Atomic Energy of Canada Limited

SOME ADVANCED RESEARCH USES OF

CANADIAN REACTORS AND ACCELERATORS

TRI-PP-71-3

by

G.A. BARTHOLOMEW, A.W. BOYD, J.A. DAVIES, J.W. KNOWLES,

M.L SWANSON, P.R. TUNNlCLIFFE, A.D.B. WOODS and J.B. WARREN

Chalk River, On tar: ,

June 1971

AECl-3907

Atomic Energy of Canada Limited

SOME ADVANCED RESEARCH USES

OF CANADIAN REACTORS AND ACCELERATORS

by

G.A. Bartholomew, A.W. Boyd, J.A- Davies, J.W. Knowles.M.L. Swanson, P.R- Tunnicl iffe, A.D-B. Woods

Chalk River Nuclear LaboratoriesAtomic Energy of Canada Limited

Chalk River, Ontario

and

J.B. WarrenUniversity of British ColumbiaVancouver, British Columbia

AECL-3907TRI-PP-71-3

Neutron Physics BranchChalk River Nuclear Laboratories

Chalk River, Ontario

TRI-PP-71-3

SOME ADVANCED RESEARCH USES

OF CANADIAN REACTORS AND ACCELERATORS

by

G.A. Bartholomew, A.W. Boyd, J.A. Davies, J.W. Knowles,M.L. Swanson, P.R. Tunnicliffe, A.D.B. Woods

Chalk River Nuclear LaboratoriesAtomic Energy of Canada Limited

Chalk River, Ontario

and

J.B. WarrenUniversity of British ColumbiaVancouver, British Columbia

ABSTRACT

A survey is given of some present applicationsof Canadian accelerators and reactors in the fieldsof ion implantation and channelling, electron pulseradiolysis, irradiation-induced defects in solids,static and dynamic structure studies by neutron scat-tering, neutron capture 7-rays, and photoexcitationof nuclear states. Electronuclear breeding and itsrelevance to the intense neutron generator program,now discontinued, are discussed briefly. A summaryis given of the beam characteristics and anticipatedperformance of the TRIUMF facility.

Chalk River Nuclear LaboratoriesChalk River, Ontario

June , 1971

AECL-3907

Utilisations scientifiques avancées

des réacteurs et des accélérateurs canadiens

par

G.A. Bartholomew, A.W. Boyd, J.A. Davies, J.W. Knowles,M.L. Swanson, P.R. Tunnicliffe, A.D.B. Woods

EACL (Chalk River)

et

J.B. WarrenUniversité de la Colombie Britannique

Vancouver. B.C.

Résumé

On donne un aperçu de quelques applications actuellesdes accélérateurs et des réacteurs canadiens dans les domainessuivants: implantation et canalisation des ions; radiolysepuisée; défauts engendrés par irradiation dans les solides;études sur la structure dynamique et statique par diffusionneutronique; rayons gamma de capture; et photoexcitationd'états nucléaires. La surgênêration électronucléaire et sesrapports avec le programme du générateur de flux intensede neutrons actuellement discontinué font l'objet de brefscommentaires. On donne un résumé des caractéristiques defaisceaux et de la performance prévue de 1*installation TRIUMF.

L'Energie Atomique du Canada, LimitéeLaboratoires Nucléaires de Chalk River

Chalk River, Ontario

AECL-3907

Acknowledgments

The authors are indebted to many colleagues whofreely aided in the preparation of this survey, especiallyto Dr. J.W. Hunt of the University of Toronto for helpfuldiscussions and the use of a figure and to Dr. T.J. Kennettof McMaster University for providing information on hisneutron experiments prior to publication.

