I{ON-DESTRUCTM TESTING: NEUTROI{ RADIOGRAPHY

In.' Application of physical methocls' ec!. Ju. Tsipenjuk, in Encycloperlia oí Ltíe Supports Systems (E)LSS), Developed under the auspices of the UNESCO, EOLSS On-line Publishers, Oxford, UK, 2004

I{ON-DESTRUCTM TESTING: NEUTROI{ RADIOGRAPHY

Erzsébet Sváb

Department of Neutron Physics, Research Institute for Solid State Physics and Optics, Hungary

Márton Balaskó

Reactor Technics Laboratory, Atomic Energy Research Institute, Hungary Keywords : Neutron Radiography, Neutron Sources, Imaging Techniques.

Content

1. Introduction

2. Principle of Neutron Radiography 3. Neutron Sources

4. lmaging Techniques

5. Neutron Radiography lnstrumentation

6. Radiography Investigations in Reseaph and Development 7. Conclusions and Future Trends

Acknowledgements Related Chapters Glossary

Bibliography Biographical Sketch

Summary

Neutron radiography (NR), an advanced technique for non-destructive materials testing, utilizes transmission of radiation to obtain visual information on the structure and/or inner processes of a given object. Over the last two decades there has been considerable development of NR techniques, and these techniques have found more and more applications. Moreover, the demand for high level technology in materials research and in industry augurs increasing interest in the immediate future. An overview is given on the principle of NR, on various tlpes of neutron sources, on imaging techniques, on instrumentation and on several recent applications.

1. Introduction

Non-destructive testing (NDT) is in widespread use in industrial R&D as well as in research laboratories. The most widely used NDT techniques are ultrasonic inspection, acoustic emission, vibration diagnostics, eddy current inspection, X-

ray radiogÍaphy, and leak detection. Neutron radiographv NR) has a special role because ofthe need for high intensity neutron sources; such sources are generally provided by a research reaitor or, in special applications, portable sources ("'Cf' isotope or accelerator based neutron source). In view of this, NR cannot routinely be used in industry although it provides useful and unique information in several fields by providing a visual image showing the inner structure and processes of a given object transmitted by neutrons. NR provides complementary or even completely original information in relation to X-ray or gamma radiography because the interaction of neutrons with material is fundamentally different from X-ray or gamma radiation.

As long ago as 1938-1944 neutron radiographs had been already been obtained by using Ra-Be source, and by means of an accelerator neutron source. However, it was not until 1950-1960 that they became routinely used. The nuclear industry used NR for testing fuel elements and control rods of atom reactors and routine industrial inspections were performed on turbine blades.

Over the two last decades there has been a considerable development of NR and such techniques are increasingly used because of the demand for high level technology in materials research and in industry. NR is employed in a wide range of investi gations, including:

1. routine test measurements in quality control, e.g. nuclear fuel rods, pyrotechnical materials, turbine blades, corrosion of aircraft, inspection of honeycomb structures in rotor blades;

2. materials science and R&D of industrial products, e.g.

environmentally friendly materials (freon-Rl34a), heat tubes, oil flow in gas turbine engines and components, refrigerator and compressor systems;

3. hydrogen diffusion in metals, oil infiltration in petrophysical model systems, thermodynamic properties of two-phase systems;

4. investigation of works of art (paintings and ancient sculptures);

5. biological and plant physiological research, e.g. root growth, distribution of water and heavy metals in plants.

The article surveys the techniques and several

principle of NR including neutron sources, imaging recent applicati

2. Principle of Neutron

Neutron radiography utilizes transmission of radiation to obtain information on the structure and/or inner processes of a given object. The basic principle of NR rs very simple. The object under examination is placed in the path of the incident radiation, and the transmitted radiation is detected by a two-dimensional imaging system, as is illustrated in Figure 1. The NR arrangement consists of a neutron source, a pin-hole type collimator which forms the beam, and a detecting system which registers the transmitted image of the investigated object. The most important characteristic technical parameter of an NR facility is the collimation ratio L/D, where I is the distance between the incident aperture of the collimator and the imaging plane, D is the diameter of the aperture. This important parameter describes the beam collimation and will limit the obtainable spatial resolution by the inherent blurring independently from the properties of the imaging system.

cenT appllcauons.

1>

Radiography lJ/

This unsharpness (/6"u- can be related to the distance between the object and the detector plane 12 and to the L/D ratrol.

-beam -r T

LJD

Converter scÍeen Radiography

lmaglng

Figure 1. General principle of radiography

Two opposing demands have to be taken into consideration when planning a radiography arrangement: if L/D is large then the neutron flux iDnn at the imaging plane is relatively weak but the geometrical sharpness is high, and vice versa. The basic relation for <D7ya is

/,

( 1 )

@NR =

r6(L/D)2

where iD, is the incident neutron flux.

In radiography imaging the attenuation coefficient p is a crucial parameter. The transmitted intensity of the radiation, d passing through a sample with an average transmission of p can be written as

,

,=Ire-!n

(3) where 1o is the incident intensity and h is the thickness of the sample. If there is any inclusion (inhomogeneity, inner structure) in the sample of thickness x and transmission p* then the transmitted intensity, I*, is given as

(2)

Ir=Ioe-ts(h-x)-P,x

(4)

If the value of p and Fx are different from each other then the presence of the inclusion will provide a contrast in the radiography image.

The attenuation coefficient vs. atomic number is plotted in Figure 2 for neutron radiation and for gamma- and X-rays. Its value depends on both the coherent and incoherent scattering and on the absorption properties of the element(s). For neutrons, p does not show any regularity as a function of atomic number, and for some of the lightest elements (H, B, Li) the attenuation coefÍicient is by two orders of magnitude greater than the corresponding parameter for most of the technically important elements, such as Al, Si, Mg, Fe, Cr. This fact is of practical importance, viz. neutrons penetrate almost all metals used for construction purposes with little loss in intensity; in contrast they are considerably attenuated in passing through materials containing hydrogen, such as water, oil or several types of synthetics. On the other hand in the case of X-ray and gamma radiation, this dependence may be characteized by more or less continuously increasing curves. This means that the radiation is absorbed to a great extent by heavy elements whereas it penetrates light materials such as hydrogen without significant loss in intensity.

Ir

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t . f f i Lc , aR.

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,{l

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cr 7'nll." " li

a n b

ipt,;

C.t.ll4 h l l . l " r t aT. ga 'h a",

a

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. b

1U a tr"21$

Atomic nilnrber

Figure 2. Attenuation coefficient (note the logarithmic scale) of elements for neutrons (separate dots), for 1 MeV gamma-ray (dotted line), for 150 keV X-ray

(solid line) and for 60 keV X-ray (dashed line).

