Надеина Л.В. Радиоэкология

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hot particles

16) the role that hot particles

play in evaluating radiation haz-

ards

p) концентрации некоторых

радионуклидов

4. Read the text and do the tasks.

Investigating fallout from nuclear testing

Hot particles & Cold War

Entering the next century, more than 2000 nuclear test explosions of

various sizes and varieties will have been recorded. Nearly all of them were

conducted during the Cold War period ending in the 1990s. Atmospheric nu-

clear tests dispersed radioactive residues into the environment. They are par-

titioned between the local ground (or water surface) and the tropospheric and

stratospheric regions, depending on the type of test, location, and yield. The

subsequent precipitation carrying the residues leads to both local and global

fallout. Concentrations of certain radionuclides can result in formation of

«hot particles» — tiny bits of materials containing radioactive chemical ele-

ments. Local fallout includes large radioactive aerosols, particles which are

generally deposited within about 100 kilometers of the test site. Local radio-

active contamination at nuclear weapon test sites additionally is attributed to

safety trials of nuclear devices that often dispersed fissile material. This ma-

terial is released in various forms, including plutonium vapour, plutonium

aerosols of various sizes, plutonium oxide particulates, plutonium-coated par-

ticles, and sizeable lumps of plutonium-contaminated structural material de-

stroyed by the test explosion. Global fallout encompasses both tropospheric

and stratospheric fallout. The first consists of aerosols that are not carried

across the tropopause and that deposit with a mean residence time of up to 30

days. During this time, the residues become dispersed in the latitude band of

injection, following trajectories governed by wind patterns. Stratospheric fal-

lout arises from particles that later give rise to widespread global fallout,

most of which is in the hemisphere where the nuclear test was conducted. It

accounts for most of the residues of longlived fission products. Nuclear fall-

out results in the exposure of people to radioactivity through internal irradia-

tion (due to inhalation of radioactive materials in air or ingestion of contami-

nated food) and external irradiation (by radioactive materials present in sur-

face air or deposited on the ground). Extensive studies in these areas have

been done. In the case of nuclear testing, evaluations of the nature of the pri-

mary event typically include analyses of radioactive material deposited on the

ground. Such studies are problematical, however, because there can be sig-

nificant alteration of radionuclide composition between the time of a nuclear

detonation and the time samples are collected for radiochemical analysis. A

process called fractionation causes samples of radioactive residues to be un-

representative of the detonation products. Fractionation begins with the con-

densation of radioactive and inert material from the fireball. The mixture may

begin to separate while condensation is still in progress because of the influ-

ence of wind, gravity and the turbulence of the atomic cloud. Further separa-

tion of the condensate occurs through various processes, including contact of

the residues with inert material. When the atomic cloud is formed, the proc-

esses of cooling, condensation, coagulation, mixing, and separation take

place simultaneously but to different extents in different regions of the cloud.

Furthermore, the initial radioactive products change in elemental form

through processes of radioactive decay.

Hot particles

Scientific understanding of the fractionation phenomena is important for

interpreting global fallout and the nuclear chemistry of the detonation process.

