U.S. patent number 3,767,947 [Application Number 05/034,734] was granted by the patent office on 1973-10-23 for miniaturized electric source.
Invention is credited to Karl Adler, Georges Ducommun.
United States Patent |
3,767,947 |
Adler , et al. |
October 23, 1973 |
MINIATURIZED ELECTRIC SOURCE
Abstract
A miniaturized electric source having a radioactive source of
.beta. -radiation and a collector for said radiation, said source
and said collector forming the terminals of the electric source,
said source comprising a metal disc having coated thereon a tritium
compound in solid state and a layer of a solid - state dielectric
being disposed between said source and collector.
Inventors: |
Adler; Karl (Grenchen,
CH), Ducommun; Georges (Feldbrunnen, CH) |
Family
ID: |
4318361 |
Appl.
No.: |
05/034,734 |
Filed: |
May 5, 1970 |
Foreign Application Priority Data
Current U.S.
Class: |
310/302; 968/504;
976/DIG.411 |
Current CPC
Class: |
G21G
4/04 (20130101); G04C 10/02 (20130101); G21H
1/02 (20130101) |
Current International
Class: |
G21G
4/04 (20060101); G21H 1/00 (20060101); G21H
1/02 (20060101); G21G 4/00 (20060101); G04C
10/02 (20060101); G04C 10/00 (20060101); G01d
007/00 () |
Field of
Search: |
;310/3A,3D |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Borchelt; Benjamin A.
Assistant Examiner: Moskowitz; N.
Claims
What is claimed:
1. A miniaturized electric source utilizing the energy of
.beta.-radiation emitted by radioactive tritium, comprising:
a. a source of .beta.-radiation comprising a metal disc having
coated on at least one surface thereof a thin layer of a solid
tritium compound;
b. a collector element comprising a metallic casing enclosing said
disc;
c. a dielectric layer of plastic foil enveloping said disc,
interposed between said disc and said collector casing and also
enclosed by said collector casing, and having a thickness and
density adapted to allow passage of said .beta.-radiation at an
energy level in the order of up to 18 keV.
2. A source according to claim 1, wherein said di-electric is a
plastic foil of a thickness in the order of 0.2.mu..
3. A source according to claim 1, wherein said source comprises a
compound of tritium with one element of the group consisting of
lithium, zirconium and yttrium.
4. A source according to claim 1, wherein said compound is applied
to said metal disc in an amount of 200 mC/cm.sup.2.
5. A source according to claim 1, wherein said tritium compound is
applied to opposite surfaces of said metal disc at a density of
about 400 mC/cm.sup.2.
6. A source according to claim 1, wherein said source is enclosed
in two plastic foils flanged down each over the rim of said metal
disc.
7. A source according to claim 1 wherein said collector is a metal
capsule enclosing said source and plastic foil and contacting said
plastic foil.
8. A source according to claim 7 wherein said collector has a hole
for passage of said terminal, the space between said terminal and
collector being sealed and insulated by means of a bead of plastic
material.
9. A source according to claim 1, wherein the collector surface
facing said source has a coating of an absorption medium preventing
reflection of electrons back toward the radioactive source.
Description
This invention relates to a miniaturized electric source of the
type having a radioactive source emitting .beta.-radiation, a
collector for receiving this radiation and output electrodes formed
by said collector and a terminal connected to said source.
Various sources of this type have been proposed in the past, but no
satisfactory results have been found for a miniaturized source
adapted for use in a watch as an example, and meeting with all
conditions such as safety, reliability suitable power output and
high life time in the order of 10 to 20 years.
Tritium (H.sub.1.sup.3, termed T in the following specification)
would be suitable as a radioactive source from a number of points
of view, particularly its half-life time and the possibility of
screening stray radiation, but no suitable technical solution has
been known allowing use of this element in a miniaturized electric
source. Due to its high ability of diffusion, vacuum used as a
dielectric between the source and the collector would be destroyed
within short time. Accommodation of a sufficient amount of
radioactive material in a miniaturized source used to be a serious
problem.
