THE NEW CHEMISTRY

Evening Post, Issue 25, 30 January 1935, Page 18

THE NEW CHEMISTRY

RUTHERFORD LECTURE

BREAKING m THE ATOM

i WHAT CAN BE DONE

'■•Lord Kutherford of;Nelson gave the Ludwig Mond Lecture in; the University, of Manchester, taking as his subject "The New Chemistry,?'; reports the "Manchester. Guardian. >:A

: "The''.older Chemistry With which you are familiar," he said, "deals with the combination of atoms and molecules to form new compounds. The chemical attraction of.one atom for another depends upon unbalanced electric or magnetic forces resident in the outer structure of the atom. The new chemistry has to deal with methods of changing one atom into another—that is, with the study -of the modes of transformation ;of the chemical atom itself when exposed to certain powerful disrupting forces. The. most potent method so far employed depends on the bombardment of the atom of matter by fast projectiles like A particles or protons. Occasionally one out of a great number of these particles by chance strikesthe;heart or nucleus of an atom. In some cases such a violent encounter may result, in the breaking-up ,of the atom into two or more lighter constituents —a veritable disintegration. In other cases a new atom of heavier mass may be formed by the incorporation of : the bombarding particle into the nuclear structure.- The-effects produced depend to a large extent on the nature of the projectile and only to a minor extent on speed. For example, the effects ; observed are in general very different for bombardment of atoms by protons, neutrons, or A' particles. During last year, definite evidence has been obtained that;we can even transform' atoms in the laboratory without the aid of fast projectiles by using very, penetrating radiations of the S-ray and Y-ray type." ■ : new-types found: ' They had not only been able to liberate fast protons and A particles of higher energy than those liberated by radium and other radio-active bodies. They had also brought to light the presence of,' unexpected and ; strange types of particles like the neutron and the positive electron now called the positron. '" They had been able ■to detect new isotopes of elements, and r even more surprising, Lord Rutherford declared, they had been able to produce a whole new class of radio-active bodies which broke up in novel ways—radioactive t bodies' which,: if they ever existed in the earth, disappearedylong ago. ."It may be that ; the radioactive elements uranium and thorium are the sole survivors of what may well have been a large group of uns.table" elements which are ' still being formed in the furnace, of our sun. 1 '

■;• After .emphasising the minute scale on which the:;. transformations., occur

with a brief reference to special electric methods and instruments used for these observations, the lecturer recalled the modern view of the nuclear1 structure ot atoms; "If we are to effect the transformation of an clement," he went on, "we must in some way. alter its, mass or its charge. This can be effectedsby adding or subtracting a particle, whether charged or uncharged, from the nucleus. This is easy in imagination, but difficult in practice. The' most "effective way so far found is the bombardment method, involving the. entry of a foreign'particle into the structure of the nucleus, and in some, cases leading to the loss of a charged particle from ' the nucleus." .', " ~'. .-'..", THE FIRST PROOF. -■:■ Tho first proof of the artificial transformation 'of an'atom' was given in 1919, Lord Eutherford explained, when it was found that the bombardment of the gas nitrogen by fast A particles gave rise to the liberation of a number of fast protons which could only come from a disintegration of the nitrogen nucleus. During the last few years, another type of transformation had been brought, to light in which: a new and strange type of particle called the neutron was expelled.' ■ "The neutron, as its name implies, carries no electric charge, but has a mass about equal to that of a proton. Since it has no charge it does not ionise the gas in : its path and consequently shows no track in an expansionchamber. At. rare intervals in'lts passage through a gas it hits the nucleus of an atom in its path and shoots it forward wjth high speed. This struck nucleus is charged ionises the gas so that its track in the gas is shown in the cloud chamber. While thes.e 'knock-ons' are comparatively rare, ■ they form-a very convenient method of detecting!the presence of the invisible neutrons and forming an idea of their velocity."' Still another striking type of trans: formation could be produced. by A particles resulting in the .artificial production of new radio-active bodies. The residual nucleus in the transformations previously.' considered, the lecturer continued, was a stable nucleus non-radio-active. A radio-active nucleus was an ; unstable type 'which broke up with the-emission of fast particles, ultimately forming another ' stable nucleus. The production of an artificial radio-active body was.first noted by M. and Mme. Ourie-Jpliot by bombarding boron with ;fast"A. particles. After discussing the'process and results; Lord Rutherford went on to mention the work of Professor Fermi and his collaborators in Borne, who found that a large number of these, radio-active bodies could be formed when the elements were bombarded by neutrons derived from the. action of A-rays on beryllium.. ■On account of the absence of charge, the neiitrpn was able to enter the structure of even a.heavy element, where the'. A particle, on account of its charge, was ihefffietiye.' "■■ ! Even the. ■ teaviest /element, uranium, when bombarded by neutrons, gave rise to :at lestst four! distinctive types of radio-active bodies'with half-periods,.of. 15 secbnds,,.4O secbhds,;l3 minuses'; and: 100 minuieSi-'lt ,was'worthy of note that all Hh'e'radio-active bodies pro-

! duced in this way broke up with tho liberation of fast negative electrons, and not positive electrons, as in the original cases found by the Joliots. ■ USE OF HIOH VOLTAGES. i It secmod clear that we, were able greatly to increase our knowledge of the isotopes, of the elements. Nono of these radio-active bodies was found in Nature. They represented unstable types of isotopes with a very limited ljfe. During. the last few months it had been found that the efficiency of the process could be increased in some cases about 100 times or more by slowing down'the neutrons. This-could be done by passing them through hydrogen or a solid material like, paraffin, which contains hydrogen. Another notable advance had been made by the use of bombarding particles produced artificially in the electric discharge and speeded up by appropriate,, methods. This involved complicated apparatus, and, in general, the use of high potentials of the order of 1,000,000 volts. In this way copious streams of fast i particles could readily be produced corresponding in number to the A particles expelled from thousands of grammes of radium. After a technical-description of results obtained and of the remarkable effects produced when the ions of heavy hydrogen bombarded a compound containing heavy hydrogen, in which caso there are two reactions, one leading to i a new isotope of hydrogen of mass .3 'and the other ,to the new isotope f helium f mass 3. Lord Kutherford concluded: "We can build heavier elements from lighter, break up other atoms . into fragments,, and produce novel radioactive elements by the score The new field of nuclear chemistry is opening up with great rapidity. Much work, of ten of a difficult technical character, will be required to prove the exact • nature of many :of the trans formations- which1 have been observed, but a very promising beginning has been made. Future work may disclose many surprises, for new and unsuspected particles may come to light. In any case, we are entering a no-man's land with the ultimate hope to throw light on the way atoms are built up from simpler particles."