It is also useful for evaluating contamination and ingestion hazards. Varia-

tions in size and type of particles are accompanied by variations in radio-

chemical composition, according to fractionation patterns. The nature and

concentrations of radionuclides, together with the size and shape of particles,

are in turn the factors determining the inhalation or ingestion hazard. Other

important scientific information concerns the chemical form in which ra-

dionuclides are present in the particles. The radionuclides present in hot par-

ticles are in general relatively inert compared to ions, atoms and low molecu-

lar mass species that are more mobile and easily available. To assess short-

and longterm consequences of atmospheric fallout — and in particular the

leakage of radionuclides from hot particles — detailed physicochemical in-

formation on this source term is essential. Usually, characteristics of source

terms have been restricted to inventory estimates, activity levels, or activity

concentrations of deposited radionuclides. Information on the physicochemi-

cal form is limited. After deposition, particles are subject to weathering and

the associated radionuclides are mobilised over time. The particle composi-

tion, possible structural changes, and the chemical conditions at the deposi-

tion site will influence the weathering rate. Moreover, the mobilized radionu-

clides can also interact with soil and sediments. Most models assessing the

transfer and consequences of radionuclide contamination assume that the ra-

dionuclides are present as ionic or low molecular weight species. This may

easily lead to an overestimation of the short term consequences of the radio-

logical contamination. On the other hand, if the particles are rather inert, as

often the case, the transfer of radionuclides will be delayed until weathering

occurs. Consequently, the assessment of the long-term consequences of ra-

diological contamination can be underestimated. It is then apparent that

unless the role of hot particles is taken into account, model predictions can be

affected by significant uncertainties. The presence of hot particles may also

render invalid some assumptions made when dealing with soil and sediment

contamination. This includes the frequent assumption that the scaling of sur-

face or mass activity concentrations to units of various magnitudes (for ex-

ample, from Bq/cm2 to Bq/m2 or Bq/km2 and vice versa) is a legitimate op-

eration. The following examples illustrate specific approaches for studying

hot particles at nuclear-weapon test sites.

Studies in South Australia

From 1953-63, the United Kingdom conducted a programme of nuclear-

weapon testing at Maralinga and Emu in South Australia. At these sites, now

completely rehabilitated, nine nuclear explosions and several hundred smaller

scale trials were performed. While the major explosions had a yield between

one and 27 kilotons, the minor trials only involved the burning and explosive

dispersal of uranium, plutonium, and short-lived radionuclides. The environ-

mental consequences of these trials were extensively studied by the Austra-

lian Radiation Laboratory (ARL) and have been the subject of a number of

publications. The most significant plutonium contamination at Maralinga re-

sulted from a series of twelve safety trials in which 22 kg of plutonium (and a

similar quantity of uranium-235) were released into the environment. The

material was dispersed by conventional explosives and little or no nuclear re-

actions took place. Plutonium was ejected vertically to altitudes up to 800

meters and was dispersed by the prevailing winds over considerable distances.

This caused the contamination of considerable portions of land. Plutonium

could be found many kilometers away from the detonation points. ARL iden-

tified plutonium in basically three forms — as superficially coated on materi-

als such as pieces of metals, plastic, wire, and lead bricks that were part of

the experimental assemblies; as tiny fragments or particles, not always visible

to the eye but easily detectable by a gamma monitor; and as very finely dis-

persed material consisting of contaminated soil particles and recondensed

plutonium articles in the same size range as the soil itself. Samples of this

material were collected and separated by sieving down to a diameter of 45

micrometers to determine mass and activity concentrations. Results showed

that the greatest mass was generally associated with the 250-500 micrometers

fraction; however, most of the activity (about 41%) was concentrated in the

fraction below 45 micrometers, which contained only 5% of the total mass.

The lowest fraction was further fractionated into seven aerodynamic sizes

ranging from 45 micrometers to less than three micrometers. In this way, the

inhalable fraction — defined as that with a size less than seven micrometers

— was also identified. Particles were also identified in an 800-gram sample

of soil (having an activity of 25 Bq of americium-241), broken down by a

process of binary separations into discrete particles. All the sample’s activity

was found to be contained in the separated 54 hot particles. The activity of

the individual particles was estimated to be in the range 0.1 to 2.0 Bq of am-

ericium- 241 and the average diameter was about 20 micrometers. The study

also identified a large number of sub-millimeter hot particles which were

analysed by high resolution gamma-ray spectrometry (to determine the ratio

of plutonium-239 to americium-241) and for biological uptake. Five sub-

millimeter particles with activities ranging from 30 Bq to 5 kBq were also

analysed by proton-induced X-ray emission spectroscopy to gain information

on their elemental composition and homogeneity. In these particles, which

were several hundreds of microns in diameter, plutonium and uranium were

found homogeneously distributed on the surface. The major elements identi-

fied were aluminum (1.8%), potassium (2.3%), calcium (1%), iron (23%),

lead (1.9% to 35%), uranium (2.9% to 0.8%) and plutonium (19%). Dissolu-

tion studies in simulated lung fluid indicated that the particles had no signifi-

cant solubility.

