NASA 

Technical 

Memorandum 

NASA TM -86518 

MECHANICAL TESTING OF LARGE THALLIUM 

DOPED SOIjIuivi IODIDE SINGLE CRYSTALS 

By Henry M. Lee 

Structures and Propulsion Laboratory 

Science and Engineering 

September 1985 

I[&BSA-Tt3-865 1 E) EECffANICaZ 1ESI"IBC OH LARGE Fu't36-17 '1E7 

THAELIUF! COPEL SOCIUa IODfCE SINGLE CBHSTBLS 

[NASA) 69 p El AC4jHE A31 CSCL 20E 

National Aeronautics arid 

Scace A~T -lstrat~otGeorge C. Marshall Space Flight Center 

MSFC - Form 3190 (Rev. May 1983) 
TECHNICAL REPORT STANDARD TITLE PAGE 

iviechanical Testing of Large Thallium Doped Sodium 

I Iodide Single Crystds 

PERFORMING ORGANIZATION NAME AND ADDRESS I 10. WORK UNIT, NO. t 

i 

George C. Marshali Space Flight Center 

Marshali Space Plight Center, Alabama 35812 

12 I Technical Memorandum I 

National Aeronautics and Space Administration 

Washington, D. C . 20546 I 

! 15. SUPPLEMENTARY NOTES i 

1 Prepared by Structures and Propulsion Laboratory, Science and Engineering. 1 

I - 

i 16, ABSTRACT 

i 

This report presents the findings of mechanicai tests performed on five thalliwn- I , 

: doped sodium iodide [NaI(Tl)] crystals. These crystals were all in the shape of 1 

! circular flat plates, 20.0 in. in diameter and 0,5 in. thick. The test setup, testing 1 , procedure, and the test data are presented. I 

I 

i k 

The report shows that these large crystals exhibit a high degree of materiai 

plasticiry, as well as a much higher strength than previously anticipated, on the order ' 

S of 500 psi. also revealed from the testing was the fact that crystals with a large 

: number of grain boundaries developed iess plasticity, and therefore less permanent ' deformation, than those with fewer grain boundaries. i 

4 

t 

i 

Sodium Iodide Unclassified - Unlimited 

WbFC - Forin 3292 (MAY 1969) 

TABLE OF CONTENTS 

SUMMARY ..................................................................... 

INTROEUCTION. .............................................................. 

TEST SETUP .................................................................. 

TESTING PROCEDURE ......................................................... 

CRYSTAL GRAIN BOUNDARIES ................................................ 

PRESENTATION OF DATA ..................................................... 

CONCLUSIONS ................................................................ 

REFERENCES .................................................................. 

APPENDIX A .................................................................. 

APPENDIX B .................................................................. 

APPENDIX C .................................................................. 

Page 

1 

1 

2 

3 

5 

10 

10 

28 

29 

31 

59 

iii 
LIST OF ILLUSTRATIONS 

Figure 

1 . 

2 . 

3 . 

4 . 

5 . 

6 . 

7 . 

8 . 

9 . 

10 . 

11 . 

12 . 

13 . 

14 . 

15 . 

16 . 

17 . 

18 . 

19 . 

20 . 

21 . 

22 . 

23 . 

24 . 

Title Page 

Test setup .......................................................... 2 

Test crystal No . 1 grain boundaries ................................. 5 

Test crystal No . 2 grain boundaries ................................. 6 

Test crystal No . 3 grain boundaries ............................... 6 

Test crystal No . 4 graiii boundaries ................................. 7 

Test crystal No . 1 failure ........................................... 7 

Test crystal No . 5 grain boundaries ................................. 8 

Test crystal No . 6 grain boundaries ................................. 8 

Test crystal No . 7 grain boundaries ................................. 9 

Test crystal No . 4 failure ........................................... 9 

Crystal No . 3 frontside 6 center displacement screening tests ........ 11 

Crystal No . 3 backside fi center displacement screening tests ........ 12 

Crystal No . 4 frontside 8 center displacement screening tests ....... 13 

Crystal No . 4 backside f) center displacement screening tests ........ 14 

Crystal No . 5 frontside 0 center displacement screening tests ....... 15 

Crystal No . 5 backside 0 center displacement screening tests ........ 16 

Crystal No . 6 frontside 8 center displacement screening tests ....... 17 

Crystal No . 6 backside 0 center displacement screening tests ........ 18 

Crystal No . 7 frontside center 8 displacement screening tests ....... 19 

Crystal No . 7 backside 0 center displacement screening tests ........ 20 

Crystal No . 3 frontside center 4 displacement maximum load test .... 21 

Crystal No . 4 frontside f) center displacement maximum load test .... 22 

Crystal No . 5 backside 8 center displacement maximum laod test .... 23 

Crystal No . 5 Pcontside f? center displacement maximum load test .... 24 
Figure 

25. 