These differences for various radiations provide the possibility to gain complementary information by using all three types of radiation together.

3. Neutron Sources

b!

,

4

The energy spectrum of neutrons in thermal equilibrium

temperature Z approximates Maxwell-distribution with a moderator at

o(E)dE _A E ,exp(-E Íbnd,E (rr)'

(s)

where O(Q is the flux per energy interval dE, A is a constant, t equals the Boltzmann constant, and T is the absolute temperature. The following terminology is used in NR:

Fast neutrons: 10 keV - 20 MeV Epithermal neutrons: 0.3 eV - 10 keV

keV Thermal neutrons: 0.005 eV - 0.3 Cold (subthermal) neutrons: < 0.005 eV.

Most NR investigations are carried out with thermal (and epithermal) neutrons obtained from research reactors. However, a number of important applications need cold neutrons. The energy of cold neutrons is smaller than the Bragg cut-off energy of metallic components. In such cases Bragg scattering is absent and, for example, the hydrogen (or boron) content of the sample gives greater contrast with respect to the metal components than for thermal neutrons.

The great advantage of reactor facilities is the high flux and the available infrastructure, which is needed to cover the multipurpose use of reactors.

Accelerator sources provide smaller flux but their great advantage is their portability. Furthermore, their "switch-on"/"switch-off' mode is especially advantageous in industrial use; moreover, there is no problem with burnt out fuel elements. The need for mobile NR equipments comes mainly from aerospace applications, such as inspection of airplane structures for corrosion early detection or inspection of turbine blades. This is the reason for such great efforts being made over the last 20 years to developing and producing a new generation of portable, accelerator based neutron sources ("DIANA" in Europe, superconducting-_-cyclotron in the UK, proton linear accelerator in the USA).

Radioisotopes 12s2cf isotope) are the simplest sources but their lifetime is rather limited and their neutron flux is lower than the other sources.

4. Imaging Techniques f

ln that neutrons are neutral particles a converter material - in NR generally a foil - is used to convert neutrons to another type of radiation, to enable them to be detected directly. Various detector systems are employed in NR: combinations of film and neutron sensitive converter foil, combinations of a light-emitting scintillator screen with a CCD camera and, more recently, imaging plates.

Depending on the object to be investigated and the task to be solved, two basic types of NR are in use: static radiography and dynamic radiography (real-time).

Both techniques provide averaged information on the investigated object in its depth. Neutron computer tomography (NCT) is a rapidly developing technique that provides information on the three-dimensional structure of a given object.

a. Static NrR records a static picture of the object to be investigated.

Even nowadays, film techniques are the most widely used. The information is not a priori obtained in digital form, but may be digitized

with a scanner or densitometer. The most recent developments are the imaging plate (IP) system and the camera-based technique, both of which are now being used to a much greater extent.

The IP is a new film-like radiation image sensor based on photo-stimulated luminescence. It consists of a specifically designed composite structure that traps and stores the radiation energy. A polyester support film is uniformly coated with a photo-stimulatable luminescent material - barium fluorobromide containins a trace amount of Eu2* as a luminescence centre (BaFBr:Eu2) - and it is then coated with a thin protective layer. The stored energy is stable until scanned with a laser beam whereupon the energy is released as luminescence. In the case of neutron sensitive IP the storase luminescent material is mixed with sadolinium oxide.

The camera-based system consists of a scintillator plate and either a low- light-level (LLL) video or CCD camera which records the light emitted by the scintillator. The images recorded by a CCD camera are inherently digital, while those of a video camera can be recorded by video recorder or can optionally be digitized by a frame-grabber. In static radiography the images recorded by the camera are integrated, and thus a static picture of good statistics may be obtained from the object.

b. Dynamic (real-time) NR is used to investigate movements inside the investigated object (flow of fluids in metal tubes, evaporation or condensation processes, two-phase systems). The imaging system consists of a scintillator plate that converts the neutrons into light which is detected by an LLL video camera with short imaging cycle or by a CCD camera.

The individual images are registered and analyzed on a time scale, they may be visualized on a monitor and recorded by a video recorder or by a computer. Compared with static NR this technique needs a relatively high neutron flux densitv: at least l0u n cm''sec''.

The characteristic features of static and dy'namic (real-time) NR imaging techniques are surveyed in Figure 3.

c. Neutron computer tomography (NCf) offers the unique capability of displaying cross-sectional slices of the samples with high resolution, and produces data which aÍe easily adaptable for 3D representation. Although tomographic techniques have been well known since the beginning of the 1970s in the field of diagnostic medicine, their initial application in the neutron field was limited by the available neutron detectors. Recently this problem has been overcome by the development (and available cost) of CCD cameras. A scintillator converts the transmitted neutron beam to a visible light pattern, and each pixel of the CCD camera acts as an equivalent neutron detector, as it visualizes only a very narrow area of the scintillating screen. If one rotates the sample, the NR images are recorded in several positions and the use of suitable software enables the 3D image of the obiect to be reconstructed.

I r r a d i a t i o n Proccssins in dark-room

oE-

of film l. Direct method with photographic film

converter: Gd foil (25pm) film öonvefter l oon/cmt l onn/cmt Scintillator screen ol-i F+Zn (Ag) ( 100 pm)

2. Transfer method with photographic fihn

Mctal foils: Dy, In, Au Íbil foil film

l00pm 3x10'n/cmt development offihn Track-etch technique using nitrocellulose film

'55Gd (n'e)l5óGd l40 keV 6Li in,ct) rHe 4.7 MeV

"'ln 1n, y;"t''In I McV ' * D y

1 n , y ; ' u t ' " D y 5 1 4 k e V l r r a d i a t i o n Processing in day-light

n + y

rril,#fi,x

nitrocellulose film Imaging Plate (Ba F Br: Eu2t + Gd

I 07 n/cm 2

oxide) technique

'u B 1n, cr ; t Li 2.3 Mev

l r r a d i a t i o n Processing in day-light

n Í 1 n

To computer

Imagingi Plate 20.l00p rn; 10ón,/om2 5. Real-time technique

l r r a d i a t i o n I P r o c e s s i n g i n d a y - l i g n t n + y

Scintillator screen ol'i F+Zn (Ag) ( 100 pm) l08n/cm:

Fisure 3. Characteristic features of neutron

lO"n/cm. óLi (n,o) ]He 4.7 MeY

radiography imaging systems.

