Handtrack, Tabernig et al. 18th Plansee Seminar 2013 RM 7

Tungsten Heavy Alloys for Collimators and Shieldings

in the X-Ray Diagnostics

D. Handtrack*, B. Tabernig*, H. Kestler*, P. Pohl*, W. Glatz*, L.S. Sigl*

* PLANSEE SE, 6600 Reutte, Austria

Abstract

Due to the excellent shielding against electromagnetic radiation tungsten based materials are typically

used for collimators and shielding components in medical imaging diagnostics. However, the

conventional manufacturing of pure tungsten sheet and foil material is quite expensive because of high

temperature sintering and thermo-mechanical treatment. A cost and material efficient manufacturing for

tungsten based material has been developed. The new technology uses dedicated mixtures of tungsten

heavy alloy powder and organic binder, which are formed and sintered to full-metallic semi-finished

products. In this work material properties are discussed and the shaping of structural parts is

demonstrated. Due to the tungsten content of ≥ 90 wt.% the material exhibits excellent X-ray absorption.

Furthermore the full-metallic material overcomes possible drawbacks of tungsten filled polymers with

respect to aging and degradation under X-ray radiation. Sheets up to 4mm thickness and foils down to

below 100µm can be produced in tight tolerances. The isotropic microstructure allows the forming of

structural parts by roll bending and deep-drawing technologies.

Keywords

Tungsten heavy alloy, metal extrusion moulding, mechanical properties, X-ray, shielding, collimator

Introduction

Due to its high density and atomic mass, tungsten exhibits excellent absorption behaviour against

electromagnetic radiation such as X-rays and -radiation [1]. For this reason tungsten based materials

are used for shielding applications in medical imaging diagnostics and therapy. In the case of X-ray

diagnostics, typical applications are collimators in the detector system and shielding parts in computer

tomography. Most of these components are sheet based applications with a thickness range of about

0.1mm to 2mm. However, the conventional manufacturing of pure tungsten sheet and foil material is

quite expensive because of high temperature sintering and several process steps of thermo-mechanical

treatment. Given by the high competition between suppliers and increased costs of tungsten powder

there is a strong drive for a cost and material efficient production of tungsten based material. Another

aspect is coming by the possible tightening of regularities (RoHS, REACH and other bans of substances)

in medical applications. The discussion about the replacement of the most widely used shielding material

lead (Pb) was intensified and activities on the search for substitutes have been significantly increased for

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of specimen

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al production

f [%]

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gure 6: SEM (B

route, te

he results re

aterial with

etermined fo

akage radia

tention was

ielding perf

ensimet is h

ble II: Equivale

material p

p

D176

n

ro

n

ro

W ro

ro

ernig et al.

BSE) images o

ested at RT a

egarding X-r

different thi

or a tube vo

ation at 60 to

paid to the

formance. U

higher than

ent lead thickn

production

process

new material

olled (conv.)

new material

olled (conv.)

olled (conv.)

olled (conv.)

of the fracture

nd 300°C resp

ray radiatio

cknesses th

oltage spect

o 80kV was

e impact of t

Under the te

the actual s

ness of D176

thickness

[µm]

430

540

780

1010

400

870

18

e surfaces of te

pectively

n shielding

he equivale

rum of 60-1

s too low for

the process

est configura

sheet thickn

and tungsten

s e

60kV

472

597

-

-

525

-

8th Plansee S

(b)

(d)

ensile test sam

capability a

ent lead thic

150 kV. For

r an exact m

sing route (c

ation, the e

ness.

equivalent lea

80kV

541

690

-

-

594

-

Seminar 2013

mples (a, c) fro

are summar

ckness of De

sheets with

measureme

conventiona

quivalent le

ad thickness

100kV

680

883

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1708

764

1684

om new and (b

rized in Tab

ensimet 176

h thickness

nt. In case

al rolled vs.

ead thicknes

[µm] for give

V 120

693

890

133

173

780

172

b, d) conventi

ble II. Using

6 and tungs

larger than

of Densime

new produc

ss of tungst

en tube volta

0kV 1

3 6

0 7

33 1

36 1

0 7

20 1

R

onal productio

sheet

sten was

n 0.7mm the

et 176 speci

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age

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(a)

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ased on the

chieve the s

ielding perf

mpared to a

aterial resul

eavy metal a

ltages betw

)

gure 7: (a) Rel

esting the D

ielding beh

ependence o

the chemic

crostructure

nd distributio

176 foil mat

vel and hom

ielding app

arameter (Fi

e different m

ad a benefit

tungsten b

)

gure 8: Basic t

ernig et al.

se data one

ame shield

formance. D

a shielding

lts in a sligh

alloy is still s

ween 100kV

ative thicknes

176 sheet m

aviour was

of the tube

al composit

e may only

on may affe

erial with a

mogeneity o

lications the

ig. 7b). For

materials (W

t in weight s

based mater

trials for shapi

e can calcu

ing efficienc

Depending o

made of lea

ht decrease

superior to

V and 120kV

ss and (b) rela

material fro

found for th

voltage wer

tion seems

have an im

ect the homo

thickness o

of absorption

e absorption

this compa

W: 19.3 g/cm

saving can o

rials offer h

(

ng of the new

18

late the rela

cy as lead (

on tube volt

ad. The dec

of shielding

lead, with a

V.

tive area dens

m the conve

he investiga

re compara

to be the ke

mpact in the

ogeneous X

of 0.09mm a

n was comp

n behaviour

rison the eq

m3, D176: 17

only be exp

igh stiffness

(b)