26. 

21. 

LIST OF ILLUSTRATIONS 

Title Page 

Crystal No. 5 backside fi center displacement maximum load test .... 2 5 

Crystal No. 3 frontside 8 stress-strain curve.. .................... 26 

Crystal No. 5 frontside 8 stress-strain curve.. .................... 2 7 
'TECHNICAL MEMORANDUM 

MECHANICAL TESTING OF LARGE THALLIUM DOPED SODIUM 

IODIDE SINGLE CRYSTALS 

SUMMARY 

To determine the structural behavior of large thallium -doped singie crystals of 

sodium iodide [NaI(TI)I, five specimens in the shape of circuiar flat plates 20-0 in. 

in diameter and 0-5 in, thick were utilized in mechanical tests at the Marshall. Space 

Flight Center's Materials and Processes Laboratory. A test fixture in a dry box was 

designed to subject each crystal to a uniforril pressure ioad across its entire surface, 

with a built-in "0" ring to prevent mdtion normal to it. Careful loading and unloading of each crystal along with precise measurements of the deformations, were used 

to generate the test data. 

Results of the testing revealed that the large crystals possess considerable 

material plasticity. It also became quite evident that the ultimate tensile strength 

(Ftu) was much higher than previously anticipated (11. Although each specimen was 

loaded in such a manner as to develop at least 50T; psi in the anaterial, only one 

extremely hydrated crystal failed during the testing sequence. 

Another phenomenon was consistently seen in testing, and that was the fact 

that crystals with a large number of grain boundaries developed less plasticity, and 

therefore less permanent deformation, than those with fewer grain bounda~ies , 

Another significant goal of the program was the development of a procedure to 

be utilized in stress screening each candidate flight crystal. The purpose for this 

screening was to eliminate any potentially weak crystal prior to assembiy into an 

experiment scheduied for extended Earth orbit, and to gain assurance that material 

yielding could be kept to a minimum, 

INTRODUCTION 

HistoricdZy , t hallium-doped sodium iodide [NaI (TI) 1 single-cry stal mechanical 

tests have been aceornplished only on small samples, with results ranging from 250 psi 

to 900 psi for ultimate tensile strength [ I] , The Mayshall Space Flight Center (MSFC) , however, is developing an experiment known as the burst and transient source 

experiment (BATSE) which will employ single crystals 20.0 in. in diameter and 0.5 

thick. Each detector will consist of a single crystal scintillator designed to ~t~onitor 

the unocculted sky for garnrna ray bursts, transient sources, and intensity variations 

of known sources in the approximate range of 60 keV to 600 KeV. This experiment 

is to be launched into Earth orbit aboard the Sp'lce Shuttle in 1988, Each crystal 

must, therefore, be able to structurally survive the normal handling, transportation, 

and launch aeee!eraliorr levels, as well as on-orbit thermal environments. 

The lack of fracture mechanics data. and the seemingly unpredictable strength 

of the crystals, coupled with the scientific desire to have as little permanent 
deformatloa? (yielding) of the material as possible, led to a testing procedure that 

wotlicl stress screen each potential flight crystal, as well as develop the needed 

mechanical ehara.cteristics 

TEST SETUP 

The basic appar8tus wed to accomplish the desired mechanical testing of the 

Nal(T1) single crystals was a test fixture held within a plexiglass glove box purged 

with dry air (about 3 percent relative humidity). The temperature and relative 

humidity in the glove box were continuously monitored. Figure 1 shows the basic 

test setup. The vacuum gage was actually a manometer filled with silicon oil. The 

test fixture itself was an aluminum structure with an "0" ring groove 0.112 in. deep 

by 0.190 in. wide and 19.5 in. in diameter. An "0" ring made of a silicon rubber 

with a Shore hardness of 30 was utilized to provide an air tight seal as well as a soft 

surface for the crystal to bear against. Displacement dial indicators were used to 

record the motion of the outer edge of the crystal just above the "0" ring and the 

very center of the crystal. These gages were capable of measuring displacement of 

each specimen ro t0.00005 in. The vacuum source was connected to a ballast tank 

which had a control valve plus a bleed valve to accurately regulate the magnitude of 

the differential pressure imposed on the test article. Because of the high density 

of NaI(T1) , each test crystal had an additional equivalent uniform pressure load of 

the crystal specimen thickness (T) times the material density (p) (= 0.066; 2si). 

