The electronic mechanism of the optical properties of alkali halide phosphors, activated by negative halide ions

A

Presented for the Degree

MASTER OlJf' SCIENCE AND' HOliTOURS in

:PHYSICS.

UNliVERSITY OP' NEW ZEALAND

1955.

Jrl--

~·

Canterbury University College

t~rop~.l1os ueed an i:nve~t1sat1M

at

aneo:tl'.:r>ttcn,

dootncal

prop$rrt1ea

or

c~~·te.ll1ne t.~!l(#$¥Jfl.ot~ of ~ll~nli halidac. ~ottwted b;v fue.r"o :tif:'<..o-toe~JtlduettvitY'₁

too

ll<1lpendanee; end asjr¥OJt~tr~,~

llno 3ttsttty the ll£~ t1 ca~~~~Jt~tion~~l

eoo~f.nlilte tnotl~. '11_{il':lvt81 depend.Emce}

ot

pccttt~

\ilHiil:§l§

'tQc.

~17 .(:~1 ~~\ (f) 0 (), Q) "0 c c::. {f) en (!) ...c:

b

COliTDTS 1\iotaticm. AcknowledgmGnts.

THE .UESIUH 0~'

2.1 ~1ethocis.,

2.2 The furnace.

2. 3 Temperature control ..

2.4 liaising mechanism.

2.,5 Annealing mechanism.

2. 6 Crystal growth.

2. 7 Crystal shaping.

CHAPTER III.

3.1 The Photometer.

3. 2 Ul tra.violet sources .. 3.:5 Slit range.

Introduction

Grystal Growth.

The Optical Instrument.

3. 4 Loss of He solution due to finite slits.

3.5 Scattered light.

4.1 The Photometer.

4.2 The Photomultiplier. 4. 3 The d.etecting sy stcun •

the l)etecti.on .ay-stem.

4. 4 The mechanical coherent detector.

4. 5 The electronic coh•rent detector.

4.6 the signal to noise ratio.

4 .•

7.

Comparison with other instrumepta.

Ol!.AP!lll "•

J•1

·fhe

bot

or;ll•

s.~ ~e

Am

oe11.

5•'

ftaol\eaoence.

5•4

Pkot01on4uot1vttv.

5.5

Gauetd.a

ma1:re1e.

VI. l'i:sperimootal

Resulte.

6.1 r~ac.tta:rot~ttd abco~t1on.

6.2

V1b~t1onal

Broa4ening.

6.3

Photoeon4uction.

6

.!t.

imiaaton..

6. 5 l!bBOt"ptiotl.

Theory.

7

.-s

Tbe Fhru~-ooruion Ptl*inc:d.ple.

7.2 Williams• caleulntioo.

1.3

Omclue1on.

66

69

73

7l~

11

81

83

86

1. Slit

functtonah

89

l. 2

'

4 !> 6 1 6 g 10 l l 12 1} 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 JQ 31 )2 )3 )4 )5 )6 37 38 39 40 41 42 4)

furnace eontrol.~stem. ~oct diag~

Control ~nit. Circuit.

The raisins meehaniem. Photo. the annealing drive. Photo.

SUpport; ball-Joint, chuck and stud.

Front view of the furnace. Photo. Back view of the furna~e. Photo.

Cr,yetal growth. Photo.

Doules. Photo.

Or,ystal pieces. Photo.

Hg-ara and HF6 output. stray light.

Dispersion a.mi alit range.

Hunge' slit approximation.

sagitta correction.

Finite slit effect on an absorption maximum.

Finite slit corr~otions. ima.l.;tsis ot' stray light.

Strey light mechanism.

D.O. null a.etection system.

A.O. detector using a commutator.

Coherertt aetector. b"'lock diagraln,.

Following.

2.7

•

Chpt.IV.

'*

Detector ~ld square wave generator. Circuit.

Shot noise influence factor.

Assembly :for absorption studies. I)hoto.

Commutator and pickup coil. Photo.

The detector. I•hoto.

The hot cell. Uiagram.

The hot cell nismantleu. F'hoto.

The hot cell assembled. Photo.

Photoconduetion arrangements.

The dark cell. Photo.

Background. Absorption and. ref'lection.

Variation o.f suri"'ace absorption.

Absorption of' thick samples.

Half-width againsttemperatur•. Emission spectrum. KBr:Cl

.Emission spectrum. RbCl: Br

Emission spectrum. Kl: Cl

Absorption spectrum. KCl:Br

Absorption spectrum. HbCl: Br Absorption spectrun1. Na.Cl: I

Absorption spectrum. KBr:l

Absorption spectrum. NaCl:F

5.1

"

Tables

1 2

'

4

5 6 7 8 9 10 l l 12

l'

Oolour centres in alkali balides •

wavelength calibration. Hg-linea .

R16 stray light ratio.

Ohpt I.

'·2

H.F6 atray light eorx·ection.

PM, current to intensity factor. Emission energies &nd widths. Emission exiatenoe.

Absorption energies a.no. widths. ·

Abaorption and emission. Approximations. Willi~ calaulation.

Gauss cu.rve slit width fur~ctions. Appendix .

Conversion of A to ev. 400Q-7000A Appendix

Conversion of A to

ev.

2000-SOOOA Appenctix.

'·'

..

6 .• 5

7.1 .

7.2

l.

A

AO, DO

B

D,d

e

E

erf'(t) ev, mav

exp₁

oY

f ¢ h H.F6 i l IIi K L;l,e m

Alternating, direct current.· Dark current.

Band width in cps.

Optica.l.d.ensity.,.

tideal = {l + e) Y observed

Energy in ev, transition energy.

f'ot

!i {u} du

Electron volts, milli -av.

lOY

Phase angle.

Slit range I observed. ·~-width.

Hydrogen arc.

Current.

Intensity or flux.

Infra red.

Kilo - ohms.

Observed. aud ideal -!-width.

afa • Absorption coefficient.

M PM gain, ~egohms.

k*(t} (2TT)-i exp (-t2; 2)

P Time constant.

P{E) Transition probability.

Q.

RO

me

t

'l

uv

v

v

w(t) x,x•

Resistance capacity. Root mean square.

Slit range, a - f'o r a single slit •

. standard deviation.

kt = zero-point energy.

1 1 l -D

Transm sa on

=

0 • Ultraviolet •.

Frequency.

Potential..

t erf (t) +

First and second uearest neighbour distances.

Reference to F. Johnson {1951) and D. Johnson (1952)

ACDOWLEOOYENTS

The writer greatlY appreciate• the privilege of working in

tho Physics Department,

c.u.c.,

and in particular the offer

of' the late Profe.ssor ll\C. Cbalk.lin !or the writer to

cornmence research work in 1»54.

A debt is f&l t to n'U1unbers ot: start and students tor their

interest and cooperation. In particular, thanks are due to Dr.

a.

'l'.P. Tarrant, iiead of the Department, f'or his counsel; Dr. N.K. Pope for theor·etieal discussions; an.d Mr. A.H.

Meilraith for mar~ discussions, both technical, and of the

nature of research.

Considerable help has been received from many people, to

whom the writer e~~ress~s his thanks.

Mr. E.L. Rowe t'or trai:ning in I..a.bora.tory techniques and general assistance.

Mr. E.D. Shipley !or suggesting th~ use of the magnetic

piol<.up device, and the design and. construction of the ring

modulator and electronic switch.

Mr H.G.T. Bennett for design of the square wave generator.

Mr. E.R. Mangin for advice on photographic reproduction, and

in particular the Lindhoff Technika camera, with which the

Mr. L. Heath and Mr. H. Higgs.

ot

the Oant'erbu.rt College

Industrial Devtlopment Department.tor construction o~ the

chuck, commutator, and hot oe11.

Mr. G.D. Green. Chemistry Department,

c.o. c. •

f'or

considerable cooptu"ation and a~sistanae.

