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S.GAMMA-RAY EXPOSURE. HAZARD DUE TO STOWAGE"OF M-774 APFSOS ROUNDS IN A

jtL" LEg'ARD C-i MAIN BATTLE TANK

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Nabonai DeenseDefence narnaie

GAMMA-RAY EXPOSURE HAZARD DUE TO STOWAGEOF M-774 APFSDS ROUNDS IN A

LEOPARD C-1 MAIN BATTLE TANKby

H.A. RobitailleNuclear Effects Section

Protecdw Sciences Division

DEFENCE RESEARCH ESTABLISHMENT OTTAWATECHNICAL NOTE 82-32

"PCX " September 1983

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ABSTRACT

The M-774 APFSDS anti-tank round contains a depleted-uranium penetra-tor of 3.4 kgram mass. Since depleted uranium is naturally radioactive, thestorage of a substantial number of these rounds inside a Leopard C-1 mainbattle tank creates a gamma radiation field within the vehicle.

Gamma-ray exposure rates have been measured using a sodium-iodidespectrometer at each of the four crew-member locations and for two turretorientations, with 59 rounds stowed in the vehicle. In all cases the measuredgamma-ray dose rates were less than a maximum of 0.17 millirad per hourobserved at the loader's position. Assuming the loader spent an entire week(168 hours) at his station, his integrated dose wouldamount to 29 mRad -approximately a factor of 4 lower than the maximum currently allowed byCanadian Forces regulations. It is therefore concluded that the M774 rounddoes not represent a significant gmma radiation hazard to Leopard C1 crew-mebers.

*4 s m / r a

RESUNE

L'obus antichar stabilisk par empennage et A sabot detachable M-774contient un p~n~trateur en uranium appauvri de 3,4 kg. Comme l'uraniumappauvri eat radioactif, la prisence d'une certaine quantitg de ces obus A

cintireeur d'un char de combat principal L3oprd kg croe un rayonnement ganmadana le char.

Les dfbits d'exposition aux rayons gamma ont ft6 mesurgs A l'aided'un spectromltre A iodure de sodium, et ce aux quatre postes de l'6quippagf.et en orientant la tourelle A deux positions. Au cours de cette exp~rience,59 obus de ce type se trouvaient dana le char. Dana tous lea cas, lea d6bitsd'exposition mesurgs ont ft4 inf~rieurs A 0,17 millirad par heure au poste duchargeur. En supposant que le chargeur passe toute une semaine A son poste,soit 168 heures, le d6bit total d'exposition serait de 29 millirads, c'est-a-dire environ 4 fois moins que l'exposition minimale tol6r~e en vertu desr~glements des Forces canadiennes. Il eat donc 6tabli que lea obus M-774presents dana le char Liopard Cl ne sont pas la source d'un rayonnementsusceptible de presenter un danger pour l'6quipage.

iii

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TABLE OF CONTENTS

Page

2. EXPERIMENT ........................................ 2

-3. RESULTS .............. ........... 3

4. CONCLUSIONS ........... ............ ........ 6

5. REFERENCES ................ ........... 7

6. APPENDIX: LISTEDý DATA ..................................... 8

ILLUSTRATIONS

1. 238-Uranium Decay Chain ..... 1......

2. Measured gama-ray dose-rates in th eo p*a'r*d...........4

3. Recorded gama-ray spectral data ........................ 5

4. Unfolded Smg a-ray flux spectrum ............................ 5

TABLES

1. Measured gama-ray dose-rates ................................. 3

II

iv

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INTRODUCTION

I. The M774 APFSDS (Armour-Piercing Fin-Stabilized Discarding-Sabot)

is an anti-armour round employing a long-rod penetrator composed of 3.4 kgramof depleted uranium (uranium in which the content of the 235-isotope has been"reduced to approximately 0.2 weight-percent). The bulk of uranium in theround is therefore of the 238-isotope and decays radioactively through theemission of an energetic alpha particle, leading to the daughter product 234-Thorium. The thorium so formed decays in turn to 234-Palladium (in anexcited state), which then decays either directly to 234-Uranium or to thesame isotope through the intermediate ground state of 234-Palladium. All ofthese transitions from 234-Thorium involve the release of both gamma-rays andbeta particles of various energies. The 234-Uranium so formed in this decaychain is alpha-radioactive but with a sufficiently long half-life that itsactivity and those of its daughters are inconsequential to the present consid-erations. Figure 1 (adapted from ref. 1) shows the relationship of theseisotopes to the originating 2 3 8U nucleus:

