Radiation monitoring device

The present invention relates to a device for monitoring alpha particles and material emitting alpha particles such as radon and its daughters. The device can also be used for monitoring other high energy particles such as cosmic rays, nuclear fission fragments, nucleon ions, and neutrons having energy between 0.1 and 200 MeV. In the operation of the invention, the high energy particles pass through and degrade tracks in a track registering material placed on a carrier substrate. These tracks are enlarged with a developing agent which etches the initial tracks. The enlarged tracks are then visualized by means of a color change in the immediate vicinity of these tracks.

FIELD OF THE INVENTION 
Monitoring of radiation, suitably of alpha particles. 
BACKGROUND OF THE INVENTION 
Radon is a naturally occurring radioactive noble gas produced by the decay 
of uranium-238 and radium-226, which are widely distributed in soil and 
rocks. Radon-222 decays by emission of alpha particles. Radon-222 
undergoes four successive decays to radon daughters; polonium-218, 
lead-214, bismuth-214 and polonium-214. Polonium-214 undergoes further 
successive decays to Pb-210, Bi-210, Po-210 and ultimately to stable 
Pb-206. 
The radioactive decay products of Ra-222 have a tendency to attach to 
ambient aerosol particles. Thus, radon and its daughters can enter the 
lungs with the air we breathe and lodge there. Two of the daughters, 
Po-214 and 218 decay rapidly, emitting high speed alpha particles (as does 
radon). If it occurs in the lungs, it can cause cell damage and lead to 
formation of cancerous cells. Radon concentration is usually expressed as 
picocuries per liter (pCi/l) or as working level (WL=200 pCi/l=1.3 
10.sup.5 MeV of potential alpha energy). Radon in high concentration 
(i.e., above 0.1 pCi/l) has been found in houses of a number of countries 
of the world. 
Radon can be detected by counting alpha particles in an ionization chamber 
(Geiger counters), it can also be detected with gamma ray counters by 
counting gamma rays emitted by its short lived daughters. Such equipment 
is expensive, bulky and highly sophisticated. Radon in houses is presently 
monitored by two devices, one is based on adsorption of radon on activated 
charcoal followed by monitoring gamma radiation emitted by its daughters 
and the other is based on the etching of latent tracks produced by alpha 
particles of radon and its daughters in certain plastics. 
The activated carbon device requires the use of a highly sensitive, 
sophisticated, and expensive gamma ray counter. The etch track device 
requires very long exposure and requires professionally qualified services 
to provide etching and counting the etched tracks. Neither the charcoal 
nor the track etch device can be used and results analyzed by an average 
house owner. There is a need for device for monitoring low concentration 
of radon that can be used and interpreted by a nontechnical house owner 
without the need for any expensive equipment and any additional technical 
services. 
Energetic charged particles, such as alpha particles, damage the material 
along their path. The damaged path, known as track (latent track), is a 
linear, highly localized region of altered physical and chemical structure 
compared to the bulk solid. The diameter of the latent tracks is 50-100 
Angstroms (0.005 to 0.01 micron). The primary alpha particles from 
radioactive decay can penetrate approximately 30 microns (micrometer) in a 
solid or liquid material. 
Certain inorganic nonconductors such as silicate minerals, alkali halides, 
insulating glasses, and organic polymers such as cellulose nitrate, 
cellulose acetate, cellulose acetatebutyrate, polymethylmethacrylate, poly 
(bisphenol-A carbonate), and a thermoset polymer of diallyl diethylene 
glycol carbonate (known as CR-39) are highly susceptible to high energy 
particles such as Cf-252 fission fragments, nucleon ions of elements, and 
alpha particles having energy of 0.1 Mev to 200 Mev. The materials that 
produce latent tracks when exposed to high energy particles are listed in 
Nuclear Tracks in Solids, Fleischer, Price and Walker, (University of 
California Press, Berkeley, CA, 1975) incorporated by reference herein. As 
the rate of diffusion and chemical attack on material in the latent track 
is substantially higher than the bulk material, the latent tracks can be 
etched. Particle track etching is a chemical process that preferentially 
removes the damaged areas and the material surrounding them. Typicaly, 
strong base solutions are used to etchants for polymeric materials. A list 
of alpha sensitive polymers, etchants and conditions to be used for etch 
development of tracks in polymers, glasses and mineral are also given in 
Fleishcher, Price, and Walker (supra). 
SUMMARY OF THE INVENTION 
There is provided a simple, low cost, user-friendly device for monitoring 
high energy particles or material emitting such particles which is self 
contained and does not require either expensive analytical equipment or 
technical service for analysis (or interpretation). 
The device comprises a detecting element and a developing means therefore. 
The element of the device in its simplest form, comprises of a substrate 
in conjunction with a layer of indicator material, which undergoes color 
change when contacted with an etchant, over which is placed another layer 
of track registering material which produces latent tracks when struck by 
high energy particles. The element, after exposure to high energy 
particles, is then activated by immersion into a developing means 
comprising a developing agent including an etchant. The etchant removes 
the degraded or disordered material from the latent tracks and widens 
them, diffusess through the etched tracks (microscopic holes) and when it 
reaches the indicator it induces a color change therein making the 
location of track visible by appearance of a spot of different color. The 
spot will grow in size with the etching time due to the diffusion of the 
etchant through the indicator layer. Suitably the etchant is a solution of 
a water soluble developing agent in a hydroxylic solvent, said agent being 
selected from the group consisting of strong acids, strong bases, reducing 
agents and oxidizing agents. 
A wide variety of materials can be used in the device. The substrate cold 
be glass, metal, or plastics which are not affected by the etching system 
or it can be another layer of the track registering material. 