5. Neutron Radiography Instrumentation

For a rough survey, Table 1 contains the leading NR facilities including the characteristic parameters. Most of the beam lines have thermal neutrons, while cold neutrons are provided at the CEA-Saclay-ORPHEE station. The beams mostly have a circular shape, but neutron guide lines have commonly a rectangular cross section. The guides for cold neutrons have relatively small fields of view but high intensity. They are often used in scanning mode, using a moving trolley for sample. The Cd-ratio value describes the content of epithermal contributions in the neutron spectrum. There are two aspects concerning these neutrons: the disadvantage by perturbing the thermal interactions with a sample

Irradiatron activation Processing in dark-room

n r y n r y

I

by neutron moderation (especially if it contains hydrogen), the advantage of the efficient use of epithermal resonance reactions in Indium as neutron detector when strong thermal absorbers should be transmitted. Therefore, it is not easy to decide which aspect is more important for the applications at a NR facility. It depends on the demands of the experiment and has to be considered individually.

The very wide range in beam formation properties depends much on the layout of the individual facility, the general performance goals and the practical applications established at the given laboratory.

Table 1. Characteristic parameters of the leading neutron radiography facilities.

. The Cd-ratio describes the content of thermalized neutrons compared to those rvith higher energies.

** Z denotes diameter

Here, we describe in details the radiography station (see Figure 4) using both the neutron and gamma radiation obtained simultaneously from a thermal radial channel of the 10 MW Budapest research reactor. ln addition, an X-ray generator can be placed at the radiography station for X-ray imaging of a given object.

O lnsidecotlimaror

@ non slrner svrcm o B.fi romlüon anJ filic(ng oilil

@ Rtu(o. shktd,ns o oubid€ co|linlalor

@ Biologiül s'c|d'ng O Poslion of Fdable X-fry 8cncrator

@ lnvcíisatd ob.jccrwü rcDol. contol mcchilsm

@ tmagrng sysen "iu

@ Nrrkrngpuanucrindicaron

@ Brckground rv umcra

@ s.". *np

@ conrol cabin

Figure 4. Simultaneous d)mamic neutron and gamma radiography station at the 10 MW research reactor in Budapest. Details of the imaging system are shown

separately in Figure 10.

Neutron and gamma radiations are obtained through a pin-hole type collimator with L/D:l70. The thermal neutron flux (D s at the sample position is 108 cm-2 s-l with a beam diameter of 150 mm. Objects under investigation, with a weight of up to 250kg and a surface area of 800mmx1000mm, can be moved into the appropriate position by remote control. An industrial X-ray generator family (50- 300 keV, 5 mA) can be placed in front of the object to investigate it under the same working conditions.

Neutron-, gamma- or X-ray radiation passing through the object is converted into light, which is detected by a high sensitivity (10-o lux) LLL video camera. The imaging cycle is 40 ms, thereby enabling medium speed movements up to about 2.5 msec-' to be visualized inside the investigated object. For neutron radiography imaging, an NE 426 converter screen is used; for gamma radiography a Nacs single crystal, and X-ray imaging utilizes a ZnS screen. Resolution of the neutron image is = 200 pm, the gamma image = 350 pm, and the X-ray image = 160 pm.

Radiography images are displayed on a monitor and stored by a S-VHS recorder.

Image analysis programs (Sapphire 5.05, QUANTEL, ItK, and Imane 1.4, KFKI, Hungary) are used (the latter contains a digitization option). More recently a Peltier-cooled CCD camera is also used, but its light sensitivity is lower than that of the LLL video camera.

In addition to the radiography image, other parameters characterizing the operation of the investigated object - such as operating time, pressure, temperature, flow velocity and power consumption - are measured and recorded.

6. Radiography Investigations in Research and Development

Neutron radiography is used mainly in technical and industrial non-destructive applications but it also offers interesting, sometimes unique capabilities to the non-engineering sciences. A survey of NR applications is given in Table 2.

Table 2. Survey of neutron radiography applications

i Area of applicat_i9l_l__**9!ig.cts__-_._l

Purpose qfjryp:Slqn

i

W ---W[--x t-'I)', ]e.',i!s-;* -:]

jAircraft and helicopter ]Aluminium, honeycomb jCorrosion' moisture, ádtláJi"ó....-l jmaintenance, turbine lund "o.npo.ite structures, ldefects, QC on residual cores of 1

lmanufacture lturbine blades lthe moulds I

n".".r*" i"d".t " -d @ .- F-T.-bly *.t-1, ac "f .l*.g.ql

! " '

tesearch l(actuators, cable cutters), lseals. isolation, lubrication i

i lnechanical and electronic i I

I, lcomponents I I

a"t"-"biÉ i"d'.t.y;'d -iop.*tt"g

""-b*ii-

-|sildy

"f fl.'d Ílo*, l"b'rc'tj."* ]

iesearch _)y1'ng,,u"iS:g:lalslrls ,_.Q9-glr tyryg_ . _i

iresearch jengine, airbag charging 'QC gas tubing i

pr'é*i""iá"á '--Maú"iá."*p"'*"k-Fva.'a.g"r;t*rrcc"f---.*-]

Fetrophysical industry and land structures. two-phase lsealings, visualization of two 1

!g!g".qL, [rocesses, oil infiltration [hases, oil-reservoir modelling I

M"t..iá1ilciá;;, .... .-ll\4;i;iiű.gy."-pÉ,

h'gl"*r{ilóy d"t.ib';ió", aC f* ".*k' i

ceramics and composite ltech ceramics, composite linclusion, density, bonding and I

9tru9!r119s structures porosity i

jö*'' .'gi*",,"g --p"*Ét"

."-pl.,,- ---ffi.te'

pe.me"bi1'ty'

"g''g;f .- ] i lreinforced concrete, boncrete, behaviour of steel in i I lconcrete with plastic-coated feinforced concrete I

j l e i n f o r c e m e n t l - i

r-:---:- :--y'- ' ^-1.- . ':- ---l--*-:---- -":-"---r:::

calorimetric devices Heat pipes. two-phases in Visualization of boiling. , I lsteel prpe (e.g. gas and jevaporation, condensation, :

l !ut..' áoti.í'i..ui.' .at.l, ].n"i*t".i zationof two-phas" l

I lrefrigerators lsystems 1

D.fáó.'d".t'y "'d - --

P^püii"*' ignter;- -ffi-a*

jordnance I -

,

inechanical structures 1

Medicine *iT.'-"iíffi;*__

B,."" ';"úó" aói'* ih;,;iiű - 'i

i i GNCT) for brain tumor I

Hol.$'' pl".t '..**h ;Seeás. plants V;,*;"t"dy őí'""id.*i"p-.'i

, , , , 1

iin soil, uptake and distribution of ,

f.i

lunidentifi ed objects, oil

lalnnngs

I

yisualization of underlying lstructures, charactertzation of the lartists' work

I

Severai NR applications from recent activities are described below.

l n

6. 1 . Calorimetric Devices 6.1.1. Heat Pipes

Heat pipes or thermosyphons have become increasingly popular in present day heating techniques. The heat transfer between the heated evaporator and the cooled condenser zones makes use of the high evaporation heat of the working fluid. Underlying the development of heat pipes is the aim of increasing the maximum possible heat transport capacity. Three basic factors influence the operation of heat pipes: the given fluid, the amount of fluid, and the innermost surface of the wall of the pipe.

