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DOSIRAD KODAK
LR115 Films ( Version 15/04/2008 )
(including instructions for use)
These consist of thin films of a special cellulose nitrate, coloured deep red and coated on a 100 µm thick polyester (PET) base. Only one side of these films is sensitive. With a needle, this sensitive side gives white scratches. This must be taken into consideration when they are used.
The thickness of the red sensitive layer of "LR115 type 1" films is 6 µm, while it is 12µm for the "LR115 type 2" films. The type 1 is especially designed for its higher sensitivity to apha particles of lower energies. The "LR115 type 1B" is a "LR115 type 1" but with a lithium tétraBorate converter screen (n, α) coated on the red sensitive cellulose nitrate layer.
The red sensitive layer of the Type 2 stripping film ("Strippable LR115 type2") must be removed from the clear PET base, while it is still wet at the conclusion of the washing stage.
The different LR115 film formats and prices, are given in the Export Price List, as well as in the French Price List.
The films are mainly intended for the dosimetry of small quantities of ionising particles (mainly "alpha particles") or neutrons. Most of the time, the object is not, as with KODAK CN85 Film (today discontinued because a too low demand), to obtain an image but to convert each impact by a particle to a perforation of the coloured sensitive layer. These perforations are called tracks, by the technicians. Nevertheless, the LR115 films can also be used to make pictures. The examination and counting of the tracks are facilitated by the great contrast between the perforations and the background when the film is examined by transmitted light, especially if a green source, of a complementary colour to that of the film, is used. A KODAK WRATTEN Filter N° 40 (green) or interferential cyan filters are recommended for this purpose.
When an exposed and processed film is viewed under the conditions suggested above, each particle which it has registered will show as a brilliant point of light which can easily be located by the naked eye, even if in the middle of a large area of film. Moreover, such tracks are easily distinguishable from superficial defects in the sensitive surface (such as those caused by dust or scratches). These perforations ("tracks") can easily be counted by use of a microscope. On a Strippable LR115, the tracks can be counted as well under a microscope or by the "Spark-Counting" method. Commercial spark-counters exist on the market. They allow to count tracks from small to large areas of strippable LR115 films. Since 2007, an optical lab is also available on the market for optical counting (equipment and special counting software). Ask us for more details.
1 - Detection and dosimetry
of thermal and epithermal
neutrons :
KODAK LR115 Films, Type 1 and Type 1B (6 µm) are specially designed for the registration of alpha particles arising from the (n,α) reaction of B10 (1.6 MeV) and Li6 (2.4 MeV). If a cadmium screen covers one part of the film, it is possible to differentiate thermal and epithermal neutrons by the following method. The part covered by the cadmium screen records only epithermal neutrons, the uncovered part records both thermal and epithermal neutrons. It is therefore easy to calculate the number of thermal neutrons by difference.
2 - Detection and dosimetry
of fast neutrons :
Neutrons cannot be converted to alpha particles at energy levels above 1 KeV. Nevertheless it is still possible to obtain tracks in the cellulose-nitrate layer. These arise from the transfer of energy from those nuclei of the constituents of the cellulose nitrate that have been bombarded by neutrons of high energy, from 1 MeV to 14 MeV. These are called nuclear recoil tracks (1) .
The use of KODAK LR115 Films, Type 2 and Type 2 Stripping is recommended for this application. However, when both thermal and epithermal neutrons are present, KODAK LR115 Film, Type 2B can be used. The differences between the successive images formed on the same film make it possible to identify thermal, epithermal and fast neutrons.
Very fast neutrons (up to several tens of GeV) can also be detected (2) by the methods described for use with KODAK CN85 Films. In this case, spallation fragments produce the tracks.
3 - Auto radiography (with
LR115 Films, Type 2) of alpha radioactive objects :
- A diffusing image without the use of a screen is obtained. This image is similar to that produced on KODAK CN85 Films by means of neutron radiography. It results either from spontaneous alpha radioactivity or from particle emission arising from bombardment.
- The technique of recording alpha particles without the use of any screen, using methods similar to those described above, can be of great value. It makes the detection of numerous alpha-particle-emitting elements possible. Elements which act as α emitters when under bombardment (such as boron and lithium) are similarly disclosed. This has enabled the practical development of the following :
• Detection of very small amounts of plutonium in urine samples (3) : due to emission of alpha particles (KODAK LR115 Film, Type 2).
• Dosage and repartition of boron (10-10 g/cm²) in steels or alloys, doped semiconductors, etc. (4). When bombarded by neutrons the boron gives rise to the ( n, α ) reaction (KODAK LR115 Film, Type 1 or Type 2).
At last, the LR115 films can also be used together with our boron ( n, α ) converter screens : BN1 (natural boron) or BE10 (pure boron10). See the "Prices List" of our products.