Studies in French Polynesia

Other investigations of hot particles were conducted in French Polynesia

by an expert team as part of the international Study on the Radiological

Situation at the Atolls of Mururoa and Fangataufa, completed in 1998. From

July 1966 to September 1974, forty-one atmospheric nuclear tests were con-

ducted there. In addition, five safety trials were conducted on the surface at

the northern tip of the Mururoa atoll, in areas generally referred to as the Co-

lette region. The safety trials were conducted to investigate the behaviour of

the core of nuclear devices under simulated faulty detonation conditions. The

core was destroyed by a conventional explosive detonation with the conse-

quential dispersion during each test of about 3.5 kg of plutonium-239 in the

form of finely divided plutonium and plutonium oxide. Although extensive

cleanup operations were done in 1982-87, plutonium hot particles were left

on the surface of the Colette region and in the adjacent sand bank in the la-

goon.

As part of the international Study, the residual contamination in the ter-

restrial environment of Mururoa and Fangataufa, including the Colette region,

was assessed by a team of scientists. A sampling campaign was organized

and coordinated by the IAEA’s Seiberdorf Laboratories and conducted in the

summer of 1996. This was followed by extensive radiochemical measure-

ments on about 300 samples. The analysis of the residual contamination in

the Colette region identified the presence of plutonium-containing hot parti-

cles. Twenty relatively large particles, ranging in size from 200 micrometers

to one millimeter, were separated from coral debris and crushed coral rocks.

They were measured by high resolution gamma spectrometry to evaluate

their activity and the ratio of plutonium-239 to americium-241. The activity

of plutonium-239 was found to fall in the range 5 to 300 kBq, although a par-

ticle with a level of about one MBq was also found. The americium-241 ac-

tivity in the particles was in the range 0.2 to 5.6 kBq. Six of these hot parti-

cles, with diameters ranging from 200 to 500 micrometers, were also studied

by optical microscopy and micro X-ray fluorescence. The observations re-

vealed that some particles had a smooth, glassy compact nature while others

appeared rough and could even be conglomerates of smaller particles. In ad-

dition to plutonium, the particles were found to contain other elements. They

included uranium and neptunium at concentrations 10 to 100 times lower

than plutonium; calcium (indicating they had a calcium carbonate matrix);

iron (indicating their metallic nature); chlorine (most likely from the sea salt);

and traces of manganese, nickel, chromium, cobalt, and titanium (probably

reflecting the composition of the steel containers of the fissile material used

for the safety trials). To estimate the distribution of plutonium in coral debris,

a 1053-gram sample was also sieved in seven size fractions. The activity of

plutonium and americium in the various fractions were measured by high

resolution gamma spectrometry. The results showed that 99.9% of the mass

and 95.8% of the activity were present in particles larger than 250 microme-

ters. Nevertheless it must be pointed out that the study did not exclude the

presence of particles smaller than 10 micrometers (containing the inhalable

fraction) with plutonium-239 activities of several hundred becquerels. In vi-

tro dissolution studies in serum simulant of six hot particles showed that the

quantity of plutonium solubilized was in all cases less than 0.07% of that ini-

tially present in the particles. This indicated dissolution characteristics similar

to those of the particles from the Maralinga nuclear test site.

Future needs

The investigation of hot particles is highly relevant to correct evalua-

tions of radiation hazards at sites which were contaminated by nuclear-

weapon testing. Studies so far, however, have led to more questions than fi-

nal answers. They indicate that the information on hot particles and particle

fractionation obtained through radiochemical, chemical and physical analyses

of debris is still too small and too scattered when viewed against the diversi-

fied nature of particles produced and the number of variables requiring inves-

tigation. Therefore, the complex phenomena which control the formation, the

chemical and radiochemical composition, and the physical and morphologi-

cal properties of hot particles and their behaviour in the natural environment

are still not fully understood.