Contents

1. Introduction

2. Ion Implantation and Channelling

2.1 Range distributions2.2 Channelling2.3 Location of; foreign atoms2.4 Lattice and surface disorder2.5 Precise orientation of crystals

3. Chemical Effects of Radiation

4. Irradiation-Induced Defects in Solids

5. Studies of Static and Dynamic Structure of Materials

6. Neutron Capture 7-Rays and Related Studies

6.1 Neutron capture y-rays6.2 High-precision ^-ray measurements6.3 Photo-excitation studies6.4 Gamma-rays following inelastic neutron scattering

7. Electronuclear Breeding and the Intense Neutron Generator

8. The TRIIMF Project

8.1 Accelerator8.2 The experimental facility

8.2.1 Proton area8.2.2 Meson area8.2.3 Applied research

9. Summary

1. INTRODUCTION

Developments in the research uses of reactors and acceler-

ators promise important advances in science and technology, we

present here a survey of recent advances in these fields from

research programs at Chalk River Nuclear Laboratories (CRNL) and

Canadian universities.

2. ION IMPLANTATION AND CHANNELLING

ion implantation and channelling are rapidly growing uses

of low-energy ion accelerators. in the semi-conductor field, im-

plantation is already a more flexible method of introducing dopant

atoms into a silicon lattice than conventional thermal-diffusion

techniques. It also has great potential value in other solid-state

applications, but successful exploitation requires a better under-

standing of the physics involved.

2 .1 Range distributions

To measure shallow penetration depths, techniques have been

developed for removing extremely uniform layers (typically 10-IOOOA)

from the surface of solid targets. The anodic-oxidation-plus-

chemical-stripping method [1-3J has provided an extensive series of

range measurements in amorphous [3J, poly-crystalline [lj and single-

crystal [2,4J targets. Other sensitive layer-removal techniques

include ion sputtering [5] and vibratory polishing [6j.

2.2 Channelling

A striking feature of these range measurements has been their

strong dependence on crystal orientation - owing to the "channelling"

process which guides ions through the "open" spaces between the rows

of atoms. This process reduces the rate of energy loss, and in-

creases the range, e.g., at 100 keV, a channelled heavy ion (xenon)

in tungsten [4] penetrates ~20 times deeper than a non-channelled one.

Channelling also reduces the radiation damage accompanying implantation.

- 2 -

Channelling was first detected in heavy-ion implantation

studies [5,7,8] at keV energies. Energy-loss experiments [9]

with thin single crystals have demonstrated that protons and

helium ions at 1-10 MeV energies (or Br and I ions at energies

up to 120 MeV [10]) become channelled and lose energy more slowly,

when injected parallel to a crystal axis or plane.

It has been shown theoretically [11] that channelled

particles cannot approach closer than ~0.lA to lattice sites;

therefore, processes requiring impact parameters smaller than

O.lA should be drastically attenuated whenever the beam becomes

channelled. Investigations of nuclear-reaction yields [12] , wide-

angle Rutherford scattering [13,14], and inner-shell X-ray pro-

duction [15,16] all verify that attenuation factors up to ~100

occur - in reasonable agreement with theory (see Fig. 1) .

The steering process is now sufficiently understood that

channelling of MeV protons, helium ions, etc. is being used as a

tool for investigating crystal properties (Sections 2.3 - 2.5

below).

2.3 Location of foreign atoms

A foreign atom on a lattice site (substitutional atom)

is shielded from a channelled beam and so a large attenua--,

tion in its interaction yield occurs. If, however, the foreign

atom is interstitial, along certain major directions it will lie

outside the "shadow" (-0.1A radius) of the atomic rows and no

;.. attenuation •• will be observed. Hence, by investigating the.inter-

action of the beam both with lattice atoms and with foreign atoms.

1.4

—x NORMALVALUE

EXR CURVE

NUMERICALCALCULATION

- 8 ° -6° - 4 ° -2° 0 c 2° 4° 6° 8°

ANGLE RELATIVE 70 <IOO> DIRECTION

10«

Fig. 1. Comparison between experimental and calculated attenuationof Rutherford scattering yield for 480-keV protons incident on atungsten crystal along the <100> direction [17].

- 4 -

we may determine the distribution of foreign atoms between sub-

stitutional and specific interstitial positions [17-19].

To apply the method, the interaction yield due to foreign

atoms must be detectable in the presence of the host atoms.