Isotope Half-Life Radiation

S 2 3 8 U 4.51 x 109 years a

234Th 24.1 days ",Y

234Pam 1.17 minutes 8y

99.87% 0.13%

2 3 4Pa 6.75 hours 8,yLi2 34 u 2.47 x 105 years a,y

Figure 1: Decay chain of 238-Uranium

2

The daughter products 2 34Th, 234pa m and 2 34 pa all have sufficientlyshort half-lives that within a ninety-day period after the initial 3eparationof the depleted uranium their concentrations reach 98Z of the maximum valuesand enter secular equilibirum with the parent 2 3 8 U. After this period ofinitial buildup the concentrations of these isotopes will then diminish inconstant ratios according to the decay of 2 3 8 U, with its characteristic half-life of 4.51 x l10 years. Conversely, due to the much longer half-life of234U its concentration will continue to increase for about 106 years, howeverdue to this same long half-life its instantaneous decay rate is very low, andconsequently the specific contribution of its decay radiation insignificant.

Particles released during these transitions include alpha, beta andgaima-rays of various energies. Alpha and beta particles, being massive andcarrying electric charge, have much shorter ranges than the gamma-raysreleased and Very few will escape the encapsulation of the penetrator rod. Aprevious study 2 established that the radiological hazard associated with therelease of alpha and beta particles by the M774 round was insignificant com-pared to the gaa-ray hazard.

Due to the long range of gamma-rays, the magnitude of the gammiahazard depends to a large extent on the number and unique disposition of theDU rounds, consequently the direction of this study was to establish thespecific dose-rates to which crewmembers of the Leopard C-1 main battle tankcould be exposed.

EXPERIMENT

As part of another experimental program at the US Army Pulse RadiationFacility (Aberdeen Proving Ground) in 1981, fifty-nine M774 rounds were in-stalled in a Leopard C-1. This number represents the full ammunition stowagecapability of the vehicle and consequently a "worst-case" situation establish-ing the maximum dose-rates to which crewmembers could be exposed. (In militaryoperations a typical vehicle would carry a mix of rounds not all of which wouldcontain uranium, consequently the actual radiological hazard would be reduced).

A 2" x 2" sodium-iodide gamma-ray spectrometer was used to determineparticle spectra from which radiation dose-rates would be calculated by foldingthe data with the appropriate fluence-to-tissue dose -onversion factors 3.Measurements were made at positions corresponding to the mid-chest location ofeach of the four crew-members, and for two turret orientations: attack (gun

3 forward) and transport (gun rearward). The driver's, loader's and commander'sseats were all positioned at their lowest travel and the detector located 47 cm

* above the seats. The gunner's seat was positioned such that an individual of180cm height would look comfortably through the gunsight. Data were obtainedat each location for twenty minutes, and during this time all hatches remainedclosed.

,'

3

RESULTS

The dose-rates measured inside the Leopard are tabulated below, inunits of mRad per hour:

Turret Location Dose Rate Statistical Error(mR/hr)

Attack Commander 0.0388 0.4%Loader 0.1561 0.2%Gunner 0.0433 0.4%Driver 0.1232 0.2%

Transport Commander 0.0508 0.3%Loader 0.1700 0.2%Gunner 0.0361 0.4%Driver 0.1517 0.2%

Mean (Average of all measurements) 0.096

Table 1: Dose-rates measured in the Leopard Cl

These data are also shown diagrammatically in Figures 2a and 2b. Itis apparent that when in either configuration, the dose-rates to the driver andto the loader are significantly higher than to the other crewmembers. This isa result of the disposition of the rounds; some (42) are stored in the hulljust to the driver's left side, the remainder (17) being stored in the turretand in close proximity to the loader, again primarily to his left. As theturret is traversed from 00 to 1800, some crew members receive a higher dose-rate as they come into closer proximity to the stored rounds, others receive alower dose-rate as they move farther away. A mean dose-rate of 0.096 mRad/houris thus calculated for all orientations and positions. Note that the errorslisted are due only to statistical uncertainties - to these must be added apossible 5% calibration error reflecting the overall uncertainty in theabsolute detector efficiency.