The indicating layer comprises either the indicator itself or a dispersant 
layer or both. The indicator may be, for example, a chemical pH dye such 
as aniline blue which undergoes color change when contacted by an etchant. 
The dispersant layer for the indicator, whose presence is not critical, 
may be a water sensitive, that is to say a water soluble, water permeable, 
water absorbing or water swellable layer, suitably a polymer through which 
the etchant can diffuse. The indicator may be in the form of a layer 
between the substrate and the track producing material. It may also be 
incorporated in the etchant system. If so the bond between the substrate 
and the track productivity should be weak for the etching system to 
diffuse along with the indicator. In such a sysatem the presence of a 
dispersant layer is desirable. The track registering material may be 
inorganic or organic, suitably polymeric and may be thermoplastic or 
thermosetting. 
The developing means is suitably a container for the etchant. In one 
embodiment, the device is provided in a kit which comprises two chambers, 
suitably transparent vials in a container, suitably a box. A perforated 
vial contains the detecting element. The other vial contains the 
developing agent including the etchant. 
The detecting element is suspended from the cap of the vial into the vial. 
The vial is removed from the box and exposed to tha atmosphere or 
suspected source of high energy particles for a predetermined period of 
time. After exposure, the cap containing the detecting element is removed 
from the perforated vial and placed onto the vial containing the etchant 
so that the element is immersed in the etchant for a predetermined time. 
The etchant will etch the latent tracks produced in the polymer and 
produce different color spots in the indicator layer under the tracks. 
The total number of the spots on the detecting element are then counted. 
The total exposure/dose can be estimated from a calibration chart of total 
number of spots per unit area per unit time of exposure. 
The actual structure of the device may have several embodiments. For 
example, the perforated vial could contain several elements. In such a 
case the elements can be removed at different times of exposure and 
activated to determine dose at different times.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The detecting element 10 has three basic components, a substrate 16, an 
indicating layer 14 and, a track registering layer 12. 
As substrate 16, there may be used any solid material which is not affected 
by the etchant system 20 and on which an indicator can be coated 
uniformly. Transparent or white (opaque or translucent) substrate is 
desirable so that the color spots can be seen. Materials such as glasses, 
metals, and plastics resistant to etchant can be used as the substrate. 
Alternatively, (as shown in FIG. 2b), a second layer of track registering 
material 12 may be used as substrate. 
Any compound which undergoes a reasonably stable color change when 
reacted/contacted with the etching system can be used as an indicator. The 
selection of the indicating compound will depend upon the etchant. For 
example, if an alkaline or acid solution is used as an etchant, a pH 
sensitive dye which undergoes color change when contacted with alkali or 
acid respectively, is required. If the etchant is, itself colored, either 
self-colored such as potassium permanganate or colored with a dye, the 
etchant itself serves as an indicator. If the etchant is an oxidizing 
agent, a reduced dye such as leucomalachite green may be used. 
The indicator layer may contain a dye per se, a dye in as dispersant layer 
or a dispersant layer per se. In the last case, the indicator (dye) could 
be in the etching solution. When the etchant breaks through the tracks and 
diffuses through indicator layer, the dye diffuses along with the etchant 
and develops color spots. 
As etchants, there may be used: 
aqueous sodium hypochlorite in the presence of sodium hydroxide, suitably 
0.5% to saturated, preferably 2%, by weight of hypochlorite and 2 to 50%, 
preferably 30% by weight of hydroxide, 
aqueous potassium permanganate, 0.5 w/w% to saturated, suitably 5 w/w% in 
the presence of sodium hydroxide 1 to 50 w/w%, suitably 35 w/w% and 
potassium hydroxide 1 to 100 w/w%, suitably 36 w/w%, 
bichromate, suitably potassium bichromate 1% to 50% suitaby 5 w/w% in 
aqueous acid, suitably a mineral acid, for example, aqueous sulfuric acid 
2 to 80 w/w%, suitably about 30 w/w%, 
aqueous alkali, suitably aqueous sodium hydroxide 1 w/w% to saturated 
preferably, suitably, but not critically, in the presence of a small 
amount (i.e., 0.1-1 w/w%) of a base compatible surfactant such as Benax 
(manufactured by Dow Chemical Corp., Midland, MI), 
and saturated aqueous potassium permanganate. 
The required etching time is both concentration and temperature dependent 
as well as solvent dependent. Thus, for a 6 micron polycarbonate film at 
ambient temperature, the breakthrough time of methanolic KOH 
(water/methanol 1:1) was 45 min. at 6N and 14 hrs at 3N. The same amount 
at 6N required only 15 min. at 60.degree. C. On the other hand, aqueous 
KOH at the same concentration (6N) requires 20 hrs. at ambient temperaure 
but only 3 hrs at 60.degree. C. 
As cosolvents may be utilized hydroxylic water miscible solvents such as: 
ethanol, methanol, glycol, acetic acid and citric acid. 
The amount of cosolvent is also of influence, the aforesaid 45 min etch 
time of 6N KOH in water/MeOH 1:1, rises to 48 hours where the water/MeOH 
ratio is 9:1. 
Further, breakthrough time is dependent on film thickness. Thus, for 
example, with a polycarbonate film activated with 6N aqueous KOH, 
breakthrough time after similar irradiation with will range from 20 hrs at 
ambient temperature at 6 microns to 300 hrs at ambient temperature at 20 
microns. 