Visualization of the processes occurring inside heat pipes is highly desirable as a means of understanding how these devices operate. With this in mind, heat pipes have been prepared from glass or with a glass window. However, experiments using equipment of this nature can be performed only under decreased pressure, temperature and heat transfer, and in this way such experiments are only able to model the real processes.

Dynamic neutron radiography is a specific method enabling one to "look inside"

heat pipes operating under industrial conditions, i.e. high pressure and temperature, and such pipes are prepared from metal tubing. Neutron radiography was successfully applied for testing a heat pipe which was a part of a flue gas-to- air heat recovery apparatus. The tube was prepared from steel of 2.6 mm wall thickness, 5 mm in diameter and 820 mm in length. The working fluid was water, which was admitted under vacuum. A valve system was situated at the upper end of the tube for filling purposes and a manometer was fitted for measuring the pressure inside the tube. A continuously adjustable power supply with a maximum power of 900 W was used to heat the pipe for 250 mm of its length; at the top of the pipe an adjustable cooling ventilator was mounted to adjust the thermotechnical parameters during operation.

Testing was carried out using three different amounts of water: the quantities used corresponded to an underírlled case' an amount similar to the critical specific volume. and to an overfilled case.

The DNR measuÍements gave the possibility to visualize the boiling and the condensation processes in the water-filled heat pipe. Pulsed boiling was visualized and analyzed up to the characteristic temperature depending on the filling quantity. Three characteristic regions were distinguished in the vertically placed tube, viz.: that region constantly filled by the liquid; a periodically wetted zone;

and a region constantly filled with vapor. The frequency of pulsation is an interesting parameter and data analysis was performed to determine it. However, difficulties arise with regard to quantitative data analysis in that pulsation is not strictly periodic; it may be termed "quasi-periodic". In this way, a mean periodicity value can be given. The value increases from 0.5 to 2Hz as a function of the increasing temperature and, simultaneously, the amplitude of the pulsation decreases. If the flow velocity is calculated from the related data of the amplitude and the periodicity of the pulsation, a constant value of = Q.4 ms-t is obtained over the whole temperature range. This means that the flow velocity of the pulsed

1 i

boiling in the periodically wetted zone does not depend on the working temperature of the heat pipe.

The dynamic pulsation of the liquid causes significant fluctuation in pressure leading to the ongoing development and collapse of large vapor plugs. Owing to the fluctuation of the temperature and pressure the thermal and hydraulic features of the boundary layer between the evaporator and the condenser zones are unstable. It can be established that for a heat pipe operating in the lower critical interval, thermal and hydraulic equilibrium do not exist and consequently none of the usual heat transfer models for calculating the important working parameters should be utilized. In this temperature range the heat transfer parameter should be determined experimentally.

The effect of tilting was studied as well. It was observed that the amplitude of the pulsed boiling decreases and the pulsation disappears at an angle of 80o to the vertical.

6.1 .2. Absorptiontype Refrigerators

The high hydrogen content of the working fluid in the aggregator tube system of absorption-type refrigerators enables one to visualize the working characteristics by neutron radiography. Aggregators or even complete refrigerator boxes can be placed into the beam, and in this way the working processes of new prototlpes can be analyzed non-destructively.

The working fluid of an absorption-type refrigerator contains 35% NH3 dissolved in water, it is known as rich solution. This rich solution flows from the tank through the heat exchanger into the boiler where it is heated to about 170' C. At this temperature ammonia gas separates from the water, goes through the vapor pump taking up water drops with it. Most of this water retums via the heat exchanger to the absorption tube system as a weak ammonia solution (about 10%

NH3). The remainder of the aqueous water condenses in the water se_parator and flows back to the rectifier leaving the practically pure ammonia vapor at 70" C - to find its way to the condenser where the temperature is about 20" C and the pressure is 25 bar. Under such conditions the ammonia vapor condenses. This ammonia fluid is blown by 2.5 bar hydrogen or helium, meanwhile it evaporates, refrigerating its surroundings in the deep-freezer unit. The ammonia vapor returns to the fluid tank through the absorber tube system and is absorbed by the weak solution and the cycle starts again.

By virtue of the high content of hydrogen in the working fluid, one can visualize the various processes by neutron radiography these include: the boiling in the bubble pump, the condensation of ammonia gas in the condenser, the formation of drops in the evaporation system, segregation and clogging, air bubbles in the fluid, and the level of fluid in the water tank.

Absorption aggregators are very sensitive to the correct position of the tubing system. Even a variation of about 3o from the horizontal position may cause a breakdown in cooling, therefore it is very important to understand the cause of this. Neutron radiography explores the critical points in the absorber tubes where liquid ammonia accumulates and creates clogging (Figure 5) in consequence of incorrect tilting angle, and this leads to a breakdown in operation.

T2

Figure 5. Clogging of the liquid ammonia in the absorber tube system leads to breakdown of the unit.

obviously all manufacturers are concemed about increasing the cooling efÍiciency of their products so a very important factor in the production process is that of discovering defects in design and to optimize the working conditions in all the different parts of the unit. Recent efforts have been focused on combining NR visualization with other types of NDT methods, viz., vibration diagnostics (VD) and acoustic emission (AE), which may be applied in industry for quality control.