Mr. G.E. Roth, Dominion X-r~ LaboratorJ,!Or the loan of a

Lindemann electrometer, portable pro.jeeto:r and e. high

resistance.

The manuscript b..'l.s been typed and the f'ina.l copies

I

prepared by ~ fiancee. Miss A. Robinson, and by Miss

M. Mitchell. »>lr. R. Wade is responsible for the binding.

Diagrwn reproduction by ):;;;:es:srs G.1: •. v. Pl'"ints Limited, Christchurch.

All ether design and construction. has been perfonned by

:the wri tar.

l''ina.ncial assistance, uuring the course of this work, was

r&ceived in 1954 from a Junior scholarship, and in 1955

studies of' negative halide ion activatea.., alkali

halides begun. by F .. Johnson and D. Johnson are continued. The fixtst stag~ of this problem is completed., a. mechanism . ·

Lhavt.ng been established. A detailed investigation of'

the experimental tecr~ique and results of these workers

is reported.

The following equipment has been built.

1) A furnace and associated control gear, raising an.d

annealing mechanism, fOll:' growth from. the .melt by the

Kyropoulos method. new t~chniq:ua of growth on a. Hickel

stud is described. :3everal bou.les may be growrJ. in ::1 o.ey.

2) A pha:se-sensi tive coheror~t null detector and. constant

amplitude square wave generator fox• use with a ~3pvkker

photometer for absorption nnd intensity measurements. The

detection lb:~i t is lOCO quanta/ sec. Optical densities a.re

ri:lproducible to the nearest (;.002 for densities of 0.2 to

2.0 over the spectral range 2l5c to 6SCOA.

3) A vacuum, hot cell ca.pable o1' maintaining ClfY stal samples

at temperatures up to 0 1'or absorption measurements at

elevated temperatures.

4) A dark cellt'or U$6 in nu.oresesnt and photoconciuctive

stucU.es.

5) A projection system for analysis

or

curves into

A number of calculations .and theoretical derivations nave been made.

1) The calet.ll<J.t1ons ot Brodersen and R\.mge are extended

and simple practical rules deduced to allow tor loss of'

resolution due to finite slits.

2) The error introduced by noise into a d.ensi ty measurement is deduced to r a Spectrophotometer lin1ited by shot noise.

J) A table for. conversion of Ar1gstro.ms to electron volts is given.

Various instrumental techniques and limitations have

,;been investigated.

l) A simple temperature control system is discussed.

2) An investigation of Ultraviolet sources shows the

superiority of a hydrogen discharge fo~absorption

uiea.surements.

3) Prism instrument~•. using a priSin with a ground base,

produce ~l. stray light background r~t a leve.l of' 10- ' ..

4) Commutators in coherent detectors a.re unreliable.

J\ repetition of' the Johnsonst work and studies of

background absorption. vibrationAl broadening. photoconduction,

fluorescence, absorption and line shape. shows that the

Dt• ~.tl11arns theory. oommero1al uae of phoapbors. nand theory rnodel. (}onfigurational oo•ortiinate

model. Crystal imperf({Otions. !i~ed f'o~ study

of single crystals of both 1on1c andnon-ionic

types, Colotn·· centres, 'rE:ible ( 1 ). ·

Need for more extensive theoretical calculations. work of F. Johnson and J. Johnson. Chalklin*s reoornmenrJn. t ionE~.

spent.

In Apr11₁ 1951, Dl' Fevd Vtilliamn publtened the det~1ls

ot

the first calcul at ton,

tram

ttrat pr1no1plee,

ot

abso~ption and luminescent spectra in a crystal pbQOpbO~•

fbi a paper probably llank:s anong the most impottant eontribu ....

tiona to the theory of solidB it4 the lnst 20 years, bc:tns tb~

first step aw~y from a purel~ phenomenological

theory.

Intet•ent 1n pbospbors steme from the insight provtd~;;d

into elect:ronic processes and their rapidly increasing

commercial use {Leverenz 19.50).. As a tool phosphors have

the double advantage of the ability to e:rfeat an eff'1cient

d1 reet conversion of a prtmax•y eici tat1on r-anging from 1 to over 1o1ev into visible photons; the ability to sto~e

potential radietion energy f'or tirnes of 1o-7 to over 101 tHlO•

In day to flay use they are found in fluorescent lampa

-200,000 Kg I y~ar, eleetrolur,'lineseen t la.-nps, t Glevi eion ~;,nd

radar cathode ray tubes - 1

oo,

000 l:.t.J

ot

phosphor• tHH~d (it.a:•ing

World ar II, x-ray se!'eens, infra-red image ;;.H:mvcrtor:::,

light fluorescent postevs saint1llat1on countera.

Special applications are found ~1s flow 1nd1c.H'lltcu•s, tempcr£iltUI<e indicators, cascade transfonnera, using contrast compression

w1 th. t•n phosphors tot' solar obr:.erve.t1ons in the ictu."ooeopG,

and as time delays for storing 1nfor-m:::.tion and controlling·

electron~.c timing ueviees.

convenient and £;:Ems1 tive indi<.H~tor of' changes

ot

corr.tposit1on•

structu~e and atomic interactions that further research will

) • ·:t1ll1sms ( 1

pertodto lattice potential.

aonduato%' one thef!le b

Hettle~ - 1n

tr-on ita

posit

the lattice ~re not involved,

applicable.

fhe conr

etectronto

tion

plus

t

tiog in thtl' reerrangc:nemt.t

t1on the oo-ord1noteg

or

th~ c~tro by a single ao-ordtnst~.

eru~traN eg~d.n5t eo-or-•1inBte contours oan be oorwtruoted. Absorptton aonmir;te of a ti.on

,.

A redtetributton

ot

electronic charge follows, ~educing the

system to a new equilibrium J>OSition... o:f'..._. minimum ener , th. e

excess ener-gy being propoga;-ed as ela:SvlO \vavee. Bf.U.Oft

occurs, maintaining the atomic nontiguration. $n4 anotbar

ment energy as the difference in E~xci tat ion ·tm.til.

enere3t that ~ torni~ cord'1gurat1one ot bcrr than that. of lGlli'feat

energy have finite probab111 ties, producing t

tention to iict

reat'rangemente arHl radlationleas pro~c1ssee.

rrne history of the onderstnn:U of the p tiot; of

(1953), the ~anroaaopia a

cul n 0

s.vmmetr;l, the umleratentiing

by crystal lattices. the analysis of the behaviouz~ of atoms

and particularly the valence electrons in perteet crystals,

achieving its l1mi t in the analysis ionic crystals bJ

Madelung and born. l'he fourth and pJi'esent pbasc centre~ ~i~bout those phenome:na which cnn he explained only in terms

ot imperfections.

,.n att t to regard the varioug types

imperf'ections f:t:•om a uniform viewpoint haa be n

Seitz ( 1952). 'rhere are six types of primary tiona;

phonone, eleatt"ons and boles, exci tons, vacant lo..t tice tes

atoms, and d1sloaat1ona.

ln

audition the~e are three

It is at~eased that the

1nteract1ons of these imperfect should b.fi

an essenti

imperfect;ions are not independent of' one anothev.

~ance the majoFlty of 1nort,:~an11} phomphore

e only in the

OCm'l!iJOt"Oi (;ll

of

microcrystalline

,

Gat,.lio:t:~ (1 _J has

need !'or study Of phosphore avail in, ttH;; 1

singl~ cn•:v·ate.l s. l~hUfilt _{i i} htlVC I'

consi 1e

tbeoret1 1ci t,y. the

suthrtmtage that the bowl is destt"'oyecl 'When

rm electron is ejected f'rom an ani on, or supplied to u

cation. 'fbe offr,cted atoms may be irreversibly d ispleeed and du:r.1ng an experiment the original oimple crystal becomes

increasingly complex. This ie often the aaae wltb high

therefore t'ilso urges studies

comronents in tbeir bonding energies.

icity of alkali halia e in ionia blnll 1 ic

structure, t1nd binary composition is ln. contrast to tho

increasing variety of colour centre poonemena - ei t~ 1 •

1954. Vaaanciee and vacancy clusters play a prominent role

.-aoancies, nesat1ve lon vaoane1~~, eouplf:d palrBS

or oppoeite m1~n, a sobstitutiouul d1VIlii1ent lOll as1:5oc

with !!l poe1t1ve ton vaoaner, mrw a. negative:~ ion vaosno,v.

phenomena

dtecua3e4

· whose

tbc:uui/abeorpt 1 OEl flr-1

the

(!; (1).

ie by

to be so ide 1rl the

eontra pbenor1wma• nnd to

in thie department.