Among the dyes that can be visualized by a basic etchant are: 
Acid blue 92; acid red 1, acid red 88, acid red 151, alizarin yellow R, 
alizarin red 5, acid violet 7, azure A, brilliant yellow, brilliant green, 
brilliant blue G, bromocresol purple, bromothymol blue, cresol red, 
m-cresol purple, o-cresolphthalein complexone, o-cresolphthalein, 
curcumin, crystal violet, 1,5-diphenylcarbazide, ethyl red, ethyl violet, 
fast black K-salt, indigo carmine, malachite green base, malachite green 
hydrochloride, malachite green oxalate, methyl green, methyl violet 
(base), methylthymol blue, murexide, naphtholphthalein, neutral red, nile 
blue, alpha-naphthol-benzoin, pyrocatechol violet, 4-phenylazophenol, 
1(2-pyridyl-azo)-2-naphthol, 4(2-pyridylazo) resorcinol Na-salt, 
alinizarin, quinalidine red, thymol blue, tetrabromophenol blue, thionin, 
xylenol orange. 
Among the dyes that can be visualized by the acidic etchants are: 
Acridine orange, bromocresol green-Na-salt, bromocresol purple Na-salt, 
bromophenol blue Na-salt, congo red, cresol red, chrysophenine, 
chlorophenol red, 2,6 dichloroindophenol Na-salt, eosin bluish, erythrosin 
B, malachite green base, malachite green hydrochloride, methyl violet 
base, murexide, metanil yellow, methyl orange, methyl red sodium salt, 
naphtho-chrome green, naphthol green base, phenol red, 
4-phenylazo-aniline, rose bengal, resazurin, 2,2'4,4',4" pentamethoxy 
triphenyl methanol or mixtures thereof. 
Representative of common oxidants (oxidizing agents) are: 
Ammonium persulfate, potassium permanganate, potassium dichromate, nitric 
acid, chlorine, bromine, iodine, Cerium (IV) sulfate, iron (III), 
chloride, potassium bromate, potassium iodate, sodium hypochlorite, 
hydrogen peroxide, manganese dioxide, sodium bismuthate, sodium peroxide, 
potassium chlorate and oxygen or mixtures thereof. 
The following table provides some representative oxidation-reduction 
indicators and their color change. 
______________________________________ 
Color change 
Indicator Oxidized form 
Reduced form 
______________________________________ 
5-Nitrol-1, 10-phenanthroline 
Pale blue Red 
iron(II) sulphate (nitroferroin) 
1,10-Phenthroline iron(II) 
Pale blue Red 
sulphate (ferroin) 
2,2'-Bipyridyl iron(II) sulphate 
Faint blue Red 
5,6-Dimethylferroin 
Pale blue Red 
Diphenylaminesulphonic acid 
Red-violet Colorless 
Diphenylbenzidine 
Violet Colorless 
Diphenylamine Violet Colorless 
3,3'-Dimethylnaphthidine 
Purplish-red 
Colorless 
Starch-KI Blue Colorless 
Methylene blue Blue Colorless 
Indophenols Blue Red 
Nile Blue Blue Red 
All leuco dyes Colorless Color 
______________________________________ 
Any insulating material which produces latent tracks when irradiated with 
high energy particles such as fission fragments, nucleon ions of elements, 
and alpha particles having energy of 0.1 to 200 MeV can be used as the 
track registering material in the device (see Fleischer, Price & Walker, 
supra, esp. p. 65-72). Inorganic materials can be coated by vacuum or 
spatter coating techniques. Though inorganic insulating materials can be 
used, organic polymers are preferred because they can be coated in form of 
thin film, either from their solution or melt. A mixture of track 
registering polymers may be used. The film should be thin enough for high 
energy particles to penetrate through. Thickness of the polymer coating 
required will depend upon the energy of the particle. For alpha particles 
of about 5 MeV energy, the thickness should be less than 30 microns, 
suitably 2 to 20 microns. For nuclear fission fragments and nucleon ions 
having higher energy, e.g. 100 MeV, the thickness could be greater than 30 
microns, suitably 30-100 microns. 
As track registering polymers, there may be used: Cellulose acetate 
(Kodacel, Triafol, Cellit); cellulose acetate butyrate; cellulose nitrate 
(Diacell, Nixon-Baldwin); cellulose triacetate (Kodaacel TA401, 
unplasticized, Bayer TN); ionomeric polyethylene (Surlyn), polycarbonate 
(Lexan, Makrofol, Merlon, Kimfol); polymethyl-methacrylate (plexiglass, 
Lucite); and polypropylene (cryovac), and CR-39. Polymers such as 
cellulose acetate, cellulose nitrate, poly(bisphenol-A carbonate) and 
CR-39 are especially preferred. 
As dispersant layer, they may be used any water sensitive material soluble 
in, absorbs, is permeable by or swollen by water. These materials include 
paper, suitably filter paper and polymers such as: agar, agarose 
indubiose, carragheean, casein, cellulose microcrystalline, chitin, 
collagen, dextran, dextrin-white, gelatin, gum arabic, rubber-natural, 
zein, alginates, alkyl and hydroxyalkylalkylcellulose, 
carboxymethylcellulose, guar gum, gum agar, gum ghatti, gum karaya, gum 
tragsacanth, hydroxyethylcellulose, hydroxypropylcellulose, locust bean 
gum, pectins, polyacrylamide, poly (acrylic acid) and its homologs, 
polyethylene glycol, poly (ethylene oxide), polyvinyl alcohol, 
polyvinylpyrrolidone, starch and its modifications, tamarind gum and 
xanthan gum. 
The system of the present invention can also be used for monitoring high 
energy particles such as neutrons which do not themselves produce latent 
tracks in the insulating materials but are capable of producing track 
producing particles such as alpha particles, proton or fission fragments 
when they interact with secondary materials such as boron-10, lithium-6, 
and uranium-235. For example, boron-10 when struck by a neutron particle, 
produces an alpha particle by a reaction known as the "(n, .alpha.) 
reaction". For monitoring such nontrack producing particles, the detecting 
element should either be in close contact with a thin film or layer of 
material capable of undergoing track producing particle reaction and have 
the radiator materials incorporated therein. These reactions and radiator 
materials which can be used for generating track producing particles are 
described by Fleischer, Price and Walker (supra). 
