Лёд и Снег · 2020 · Т. 60 · № 2

УДК 551.321

doi: 10.31857/S2076673420020032

Employing X-ray computed tomography for the non-destructive ice cores analysis

¹Institute of Geography, Russian Academy of Sciences, Moscow, Russia; ²Lomonosov Moscow State University, Moscow, Russia

^*Khaisasha_@mail.ru

Применение методики компьютерной томографии для неразрушающего

анализа ледниковых кернов

А.Г. Хайрединова^1,2*, С.С. Кутузов¹, В.Н. Михаленко¹, Д.В. Корост², А.Н. Хомяк²

¹Институт географии РАН, Москва, Россия; ²Московский государственный университет имени М.В. Ломоносова, Москва, Россия

^*Khaisasha_@mail.ru

Received January 24, 2019 / Revised June 6, 2019 / Accepted September 19, 2019

Keywords: cryothermos, high-resolution density records, ice (glacial) cores, the Caucasus, X-Ray computed tomography.

Summary

Computed t omography (CT) i s a n ondestructive hig h-resolution wa y t o investigate t he t hree-dimensional

structure o f s amples (ice , r ock, et c.). ἀ e r esults o f CT a nalysis o f g lacial co res co nsisting o f firn a nd ice

extracted on the Western plateau of the Elbrus Mountain (5100-5150 m a.s.l.) in the summer of 2017 are pre-

sented in the article. ἀ e core taken from the depth of 20.31-21.87 m and consisting of three sections (aver-

age length is 52 cm each) was analyzed. In order to maintain the natural negative temperature of the glacial

core, a special cryothermos has been created. It conserved the temperature at the level of -25 °C. Data on the

structural features of the s amples and the three-dimensional pattern of the ice-firn density were obtained.

Correlations b etween the density and some chemical elements had been established. ἀ e CT d ata made it

possible also to determine sizes o f ice cr ystals. Comparison of cross sections of cores with firn and ice t hin

sections (30 in t otal) has shown that the crystal structure is best displayed in t he ice in ter-layers since it is

impossible to determine reliably sizes of the firn grains at the given survey resolution. Also, the use of the CT

method made it possible to determine inclination of the firn layers within the ice core, which is caused by the

inheritance of the slope of the surface microrelief and internal inhomogeneities of the firn thickness. Calcula-

tions showed that the angle of inclination of the layers varies from 6 to 9°.

Citation: Khairedinova A.G., Kutuzov S.S., Mikhalenko V.N., Korost D.V., Khomyak A.N. Employing X-ray computed tomography for the non-destructive

ice cores analysis. Led i Sneg. Ice and Snow. 2020. 60 (2): 182-191. doi: 10.31857/S2076673420020032.

Received January 24, 2019 / Revised June 6, 2019 / Accepted September 19, 2019

Ключевые слова: данные плотности высокого разрешения, Кавказ, компьютерная томография, криотермос, ледниковые керны.

Методика компьютерной томографии позволяет получить снимки послойных срезов леднико-

вого керна с помощью рентгеновских лучей. В работе представлен анализ кернов с Западного

плато Эльбруса с помощью компьютерного томографа РКТ-180. Для поддержания естественных

условий керна был создан специальный криотермос, который препятствует таянию образца и

изменению структуры фирна во время съёмки. Исследована внутренняя структура керна, уста-

новлены размеры кристаллов в разных слоях, найдены неоднородности и получена трёхмерная

картина плотности льда.

