JPH0460320B2 - - Google Patents

Description

[Detailed Description of the Invention] Background of the Invention This invention produces ⁷ ₃ Li (p, n) ⁷ ₄ by colliding protons.
Regarding the lithium target for generating neutrons by the Be reaction, and further detecting the presence of selected substances in the ore, such as the gold content of the gold-bearing ore, by neutron activation analysis. Relating to a device for

In an actual gold ore classification plant, several
It is necessary to be able to process 10 tons of ore and therefore rapid analytical tools must be used. One suitable method is ¹⁹⁷ Au(n, n′γ) ¹
This is a neutron activation method that uses ^{the 97m} Au reaction to activate the gold present in the ore lump, and the ^197m Au nuclide generated in this way decays with a half-life of approximately 7.8 seconds and has an energy of 279 keV. emits gamma rays.
British Patent Specification Nos. 2055465B and 2101304A (respectively, U.S. Patent No. 4340443 filed May 27, 1982 and U.S. Patent Application Serial No.
No. 383686) discloses an apparatus for classifying gold-containing ores, in which
The ore mass is activated by the above reaction and the emitted gamma radiation is then detected and analyzed to assess the gold content of the ore.

Such ore classification plants require a powerful source of fast neutrons to cause activation, and one possible source is coating on a silver backing plate and being bombarded by protons. The target consists of a lithium layer. However, the impact effect generates heat and hydrogen in the target, which are detrimental to the structure of the target. In the targets mentioned above, hydrogen bubbles, for example, tend to form at the interface between lithium and silver.

SUMMARY OF THE INVENTION According to the present invention, a lithium target is provided that includes a relatively thin layer of lithium coating on one side of a backing plate made of metal, the metal does not form an alloy layer at the interface;
Additionally, hydrogen diffuses through the metal at a rate that does not create bubbles at the interface.

Preferably the backing plate is niobium. Desirably, channels are provided for the passage of cooling fluid upon thermal contact with the other side of the backing plate.

Thus, although the target according to the present invention provides a source of high-energy neutrons, it is expected that less damage will be sustained by the target than with known targets, and furthermore, even though the target has a significant thickness of alloy layer Since the lithium thickness is well defined due to the lack of formation, this target provides a relatively well defined energy range of neutrons.

The present invention also provides an irradiator for irradiating a mass of ore to detect the presence of selected materials within the mass, the irradiator including a lithium target as described above for neutrons.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1, a gold ore classification device comprises a rock crusher and classifier 2 into which mined ore is fed, in which the ore is crushed into agglomerates and further , a stream of clumps corresponding to a mesh size of approximately 75 mm emerges therefrom, while clumps smaller than a mesh size of approximately 35 mm are rejected. The stream of lumps is passed through an irradiation chamber 4 adjacent to a lithium target 5, which will be explained in more detail later, and then all the lumps have an energy of 279 keV resulting from the decay of the ^197mAu nuclide. Therefore, γ means that gold is present in the ore lump.
It is passed through a gamma ray detector assembly 6 configured to detect the rays. Each lump of ore is individually examined by the detector assembly 6 to determine whether its gold content is above or below some predetermined concentration. The critical concentration is typically
Within the range of 0.5 to 5ppm, e.g.
May be set to 1ppm. Each lump of ore is
Thereafter, the classifier 8 configured by the cable 7
In response to a signal from the detector assembly 6, each lump of ore is passed into one of two outlets depending on whether the concentration of gold in the lump is higher or lower than a predetermined concentration. Classify into one side of the flow.

The crusher and classifier 2 and the classifier 8 are of a type well known in the prior art, while the detector assembly 6 is disclosed in more detail in the above-incorporated specification and is machine and classifier 2, classifier 8, and detector assembly 6
is not the subject of this invention.

Referring to Figure 2, lithium target 5
forms one end of an evacuated beam tube 10 along which a 1 mA beam of protons with an energy of 4.5 MeV passes during operation of the apparatus of FIG. The target 5 includes a layer 12 of lithium coated with a thickness of 0.3 mm on one side of a circular plate 14 of niobium; Exists on the sides. Some of the conduits 16 are
It is defined through the plate 14 near the other side of the plate 14.

In operation of the apparatus of FIG. 1, a beam of protons is accelerated down beam tube 10 and impinges on target 5, and a cooling liquid such as water is added to conduit 16.
to remove heat from the plate 14. The temperature of target 5 is monitored and is 186℃.
This ensures that it remains below the melting point of lithium, and furthermore that the beam avoids moving over the surface of layer 12 and heating it locally.

