US3718606A

US3718606A - Silver halide monocrystal particle-tract detectors doped with manganese

Info

Publication number: US3718606A
Application number: US00086277A
Authority: US
Inventors: G Haase; E Schopper
Original assignee: Agfa Gevaert AG
Current assignee: Agfa Gevaert AG
Priority date: 1969-11-21
Filing date: 1970-11-02
Publication date: 1973-02-27
Anticipated expiration: 1990-02-27
Also published as: JPS4836915B1; DE1958425A1; FR2068576B3; GB1290032A; FR2068576A7; BE758970A

Abstract

The photographic properties in particular the light sensitivity of silver halide monocrystal-track detectors are highly improved by adding manganese ions as doping agents.

Description

United States Patent 91 1 3,718,606 Haase et al. 1 Feb. 27, 1973 1 SILVER HALIDE MONOCRYSTAL 1 References Cited PARTICLE-TRACT DETECTORS DOPED WITH MANGANESE UNITED STATES PATENTS [75] Inventors. Gunter Ham, Frankfurt am Mal-n; 3,362,797 1/1968 Shaskolskaja ..252 1 Erwin schopper, Koenigstein/Tau 3,548,191 12/1970 Schultz ..252/408 nus, both of Germany [73] Assignee: Agfa-Gevaert Aktiengesellscllaft,

Leverkusen, Germany Primary Examiner-John T. Goolkasian [22] Flled' 1970 Assistant Examiner-M. E. McCamish [21] Appl. No.: 86,277 Attorney-Connolly and Hutz [30] Foreign Application Priority Data 1 ..P l 8 42 .9 Nov 21 969 Germany 9 5 5 ABSTRACT US. Cl. t t R, The photographic properties in particular the [5 Into u G011 ensitivity of ilver monocrystal tra k d t ctor [58] Field of Search ..252/408, 1; 250/83 R, 83.1;

23/300, 304, 295, 87 R, 91, 205, 204 R, 367; 96/50 R, 94 R, 94 BF, 120, 110,119 R; 148/].6

are highly improved by adding manganese ions as doping agents.

4 Claims, No Drawings SILVER HALIDE MONOCRYSTAL PARTICLE- TRACT DETECTORS DOPED WITH MANGANESE This invention relates to particle-track detectors based on silver halide monocrystals whose sensitivity and fogging are improved by the addition of specific doping agents.

Solid state particle'track detectors for detecting tracks of ionizing particles are being used to an increasing extent in the investigation of atomic particles in nuclear physics, above all in the physics of cosmic radiation and in modern heavy-ion physics. In cases where they are intended to be used for quantitative measurements, particle-track detectors of this kind have to meet certain requirements, more particular the particle track must be developed in a clearlyreproducible manner which is characteristic of the interaction of the particle to be investigated with the solid.

The particle track has to provide as much information as possible on the particle. It should also lend itself to quick and easy evaluation.

Since the defects which an ionizing particle produces in a solid are submicroscopic in their dimensions, a mechanism by which the track can be amplified should be available for photooptical evaluation, for example for rendering the track visible. The defects produced by the ionizing particle in the solid represent the latent image of the particle track which is developed by the amplifying mechanism. The more details characteristic of the particle the amplified particle track discloses, the more effective the detector will be.

Two amplifying mechanisms have acquired practical significance:

l. Selective etching of the solid along the particle track.

2. The deposition of a new phase along the track.

Etching has acquired significance inter alia in the case of mica and a few glasses, especially organic glasses. The process of selective etching along the particle track is essentially based upon the fact that bonds broken along the track make the etching process much easier. Unfortunately, etching involves several difficulties which seriously restrict the utility of this technique.

The most serious disadvantage of the etching process is that valuable details are often lost, above all in the case of long particle tracks, because the etching medium has to penetrate through the solid from outside along the track and the etching channels available for this purpose are extremely narrow with the result that in many cases the etchingmedium is unable to penetrate sufficiently deeply into the solid detector. For this reason, it is not generally possible to amplify interrupted particle tracks.