This gravity load produced a maximum stress of +31 psi on the surfaces of the 

crystal at the center. 

In addition, every specimen came with an arrow (0) mark on the edge to 

illdieate the frontside or backside of the crystal. The position of the arrow was 

carefully noted prior to each series of tests. 

DISPLACEb'ENT # 1 /I2 

INDICATORS 

-TEST SPECIMEN 

"0" RING 

- FIXTURE 

DISPLACEMENT 

-- I NnI C,q?'ORS 

-VACUUM GAGE 

Figure 1, Test setup 
TESTING PROCEDURE 

Mechanical testing of each test crystal consisted of loading each crystal to limit 

ioaci ( 0.23 psi) and returning to zero load, then reloading it to 1.4 "Limes limit load 

(0.35 psi) and back to zero load. This process was performed on both sides of each 

specimen, and was utilized as a development screening sequence for all prospective 

flight crystals. Three crystals were then loaded to over 3 times limit load (1.00 psi). 

Two crystals were also cycled 20 times to 1.4 times limit and then reloaded to over 

3 times limit. This last series of tests was accomplished to determine if any significant degradation in crystal strength occurred due to cyclic loading. Table 1 depicts 

the test history for each crystal. 

The actual testing of the crystals consisted of the following typical procedure: 

a) Purge the drybox to less than 10 percent relative humidity. 

b) Carefully place the crystal specimen in the "0" ring and center it on the 

fixture; note which side is in tension. 

C) Swing the dial indicators perpendicular to the crystal surface and lock in 

place. 

d) Purge the drybox to less than 10 percent relative humidity. 

e) Close control valve on vacuum ballast. 

f) Start vacuum pump. 

g) Take an initial reading on manometer and dials. 

h) Open control valve slowly and adjust to give proper manometer reading. 

i) Allow system to equilibrate, then read manometer and dials. 

j) Readjust for each pressure desired and read manometer and dials after 

equilibrating the following pressures : 

1) Limit load pressure (screening) psi 0.0, 0.05, 0.15, 0.20, 0.23, 0,15, 

0.10, 0.05, 0.0. 

2) 1.4 x limit load pressure (screening) psi 0.0, 0.05, 0.10, 0.15, 0.20, 

0.25, 0.30, 0.35, 0.25, 0.15, 0.05, 0.0. 

k Swing dial indicators away from specimen, remove crystal and turn it over. 

1) Repeat steps (b) through (j). 

All other testing was accomplished utilizing a similar routine. 
TABLE 1. CRYSTAL TEST HISTORY 

"NOTE: Crystal #4 failed at 3 X Limit pressure 
CRYSTAL GRAIN BOUNDARIES 

A total of seven crystal specimens were used at MSFC for mechanical testing, 

AIP seven were 20.0 in. in diameter and 0.5 in. thick. Each was seded in an znvironmental plastic bag, and included with it was a blue line drawing of every grain 

b~undary. Test crystals numbers 1 through 4 had a large number of grain boundaries 

as shown in Figures 2 through 5. Only crystals numbers 3 and 4 were tested from 

this lot, since numbers 1 and 2 were destroyed in shipment to MSFC. Figure 6 

reveals an overlay of the grain boundaries and the handling fracture lines for crystal 

number 1. It is evident from this figure that the grain boundaries played an 

insignificant role in crack propagation. In contrast, test crystals numbers 5 through 

7 had a smaller number of grain boundaries as seen in Figures 7 through 9. Figure 

10 graphically depicts the fracture induced by uniform pressure loading for crystal 

number 4. These fracture lines definitely appear to be related to the grain 

boundaries that are shown in Figure 5. Although crystal number 4 was probably 

weakened because of extreme hydration during its testing sequence, failure still 

occurred near 500 psi of material stress. 

Figure 2. Test crystal No. I grain boundaries. 
Figure 3. Test crystal No. 2 grain boundaries. 

Figure 4. Test crystal No. 3 grain boundaries. 
Figure 5. Test crystal No. 4 grain boundaries. 

BREAK 

Figure 6. Test crystal No. 1 failure. 
Figure 7. Test crystal No. 5 grain boundaries. 