A cross sectional view of the detecting element 10 of the device is shown 
schematically in FIG. 1a. A substrate 16 is coated with a very thin layer 
14 of an indicator dispersed in a suitable medium having a thin (1 to 30 
micron) upper layer of track registering material 12. The element 10 is 
exposed to high energy particles or material producing such particles. The 
particles, for example, alpha particles from radon and its daughters will 
produce latent tracks 18 in the track registering polymer 12, as shown 
schematically in FIG. 1b. After the exposure, the element is activated by 
placing it in etchant 20 as shown in FIG. 1c. The etchant 20 starts 
etching the latent tracks 118. When the etchant reaches the indicator, it 
changes its colors and it appears as a tiny spot 119 of color. With time, 
the tracks widen and more etchant diffuses through them and the spots grow 
in size. The etchant 20 diffuses through the indicator layer 14 in all 
directions and the spots 219 grow in size as shown schematically in FIG. 
1d. Larger spots can be seen with the naked eyes and can be counted. If 
the concentration of the tracks is high, some of the spots would merge 
into one another. 
Some high energy particles will not penetrate through the polymer and hence 
would produce partially penetrated latent tracks 18 as shown in FIG. 1b. 
The etchant will take longer time to etch and break through the partially 
penetrated tracks. Such tracks will appear as the new smaller dots 219 as 
shown in FIGS. 1c and 1d. Some partially penetrated tracks may not appear 
at all by the time the spots appeared earlier merge into one another. 
Penetration of high energy particles through the track producing material 
will depend upon the energy of the particle and the thickness of the track 
producing material. High energy fission fragments having energy of 100 MeV 
can penetrate substantially deeper than alpha particles having energy of 5 
MeV. 
Alternate embodiments are illustrated in FIG. 2. These are characterized by 
the use of two layers of track registering material. 
Device 310, in FIG. 2a, the substrate 316 is suitably a transparent film, 
such as mylar and carries indicator layer 314 on either side. These layers 
are covered with registering layer 312. Since the film is transparent, the 
intensity of image is doubled. 
A similar effect occurs in the FIG. 2b device 410 which comprises a 
dispersant, suitably polyvinylalcohol layer 415 containing the indicator 
sandwiched between track registering layers 412. 
The indicator and track registering layer may be coated onto the substrate 
by methods well known in the art. A wide variety of coating equipment is 
readily available. Common coating methods are air knife, brush, calender, 
cast coating, curtain dip, extrusion, blade floating knife, gravure, kiss 
roll, off-set, reverse roll, rod, spray, and squeeze roll. These methods 
have been recently reviewed (K. J. Coeling, and T. J. Bublick, Encycl. 
Polym. Sci. Eng., Vol. 3, 552-615 (1986)). Most of the above methods can 
be used for a wide range of base materials, such as polyester, and coating 
compositions such as dyes dispersed/dissolved in a suitable medium and 
track registering polymers such as cellulose nitrate and polycarbonate. 
Lamination is a process of uniting two or more layers of different 
materials into one, by action of heat or pressure. Like coating, there are 
a large number of lamination processes. Films of cellulose nitrate, CR-39 
or polycarbonate can be laminated on to a dye coated substrate. The 
detecting element can also be prepared by coating the dye solution on the 
substrate followed by lamination of track producing polymer. 
The field device is illustrated in FIG. 3 and comprises two jars, 50 and 70 
in enclosed container 60. Jar 50, containing the detecting unit 10 and the 
other jar 70 containing the developing solution 20. Detecting unit 40 
comprises element 10 mounted under cap 32 is mounted having a flange 34 
with internal screw threads 36. The cap 32 is placed in a perforated (52) 
jar 50, having screw threads 54 which interact with threads 36 to form the 
detection device as shown in FIG. 3c. The purpose of enclosing the element 
10 in jar 50 having holes 52 is to prevent finger prints during the 
handling while allowing the track registering material to become exposed 
to radon gas through holes. The developing jar 70 contains an appropriate 
amount of the developing solution 20 and is suitably a transparent plastic 
jar as shown on right hand side of FIG. 3d. 
The detection unit 40 in jar 50 (FIG. 3c) is removed from the box 60 by the 
consumer and exposed to radon atmosphere, e.g. in the basement for a 
certain period of time. After the exposure, the unit 40 is removed from 
jar 50 which is discarded. Cap 32 carrying the detection element 10 is 
then placed on the development jar 70 as shown in FIG. 3e. As the threads 
36 of the cap 40 match the threads 74 of jar 70, jar 70 can be closed 
tight. The developer 20 will etch the latent tracks 18 produced by the 
alpha particles. Once the spots appear and grow to a desired size (or 
after certain pre-determined time), the cap will be unscrewed and the 
element washed under water. Total number of the spots may be counted and 
concentration of radon can be determined from the chart of number of spots 
per device versus days of exposure or calibration curves. The chart or 
calibration curve can be included in the package along with the other 
literature on how to use the device. 
In the field device described above, one can use any shaped substrate, 
e.g., solid cylinder or rectangle, coated with the dye and the track 
producing polymer. The consumer can be provided with an exposure jar 
containing more than one element for multi-exposure. 
Although the invention has been described with regard to its preferred 
embodiments, it should be understood that changes and modifications 
obvious to one having the ordinary skill in his art may be made without 
departing from the scope of the invention, which is set forth in the 
claims which are appended thereto. Substitutions known in the art which do 
not significantly detract from its effectiveness may be employed in the 
invention. 
