Aston Aston

Aston, inventor of mass spectrometer

Franciswi11iamaston 1877- 1945

Aston is a British physicist. Engaged in isotope and mass spectrometry research for a long time. He made a mass spectrometer with high focusing performance for the first time, and used it to measure the isotopes and abundances of many elements, thus affirming the universal existence of isotopes. At the same time, according to the study of isotopes, he also put forward the integer law of element mass. Therefore, he won the 1922 Nobel Prize in chemistry.

Previous experiments and preliminary results

1897 Thomson Joseph John, a famous British physicist, discovered electrons in the qualitative and quantitative study of cathode rays. Cathode rays are a stream of electrons. This discovery quickly aroused strong repercussions. People only know that there are electrons smaller than atoms that make up all elements, and atoms are also separable. This attracts more scientists to study cathode rays and explore atomic structure.

1898, German physicist Wayne found that not only cathode rays will be deflected in magnetic and electrostatic fields, but also some positive ion streams will be affected by magnetic and electrostatic fields. This positive ion flow from the gas discharge tube is also called positive ray. Thomson 1905, who has made great achievements in cathode ray research, turned to study positive rays. In his research, he found that when neon was charged into the discharge tube for experiment, under the action of magnetic field or electrostatic field, two parabolic trajectories of positive rays appeared. Further study, he measured that the atomic weights represented by these two parabolas were 20 and 22 respectively. At that time, it was recognized that the atomic weight of neon was 20. 18. So Thomson thinks it may be neon (Ne) and a mixture of neon and H2. Although Soddy had put forward the concept of isotope at that time, Thomson held a negative attitude towards this concept, so he could not make a more reasonable explanation for his experimental results.

Aston, who graduated from Birmingham University, England, has shown his outstanding talent in making experimental instruments and skills during his university study, especially when he was a graduate student in physics. After graduation, his tutor Yin Boting left him as an assistant. At this time, Thomson, as the director of Cavendish Laboratory, a famous scientific research institution, urgently needs to hire an assistant, an assistant who is good at making instruments and has certain experimental skills. For Aston's faster development and better future, Yin Bo Pavilion generously recommended its proud assistant Aston to Thomson. In this way, Aston came to this talented Cavendish laboratory and started a new research career.

Thomson gave Aston an important task, that is, to improve the gas discharge experimental device he was working on at that time, so as to determine the deflection of positive rays in electromagnetic field more accurately, and thus determine the composition and atomic weight of neon. Under the guidance of Thomson, the clever Aston made a spherical discharge tube and a notched cathode, improved the vacuum pump, invented a solenoid that can check the vacuum leakage of the discharge tube and a camera that can shoot parabolic trajectories. These improvements have obviously improved the experimental level and improved the experimental methods. By improving the device, they arranged the electric field and the magnetic field in front of each other, but the directions were perpendicular to each other, and the force was parallel to the normal ray but in the opposite direction. In this experimental device, under the action of two kinds of fields, the normal rays are deflected in opposite directions after passing through prisms made of different glasses, and then focused on the same point, so that the isotopes of gas elements detected in the photosensitive film B will be different because of the different atomic weights and the different speed of the normal rays, resulting in different curvatures of the deflection curves. Based on this, isotopes and their atomic weights can be measured.

Young Aston has an active mind and dares to accept new things. He is different from Thomson. When he carefully studied Sudi's isotope hypothesis, he immediately thought that this hypothesis could be established. He used the concept of isotope to explain his findings in the experiment. Under the action of electromagnetic field, two parabolic trajectories of positive rays appear, indicating that isotopes do exist. Because of the different mass of isotopes, the diffusion speed is also different, and a beautiful parabolic trajectory appears. In order to confirm this more clearly, he first separated neon isotopes by fractionation technology, then by diffusion method, and finally accurately determined their atomic weights, which confirmed the existence of Ne20 and Ne22. 19 13 At the meeting of the All England Association for the Advancement of Science, Aston read out the papers written by these works and made an experimental demonstration, showing two neon isotope samples. Colleagues spoke highly of his research. He won the Maxwell Prize for it.

Invented mass spectrometer to prove isotopes

After the outbreak of World War I, Aston was drafted into the army and went to a department of the Royal Air Force to engage in wartime scientific research. Although he was in a military camp, he never forgot to think about and sort out the research on orthorays and isotopes some time ago. Imagine if an instrument could be invented to determine the existence of isotopes in various elements. Then he can make a new breakthrough in his research. To this end, wait until the war has just ended; He hurried back to Cavendish's laboratory and started a new research.

Shortly after Aston returned to Cavendish Laboratory, Thomson became the dean of Trinity College, Cambridge University, and the famous physicist Rutherford took over Thomson's original job and became the head of Cavendish Laboratory. Rutherford first put forward the theory of random variation of radioactive elements, so he understood the isotope hypothesis. He gave great encouragement and specific guidance to Aston's work, which made Aston more confident to realize his plan.

Aston designed a new instrument, which consists of ion source, analyzer and collector, according to his original improved gas discharge device for measuring positive rays and referring to the principle of spectral analysis at that time, for analyzing isotopes and measuring their quality and abundance. This is a mass spectrometer. The ion source is used to study the isotopes of substances to form ions, and then the ions flow through the analyzer. Under the action of constant electric and magnetic fields, the ions of each isotope arrive at the collector through different paths because of their different masses, and the mass and abundance of each isotope can be measured from their positions and intensities on the collector. This instrument developed by Aston, which can also be called positron spectrometer, studies the crystallization of positron and isotope. The accuracy of the measurement results of this instrument reaches one thousandth. Therefore, using this instrument can help Aston show his talent in isotope research.