~.:._,I

1

o( ~ 5·1 .l

c:( , 6.11

nigh enc.1trgy band o!' nn F om:re:rce ..

ton to

i

5 •

1:11' a entre ..

R2 centt'e.

A,B bands.

li centres.

negat1va ion vao~nc1 • de Boer m04$l. From addition of exees& metal to • bal14e

followed bJ quenctling, or ionising

Pad1at1ons, ~'hen other banda alao appear;

Chat"ect'er1$t1c

ot

the c:n.~tyst&l.f not of metal v&pour used.

I~ar:i'

KF

L101 .t~~lOl 1\0l ltbOl OsCl 3.63 2.73 .).20 2.64 2.19 2.00 2.03

Nf*Ht" .W:~r R1~13t~ .t:I h:bl

2.29 1. 98 ;.n:; 1 f'>e'<

• vv 1.60

6;.

of vaaancies occurs ot 1t52ev in KJl, 1.12 in

Na;l, 1. 90 in 1,101• ~"rom 1on1~aticm of an F

eentre b¥ F- light at ~oom temperature Gnd

tr~naport of the vacancy thus formed. 'rb.is

also produces H1₁r,~2 A,:~,l~ bands in the neap IR.

One oxcesa electron near two negative ton .

vaoaneiea.

f's1r of' bound F centres. ~xiotence still in doubt.

ii band.

Tl centres.

U band.

scott, Smith nnd ThOOlPSOn (1953).

AntimoPpn

ot

1'' ·otmtl'~~e, hole and posit! ve

ton

vaeaney.·

radi tion - as are othm- V bands.

above -1

oooo.

Unstabl-e

•:rt~vo post tivo ion vacancies with one holG,

analogous to };₁ centre. ~'1₂, V ₃ obsm:ved by Mollwo in ar-yetsle containing e.:-i•.1ess huloccm..

two positive ion vaoonaies with ttYO hol.os,

analogous to centro.,

,;,,1ee bani sm t:nlcc ert aith

{1951).

~eaults by ~orcndort

naol

KCl

y.,,

,.;I

V bands at liquid belium temperatures. Configuration co-ordinate model.

theory by lt\fllia"lls {1951a).

Il

{ 1952) .. substitutional

Er,

U•light below -1oooo proauaes an IX band. KOl 6.,74₁

a •.

])ival.ent halides ln. a.l.k$l1

haltaee.,·Dtscovettsd

~ixect eJstema. studte~

ot

¥1

v centres 1n

srsttJms

ot

tot•r~

· Halogen ion

cent .. es.

MX: MX:toc:. I:'ioneer wo~k by tln~u~cUr.<~IEJ:%1'

(1953).

John.$on ( 1 951 ) • abnol"'ptton due to exoi tan lev

f

u. Johnson ( 1 t

4. 82, 4. 5.3(

c.

21); 4. 85, 4. 67

{c.

30)

~£1der { 1955). rlorm

ot

temperature dependence,

line shape, an1se1on, ae:rcr photooonducttv1t7•

aoo aoublet at~uoture₁ sb.owa valldi t7 of

further interactions and pttenomena 1a rathe~ 111te building e. house on aand.

la t t to ttll libr~n,tes wi tb pa.rt1all~1' undigested

tacteJ

surel7 1 t 1a to inoreese ou~ knowledge and unde~otandtng

ot

baste principles.

'

many

ot

the explanations anu m~chanisma of' appa:t""entl.y well

phosphor phenomena.

tor nearly thirty years.

novel or ditficul t in his c~J.eulrltion .. i ad

J.ct us

hope thriilt future rforke:rs 'vill fol1ow in ;:~r, ~.111i~l:sm f'ootr';,teps. The work performed 1n this depat .. trnent sprang from the

need fo1~ detailed study of simplG crystal systems"' Alkali

hal1dea containirig negative halogen ions were chosen a~ a

tool.

in the last section of Table (1) .. P. Johnson d!soove~ed the

abeoroptlon peaks in NaOl:li', l:~e.~'\t•:Cl, NaCl:Brt Naol=I-,

obtained the absorption energies, made an empirical calculation

10.

tbeGe leVOlf!J '\f1 tb 8ltC1 ten levela fO:rnted bJ' iti.OO~Ol'Qtin;&

tbe

lt wea tnaggeat•

with tb$ doublet ground states of' th0 rm.l.lde ior.m,

the shift

or

penk abeorpt1tm to lower er1erg1ea ''ms

txtom that cr Dr. l''er>d ~a111sms :t'or

obtained the sbso:rpt1on enet'gy for

.

_"

It 1& the

•

and di

i.nted out tbe simi

ion with those

d:Hi nnt ance the subject.

assoetate«

1 the

time he was my Bupervisor he was Bape:;cially oletn." on two points.

F1rstly11 that a thorough enalyaio be; made

or

the experimental

tecb.n1qua t

~"rom the beginning 1 t w~aH:l r that f:ll

e.xperimentol ~na theoretical 1nvest1gnt1on of the

more than eoul~l reasonably be

expected of an M., :·;c. student.

in the

'throughout the

been on the anslJe1e,

design.

eonstruetion, and tcating of

1.f.

Department will be able to proceed ,aa (!Uiekly sri.\\ ettioient.., 1; • posatble. lt;tuipmen:t been bu1l t to a.llow et~ut.H.es

ot

cpysta.l g~owtb, annealing proeeaaes, al::ulorpt ion and ent1aston spectra, pbotooooouotion,

llnd

the

efte~ta

ot

temperatur~

on

the spectra. aeverel crystale oa.n be gttown ln one day and their properties meal).nJ~eti the ne:xt. ln. the couX"aG of this

development,

however~, sufficient r~eulta have

been

obtatnetl to establish the nature of' tbe eleebtonics rnecbantam, and at

pt'esent a paper is being pr-Bp~ed for publication. I~ 1a

described will help ou-r ultimate understmlding

procease~.

·work in this

period of 44 • 1 nvol vir..e

Februar:. April to :\ugust,

March to June.

Methode.

ture. control ..

Seed crystal.

shaping.

Polishing.

technique.

12.

Operation. Block ~m.o tackle

{ 2. 1) O!YS'ri~J. GSOW!li.

U$eable e~;vstals of convenient s1~e are us1.ura.lly

from tbe melt• by vat"ious techniques ·many

ot

wbi~b ~o

tiiecueeed bt '~erfoee, Johnson anrl ( 1949).

1) 'l'be moving crucible metho!l

ot

J:!r.tdgman. A crucible

contatntng

tbe

melt

la

lowered

through a fixed

thermal gradient.

2) The atationary oruaible

A erucihle eontt1.ining the melt is cooled in a slowly

changing ther•m;::~l gradient.

3) The b:Y'flopoulos technique of' drawing a seed from the melt.

4) r~utectte melt growth. relying on special properties a

low temperate phmse.

5) The Verneu11

oxyhydrogen torch is collceted as a molten drop on a t>efactory rod.

6) Growth from the vapour phase.

mater 1al io

All but (lt.) (5) or (6) could be use:1d with eonvcnionoe for

the growth of alkali halides. hniQue (7)

espeatall,v promising. It vtas not investigated since

built b1 Johnson F {,36) existed rot< m:thod (1). It

capable or producing opt1eully excellent crystals

very gret\lt advantages. Firstly the technique is vr'r·y simple,

work involving 1mpur1 ties no J~tet-rdns:t1on or the 1mptn•1ty

content would be neeeaea~y stnoe all the impurity will Investigation of this technique woold be very Vt~lusblra.