Simultaneously, with the NR measurement VD signals were detected by vibration sensors and AE signals by acoustic emission sensors placed on the crucial points of the tested cooling unit. It was observed by NR that the correct operation of the bubble pump (Figure 6) is very sensitive to hydrogen pressure. Boiling of ammonia gas from the rich solution takes place at this part of the unit, and it is accompanied by noise. By mean of VD this weak noise was detected and a difference was measured for the well operating and for the defective units. The VD water-fall diagrams show a stationary state for the "good" unit whereas it is completely irregular for the "defective" one (see Figure 7). Unfortunately the highly informative nature of the VD results is offset by the need for measurements to be performed in a noise-shielded laboratory because the frequency of noises from the surroundings is in this range. It would be extremely expensive to realize in the factory such ideal conditions. On the basis of the findings the AE method was utilized for testing the refrigerator units. The sensitive frequency of the AE method is above 100 kHz, thus noise from the surroundings does not cause any disturbance. Investigations have shown that boiling in the bubble pump generates high frequency noises as well. Thus, it was possible to measure very different spectra by AE for a well operating unit in comparison with one that was not working well. This is illustrated in Figure 8 as a function of running time. It is evident that the "sum of AE events" for the "sood" unit is three times more than that for a "defective" one.

t3

Figure 6. Neutron radiography image of the bubble pump.

Frequency band [kHz]

(a)

0 5 1 0 t 5 2 0 1 . 5

F;;q;.*y ú;"d rkH"i (b)

Figure 7. Vibration diagnostics water-flow diagram measured at the bubble pump (a) for a "good" and (b) for a "defective" cooling unit.

0 5 1 0 t 5 2 0

I 4

Sum ofAE events Temperature IoC]

220,0 200.5 1 8 1 . 0 1fl.5 147.0 tzz.5 103.0

83.5 64.0 44.5 25.0

"Defective"

300 270 240 2\0 180 150 tzl

90 60 30 0

Temperature

Figure 8. Acoustic emission curves for a "good" (solid line) and for a "defective"

(dashed line) absorption-type refrigerator.

It was established that simultaneous application of DNR, VD and AE techniques is appropriate for detecting noise events and understanding their origin in absorption-type refrigerators. On the basis of results it was proposed that customized AE equipment be installed at a refrigerator works, and that it would form an integral part of the quality assurance system.

6. I .3. Compresslon-type Refrigerators

Recently, manufacturers have devoted a great deal of effort to developing new constructions of compression-type refrigerators based on the use of the environmentally friendly R-134a Freon cooling agent instead of the previously used chlorofluorocarbons (CFCs). CFCs comprise one of the so-called

"greenhouse" gases and may thus be in some way linked with the problem of global warming of the earth, although their significance is thought to be comparatively minor. Many CFCs were previously used as the working fluid in refrigerators, freezers and air-conditioning units. The development of safe, effective materials is one of the most difficult challenges facing industry throughout the world. Much work has been focused over the last decade on finding suitable ozone-benign replacement materials. According to the Montreal Protocol (1986) which was formulated at the lntemational Conference "Saving the ozone layer" the following reduction rates for CFC products were accepted: "in the year 1993 - consumption cut to 80% level, and in 1998 - consumption cut to 50% of the 198ó level, and similar cuts in production''.

Dlmamic neutron radiography has been used successfully in R&D of compression-type refrigerators working with R-134a as a cooling material. The problem with R-134a is that its oil soluble capability is lower than that for the previously used R-12, and this causes several problems in the newly developed constructions. Visualization and analysis of intemal processes provide useful information for designers of new prototlpes, or as a means of finding the reason

"Good"

Running time fmin]

1 5

for defective functioning. It is very important to know the segregation points;

these may be visualized by NR. Figure 9 shows the segregation of the synthetic lubrication oil on the surface of R-134a in the evaporator puffer. This thin layer hinders the evaporation of R-134a leading to a decrease in the cooling efficiency, and it is missing from the lubrication process of the compressor bearing as well.

As a result of the DNR investigations the flow conditions were optimized in the puffer by changing the ratio of the cooling agent and the lubrication oil.

Figure 9. Segregation of synthetic lubrication oil on the surface of R-134a Freon cooling agent in the evaporator of a compression-type refrigerator.

Noise parameters of the freezers, however, are still higher than the value allowed by the relevant standard. Measurements in the quiet-room of the factory's research laboratory have not been able to provide a definite explanation for the origin of the noise. With the aim of finding the origin of the noise in various prototypes simultaneous DNR, VD and AE measurements were performed. The experimental set-up for the simultaneous use of these three NDT techniques is shown in Figure

10. The whole refrigerator box is placed in the neutron beam, and the freezer is equipped with VD and AE sensors, as well. The schematic layout of the cooling unit is also shown in the Íigure to demonstrate the characteristics of its operation' The compressor (lubricated and cooled by oil) pumps the Freon into the condenser at 20 bar, the pre-cooled gas passes through the capillary to the evaporator system, the liquid Freon evaporates in the flat tube system of the deep-freezer unit meanwhile it refrigerates its surroundings. The cycle continues with the gas returning to the compressor on the pumping side through a filter. This cooling unit consists of copper and aluminum components of about 1 mm thickness. Thus the inner flow processes may be visualized. However, measurements during operating conditions may be performed on units covered by a heat insulator, which slightly decreases the quality of the radiography image.

I {r s't "sile u'e controll

Ii$íl.ry$

ffiil$

l i l, Yi;nll*.

lillrlli

Srgregated hrbri

it{ l }.f y| $Jí

$í|

t 6

Refrigerator

Operatormicrophone EeUIpMENT Vibration

Figure 10. Experimental set-up of simultaneous d)mamic neutron radiography, vibration diagnostics and acoustic emjssion measurements on a compression-type

retrlgerator

By means of DNR it was visualized that the intensive noise was generated at the junction of the capillary and the suction tubes. The low temperature, low pressure gas in the suction tube was heated by the hot and high pressure gas of the capillary tube, and this hindered its quiet streaming to the compressor. The liquid suddenly evaporates and this phenomenon generates a strong howling noise. This intensive, disturbing noise is present during the entire compressor running time, even after the compressor has stopped.

Using the VD method, the noise phenomena were analyzed in a more quantitatrve way. These signals were measured during the above described process, and the frequency spectra detected are shown in Figure 11 in a water-flow diagram. The duration of each curve is 1 sec. Characteristic signals were measured at the frequency band of 200-300 Hz. At the 90'n sec after the start of the compressor - when the howling noise appears - the intensity of the signals increases, and they are present during the entire operation period. Even if the compressor stops (at the 300'n sec), these noises are still measurable for a while.

T7

Compressor start

Frequency band IkHz]

Figure 1 1. Vibration diagnostics water-flow diagram measured at the suction tube of the compressor block.

Acoustic emission measurements were performed, simultaneously, in the frequency band above 200 kHz to measure the upper harmonics of the vibration diagnostics signals. The temperature was measured at the suction tube and the sum of the AE events was measured at the same position. Figure 12 summarizes the temperature values (dashed line) and the sum of the AE events (solid line) as a function of runnins time.