Among the many close-encounter processes available, one with

sufficient discrimination can usually be found - provided the

-4atomic concentration of foreign atoms exceeds ~10

Two cases, gold and antimony implants in silicon, are

illustrated in Fig. 2. For the gold atoms, the yield shows

negligible orientation dependence - indicating that none are on

lattice sites. For the antimony, the yield is strongly attenu-

ated when the beam enters parallel to a low-index (<110>) direc-

tion, indicating that almost all are sinstitutional. This

technique has been used extensively in determining the substitu-

tional fraction of various implanted dopants in semi-conductors

[19].

2.4 Lattice and surface disorder

The large attenuations in yield due to channelling can also

be used to study lattice disorder in the implanted region.

Atoms displaced from their regular sites by more than O.lA inter-

act with the channelled beam, thereby reducing the attenuation

factor. The channelling behaviour of 1.0-MeV helium has provided

quantitative information on the amount of lattice disorder in

implanted semi-conductors [18,20] as a function of dose,

annealing temperature, etc. Energy analysis of the backscattered

helium enables lattice disorder to be studied as a function of

depth [21].

- 5 -

2000

1500

auen

2 IOOO

<•o

500

Impurity atom

displaced from

lattice site (gold)

Impurity atom

on lattice site

(antimony)

Siliconlattice

38 37" 36 35 34 33

TILT ANGLE (degrees)

Pig. 2. Backscattering yield of 1.0-MeV helium ions from substitutionallylocated implanted atoms (antimony) and from randomly distributed ones(gold) as a function of the angle of incidence relative to the <110>direction. The yield from the silicon crystal substrate i s included forcomparison [19j.

- 6 -

2.5 Precise orientation of crystals

Channelling provides a simple method [12] for orienting

crystals to an accuracy of 0.02°. For this purpose the Rutherford

scattering technique is useful because of its universal applicability.

Also, by measuring the energy spectrum of the back scattered beam,

one detects the channelling behaviour at different depths beneath

the crystal surface. Hence, the method determines the crystal

orientation as a function of depth, thus providing information

on the mosaic spread along the beam direction.

3. CHEMICAL EFFECTS OF RADIATION

Knowledge of the chemical effects of radiation has been

greatly increased by the use of accelerators producing short

intense pulses of electrons. The major use has been in pulse

radiolysis, a technique in which the growth and decay of transient

species generated in a material by the electron pulse are followed

by fast detection methods. This technique, with nanosecond and

microsecond electron pulses, has been applied in various Canadian

laboratories [22] to the determination of the optical spectrum

and rate constants for the reactions of transient species in

irradiated aqueous solutions and other liquids. Recently the

behaviour of the solvated electron, the major reducing species

in irradiated water, at much shorter times has been determined

by Hunt and collaborators [23] who have reached a time resolution

of ~20 psec using fine structure pulses from the 40 MeV linear

electron accelerator at the University of Toronto. Each of these

<10 psec pulses produces a Cerenkov light flash in air and a

- 7 -

transient absorbing species in the irradiated material. By using

the Cerenkov flashes as the analyzing light and by delaying these

light flashes with respect to the electron pulses by a variable

light path, the growth and decay of the absorbing species can be

determined with a resolution of 20 psec. The principle of this

technique is shown in Fig. 3.

In applying this technique to aqueous solutions [24] it is

found that no precursor of the solvated electron is observed in

times greater than 20 psec, and moreover that the addition of

high concentrations of H-O-, acetone, or nitrites reduces the

initial yield of the solvated electron but high acid concentra-

tions do not. This reduction is ascribed to the reaction of the

solutes with the solvated electron precursor which is believed to

be a low-energy electron. These results are of fundamental

importance not only in basic radiation chemistry but also in

radiobiology where high solute concentrations often limit the

lifetimes of the primary species to picoseconds.

Pulse radiolysis of gases requires, in general, pulse

intensities 10 x higher than those obtainable from pulsed Van de

Graaffs and linear electron accelerators. Such intensities can

be obtained from capacitor discharge type pulsed sources

(Febetrons) . These sources have been used at CRNL L25J for the pulse

radiolysis of gases and more extensively for determining the

yields of stable products. The advantage of these sources for

this latter work is the extremely high dose rates generated -

~10 2 8 eV«g "^sec"1, some 10 1 2 times those in Co sources.