Johnson F {37) chose the ~ridgman method bcesuee

tt

ta

automatic. '!'his ia 1 til& main tU.sadvantage, 1 t ia too

automatic. one has to watt a week to know whetbe:t* a

s~tta-factory crystal has grown o~ not. or the crucible baa leaked.

It

the crystal is unautisfactory it is necessary to start

again. tn the method to be described a useable erystal can

be g!'O\'Hl in 4 hours and the f'urnaec ready to gz~()W another. Techniques ( ·1;; \2) {3) a.t·~J in principle tndonticr:il for

crystal. Choice between them rests on the tecbnolo£;1Cal

ease of £H.lpplying the condi tiona suit;;l:lle fot• ;:::rowtb. ;Jtrong

(1930) summarizing the experience of mana worker•s l'lf3ts fiva

condi tiona which ensure growth.

1) Cttrstallization must stsrt at a e1ngle point. other•wi~S()

the oryetal may be multicryatalllne.

salt. 'this helps orientation and prevents twinning.

J) Temperature iaothermals within the crucible should be as nearly horizontal as possible to prevent convection

rclat1.<ve to the crystal e.l.c;nvly and uniformly so that tb~

C:t?ystf\11 latd down at this ~Jurtace will be aouna

ooa

flawl.eas.

4)

the crystal has been foPme4 the bottom and top

ot

the cu'tystal muet be brought to the same temperature to avoid strains.

During

g~owth

the

cr3stal

ts

in a

thettmal gradient of about 2000/cm, end i t the padtent ta pl'e&erved ae the temperature 1e lowet-ed, sa in the

Johnson technique, considerable strains will be set up

due to the un~ tempet"':clture.

cooling ~atee- especially near room

plaatla eo that immediate

gt~owth pr•oduct:;a no strain ..

alkali halides are fah"lY of the i

5) The crystal must be remove{l from its eontminm: or

holder before cooli

contraction of the holder.

A comparison of the :Kyropouloe

given by )., rhe

outotrmd1ng-t!tt1vantaDcs

or

the hyropoulos method are ease of' ient

control the proce£~s oan be interrupted during growth. io

'!'be existing equipment was rebuilt to allow growth by tbe

!~yropoalos method, but the lO\'Wering meohanism used by

Johnson for

the Bridgman method can

be

easily attached

it

required.

Tbe fUrnace

and control

gear were made to be

ver-satile as it \vas hoped to perform studies

ot

the annealing process and the possibility of using the technique

tor

16 •.

The fut-nnee need not be as

large as

it

1&.

~H.n.ce heat loss 1s proportion$! to area, the power to he

contx-olled vatt1ee as th~ square

ct

a 1i3Plcal line~ d!menaton.

Oructblea used by paat workers und aur1ng tbe p~e.sent wottk

were 2 ... t.n tU.ameter or lees whereas tbe internell 41ametev

or

convenient.

been entirely recOn$tructed, \vben it was reall~ed, evident!¥

not by Johnson that useable crystals ue be only 1 1 mm

in section, fot• this is the

Spekker .Photometer where the

{2. 3)

providing both proportional

controller, for t;he \vork to

ttJOUffh two 1nuepen.dont cizleui ts

integral re~ponGe control,

ted from a mirror galvono.:."!leter:•, placed 1n a

potentio-meter cit>ot.li t w1 th the thermocouple, was either incident on a

photocell or not,

dependent on

tbe galvonomet~ indicating

above or below balantje.

a sunvic connected ~ resistance into or out of the tux-nace

mupply e1rcuit, Figure {2). !n tbo p~ev1oue wot-k the

thermo-couples were merely dangled in t;he radiation field of tbe

furnace, an11 with the above simple contx-oller control was

inadequate, evidently due to the poor ei'ficiencv or radiation

tvansfer to the t hemocoupla/1n a ceramic bloelt, supporting

the e.rucible, when the thet-mal contact. ot: f'u)'\nac:e wall anti tbevmocot.tpl~ is goo4, the simple c-ontroller wa.s totUtd to

Xt would

servo-mechantam to bave only one aont~olling time constant,

and a1nce tbe controller delay cannot be removed tbe rurntloe

be assisted it the fu:rnaoe were ennallel"•

In tiee 1 t has been found &ut*f'ioient to place tho

the CPUCible 1n the lniddle Of the

to switch on botb heaters till the salt melted; start the

controller €md swi tab off the hot tom heater. Both tbe

elaborate simple controle su one disadvantage.

that neeeesery

tor

the contl"oller to sw1 tch on tho power - due to a temporary

were re:zAd to 1°0 on a Cambridge un1p1vot 0-10

m1oroamp

meter

or by watching the galvanometer spot.

It ("!ppear that occur ove1,. a range grt~a tel' than 1 - 25mrn/hour (

wi tb optimum ratee> of }mm/hour t'or pure halides.

tb

1947)

Jtange o:r epoedg is gi van bN a mechanism using the bloek r.md

40 t•ph synchronous motor ivee tbe 40 : 1 worm tached to an u J1. ";., screw.

ball bee.ring pulley and

a ol ?1re fixed to the moving block and the baeo plato.

18.

complete

oiJ:'icUit

or

cbor-4 around

tbe

ti:ced pulleg

the

raising

rate 1n nnn/hOur is tbe numbei'

ot

1_{loop$'• · •}

A m1orosw1toll on tbft beme pltlte,operat.~a by tbe moving bloc:t,entcheG a

changeover relt13 wnioh tYI1tcbes

ott

the raialng· motor aM

1s px-ovtd~d and varioua olamps to flllotv

cbange ot

the nu.mbe~

ot

loops. 'the ~ai Bing meehanism WtUil not UiUtd ·ve~9

often._

Menstes

(1952)

points out that e1nce

the

soli4 is aent~Jel*

than

the liquid the level in the cr-uoibl.e automattoal17 falls.

Tbts is

v~ry eonven1ent.

a 1 ~ 10 on a j" ~:\luminium

disc th :l?b1s disc l"uns on t:\htJ.ft

attaahecl to a Ol1L'1l ~·1 rewound. ontiomcter t~ (.t

firmly attached to th1s sbaft ~'IH:'!rew1ng up the

•

tch' nut

which rorot:~s a cono~ntrtc oylindet- to bco.r on the distH~. .'hen

in c trout t the meahar.risrn will lower the fux-ma.oe temperatura

Iii th this

stud on 1-vhioh it grew and placed in a preheated box of

workers - pl&tintF', silica e:;ltru.u~, fJ('Jraoluin, iron.

Vitreous ai 11aa has be!f:·n found ccn:tv,:"rlient proviuc.::l that r:t!'tcr

it aoola, el~e it adberea ta the silico ond the crucible

8aah arucihleo are readily cleaned by heating or'

soaking in watar.

a

the cooli nq; mea hani Hm if.::J Pl"'ovt JeJ.I by nickel coated

braes chuck with eaoy-flow joints, and water cooled;

u;i (·r::)

" gure ::; •

of' u s.e. cc

in coolin~ the chuck. No~nally it is run at

One of the erporent difficulties of the tyroJoulos

method is the need for a eeed crystnl.

stittable piece from the solid maee.

method.

is however 0U1cker to proceed ns helow.

evidently tried growth directly on to platinum.

shaped nickel studs were fitted into the end of the chuck.

diameter bas been grown at tbe rate

or

1

Ocov"hour..