It is also known that the tracks left by ionizing particles can be detected in silver chloride monocrystals. In this type of detector, a new phase is preferably deposited along the particle track. In the case of silver halide monocrystals, this new phase consists essentially of silver.

The silver chloride monocrystals are superior to the aforementioned solid state particle-track detectors in which the particle tracks have to be amplified by an etching process, in particular by virtue of the fact that, in the case of silver chloride monocrystals, the amplifying and developing process can be carried out very quickly and easily. In the amplifying process, the

monocrystal in which the particle track was recorded is uniformly exposed with high-energy light, preferably ultra-violet light.

The developing process can be explained as follows: Electron-defect electron pairs are produced in the crystal through the exposure to light. The electrons are trapped along the particle track in interchange with silver ions from the disturbed regions. The track is thus stabilized and then amplified. In principle, this process is comparable with the elementary photographic process. The original track is the latent image of the track, so that amplification corresponds to photographic development.

The disadvantage of these silver chloride monocrystal detectors originally lay in their inadequate reproducibility. This disadvantage was obviated by using high-purity silver chloride for producing the detectors. It is known of high-purity silver chloride that it is basically non-sensitive and unsuitable for the production of detectors. However, silver chloride monocrystals of this kind can be sensitized for ionizing particles by the addition to them of small quantities of certain foreign substances, such as cadmium or lead for example. Reference is made in this connection to the article by K. Breuer, G. I-Iaase and E. Schopper in Brit. J. Appl. Phys, 18 (1967), 1824 et seq. and the article by K. Breuer, E. Schopper, G. Haase and F. Zorgiebel in Phot. Korrespondenz 104 (I968) 76 et seq. The silver chloride crystals doped in the manner described show a level of sensitivity to ionizing particles which is adequate for many purposes. They are also advantageous insofar as they do not record gamma-rays, X-rays and electrons so that no disturbing background is produced by these rays.

Unfortunately, silver chloride monocrystals doped solely with cadmium did not satisfy practical requirements for more accurate quantitative measurements on tracks left by ionizing particles, either in regard to sensitivity or, more particularly in regard to the background, i.e., the signal-noise ratio. The background adversely affecting evaluation of the particle tracks is essentially attributable to l. the lattice defects which are present in the crystal,

i.e., before particle irradiation, and which can never be completely eliminated, especially distortion of narrow-angle grain boundaries of general sub-structures which, like the lattice defects produced by particle irradiation, are decorated with silver along the tracks during the amplifying process; 2. Silver particles produced by photolysis during amplification, being statistically distributed We now have found silver halide monocrystal detectors for recording tracks of ionizing particles which contain manganese ions as doping agents.

The addition of manganese considerably increases the sensitivity of the crystals and the information content of particle tracks and largely eliminates the background interfering with the evaluation of the particle tracks. More particularly, the optical crystal haze caused by deposits in the silver halide monocrystal detectors doped with cadmium is completely avoided. The particle tracks in the silver halide monocrystal detectors doped with manganese are extremely finegrained and are visible in every detail on an optically substantially clear background, being particularly suitable for accurate quantitative measurements.

The concentration of the manganese ions can vary within wide limits. In general, concentrations of from 100 ppm to 3,000 ppm of manganese ions, based on the weight of the silver halide, preferably silver chloride, have proved to be sufficient. Additions of from 500 to 1,500 ppm are preferred.