EXPERIMENTAL 
Example I 
Preparation of Stock Solution of Cellulose Nitrate 
To 24.3 g of the cellulose nitrate powder containing 30% ethyl alcohol 
124.7 g of ethyl acetate, 4 g of isopropyl alcohol, 5 g of butyl alcohol, 
8 g of cellusolve acetate (ethylene glycol monoethyl ether acetate), and 4 
g dioctylphthalate were added sequentially. The mixture was mixed 
thoroughly until clear to provide a 10% cellulose nitrate solution. This 
stock solution may be diluted with ethyl acetate to obtain other diluted 
solutions. For example, in order to obtain 4% solution of cellulose 
nitrate, 40 g of the stock solution was diluted to 100 ml with ethyl 
acetate. This 4% solution was used for preparation of track producing 
polymer coating. 
In accordance with the above procedure, in place of cellulose nitrate, 
there may be used cellulose acetate, cellulose acetatebutyrate, 
polymethylmethacrylate, and poly (bisphenol-A carbonate). 
Example II 
Preparation of Dye Solutions 
0.5 g of aniline blue (water soluble) was dissolved in 100 ml of methanol 
with stirring. The resulting solution was filtered to remove suspended 
impurities. 
In accordance with the above procedure, but in place of aniline blue, 
solutions of other dyes were also prepared, namely: 
60 mg Brilliant Yellow+150 mg aniline blue in 50 ml methanol. 
625 mg Brilliant Yellow+480 mg Brilliant green in 50 ml methanol. 
100 mg bromophenol blue in 10 ml of methanol. 
100 mg phenolphthalein in 10 ml of methanol. 
100 mg thymolphthalein in 10 ml of methanol. 
100 mg phenolphthelein+100 mg thymolphthalein in 20 ml methanol. 
Example III 
Preparation of Aniline Blue Solution Containing Cellulose Nitrate 
To 100 ml of 0.5% stock solution of aniline blue of Example II, 10 ml of 4% 
cellulose nitrate in methanol was added. 
Example IV 
Preparation of Element by Spin Coating 
(a) A circular glass plate (30 cm diameter) was thoroughly cleaned. The 
cleaned glass plate was placed on turntable and spun at 78 revolutions per 
minute (rpm) at 30.degree. C. in a clean room. 5 ml. of 0.5% solution of 
aniline blue in methanol of Example II was poured on the spinning glass 
plate. A uniform thin coating of aniline blue was obtained. After ten 
minutes, 10 ml of 4.0% solution of cellulose nitrate in ethyl acetate was 
poured on the dye coated glass plate which was still spinning at 78 rpm. 
(b) In accordance with the above procedure, but in place of aniline blue in 
methanol, there is employed 5 ml. of 0.5% solution of aniline blue in 
methanol containing 0.4% cellulose nitrate prepared as in Example III. 
Example V 
Irradiation with Polonium 210 alpha source 
Detection elements prepared in Example IV(b) were irradiated with alpha 
particles from polonium-210 (activity 500.mu./Ci). The source was quickly 
moved over the element at a distance of about 0.5 cm. The irradiated 
elements were activated by treatment with 6M aqueous KOH solution at room 
temperature. 
FIG. 4 comprises a series of photographs illustrating the appearance and 
growth of the spots. [A piece of inch-graph paper was placed behind the 
device while taking the photographs]. The color of the coating was blue 
and the spots were red. After about three hours tiny red spots started to 
appear. The spots grew into a millimeter size spots within a further hour. 
A small fraction of new spots continue to appear during the etching, 
probably, due to partially penetrating tracks. 
In accordance with the above procedure and using detecting elements 
prepared as in Example IV(b) but coated with 1.8% solution (rather than a 
4% solution) of cellulose nitrate were irradiated with alpha particles 
from polonium-210. The elements were activated with 6M aqueous KOH 
solution at room temperature. After about ten minutes tiny red spots 
similar to those shown in FIG. 4 started appearing and growing with time. 
Example VI 
Irradiation with Plutonium-235 alpha particles 
The detecting elements described in Example IV(b) were irradiated with 
plutonium-235. Two sources with two different concentrations/intensities, 
1 and 100 alpha particles per second per square centimeter were used. 
Plutonium-235 emits alpha particles of 5.1 MeV. After irradiation the 
devices were activated with 6M KOH and number of spots which appeared 
between 3 and 3.5 hour at room temperature were counted. FIG. 5 shows a 
plot of alpha spots observed (excluding spurious spots and tiny spots 
appearing later on) versus radiation time. Using a curve similar to that 
shown in FIG. 5, total flux of alpha particles can be estimated. 
When the dose of the alpha particle was higher, above 100 second of 
irradiation, a picture of the source becomes visible. The results indicate 
that the element can be used to visualize radioactive (alpha emitting) 
materials. 
Example VII 
Exposure to Radon Gas 
Detecting elements of Example IV(b) having coatings of aniline blue as the 
pH dye and cellulose nitrate as the alpha sensitive polymer, were exposed 
to radon gas. The concentrated of radon was 42 pCi per liter. The elements 
were exposed to radon for 2, 5, and 7 days. After the exposure the 
elements were activated with 6N KOH and red spots which appeared between 3 
and 3.5 hour at room temperature were counted. Table 1 gives average 
number of spots per 25 square centimeter of element exposed to radon. Each 
element has 200 square centimeter area. 
TABLE 1 
______________________________________ 
Track-spots in Cellulose Nitrate Film 
Upon Exposure to Radon 
Sample Exposure Track Spots 
Average Spots 
# Time (days) in 25 sq. cm. 
per 25 sq. cm. 