11\ elmple

analysis 1 1 thst a rough gu1 is, length

·or

crystal. ·

time ..

and Miller (1 )

give man~ practit~sl details the t'abrieH tion of 1

ba11des. The ele~lvage planes Mt'e ~c:adily found. by t•;stther

quickly foroing a corner of e on to t

rough gri 1 gri excellent.

thie fJOint and tht"J

Jd in

ar1 t:lr imrry ar~n scraper Eiven t~ light tap, rcecHiil.)t cleaves

the crystals. Ther-e may t:a some auvantage to this

under water or parafin. The aurtace oharaaterlstlaa

or

all

such crystals inelur.Ung some ceen in othet- laboratories are

rather veviable due to many .fine lines on the sur-:race.

Hence throoghout thi(') work e11 stn"'rnces have been poliehed

1mmedietely l;r::fore measuremento,. of &bfaorptton.

(Jccasionall,y flhen only ~a small boule 1s g.t"own i. t is more convenient to grind a piece t.o shape ratf'wr•

it.

run

at top speed nnd ater moist Co to

expeotation therHt crystals may be handleq Quite roughly. nnd

21.

lathe cbuol't. an4 kept wet... tbi.s requiree e~re. but would be ..

reatltly done it a diamond tmpl~iiJrt.;~nated t\1teel disc

ot .

sitnil.m:< thickness were ti!Vsileble.

t•otisbing is. per-formed 1n two S!t&gee. A grinding

blank !a prepat>etl b1 grindi between two pteoen- of Jillate

glass a

drop

ot watar and a trace of 600

emery.

wa.sbed ana. dry one breathes. on the r;t~ot.ula surface

pollcsbing, soon tis the pl,;-;1,te to tee:'l

tn.~ystal it"> 1d;:ly slid otr the plate olean~d.

begin a teky tbe

ionfl the cryt.:ifa:tl tlii.U'"faee will he 1 olean

ruhbe~~ 11.i{htly and quickly on a soft cotton cloth

tightly stretched over a pieaa of glass moistened

with a trace of aleohol. iJrhia produees uniformly optiOf:ll.ly

excellent st.n•f'&oer;, in a vel"'l/ short time. If the rm~ttace should deteriorrite 1 t only is neeeesary to ~erub 1 t on the cloth.

A tectm 1que pointed out by >lowinski ( 1954) tres eonsider~::~bly a~o~e 11 but produces slightlv b~tt(t;:r ii:&tJI'facH:'li'h

After- the oryntal b.a!.?l t.HJ~m rough gt•ound on the aaa

grinder 1 t ia rubbed on a 1D1 lap ~ligbtlg moi with

brine. The f'inal polish is given tb ·the lap bal"ely

motetened with water.

I

I

R;l~7f

•

I

k;iifi;~

I

I

Power...t Variac 1 ~ 1

sane

controlled

power

Potentiometer I • I GalYO

J---

-J

PE cell

Btas Yoltage

Signal Yoltage

Furnace 1 -Thermocouple

40

fJ4o

Variac

X _Neon ... _6.3v

::Q

u

ron_.__

1

. 1

3534

100K 50X '::'

!HE RAISn~ ~ORANI~.

Thia is

desc~ibed tn tlle text. I~cmt the

lett la the f4UtO'ttlatic contfl'o1, mtc71!"omt1 tcb

and ~~al

control.

La1

sha~ts ·ar~

of

stlve~

FIG. 4 THE ANREALING iliECHA.NISM. This 1s

described in the text,. Clutch nut and 1:-..nob

are on the right ot the panlll,the top of which

FIG" 5

and Bnll-jo1nt

the Support,

B

=

B:ron.ze

B

Ohnok: Nickel

coated ..

0

Bt11d (N1)

SQJ\LE 1 :1

cooled

Ohuck,

; and

position .. t

E

=

IUteotio weld - take apart here.

0 = Oil-well

FIG. 6

On the left is the raising mecbani•. the ebuck,

stud and thermocouple are in position on the

centre of the furnace, but the 111um1nat1r~ lamp

is swung up. as is the viewir~ mirror, seen

behind the chuck. The lower unit ot the

controller is the power unit and the upper the

controller prope~ Leads to the gaJ.vonometer and

photo cell run above the sink, whEU:'e thermometers are

placed to measure the :l.nnow u.nd. e.xflow water

FIG. 1 Rear view of FUilNAC.E an.d. CONTROLLER.

the aru1ealing drive may be seen to the left rear

of the su.nvies. in the lower unit of the controller.

li'IG. 8 CRYSTAL GRO~ttH. A photograph taken in

the viewing mirror near the completion

or

growth

ot' :ar- in KCl. .Dimensions are approximately full

si~e. The glow of the fu mace ean be seen between

the ceramic block and. the furnace wall. The ehuek

supf~ort shaft - uirect image - is out of focus ..

Notice. that by achieving radially syMetrical

heating and cooling, as suggested by Menzies, no

raising is required.· In the J!'igu:re rau.ial. growth

FlO. 9 Nickel studs and some sample boules.

Notice the multicrystalline nature, composed of

OHAPl'lSR III

Flux attenuator.

lble procedures

or

position.

Ultraviolet oourcee. Difficulty ot achieving

i1 i ty. ious eourcen.

intensity. lapge intensity change acrose the

spectrum"

phosphor.

311 t range.

lamp for calibration.

Optimurn sl:t t set tinge. spersion.

ita.

Brodersen•s calculation.

~~ 1 t 1

r

",(. ,.,

'

lt

.r .. ppr>ox ma . on rom ~ .• ro ... eFsE'm t1 reau ..

Use of a

Resolving

2 '") 2

principle. ·

=

1' + a • Modiftcat of

Runge's work. i

ti.on

Scattered light. Tests. :rements. with gla:::a slah.

Spectral analysis of stray.light. Triple reflection

scattering mechanism. 'd~nergy argument.

t;.1) ·rm~ .PUO'rOMl/r;i~It. This unit is briefly described by

F. Johnson (,58). It is, however, theheart

ot

the

measurements and several important factors will be mentioned.

?he flux attemuator of the ~}peldtev Photometer, pl.aaed ·

1mmedhttely behind the Fresnel llhomb beam splitter, consists

of a fixed upper aperture of width

o.soo

em, and a variable lower aper ture fed by a $Crew of pitch 16 thread~omt

carrying at ita lower end an aluminium cylinder, attaohe4 to

which ia a sleeve, calibrated 1 n terms of dens1 ty log A •j,p,., )1\. •

1 */1

=

A'f,s.

d

=

_{log10 1'/1}

t~ dem:!ii ty N·odirlL~ invo1Vei:1 four t;.lOurees of' err·or ..

cirele was sot into the dPum cylinder with a turned \vooden

plug.

the position of the moveable slit, with a Pye travelling

microscope, of quoted accuracy better then o.0005cm, and

found to be a linear fUnction of the circle setting.

(2) The d - calibrations may not be consistent. Here, oa1nt;!_

~,.,

function of d.

error in reading the d- sctale.

(3) i'he screw may be tneorreotly zel!'oed at an aperture

A =A' + a.

(la.) The d!*um sleeve has be~:n ~l1epl.aced b7 a q revs wtth

referenoe to the above false origin,

t..~easuring Q revs, around the sleevE'! from d •

o,

the

true drum: reading

a -

log (1-

f ( •

q)}

= log h '/~t ss calibrated by the

Thetrue density, hov.-ever ,) =log {r:~• +a) /a

and

'• D : R + log (1 + t \ I

=

e

(1 - 1 ) since it is measur Substituting in

D

=

lo~t:: ( 1 + a/ ;,• ) - log ( 1 o-d +

1

rl,)

\;hf·n f'ixirl{i the sleeve to tbt~ drum ther•e are two possible

( 1 ) _4(d

=

_{o) =} A' using a travelling microscope.,

requires t'11emantling the photometer, and is tricky to aet to

· better than • 001 em. In ( 1) 1!' both D₁ d :::: o there remains

l&t>ge d.