The ions of tetravalent manganese are particularly effective. In this case, doping can readily be achieved for example by the addition of manganese (II) salt solutions to the silver halide, followed by melting in a chlorine atmosphere. The silver halide monocrystals doped with manganese are then grown in a chlorinecontaining atmosphere. At relatively high chlorine partial pressures, gas bubbles can be formed in the silver halide monocrystals doped with manganese. Formation of gas bubbles can be avoided forexample by reducing the chlorine partial pressure, by adding an inert gas, for example nitrogen and by reducing the rate at which the monocrystals are grown. For example, a gas atmosphere which had a total pressure of 400 Torr and which contained chlorine with a partial pressure of 5 Torr and nitrogen with a partial pressure of 395 Torr, has proved to be favorable.

The particle-track detectors according to the invention can be used for determining particle data, for investigating particle reactions and nuclear fission and for investigating decay mechanisms even of extraheavy nuclei, for identifying isotopes of high-energy ions and for investigating isotope compositions of solar radiation or cosmic radiation and for determining the sources of this radiation. These detectors are particularly suitable for recording the tracks of heavy ions.

The tracks of ionizing particles can be amplified in the usual way in the detectors according to the invention by uniform exposure to short-wave light, especially ultra-violet light. Thus, very distinctly developed tracks can be obtained on a clear background. In this respect, the detectors are superior to conventional photographic emulsions for recording nuclear tracks nuclear track emulsions"). These materials consist of a supported silver halide gelatin emulsion layer of high resolving power. In general, it is not possible to obtain in these photographic emulsions particle tracks as sharp as those in the detectors according to the invention. In addition, the photographic emulsions usually have a much greater disturbing background because they are also sensitive to gamma-rays, X-rays and electrons.

In the detectors according to the invention, the tracks of ionizing particles can be amplified substantially over any part of their entire length, even in cases where they are interrupted, i.e., where relatively few or undisturbed crystal regions in which the track is interrupted are situated between the more strongly disturbed crystal regions produced by the ionizing tracks passing through. This automatically follows from the nature of the amplifying process since, during the amplifying process which takes place inside the volume, electrons and silver ions are deposited wherever lattice defects have been produced by the ionizing particles passing through. In this respect, the detectors according to the invention are generally superior to detectors of the kind in which the track is amplified by etching. The etching process begins at the surface of the detector where the ionizing particle has entered the crystal and continues along the track of the particle into the interior of the crystal so that fresh etching solution has to be supplied along the channel already formed by the etching process. With interrupted particle tracks, the etching process is liable to stop at the end of a track section because the etching solution cannot then penetrate sufficiently quickly into the adjacent undisturbed region of the crystal, so that the following sections of track which are not continuous with the previous track can no longer be amplified. In some cases, in the case of interrupted particle tracks, a less disturbed or even undisturbed crystal region between two track sections may be penetrated by the etching solution if the time allowed for the etching solution to act is considerably increased. In that case, however, the etching solution also continues to act during this period in that portion of the track which was etched first and which has therefore been amplified, with the result that this first section of track becomes greatly increased in width and may acquire a pronounced cone shape. However, this seriously impairs the reproducibility of the track and the accuracy of evaluation. The detectors according to the invention are completely free from such disadvantages.

The possibility provided by the silver halide monocrystal detectors according to the invention of amplifying, with uniform distinction and high reproducibility, even those particle tracks which start at some depth within the detector, opens up fields of application for these detectors in which other solid state particle-track detectors of hitherto known type could not be used with the same assurance and accuracy. An example of this is the study of the run-down of decay processes as a function of time. If the particle tracks are amplified at a first point in time t and then at a point in time 2,, it is possible to determine which tracks have been added during the time interval t,--t,,, i.e., which new decay processes have occurred inside the detector during the time interval t,r,,.

In many cases, uniform exposure with the short-wave light producing the electron-defect electron pairs is sufficient in detectors according to the invention for amplifying the particle tracks. However, this method of amplification can easily be improved in the detectors according to the invention in order to amplify particle tracks situated at almost any depth inside the crystal. This was not possible with conventional solid state particle-track detectors.