Figure 8. Test crystal No. 6 grain boundaries. 
Figure 9. Test crystal No. 7 grain boundaries. 

Figure 10, Test crystal No. 4 failure cra.cks. 
PRESENTATION OF DATA 

The most informative way of revealing the mechanical testing results is to 

present plots of differential pressure versus center displacement for both sides of a 

particular test specimen. Also included on these plots is differential pressure versus 

stress at the center of the crystal as calculated by flat plate theory [ 21 . The equations for a circular flat plate under a uniform pressure load are shown in detail in 

Appendix A of this report. Data are presented for limit pressure, and 1.4 times 

limit pressure loadings on the same plot for each side of the test crystal. These 

plots can be seen in Figures 11 through 20 for test crystal numbers 3 through 7, 

respectively. Three specimens were also loaded to over 3 times limit pressure (known 

as maximum loading 1.0 psi). This pressure was an equipment limitation and was 

chosen because it was previously thought that none of the crystals could survive 

that high a load. Plots of the differential pressure versus center deflection for the 

three crystals loaded this way are shown in Figures 21 through 25. The raw data 

necessary to produce each of these plots are tabulated in Appendix B. 

In addition to the aforementioned plots, Figures 26 and 27 depict stress-strain 

curves generated from the maximum loading tests for crystals numbers 3 and 5. The 

method utilized to create these curves is shown in Appendix C. 

CONCLUSIONS 

Large thallium-doped sodium iodide crystals developed a significant amount of 

material plasticity (>0.1 percent elongation) and withstood near 500 psi material stress 

during mechanical testing at MSFC. In addition, test crystals with a large number 

of grain boundaries proved more elastic, and therefore showed less permanent 

deformation after testing than those with fewer grain boundaries. At this time, no 

clear correlation of ultimate strength and the number of grain boundaries can be 

seen in the testing of five crystals. It is desirable, however, from a science perspective to utilize those crystals which exhibit minimal permanent deformation for flight 

units on the BATSE. The following guidelines have been established for crystal 

screening of potential flight units after loading both sides to 1.4 times limit pressure: 

a) Crystals developing permanent deformation less than 0.001 in. will be 

classified as highly desirable. 

b) Crystals developing permanent deformation greater than 0.001 in. but less 

than 0.0025 in. will be classified as acceptable. 

c) Crystals developing permanent deformation greater than 0.0025 in. will be 

classified as unacceptable. 

No noticeable degradation of crystal strength was observed during the cyclic 

load tests. Twenty load cycles at 1.4 times limit were placed on two crystals for this 

series of tests. Twenty cycles was clzosen because it represents about four times 

the expected number of limit load cycles on the shuttle liftoff. These two crystals 

were subsequently reloaded to over three times limit load with no reported failures. 

----c 

0 to LIMIT PRESSURE 

0 to 1.4 X LIMIT PRESSURE 

CENTER DISPLACEMENT, IN 

i I I I 

100 200 300 400 

CENTER STRESS, PSI 

Figure 12 CF~ stalNo 4 backside f/ center displacement screening test. 

LSd '2XflSS2Xd 'TVILN3X2ddICI 
PSd "M~S32d WILNZXZddIa 
--_-- 0 to LIMIT PRESSURE 

0 to 1.4 X LIMIT PESSUm 

CENTER DISPLACEMENT, IN 

I I 1 

100 200 300 400 

CENTER STRESS, PSI 

Figure 16 Crystal No. 5 backside ft center displacement screening test. 
-_--- 0 to LIMIT PRESSUFS 

0 to P .4 X LIMIT PESSUE 

CENTER DISPLACEMENT, IN 

1 L I I I 

100 200 300 400 

CENTER STRESS, PSI 

Figure 17'. Cryst$ No - 6 frontside 6 center displacement screening test. 
rn H 

Cn x 

2 2 

I4 

P-! 

X 

ISd 'ZBWSSZX~ 'TVLLN383661CI 
----- 0 to LIMIT PRESSUZ 

0 to 1.4 X LIMIT PPSSSUBE: 

CENTER DISPLACEMENT, IN 

I 

180 

i 

200 

I 

300 

I 

400 

CENTER STRESS, PSI 

Figure 19. Crystal No. 7 frontside B center displacement screen test. 
0 to LIMIT PRESSURE 

0 to 1.4 X LIMIT PRESSURE 

0.002 9.004 0.006 0.008 

CENTER DISPLACEMENT, IN 

I 1 I I- I 

100 200 300 400 

CENTER STRESS, PSI 

Figure 20. Crystal No. 7 backside 0 center displacement screening test. 
CENTER DISPLACEENT, IN 

i I I 1 I - 

100 200 300 400 

CENTER STRESS, PSI 

Figure 21, Crystal No. 3 frontside B center displacement maximm load test. 
STRESS 

CENTER DTSPLACElEKT, PN 

t 1 I I I 

100 200 300 400 

CENTER STRESS, PSI 

Figure 22. Crystal No. 4 frontside 0 center displacement maximum load test. 