D176 sheet m

8th Plansee S

ative thickne

(Fig. 7a). Th

tage the thic

crease of tu

g capability

a potential f

(b)

sity of tungste

entional an

ated range o

able for both

ey factor fo

case of thin

X-ray absor

and an optim

parable to a

r described

quivalent le

7.6 g/cm3, P

pected for tu

s and streng

material; (a) be

Seminar 2013

ess of tungs

he pure W s

ckness of W

ungsten con

y in compari

or thickness

n and tungste

d new proc

of tube volta

h D176 mate

r controlling

n foil materi

ption behav

mized micro

a 0,085mm t

by the rela

ad thicknes

Pb: 11.34 g

ube voltages

gth, new de

ending, (b) rol

sten and De

sheet mater

W sheets ca

ntent to 92.5

son to pure

s reduction

en heavy alloy

essing route

age. The re

erials. The n

g the shieldi

al, where th

viour. Howe

ostructure g

thick W foil

tive area de

ss is normal

/cm3). For

s between 1

esign conce

(c)

l bending and

ensimet she

rial exhibits

an be reduc

5 wt.% by u

e tungsten.

of about 40

D176 in comp

e, no influe

elative thickn

nominal tun

ing capabili

he tungsten

ever, testing

gave eviden

material. F

ensity is an

lised by the

a direct sub

100 to 130

epts can be

d (c) deep draw

R

eet material

the best

ed up to 50

sing a D176

However, th

0% for tube

parison to lead

nce on the

ness and its

ngsten cont

ty. The

n grain size

g of the new

nce that the

or dynamic

interesting

e density of

bstitution of

kV. Howev

realized.

wing.

M 7

l to

0%

6

he

d.

s

ent

w

c

f

ver,

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In

ca

su

co

be

8 c

Fig

Fig

Fo

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me

Co

In

an

de

me

ma

tig

is

rol

hig

ndtrack, Tabe

order to ev

rried out. S

ccessfully d

nventionally

eneficial for

c.

gure 9: D176 fo

diagnos

gure 10: D176

oil and shee

ypical applic

edical diagn

onclusion

this work a

nd sheet ma

edicated mix

etallic semi-

aterial of thi

ht tolerance

characteriz

lled materia

gher room t

ernig et al.

aluate the f

amples from

demonstrate

y produced

shaping ge

oils for 1D col

stics.

sheet materia

et based pro

cations of D

nostics are s

n innovative

aterial was d

xtures of tun

-finished pro

icknesses b

es. The new

ed by a liqu

al. In tensile

emperature

feasibility of

m these stu

ed on sheet

material th

eometries. E

limators in hig

al as X-ray shi

ototypes hav

D176 materia

shown in th

e, material a

developed.

ngsten heav

oducts. No

below 0.1 an

w tungsten h

uid phase si

e tests the n

e ductility in

18

f designs, b

udies are pre

ts with a thi

e higher du

Even deep d

gh resolution X

ielding compo

ve been pro

al as 1D-co

he Figs. 9 an

and cost eff

The techno

vy alloy pow

polymeric b

nd sheet ma

heavy alloy

intered micr

ew materia

reference t

8th Plansee S

basic experi

esented in

ickness in th

uctility of the

drawing is p

X-ray detector

onents in medi

oduced and

ollimators in

nd 10.

fficient manu

ology establ

wder and or

binder resid

aterial of th

y material (D

rostructure

al exhibited

to a Densim

Seminar 2013

ments for s

Fig. 8. Bend

he range of

e new mate

possible with

rs (copyright S

ical diagnostic

d passed qu

X-ray detec

ufacturing r

ished is the

rganic binde

duals are lef

ickness up

Densimet® D

without anis

comparable

met material

haping the

ding and ro

f 0.5 to 2 mm

rial, especia

h the new m

Siemens AG) f

cs.

ualification te

ctors and sh

oute for tun

e metal extr

er are forme

ft in the fina

to 3 mm ca

D176: 92.5

sotropy as s

e strength v

l produced b

new materi

oll bending w

m. In comp

ally at RT, p

material as s

for medical im

ests succes

hielding com

ngsten heav

rusion moul

ed and sinte

al material c

an be produ

wt.% W, re

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Handtrack, Tabernig et al. 18th Plansee Seminar 2013 RM 7

a sintered block. Due to the high tungsten content the material exhibits excellent shielding capability

against X-ray radiation which was expressed by a high equivalent lead thickness in the air-kerma test. In

comparative testing the D176 sheet material produces by the conventional and new processing route at

tube voltages of 60 to 150kV, there was no influence of the manufacturing route on the shielding

behaviour found. Foil and sheet based prototypes have been produced and passed qualification tests

successfully. The application as 1D-collimators in X-ray detectors and shielding components in medical

imaging diagnostics was demonstrated.

References

1. W. Schatt (ed.), K.-P. Wieters, B. Kieback (co-author), Powder Metallurgy Processing and Materials,

pp. 414-416, EPMA, Shrewsbury, (1997)

2. D. Chaiat, High Density Tungsten Powder Filled Polymer, Proceedings of the Powder Metallurgy

World Congress and Exhibition, Vol.3, EPMA, Shrewsbury, pp. 361-367, (2010)

3. K. Yue et al., A new lead-free radiation shielding material for radiotherapy, Radiat Prot Dosimetry, 133

(4), 256-260, (2009)

4. IPR WO2007147792-A1 (2007-12-27). H.C. Starck GmbH. DE 10 2006 029 101.8 2006-06-22

5. IPR WO2008003108-A1 (2008-01-10). PLANSEE SE. AT GM 529/2006 2006-07-06

6. E.B. Podgorsak (ed.), Radiation Oncology Physics: A Handbook for Teachers and Students,

International Atomic Energy Agency, Vienna, (2005)