Sum ofthe AE events Temperature ["C]

Sum ofthe AE events

+10 +8 +6

L A

TL

0

- L

Á -6 -8 - 1 0

do do jio óo

5000 4500 4000 3500 3000 2500 2000 r 500 1000

500 0

Temperature

Running time Isec]

Figure 12. Sum of the acoustic emission (AE) events (solid line) and the temperature (dashed line) as a function of running time at the suction tube of the

compressor 0 60 120

Compressor Í start

180 240 300 3ó0 Compressor

I

1 8

After starting of the compressor, the temperature decreases rapidly from + 10. C to - 7" C. After the 90'n sec - when the howling noise appears - a rapid increase of the AE events is detected, and the temperature is practically stable at - 9" C. The increase of the AE events is measured during the whole running time while the howling noise is present. After the compressor stops (300th sec) the temperature increases rapidly up to + 6o C whereas the AE events slightly increase for a while (similarly to the characteristics of the VD signals), and thereafter they stabilize.

It was established that simultaneous application of DNR with vD and AE techniques is capable of detecting noise events and understanding their origin in compression-type refri gerators.

6.1.4. Thermostats

Thermostats are important elements of the temperature regulation technique in industry. Usually, they consist of a cylindrical sensor connected by a capillary tube to a membrane. Within the sensor is a liquid propellant. When the sensor is subjected to heat the propellant expands and passes through the capillary tube whereupon the membrane is deformed. This minute motion mechanically actuates an electrical contact, and the heating power is switched off.

a. High temperature thermostats

A series of thermostats operating in the temperature range from 80o C to 250. C was tested with the aim of finding the origin of their defective functioning. By means of DNR the inner process was visualized at different temperatures both in the cylindrical sensors and in the corresponding membranes. Figure 13 shows the DNR image of the sensors and that of the membranes at25o C.

Figure 13. Neutron radiography image of sensor tubes and membranes at25" C.

1 9

It is clearly seen that some of the sensors are practically empty (Nos. 3 and 4) and the other sensors are not homogeneously filled with the propellant. The temperature was increased step by step and it was checked how the propellant reached the membranes. At 250" C the membranes were filled with the propellant and the sensors were depleted. By subtracting the intensity distribution (NR image) measured a! 25" C from that measured at 250" C, it was established that no intensity change no fluid transport has occurred for the defective thermostats.

In this way, it was clarified that the problem with the sensors originated as an error in mass production, especially in the filling process.

b. Low temperature thermostats

Temperature control of the domestic refrigerator is solved by a low temperature thermostat. Here a capillary tube is used as a sensor, containing as propellant gas the same material as the cooling agent, viz. the environmentally friendly R-134a.

By increasing the temperature the propellant gas expands and it deforms the membrane above 15 oC. This minute motion mechanically actuates an electrical contact, thereby the compressor is started. After a certain time (= 10 minutes) the gas cools down and it condenses. When condensation takes place the pressure is drastically reduced and the compressor is stopped by the membrane.

The goal of the study was to explain the cause of the delayed starting of the compressoÍ. The supposed cause of this defective operation was the incorrect functioning of the thermostat. First of all a special small cooling tower was designed with the aim of avoiding the disturbing effect of neutron scattering of the insulation materials of the box. Within the special tower is a double level, water cooled Peltier-block which contains a microbox at a minimum temperature of - 40 'C. Its NR image is illustrated in Figure 14.

Figure 14. Neutron radiography picture of double level, water cooled Peltier- block.

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Since the behavior of the propellant gas depends on the position of the thermostat sensor it was possible to investigate it by this rotatable arrangement. Figure 15 shows the long, liquid gas column at - 40 oC in the vertical position of the sensor.

When the compressor switched off, the temperature began to increase slowly and the length of the liquid was reduced slowly. At - 5 oC the residual column suddenly collapsed generating a relatively strong pressure change in the capillary tube whereupon the membrane restarted the cooling procedure. After some seconds the liquid returned to the sensor and the cooling was stopped immediately. This finding proved to be the explanation for the delayed starting because the compressor has a contact breaker to avoid damage caused by the repeated starting. The circuit waits for five minutes after such an event before it switches on the power again. By adjusting the thermostat to the correct mounting position, the vertical outflow of the sensor was avoided and the problem was solved.

Figure 15. Liquid propellant column in the sensor at - 40' C.

2 l

6.2. Petrophysical Application

Research on hydrocarbon reservoirs involves modeling the geometry and distribution of porosity and permeability features. [n the framework of this project the characteristic features of oil infiltration were visualized and analyzed by DNR image processing on Visingsö sandstone specimens received from Sweden. The specimens were composed of quartzarenite in which quartz grains dominated with minor feldspar and lithic fragments, their dimensions were 86.5x34x15 mm3.

In the experimental set-up heavy water (DzO) and oil were infiltrated at 0.1 bar pressure at given time intervals into the supply inlet of the specimen, using a fine adjustment regulator and electromagnetic valves. In the course of this process DNR images were taken at 2 minutes intervals. Each experiment lasted 46 minutes.

From the series of DNR. images for detailed quantitative analysis was chosen that one registered at the 20'n min (insert in Figure 16). A well separated, layered and clearly distinguishable structure with a non-permeable inclusion in it appeared. In order to quantify the oil distribution of the modeled Visingsö sandstone the x- profile of the pertinent gray levels in the 0+ 255 interval (O:black, 255:white reference value) at the median line was gauged as delineated in Figure 16. The low gray level values belong to high neutron absorption, the high gray level values to the transparent, regions. The corresponding 3D gray level distribution (Figure 17) as a mathematically obtained image was used for further recursive image analysis in order to reveal a more detailed petrophysical structure. As a result of this approach intensive (A), intermediate (C) oil infiltration zones and a region of the residual D2O (E) were observed. Also clearly distinguishable were the transient boundary layers between the above mentioned zones (J and F). Also precisely discemible were a non-oil-permeable inclusion (B), layered structures (I), (H), the porosity (G), as well as the flow-paths between them (D).

Fluid infiltration was explained and interpreted by applyrng mathematical modeling using negative exponential, reciprocal and Gompertz functions. Such modeling supported the view that fluid permeation dynamics is of inherently time- varying complex non-linear nature. At the 5'n min after commencing the oil supply, an infiltration rate of I-2 cm2 min-l was calculated.

- í50

g

g tooE

20 30 a0 30 60 70 E0

x*íd||..t th. mdhn p.d oíthé.p.c|nEí (mm+

Figure 16. DNR image registered at the 20tn min of the oil infiltrated Visingsö sandstone specimen (inserted image) and a gray level spectrum along the median

x-profile of the specimen.

