ES2238157A1 - X ray shield glass screen lead thickness equivalent meter has a cursor based graduated scale with a support - Google Patents

Abstract

Rule of reflexible calculation and method to measure the thickness lead equivalent of the used crystals like screens for the protection of the persons against X rays comprises measuring thickness of a crystal by reflectance in the polished parallel faces of person, with reglilla and magnifying cursor. Rule of reflexible calculation and method to measure the thickness lead equivalent of the used crystals like screens for the protection of the persons against X rays comprises measuring thickness of a crystal by reflectance in the polished parallel faces of person, with reglilla and magnifying cursor, characterized to have a bracket that allows to its support in the crystal with a non-limitative inclination of 45[deg], consisting of bracket of a cut in its bottom portion and for being broader in the ends of his bottom portion, with the intention of allowing the slippage of the cursor throughout the rule while supported one in the crystal stays this one, in such a way that mentioned ends also serve as top for the slippage of the cursor.

Description

Flexible calculation rule and method to measure the equivalent lead thickness of the crystals used as screens for the protection of people against X-rays.

The technical sector to which it belongs is invention is that of manufacturing, construction, assembly and use of crystals as screens for the protection of people against x-rays

Background of the invention

The usual determination of protection against X-rays of the crystals used for this purpose leads to out using x-ray sources or generators, detector radiation and evaluation of the dose of radiation that reaches the other glass side; both the procedure and the devices are well known and described in the literature.

The method and device that constitutes the object of this invention, constitutes an alternative to said method conventional, when radiation generators are not available and you want an approximate check of the crystals, being able to make said estimate in a simple and fast way, with a degree of approximation sufficient.

The method used here is based on the crystal thickness determination based on the optics of reflection on the front and back faces of a face crystal polished parallels, constituting a kind of calculation rule that handles parameters related to this measure and magnitudes related to X-ray protection. We do not know background of any device or method, other than the outlined above, applicable to the proposed problem, although yes of ingenuities that use physical principles that are partially used here.

Thus, as regards the determination of thickness by the cited reflection method there are some precedents of this type of invention; let's review the patent US3320849 (1967) consisting of a sheet with some signs conveniently drawn and spaced whose observation with a 45 degree inclination after reflection on both sides of the glass allows, by elementary optics, the determination of the thickness of the crystal; the patent is restricted to ordinary glass and most usual thicknesses of commercial crystals. There are others patents that describe more sophisticated devices, although based on similar physical principles, which either pursue obtain greater accuracy in thickness measurement or try of said measure in more complex situations; so it is worth mentioning example, patents JP2000111317 (2000), RU2141621 (1999), US1875665 (1932), US1756785 (1930), US1503543 (1924).

As regards the calculation rules, these are well known and there are a variety of them applicable to very different situations: well, a ruler with magnifier cursor it can be found, for example, in US4757616 (1998); in Regarding our field of application, rules are known of application calculation at different magnitudes related to the radiation protection; especially the GB901502 patent (1962), is applicable to the calculation of protective screens against radioactive sources However, such rules are only of application to calculate and not to perform physical measurements of objects or substances, such as crystals, therefore, not They apply to the proposed problem.

In short, none of the devices mentioned here is applicable to the protection assessment against X-rays of the crystals used in this field of activity and the device proposed here constitutes a solution simple alternative to the proposed problem, in the absence of X-ray generators and radiation monitors.

Description of the invention

The protection of a crystal against X-rays it depends on the characteristics of the radiation source, on its thickness and its mass attenuation coefficient; for you do monoenergetic, the equivalent linear thickness of a crystal with relation to lead, that is the thickness of glass that attenuates exactly the same as a given thickness of a lead sheet under given conditions, it is given by the expression:

x_ {g} = [(\ mu / \ rho) _ {Pb} / (\ mu / \ rho) _ {g}] \ (\ rho_ {Pb} / \ rho_ {g}) \ x_ {Pb}

where (µ / \ rho) g and (\ mu / \ rho) Pb x are the attenuation coefficients crystal and lead masses respectively y x_ {g} y x_ {Pb} the equivalent linear thicknesses of both materials; he mass attenuation coefficient of the crystal, can be calculated with good approximation attributing additive properties, so that:

(\ mu / \ rho) _ {g} = \ Sigma \ g_ {i} \ (µ / \ rho) i

where g_ {i} is the mass fraction of the crystal to which the element whose coefficient of Mass attenuation is (µ / \ rho) i. So, based on what above and to solve the problem of knowing the equivalence in lead of a given crystal, is based on the following three premises, which can be considered as justified approximations practices;

to)

Be consider that the mass attenuation coefficient of the crystal is between the crystalline base and the lead, to the extent that the addition of oxides of this metal replaces the base.

b)

The adding lead to the crystal increases its density and consequently its  refractive index; a linear expression can be used with good approximation between these last two magnitudes (n = a \ rho + b).

