visible region is better than the transmission of the
single crystal of the first crystallization (see Fig. 7,
curve 2). The difference between the transmission levels
of the studied single crystals is insignificant. In our
work we used high quality raw materials with a low
level of uncontrolled impurities. Therefore, the
parameters of single crystals after two crystallizations
improved compared to the annealed crystal of the first
crystallization.
CONCLUSIONS
Technological principles of growing scintillation
crystals
arch
PbWO4 have been developed, observance of
the principles of which allows to control the
stoichiometric composition of the charge during the
growth of crystals. Methods for improving the optical
parameters of lead tungstate crystal from archaeological
lead have been developed. It is shown that the
photochromic effect in
arch
PbWO4 crystals at extremely
low impurity content is associated with deviations from
the stoichiometric composition of the crystal. The
introduction of excess lead oxide into the charge during
crystal growth and the use of double crystallization
allows to consistently affect various defects in
arch
PbWO4 crystals and significantly improve the optical
and scintillation parameters of these single crystals and
scintillators based on them.
REFERENCES
1. G.P. Kovtun, R.S. Boiko, F.A. Danevich et al.
Development and properties of cadmium and lead
tungstate low-background scintillators for double beta
decay experiments // Nuclear Physics and Atomic
Energy. 2014, v. 15, N 3, p. 92-100.
2. U. Dore, D. Orestano. Experimental results on
neutrino oscillations // Rep. Prog. Phys. 2008, v. 71,
р. 106201.
3. R.N. Mohapatra, S. Antusch, K.S. Babu, et al.
Theory of neutrinos: a white paper // Rep. Prog. Phys.
2007, v. 70, p. 1757-1867.
4. J.D. Vergados, H. Ejiri, F. Simkovic. Theory of
neutrinoless double-beta decay // Rep. Prog. Phys.
2012, v. 75, p. 106301.
5. F. Cappella, A. Incicchitti. Techniques for
Background Identification in the Search for Rare
Processes with Crystal Scintillators // Physics. 2021,
v. 3, issue 2, p. 187-206.
6. D. Poda. Scintillation in Low-Temperature
Particle Detectors // Physics. 2021, v. 3, issue 3, p. 473-
534.
7. M.B. Gromov, A.S. Kubankin, A.V. Shchagin.
Numerical Simulation of Radiation Anisotropy of the
Pyroelectric Neutron Generator Moscow University //
Physics Bulletin. 2019, v. 74, issue 2, p. 144-148.
8. L. Pattavina, N.F. Iachellini, I.Tamborra. Neutrino
observatory based on archaeological lead // Phys. Rev.
D. 2020, v. 102, p. 063001.
9. A. Alessandrello, C. Cattadori, G. Fiorentini, et al.
Measurements on radioactivity of ancient roman lead to
be used as shield in searches for rare events // Nucl.
Instrum. Methods. 1991, sect. B, v. 61, N 1, р. 106-117.
10. A. Alessandrello, F. Allegretti, C. Brofferio, et
al. Measurements of Low Radioactive Contaminations
in Lead Using Bolometric Detectors // Nucl. Instrum.
Methods. 1993, sect. B, v. 83, N 4, р. 539-544.
11. F.A. Danevich, S.K. Kim, H.J. Kim, et al.
Ancient Greek lead findings in Ukraine // Nucl. Instrum.
Methods. 2009, sect. A, v. 603, N 3, р. 328-332.
12. F.A. Danevich, A.S. Georgadze, V.V. Koby-
chev, et al. Application of PbWO4 crystal scintillators in
experiment to search for 2 beta decay of Cd-116 // Nucl.
Instrum. Methods Phys. Res. A. 2006, v. 556, р. 259-
265.
13. V.D. Virich, Yu.V. Gorbenko, G.P. Kovtun, et
al. Refining ancient lead by vacuum distillation // East
Eur. J. Phys. 2016, v. 3 N 4, р. 60-65.
14. В.А. Извозчиков, О.А. Тимофеев. Фотопро-
водящие оксиды свинца в электронике. Л.:
«Энергия», 1979, 143 c.
15. D. Risold, J.I. Nagata, R.O. Suzuki. Thermo-
dynamic Description of the Pb-O System // J. Phase
Equilib. 1998, v. 19, р. 213-233.
16. M. Globus, B. Grinyov, Jong Kyung Kim.
Inorganic Scintillators for Modern and Traditional
Applications. Press. “Institute for Single Crystals”,
Kharkov, Ukraine, 2005, 408 p.
17. R.Y. Zhua, D.A. Maa, H.B. Newman, et al. A
study on the properties of lead tungstate crystals // NIM
A. 1996, v. 376, issue 3, р. 319-334.
18. M. Kobayashi, M. Ishii, Y. Usuki, et al.
Scintillation characteristics of PbWO4 single crystals at
room temperature // NIM A. 1993, v. 333, issue 2-3,
р. 429-433.