Introduction

alyzing the ice cores. The presence of drawbacks,

even in most advanced techniques employed over the

An importance of gaining information from high

past decade, leads to attempts to create new analyti

altitude ice cores is constantly increasing due to the

cal methods. For example, the development of the

global warming. In comparison with Greenland and

continuous flow analyses (CFA), automated chemi

Antarctic regions, which have slower response to the

cal method, permitted to pump samples and reagents

climate changes, mountain glaciers are dramatically

continuously through a system of modules intercon

retreating and disappearing. A wide range of methods

nected by tubing [1]. Employing the laser ablation

is available for studying ice cores presently: chemis

mass spectrometry with inductively coupled plas

try, isotopes, trace elements etc. A variety of most

ma (LA-ICP-MS) produced detailed information

advanced modern technologies are employed for an

about isotopic and chemical composition in sam

 182 

A.G. Khairedinova et al.

ples [2, 3]. The method allows getting ultra-high-

Full-length ice core CT was suggested by Voland

sensitivity chemical analysis at the ppb-level without

et al. [12], however, it required substantial techno

any special preparation of the sample. The problem,

logical support. In the first attempt, the idea was to

however, remains in most of the methods that is re

investigate the structure of ice cores before transpor

lated to the destruction of samples during the analy

tation that lead to applying ice core CT for the first

ses. Ice is essentially lost in the process and become

time in the field (Kohnen station, DML, Antarcti

unavailable for other types of analyses.

ca). Subsequently, a research group from Alfred We

Computed tomography is a well-known tech

gener Institute created a laboratory with X-Ray CT

nique for obtaining cross-sectional images. In the

system inside a freezer room maintained at -25 °C.

last decade, this method has become widely rec

The main goal of our study was to further develop the

ognized and emerged as a leading analytical tool in

methodology for the full-length ice core CT analy

many areas [4, 5]. Computed tomography system al

sis and to evaluate the adequacy of the CT method

lows obtaining a three-dimensional distribution of

for studying ice core stratigraphy. Here we present

the X-ray absorption values in the entire volume of

the first CT results of shallow firn core from Mt. El

the sample within the limits of the resolution. All

brus A CT system enables analyzing ice cores, de

X-ray opaque elements give signal through densi

termine the porosity, compare the visual stratigra

ty and chemical composition differences. The mor

phy and chemistry and to correlate those results to

phology and pore size, caverns, cracks, and in

the ice core thin sections. Since high image qual

clusions are analyzed. The main advantage of the

ity is required to get precise results, a vast amount

method is the non-invasiveness (using intact ice sec

of measurement data was produced. We discuss the

tions) of the samples [6, 7]. Since ice cores are very

advantages and possible further development of CT

precious, the main advantage in using Computed To

analyses for ice core studies.

mography (CT) is that it does not affect further pro

cessing of samples. The analysis cost is relatively low,

while the amount of information obtained is substan

Data and Methods

tial. CT method should be used before other analy

ses. The use of non-destructive CT method does not

The Caucasus mountains are situated between

affect subsequent work with the samples [8].

the Black and the Caspian seas in the south of Rus

Initially, the technique of computed tomography

sia. Ice core drilling took place at Mt. Elbrus, locat

was used in medicine and made a revolution in the

ed in the Central Caucasus Mountains. A shallow

field as it became possible to obtain information about

ice core with a diameter of 9 cm and total length of

the internal structure of the human organism without

24 m was extracted from the Western Elbrus Plateau

surgery. Almost the same equipment and software for

in the summer of 2017. The drilling site was located

interpretation of the X-ray survey can be used for sci

at an elevation of 5115 m [13]. Three sections (an av

entific purposes for sediment or ice core analysis. The

erage length of 52 cm) extracted from the depth of

first attempts to include CT in the principal methods

20,31-21,87 m were used in this study. In order to

of ice core studies were made in 1990 when J.M. Bar

perform the CT analysis for the full-length ice core,

nola and his colleagues used X-Ray tomography for

the freezing temperature had to be maintained during

3D reconstruction of the Vostok firn structure [9].

the imaging session. For this purpose, we used a spe

A related method of micro-tomography is presently

cial cryogenic thermos of 100 mm diameter. It con

in rather high demand [10]. One of its disadvantages

sisted of a polyvinyl chloride pipe with sealed ends

is the necessity of laboratory sampling. The general

and double walls. The antifreeze between the walls

principle of the method is similar to the ordinary CT,

was cooled at -25 °C. The cryothermos may accom

however, micro-CT permits studying the inner struc

modate 1 m long core sections and maintain a suit

ture with high resolution (several microns) [11]. An

able temperature for approximately 5 hours. To test

other problem of working with CT is the necessity of

the ability of the CT system to analyze full length ice

maintaining below-zero temperature. Sneed et al. [2]

cores the artificial ice core (diameter 9 cm, length

tried to solve this problem by constructing a cryocell

30 cm) was made. It contained ice, firn, snow, and

that would permit to do laser ablation inside the cryo

some mineral particles. Artificial core was made by

system while minimizing the sampling area.