0.080 0.120 

CENTER DISPLACEMENT, IN 

I I 

200 300 

CENTER STRESS, PSI 

Figure 24. Crystal No. 5 frontside 8 center displacement maximum load test. 
CENTER DISPLACEMENT, IN 

CENTER STRESS, PSI 

Figure 25. Crystal! No. 5 backside 0 center displacement maximum load test, 

PSd ' _B SSBXLS 
REFERENCES 

1. GSFC Letter, September 24, 1980, C. Haehner and T. Heslin to 3. Angelo, 

MOR Bend Test Results for NaI(T1) and Additional Elastic Moduli Measurements. 

2. Roark, R. J. : Formulas for Stress and Strain. McGraw-Hill Book Company, 

New York 4th Edition, 1965. 
APPENDIX A 

CIRCULAR FLAT PLATE EQUATIONS 

The maximum deflection as well as the maximum stress in a circular flat plate 

depend upon the mechanical properties of the material, geometry of the plate, type 

of loading, and boundary conditions. 

The analytical expressions [ 21 below, depict the maximum deflection and maximum stress for an isotropic material loaded with a uniform pressure across the entire 

surface, and with the edges constrained normal to the plate. 

3PtR 4 

Y - 2 3 [(m-1>(5m + 111 (deflection) 

max 16Em T 

and 

where 

'max = maximum center deflection 

'max = maximum center stress 

E = rnodulus of elasticity 

m = reciprocal of Poisson's ratio 

v = Poisson's ~atio 

p = weight density 

R = radius of plate 

T = thickness of plate 

(stress) 

P -- differential pressure from vacuum source 
E = 3.8 x lo6 psi 

v = 0.31 

p = 0.1323 lblin. 3 

R = 9.75 in. 

T = 0.50 in. 

NaI (TI) Properties 
APPENDIX 13 

TABULATED TEST DATA 

The following tabulated data represents the measured data for each crystal test, 

Data from deflection gages numbers 1 through 3 were recorded versus the differential 

pressure calculated from the manometer. Gage numbers 1 and 3 were averaged to 

yield the edge displacement over the "0" ring. To calculate the net center displacement of the crystal, the average edge motion was subtracted from the gage number 2 

reading. 
CRYSTAL $/ 3 

POSITION OF ARROW: '$ 

4/5/85 

TEST DATE 

TEST TYPE: LIMIT PRESSURE - 

oool-lo 

mcncnoo 

4-cncnr.cn 

000000 

...... 

000000 

+ Z n 

W 

nC3- 

grlH 

II 

oool-lo 

mcncnoo 

mcncnr.cn 

000000 

..a*.. 

000000 

m 

cn 

cn cn i-- m 

oool-lo 

mcncn00 

000000 

ld 

A 

P-l cn 

a w PI 
If I.. .....a 
CRUSTAL Sf: 3 

POSITION OF ARROW: 8 

61 

GAGE {I1 

(IN) 

G3 

GAGE /I3 

(IN) 

G2 

GAGE $f:2 

(IN) 

TEST DATE 5/6/85 

TEST TYPE : > 3 X LIMIT PRESSURE 

EDGE 

GE = G1 + 6312 

(IN) 

CENTER 

GC = G2 - GE 

(IN) 

CRYSTAL #/ 4 

POSITION OF ARROW: f? 