19. S. Baccaro, L.M. Barone, F. Castelly, et al. Lead
tungstate (PbWO4) scintillators for LHC EM-
calorimeter // Radiation Physics and Chemistry. 1998,
v. 52, issue 1-6, р. 635-638.
20. V. Bondar, S. Burachas, K.A. Katrunov, et al.
Photochromic effect and its influence on scintillation
properties of CdWO4 and PbWO4 crystals // Nucl. Inst
and Meth A. 1998, v. 411, p. 376-382.
21. S.F. Burachas, A.A. Vasil'ev, M.S. Ippolitov, et
al. Influence of cluster defects of variable composition
on the optical and radiative characteristics of oxide
crystals // Crystallography Reports. 2007, v. 52, issue 6,
p. 1088-1093.
22. М.В. Коржик. Физика сцинтилляторов на
основе кислородных монокристаллов. Минск:
«БГУ», 2003, 263 с.
23. E. Auffray, P. Lecoq, M. Korzhik, et al.
Improvement of several properties of lead tungstate
crystals with different doping ions // NIM A. 1998,
v. 402, p. 75.
24. M.V. Korzhik, V.B. Pavlenko, T.N. Timo-
schenko, et al. Spectroscopy and Origin of Radiation
Centers and Scintillation in PbWO4 Single Crystals //
Physica Status Solidi (a). 1996, v. 154, issue 2, p. 779-
788.
https://af.booksc.org/g/Mohapatra,%20R%20N
https://af.booksc.org/g/Antusch,%20S
https://af.booksc.org/g/Babu,%20K%20S
https://ui.adsabs.harvard.edu/#search/q=author:%22Poda%2C+Denys%22&sort=date%20desc,%20bibcode%20desc
https://link.springer.com/article/10.3103/S0027134919020085
https://link.springer.com/article/10.3103/S0027134919020085
https://link.springer.com/journal/11972/
https://link.springer.com/journal/11972/
https://www.etis.ee/Portal/Publications/Display/b3a0e901-5f30-4960-8c0d-24e9d22232fc
https://www.etis.ee/Portal/Publications/Display/b3a0e901-5f30-4960-8c0d-24e9d22232fc
https://www.etis.ee/Portal/Publications/Display/b3a0e901-5f30-4960-8c0d-24e9d22232fc
https://www.etis.ee/Portal/Publications/Display/b3a0e901-5f30-4960-8c0d-24e9d22232fc
https://www.sciencedirect.com/science/article/abs/pii/0168900296002860#%21
https://www.sciencedirect.com/science/article/abs/pii/0168900296002860#%21
https://www.sciencedirect.com/science/article/abs/pii/0168900296002860#%21
https://www.sciencedirect.com/science/journal/01689002/376/3
https://www.sciencedirect.com/science/article/abs/pii/016890029391187R#%21
https://www.sciencedirect.com/science/article/abs/pii/016890029391187R#%21
https://www.sciencedirect.com/science/article/abs/pii/016890029391187R#%21
https://www.sciencedirect.com/science/journal/01689002/376/3
https://www.sciencedirect.com/science/journal/0969806X
https://www.sciencedirect.com/science/journal/01689002/376/3
https://www.sciencedirect.com/science/article/abs/pii/S0168900298003465#%21
https://www.sciencedirect.com/science/article/abs/pii/S0168900297010887#%21
https://www.sciencedirect.com/science/article/abs/pii/S0168900297010887#%21
https://onlinelibrary.wiley.com/action/doSearch?ContribAuthorRaw=Korzhik%2C+M+V
https://onlinelibrary.wiley.com/action/doSearch?ContribAuthorRaw=Pavlenko%2C+V+B
https://onlinelibrary.wiley.com/action/doSearch?ContribAuthorRaw=Timoschenko%2C+T+N
https://onlinelibrary.wiley.com/action/doSearch?ContribAuthorRaw=Timoschenko%2C+T+N
https://onlinelibrary.wiley.com/journal/1521396x
https://onlinelibrary.wiley.com/toc/1521396x/1996/154/2
ISSN 1562-6016. ВАНТ. 2022. №1(137) 211
25. M. Nikl, K. Nitsch, J. Hubler, et al. Slow
components in the photoluminescence and scintillation
decays of PbWO4 single crystals // Phys. Stat. Sol. (b).
1996, v. 196, issue 2, p. 311-323.
26. M.V. Belov, E.E. Devitsin, V.A. Kozlov,
L.S. Popov. Characteristics of scintillating PbWO4
crystals produced at different growing-conditions //
Proc. IEEE Nucl. Science Symposium, San-Francisco,
1993, р. 270.
27. S. Baccaro, P. Bohacek, B.Borgia, et al.
Influence of Gd
3+
Concentration on PbWO4:Gd
3+
Scintillation Characteristics // Phys. Stat. Sol. (a). 2000,
v. 79, issue 2, p. 445-454
28. М. Kobayashi, Y. Usuki, M. Nikl, et al.
Inorganic Scintillators and their applications / Ed.
V. Mikhailin. M.: “Moscow State University”, 2000,
p. 137.