(2) Close apet•ture - light t~inger pressure, - 1. e., D = co

and the erro~ term is a conetant.

ft):r 1 ( d t= 0)

,=

1 •

u =a

+ log (1 +

a/A') l/I'

25. ModifYing

thl,.

to

allow

In adjusting the lemp, d is a~t to o, ax1d the ltiunp adjusted till

'1J = o; i.e., I'/1' • {1 + tJ/A1} .... with thia piJoeedure n/A' is

c. o1 - gt v1ng

:o

=

dj to an aecu:racy set by the aarevt and tha

maker'& calibration.

1a accuPJlte this p~ooeu1ure is rel1af.:~le with an e1'lz."o~ less tnan

that of reading the

a -

sc:t.lle.

tho i tton is otwiticf:l.l, e~pee1ally in a VeJ:>tical

dir.:NJtion ·when r::.m 0.1 rmn shift ehangea the dene1tu b;r o.OL;t,

due to t h.;, N:'if-11 d 1'11 v er•gen.ce .from parallel1 sm of · the tv:o bC{clmB

m'il the t4C)t:t:roe moves ott' the axis of' the instrument. e:.tnd the consequent mo:t~e rapirl vignetting

ot

one beam thax1 the othett.

'rhe transverse fmd longti tudinal poai tiona ar-e 5 and 50 t1mes

less cri tioal.

suppor-t.

(3 •. 2) ULftAV!Ol,Jfo)f aOUROBS •.

It is known tbat the two previous work$N~ ~perienoe4 oonsldet-$bl~ d1ft1culty in eotd:eving atab111t1 and roelia•

b111 t; in their meu.s;ur.ements, as was tb.e ease wi tb ·Macr)onal¢1

( 1953), (un .. eoord(1d). ·~\s 1s pointed out els~wbet"a; these d1ftic~lt1ea cent~e $round;

1) The u·ae

ot

a

o.c.·

~easu:ring technique.

2) I~w Pf• are output, and the predominating influence

ot.

3) Cone1dert~ble str~:w light with the llg- source, and

random intensity variations.

Johnson F (65), vli1th reference to tbe Hg- at>c₁ implies that

the method used h~d cuffioient sensitivity only on an

emission line, ana in fact hie ro('~asurentents w-eroe msu!e

photographically. In using- an Hli'6 J·o~naon

n

(49) al2mits

.

the need for wide ali ts, Hence an. investigation of var>iOtls

t '}400' t •.

sourcaa was run . a ~ n.

1) A h.ydrog(~n lnmr,.), type HF6, though stablE.~ hact lo1f; in.tenai ty.

2) An ot~dinary D.(;;. aro had fair intensity at an arc current

of

5

amp. The arc waa unstable and wandered over tbe

carbons. A perpendicular ar•rane~oment of the eaPbon.n

was used so a~ not to obstruct the red1atton from tha

poaitive crate~.

3) J1. bo:~ type l!!t8 lamp, 250 h' Hg•are was convenient. hatl

reasontible output, hut the arc wandered.

tntensf.ty carbons (6

m.m.)

t~ae s1m11~~ tc the o!"d1nary arc

tor

<U.tl'l'eta belov1

1,;

OPt Above 15 amp the reQ.i.ation

ln.ot"eaaed

con&idettably both

at 2400

A and also

tn

perpendicular· carbon arrar~.gement eaused the pos1tlve tJ~u .. bon

to erntet .. 41agonally, and. mo~t of the t-adtat1on was

lost.

'!'be burnitlg rate became alal'm1ngl.N' nigh above 1' amp.

5} Tungsten eleott-odes gave high 1ntena1t1 w1 th

a

carttent

ot 3 amp. However, the· a~c was very unstable and would not born for more than a minute. at a time. !be posttive

electrode burned rather quicklY and.oloude ot tungsten oxtde

7)

A tungsten ive and a e positive gsv a fairly

high intensity and reasonably stable arc which run :ror

several minu vd. thout ad~ustraent. l"tmgsten oxi wnn

still troublesome but n.ot nearly as as before.

From these testa the fl.g-are would rttppear superior> f'rom

the point or view of intenei ty and oow-enien.ce, as the nir

operat at~cts are trick1 to use and um:oeliable. work

in the - 250~1 A region a tungsten source enelosc;:l in an

inert &tmosphet .. e WOUld be WO!"tby Of investigation. All

auoh sources. howeve~. have the grave difficulty of large

intensity variation across the spectrum enhancing stray

28.

shown:

, · A nun:iber of other..- ~Jx'U~ weJ:~~e 1nvett1sate4 an4 tbt

.

·

was

.

4ttohavse tube

tPom

a 160 blended t¥Pe & lampjtoontl \O

be most

eon.ventmt

tor

wa:velength ca11bration, WStb linea

at;

fABI,.E

a

;zzo

5!&1 4992

4J.2$

4080 '4:.9!17 ,3J!t2 3~2 J.Q.g6 2.2§.7

2925

2699

2!2!\

2643 2537

24&4

-with the fluorescent eye piece eal:tbration.

2.§.24

2464

3906.

_Ji20

₃₃₉₀

280S

-.

2.!22

.

2400 2380

.\.

Tb.e use of a phoepbor. Wt:H'~ considered us a me ana

ot

Since an

interrupted light bea~ 1e used, the phoapbor decay time

to be short, so th.~t a 40 cps equa.re waV'e would be trnnemitted with litt loan. Z1nc ~ulphide has a high conversion

efficiency '~JUt e.:litcessi ve decay time. V~1oua oils an4

vaeelines were tried, and although their decay times appea:red

short

enough their

conversion etflc:tenctea wett-e ·eo low tb.at

losa ot output resulted.

It

would

appeax-.that sodium

salicylate applied to

the

bN

dtseolving

tn

MetbVl alcohol

: would be wortbf of investigation since 1 t bas the advantage

ot

oonatant quantum etttelenc.v 1000 .... 3000 A. - ~~atanable

0

·5=

/.

5\

I

(\J

(3.3) SLlf RANGE.

throughout the experimental wo~k entrance and ex1

t

$11 te

have been set the same • the optimum position •. Fort

tt

the

Slit Widths are a,.b the energy reaching the cffctor· varieS Q.Q

ab,and the slit range as a+ b • If ab is constant, a + b

•

is a minimum for a

=

b. This was veritied by traversing tbe

broadened Rg-line 4050A. The variation

ot

I'esolution for

tb < a < 2b is small.

Brodersen { 19.54) shows that. a quantity conveniently

describing the actual resolving power of a monochromator is

the effective slit range Se related to the minimum value ot:

Se, So = Bo ( v) a quantity eha:t"acteristic of' the monochromator,

and ag the geometrical slit range by Be2

=

so2 +

The optimum slit width is of the order J...f/a where f is

the focal length of the collimato~ mirror and a is the width

of the beam leaving the prism, Forsythe

(1937).

For the

Hilger UV monochromator a

>

o. 5em, f is 27.5em. Hence, for

A. - 3000 A, this is less than

o.

01·· mm, whereas the work

report-ed here is with slit widths 1o-20 times greater, so

s

₀ can be neglected and Se

=

Sg =

s

say.

The A scale of the Hilger instrument has been checked

agtnst the Hg-aro and found to be accurate to about 1A from

2000-4000 A. Hence, take the calibrated A. -sleeve as

correct and use it to·caloulate the angular dispersion

d9/dA Figure (12); giving the slit range for 2 equal slits

Hartmann's formula ma, be written

•

••

and

•

•

•

n

=

n

+ o(E~1-Eo-1)-1

dn

=

OEa

I

(E-Eo) 2

n

o

dx

=

rg.

~·

dE dE = K (E - E_{0 )}2

100

so

10

1

2 3

4

5

ElectPOn Tolts.

FIG. 12

Hilger t1V ·11onoobromator,

Slit

range

and

41ap•ra1on.

s .