22

Figure 17. Recursive 3D intensity histogram of the DNR image (Figure 16) with the notation of the characteristic regions. A: an intensive oil infiltration zone; B: a

non-perrneable-to-oil inclusion; C: an intermediate oil infiltration zone; D: flow- paths between pores; E: a residual heavy water region; F: boundary layer between

infiltrated oil and that of heavy water; G: porosity; I, H: heterogeneous, layered petrophysical structure; J: transition boundary between intensive and intermediate

oil infiltration.

6.3. Application in Plant Physiology

Non-destructive in situ and in vivo investigations of structures, transport processes, and distribution constitute the leading edge of the most advanced biological, including plant physiological research. The applicability and the potential of DNR are of considerable importance in this field. In particular for visualizing and analyzing the uptake and distribution of water during germination in bean seeds and that of heavy metal trace elements (Gd, Sm, Cd) in roots and leaves. Some recent results are presented here.

a. Water uptake and distribution during germination of bean seeds

The time progression of imbibition, germination and primary root growth of bean seeds was analyzed by DNR imaging. A specially designed aluminum cassette, inertly lined with water-proof plastic foil and transparent to neutron radiation was prepared. The bottom of the sample holder was filled with water, over that a sterilized two-layer gauze with good capillary characteristics (the "diffusion zone") was placed and then the bean seeds were put on the surface of the diffusion zone with the strophiole facing downwards. Seven seeds were placed in a sample holder separated vertically from each other with an aluminum sheet, and the 8'h box was kept blank to serve as a reference. Throughout the work the germinating seeds were in a plant-rearing unit whose dimensions allowed it to be placed for irradiation in a neutron beam. As an example Figure 18 shows the NR image of the bean seeds in the t:2800th min of the germination process, this being a crucial stage of seedling development, viz., the opening of the cotyledons starts. It can clearly be seen that in the 7'n seed position, where the primary root growth almost reached the bottom of the sample holder, the cotyledons are apart.

23

Figure 18. Neutron radiography image of the bean seeds at the 2880th min of the germination process. The opening of the cotyledons for the 7th seed may be seen.

The gray level values of the NR imageJ depending on the water content - were analyzed in order to identify the crucial time series for germination in relation to water uptake. It was established that within the bean seeds there are three distinct zones. Statistical data analysis by non-hierarchic cluster analysis led also to three distinct groupings (Figure 19): {A} the evaporation zone of the cotyledon that was contiguous with the air; {B} the absorption zone, the lower cotyledon of the bean that faced the water layer of the diffusion zone; {C} the accumulation zone formed inside the bean seeds on the facing planes of the cotyledons. It is supposed that the accumulation zone forming in the facing surfaces of the cotyledons may contribute, presumably via physical and physiological mechanisms, to the opening of the cotyledons. Physically, the assumption is that from the boundary layer of the absorbing cotyledon the water evaporates and condenses on the boundary layer of the cotyledon; physiologically the interpretation is that the surface cells become turgid and thus in a pressurized state, thereby contributing to the opening of the cotyledons. It cannot be excluded that the two above mentioned mechanisms do not take place simultaneously.

Gray |éVe|s 104

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|':.' FÉ B I B

{: accun]u|alion ]ol}é

83 93 .t03 í13 |23 í33

Gray levels

Figure 19. Non-hierarchic cluster analysis of water distribution zones in the cross section of the bean seeds. {A}, {B} and {C}denote evaporation, absorption and

accumulation sections forming in the cotyledons, respectively

24

b. Environmental aspects: distribution and transport of heavy metal trace etements in plant tissues

For nutrition research, in vivo and in situ qualitative and quantitative images of the transport and distribution processes of plants are helpful in revealing the role of the elements. This statement is especially valid for those elements whose biological importance is either less studied or not yet revealed. The need for knowledge of the role of heavy metal trace elements has been increased recently due to increased air pollution and increased use of artificial fertilizers. In a model experiment the transport patterns for Gd, Sm and Cd were investigated in the primordial leaf tissues of the bean using DNR. Bean plants (Echo Elit variety) were grown in a specially designed aluminum cassette (as described in the previous paragraph) which was filled with D2O during the measurement. Then 1 cm' D2O containing 1.6 mg Gd and Sm and 2.6 mg Cd, respectively, was dropped with a syringe on the adaxial surface of the main vein. The high neutron absorption of Gd, Sm and Cd enables the DNR imaging of the distribution patterns of these elements in vivo and in situ in the neutron transparent DzO. The semi quantitative analysis of the time kinetics of apoplast transport was based on pixel count distribution histograms of the pertinent gray levels represented areas.

The initial drops of Gd, Sm and that of Cd under the experirnental conditions were clearly observed, as shown in Figure 20 for the Gd drop in the bean leaf and its 2D projection.

Figure 20. A Gd drop and2D projection in leaf tissue.

It was established that the transport of the trace elements Gd, Sm and Cd in the leaves was different for each of them. For 60 minutes the Gd was transported in the main and lateral vascular systems, then there was a penetration into the intercostal tissues. In the same time interval the Sm was transported from the initial drop in the direction of lateral tissues possibly involving cell walls and intercellular space. As regards Cd movement, in the course of 30 minutes, it took place longitudinally in the main vein.

Lr order to clarify more precisely the biological function of rare earth elements, it is essential to understand the long distance transport and distribution within plant

25

organs and tissues. The Gd(NO3)3 dissolved in DzO served as a Gd root nutrient Source. From the root zone 50oÁ of Gd was taken up by the 25th min, and by the 50th min 7OoÁ as was calculated by integrating the pixel counts. It was definitely identified that during the 25 minutes an explicit upward transport involving xylem vascular elements loaded the vascular system of the primordial leaf with Gd. For the next 25 minutes till the 50th min the intercostal mesophyllum tissues of the primordial leaves were charged. The most interesting finding was that after the 50'n min the primordial leaf became an exporter of Gd.

7. Conclusions and Future Trends

Radiography imaging with simultaneous recording of external parameters of the objects under investigation enable one to carry out detailed studies of the behavior of processes inside objects as a function of different working parameters, e.g.

power consumption, volume of the transport of the cooling mixture, tilting angle, temperature at different points of cooling units, and so on. This helps one to understand the main features of mechanical and thermodynamic processes developing in the given object and it provides a unique means for a wide circle of manufacturers to improve their products.

Simultaneous application of NR with other NDT techniques such as AE and VD provide a possibility for experts in industry to detect noise events and to understand their origin in various thermodynamic devices. On the basis of results, it was proposed that dedicated AE equipment be installed and built to form apaÍt of the quality assurance system.