Raw data recorded during the eight measurements were also combinedwith equal weight and the resulting pulse-height spectrum shown in Figure 3.Thus, these data represent the mean spectrum recorded over a 160-minute periodwithin the vehicle. After unfolding (correction for detector response andefficiency), a mean gamma-ray flux spectrum is also shown in Figure 4. Theobserved peaks near energies of 0.75, 1.0, 1.45 and 1.8 MeV correspond verywell with the expected intensities due to the major transitions of 234Pam(ref 4), thus identifying this isotope as dominant in the production of gammaradiation from the M774 round.

Numerical data corresponding to the spectrum of Figure 4 are to befound in the Appendix.

4

Loaderi

Comander Gunner. Driver.

Figure 2a: Doserates measured in the attack configuration (UR/hr)

11

Loader Driver

Figure 2b: Doserates measured in the transport configuration (UR/hr).

5,

~S

105

10 t ii- I 1s 20 2500 50 t 5 0 5

Channelligure 3: Sum of recorded gamma-ray spectra.

103 - - -

> 102

-:3 10

0 0.5 1.0 1 - -

Gamrm-ray Energy, MeVFigure 4: Unfolded mean gamma-ray flux snectrumn.

6

CONCLUS IONS

The mean gamma radiation dose-rate resulting from the storage offifty-nine depleted-uranium M774 anti-armour rounds in a Leopard C-i mainbattle tank has been determined experimentally as 0.096 mRad per hour.The maximum dose-rate measured was found at the loader's station when theturret was in its transport configuration (i.e. gun rearward) and equalled0.17 mfad per hour. At such adose-rateif the loader spent an entire week(168 hours) in this location his accumulated ga-ma-ray dose would amount to29 mRads, or approximately one-fourth of that currently permitted atomicenergy workers in Canadal and members of the Canadian Forces. 6

Under actual circumstances the weekly dose received by Leopard C-1crewmembers would be much less than this for three reasons: firstly not allrounds in a typical tank would be of the M774 type, secondly the averagecomplement of all rounds would naturally be less than the iuaximum stowagecapability of the vehicle, and finally a crewmember would not be confined foran entire week without respite inside the vehicle.

For these reasons it must be concluded that the storage of the M774APFSDS round in Leopard C-l main battle tanks would not result in a signifi-cant exposure of the vehicle crew to gamea radiation.

ACKNOWLEDGEMENT

The author is grateful for the assistance of the staff of the USArmy Pulse Radiation Division at the Aberdeen Proving Ground in co-ordinatingthe loan of the M774 rounds and providing the necessary resources to enablethese measurements.

7

REFERENCES

1. "A Handbook of Radiation Shielding Data"; J.C. Courtney (Ed.),Louisiana State University ANS/SD-76/14; Baton Rouge. LA;July, 1976.

2. "Radiation Characterization and Exposure Rate Measurements fromCartridge 105-mm APFSDS-T, XM774"; W.T. Bartlett, R.L. Gilchrist,"G.W.R. Enders, Battelle Pacific North,-est Laboratories; PNL-2947,Richiand, WA; Nov, 1979.

3. "Dose Rates in a Slab Phantom from Monoenergetic Gamma-rays";H.C. Claiborne and D.K. Trubey; Nuclear Applications and Technology,8, 450 (1970).

4. "Atomic Data and Nuclear Data Tables", 13, No 2-3 (1974), page 279.

5. "Atomic Energy Control Act", Canada Gazette Part II, Vol 108, No 12,26 June 1974.