This invention aims to overcome the above difficulties and to
provide a miniaturized source of high power output and life time,
extremely low volume and simple construction. This is achieved by
providing a source comprising a tritium compound in a solid state,
a layer of said composition being deposited on at least one surface
of a carrier, and the space between said source and said collector
comprising a layer of a solid - state dielectric having a thickness
and density proper for allowing passage of said .beta.-radiation at
an energy in the order of up to 18 keV and for electrically
insulating said source from said collector. When using T in a
chemically bound solid state the problem of diffusion does no
longer exist or may in any case be neglected. Even though T and He
produced during operation will diffuse into the space between the
radio-active source and the collector during operation, such gases
will be contained in such a small amount between the radioactive
source and the collector that passage of the .beta.-radiation and
ionisation are no problem. As far as ionisation of minute cushions
of gases occurs, this is without effect because the electrical
insulation between the radioactive source and the collector is
obtained by said layer of solid - state dielectric. For these
reasons and since the space between radioactive source and
collector need not be evacuated, the casing of the source must not
be tightly sealed. Gases developed in the source such as He and T
do not build up pressure in the casing but will easily diffuse or
flow through small leaks into the ambient atmosphere. Therefore,
substantially atmospheric pressure exists in the source this being
particularly advantageous because chemically all available
compounds of T are relatively unstable under low pressure.
This invention will now be explained in detail for one embodiment
of which a cross section is illustrated on a substantially enlarged
scale in the accompanying drawing.
The source which is of circular shape has a metal disc 1, for
instance of copper, serving as a carrier for the radioacive
material. This material is applied to both surfaces of disc 1 in
very thin layers 2. The thickness of such layers 2 is suitably
selected in relation to the absorption of .beta.-radiation of the
available energy therein such that the radiation emitted from the
innermost portion of such layers still leaves the layers in an
significant amount.
The radioactive material used is a compound of T with an element of
suitable affinity. LiT.sub.3 is used in the illustrated embodiment,
but any other composition may be used. Similar compounds exist with
Zirconium, Yttrium and other elements. The use of the one or other
of the available compounds is a question of chemical stability and
price. In the illustrated embodiment LiT.sub.3 is applied to
carrier 1 in a density of 200 mC/cm.sup.2. The coated surface of
disc 1 is 2 cm.sup.2 so that the total amount of LiT.sub.3 is 400
mC in the new state of the source, and it will still be in the
order of 200 mC after about 10 to 15 years.
The radioactive source formed by carrier 1 and layers 2 is
enveloped by foils 3 of plastic material flanged down and
over-lapping each other along the edge of disc 1. Foils 3 are
extremely thin in the order of 0.2.mu. when their density is
1g/cm.sup.3, this thickness being proper on one hand for allowing
passage of the .beta.-radiation from layers 2 through foils 3 and
on the other hand for electrically insulating the radioactive
source from the collector. The collector is formed by a metallic
casing 4 for instance of steel comprising two shells frictionally
engaging each other along the rim. Each shell of the casing is
coated at its inner surface with a layer 5 of graphite serving as
an absorbtion medium avoiding reflection of electrons from the
collector back towards the radioactive source.
The casing 4, layer 5, upper plastic foil 3 and upper layer 2 of
LiT.sub.3 have a hole for passage of a terminal wire 6 soldered to
plate 1. A metallic screen 7 is fixed on terminal wire 6 for
collecting possible radiation passing through the hole of the
collector. Screen 7 and the inner end of terminal 6 are imbedded in
a bead 8 of plastic material, this material filling also the space
between terminal 6 and the collector 4, 5, whereby all parts are
properly insulated from each other.
In operation the .beta.-radiation emitted by layers 2 passes
through foils 3 and is collected by collector 4, 5. In this way the
collector is charged to a high negative potential relatively to
disc 1. Due to the extremely thin insulating foils 3 between the
radioactive source and the collector the electric source has a
relatively high capacity in the order of 1,000 pF. This is
advantageous particularly when the source is loaded by an
oscillator as is usual in electric timepieces,where the current
consumption is highly variable.
Manufacture of the source is of similare simplicity as its design.
After application of LiT.sub.3 - layers 2 and of terminal wire 6 to
disc 1, foils are loosely applied and then clamped between layers 2
and layers 5 of the collector and simultaneously flanged round the
edges of disc 1 by applying and closing casing shells 4. No
evacuation or sealing procedure is required except for application
of the insulating bead 8.
The source is extremely compact and flat and is thus highly
suitable for use in watches where it may be accommodated at one
side of the timepiece, or in any other miniaturized electric or
electronic instrument.
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