sequential adding layers of water, snow and firn sam

 183 

Ледники и ледниковые покровы

Fig. 1. Computed Tomography system:

a - scheme of the mutual arrangement of the sys

tem elements and the sample in a three-dimension

al coordinate system with the main system parts:

the source of X-rays, the object of study, the detec

tor, fixing the level of radiation absorbed by the ob

ject; b - photo of a CT-180 tomograph located at

the Geological Faculty of Lomonosov Moscow

State University. The main parts of a CT scanner

are: 1 - a protective cabinet; 2 - a core holder; 3 -

a mobile support of an X-ray apparatus; 4 - an

X-ray detector moving along the core; 5 - a PC for

processing CT data (http://geologika.ru/)

Рис. 1. Система компьютерной томографии:

a - схема взаимоположения элементов систе

мы и образца при съёмке в трёхмерной систе

ме координат с основными узлами: источник

рентгеновских лучей, объект изучения, детек

тор, фиксирующий уровень излучения, погло

щённого объектом; b - фотография компью

терного томографа РКТ-180, расположенного

на геологическом факультете МГУ имени

М.В. Ломоносова (http://geologika.ru/). Основ

ные части томографа: 1 - защитный шкаф; 2 -

кернодержатель; 3 - подвижная опора рентге

новского аппарата; 4 - детектор рентгенов

ского излучения, перемещающийся вдоль

керна; 5 - ПК для обработки данных КТ

(http://geologika.ru/)

ples collected earlier on Elbrus glacier into the plastic

ple. The attenuation depends on the density and the

tube. The tube was then frozen (-20 °C). Additional

atomic number of the material from which the object

ly, layers of mineral particles collected in Elbrus were

is composed. When X-Rays pass through a material,

also added. The CT system consists of the X-Ray

the radiation absorption level can be associated with

source, an object of the study and the detector, that

four types of interaction: photoelectric absorption,

determine the level of radiation absorbed by the ob

Compton scattering, the formation of electron-posi

ject (Fig. 1, a) [12].

tron pairs, and coherent Rayleigh scattering. The set

A separate two-dimensional image correspond

of obtained X-ray patterns is then recalculated into a

ing to the intensity of X-Ray radiation after passing

set of density sections that reflect the internal struc

through the sample forms the shadow projection.

ture of the sample. This operation is called recon

The main principle of computed tomography is to

struction. The most common way to display CT den

obtain a set of such projections from different an

sities is to distribute the shades of gray on the graphic

gles. This is usually accomplished by its subsequent

slices formed by the system during reconstruction.

stepwise rotation. In addition to the x-ray projection

Lighter shades correspond to a higher density, and

of the sample, information about the spatial reso

darker colors correspond to a lower density. A com

lution of the object, the source, and the detector is

puted tomograph RCT-180 at the Geological De

recorded in contrast with classical X-Ray radiogra

partment of Lomonosov Moscow State University

phy [4]. The brightness (different gradations of gray)

was employed in this study (see Fig. 1, b).

on the X-Ray shadow projection reflects the attenu

This instrument is used for the study of rocks,

ation of X-Ray radiation, because of the scattering

soils, unconsolidated bottom sediments, biological

and absorption of the signal passed through the sam

samples, etc. It allows scanning cores with a length

 184 

A.G. Khairedinova et al.

of 1 m and with a diameter of 10 cm. The scanner is

els). Here we also used the results of the chemical

characterized by a 150-250 μm spatial resolution,

and isotopic composition of the Mt. Elbrus ice core.