10 p secELECTRON PULSE 8 CERENKOV LIGHT

\

ABSORBINGPRODUCT

00

vCERENKOVANALYZING

LIGHTPig. 3. Principle of the stroboscopic pulse radiolysis technique. Theupper line shows the fine structure electron pulses and the simultaneousflashes of Cerenkoy light. The lower line shows the production and rapiddecay of an absorbing product following each fine structure pulse. TheCerenkov light flashes are delayed for a variable period and used asanalysing light flashes to measure,the concentration of the absorbingproduct. Reproduced from ref. L 23 J.

- 9 -

Although the primary yields of ions and radicals in gases

are unchanged at these dose rates, the lifetimes are different,

e.g., at atmospheric pressure, the lifetime at low dose rates is

<v,10 ̂ sec while at 10"eV-g -sec it is much shorter, <10~°sec.

Consequently at high dose rates, many of the ionic reactions with

products, impurities and the walls that occur at low dose rates,

are eliminated. The ionic mechanism is then also much simpler and

the results give a much better understanding of the radiation

chemistry as shown with several simple inorganic gases [26,27].

For example, the high-dose-rate yield of ozone from oxygen is

12.8 ± 0.6 molecules per 100 eV and the low-dose-rate yield is

6.3 ± C.6. The difference is explained as due to electron transfer

at low dose rates from oxygen to ozone so that the neutralization

of positive oxygen ions is by negative ozone ions giving 0, and 0_.

At high dose rates neutralization is by the negative oxygen ion

giving 0» and two oxygen atoms. Similar results are obtained with

CO, and H2S. in all of these gases the difference between the high

and low dose rate yields is a multiple of the electron yield and the

addition of an electron scavenger, e.g. SFg, reduces the high-dose-

rate yield to the low-dose-rate yield.

4. IRRADIATION-INDUCED DEFECTS IN SOLIDS

Studies of defects in solids have great practical significance

for the understanding of optical, electrical, mechanical and dif-

fusion proper ties of ionic crystals, metals, semiconductors and

insulators [28]. Irradiation-induced defects influence the strength,

ductility, and creep resistance [29] of reactor structural

materials. Furthermore, the behaviour of other materials

-10 -

such as superconductors, thermionic devices and transistors in

a radiation field is pertinent to reactor and space technology,

and is directly related to point defect properties.

At CRNL, defects introduced into metals and semiconductors

by irradiation with Co gamma rays, 1.5 MeV electrons from a

small Van de Graaff accelerator, and fission neutrons from the

NRX and NRU reactors have been investigated over a wide tempera-

ture range.

Irradiation-induced defects, such as vacant lattice sites

and interstitial atoms, are generally immobile for irradiations

below 20°K. During annealing, these defects combine with one

another or with impurity atoms. By identifying specific defects,

these annealing processes and the resulting changes in bulk pro-

perties can be analysed. One such defect is the divacancy in Si,

which has been identified by infrared absorption and photoconduc-

tivity methods, and its production rate measured during electron-

and neutron-irradiation at 10°K and during subsequent annealing

up to 600°K [3O,3l3.

Fission-neutron irradiation produces damaged regions of

about 10,000 atomic volumes, containing approximately 100 point

defects in various combinations. The nature of the damaged regions

has been investigated by electrical and optical methods [30,313, and

by transmission electron microscopy [32]. It is concluded that the

damaged regions in Ge and Si are; divacancyrr ich and still

- 11-

crystalline [31,32]. In metals, the influence of collision

chains along close-packed rows of atoms has been shown to affect

the distribution of neutron-irradiation-induced defects [33].

5. STUDIES OF STATIC AND DYNAMIC STRUCTURE OF MATERIALS

Neutron beams from reactors are used, at both CRNL and

McMaster University, to study the static and dynamic structure

of crystalline, liquid and magnetic materials. The experiments

are interpreted in terms of a microscopic description of the

mutual interactions of the atoms, or for magnetic materials, of

the magnetic moments. These microscopic interactions determine

the more familiar macroscopic thermodynamic and transport pro-

perties such as the heat capacity, thermal conductivity, thermal

expansion, crystal stability, etc. The connection between the

macroscopic property and the results of the neutron scattering

experiments may be straightforward in some cases (e.g. heat

capacity) but difficult to make in others (e.g. thermal conduc-

tivity and thermal expansion). The understanding of phase

transitions on a microscopic level is an important fundamental

problem in the physical properties of materials, various aspects

of phase transitions have been studied by neutron scattering.