C)

The lead equivalence of the crystal increases proportionally to its thickness.

The thickness of the glass can be measured by the Reflection method on the front and back sides of it. The density of ordinary leaded glass, such as recommended for X-ray protection, can be known assuming the relationship linear indicated in b); although this relationship is not necessarily conversely true, that is, the procedure is not application for all crystals, yes it is for those used as protective screens like the ones at hand, based on a high content of lead oxides.

Therefore, by the method described, for a type of given crystal, of known density and refractive index, is possible to determine its equivalence in lead (x_ {Pb}) by measurement of its thickness x 'g, the first being expressed in direct proportionality relationship with the second:

x_ {Pb} = k \ x '{g}

where k is a coefficient characteristic of each crystal that can be expressed in mm of lead / mm of crystal.

When the refractive index of the crystal is not known, but its thickness x_ {g}, the joint knowledge of this thickness and that measured by reflection on the parallel faces of the Crystal allow you to determine its equivalence in lead. An expansion graph of these considerations allows to write this equivalence as follows:

x_ {Pb} = \ alpha \ x_ {g} + \ beta \ x '{g}

that is, as a weighted sum to α and β factors of the actual and measured thicknesses. This allows to measure the equivalent thickness in lead sought by a simple operation of sum of scales.

These considerations provide a basis conceptual enough to understand the basics of this invention, which consists of a device in the form of a rule of linear type calculation that is reflected in the intended crystal measure, thus combining measurement and calculation into a single instrument necessary to measure lead equivalence of crystals used as screens for. the protection of people against x-rays. Calculation rules are widely known therefore its description is not necessary; however, the rule of  This invention has a support that allows its support in the glass with a certain inclination, being your choice preferred 45º. The cursor of the rule, which is provided with vertical stripes visible both from the front and rear of the ruler, can slide between two protruding stops of the rest of the rule to allow it to slide.

The back of the ruler bears a drawing in form of two semi-straight joined by one end and forming an angle acute, one of them horizontal and the other inclined and without marks or graduation. When these lines are reflected on the previous faces and back of a glass with parallel polished faces a reflection image in which the oblique line reflected in the first face of the same intersects the horizontal line reflected on its back face at a point that is far from the end a certain quantity d 'related to the thickness of the crystal and its index of refraction; the inclination angle of both lines can be chosen so that, for a given index crystal of refraction, the quoted amount matches the thickness of the crystal and as a non-limiting extension can make that value match twice that thickness, for greater clarity in the intersection display.

The front part of the ruler has several scales names, all metrics with scale support rectilinear, whose number depends on the number of situations that want to contemplate and built on the basis of relationships functional indicated above; so, several of them respond to the relation x_ {Pb} = k x 'g and allow reading in them directly the lead equivalence of the crystal (by the intersection of the ruler of the ruler with the scale) when the index of real refraction of the same coincides with the one for which it has been designed the scale; these scales are designed for types of common well-known crystals used in this field of technique.

The rest of the scales are applied to crystals. whose thickness is known, thus obtaining, in general, a greater precision than the standard value provided by the scales above and are designed so that they represent together the expression x_ {Pb} =? x_ {g} +? x 'g; the half of them are millimeter scales (αx_ {g}), to read in them the actual thickness of the glass, while the other half are designed to read in them the equivalent thickness in lead (βx 'g). Both are used together to give the lead equivalent of the crystal for conditions given. These scales are located in the lower part of the part front of the ruler, so that scales of the type βx 'g remain in the sliding slide, while the others are located in the fixed section of the ruler support, above and below the slider.

The objective of the back cursor stripe is determine exactly the cut-off point of the two images that they are formed by reflection on the parallel faces of the crystal, while its front stripe, which is coincident in situation geometric with the posterior, it serves to determine the intersection With the front scales.

The different lines, scales and brands of the rule can be recorded in it, or they can be adopted any of the methods used for this purpose in the graphic arts industries or any others in this sector industrial.

Brief description of the drawings

For a better understanding of this invention are attached on a separate sheet drawings in which non-limiting example title, the essence of the present invention and a practical case of realization of the same.

