US3280331A - Radiation shield having a plurality of strings rotatable between an open and closed position - Google Patents

Description

Oct. 18, 1966 c. c. ABT ETAL 3,280,331

RADIATION SHIELD HAVING A PLURALITY OF STRINGS ROTATABLE BETWEEN AN OPEN AND CLOSED POSITION Filed Nov. l5, 1963 INVENTORS Czlel 6.1987' United States Patent 3,280,331 RADIATION SHIELD HAVING A PLURALITY OF STRINGS ROTATABLE BETWEEN AN OPEN AND CLOSED POSITION Clark C. Abt and George F. Vanderschmidt, Cambridge,

Mass., assignors to the United States oi America as represented by the Secretary of the Air Force Filed Nov. 15, 1963, Ser. No. 324,141 3 Claims. (Cl. Z50-108) This invention relates to a radiation shield for use in areas of radiation of different energy levels.

One object of the invention is to provide, with a given amount of mass shielding, protection which may be used selectively for both high energy and low energy radiation.

Another object of the invention is to provide a radiation protective shield, from a given rnass of radiation shielding material, which will reduce the density of high energy radiation in one selected position and which will absorb substantially all of the low energy radiation in another selected position of theI shield.

These and other objects will 'be more fully understood from the following detailed description taken with the drawing, wherein:

FIG. l shows a conventional radiation shield for use in a field of high energy radiation;

FIG. 2 shows a conventional radiation shield with less mass than the device of FIG. l in a field of high energy radiation;

FIG. 3 is a schematic showing of a radiation shield according to the invention in its high energy shielding open position;

FIG. 4 shows the device of FIG. 3 in its low energy shielding closed position;

FIG. 5 shows a modification of the device of FIG. 3 in its high energy shielding position; and,

FIG. 6 shows the device of FIG. 5 in its low energy shielding closed position.

It is a well-known principle of nuclear physics that energetic particles such as electrons, protons, and neutrons penetrate a given type of mass shield to a depth proportional to their energies. If a threatening shower of, say, solar protons has an energy of up to 30 billion electron volts (b.e.v.), then mass shielding sufficient to stop 30 b.e.v. energies, as shown in FIG. 1, will stop all of the particles, and mass shielding not suciently thick to stop 30 b.e.v. particles, as shown in FIG. 2, will let all the 30 b.e.v. particles through with reduced energy. This is sometimes called the principle of range of penetration of 'high energy particles. Now, if there is a fixed area to be protected against radiation shielding, and only a given quantity of shielding material available, it has heretofore ybeen assumed that the optimum distribution of this material is in a uniform layer over the area to be protected. This is not necessarily the case and, as a matter of fact, in those cases where the thickness of a uniform layer of material available for shielding is less than the range of penetration of the expected radiation, the shielding will not only be ineffective but may actually increase the hazards to human Ibeings relying on it by reducing the energy of the penetrating radiation to a lower level at which it may have enhanced biological effectiveness.

According to this invention, slats or strips of shielding material are uniformly spaced over the area to be shielded.

While it is true that radiation enters through the space between the slats, the slats can now be perhaps some two times as thick as the original uniformly distributed shielding material and, if the original uniformly distributed material was just over half as thick as it needed to be to stop the radiation of a given energy, then if half the area is covered with strips twice the thickness of the original uniform area, the effective flux will be cut in half. The energy of the radiation that passes through the gaps between the slat shield will of course be undiminished, but p the flux density will *be cut in half and, therefore, the biological effectiveness of the radiation will be correspondingly reduced. In the conventional application, where the same weight of shielding was applied uniformly, the flux was not diminished at all since the' energy of the particles was suiicent for all of them to pass through the shielding, the only eect being the reduction of the energy of the radiation passing through the shielding. The reduction of this particle e'nergy could enhance its lethality to biological organisms at worst and, at best, would leave its lethality relatively undiminished.

Since a man might be killed if he were to remain stationary behind such a shield, it is necessary that the halfarea protected by the strips be mixed somehow with the half-area that is unprotected. This can usually be achieved by the movement of the man behind the shield but, if this is not possible, movement of the shield may be required. In many cases, however, the shield will be used with vehicles that are moving with respect to the radiation source so that no additional movement of the shield is required. In space applications the shield may be rotated around the space craft or, in some cases, the space craft itself may be rotated so that the radiation will not be concentrated in certain strip areas of the body.