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of this document)
1 – Handling the film before
use :
- The LR115 films are unaffected by electrons or by radiations in the electro-magnetic spectrum (such as gamma rays, X-rays or infra-red radiations visible light). They are therefore be handled without risk where such radiations are present.
- It is nevertheless recommended that the precautions given below should
be observed :
• Take care to avoid any form of abrasion, such as that arising from mechanical rubbing, folding, pressure, etc.
• For long keeping of all the LR115 films, over 12 months, store the films in a cool dry place : temperature below 10°C, relative humidity 50% or below. In a frig, place the boxes of films in air tight plastic bags, to avoid humidity cycles. Allow them several hours before use to reach the ambient temperature.
• As far as possible, wear cotton gloves when handling the films.
2 – Processing LR115 films :
2-1- General recommendations:
• The tracks recorded by these films are not directly visible and must therefore be intensified by treatment in an alkaline solution. The etching bath recommended for this purpose is a 10% (2.5N) solution in distilled (or permuted / Ca-Na exchanged) water of analytical-grade sodium hydroxide (caustic soda).
• The strength of the etching bath affects heavily the results obtained. The bath must therefore be prepared exactly and be maintained at the correct strength.
• Care must be taken to allow for the effects of evaporation, especially when processing at 60°C and also for that of absorption from the air carbon dioxide which will combine with the sodium hydroxide to form less-alkaline sodium carbonate.
• The etching bath should not be agitated. But a very slow films movement can homogenise the films etching. An uniform temperature should be maintained by means of a efficient water jacket. The mean temperature during the whole etching process has a very high effect on the etching efficiency (tracks number).
• Surface-active agents, such as detergents, organic solvents, adhesive tapes, iron or bad stainless steel, ball-point or felt-pen inks may lead to adverse reactions and should therefore not be allowed. If not, they can contaminate the etching bath and sometimes destroy the cellulose nitrate.
2-2- Processing the LR115 films :
For the LR115 type 1B, after exposure and before etching, it is necessary to remove the incorporated converter screen by washing the film in water, at a temperature below 25%C, until the complete disappearance of the screen.
• LR115 film, type 1 and type 1B : Etching bath at 10% of analytical-grade of NaOH. Etching time 25 to 40 minutes. Stable bath temperature 60°C (fluctuation < 0.5 °C).
• LR1155 film, type 2 : Etching bath at 10% of analytical-grade of NaOH. Etching time 75 to 100 minutes. Stable bath temperature 60°C (fluctuation < 0.5 °C).
• Strippable LR115 type 2 : Same process procedures, as those given for the "non-strippable" LR115. Except that immediately after the completion of washing, the red sensitive layer should be stripped, in case of spark-counting (not in case of optical counting). This is quite easily done by pinching one of the corners of the film between the thumb and the index finger. All that is then required is to pull the sensitive layer in a direction parallel to the base until the two are completely separated. Never "peel off" the red layer before processing.
For all the LR115 films, after the conclusion of this process, the film should be washed in acidified water (by HCl up to PH » 3), or distilled water, at least 30 to 40 minutes, with agitation. After this wash time, make a final rinse of 2 minutes at 20°C in a distilled water (at least in a permuted water).
2-3- Interpreting the etched films :
The trace (tracks) counting on the etched LR115 film can be carried out by different methods : through a microscope by naked eye or automatic, by spark-counting of the strippable LR115 film or even by photographic enlargements.
Instead of counting the tracks, the LR115 also allows to make pictures, like was doing the CN85 film. For some uses, the LR115 can easily replace the discontinued CN85 film. For instance, it allows to make alpha auto-radiographies of materials. It also allows to make neutron radiographies when use behind a converter screen (n,s) like our BN1 or BE10 screens or directly if "B" type of LR115 are used (B = borated).
For the microscope counting, it is proposed to varnish the film surface before counting. The best are formophenolic varnishes. Such a varnish considerably reduces the light diffusion of the etched film surface as well as the light diffused by the tracks. So, a higher number of small tracks can be seen and counted and a luminosity measure can be made, even through the counting microscope simultaneously with the counting itself. Higher than a minimum thickness of varnish, the quantitative results become totally independent of the varnish thickness. This residual luminosity is important for the quantitative counting adjustments, since the number of tracks increases when the residual thickness decreases, that is when the residual luminosity increases.
2-4- Storage of the etched films.
Etched LR115 films can be kept in stock more than 10 years, without trouble, varnished or not. It allows to re-read the old LR115 films in case of need. On the contrary, due to its very high instability, it was definitely impossible to keep the CN85 films after etching. At that time, photographic reproductions were strongly recommended.
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