TOXICITY OF RADIOELEMENTS
APPLICATION OF CELLULOSE NITRATE FILMS FOR ALPHA
AUTORADIOGRAPHY OF BONE
Alan Cole,* D. J. Simmons, Helen Cummins, F. J. Congel, and Jacob Kasiner
Sr nTENOT Meee ene ER
When an alpha particle strikes the surface of a
dielectric material such as a cellulose nitrate foil and
gives up more energy per unit distance along its trajectory than the critical value of the material, latent
etchable tracks are produced.“ The ionization and
subsequent electrostatic repulsion produced by the
particle creates vacancies along its path by ejecting
ne
HOES ~ cae rateaM Re
atoms from the nitrocellulose molecules into interstitial positions. The resulting molecular fragments
TERARORIReo capt rey
te
ae
Cellulose nitrate can be used to record the tracks of alpha
particles from bone and may have some advantages over nuclear emulsions. The tracks are made visible by etching the
cellulose nitrate film with NaOH and no darkroom is required. Beta rays and electrons do not produce tracks, so
background fogging is eliminated. The etching process makes
visible only those alpha particle tracks which penetrate the
film, so the attainable resolution may be better than that of
nuclear emulsions. Finally, the alpha tracks are enlarged and
so may be more easily counted by a photoelectric scanner.
tion and etching which has produced high quality
autoradiographs of bone sections from mice injected
intravenously with a monomeric solution of 1% sodium citrate with 90% ultrafilterable °Pu (0.1
pCi). The animals were sacrificed 6 days after injection. The long bones obtained at autopsy were
fixed in 95%
alcohol, embedded undecalcified
in
methyl methacrylate, and were cut on a high speed
rotary saw longitudinally at 100 ». The tissue sections
had been used previously to prepare contact auto-
radiographs using Kodak Type A autoradiographic
plates, and the results of that study have recently
been published by Rosenthal et al.
Weprepared a stock solution of nitrocellulose according to Benton’s‘*) method: 17 g_ nitrocelluloset
were first dissolved in a solvent composed of 5.1 g
isopropyl! alcohol, 4.0 g butyl alcohol, and 8 g cello-
solve acetate. This solution was then dissolved in
61.9 g ethyl acetate, and 4 g dioctyl phthalate were
are more soluble than the parent molecule.“-®) The
process of recording alpha particle tracks in nitrocellulose foil by etching radiation damaged sites has
been called alphagraphy. It is a simple and direct
method, and because nitrocellulose films offer certain technical advantages over photographic nuclear
emulsions, it has found application in health physics
as an autoradiographic detector film. In practice,
we diluted 25 ml of the stock solution by adding 75
films are insensitive to electrons, thermal neutrons, or
the dilute cellulose nitrate solution for 10 sec. The
slides were removed vertically and allowed to drain
for dosimetry.) This technique can discriminate between heavyand light charged particles, and thus the
gamma irradiation. In addition, they will not fog
during long term exposures, they are remarkably
stable, and they can be processed (etched) in daylight and at room temperatures.
It is possible to prepare thin films of cellulose ni-
trate which are selectively sensitive to alpha par-
ticles which have an energy range up to 5 MeV. This
suggested that the technique might be useful when
high resolution autoradiographic studies are required
to visualize the tissue localization of bone-seeking
added as a plasticizer. The mix was permitted to age
for 4 days to achieve chemical equilibrium before use
ml ethyl acetate in order to obtain thin (3 ») detector
films,
Autoradiographs were prepared by simply dipping
the bone sections mounted on microscope slides into
for an additional 10 sec. The underside of each slide
was wiped free of the solution and the preparations
were air dried horizontally overnight under a glass
dish to avoid contamination with dust. The coated
slides. were then annealed at 70° C for 4 hr to temper
the detector film as recommended by Benton,‘
and were wrapped in aluminum foil during the exposure period. The autoradiographs were developed
in a stendor dish by etching the detector films with
radioisotopes such as plutonium and radium. Wewill
6.5 N NaOH at 24° C for 2 hr. Since the rate at
which the hydroxyl ions attacked the radiation dam-
* Present address: Department of Anatomy, The Bowman
Gray School of Medicine, Winston-Salem, North Carolina.
lulose RS 11.8-12.2% Ne, 5+ to 6-sec viscosity, 30% isopropyl
alcohol by weight.
describe a method of cellulose nitrate film prepara-
Tt Hercules
Powder Co..
Wilmington, Delaware:
nitrocel-