In the case of relatively thick crystals and tracks situated deep inside the crystal, the electrons required for the amplification process can be made to penetrate sufficiently deeply into the interior of the crystal by exposing the crystal impulse-fashion to the short-wave light producing the electron defect electron pairs, whilst asynchronously pulsed electrical field is applied to the crystal so that, for the duration of each of the shortterm exposure impulses, there is effective in the crystal an equally brief electrical field which causes the electrons produced by the exposure impulse, and only these electrons, to drift through the crystal volume. This method of combining pulsed exposure with pulsed electrical fields is generally known in the physics of solids, for example for determining the lives and ranges of electrons in the solid (cf. the references in the aforementioned works). Short-lived electrical field impulses are used in this method of track amplification in silver halide monocrystal detectors because they avoid the troublesome movement of silver ions which would occur in longer lasting electrical fields.

In the case of relatively thick crystals and tracks situated deep inside the crystal, the advantage of the weak background and the absence of crystal haze in the detectors according to the invention as compared with detectors of silver halide doped solely with cadmium, is particularly noticeable. In the case of detectors with a relatively strong background or relatively pronounced crystal haze, for example in the case of crystals doped with cadmium in high concentrations, deep lying tracks could not be evaluated at all, or with far from the required degree of accuracy.

Both embodiments of the amplification process used in the detectors according to the invention, i.e., solely by uniformly exposing the detectors to short-wave light or by pulsed exposure with short-wave light in a synchronously pulsed electrical field, are characterized in their simplicity and stability to interference. After the particle track has been recorded, the detectors are not exposed to any liquids so that any disturbances which might be caused by liquids are avoided. lt is worth mentioning here the sensitivity of the etching methods in this respect and the swelling and distortion phenomena which occur in the conventional photographic processing of nuclear track emulsions.

EXAMPLE An aqueous solution of manganese (ID-chloride (p.a.) is added through a pipette to 99.999 percent pure silver chloride in powder form in such a way that a silver chloride containing 1,000 ppm of manganese is obtained. The mixture is dried in the pipette in a drying chamber. The silver chloride doped with manganese is then fused in the pipette. The melt is introduced between two quartz glass plates heated to about 550 C. the gap between which is set at about 200 p. by small rods of quartz glass. On cooling, a polycrystalline manganese-doped silver chloride wafer is obtained. The sandwich consisting of the two quartz glass plates and the silver chloride wafer between them is introduced into a horizontal quartz glass tube which, following evacuation, is filled with a gas mixture with a total pressure of 400 Torr consisting of chlorine with a partial pressure of 5 Torr and nitrogen with a partial pressure of 395 Torr. Thereafter, a tubular oven is passed over the quartz glass tube with such a temperature gradient and at such a s eed that the polycrystalline rnan anesedoped silver c loride wafer 15 converted in a nown manner through fusion into a monocrystal which can be detached from the quartz plates by immersing the sandwich in water.

Following irradiation with the ionizing particles to be investigated whose tracks are to be recorded, the silver chloride monocrystal doped with manganese is uniformly exposed to a high-pressure xenon lamp with a filter between the light source and the detector so that only a narrow wave length range around 417 nm is effective. The intensity of the short-wave light directed on to the monocrystal amounts to about 10 quanta/cm sec. The exposure time is about 20 to 30 minutes.

We claim:

1. A silver halide monocrystal detector for recording the tracks. of ionizing particles containing a doping agent, said doping agent containing manganese ions.

2. A detector as defined in claim 1, containing manganese ions in quantities of from 500 ppm to 1,500 PP 3. A detector as defined in claim 1, containing ions of tetravalent manganese.

4. A detector as defined in claim 1, wherein the silver halide is silver chloride.

Claims

2. A detector as defined in claim 1, containing manganese ions in quantities of from 500 ppm to 1,500 ppm.
3. A detector as defined in claim 1, containing ions of tetravalent manganese.
4. A detector as defined in claim 1, wherein the silver halide is silver chloride.