It is apparent that the phenomena leading to the formation of hot parti-

cles and their behaviour in the ecosystems are complex. Thus, any generali-

zation must be advanced with caution. It is believed that further progress in

this area will require multi-disciplinary teams of scientists. They should in-

clude physical chemists, specialists in non-destructive microanalytical tech-

niques, radiochemists, nuclear physicists, and health physicists. It also must

be pointed out that hot particles of various sizes and composition containing

actinides, fission or activation products are released to the environment from

other sources besides nuclear testing. For example, they were produced by

the Windscale pile fire in 1957, the B-52 aircraft crash at Thule in 1968, the

satellite Cosmos crash in Canada in 1978, and the Chernobyl accident in

1986. Hot particles have also been released to the environment at nuclear fa-

cilities contributing to the production of fissile material for nuclear-weapon

programmes. In general, any facility for the processing of nuclear material is

known to release small, but detectable, amounts of radioactive and nonradio-

active isotopes to the immediate environment. These releases, which are of-

ten insignificant from the radiation hazard point of view, can be in the form

of waste streams, aerosols, or particles and can be found at some distance

downwind or downstream of the point of release. The same modern analyti-

cal techniques used to investigate hot particles from nuclear testing can be

applied to studying other sources of environmental radioactivity. They enable

scientists to measure extremely small amounts of chemical elements and iso-

topes present in released radioactive materials, thereby providing information

about the process which formed them. Hopefully in years ahead, more studies

on hot particles will be carried out at sites that have been contaminated by

nuclear-weapon testing and various types of nuclear accidents, and at sites

near nuclear installations. The work will benefit from advances in instrumen-

tal analytical techniques. It will further lead to greater understanding of the

role that hot particles play in evaluating radiation hazards, and in providing

information on the type and purpose of the facilities that generated them.

(Pier Roberto Danesi «Investigating fallout from nuclear testing. Hot

particles and the Cold War», IAEA Bulletin, 40/4/1998)

Grammar in Use

Forms of Gerund

Forms of Gerund Active Voice Passive Voice

Simple Gerund contaminating being contaminated

Perfect Gerund having contaminated having been contaminated

Forms of Participle

Forms

of Participle

Active

Voice

Passive

Voice

Present

participle

contaminating being contaminated

Past

participle

–––––– contaminated

Perfect

participle

having contaminated having been contaminated

4.1 Analyse these sentences with ING-forms

1. Further separation of the condensate occurs through various processes, in-

cluding contact of the residues with inert material.

2. During this time, the residues become dispersed in the latitude band of in-

jection, following trajectories governed by wind patterns.

3. Concentrations of certain radionuclides can result in formation of “hot

particles” — tiny bits of materials containing radioactive chemical elements.

4. Scientific understanding of the fractionation phenomena is important for

interpreting global fallout and the nuclear chemistry of the detonation process.

5. Entering the next century, more than 2000 nuclear test explosions of vari-

ous sizes and varieties will have been recorded.

6. The lowest fraction was further fractionated into seven aerodynamic sizes

ranging from 45 micrometers to less than three micrometers.

7. Nearly all of them were conducted during the Cold War period ending in

the 1990s.

8. The Australian Radiation Laboratory identified plutonium in basically

three forms — as superficially coated on materials such as pieces of metals,

plastic, wire, and lead bricks that were part of the experimental assemblies; as

tiny fragments or particles, not always visible to the eye but easily detectable

by a gamma monitor; and as very finely dispersed material consisting of con-

taminated soil particles and recondensed plutonium articles in the same size

range as the soil itself.

9. They are partitioned between the local ground (or water surface) and the

tropospheric and stratospheric regions, depending on the type of test, location,

and yield.

10. It will further lead to greater understanding of the role that hot particles

play in evaluating radiation hazards, and in providing information on the type

and purpose of the facilities that generated them.

11. It also must be pointed out that hot particles of various sizes and compo-

sition containing actinides, fission or activation products are released to the

environment from other sources besides nuclear testing.

12. The same modern analytical techniques used to investigate hot particles

from nuclear testing can be applied to studying other sources of environ-

mental radioactivity.

13. Hot particles have also been released to the environment at nuclear facili-

ties contributing to the production of fissile material for nuclear-weapon pro-

grammes.

14. The subsequent precipitation carrying the residues leads to both local and

global fallout.