Taking into account the practice of present applications and the future trends of neutron radiography, a great demand can be expected in the following fields:

Objects of great individual value (aircraft, spacecraft, space rockets and devices used in the nuclear industry and in defence).

Objects of relatively small individual value but produced in great quantities (household refrigerators, coffee percolators, batteries, valves and circulating pumps).

Objects whose development is delayed due to unforeseen problems.

Complex radiography can significantly help designers by detecting hidden defects of the prototypes.

NR has great perspectives in non-industrial applicatíons, especially, in biological and plant physiology research to visualize various in situ and in vivo transport and distribution effects.

Neutron computer tomography is a relatively new and rapidly developing technique and, undoubtedly it represents an important tool in the field of NDT to receive 3D visual images from the inner structure of obiects and to detect inhomogeneities in 3D projection.

Acknowledgements

The authors are most grateful to Dr F. Kőrősi for having initiated the plant physiology applications and for performing image data analyses of petrophysical

26

and plant physiology measurements' to G. Endrőczi and to A. Péter for participating in vibration diagnostics and acoustic emission measurements. This work was supported by grants OTKA-T029433 and IAE-9609.

Related Chapters

Click Here To Vicrv The Relatcd Chaptcrs

Gtossary

AE: Acoustic emission CCD: Charge coupled device

DNR: Dynamic neutron radiography GR: Gamma radiography

IP: Imaging plate

LLL camera: Low-light-level camera NCT: Neutron computer tomography NDT: Non-destructive testing

NR: Neutron radiography QC: Quality control

R&D: Research and development VD: Vibration diagnostics

XR: X-ray radiography

Bibliography

Balaskó, M.' Sváb, E', Cser, L' (1987). Simultaneous dynamic neutron and gamma radiography.

NDT International 20, 157-160. [A description is given here of the first simultaneous dynamic neutron and gamma radiography station.]

Balaskó' M., Kőrösi' F.' Sváb' E. (l999). Modeling of oil infiltration and distribution in sandstone applying dynamic neutron radiography. Proc. 6" Word Conference on Neutron Radiography, Osaka, Eds. S. Fujine, H. Kobayashi, K. Kanda, Gordon and Breach Science Publ. Pennsylvania, pp. 441-448. [Experimental details and mathematical evaluation of neutron radiography images are presented for a petrophysical application.]

Bromley, A. (1983). Neutrons in science and technology. Physics Today 3l-39. [It provides a survey on widespread applications of neutron radiography.]

Domanus, J.C. (1992). Practical Neutron Radiography (Kluwer Academic Publ. The Netherlands). [A useful book describing the principle of neutron radiography technology.]

Hardt von der, P. and Roettger, H. (1981). Neutron Radiography Handbook (D. Riedel Publ.

Company, The Netherlands). [This is the first relevant book on neutron radiography.]

Harms, A.A. and Wyman, D.R., (1986). Mathematics and Physics of Neutron Radiography (D.

Riedel Publ. Company, The Netherlands). [This book presents the theory of neutron radiography.]

Kőrösi' F., Balaskó' M., Sváb, E. (1999). A distribution pattern of cadmium, gadolinium and samarium ins Phaseolus vulgaris plants as assessed by dynamic neutron radiography. Nuclear Instruments and Methods in Phyics Research A424, 129-135. [This paper presents the first plant physiology application of neutron radiography to visualize heavy metal trace elements distribution in plant tissues.]

Péter, A., Pellionisz, P' (1983). Mobile acoustic emission laboratory for plant surveillance' on-line monitoring of continuous process plants. (Ed. P.W. Butcher, Ellis Horwood Ltd., London) pp.

27

313-324. [The basic relations of the acoustic emission technique are described here and details are given of a mobile acoustic emission laboratory.]

Whittemore, W.L. (1990). Neutron radiography. Neutron News 1,24-29. lThis is a review paper with special emphasis on the possibilities provided by cold neutrons.]

Ilorld Conferences on Neutron Radiography (WCNR) Proceedings.' flnternational conferences on neutron radiography are organized periodically in every 3-4 years since 1981, enabling the latest work to be presented; practically all neutron radiography laboratories are represented on these meetings.l

WCNR-1, San Diego (1981). Eds. J.P. Barton, P. von der Hardt, Riedel Publ., The Netherlands WCNR-2' Paris (1986). Eds. J.P. Barton, G. Farny, J..L. Person, H. Röttger, Riede| Pub|., The Netherlands

WCNR-3, Osaka (1989). Eds. J.P. Barton, S. Fujine, K. Kanda, G.-I. Matsumoto, Kluwer Academic Publ., London

WCNR-4, San Francisco (1992). Ed. J.P. Barton, Gordon and Breach Science Publ. Pennsylvania WCNR-5, Berlin (1996) Eds. C.O. Fischer, J. Stade, W. Bock, DGZFP, Berlin WCNR-6, Osaka (1999). Eds. S. Fujine, H. Kobayashi, K. Kanda, Gordon and Breach Science Publ. Pennsylvania

Biographical Sketch

Erzsébet SVAB graduated as a physicist in 197l at Eötvös University in Budapest. Her main research f,teld is materials science using neutron diffraction and neutron radiography. The most important results have been obtained on the atomic and magnetic structure of various oxides and on the short range order of amorphous metallic alloys. She has successfully applied the isotope substituted method for determining partial struature factors and pair correlation functions of various disordered systems. As leader of neutron diffraction research work she initialized the construction and installation of neutron diffractometers at the Budapest research reactor. She is involved in wide range of neutron radiography tasks, especially in the visualization and analyses of inner processes, such as flow of fluid, boiling, evaporation, condensation in closed objects during operation. Apart from her research work she is an active member of a number of Hungarian scientific committees and has organized several schools and international conferences. Number of scientific publications is more than 150.

Márton BALASKó graduated as an electrical engineer from the Technical University' Budapest it 1912. He was a principal member of the team that designed and established the radiography station at the Budapest research reactor utilizable for simultaneous neutron-, gamma- and X-ray radiography inspection. As leader of the radiography group he is concerned with its multifarious industrial applications. In addition, he is interested in the application and combined use of radiography with other non-destructive testing methods, e.g. thermovision, vibration diagnostics and acoustic emission, and is making great efforls to establish these methods - as transfer techniques of radiography inspections - in industry's quality control systems. He is among the charter members of the European Neutron Radiology Working Group, a member of the board of the International Society on Neutron Radiology and active member of the International Programme and Organizing Committees of Radiography Conferences and Workshops. Number of scientific publications is more than 100.

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