DE1764876B1 - Metal hydride containing target for generating neutrons - Google Patents

Description

The invention relates to a metal hydride-containing target for generating fast neutrons by bombarding them with deuterons. This means that the target loaded with the heavy hydrogen isotopes deuterium or tritium is bombarded with a deuteron beam with an energy of several 100 keV and emits ^{neutrons according to the known nuclear reactions D (d, n) 3He; T (d, n) 4} He neutrons. Such targets are known from French patent specification 1408 536.

The currently known targets contain the hydrogen isotopes in the form of metal hydrides, the deposited on a passive substrate (such as silver, copper, molybdenum ...) using known processes have been. These passive supports or brackets enable the target to be mounted in the beam path of the deuterons of an accelerator and at the same time a distribution of the impact of the deuterons on the target material. Of course, a good one Functioning of the targets and usable reproducibility of the results are particularly good Adhesion of the hydride layers on the holder or base beforehand. The effects must continue the intense irradiation of the target should be as low as possible so that the under the designation "Spraying" or "sputtering" is a well-known phenomenon of the detachment of atoms from the Target material is avoided. After all, it must be as high as possible and slowly over time decreasing neutron flux, a deuterium or tritium compound that is as chemically stable as possible be used which contains the largest possible amount of the hydrogen isotope under consideration. For this reason, the previously common targets were covered with a thin layer (in the

ίο area of 1 mg / cm ² ) formed from a hydride of the metals titanium, zirconium, yttrium or the neighboring rare earths. Although targets of this type have good heat resistance and can contain significant amounts of tritium and / or deuterium, perfect adhesion of the hydride layers to their supports or supports is not always guaranteed, which makes reliable manufacture problematic and otherwise limits the service life of these targets.

This poor adhesion is particularly related to the noticeable increase in volume of which accompanies the formation of the metal hydrides. For example, the change in density corresponds to from the metal to the corresponding hydride, as shown in the table below, an increase in volume, which can be between 12.5 and 13.5% depending on the metal:

Zr

ZrH ₂ material
Hf I HfH ₂

Ti

I TiH ₂

density

Increase in volume

6.4

5.625

12.5% 13.3

11.48

13.5%

4.5 3.75

13.3%

The object of the invention is therefore to provide targets for the generation of neutrons with improved Behavior, especially better adhesion to the surface and less change during of operation and thus a longer service life.

In the case of the targets mentioned at the outset, this object is achieved according to the invention by a layer from a mixture of hydrides from at least one metal each from two different groups, from one of which increases in volume during hydrogenation and the other decreases in volume shows. The respective amounts of these two metals are chosen so that the mixture has only a small change in density regardless of its hydrogen isotope content.

According to the invention, the targets are accordingly made from at least two different metals produced that a reactive containing the hydrogen isotope to be introduced into the target Are exposed to a hydrogen atmosphere and thereby form hydrides, one of which is a minor one and the other has a higher density than the metal, so that the expansion and contraction of the material cancel each other.

The metals of the first group (which experience an increase in volume during hydride formation) can from selected from the group of zirconium, hafnium, titanium, yttrium or rare earth metals, while calcium, strontium, ytterbium or europium are used as metals of the second group will. For example, the contraction observed in the formation of ytterbium hydride is about 13.5 percent by volume, and it is in the region of 19% for europium hydride.

The procedure used to produce such targets is known and encompassed per se the following measures:

1. Manufacture of relatively thick targets

The desired metal hydride mixtures are made from a powder mixture of metals of the specified groups (in such proportions that the change in density during the Hydrogenation is practically zero). So you can e.g. one made of 50% hafnium and 50% Ytterbium or a mixture formed from 55% neodymium and 45% ytterbium for this treatment Select. This metal powder mixture is then used in the desired form to be introduced into the target Isotope-containing hydrogen environment subjected to a hydrogenation reaction. The received The hydride mixture is then at high temperature in the presence of the same hydrogen isotope sintered in such a way that a compact tablet a few tenths of a millimeter thick and a slightly larger one Preserved diameter than would correspond to the diameter of the bundle of deuterons that hit it. This tablet is then inserted into a holder or base that conducts heat well.

In addition to high mechanical stability, the targets produced in this way have a noticeable

stop at the desired hydrogen isotope, which overall ensures a considerable service life. Finally, due to the thickness of the hydride layer, deuteron beams of high energy and thus large penetration depth can be used.

2. Manufacture of thin targets

As in the previous example, a powder mixture of metals from the two groups mentioned is used to form a compound or composition which does not undergo any dimensional changes during changes in the hydrogen isotope content. In addition, a holder or base of good strength or rigidity and excellent adhesion to the hydride as well as good thermal conductivity is achieved. This first polished and ultrasonically cleaned in pure alcohol base (10- ⁶ mm Hg; 500 ° C) is in a high vacuum at elevated temperature degassed. The two selected metals are then deposited in a high vacuum using conventional methods at a controlled speed (on the degassed substrate). The metal film obtained is then heated in a deuterium and / or tritium atmosphere until the desired amount of the isotope under consideration is absorbed. The targets obtained in this way show a considerably improved adhesion and higher resistance to the phenomenon known as “spraying” or “sputtering”.

Claims (4)

Patent claims: 1. Metal hydride-containing target for the generation of fast neutrons by bombarding with Deuterons, characterized by a layer made up of a mixture of hydrides at least one metal each from two different groups, one of which during the Hydrogenation shows an increase in volume and the other shows a decrease in volume. 2. Target according to claim 1, characterized in that the metals of the first group selected from the metals zirconium, hafnium, titanium, yttrium or rare earth metals will. 3. Target according to claim 1, characterized in that the metals of the second groups can be selected from the metals calcium, strontium, ytterbium or europium. 4. Target according to one of the preceding claims, characterized in that the respective Proportions of the metals of the first and second group are chosen such that the Material expansion and contraction during hydrogenation regardless of the hydrogen concentration mutually compensated in the target.