______________________________________ 
L1 2 29 29 
L2 2 35 
L4 2 25 
L5 2 28 
M1 5 60 64 
M2 5 67 
M4 5 65 
M5 5 62 
H1 7 100 96 
H2 7 101 
H4 7 93 
H5 7 88 
Cortrol-1 
7 3 
Cortrol-2 
7 5 
Cortrol-3 
7 3 4 
______________________________________ 
Note: 
The concentration of radon was 42 pCi per liter. 
Example VIII 
Variation in Time Required for Appearance of the Spots 
Detecting elements prepared according to procedure described in Example 
IV(b) were irradiated with alpha particles according to procedure 
described in Example V. The elements were activated with etching solution 
containing different concentrations of KOH, water, ethanol and glycerol. 
The time required for appearance of red spots were noted. The results are 
reported in Table 2. The results shown in this table indicate that the 
concentration of KOH can be substantially decreased and the time required 
for emergence of the color spots can be varied from 1 to 16 hours by 
adding nontoxic agents such as ethanol and glycerol. 
TABLE 2 
______________________________________ 
Variation time required for emergence of the spots for 
20 micron cellulose nitrate coating. 
Solvent 
Co-Solvent KOH (molar) 
Time (hour) 
______________________________________ 
Water -- 6.0 3.0 
Water -- 2.0 4.0 
Water Ethanol (6%) 2.0 2.2 
Water Ethanol (16%) 2.0 1.1 
Water Glycerol (66%) 
2.0 24 
______________________________________ 
Example IX 
Knife Coating 
A polyester film 18".times.12" was placed flat on a x-y recorder and was 
held in place by built-in suction of the recorder, a Bird-type wet film 
applicator of cut depth 0.0015 inch was placed against the arm of the 
recorder at one end of the polyester film. 5 g. of the dye (indicator) 
solution (0.05 g of aniline blue and 1.0 g of polyvinylalcohol in 4 ml of 
water) was poured in front of the applicator in a straight line. The arm 
of the recorder was then allowed to scan across the face of the polyester 
film causing the dye to form a thin uniform wet film of polyvinyl alcohol 
containing the dye. The solvent (water) was allowed to evaporate for a day 
to provide thin uniform coating. Cellulose nitrate was coated over the dye 
coating using the same techniques, that is, with about 10 g of 4% solution 
of cellulose nitrate prepared according to Example I, using the wet film 
applicator of 0.006 inch cut depth. The solvents were allowed to evaporate 
for an hour to get thin uniform coating of cellulose nitrate over the dye 
coating. 
Using the procedure described above, elements having different thicknesses 
of the dye coating and that of cellulose nitrate, were prepared by using 
Bird type wet film applicators of different cut depths (0.0015 to 0.006 
inch) and were used. 
Using the procedure described above, elements were prepared using aniline 
blue dispersed in different media such as gum arabic, and mixtures of gum 
arabic and polyvinylalcohol. 
Using the procedure described above, elements were prepared by using water 
soluble dyes, such as bromophenol blue, and cresol purple, dispersed in 
water soluble polymers such as polyvinyl alcohol and gum arabic. 
Example X 
Irradiation with Alpha Particles from Polonium-210 
The elements prepared according to procedure described in example IX were 
irradiated with alpha particles from a radon daughter (polonium-210) and 
activated with 6N aqueous KOH according to the procedure described in 
Example V. Red colored spots similar to those shown in FIG. 4 appeared 
within 30 minutes at room temperature. 
Example XI 
Elements having Coatings on Both Sides of Substrate 
An element, as shown in FIG. 2a, was prepared by coating aniline blue and 
cellulose nitrate according to the procedure described in Example IX. The 
element was then turned upside down, and the other side of the element was 
similarly coated. This provided an element having coating of aniline blue 
and cellulose nitrate on both the sides of the polyester sheet. The 
coatings of both the sides were irradiated with alpha particles from 
polonium source according to procedure described in Example X. The element 
was activated by dipping the element in a solution of 6N aqueous KOH. Red 
spots were observed on both the sides. 
The objective of coating a transparent substrate on both sides was to 
demonstrate that the size of the final device can be reduced to half. In 
the field usable element both the sides will be exposed to radon 
atmosphere. When the device is activated, the spots will develop on both 
the sides. The coating is so thin that it would appear as if the coating 
and the spots are on one side only. 
Example XI 
Preparation of Elements by Lamination (FIG. 2b) 
In order to demonstrate that commercially available lamination 
technique/equipment can also be used for preparation of the elements, some 
elements were prepared by lamination as described below. 
A 8.times.12 inch piece of "KRAFT" type release tape paper coated with thin 
film of plastic followed by a coating of a silicone compound, obtained 
from Mactac Inc., Stow, Ohio and Tinicum Research Company, Frenchtown, NJ, 
was placed on a x-y recorder. 
Cellulose nitrate was coated by placing about 5 g of 4% solution of 
cellulose nitrate prepared according to Example I, in front of the wet 
film applicator in a straight line. The arm of the recorder was then 
allowed to scan across the face of the release paper to form a thin 
uniform wet film of cellulose nitrate. The solvents were allowed to 
evaporate for an hour to get thin uniform coating of cellulose nitrate. 5 
g of indicator solution (0.05 g of aniline blue and 1.0 g of 
polyvinylalcohol and gum arabic in 4 ml of water) were poured one side of 
the cellulose nitrate coating in front of the wet film applicator in a 
straight line. The arm of the recorder was then allowed to scan across the 
face of the coating causing the dye to form a thin uniform wet film of 
polyvinylalcohol containing the dye. The solvent (water) was allowed to 
evaporate for a day to get thin uniform coating of the dye on cellulose 
nitrate. A pressure sensitive adhesive tape was laminated over the dye 
coating. The assembly was turned upside down and the Kraft release tape 
was peeled off to provide the detecting element, that is, an adhesive tape 
having coating of aniline blue and cellulose nitrate. Because the KRAFT 
release film is coated with a special silicone releasing compound, it only 
adhered weakly to cellulose nitrate coating. Hence after lamination it was 
easier to peel off the release film. 