The most general experiment entails measuring the dynamic

structure factor, S (Q,o>), where fiQ is the momentum transferred to

the specimen during scattering and too is the energy transferred [34J,

over the complete range of Q and <a. The scattered neutron intensity

is directly related to S (Q̂ <o) which contains detailed information

- 12 -

on both the positions and motions of the atoms or the magnetic

moments. Measurements are carried out with various types of

neutron spectrometer which essentially determine the incident

neutron wavelength, the scattered neutron wavelength, and the

angle of scattering. The most widely used methods [35J for

neutron wavelength determination involve either crystal dif-

fraction or a mechanical rotor system with electronically-

measured time-of-flight. A comparison of these two methods has

been made by Woods et al. [3e]; a significant advantage of the

crystal diffraction method arises from the constant momentum-

transfer mode of operation [37].

Spectrometers employing the crystal diffraction method

for neutron wavelength determinations are in use at the McMaster

University reactor and the NRU and NRX reactors at CRNL. Of the

four instruments at McMaster one has the capability of measuring

the neutron energy after scattering while the others do not.

There are four spectrometer facilities at NRU, one of which is

owned and operated by McMaster University, and one at HEX; all

are capable of measuring the scattered neutron energies.

When only static (crystallographic) information is re-

quired., only the quantity

(Q) = J S(Q,

need be determined. This can be measured directly by either X-ray

diffraction. While X-rays are more generally useful

, there are certain cases, .e.g. for

- 13 -

the determination of magnetic structures and for differentiation

between atoms of similar atomic number, in which neutron scattering

can make significant contributions.

In crystalline materials the important features of S(Q,CD)

are often sharp peaks in the scattered energy distributions corres-

ponding to well-defined excitations, in particular, the frequencies

and wavelengths of the modes of vibration of the crystal lattice may

be determined by measuring the positions of such peaks as a function

of Q and a). Such measurements have yielded valuable information on

the nature of the interatomic force systems in many crystals [35]

including a wide range of metals, alkali halides, semiconductors.,

and ferroelectrics. More recently, complicated molecular crystals

and organic materials have been studied [38]. Similar investigations

have been carried out for a wide range of magnetic materials [35,38].

The relationship of such measurements to the stability of various

structures is quite marked in some cases but obscure in others.

Experiments with alloy systems L39,40] show strong dependences of

their lattice vibrational spectra on composition, and detailed con-

sideration of these dependences may be important in the ultimate

understanding of the phase diagrams for these materials. The obser-

vation [4l] of very temperature-dependent modes of vibration has led

to a deeper understanding of phase transitions in ferroelectric

materials. : :

An example of a material for which S(Q,o>) has been studied [42]

over a large range of energy and momentum transfers is liquid helium

which becomes super fluid at 2.17° K. Several fundamental properties

- 14 -

related to the normal-to-superfluid transition have been demon-

strated. The measurements provide data for stringent tests of

the theories of liquid helium, none of which are fully satisfactory

at the present time.

A second application of reactors and accelerators for

research in the dynamic properties of materials is in the pro-

duction of strong positron-emitting radioactive sources which are

used for positron-annihilation experiments. Measurements of the

angular correlation of gamma rays emitted when a positron and an

electron annihilate in a sample of some material give valuable in-

formation about the momentum distribution of the electrons in that

material [43]• Such experiments are underway at several Canadian

universities and at CRNL. Some of the required sources are ir-

radiated in the NRU reactor, and in the Whiteshell Nuclear Research

Establishment WR-1 reactor; others are made in various accelerators.

6. NEUTRON CAPTURE y-RAYS AND RELATED STUDIES

6.1 Neutron capture y-rays

The results of neutron capture 7-ray studies are applied in

nuclear spectroscopy [44,45], in the design of shielding for reactors

and other sources of neutrons [46J, and in prompt activation analysis

for identification of chemical constituents of materials [47].