TEST DATE 4/11/85 

CRYSTAL j/ 4 

POSITION OF ARROW: 

n V 

TEST DATE 4/11/85 

TEST TYPE: 1.4 X LIIIIT PPXSSURE 

EDGE 

GE = G1 + G3/2 

(IN) 

CENTER 

GC = G2 - GE 

(IN) 
CRYSTAL $1 4 

POSITION OF ARROW: 6 

GI 

GAGE $\I 

(IN) 

G3 

GAGE $13 

(IN) 

G2 

GAGE /\2 

(IN) 

0. . 0 

0.0065 

0.0131 

0.0187 

0.0244 

0.0302 

0.0339 

0.0402 

0.0463 

0.0536 

0.0644 

0.0746 

0.0882 

0.0997 

Gage bottomed 

0.1154 

0.1103 

0.1000 

0.0847 

TEST DATE 5/7/85 

TEST TYPE: >3 X LIMIT PRESSURE 

EDGE 

GE = GI + G3/2 

(IN) 

CENTER 

GC = 62 - GE 

(IN) 
' i' 

noGdH 
Cf, 

cr) 

ul 

oorlrlo 

rnbrnrnrl 

u3bCndrn 

OOOOQO 

...... 

000000 

...... 

dooooo 


CRYSTAL # 5 

n 

POSITION OF ARROW: -v 

G2 

GAGE #2 

(IN) 

TEST DATE 5/8/85 

TEST TYPE: >3 X LIMIT PRESSURE 

(CONT ' D) 

EDGE 

GE = G1 4- G3/2 

(IN) 

CENTER 

GC = G2 - GE 

(IN) 
CRYSTAL $/ 5 

POSITION OF ARROW: 

s. u 

G1 

GAGE $/1 

(IN) 

G3 

GAGE $13 

(IN) 

G2 

GAGE $12 

(IN) 

TEST DATE 5/9/85 

TEST TYPE: >3 X LIMIT PRESSURE 

EDGE 

GE = 61 + G3/2 

(IN) 

CENTER 

GC = G2 - GE 

(IN) 
CRYSTAL $1 5 

POSITION OF ARROW: fi 

TEST DATE 5/9/85 

TEST TYPE: '3 X LIMIT PRESSURE - 

(CONTINUED) 

CRYSTAL $1 6 

POSITION OF ARROW: 4 

TEST DATE 5/1/85 
POSITION OF ARROW: v 

TEST DATE 5/1/85 
CRYSTAL $/ 6 

Tl 

POSITION OF ARROW: 9 

G1 

GAGE $/1 

(IN) 

G3 

GAGE .$/3 

(IN) 

TEST DATE 5/1/85 

TEST TYPE: 1.6 X LIMIT PRESSURE - 

G2 1 EDGE I CENTER 

GAGE .$I2 

(IN) 

U 

,I 

II 

I......... 
t-i 

A 

Pl rn 

a w CL 
CRYSTAL $/ 7 

POSITION OF ARROW: a 

G1 

GAGE {/I 

(IN) 

G3 

GAGE $13 

(IN) 

G2 

GAGE $/2 

(IN) 

TEST DATE 5/2/85 

TEST TYPE: 1.4 X LIP'IIT PRESSURE 

EDGE 

GE = G1 + 6312 

(IN) 

CENTER 

GC = G2 - GE 

(IN) 
APPENDIX C 

STRESS-STRAIN CURVE GENERATION 

Stress-strain curves for test crystals number 3 and 5 were developed using the 

raw measured data from the three (3) times limit pressure load tests. The enclosed 

tabulations reveal the procedure for this calculation. 
U> 

0 

TEST CRYSTAL #3 STRESS-STRAIN 

DATA AP VACTUAL CJPRESS. ONLY Gc Esec x lo6 

POINT (PSI) (PSI) (PSI) CENTER DISP. (IN) SECANT MOD. (PSI) STRAIN (IN/IN) 

NOTE: (Tactual = press. cnly + gravity. 

G - = measured center deflection 

EEec = 49665.29 delta P/Gc 

€2 = press. only/Esec (data plotted in Tactual versus ) 
'I'ES'r CKUS'CAL # 5 STI<I<SS-STRAIN 

DATA C, 1' CACTIIAL CPIII<SS ONLY 

c Esec X lo6 

POINT (PSI) (PSI) CENTER DISP. (IN) SECANT MOD. (PSI) STRAIN (IN/IN) 
APPROVAL 

MECHANICAL TESTING OF LARGE THALLIUM DOPED SODIUM 

IODIDE SINGLE CRYSTALS 

By Henry M. Lee 

The information in this report has been reviewed for technical content. Review 

of any information concerning Department of Defense or nuclear energy activities or 

programs has been made by the MSFC Security Classification Officer. This report, 

in its entirety, has been determined to be unclassified. 

9 c& 

A. A. McCOOL 

Director, Structures and Propulsion 

Laboratory 

*US. GOVERNMENT PRINTING OFFICE 1986-631-058/20055