The elements prepared by the above lamination technique were irradiated 
with alpha particles from polonium-210 and activated with 6N aqueous KOH 
solution. The laminated devices also showed colored spots similar to that 
shown in FIG. 4. 
Example XII 
Self-standing Element (FIG. 2b) 
A 8.times.12 inch piece of Kraft release paper was placed on a x-y recorder 
and first coated with 10 g of 4% solution of cellulose nitrate using wet 
film applicator (0.006 inch cut depth). The coating was allowed to dry for 
a few hour. The Krfat release paper coated with cellulose nitrate was 
further coated with 8 gram of aniline blue solution (100 mg of aniline 
blue dissolved in 9.9 gram of 10% solution of polyvinylalcohol in water) 
using the wet film applicator (0.0015 inch cut depth). The coating was 
allowed to dry for a day. The Kraft release paper (coated with cellulose 
nitrate and aniline blue in polyvinylalcohol) was then further coated with 
10 g of 4% solution of cellulose nitrate using wet film applicator (0.006 
inch cut depth). The coating was allowed to dry for a few hours. The Kraft 
release paper was then carefully peeled-off from the coatings. The 
coatings were in the form of a film, that is, a film of polyvinylalcohol 
containing aniline blue sandwiched between two films of cellulose nitrate. 
Both the faces of this element were irradiated with alpha particles from 
polonium-210. The element was then activated by dipping in solution of 6N 
aqueous KOH. The time required for KOH to breakthrough and colored spots 
to appear was 60 min. 
Example XIII 
Need for Space for Diffusion of Etchant 
A piece of Mylar film was coated with 5 g of a pressure sensitive adhesive 
(UR 1025, a synthetic latex supplied by United Resin Inc., Brooklyn, New 
York) containing 1% aniline blue using Bird type wet film applicator 
(0.006 inch cut depth). The solvent was allowed to evaporate for a day. 
Cellulose nitrate was coated on to the adhesive layer from 4% solution in 
ethylacetate using the wet film applicator. The resultant element was 
irradiated with alpha particles from polonium-210 and activated with 6N 
aqueous KOH. No red spots were observed even after two days. Absence of 
red spots indicates that layer under the alpha sensitive film does not 
allow KOH to diffuse through because water cannot diffuse through the 
adhesive layer containing the dye. 
Example XIV 
Need for Space for Diffusion of Etchant 
A peice of a pressure sensitive adhesive tape (Macfilm of Mactac Corp., 
Stow, Ohio) was coated with 1:1 thymolphthalein-phenolphthalein from their 
3% solution in methanol. A 6 micron film of poly(bisphenol-A carbonate) 
was laminated onto the dye coated adhesive tape. The resultant device was 
irradiated with alpha particles from polonium-210. The device was 
activated with 6N aqueous KOH. No red spots were observed even after two 
days at room temperature. 
EXAMPLE XV 
CR-39 as track producing polymer 
CR-39 is a polymer of diallyl diglycol carbonate. Diallyl diglycol 
carbonate is a liquid at room temperature. Polymerization of diallyl 
diglycol carbonate is initiated with a radical initiator such as benzoyl 
peroxide or diisopropyl peroxydicarbonate. Benzoylperoxide requires longer 
time and higher temperature (above 100.degree. C.) to cure. Diisopropyl 
peroxydicarbonate, referred to as IPP, is capable of polymerizing diallyl 
diglycol carbonate at low temperatures (20.degree.-50.degree. C.). 
However, IPP is very unstable (explosive) at room temperature. 
0.5 gram of the mixture (82) of diallyl diglycol carbonate containing 4% 
diisopropyl peroxydicarbonate was placed between two sheets of PET (84) 
(polyethylene terephthalate) (as shown schematically in FIG. 6). One of 
the PET sheets (8.times.11 inch) was larger than the other (7.times.10 
inch). The sandwich was further sandwiched between two glass plates (86) 
(9.times.12 inch). The assembly was placed in an incubator at 60.degree. 
C. and about 10 lb of weights were placed on the assembly. After 24 hours 
of curing, the glass plates were removed. The PET sheets were separated at 
one corner and one sheet was carefully peeled off. The film (182) of CR-39 
(crosslinked diallyl diglycol carbonate) remained weakly adhered to one of 
the PET sheets. A wide tape (92) having a coating of a moist, water 
soluble gum (94), containing (or having layered thereon) aniline blue (96) 
was applied on to the film of CR-39 followed by careful peeling off of the 
PET sheet. This constitutes the detecting element. The whole process of 
preparing the element is shown schematically in FIG. 6. 
The elements of CR-39 thus prepared were irradiated with alpha particles 
from polonium-210. Color spots and the impression of the source similar to 
those observed with cellulose nitrate in FIG. 4 were observed in six hours 
upon activation of the element with 6N aqueous KOH. 
Example XVI 
Preparation of element using polycarbonate film 
A solution of phenolphthalein-thymolphthalein 1:1 in methanol was coated on 
a 6 micron polycarbonate [poly(bisphenol-A carbonate)] film. After drying, 
the opposite, the uncoated, surface of the polycarbonate film was exposed 
to Po-210 alpha source (activity of 500 .mu./Ci) for different times 
ranging from a few seconds to a few hours. This film was then placed flat 
on a strip of filter paper on a glass plate with the dye coated face of 
the film in contact with the filter paper. 6N aqueous KOH was placed on 
top of the irradiated surface of the film and the time required for KOH to 
break through the tracks and for colored spots to appear was noted. The 
blue colored spots appeared after 20 hours at room temperature 
irrespective of irradiation time. 
