Dose-Dependence of Pb-Ion Implantation Damage in Zirconolite, Hollandite, and Zircon*
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DOSE-DEPENDENCE OF Pb-ION IMPLANTATION DAMAGE IN ZIRCONOLITE,
HOLLANDITE,
AND ZIRCON*
T.
J.
HEADLEY,
G. W. ARNOLD,
and C. J.
M. NORTHRUP
Sandia National Laboratories, Albuquerque,
New Mexico 87185,
USA
INTRODUCTION The long-term stability of nuclear waste forms is eration in
an important consid-
their selection for safe disposal of radioactive waste.
Sta-
bility against long-term radiation damage is
particularly difficult to
assess by short-term laboratory experiments.
Much of the displacement
damage in high-level waste forms will be generated by heavy recoil nuclei emitted during the Hence,
a-decay process of long-lived actinide elements.
an accelerated aging test which reliably simulates the a-recoil
damage accumulated during thousands of years of storage is recent approach to this simulation is Pb-ions.I-
6
If
desirable.
One
to implant the waste form with heavy
the validity of this approach is
to be fully assessed,
two
important questions which have not yet been investigated must be answered. (1) Is
the structural damage,
including cumulative effects,
similar for
irradiation by Pb-ions and a-recoil nuclei in a given material? the dose-dependence of the accumulated damage similar?
investigation was to assess the extent of these similarities in materials.
We utilized transmission electron microscopy (TEM)
terize the radiation damage and measure its
(2)
Is
The purpose of this selected to charac-
dose-dependence.
Synthetic crystalline zirconolite and (Ba,Ti)-hollandite,
and natural
crystalline zircon were implanted with Pb-ions over a wide range of equivalent a-doses and then characterized by TEM. are component phases in 7
titanate ,
8
and SYNROC,
Zirconolite and (Ba,Ti)-hollandite
titanate-based ceramic waste forms such as Sandia 9
while zircon is
a mineral whose radiation damage
and metamictization from natural a-decay have been studied extensively. For comparison,
natural samples of alpha-damaged zirconolite and zircon,
which had received known a-doses,
were also characterized by TEM.
Natural
samples of (Ba,Ti)-hollandite were not available for comparison. *This work performed at Sandia National Laboratories supported by the U.S. Department of Energy under contract DE-AC04-76DP00789.
380 EXPERIMENTAL Pb Implantations. (CaZrTi Cs 2 0,
2 0 7 ),
The materials implanted were synthetic zirconolite
synthetic (Ba,Ti)-hollandite
(BaAl
2 Ti 6 O1 6
) containing 4.7 wt. %
and highly crystalline zircon (ZrSiO4 ) from Mud Tank, Australia.
The
materials were crushed and thin flakes were collected on holey carbon substrates on TEM support grids.
These specimens were then implanted with Pb-
ions in an accelerator using multiple energy (40-240 keV) implants to achieve uniform energy deposition with depth.
4
Maximum damage depth was - 600 A so
that only the thinner edges of flakes were damaged through their full thickness. The energy deposited in displacement processes for Pb-ion doses was con-
10
verted to equivalent a-doses using the computer codes of Bri
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