Thus, Figure 1 shows a rear view of the ruler (4) with its cursor (1) and the drawing formed by the half-lines (2 and 3). Figure 2 is a front view of the same in which appreciate, in addition to the cursor (14), the name scales (5 a 12), its location with respect to the slide and the supports lower (13) of the rule with its corresponding setback for allow cursor sliding. Figure 3 is an image of the straight profile: the bottom detail shows the supports protrusions (23) that support the rule in the glass with 45º shear cut, allowing the sliding of the cursor (25). The upper detail shows the cross section of the dovetail gutter (24). Figure 4 shows the image that is observed by reflection in the glass (18). Be appreciate the reflection of the inclined lines on the first face of the crystal (19), on the back (20), the reflection of the cursor (22) on the first face of the glass; also appears the distance d '(21) of intersection of the cursor line with the image (19). Figure 5 is an image of the rule -support (17) and cursor (16) - resting on the glass (15), with an inclination of 45º.

Description of a preferred embodiment

An example is described below. limiting of the present invention. It consists of a device in form of linear type calculation rule that can be supported by the glass with an inclination of 45º, by means of a support (13) that It consists of a 45º cut in the bottom of its lower part (2. 3). The rule is rectangular and preferred but not limited to plastic material or any other material appropriate that exists in the market. The sliding slide (24) is accessible only by its front, so that the rear is completely smooth The cursor (1 and 14) of it has paths vertical stripes visible both from the front and back of the ruler, both stripes being geometrically coincident; he Cursor support consists of two transparent sheets, preferably of plastic material, its front face being domed, in order to serve as a magnifier. The rule is more wide at the ends of its bottom, thereby configuring the supports indicated above, in order to allow cursor slide along the ruler while holding this supported on the glass and in such a way that said ends serve also stop for cursor sliding (13).

The back of the ruler has two straight lines (2 and 3) coincident by the vertex forming an acute angle of 21.81º, which has been chosen so that the quantity d '(21) match twice the thickness of the glass glass ordinary (n = 1.52), which constitutes the preferred option of the invention; one of them is horizontal and constitutes a segment whose ends match the extreme positions of the back stripe of the cursor. The other line is oblique and the set formed by the two straight lines is located and centered on the back of the ruler, so that the horizontal line is near the bottom of the same and the intersection vertex of both lines is of the right side when the ruler is observed from its rear.

The front of the ruler has been engraved eight Nominal scales The slide rule divides the rule into three zones and the location of these scales is as follows: four of them (5,6,7 and 8) are located in its upper part, which is the wider, two of them (9 and 10) in the reglilla (upper part and lower, respectively) and the other two (11 and 12) in the part lower, so that scales (8) and (11) border below and by up respectively with the slider, remaining facing the scales (9) and (10) of it. The scales are located in such a way that its zero coincides with the extreme position left of the front stripe of the cursor, when the ruler is observed from its front part; from the same perspective and for its identification and easy reading, on the left margin of the rule may appear the letter or alternatively the title representative of the scale and on the right margin the magnitude that represent or units of measure.

\hbox{( clear-Pb ;}

n=1,54; \rho=1,6 gr/cm^{3}) y la tercera (7) para cristal plomado de densidad intermedia entre los utilizados para este propósito (n=1,76; \rho=4,8 gr/cm^{3}) y para una tensión máxima de 150 kV (para tubos de rayos X). Las cinco escalas siguientes representan conjuntamente la expresión del tipo x_{Pb} = \alpha x_{g} + \beta x'_{g}; tres de ellas (8, 11 y 12) son escalas milimétricas (\alphax_{g}), para leer en ellas el espesor real del cristal, mientras que las otras dos escalas (9 y 10) están diseñadas para leer en ellas la equivalencia en plomo (\betax'_{g}). Dos escalas (8 y 9) se utilizan conjuntamente para dar el espesor equivalente en plomo del cristal ordinario y plomado para una tensión máxima de 150 kV; otras dos escalas (8 y 12) se utilizan conjuntamente para dar este espesor para una fuente radiactiva de Co-60 y finalmente otro par de escalas (10 y 11) se utilizan conjuntamente para el mismo propósito para una fuente radiactiva de Cs-137.The eight scales are metric scales with rectilinear scale supports and are constructed based on the functional relationships indicated above; the first three are of the type x_ {Pb} = kx 'g, the first (5) being constructed for ordinary glass (n = 1.52; \ rho = 2.5 gr / cm3). The second scale (6) is for use with leaded acrylic visors

 \ hbox {(clear-Pb;} 

n = 1.54; ? = 1.6 gr / cm3) and the third (7) for intermediate density leaded glass among those used for this purpose (n = 1.76; \ rho = 4.8 gr / cm ^ { 3}) and for a maximum voltage of 150 kV (for X-ray tubes). The following five scales together represent the expression of the type x_ {Pb} =? X_ {g} +? X 'g; three of them (8, 11 and 12) are millimeter scales (? x_ {g}), to read in them the real thickness of the crystal, while the other two scales (9 and 10) are designed to read the equivalence in them in lead (βx 'g). Two scales (8 and 9) are used together to give the equivalent lead thickness of ordinary and leaded glass for a maximum voltage of 150 kV; two other scales (8 and 12) are used together to give this thickness for a radioactive source of Co-60 and finally another pair of scales (10 and 11) are used together for the same purpose for a radioactive source of Cs-137.

