Radiant energy – Radiation controlling means
Reexamination Certificate
2000-08-30
2002-09-03
Berman, Jack (Department: 2881)
Radiant energy
Radiation controlling means
C378S034000, C378S084000, C378S145000, C451S056000, C385S031000, C250S251000
Reexamination Certificate
active
06444994
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field of the Invention
The present invention relates to an apparatus and method for processing the components that constitute a neutron lens for converging or diverging a neutron beam.
2. Prior Art
A neutron beam has the following features which are different from an X-ray or a photon, (1) strong mutual reaction with atomic nuclei, (2) similar energy and wavelength thereof to those of motions or structures at the atomic level, (3) retention of a magnetic moment, (4) intense penetrating power, etc. Therefore, when the position of an atomic nucleus is to be studied, for instance, to have information about the position of a hydrogen atom in an organic material, which is very difficult to measure by an X-ray diffraction method, a diffraction experiment using a neutron beam is indispensable. In addition, because the spin of a neutron is ½ with a magnetic moment, the magnetic structure of a substance can be investigated conveniently. Furthermore, when the interior of a large object such as an industrial product is to be studied using radio active rays, because a neutron beam has a high penetrating power, fluoroscopy can be used.
However, because neutron beams cannot be generated easily, the sites are limited to nuclear reactors, accelerator facilities, etc. Consequently, a neutron beam must be guided efficiently from the neutron source to the application device in order to irradiate a small sample with a high-density neutron beam. For this purpose, it is essential to have a technology such that the neutron beams can be made parallel and then to make the beams converge sharply.
Recently, the aforementioned technique using neutron beams has been attracting wide attention for analysis etc., and the same applicant as for the present invention has proposed an element for converging or diverging a neutron beam (Japanese patent application No. 60630/1999, not published). In the following paragraphs, this element is called a “neutron lens.”
FIG. 1
shows the principle of refraction of a neutron beam by a substance. Mutual reaction between the neutron and the substance occurs mostly with the atomic nuclei contained in the substance and as a result of this reaction, incident neutrons lose part of their kinetic energy when they enter the substance, and the neutrons are slowed down tangentially and normally to the surface boundary of the substance. Therefore, as shown in
FIG. 1
, a neutron beam entering obliquely through the boundary surface of the substance is refracted with a refractive index of less than
1
. At this time, substances which are known to have a refractive index of less than 1 for a neutral beam include O, C, Be and Fe among those with naturally occurring isotopic concentrations, and deuterium D among separated isotopes.
FIG. 2
shows the principles of a neutron lens. This figure illustrates the condition in which a beam of neutrons (beam
16
) is incident to a sheet-like member
11
. On the surface of the sheet-like member
11
straight protrusions
12
are formed each of which is composed of a substantially vertical surface
14
and an inclined surface
15
. A neutron beam
16
entering the inclined surface
15
of the straight protrusion
12
is refracted with an index smaller than 1 as shown in FIG.
1
. However, the angle &dgr; of a single refraction is so small that, for instance, when the sheet-like member is composed of polytetrafluoroethylene (PTFE) with a high neutron transmission rate and the inclined surface
15
of the straight protrusion
12
makes an angle &agr; of 45° to the surface of the sheet-like member
11
, the angle of refraction &dgr; of a neutron beam with a wavelength of 14 Å impinging vertically onto the sheet-like member
11
is only 0.14 mrad.
FIG. 3
is an isometric view of a neutron lens capable of converging neutron beams, and
FIG. 4
shows the section through the line A—A of the lens. The neutron lens is composed of a main portion
20
and upper and lower ring-shaped outer frames
21
,
22
that hold the main portion. The neutron lens is assembled by fastening screws
24
into pins arranged between the two ring-like outer frames
21
,
22
hat sandwich the main portion
20
.
FIGS. 5A and 5B
show the structure of the sheet-like components of the main portion
20
. The main portion
20
is constructed by laminating a number of sheet-like components
25
each of which is provided with a hole
32
at the center thereof. The closer the sheet-like component is to the top, the larger is the hole bored in the center, and there is no hole in the center of the bottom sheet-like component. Therefore, the main portion is shaped like an earthenware mortar, that is, the center is a concave cone shape. In the example shown in
FIG. 4
, there are
33
sheet-like components
25
laminated together. Reference numbers
33
a
to
33
d
indicate holes for the pins
23
.
In
FIGS. 5A and 5B
, the sheet-like component
25
is composed of a thin sheet with ring-shaped protrusions
31
which have a triangular shape in section, formed coaxially and continuously in the radial direction. The inclined surface
3
A of a ring-shaped protrusion
31
with a triangular shape in section, forms an incident surface inclined to the axis of the incoming neutron beam, and the rings face inwards in coaxial circles, that is, towards the center line of the neutron lens.
Neutron beams, traveling in a direction parallel to the axis of the neutron lens, shown in
FIGS. 4
,
5
A and
5
B, enter through the inclined surfaces of the ring-shaped protrusions
31
formed on each sheet-like component, therefore the beams are deflected towards the center line of the neutron lens. Neutron beams entering near the center line are deflected through smaller angles because the beams pass through a relatively small number of ring-shaped protrusions, however, neutron beams entering near the outer periphery are deflected more as the beams penetrate a larger number of ring-shaped protrusions. Consequently, this neutron lens performs a similar function to that of a convex lens in an optical system, and can concentrate the neutron beams into a small area.
If the inclined surfaces
31
a of the ring-shaped protrusions
31
are made in outward facing concentric circles in the opposite way to
FIGS. 5A and 5B
, the neutron lens can function as a concave lens does in an optical system with the same configuration as shown in
FIG. 4
, thereby neutron beams can be made to diverge.
The sheet-like component
25
should be formed using a substance that has a refractive index of less than 1 for a neutron beam as described above. In the case of elements with naturally occurring isotopic compositions these are substances including the elements O, C, Be and F, and deuterium D in the case of enriched isotopes. Practical materials for these substances are the aforementioned polytetrafluoroethylene (PTFE), graphite, neutron-modified polyethylene wherein the hydrogen is changed to deuterium, etc.
Of these materials, graphite (hereinafter simply called as carbon) is readily available at a rather low cost, therefore, it is required that the above-mentioned sheet-like components should be formed from carbon plates.
However, carbon has the problem that because of its hardness and brittleness, it cannot be machined into the preferred shape by a conventional means of processing, for instance, by cutting, as the edge of the ring-shaped protrusion
31
becomes chipped. Furthermore, a large number of sheet-like components
25
must be stacked together to produce a neutron lens, therefore the thinner the sheet-like components
25
, the better it is to make the neutron lens small, that is, it is desirable to make the sheets as thin as about 1 mm. However, a thin carbon sheet suffers from the problem that it is damaged even by the small machining force caused by machining. In addition, to precisely deflect neutron beams, the inclined surfaces
31
a
of the ring-shaped protrusions
31
should be made very accurately. In addition, to transmit the neutron beams with minimum losses, irr
Morita Shinya
Moriyasu Sei
Ohmori Hitoshi
Shimizu Hirohiko
Yamagata Yutaka
Berman Jack
Fernandez Kalimah
Griffin & Szipl, P.C.
Riken
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