Neutron capture -y-ray studies at both the CRNL and McMaster reactors

are pursued primarily to obtain spectroscopic information; they have

beliefitted greatly from the introduction of Ge(Li) detectors first

developed at CRHL 148]*

- 15 -

At the NRU reactor, coaxial Ge(Li) detectors of volumes up

to 55 cm are used with a fast chopper of Brookhaven design [49]

and a neutron time-of-flight system for measuring 7-rays following

resonance capture of neutrons with energies from 0.025 eV to a few

keV. Information on 7-ray spectral distributions, nuclear level

structure and properties of 7-ray transitions from resonances is

obtained [50J . Together with measurements of angular and polari-

zation correlations of 7-rays following thermal neutron capture

made at the NRX reactor [5l] and of 7-ray spectra following the

(d,p) and other reactions made with the CRNL Tandem van de Graaff

accelerator, these resonance capture 7-ray experiments are pro-

viding a more complete understanding of the mechanism of radiative

capture [52].

Gamma-rays following thermal neutron capture have been studied

at the McMaster reactor with Ge(Li) detectors singly and in coinci-

dence [53,54]. In this arrangement a well-collimated beam of

neutrons passes up a vertical beam tube from a region near the core

to the target and detector mounted on a bridge over the reactor pool.

High-resolution 7-ray spectra have been obtained for many elements

throughout the periodic table and much new information on the level

structure of nuclei has been extracted L55J. Delayed coincidence

techniques are also used at this reactor for measuring lifetimes of

states populated in (n,7) reactions [56J.

6.2 High-precision 'V-ray measurements

A double-flat-crystal diffraction spectrometer at the NRU

reactor can be used for the relative comparison of 7-ray energies

between 50 and 2000 keV to a precision of 2 ppm. This precision

- 16 -

is achieved with the aid of an optical interferometer which

measures the angle between the two diffracting crystals to a

precision of ±0.005 arc-seconds [57]. The spectrometer is

presently being used to determine the wavelength of the anni-

hilation radiation relative to the standard tungsten X-ray

= 0.2090142 (±4.4 ppm)iL By combining the result of this

measurement with the value of the Rydberg constant (known to

0.1 ppm) a value of the fine structure constant, a, will be

obtained to an accuracy of 2-3 ppm. Because this method is

almost model-independent, the value of a obtained should provide

an important test of quantum electrodynamics.

6.3 Photo-excitation studies

A variable-energy y-ray facility [58] at the NRU reactor

provides a beam of about 1 quantum sec~'eV~*cm~ and energy reso-

lution about 2% between 3 and 8.3 MeV. In this instrument a

divergent beam of the 8.99 MeV y-rays of Ni, from neutron capture

in a nickel sample in the reactor, is Compton-scattered from a

curved aluminum plate in such a way that radiation of one energy

converges to a narrow beam at the target position. The energy of

the scattered radiation is varied by changing the mean scattering

angle.

This beam of y-radiation with variable energy has been used

to excite nuclear resonances between 5 and 8 MeV in bismuth, gold,

and both natural and radiogenic lead. Prominent peaks are observed

in the scattered spectrum detected in Hal and Ge(Li) detectors.

- 17 -

These peaks correspond to nuclear resonances 5-30 eV wide, many

of which have not been detected by other means.

The variable energy beam has also been used to investigate

fission cross sections and angular distributions of fission pio-238 2^9

ducts of U and Th following absorption of y-radiations

between 5 and 8.0 MeV [59]. The photofission cross sections

show well defined peaks that can, with the aid of the angular

distribution information, be identified with saddle-point con-

figurations predicted by current theories of fission.

6.4 Gamma-rays following inelastic neutron scattering

The large fission-neutron flux characteristic of light-

water enriched-fuel reactors is used at the McMaster reactor to

study the (n,n'7) reaction [60 J. Samples are placed in a region

of high flux in a tangential beam port and shielded from thermal

and resonance neutrons by annular cadmium and boron filters. The

7-radiation from the (n,n'Y) reaction is Doppler-broadened and

hence readily identified. Detection is achieved with a Ge(Li)-

Nal(T£) annular pair spectrometer. Although the neutron spectrum

is broad and continuous, quantitative information concerning cross

sections and spins has been obtained.