100 × 100 × 1000 mm active area and 160 kV in

The isotopic composition was measured in Climate

tensity. The stage rotates for full 360°, in 0.3° steps,

and Environmental Research Laboratory, St. Pe

with carriage lift 0.2 mm. For the artificial core, the

tersburg, while major ions were studied in the Insti

following parameters were used: 1.5-5 mA amper

tute for Geosciences and Environmental Research,

age, 160 kV intensity, and 115 μm spatial resolution.

Grenoble, France [14].

For Elbrus ice cores the parameters of computer to

mographer retained the same, except for the spa

tial resolution (230 μm). The average survey time

Results

was approximately 1.5 hours. The data reconstruc

tion was performed using the TomoViewer software,

The test core. The artificial ice core contained

Geologika (Novosibirsk). The data were processed

ice layer, firn and firn with ice lenses to represent

on the Dell Precision T5500 workstation using soft

the variety of the possible structures in real ice cores

ware products: Data Viewer, CTan (calculations and

(Fig. 2). We also added fine mineral particles from a

construction of 3D models of radiopaque compo

snow sample collected previously in snow pit in El

nents) and CTVol (visualization of volumetric mod

brus as well as some coarse particles collected from

Fig. 2. Artificial ice core:

a - a photo of the ice core with a scale bar (length of the core is 20 cm); b - stereological visualization of a longitudinal section of

the core with its internal structure; brightness (various shades of gray) reflects the difference in absorption; based on this, areas of

ice core with different composition were identified: black color (maximum absorption) - air inclusions, dark gray - firn, gray - ice,

white (minimum absorption) - mineral inclusions; c - ice core cross sections: 1 - core interlayer with firn (dark gray color); 2 -

core interlayer with ice (gray color) and the formation of air bubbles (black color); 3 - core interlayer with ice; 4 - core interlayer

with mineral inclusions (white color) and ice. The orange lines indicate the places of the core cross-sections

Рис. 2. Искусственный керн:

a - фотография керна с масштабной линейкой (длина керна 20 см); b - стереологическая визуализация продольного

среза керна с его внутренним строением; яркость (различные оттенки серого) отражает разницу в поглощающей способ

ности: чёрный цвет (максимальное поглощение) - включения воздуха; тёмно-серый - фирн; серый - лёд; белый цвет

(минимальное поглощение) - минеральные включения; c - поперечные срезы керна: 1 - прослой керна, вмещающий

фирн (тёмно-серый цвет); 2 - прослой керна, состоящий из льда (серый цвет) с образованием пузырьков воздуха (чёр

ный цвет); 3 - прослой керна, состоящий изо льда; 4 - прослой керна с минеральными включениями (белый цвет) и

льдом. Оранжевые линии соответствуют поперечным срезам керна

 185 

Ледники и ледниковые покровы

the rock outcrops near the drilling site. Fig. 2, b

for Mg. The ion concentrations level off in sec

shows the stereological visualization of the artificial

tion 43. This distribution is due to the presence of a

ice core. Main structure heterogeneities were detect

large amount of dust in ice in the section 41. A dou

ed. The brightness (different gradations of gray) on

ble peak of calcium, corresponding to two dust lay

the X-ray shadow projection reflects the attenuation

ers in the ice core is observed also in Fe profile (sec

of X-ray radiation, due to the effects of scattering

tion 41). When considering the dependence of the

and absorption of the signal passed through the sam

presence of chemical inclusions on optical density, it

ple. The cross sections with contrasting media are

was revealed that the high concentration of Ca indi

shown, namely mineral inclusions, ice, firn and air

cated the dust layer that can be identified by CT.

bubbles (see Fig. 2). The optical density corresponds

In Fig. 4 separate dense horizons are observed,

to the degree of of Х-rays attenuation of transpar

which are reflected in the variations of chemical ele

ent objects or reflection of light by an opaque object.