4.2 Fill in the prepositions in the following sentences.

of(×16), in (×7), across, with(×2), about, on(×2), out(×2), at, by(×2)

near, from, besides, to

1) The first consists …. aerosols that are not carried ……… the tropopause

and that deposit …….. a mean residence time of up to 30 days.

2) The mixture may begin to separate while condensation is still ….. pro-

gress because …… the influence ….. wind, gravity and the turbulence …..

the atomic cloud.

3) Results showed that the greatest mass was generally associated …… the

250-500 micrometers fraction; however, most …… the activity (……. 41%)

was concentrated ….. the fraction below 45 micrometers, which contained

only 5% ….. the total mass.

4) ……. these particles, which were several hundreds ……. microns …. di-

ameter, plutonium and uranium were found homogeneously distributed ……

the surface.

5) …… addition …… plutonium, the particles were found to contain other

elements.

6) The investigation ……. hot particles is highly relevant to correct evalua-

tions …… radiation hazards ….. sites which were contaminated ……. nu-

clear-weapon testing.

7) Therefore, the complex phenomena which control the formation, the

chemical and radiochemical composition, and the physical and morphologi-

cal properties …….. hot particles and their behaviour ……. the natural envi-

ronment are still not fully understood.

8) It also must be pointed ……. that hot particles ……. various sizes and

composition containing actinides, fission or activation products are released

to the environment …… other sources ……… nuclear testing.

9) Hopefully ……. years ahead, more studies …….. hot particles will be car-

ried ……. ……. sites that have been contaminated ……. nuclear-weapon

testing and various types ……. nuclear accidents, and ……. sites ……. nu-

clear installations.

10) Concentrations ……. certain radionuclides can result …… forma-

tion …….. «hot particles» — tiny bits …….. materials containing radioac-

tive chemical elements.

5. Read the following text and fill in the missing words and word combina-

tions.

the activity of each particle; roughly avoid in shape; the presence of zirco-

nium; local mineral origin; the presence of thorium; was sampled to; only

two alpha-emitting particles; speculative and highly uncertain; «undis-

turbed» pasture

Evidence of 1) ……………………… was found in grass samples col-

lected from 2) …………………. . One particle was found to be of

3) ……………….., the alpha-activity being due to 4) ………………….. . It

was not possible to definitively characterise the other particle, but

5) ………………. raises the possibility of it being a fragment of nuclear fuel

cladding. The particles were both 6) ……………….. and measured ca. 20

μm along their long axes and 5 to 10 μm across. An upper limit for

7) …………….. was estimated to be of the order of 1 × 10

-3

Bq.

The frequency of each type of particle, based upon a ratio of the area

that 8) ………………… the total area encompassed by the sampling pro-

gramme, was estimated to be one particle per 14 m

(or 0.07 m

-2

). However,

this estimate must be regarded as 9) ………………… since it is based on two

single observations only.

6. Read the following word combinations and give the Russian equivalents.

~ a person exposed to radiation –

~ radioactive contamination –

~ radiation exposure –

~ a contaminated person –

~ released into the environment –

~ external contamination –

~ comes into contact with a person's skin –

~ enter the body through an open wound –

~ internal contamination –

~ swallow or breathe in radioactive materials –

~ are deposited in different body organs –

~ give off a form of energy –

~ for a person to be contaminated –

~ other people or surfaces that they touch –

~ hug other people –

~ the body fluids (blood, sweat, urine) –

~ decrease the risk of internal contamination –

~ reduce the length of time –

~ to avoid getting radioactive material –

~ using lots of soap and lukewarm water –

7. Translate these sentences into English.

1. В организм человека «горячие частицы» поступают пероральным и

ингаляционным путем. Они, прежде всего, осаждаются в трахеях и

бронхах, легочной ткани, а также в желудочно-кишечном тракте.

2. Частицы с высокой активностью образуют подвижные (например, в

макрофагах, скоплениях слизи) и неподвижные

(в рубцах) «горячие

точки».

3. Во время прохождения через легкие и при циркуляции через регио-

нальные лимфоузлы облучаются форменные элементы крови с возник-

новением лимфопении и других гематологических изменений.