6. "General Ionizing Radiation Safety"; Canadian Forces Technical OrderC-02-040-004/TP-000, 5 June 78.

S. .. . *. . . -. . ..........

8

APPENDIX: LISTED DATA

The data listed below comprise the mean gaina-ray flux spectrumrecorded within the Leopard C-l, corresponding to Figure 4 in the main text.

GROUP UPPER PARTICLE FLUX ERROR ERROR RUNNINGENERGY (PARTICLES/ (STD. (M) INTEGRAL(HEY) CM2-MEV-SEC ) DEV.) (ICNZ-SEC

2 0.2 2.987E+02 4.SSE-01 0.17 2.S97E+013 0.3 1.925E+02 4.24E-01 0.22 4.912E+014 0.4 1.036E+02 a.O1E-O1 0.39 5.947E+015 0.5 8.292E+01 4.09E-01 0.49 6.776E+016 0.6 5.739E+01 3.91E-01 0.68 7.350E÷017 0.7 4.558E+01 4.22E-01 0.93 7.806E+01a 0.9 5.878E+01 4.07E-01 0.69 9.394E+019 0.9 2.472E+01 3.U3E-01 1.60 9.641E+01

10 1.0 5.210E+01 4.10E-01 0.79 9.162E+0111 1.1 2.787E+0! Z.S9E-01 1.07 9.441E+0112 1.2 7.203E+00 2.O8E-01 2.89 9.513E+0113 1.3 5.173E+00 1.91E-01 3.69 9.565E+0114 1.4 4.202E+00 1.SSE-01 4.42 9.607E+0115 1.5 4.309E+00 1.76E-01 4.09 9.650E+011s 1.1 2.763E+00 1.50E-01 5.41 9.677E+0117 1.7 1.862E+00 1.45E-01 7.78 9.696E+0l19 1.8 3.591E+00 1.47E-01 4.08 9.732E+0119 1.9 2.930E+00 1.0SE-01 3.62 9.761E+0120 2.0 4.07SE-01 4.95E-02 12.14 9.735E+0121 2.1 1.432E-01 3.91E-02 27.27 9.767E+0122 2.2 1.408E-01 3.57E-02 25.32 9.768E+0123 2.3 1.113E-01 3.OE-02 27.65 9.769E÷0124 2.4 8.754E-02 2.95E-02 33.74 9.770E+0125 2.5 1.213E-01 2.21E-02 18.18 9.771E+01

TOTAL FLUENCE = 9.771E+01 /CM2-SEC

.-- . .

9

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:1 DOCUMENT TITIE

GAMMA-RAY EXPOSURE HAZARD DUE TO STOWAGE OF M-774 AP-FSDS ROUNDS IN ALEOPARD C-i MAIN BATTLE TANK

4. DESCRIPTIVE NOTES (Type of opcor, arid ,ncius"e dstss

Technical NoteSAUTHORISI ILS01 no~vW. hi~nt wEt. meAS.m -ntwil

ROBITAILLE, H.A.

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13. ABSTRACT

The M-774~ APFSDS anti-tank round contains a depleted-uranium penetra-,

se-,tor of 3.4 kgram mass. Since depleted urpnium is naturally radioactive, thestorage of a substantial number of these rounds inside a L'eopard C-I mainbattle tank creates a gamma radiation field within the vehicle.

Gdmma-ray exposure rates have been measured using a sodium-iodidespectrometer at each of the four crew-member locations and for two turretorientations, with 59 rounds stowed in the vehicle. In all cases the measuredgamma-ray dose rates were less than a maximum of 0.17 millirad per hourobserved at the loader's position. Assuming the loader spent an entire week(168 hours) at his station, his integrated dose would amount to 29 mRad-3-pproximately a factor of 4 lower than the maximum curzent~ly allowed byCanadian Forces regulations. It is therefore concluded that the M774 rounddoes not represent a significant ga-mma radiation hazard to Leopard Cl crew-members.

.46

10

UNCLASSIFE

KEY WORDoS

Gaimma-rayRadiationHazardLeopard C-1Main Battle TankArmour-piercing round

Depleted uranium

no.TMucTIONS

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