ments. Pronounced in density is only the dust layer

Optical density can be calculated using the formula

in which concentrations of all chemical elements are

OD = log₁₀ (I₀/I), i.e. I₀ - incident optical intensity,

rising. However, this may be due to the sampling

I - transmitted optical intensity. The types of objects

technique in 10-cm increments, which could cause

with the highest values of optical density (270 and

the chemical signal to be blurred or not manifested

more) are the dense mineral inclusions. The average

at all. The section shown in the red frame in Fig. 4, a

value of the optical density for ice in an artificial core

and b has the highest density values. When compared

is 120-150. The optical density of air approaches 0.

with the gradations of the artificial core, it was sug

Considering the results of artificial ice core, the inner

gested that the formations may be separate mineral

structure heterogeneities in the natural ice cores can

dust particles. It is possible that individual dust par

be detected using the same approach.

ticles in the ice core can be observed using the CT

Shallow core-2017. The Elbrus shallow firn

technique. The problem that arises when interpreting

core was dated using well preserved seasonal sta

data is the separation of noise and the signal from the

ble isotopic oscillations. The seasonal amplitude of

actual crystals. For their separation, it is necessary

δ¹⁸O change was 25.2 ‰, with average values being

to create criteria for the selection of density classes.

-25 ‰ in winter and -10 ‰ in summer respective

Under low resolution imaging conditions, it is often

ly. The ice core covers the period of 2012-2017 with

difficult to find an increase in the density reflected in

mean annual accumulation rate of 2200 mm w.e.

CT images corresponding to an increase in the con

Three sections used in CT analyses correspond to the

centration of inclusions. These shortcomings should

layers accumulated during the warm season of 2012.

be considered in future studies.

A detailed description of section’s stratigraphy was

Another important advantage of this technique is

made in the cold laboratory. It was revealed that the

the ability to trace the inclination of the layers in three

cores are composed mostly of firn and contain min

dimensions (see Fig. 4, c), since usually information

eral particles. Ice layers and dust horizons can be

about the 3D structure of the ice layers is not avail

visually identified. The distribution profiles of the

able. It is possible to clearly trace the firn layers and

main chemical elements are presented in Fig. 3 to

calculate their angle of inclination relative to the bore

gether with density characteristics of the core. The

hole. The firn core from the depth of 2020-2180 cm

density was measured in cold laboratory using dis

is composed of firn and the inclination, in this case,

crete sections for every 10 cm. The maximum density

is due to the influence of the surface microrelief and

of 0.8 g/cm² was observed for the layers at the edge of

possible internal inhomogeneities. The calculations

sections 42 and 43. The distribution profiles of Ca²⁺,

showed, that the angle of inclination of the layers in

Mg⁺, NH₄₊, SO_42-, and Fe²⁺ were analyzed to find

the studied sections varies from 6 to 9°. With further

similar patterns.

use of the CT technique for deeper core sections such

The values for all ions were elevated in section 41:

information may provide insights into basal ice flow

for Ca the maximum value is 100 ppb, for Mg -

disturbances. Such information is important to verify

80 ppb, for NH₄ - 800 ppm, for SO₄ - 1850 ppm,

the ice flow and depth age modelling.

for Fe - 60 ppm. Concentrations decreased in

Structural features. The method of computed to

section 42: NH₄ = 400 ppm, SO₄ = 600 ppm,

mography allows determining the internal structure

Fe = 25 ppm, and the minimum are equal to 10 ppb

of the core. According to the obtained CT data, it

 186 

A.G. Khairedinova et al.

Fig. 3. The distribution profiles of the density, chemical elements, CT data and visual images in three sections of ice

cores (sections 41-43) from the depth 20,31-21,87 m.

Dashed blue lines indicate the boundaries between core sections. The distribution profile: a - density measured in freezer condi

tions every 10 cm: b - Ca and Mg; c - NH₄ and SO₄; d - Fe, horizons of mineral dust and ice interlayers; e - photographs of sec

tions with visible layers of dust and ice horizons; f - stereological visualization of sections with identified internal heterogeneity

Рис. 3. Графики плотности, химических элементов, КТ-данных и фотографии ледниковых кернов в трёх

секциях керна (секции 41-43) c глубины 20,31-21,87 м.