7. ELECTRONUCLEAR BREEDING AND THE INTENSE NEUTRON GENERATOR

The significance to atomic energy of neutrons from heavy

nuclei excited to high energies and the possibility of electro-

nuclear breeding of fissile material, with high-energy particle

- 18 -

accelerators was early recognized by Lewis [6l]. An important

parameter, the neutron yield per unit of bombar ding-par tide

energy, was measured by Fraser et al. [62]. Their results show

~50 neutrons/proton are produced in large targets of uranium

bombarded by 1 GeV protons [63,64] with an accompanying energy

release approaching 70 MeV/neutron.

Possible electronuclear breeders would use as a target

238U or 232Th cooled by Pb-Bi with a 2 3 8U or 232Th blanket, the

target and blanket heat generating electricity. With sufficiently

high, and apparently attainable, accelerator efficiencies, the

fissile fuel cycle could be closed for only a few percent net

output power feedback [65]. Current estimates of accelerator

and target capital and operating costs indicate that the electro-

nuclear process is not now economically competitive. Nevertheless,

increases in the value of fissile material and improvements in

accelerator technology could make the process economic in the

future.

The intense Neutron Generator (ING) [66,67], proposed byf

Atomic Energy of Canada Limited in 1967 as a multi-purpose research

facility, was based on electronuclear production of neutrons in a

lead-bismuth target •• Although the proposal was not accepted for

financial reasons, a brief mention of its capabilities is relevant

for future planning in this field. While not intended as a study

This target would produce ~20 neutrons/proton and ̂ 23 MeV/neutxbh

[61].

- 19 -

of electronuclear breeding primarily, ING would have developed

pertinent technology. .A linear accelerator was to produce 65 mA

of protons and 0.75 mA of negative hydrogen ions at 1 GeV,

continuously. An intense thermal-neutron flux (10 n-cm'^sec"^)

at the main target bombarded by the proton beam, would be used

for research in the materials, solid-state, nuclear, and reactor

sciences and for production of radioactive isotopes of both

research and commercial value. The negative ions would provide

both a low-current beam for electronuclear studies and a high

intensity meson source for research and possibly for cancer

treatment.

8. THE TRIUMF PROJECT

8.1 Accelerator

Four universities (University of Alberta at Edmonton,

Simon Fraser University, University of victoria and University

of British Columbia) are constructing a meson workshop on the

UBC campus, Vancouver. Completion is anticipated in 1973.

The accelerator is a six-sectored azimuthally-varying-

field cyclotron providing H~ ions to 500 MeV [68,69] with currents

of 100 nA at 500 MeV and 400 \iA at 450 MeV. The current is limited

by beam spill and consequent activation from the dissociation of

the negative ions. Virtually 10056 extraction will be accomplished

by stripping the ions to protons in a thin foil, the energy of the

- 20 -

extracted protons being continuously variable from 150 to 500

MeV. The microduty structure of the beam, with RF flat-topping,

will be one 11 nsec burst every 44 nsec The energy resolution

of the 500 MeV beam will be ±600 keV, although this may be

reduced to ±100 keV at reduced current.

8.2 The experimental facility

Figure 4 shows the initial experimental layout with two

extracted beams, one of 10 \xA directed left into a Proton Area,

and the main beam directed right into a Meson Area followed by

a neutron source. These beams will be used as follows:

8.2.1 Proton area

Four facilities will be provided.

- Scattering chamber for multi-fragment disintegration

studies providing for nuclear spa Hat ion, proton-induced

fission and other studies.

- Liquid deuterium (or hydrogen) target for production of

fast monoenergetic neutrons, polarized neutrons and

polarized protons. These beams, with fluxes given in

Table I, will be of value in nucleon-nucleon scattering

studies and will be complemented by a primary polarized

proton beam from the accelerator.

- Simple magnetic spectrometer for studies of neutron

production of pions, etc.

- Irradiation facility for short lived spallation products

and radiochemistry.