Using the procedure described above, but activating with 6N aqueous NaOH in 
place of KOH, the time required for the alkali to break through the tracks 
and spots to appear was 30 hours at ambient temperature. 
Example XVII 
Effect of Concentration of Etchant 
Using the procedure described in Example XVI, elements were prepared using 
polycarbonate of 6 micron thickness. The elements were activated with 3N 
and 6N KOH in water:methanol (1:1). The time required for KOH to break 
through the tracks and spots to appear was noted. The time required for 
the spots to appear decreases with increase in concentration of KOH and 
methanol. The 6N and 3N methanolic KOH require 0.75 and 14 hours 
respectively at room temperature for the spots to appear. 
Example XVIII 
Effect of Temperature of Etching 
Using the procedure described in Example XVI, elements were prepared using 
polycarbonate of 6 micron thickness. The elements were activated with 6N 
aqueous KOH and 6N methanolic (water:methanol, 1:1) at room temperature 
and at 60.degree. C. The time required for KOH to break through the tracks 
and spots to appear was noted. The time required for the spots to appear 
decreases with increase in temperaure of etching, 6N aqueous KOH requires 
20 and 3 hours at room temperature and 60.degree. C. respectively while 6N 
methanolic KOH requires 45 and 15 minutes at ambient temperature and 
60.degree. C. respectively for the appearance of the spots. 
Example XIV 
Effect of concentration of co-solvent for KOH 
The devices described in Example XVI were activated with different 
concentrations of KOH and additives. Aniline blue was used as the dye. The 
time required for KOH to breaktrhough and to induce color change from blue 
to red is shown in Table 3 below. 
TABLE 3 
______________________________________ 
Conc 
KOH Additives Conc. Additives 
Breakthrough Time 
______________________________________ 
6N KOH MeOH 50% 45 min. 
6N KOH MeOH 30% 2 hr 
6N KOH MeOH 10% 48 hr 
3N KOH MeOH 50% 24 hr. 
______________________________________ 
Example XX 
Use of Different Dyes 
Using the procedure described in Example XVI, elements were prepared using 
polycarbonate of 6 micron thickness and several other dyes. The elements 
were activated with 6N aqueous KOH. Different colored spots appeared after 
6 hours at room temperature. The color change of the dyes when KOH broke 
through is listed in Table 4 below: 
TABLE 4 
______________________________________ 
Color 
Dye Dye coating Spots 
______________________________________ 
Bromophenol Blue Yellow Blue 
Phenolphthalein Colorless Pink 
Thymolphthalein Colorless Blue 
Aniline Blue Blue Red 
Brilliant Yellow + 
Green Red 
Aniline Blue 
Brilliant Yellow + 
Green Red 
Brilliant Green 
______________________________________ 
Example XXI 
Preparation of element using polycarbonate film of different thicknesses 
Using the procedure described in Example XVI, elements were prepared using 
polycarbonate of 6 and 20 micron thickness. The elements were activated 
with 6N aqueous KOH. The time required for KOH to break through the tracks 
and spots to appear was noted. The time required for KOH to break through 
the tracks increases with increase in thickness of the film. 6 and 20 
micron films required 20 hrs. and 300 hrs. at ambient temperature for 
emergence of spots. 
Example XXII 
Field Usable Devices (Kit) 
A glass slide was coated with aniline blue by dipping in 0.5% solution of 
aniline blue in methanol. After drying the coating was coated with 
cellulose nitrate by dipping into 4.0% solution of cellulose nitrate in 
ethyl acetate. After exposure to alpha particles from polonium-210, the 
glass slide was placed in 6N aq. KOH solution at room temperature. The red 
colored spots developed in about 2 hours time and grew bigger till they 
merged in to each other. 
Example XXIII 
A film of 20% polyvinyl alcohol (100% hydrolyzed) was coated on a glass 
plate using a 0.003" Bird type applicator. This film was dried at room 
temperature for 2 days. A film of 4% cellulose nitrate solution was then 
coated on the above, using the same Bird type applicator. This was then 
dried at room temperature for 4 hours. 
A portion of the above device was then exposed to as one source of alpha 
particles for 10 seconds. The exposed area was then covered with a dye 
solution comprising Aniline Blue in 6N aq. KOH. After 40 seconds, the dye 
solution was removed with a dropper, the exposed area very carefully wiped 
a with paper towel and a 5% HCl solution poured onto the exposed area. 
Within a few seconds, blue color appeared in the polyvinyl alcohol layer 
where the device had been exposed. 
This indicates that it is not necessary to have a dye in indicator layer 
under the alpha sensitive film. The dye can be introduced along with the 
etchant to detect visualize particle penetration. 
Example XXIV 
A film of 4% cellulose nitrate solution was coated on a glass plate using a 
0.003" Bird type applicator. This film was dried at room temperature for 4 
hours. 
A portion of the above device was then exposed to a strong source of alpha 
particles for 10 seconds. The exposed area was then covered with a dye 
solution comprising Aniline Blue in 6N aq. KOH. After 40 seconds, the dye 
solution was removed with a dropper, the exposed area very carefully wiped 
with a paper towel a 5% HCl solution poured on the exposed area. Within a 
few seconds, blue color appeared between the glass plate and the cellulose 
nitrate film where the device had been exposed. 
This indicates that it is not necessary to have an indicator layer under 
the alpha sensitive film. The dye can be introduced along with the etchant 
to visualize alpha particle penetration. 
While Examples XXII and XXXIV indicate that the device is operative without 
a dye in the indicator layer or indeed any indicator layer.