10.

de

-dA

1

{).4) tOSS tllt' RES01:..lJftO~ ll\J AN .~!\:lORP:t'IOlf SPEO:tlttltl l)UE ftl rn~tr~ ~U..t!'f'$.

l~t!Vloua wot-k on slit Width crf!O~$ watt l$rg~13 ~ot~Cerne4 wi ttl tiJ.H!H~tral lines. Only reoentlN !t~dy and Young. { 1949) gave a rlgoroue trentment f!>t eli t w1dth f.irl.'-ora for the gentt-al ease

ot

a oontinucuti absor~t1on cu~v-e, but their re.ault 1•

too complex

tor

practte$1 purposes. Again .otbex- wo~kera₁

such as Eherha~tlt ( 19!'>0), who

:tits

the ~bsorption curve ut

th$. maximum 'hV a pa~abola, matte rather or~de appt;oo:.d.mutions. 'the mtdn ohjf,~Ction, however, to many of tbe$e practical rftoint

~;r v!c;,;w approi:lchee is that they ~iBcuae abeorpt1on i.n terwa of

trensmi~sion - e.g., :allis ( 1951) .... whereas the phtsioally

t~ignifioant quantity is related by a faetol" to opt1oa1 dens1 ty.

It would appear that the trood in. mothltt~.n 1netJ.'I<umentat1on ta

to calibrate the inten$1ty eompBPitor in optical

density-Daniell and Brackett

(1953)

-as on

tbe

Spekke~ photometer.

Many ot the results for correcting, ~or the ettect ot

t1n1te

sl1 ts

on

emission lines could be used 1t dens! ty were

convert~d to intensity, eort"eated and reconverted. 'l'hi.s

would be t:~ ted.ious proceslll even

tor

one t'urve an~1 as will he

shown, unnecessary.

Broderaen (195!~) taltett a middle aouroe and dor:i'iloe

etepeoia11y t-are in ultJ-tt'f!Olet abaorptton epect~a, ;t,et US

ooDa14er

a eonttnuotus ab•orpttott

CQM'~

eta a

vet!-;

wtf)e · ·.

absottptton 11ne. typical caae

tor

s.J).. alkali 1tn];Hlr1 1!3,

peak absorptlon at 4,8 ev, half•ntttb 0.4 ev, slit

not necei!H!!.t'U'•ily Gaues1an - ~g., ttmt due to F c.entres; .

~3e1t!, Thaory

ot

t1ol1d$ (663) • Richwda. and Burton (1949)

found ''that for solid and .:U.qo14 specimens, even With

mae

I

will be lees than !);'~; tn general about 2~~~ ·the correction

will not be. critically dependent on the assumed ideal shape,

and the Gauss torm ia of metheznat1cal convenience. Hence

Br-odersen t s analysis fott absorption lines ma:y 'be used as it t;tands.

tbe observed 1.ntensitv lobs

and

f

••

_

1

v.•*·"

- ~ 1desl. uv

v,-s

''·

.,_. »

0.2, th_..e 1a ltll£ erro'

ln ustna

10° • 1~2 • .;

n

(2)

wta.n .,.,

tin~ lt ... f:r -J.Q

0 oba

wh&-re w(t) • t el"t'- {t) + 1~(6)

At ~: •

o.p

•

2 (2TT) • tdml;~~~r£gl

From 'Brotlersen '• nwn~lcn dot& (lila

rts •

.J) \ti'e 4BP1Ye Ftpre ( 1

J).

llot!c•, that tbou£;b t1Qba/D_{0 le}

depentont

t?D.

D₀ the reaultu at'~~e given toJ:~> m o 1121418 wbefteaa in W

absottptton apeett-$ '\tul ues or a m be i 1 • tn the

onlu to 0.01

Since we bave ab.own

tor·

a (lfause

curve

th~it t t

le:e;lttm~te

to

u~~e 1oll

=

1•2 • .:;, IJ tb0 1nteg%•al (i)

tn Dldcal• Honea tine sup~l~i)Oif:l1t1on J;i:t>1oc1ple holdG.

i$ we :r1od the ertect on a ::;ultiplttJ our'\'c by cval:t.uattng

thEl etfnot on the single curves and adding thEJ! Paeult ••• or

vtoe v~.u~·$a. this alao folloTm f.Nrn ott'~ modittcation

ot

RuDge's

wor-k,ae

the rfJ!sult

1.,

independent; to the ft!'at

oncw,

ot

the rcrm

ot

Dtdoal•

It

alao

to1lowa at our level

ot

epprox!aBtlon

tha•

. .. . . . .

. .

. Jlt..

f.t11 Ob$e"'-'• ideal balt-wtdtb• This s.a an. e:atl'etraelN valuable

ltlt.4e, a1

le

the toot

that

tor

m'l

the

tl

..

al

tm4

obsewed.

cttll*Vte

eroaa at x

=::t· 1

~.

. .·. .. .

·.

. .. i

.

.

. fte twlcttoa.a

w(t) • l(llf)

•llf.

[!l -

tt(ll.!l

tunro

b~

tabalstd

' . ·.. t"

foP

var1Me

•aluse

or

t 1n tbe t

Appemtu,

ani the

oorreetiotl

• ·eub

that

D ... (1

~

e) n ₁

~oP

the ma:.d.tallm Yaltte, ta

tleal oba

papbed

t~ Flatu~• (iS)

agatnat h, where

h

=

slit·

.Nnge/obaewett

~,_width .

uee ( 3) in pract :Lee \<Vould be 1mpose1bly tedious.,

ana.

wonld

not be 3ttstifled by t~..e errall correot1.on neeessaey • ·rbe followtn.~ provides a pract1eel solution., !J:b$ ~tb.Od

ta

e modification of

that due

t~ Runge and Paschen (1897). l~t

tho optical 4ensitr at

the apectral pns\tion ,. -usually f'requenc:~ or ev - bo D

=

(T

ideal t Oonsid.er a source with a

elowlr

~Tinr; intensity distriblltion

• e.g. an

H-are •

aucb tbat over

the

v-

~anges

considered below

tta

dtatPtbu:t'-on mQ' be

t9ken

ae

a constant, un1t1•

Itenoe

the

tnt.ents~t.ty 41atnbtatlon aft~• tbe absor-ber ie f'(v)

=

eQ (•ll ) .. (, . 10 1

Thi$ ia a veJ![/ minor app10¥1HlStion fott

the

in tenet ty 4iatr1btttton

or

the tt-aN below 4000A is veey neat'lV line~ and the tore ot t(v

ta

aot

~qutPe4 in

the tollcwing

.-na11e1e.

ConstdeP &qual alit l'angea,

e.•

q.v., centred on Jt. At s + v the t:m.ase

ot

tt>.e ent.t-anoe sltt baa intens1tsr r(x + v)

or

Which

the tl'act1cn

!:I

ie

ooUeeted at

the

extt

);5.-allt. Note that

thia

implies a t~1~ular eltt

tunotion,.

area a2, base !~at lu agreement with Bl'_oders~n ( 195.;) )• u~e ,,,.,.. ( 13}.

For all pta t' lying- on one ttlue

ot

ltt

tlle col.leote4 Gtlt:JX'fJY la

/ 11

~

(x +'f)

4V

,Q

For

all

pte v

lying

on the

oth~l'l

side

ot

x, tbe collected

~;'ltlft»gJf

ts

( 8

a-v

j

0

-;-t

(x-v) dV

•'• 'l'otal energy li'(:c) "' [ • : (t' (x+v) + t(x•v)) av) (S) )

Note the e1milal.>ity ''etween this and (1).

~

The total energy collected fl?om the eomparlaon beam is a.)

(5) may be solved fo~ t(x) 'b1/ expanding as a TSN1or

ditt'ePence ser:tes tn v, performing tne integratio-n, and

1nvel't1ng by liewton •e method; g1 ving

wbe.re

•

•••

· at(x)

=

F(:r) -

!

f

1(x) + ,. u •

6

.