Referring now to FIG. 3 of the drawing which shows a Slat shielding device according to the invention, a plurality of slats 10 of shielding material are spaced apart by a distance equal to less than half of their thickness T. Each of the slats 10 is geared to a rack shown schematically at 11 by means of gears 12. A shield operating mechanism 13 is provided to selectively rotate the slats from the opened position shown in FIG. 3 to their closed position as shown in FIG. 4. It is obvious that other means may be provided for rotating the slats. In the position shown in FIG. 3, which is for use in high energy radiation, the slats are in their open position so that they will reduce the flux density of the radiation passing the shield.

If the device using the shielding is moved to a low energy radiation environment, the slats may -be rotated to the position shown in FIG. 4. The spacing of the slats should be such as to provide sutiicient overlap to provide protection for the low energy radiation t0 be encountered.

Instead of overlapping sections, abutting sections may be provided as shown in FIGS. 5 and 6. In this arrangement, the slats 20 have matching curved ends to permit rotation between their closed abutting position and their opened position. rlhe operating means may be the same as in FIGS. 3 and 4.

There is thus provided a radiation shield which will provide substantially complete protection from low energy radiation in one position and which can be rotated to a second position to provide partial protection from high energy radiation without a change in the total mass.

While certain specific embodiments have been described, it is obvious that numerous changes may be made without departing from the general principle and scope of the invention.

We claim: 1

1. A device for shielding against energetic particles such as electrons, protons and neutrons comprising, a plurality of slats of shielding material, having a thickness approximately equal to twice their width, rotatably mounted and spaced from each other by a distance not greater than half their thickness and approximately equal to their width, and means for rotating said slats between an open and closed position to provide a reduction in the flux density of high energy radiation in the open position of said slats and to provide substantially complete absorption of low energy radiation in the closed position of said slats.

2. A device' for shielding against energetic particles such as electrons, protons and neutrons comprising, a plurality of slats of shielding material, having a thickness approximately equal to twice their width, rotatably mounted and spaced from each other by a distance not greater than half their thickness and approximately equal to their width, and means for rotating said slats between an open position wherein the slats are spaced apart in substantially parallel relation to each other to provide a reduction in the flux density of high energy radiation and to a closed position wherein there is no space between the 4slats to provide substantially complete absorption of 10W energy radiation.

3. The method for obtaining optimum radiation shielding effectiveness with a fixed mass of shielding material comprising, spacing a plurality of elongated slats of radia tion shielding material, having a thickness approximately equal to twice their width, apart by a distance of not greater than one-half the thickness of the slats and with the spaces between the slats approximately equal to the Width of the slats, providing rotation for said slats about their longitudinal axis to thereby permit reduction of the ux density of high energy radiation in one position of said slats and substantially complete absorption of low energy radiation in another position of said slats.

References Cited by the Examiner FOREIGN PATENTS 635,489 3/1928 France,

RALPH G. NLSON, Primary Examiner.

S. ELBAUM, Assistant Examiner.

Claims (1)

1. A DEVICE FOR SHIELDING AGAINST ENERGETIC PARTICLES SUCH AS ELECTRONS, PROTONS AND NEUTRONS COMPRISING, A PLURALITY OF SLATS OF SHIELDING MATERIAL, HAVING A THICKNESS APPROXIMATELY EQUAL TO TWICE THEIR WIDTH, ROTATABLY MOUNTED AND SPACED FROM EACH OTHER BY A DISTANCE NOT GREATER THAN HALF THEIR THICKNESS AND APPROXIMATELY EQUAL TO THEIR WIDTH, AND MEANS FOR ROTATING SAID SLATS BETWEEN AN OPEN AND CLOSED POSITION TO PROVIDE A REDUCTION IN THE FLUX DENSITY OF HIGH ENERGY RADIATION IN THE OPEN POSITION OF SAID SLATS AND TO PROVIDE SUBSTANTIALLY COMPLETE ABSORPTION OF LOW ENERGY RADIATION IN THE CLOSED POSITION OF SAID SLATS.

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