Пунктирные голубые линии - границы между секциями кернов. Профили распределения: а - плотности, измеренной в

условиях морозильной камеры через каждые 10 см: b - Ca и Mg; c - NH₄ и SO₄; d - Fe, горизонтов минеральной пыли и

прослоев льда; e - фотографии секций керна с видимыми прослоями пыли и ледяных горизонтов; f - стереологическая

визуализация секций с выявленной внутренней неоднородностью

Fig. 4. Stereological visualization of ice cores:

a - lower part of section 41; b - section 43 with dif

ferent absorption of horizons; in the red rectangles -

presumably mineral dust particles; c - upper part of

section 41 with visible slope of the firn layers

Рис. 4. Стереологическая визуализация лед

никовых кернов:

а - нижняя часть секции керна 41; b - сек

ция 43 с различными по абсорбционной спо

собности горизонтами; в красных прямоуголь

никах - предположительно минеральная пыль;

с - верхняя часть секции 41 с видимым накло

ном слоёв фирна

 187 

A.G. Khairedinova et al.

is possible to identify individual stratigraphic layers,

the samples do not need to be cut and melted. In this

without cutting of the samples. In addition, using

study, it was possible to solve the problem experienced

the CT technique allows distinguishing the crystals

by the previous researchers employing the CT tech

composing the individual density layers according

nique, related to maintaining the proper temperature

to their size. In order to test whether the resulting

conditions for the ice. A special cryothermos was de

image also provides information on the size of the

signed, that does not require any special investments,

crystals, a comparison was made with the firn and

as in the case of using a special walk-in freezer labora

ice flat-surface vertical sections. The sections were

tory. However, at this point cryothermos is not com

made for each horizon, distinguished visually by stra

pletely satisfactory and needs to be further improved,

tigraphy for all three sections (a total of 30 thin sec

since it was not able to maintain the proper condi

tions). Subsequently, a comparison was made of ver

tions for the ice for more than 5 hours. Reliable re

tical sections and horizontal core sections using CT.

sults were obtained for the test ice core. That sample

Below we list the most illustrative examples. The

was characterized by a large contrast in composing

horizontal sections of various parts of the core were

media. Density, porosity and structural features of the

obtained using the DataViewer program. In this case,

Elbrus core sections were determined. Correlations

mineral inclusions are absent, therefore the densest

with several (Ca, Fe) chemical elements were found.

layer (ice) is displayed in white. The core section 43

The question of whether it is possible to decipher in

consisted of firn with some ice layers up to 4 cm thick

dividual dust particles in large-scale dust horizons still

(Fig. 5). The ice layers, shown in the first cross sec

remains open and needs further verification. Informa

tion, have a crystal size of up to 6-8 mm. They are

tion on the crystals size can be obtained using the CT

characterized by the highest contrast and are easily

data especially when there is a high contrast with the

detectable on the CT images. The second cross sec

background medium. It should be noted that the ob

tion depicts the firn that is representative for most of

tained CT data were characterized by a large amount

the core used in this study. As seen in the cross sec

of noise. To identify all structural heterogeneities and

tion, the crystals have dimensions on the order of

clearly separate between inclusions and the noise, it is

0,1-0,5 mm. They are not distinguishable on the CT

necessary to carry out the imaging with higher resolu

image and are revealed only as noise. The third sec

tion. This will require substantially greater computer

tion displays a coarse-grained firn, the crystal size of

storage capacity. In further studies, it is necessary to

which reaches 1 mm. Such firn can be identified by

pay close attention to the choice of spatial resolution,

the results of a CT scan. However, there is an ambi

to design a longer-lasting cryothermos for maintaining

guity in the correct interpretation of such horizons

the proper temperature conditions for the ice cores,

associated with a large amount of noise.

and to study a greater number of firn and ice cores to

Thus, the use of computed tomography allowed

fully explore the possibilities of a CT method.

identifying heterogeneities in the structure of the ice

core. They were not recorded when the core was pre

Acknowledgments. The research was supported by the

viously inspected visually. Moreover, in some cases,

Russian Science Foundation (project № 17-17-

it was possible to identify patterns of crystals of dif

01270). We thank I.I. Lavrentiev, A.A. Polukhov,

ferent sizes in the image. However, only contrast

A.A. Abramov and all the participants of the expedi

ing media with a large difference in the size of crys

tion to Elbrus in 2017. We also thank A.M. Grachev

tals are confidently distinguished on the background

for valuable comments and text edits during the man

of fine-grained firn: the ice and coarse-grained firn.

uscript preparation.