30.4 m

•24.4 m—*i -30.4 m 54.9 m

MAINTENANCEBRIDGESTORAGE

RADIOCHEMISTRY

AREABEAM DUMP

MESONAREAPOLARIZED

NEUTRONS n a p

PROTON AREA

MESONPRODUCTIONTARGETS

SERVICE ANNEXa

CONTROL ROOM

NEUTRONSOURCE

CELL FOR PROTONIRRADIATION

BIO/MEDICAL FACILITY

INITIAL

EXPERIMENTAL AREA LAYOUT

HI

Pig. 4. Plan view of TRIUMF facility at experimental floor level,

- 22 -

TABLE I. TRIUMF SECONDARY BEAM FLUXES FOR 10 jiA PROTON BEAMS

UNPOLARIZEDFASTNEUTRONS

D(p,n)2pat 0°En = 495 MeVAE ±3 MeV(FWHM)

Liquid Da_Target1.7 gm*cm (10 cm long)Yield into ±0.5° ^2.5xlO8 particles•sec"Flux at 8 metres _x _a1.2xl0s particles-sec -cm

POLARIZEDFASTNEUTRONSPn = 34%

D(p,n)2pat 276

E =430±25 MeVn

Target as above4xl07sec particles into ±0.5°Flux at 8 metres

_ i1.8X105 particles-sec" 'cm

-2

POLARIZEDFASTPROTONSPp = 51%

H(pJp)Hat 15°E =460±l MeV

Liquid Ha Target1 gin-cm6Xl08sec~ particles into ±0.5°Flux at 8 metres _x3xlOs particles-sec" -cm"

-3

- 23 -

8.2.2 Meson area

The main beam bombards two t a r g e t s . The f i r s t , of thick-

ness 4 grams carbon equivalent , w i l l be of water, beryllium or

copper. Pions a t a small angle w i l l feed a lOm-long channel

with r e so lu t ion ±250 keV a t 200 MeV tunable from 50 MeV to 300

MeV. The y ie ld of w mesons at the channel exi t with 100 \Xh

7 + —1 —1

500 MeV incident protons w i l l be 20x10 tr -MeV -sec from a

water t a r g e t . This channel i s designed for pion-nuclear in te r -

act ion s t u d i e s . A high resolu t ion channel for 20-100 MeV pions

w i l l be added l a t e r .

The second t a rge t w i l l be of beryllium 13.4 cm long de-

signed for a maximum 7r f lux . One channel, of large aperture

and maximum flux, w i l l feed ir mesons of 30 to 110 MeV to a

rad iob io log ica l and radiotherapy area , and should provide dose

r a t e s comparable to those used in x-ray tumor t rea tments . A

second shor t (7.6m) channel w i l l provide stopping pions with

t o t a l f luxes ~6xlO ir -sec and ^18x10 w -sec . Slow muons,

r e t a in ing t h e i r po la r i za t ion , w i l l a l so be ava i lab le . Many

"pa r t i c l e " experiments, e . g . study of r a r e decay modes and

muonium-antimuonium t r a n s i t i o n s , and atomic experiments, e .g.

mesic X-rays and muonium chemistry, a re planned.

The degraded beam f ina l ly passes through a proton i r r ad ia -

t ion f a c i l i t y into a water-cooled na tu ra l uranium t a r g e t surrounded

by a D2O-graphite moderator. Thermal neutron fluxes of 2x10—2 — 1

n-cm -sec will be produced.

- 24 -

8.2.3 Applied research

The close proximity of hospitals makes practical the ex-

ploitation for medical purposes of TRIUMF facilities for meson

beams, isotope production and activation analysis.

Proton beams enable the production of very-high-specific

activity isotopes. There are a nuinber of isotopes of commercial

22 57 123 15interest (e.g. Na , Co , I , 0 ) which can only be made by

this means.

9. SUMMARY

Research with applications in the materials and nuclear

fields, carried out recently at Canadian reactors and accelerators,

has been reviewed and some directions of future growth indicated.

It is found that, with a variety of these facilities ranging from

modest to large size, a well-balanced and vigorous program foster-

ing new technology within the country may be achieved.

- 25 -

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