He first continued his pre-war research with this new instrument, and re-measured neon, proving that there are indeed two isotopes Ne20 and Ne22 in neon, and because their ratio in neon is about 10: 1, the average atomic weight of neon is about 20.2 (later, it was found that there is a third isotope Ne2 1 in neon, and the average atomic weight of neon is 20. Subsequently, Aston used a mass spectrometer to determine the isotopes of almost all elements. The experimental results show that isotopes exist not only in radioactive elements, but also in non-radioactive elements. In fact, isotopes exist in almost all elements. At first, Sudi and Richards confirmed the existence of isotopes based on the decay products of radioactive elements. Now, with the help of mass spectrometer, people find that the existence of isotopes is a common phenomenon. Aston found 202 isotopes in 7 1 element. For a long time, elements have been the main object of chemical research. Until today, because of Aston's outstanding work, people have discovered that elements have such rich content.

Isotope research solved two unsolved cases.

The use of mass spectrometer and isotope research have also solved a long-standing controversial and confusing problem. Since 18 15 British doctor prout put forward the hypothesis that the atomic weight of all elements is an integer multiple of the atomic weight of hydrogen, people have been dubious about this hypothesis. At first, some chemists thought it was reasonable, but the result of accurate determination of atomic weight only made them depressed. When Mendeleev put forward the periodic law of elements, which revealed the regularity of internal relations between elements, some chemists re-examined the prout hypothesis and thought it might be correct. At that time, crookes, a British chemist, put forward in a paper entitled "The Generation of Elements": "The so-called elements or simple materials are actually compounds, and all elements are gradually condensed from a primitive substance". Starr's accurate determination of atomic weight once again denied prout's hypothesis. Of course, the scientific community cannot accept crookes's point of view.

Mendeleev's periodic law of chemical elements is considered to be reliable, but in the periodic table, the arrangement positions of potassium and argon, cobalt and nickel, tellurium and iodine are not in the order of atomic weight, but in the opposite order. Why? Until the beginning of the 20th century, people were still confused.

Aston used mass spectrometer to study isotopes of many elements, which not only pointed out that almost all elements have isotopes, but also confirmed that an element in nature is actually a mixture of several isotopes of the element, so the atomic weight of the element is also the average atomic weight obtained according to the different proportions of these isotopes in nature. Chlorine, for example, has always been regarded as the best example to refute the prout hypothesis. Its atomic weight is 35.457. According to the determination, there are two isotopes of chlorine in nature: Cl35 and Cl37. Its abundance is cl35: cl37 = 3: 1, and the so-called abundance is the isotope percentage of this element in nature. So the atomic weight of chlorine is neither 35 nor 37, but 35.46. This is why the atomic weights of most elements are not integers. So Aston is talking about the integer law of element mass. Why is there an integer law for the quality of elements? As the secret of atomic structure is uncovered, the basic particles such as protons and neutrons are revealed, and this problem will be solved.

Aston's determination of isotopes and their abundances shows that there are three isotopes of argon and potassium, and their abundances are: Ar36: Ar38: Ar40 = 0.31:0.06: 99.63, k = 39: K40: K41= 93.31:. 102。 Although the average atomic weight of neon is larger than that of potassium, its atomic number, that is, the nuclear charge of atoms is indeed smaller than that of potassium, so Mendeleev's periodic table of elements is correct. So are cobalt and nickel, tellurium and iodine. So Aston's isotope research solved another unsolved case.

Aston's work was immediately highly praised by the scientific community. In a letter to several colleagues, Rutherford said: "Aston discovered isotopes of neon, chlorine, mercury and other elements with his invented mass spectrometer. I looked at all the relevant photos, and the results seemed positive. Aston is a good experimenter and very skilled because he has worked hard for many years and deserves this success. "

Excellent traditions and rich activities.

Aston has a famous saying: "More instruments should be made and more measurements should be made." This is actually a tradition of Cavendish laboratory, which requires scientists to learn to make their own instruments and do their own experiments, and to become excellent scientists through the training of basic experimental skills. This famous saying is also a portrayal of Aston's own scientific research career. After he won the Nobel Prize in chemistry in 1922, he still insisted on working in the laboratory and made further improvements and perfection on the mass spectrometer, so that he later made three mass spectrometers with an amplification of 2000 times and an accuracy of1100000. At present, the mass spectrometer has detected 489 isotopes on the earth, including 264 stable isotopes and 225 natural radioactive isotopes. In addition, more than 2000 kinds of artificial radioactive isotopes have been discovered. Of course, there is another important contribution from Aston in the process of building this treasure house of knowledge.

Aston is not only good at experiments, but also an excellent experimenter with a wide range of interests and profound knowledge. In order to adjust his long-term hard life in the laboratory, he likes traveling very much and insists on taking part in sports. Like his superb experimental skills, he is also a skilled photographer and amateur musician. In a word, his life is far less monotonous than many people think. He is also an entrepreneur who is good at raising funds and has business ability. Among the huge assets accumulated by Trinity College of Cambridge University today, Aston raised it that year.

1945165438+1On October 20th, Houston died of illness at Cambridge University at the age of 68. His outstanding contribution to science won him many honors. In memory of him, many instruments made and invented by him were specially preserved and displayed in London Museum and Cavendish Laboratory Museum.