As a result of the reaction of ⁷ ₃ Li(p,n) ⁷ ₄ Be, approx.
An intense flux of fast neutrons with energies between 0.6 MeV and 2.8 MeV is generated from the target 5 and irradiates the ore mass passing through the adjacent irradiation chamber 4 (see FIG. 1). The energy range of neutrons is
It is determined by the energy of the incident protons and the thickness of the lithium layer 12. The gold nucleus, i.e.
The cross section for activating ¹⁹⁷ Au is approximately 2.5 MeV
is maximum for a neutron with an energy of
Neutrons with energies between 0.6 MeV and 2.8 MeV can cause this activation, but activation by (n,p) reactions of other components likely to be present in the ore, such as aluminum and silicon, is It has insufficient energy to cause it. Neutrons with energies below about 0.6 MeV do not activate gold nuclei, but do cause activation, for example, by the (n, gamma) reaction of aluminum. Since no significant degree of alloy formation occurs at the interface between the niobium plate 14 and the lithium layer 12, its thickness is well defined and
It is selected so that neutrons with energies below 0.6 MeV are not generated.

These protons, which do not undergo the above-mentioned reaction with the lithium atoms, emerge from the lithium layer 12 into the niobium plate 14 with an energy of about 3.3 MeV, which is further converted into heat by collision with the niobium lattice. It fades and disappears. Thus, hydrogen atoms are generated in the niobium plate 14 (ie, protons whose velocity has been reduced) and further diffuse through the plate 14 to emerge from the side facing away from the incident proton beam. Therefore, there is no tendency for hydrogen to accumulate at the interface between the niobium plate 14 and the lithium layer 12.

Target 5 has been described as being cooled by passing a cooling fluid through conduit 16 defined through plate 14. Alternatively, grooves (not shown) may be defined on the side of the plate remote from the lithium layer 12, which grooves are connected to the copper shield plate so as to define conduits for passing the cooling fluid. It will be appreciated that it is covered by Additionally, a copper raised section (not shown) is brazed onto that side of the plate 14;
Additionally, it may be covered with a copper shield (not shown) to define a conduit for passage of cooling fluid.

The preferred material for plate 14 is niobium, but
Other materials such as copper may also be used as long as it does not form an alloy layer at the interface, and
It will also be appreciated that hydrogen diffuses at a sufficient rate at operating temperatures so that it does not accumulate at the interface and form bubbles.

[Brief explanation of the drawing]

FIG. 1 is a flow diagram of a gold ore classification apparatus including a lithium target according to the present invention. FIG. 2 is a cross-sectional view of the lithium target of FIG. 1. In the figure, 2 is a crusher and classifier, 4 is an irradiator, 5 is a target, 6 is a detector, 7 is a cable, 8 is a classifier, 10 is a beam tube, 12 is a lithium layer, 14 is a receiving plate, and 16 is a Shows the conduit.

Claims (1)

Claims: 1. A relatively thin layer 12 of lithium coating on one side of a metal backing plate 14, said metal not forming an alloy layer at the interface;
and a lithium target, characterized in that hydrogen diffuses through the metal at a rate such that no bubbles are formed at the interface. 2. The target according to claim 1, wherein the receiving plate 14 is made of niobium. 3. A target according to claim 1 or 2, comprising means 16 for cooling said receiving plate 14. 4 The cooling means 16 has a channel 1 for passing a cooling fluid during thermal contact with the receiving plate 14.
6. The target of claim 3, comprising: 6. 5. An irradiator for irradiating a lump of ore to detect the presence of a selected substance in the lump, which includes a lithium target as a neutron source, and the lithium target is attached to one side of the metal receiving plate 14. comprising a relatively thin layer 12 coated with lithium thereon, said metal not forming an alloy layer at the interface;
An irradiator characterized in that hydrogen diffuses through the metal at a rate such that no bubbles are generated at the interface. 6. The irradiator according to claim 5, wherein the receiving plate 14 is made of niobium. 7. The illuminator of claim 5, wherein said target includes means 16 for cooling said receiving plate 14. 8 The cooling means 16 has a channel 1 for passing cooling fluid during thermal contact with the receiving plate 14.
8. The illuminator of claim 7, comprising: 6.