Благодарности. Работа выполнена при поддерж

Conclusion

ке Российского научного фонда (проект № 17-

17-01270). Мы благодарим И.И. Лаврентьева,

The method of computed tomography was test

А.А. Полюхова, А.А. Абрамова и всех участников

ed on artificial and actual ice cores. The technique

экспедиции на Эльбрус в 2017 г. Также авторы

has several clear advantages. Compared with microto

выражают благодарность А.М. Грачеву за цен

mography, ordinary CT allows examining samples

ные советы и коррекцию текста во время подго

up to 1 m length. It is non-destructive, meaning that

товки статьи.

 189 

Ледники и ледниковые покровы

Применение методики компьютерной

стости и структурных особенностях. Установле

томографии для неразрушающего анализа

ны корреляции с рядом химических элементов, а

ледниковых кернов

также явная зависимость оптической плотности

по результатам КТ от содержания кальция. Лед

В настоящее время при изучении ледниковых

никовый керн с глубины 2020-2180 см сложен

кернов используется большое число современных

фирном, наклон которого обусловлен унаследо

методов. Однако многим из них свойственны не

ванностью микрорельефа поверхности и возмож

достатки, связанные с разрушением и таянием об

ными внутренними неоднородностями. Расчё

разца при анализе, что препятствует дальнейшему

ты показали, что угол наклона слоёв в изучаемых

использованию кернов. Компьютерная томогра

секциях изменяется от 6 до 9°.

фия (КТ) - способ получения послойных срезов

Метод компьютерной томографии позволяет

объекта с помощью рентгеновских лучей. Яркость

определить внутреннюю структуру керна. Также

(различные градации серого) на рентгеновской те

по данным КТ можно получить сведения о раз

невой проекции отражает ослабление рентгенов

мерах кристаллов. Было проведено сравнение по

ского излучения за счёт эффектов рассеивания и

перечных срезов кернов КТ со шлифами фирна

поглощения сигнала, прошедшего через образец.

и льда. Шлифы были сделаны для каждого гори

Ослабление зависит от плотности и атомного числа

зонта, различаемого визуально по стратиграфии

материала, из которого состоит изучаемый объект.

для всех трёх секций. Общее число шлифов - 30.

Преимущество метода КТ - его быстрота: затраты

Далее было проведено сопоставление шлифов и

непосредственно на съёмку - минимальные, при

горизонтальных срезов керна по КТ. Установле

этом объём получаемой информации - весьма су

но, что лучше всего кристаллы отображаются при

щественный. В нашей работе использовался ком

большом контрасте с фоновой средой. В данном

пьютерный томограф РКТ-180 на геологическом

керне фоном служил мелкозернистый фирн, на

факультете МГУ имени М.В. Ломоносова. Метод

контрасте с которым в результатах КТ были вы

компьютерной томографии был протестирован на

делены ледяной горизонт и горизонт с крупно

искусственном и настоящем кернах (ледниковые

зернистым фирном. Значительный недостаток

керны с Западного плато Эльбруса). Авторы реши

полученных данных КТ - большое количество

ли проблему, связанную с поддержанием темпера

шумов. При дальнейших работах необходимо с

турных условий льда, которая была у предыдущих

повышенным вниманием подойти к выбору про

исследователей КТ-методики. С этой целью был

странственного разрешения, создать термос с

создан специальный криотермос, поддерживаю

увеличенным временем сохранения температур

щий температуру на уровне -25 °С.

ных условий льда, а также изучить большее число

В результате работы с секциями керна Эль

образцов ледниковых кернов для выявления се

бруса получены данные о его плотности, пори

зонных и годовых закономерностей.

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