All scales are linear with the following step values and graphic range: (5) -0.02 mm Pb; 3,714 mm-, (6) -0.02 mm Pb; 0.845 mm-, (7) -0.2 mm Pb; 0.953 mm-, (8) -0.2 mm; 0.375 mm-, (9) -0.2 mm Pb; 0.241 mm-, (10) -0.2 mm Pb; 0.257 mm-, (11) -0.2 mm; 0.406 mm-, (12) -0.2 mm; 0.425 mm-.

Thus, when we place the rule on viewfinder (15 and 18), the intersection is observed by reflection of the horizontal line reflected on the second face of the glass (20) with the oblique reflected on the first face (19). If it takes the back cursor to this intersection, the intersection of front cursor with scales (5), (6) and (7) give their thickness equivalent in millimeters of lead, for ordinary crystal, leaded plastics or acrylics ("clear-Pb") and medium density leaded glass. Also displacing the ruler mobile, until said intersection, so that the origin of the scales (9) and (10) now match the front cursor, the rest of the scales allow us to know more accurately said lead equivalence of the crystal; thus, for a maximum tension of 150 kV reads the actual glass thickness on the scale (8) and for Co-60 on the scale (12) and in both cases aided by cursor the equivalent thickness in lead is read on the scale (9); for Cs-137 the scales (11) are used (thickness real) and (10) (lead equivalence) respectively, with the same process.

Indication of the manner in which the invention is susceptible to industrial application

The present invention is susceptible to industrial application in the verification of the correct protection against x-rays of the most commonly used crystals as screens for this purpose (ordinary glass, leaded glass and leaded acrylic). It constitutes a practical and simple alternative to use of radiation sources and monitors in their absence, especially when a quick and indicative measure of Proper protection of these crystals.

Claims (4)

1. Rule of flexible calculation and method to measure the equivalent lead thickness of the crystals used as screens for the protection of people against X-rays, which is the type of those that measure the thickness of a crystal by the reflection method on the polished parallel faces thereof, with a slide (24) and magnifying cursor (1 and 14), characterized by having a support (13) that allows its support on the glass with a non-limiting inclination of 45º, said support consisting of a cut in zi7alladura of its lower part (23) and for being wider at the ends of its lower part, in order to allow the cursor to slide along the ruler while maintaining it resting on the glass, in such a way so that these ends also serve as a stop for the sliding of the cursor. 2. A flexible calculation rule and method, according to claim 1, which has a drawing in the back part in the form of two semi-straight lines joined by one end, one horizontal (3) and the other inclined (2) forming an acute angle , chosen so that the intersection of the two images that are formed by reflection of this image on the front and back sides of the glass, when these are observed under a certain angle, give an integer multiple of the thickness of the crystal, characterized by not having of marks or any graduation, being able to determine said intersection through the sliding cursor (1). 3. A flexible calculation rule and method, according to claims 1 and 2, characterized by presenting several nominal scales (5 to 12), all of them metric with rectilinear scale supports, which in conjunction with the thickness measurement of the crystal allows to know its equivalent thickness in lead, for conditions given and constructed in accordance with the functional relationships: x_ {Pb} = kx '_ {x} {x} {pb} = \ alpha x_ {g} + \ beta x' g, where x_ {Pb} is the equivalent lead thickness of the crystal, x 'g and x_ g the measured and actual thicknesses, respectively, and where k,? and? are constants that have been determined assuming additive properties to the mass attenuation coefficient of the crystal, proportionality between the lead equivalence of the crystal with its thickness and linear relationship between the density of the leaded glass (used in this field of the technique) and its index of refraction. 4. The flexible calculation rule and method according to claims 1 to 3, characterized in that several scales are constructed on the basis of the functional relationship: x_ {Pb} = kx 'g, these scales remaining in the fixed part of the rule support and because the rest of the scales are built on the basis of the functional relationship: x_ {Pb} = \ alpha x_ {g} + \ beta x '_ {g}, with half of the latter millimeter scales being they represent the summing αx_ {g}, while the other half obey the summing βx 'g, leaving the first half in the fixed section of the support and the second half in the sliding slide.