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Thursday, October 20, 2005

The great achievement (El gran logro).


When one reads critically the work of Pierre of Latil: “Enrico Fermi. 1966. The man and his theories”. P.S. Erickson, Inc. N.York. Library ICPNA. Lima-Cercado. Code: B539.7L35, notices themselves of the enormous influence of this wise Italian,http://www.astrocosmo.cl/biografi/b-e_fermi.htm, on the modern processes of teaching-learning, that go since their school epoch, very influenced by their tutor: the friend of family and engineer A. Amidei, the conversations maintained with their friend and disciple: Emilio Segré, later also Nobel prize (by the discovery of the antiproton), their investigations, their full family life and their enormous practical spirit. Today I will comment and I surrender very intense, the Chapter: X (pp, 100-125), where they are described in detail, the arduous given steps, for the structuring of the first controlled nuclear reaction in chain, prior step for the subsequent construction of the atomic bomb. In the middle of 1939, L. Szilard, E. Wigner and E. Teller, requested to A. Einstein, their mediation before the president D.Roosevelt, in order to obtain helps for the investigations that were carried out around the fission of the uranium. By then it was large the pessimism, few wanted to help economically to whom they worked in nuclear fission, because although they had general concepts, to pass from there to the forge of the chain reaction, was an almost utopian task. More, as always it has happened, in 1939, emerged a practical, immaculate, logical, and serene mind, capable to order coherently all that was previously known.

Rutherford first and later Hahn and Strassmann, after to bombard with electrons the atomic nucleus, would obtain emissions of alpha radiation. By its side, Fermi after to bombard the atomic nucleus with neutrons, would obtain radiation beta. Although bombarding uranium, additional neutrons were obtained, themselves did not manage to produce reactions been self-sustained, because most neutrons were lost, absorbed by the hydrogen (H), of the water, being become deuterium (D). Joliot and their french group they tried to negotiate this difficulty employing heavy water. The D, that replaced the H, did not grasp neutrons. However the alone heavy water was manufactured in Norway and its transportation to USA, was very difficult. The solution would come then from the hand of the practical spirit of Fermi, who began covering uranium with graphite, since the nucleus of the coal having the double one of mass that the H, did not absorb neutrons. Fermi consumed a lot of energy trying to obtain enough pure graphite, to eliminate its impurities and to impede that the radiation, itself to spread for the city.

To build the first atomic pile, Fermi covered uranium oxide dust by aluminum, and putting it to the interior of the graphite. As in spite of this adaptation, they continued being lost a 12% of neutrons, Fermi decided to add more graphite to the battery. This, growed up (in the interior of a squash field, of Chicago), and came be 6 meters tall. To impede the radiation, the Goodyear covered with sheets of rubber the sports field. 4 powerful bars of cadmium (absorbent of neutrons), that facilitated or stopped (according to they were placed or withdrew), the chain reaction. When on December 2, 1942, the first chain reaction controlled was produced, Fermi said: “the fission has begun”. E. Wigner, brought then a bottle of Chianti beverage immediately for all the presents polished by the dust of coal, writing subsequently its names around the empty bottle. A. H. Compton chief of the project in Chicago said cryptically (on account of the war), to its superiors “the Italian navigator has set foot in the new world”. On the other side they answered: “and how are the natives behaving”...” very well”.
El gran logro

Cuando uno lee críticamente la obra de Pierre de Latil: “Enrico Fermi.1966. The man and his theories”. P.S. Erickson, Inc. N.York. Biblioteca ICPNA. Lima-Cercado. Código: B539.7L35, se percata de la enorme influencia de este sabio italiano, sobre los modernos procesos de enseñanza-aprendizaje, que van desde su época escolar, muy influenciada por su tutor : el amigo de familia e ingeniero A. Amidei, las conversaciones sostenidas con su amigo y discípulo : E.Segré, más tarde también premio Nobel (por el descubrimiento del antiprotón), sus investigaciones, su vida familiar plena y su enorme espíritu práctico. Hoy comentaré un capitulo muy intenso, el X (pp 100-125), donde se describen en detalle, los arduos pasos dados, para la estructuración de la primera reacción nuclear en cadena, controlada, paso previo para la posterior construcción de la bomba atómica. A mediados de 1939, L. Szilard, E.Wigner y E Teller, solicitan a A. Einstein, su intermediación ante el presidente D.Roosevelt, a fin de conseguir ayuda para las investigaciones que se realizaban en torno a la fisión del uranio. Por entonces era grande el pesimismo, pocos querian ayudar económicamente a quienes trabajaban en fisión nuclear, porque aunque se tenían conceptos generales, pasar de ahí a la forja de la reacción en cadena, era una tarea casi utópica. Más, como siempre ha sucedido, en 1939, emerger1a una mente serena, lógica, pulcra y práctica, capáz de ordenar coherentemene todo lo conocido.

Rutherford primero y más tarde Hahn y Strassmann, trás bombardear con electrones el núcleo atómico, conseguirían emisiones de radiación alfa. Por su lado, Fermi trás bombardear al núcleo atómico con neutrones, obtendría radiaciones beta. Aunque bombardeando uranio, se conseguían neutrones adicionales, no se lograba producir reacciones autosostenidas, porque la mayoría de neutrones se perdían, absorbidos por el hidrógeno (H), del agua, siendo convertidos en deuterio (D). Joliot y su grupo francés trataron de sortear esta dificultad empleando agua pesada. El D, que reemplazaba al H, no captaba neutrones. Empero el agua pesada solo se fabricaba en Noruega y su transporte a USA, era dificil. La solución vendría entonces de la mano del espiritu práctico de Fermi, quien empezó cubriendo uranio con grafito, ya que el núcleo del carbón al tener el doble de masa que el H, no absorbía neutrones. Fermi consumió mucha energ1a al tratar de conseguir suficiente grafito puro, eliminar sus impurezas e impedir que las radiaciones, se esparcieran por la ciudad.

Para construir la primera pila atómica, Fermi acondicionó polvo de óxido de uranio cubierto por aluminio, al interior del grafito. Como a pesar de esta adecuación, seguían perdiéndose un 12% de neutrones. Fermi decidió agregar más grafito a la pila. Esta, al crecer hacia arriba (en el interior de un campo deportivo, de Chicago), llegó a tener 6 metros de altura. Para impedir la radiación, la Goodyear cubrió con sábanas de goma el campo deportivo. 4 poderosas barras de cadmio (absorbentes de neutrones), facilitaban o detenian (según se colocaran o retiraran), la reacción en cadena. Cuando el 2 de diciembre de 1942, se produjo la primera reacción en cadena controlada, Fermi dijo : “la fisión ha empezado”. E. Wigner, trajo entonces una botella de Chianti bebida de inmediato por todos los presentes embetunados por el polvillo de carbón, escribiendo a continuación sus nombres alrededor de la botella vacía. A.H.Compton jefe del proyecto en Chicago dijo crípticamente (a causa de la guerra), a sus superiores “un navegante italiano a puesto sus pies en el nuevo mundo”. Del otro lado contestaron : “y como se comportan los nativos”...” muy bien”.

4 Comments:

Anonymous Anonymous said...

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12:55 AM  
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3:56 AM  
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4:38 AM  
Anonymous Anonymous said...

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3:43 AM  

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