F1 • · {F(x+a) + Flx-a)) - i:l~(x)'

~

F t: +

ia

:r;t, to

too

first order

(6)

(7)

!he obeervea tiens1t3' Dobe 1a obt.ainett by comparing the signal

t~ough the absorber to that in the comp~1son lHllli:llil•

F

oo'be

=

--log

10; bN (4) {6}

=

1.\

-lo;

10 (1.+

ft.a)

natng

(4), (7)

-

~..

les~_~,.e

l F l

.

,

Now 10 »oba•=t- ·

t::

i(exp

10

~»oba(:¢} 4-Gba(~+a))

.· .} expio{.o-cba

(x)·~obe{&•aljJ.

i.

But

tor

a smt!tll,

»

(x) - a(~

!

a1

1& m.asll, expan41ng

. . . Ft

•'• 10»obs

'7

•

log₈10

<»otu,,(x} ....

~

{D{x+a)+l>(x•a)))

• lose10 • Da, aau, · wh1o~ we will attll the aas;t tte.

. 1!'

Subatttnattng tot'

.=t

in (9) and noting

t

lt*f

~

• 1o""'Doba1 ae

in Newton'9 metbo4.

· · log. e

Dtaeal • »oba+ ,, ..

6

1

_{2 ..}

_{1ooobs .1o-}000_{~\.loee10 DJ,}

:n. 1 1}..

=

.vobs•

6

.;;..t.

In Figure (14) D1 ~ AB

ln Figure (16) we show the undet>oorrection as a ;:c;; of

D₀₁ideal, wben using the sagitta .cor-Motion; as devived

tx-om

numer1oal calculations of the requi!i'ed cor-rection for

the maximum point, at which the correction

1a

largest•

uetns

the

prevtoua

results

tor a Gause curve.

Notice:

1) The result ts independent of

tbe meaning

of~ and

tb&

rom

ot

n.

2} The method undereor~ects, na is to be expected s.tnoe we have made only a ttrost ordex- approXimation,

3) J5elow

o.

25 the er:ror is n~glig1ble,

4)

With

a

density

st.gn!ticanoe level

of

o.o1

the corrected CUFVEt will ttot differ signtttoantly troom the id$31 fo:tt

Intensity v

--~-'l"""""""'-·-1·-·-.,

/',i

/

.

Slit /

!'\.

I.

•

tnnctton /

₁

/

.

_{" I}

/ I ~~

a

...

Ent~oe slit

image

FIG. 13 Range triangular slit approximation.

x- a x +a

. Correct 1 on

=

_D1/6

=

AB/6

1.0

0

0 2

4

6

8

m

I: s/tT

FIG.

15

Ettect

ot

a finite el1t an the

e = ~ oorreo,1on

5

0

to Dobs.

e

lP!G. 16

Slit width correot1one.

%

Underoorreot1on

to Do~ideal

h • alit range Obe !-width

0.5

1.0

x•

wa1

4eo1ae4

to uee e

th!n

mlot*O~Stcope

oovel'

s1aaa

fU!

a etandw4 $bsoPber to'l:' 't$lt1ns tU.trulit1vlt¥ of the

abs.orpt1o;netEt:r and c&mJUl1'1ftS

tn•

1D'6 anti tbe l!g•aro,;

beoau•• ot 1 te conv:entence

ant

sui table 4• :rllltlge

tt-om

asoo-)JQO

A.

Using the

Mg-~c

eource, low d• rea.!ling& waite

obtalne4 below 2700 A. the

glees

we.s teated on tbe

Ctum:ttttry :OepEt.rtment's UVlep4)lt₁ a photoeleotr1c 1netrt;n!lent.

Comparing :results:

100A's 35

.:;o

29 28

21

46

25

Uv-:lspelt

.o;,

_{.04 .24}

.47

.84

1.4 2,0 2 2

:3pe:tr..ker

_•

_{.04 .25}

_.47

.as

_1.4 .60 1.,3 .12

This 1nd1c~tes considerable ~et:rau ligbtu in tbe region lees

than 2100 A.

The follow1rag steps were taken in the bope

at

removing

the tr-ouble.

1)

fbe

ehoppe~ dtno and the !.nt~nal walla

ot

the

mono-cb.romstor, eollimato~ tube, and l"'M houa1ngs were painted wltb.

a matt blaak paint having a r-eflf,otion coeft1o1ent

or

~bout 2;~r; a• determined using a ifioston expoetn'e meter.

2) Nume~ous d~&I,hN .. uns of matt 'blae:lt card were placed in tbo

collimator: tubes, along the axes of the spherical t1litorors and ahtelda placed acroru~ the faeaa of the prism ana mirrors eo

that oal.J" a

vert

narrow bet>.m p!!!uJstng tilong the collimator

axts could pass out

ot

the exit

Bltt.

v..-lotu~ poad.tlow wlthin the tnonoc~omator, to part1~ul~l'

near the sli ta

wt

tb the hope

ot.

making the

etfect

wo:tee.

4} Buns were made in tbe d$ll'kf wltb th$ fluorti$CMt light&

on antt th$ cover Xtemovea, and at •~toue slit widths, l~ont

of tbeee gave a detectable change

ot

tbe

tabove

t"esult,

1n41oat1ng that the erteet was not due •o the wall&, mtwoP.

or ret'"lect1ona at tbe tacea

ot

the pvtam, ox- th~

sartrountUnga.

5) Measurements were made Witb a galvonometeP db,.eet1$

connected to the 'fhe result& we~e the Banteli! ltencfl the eff'et~t is not caused by the detecting $~Stem.

6) A pi ace of bla.eic;,: UV glass tPtu.tmd tting radiation bBlow 4000 on1 y, was pl!at:.led directly 1 n front or th(i

the att'ay light e,ffeot disappe;:.u>ed Uv x.~c,:.::ct;:l.ts

we:re repl"Odueed. In the rE':giou

;;ooo -

4000 l't the ineidr~nt

radiation p2S$t":S freely through. both the glass tlfid tho tnf

gla.ss and in this r(;~gion the Hg-arc output ie vcPy higrt.

the high output trom _"·...

,;woo -

_. 4000 Purtber.- the only conceivable untested ef'fect is rnul tiple ;retlect1one or

scatter

vii thin

the priam,

Assuming that tb1a scattering );ltaooeiiui 1a not ee:tecttve,

all wavelengths

will

be scattered to a

oe~ta1n

extent; and

the l"'M eu:rrent therefrom should be tai:rly indepen4ent

ot

pr1am setting.

atan4•1'1 sbsQrber. . 'rhi.e paeoea ,000 - 4000 A 11adtation

tatrly

tJteely, but

in

tbe region 111

qu•ttoa has a

4e•tt7

gx-eatef' than 200. lter.loe the meaat»,:\~4 4enal t:y ia a

U•••'

measure

ot

the ncattor$4 rtul1ation.

tat

1₀ be .the 1nten.e1 ty of the $tant1~11 beam.

1 ... attex- tbo absoz.ber.

i ₈

••••••*•••••••••

ot the

scattered

beam.

'lbe signal atter the &.baoPb

er,

1 '~' i~

=

1

01

o-n

+ 18

The eompartscn signal ta (1₀ + 1n) ~q-d trlhel'Et D,d is the

true, n't&t.lSttttea den~Si

t:r.

•'• (1_{0 •·} 1_{8 )} 1o-d

=

1₀ 10-D +· 1₆

In thia e~:Se Tl ) 200,. hence negleet 1 o-ll.

Now 1_{0 • is}

=

r sayt is the quarltity me&su~ed in a

determination or the fM output fox- a given source ngainat

wavelength.

•

•• is

fhe !te&alt• are shown in ~~igura (11) and 1n.dtoate tbat the

assumption 1& reasonable. Asaoc1attng 1a w1 th

tne

,ooo-4000/i t'eg1on the ratio of the 1ntens1ttes is

ot

tbe

order

1o-J.

At th1e stage a Bellingh.e."TT ~tanley

uv

monoc~o~tov

w1 th Li ttroow mounting became available. This allo~·t::d an