29. L. Nagornaya, V. Ryzhikov. Fast scintillatorset
based on large heavy tungstate single crystals.
Chamonix, France, 1992, р. 367-374.
30. M. Nikl, K. Nitsch, S. Baccaro. Radiation
induced formation of color centers in single crystals //
Journal of Applied Physics. 1997, v. 82, issue 11,
p. 5758-5762.
31. S. Burachas, S. Beloglovski, Yu. Saveliev, et al.
Physical principles of industrial growing technology of
lead tungstate (PWO) for high energy physics
applications // Functional Materials. 2005, v. 12, N 2,
p. 287.
32. S. Burachas, Yu. Saveliev, M. Ippolitov, et al.
Physical origin of coloration and radiation hardness of
lead tungstate scintillation crystals // J. Cryst. Growth.
2006, v. 293, р. 62.
33. P. Belli, R. Bernabei, V.B. Brudanin, et al.
Search for double beta decay of
106
Cd with an enriched
106
CdWO4 crystal scintillator in coincidence with
CdWO4 scintillation counters // Universe. 2020, v. 6,
p. 182.
34. F.A. Danevich, I.K. Bailiff, V.V. Kobychev, et
al. Effect of recrystallisation on the radioactive
contamination of CaWO4 crystal scintillators // NIM in
Phys. Res. Section A. 2011, v. 631, issue 1, р. 44-53.
Article received 06.12.2021
арх
PbWO4 С УЛУЧШЕННЫМИ ОПТИЧЕСКИМИ ПАРАМЕТРАМИ
ИЗ АРХЕОЛОГИЧЕСКОГО СВИНЦА
А.Г. Якубовская, И.А. Тупицына, А.М. Дубовик
Приведены технологические основы изготовления кристалла вольфрамата свинца из археологического
свинца для применения в низкофоновых экспериментах по поиску редких событий. Исследовано влияние
условий получения монокристаллов
арх
PbWO4 на фотохромный эффект в монокристаллах. Путем
минимизации отклонений от стехиометрического состава удалось улучшить оптические параметры
монокристалла вольфрамата свинца. Полученные монокристаллы с применением двойной кристаллизации и
введением избытка
арх
PbO позволяют последовательно влиять на различные дефекты в кристаллах
арх
PbWO4
с улучшенными характеристиками
арх
PbWO4 З ПОКРАЩЕНИМИ ОПТИЧНИМИ ПАРАМЕТРАМИ
З АРХЕОЛОГІЧНОГО СВИНЦЮ
Г.Г. Якубовська, І.А. Тупіцина, О.М. Дубовик
Наведено технологічні основи виготовлення кристала вольфрамату свинцю з археологічного свинцю
для застосування в низькофонових експериментах із пошуку рідкісних подій. Досліджено вплив умов
одержання монокристалів
арх
PbWO4 на фотохромний ефект у монокристалах. Шляхом мінімізації відхилень
від стехіометричного складу вдалося поліпшити оптичні параметри монокристала вольфрамату свинцю.
Одержані монокристали із застосуванням подвійної кристалізації та введенням надлишку
арх
PbO дозволяють
послідовно впливати на різні дефекти в кристалах
арх
PbWO4 з покращеними характеристиками.
https://scholar.google.com/citations?view_op=view_citation&hl=cs&user=HXPCx5QAAAAJ&cstart=20&pagesize=80&citation_for_view=HXPCx5QAAAAJ:9yKSN-GCB0IC
https://scholar.google.com/citations?view_op=view_citation&hl=cs&user=HXPCx5QAAAAJ&cstart=20&pagesize=80&citation_for_view=HXPCx5QAAAAJ:9yKSN-GCB0IC
https://scholar.google.com/citations?view_op=view_citation&hl=cs&user=HXPCx5QAAAAJ&cstart=20&pagesize=80&citation_for_view=HXPCx5QAAAAJ:9yKSN-GCB0IC
https://www.researchgate.net/profile/Bi-Zadneprovski/publication/41763264_Characteristics_of_scintillating_PbWO_4_crystals_produced_at_different_growing-conditions/links/57eae28a08ae91a0c8d3f1f0/Characteristics-of-scintillating-PbWO-4-crystals-produced-at-different-growing-conditions.pdf
https://www.researchgate.net/profile/Bi-Zadneprovski/publication/41763264_Characteristics_of_scintillating_PbWO_4_crystals_produced_at_different_growing-conditions/links/57eae28a08ae91a0c8d3f1f0/Characteristics-of-scintillating-PbWO-4-crystals-produced-at-different-growing-conditions.pdf
https://onlinelibrary.wiley.com/toc/1521396x/2000/179/2
https://aip.scitation.org/doi/abs/10.1063/1.366441
https://aip.scitation.org/doi/abs/10.1063/1.366441
http://www.functmaterials.org.ua/contents/12-2/fm122-19.pdf
http://www.functmaterials.org.ua/contents/12-2/fm122-19.pdf
http://www.functmaterials.org.ua/contents/12-2/fm122-19.pdf
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