Lawrence Berkeley National Laboratory Recent Work

Home , Albert Ghiorso

Title DISCOVERY OF LAWRENCIUM, ELEMENT 103

Permalink https://escholarship.org/uc/item/985777zx

Author Latimer, Robert M.

Publication Date 1961-11-01

eScholarship.org Powered by the California Digital Library University of California UCRL 9778

cy 2

UNIVERSITY'OF CALIFORNIA

Crn m t OXarewe lZadiavion

f A I f I

TWO-WEEK IOAN COPY

This is a Library Circulating Copy whIch may be borrowed for two weeks. For a personal retention copy, call Tech. Info. Division, Ext. 5545

BERKELEY, CALIFORNIA DISCLAIMER

This document was prepared as an account of work sponsored by the United States Government. While this document is believed to contain correct information, neither the United States Government nor any agency thereof, nor the Regents of the University of California, nor any of their employees, makes any warranty, express or implied, or assumes any legal responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by its trade name, trademark, manufacturer, or otherwise, does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agencythereof, or the Regents of the University of California. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof or the Regents of the University of California. MtON - Eflcf Ic

U1lVEiSjjy OF CAUFURNIA DISCOVERY OF LAWRENCIUM, ELEMENT 103

By Robert M. Latimer

Reprntod from THE SCIENCE TEACHER, Vojume 28, Number 7, November 1961 Copyright 1961 by the NATIONAL SCIENCE TEACHERS ASSOCIATION, 1201 Sixteenth Streel, NW., Wa5Nngton 6, D.C. I DISCOV RY ()IF Lawrencium

V !

- s M2A C .5.

•-• V.. - c - k.

Comprehensive studies of the nucleus are possible with high energy accelerators. Shown is a beam of deuterons with an energy of 60 million electron volts emerging from the target chamber of the University of California 60-inch cyclotron. The deuteron beam is visible (in a dark room) because of the ultraviolet light given off when the deuterons strike air molecules.

By ROBERT M. LATIMER The modern Periodic Table of Ele- meats (Figure 1) is somewhat changed Chemist, Lawrence Radiation Laboratory, University of California, Berkeley, California from the fanciful chart used by the early alchemists and scientists for the ARLIER this year a new element, ment. The discovery was made by elementary substances of nature (lire, E lawrencium (Lw), was discovered nuclear cheniists Albert Ghiorso (co- water, air, etc.). Only nine elements at the Lawrence Radiation Laboratory discovcrer of eight other new dc- were included in the references used by in Berkeley, California. This now be- merits), Torhjorn Sikkeland, Alnion E. experimenters in the sixteenth century, comes the fifteenth "man-made" dc- Larsh, and Robert M. Latimcr. but their work did make a contribu- rf HHo .0000 5 6 7 8 Li Be S C N 0 F No 17 933 092 00?? 14 000 0.000 900 90j83 Il 82 3 15 15 6 I? 18 Na Mg Al Si P S Cl A 02.991 2432 2696 20 aO 1 309751 32066 35.'57 39944 18 23 27 22 23 24 25 26 21 28 fTT 37 32 33 34 35 t Ic Ca Sc Ti V Cr Mn F0 Co Ni Co Zoo Go Go Ac Br Zr 39100 4000 4.90 42.30 0339 5271 940.1 9505 9094 907 633-1 6339 6972 2760 749 7096 39916 03.00 31 38 39 40 41 42 43 44 45 46 41 46 1 4s 50 II 52 53 54 RIo Sr Y Zr Nb Mo Tc Rn Rh Pd A I Cd In Sn Sb I X0 05.40 01 63 00 92 922 929? 0595 101 I 779? 10?, 410 7 900 11114? 14 62 11070 2:76 12701 1263? 31.30 55 56 .51-17 73 73 14 15 78 II 78 ohio 81 82 83 64 89 86 Co Be t HO T. W Re Oo Or Pt A. Hg TI Pb Si Po At Rn 0O1.. ?37?? 32:36 7650 0025 0770 00?? 7302 )32?95 .....?2C6?J43? 2372 27690 -. - 81 86 86-703 (104) (135) (III) (1011 1128) Fr Re A 1211403 .....

0. t Id 7 2 58 59 60 67 52 63 64 65 88 61 66 69 10 71 La Co Pr- Nd Pm Sm Eu Tb Dy Ho Er Too Yb LU

00 23s

FIGURE 1 Periodic Table of the Elements. The synthetic elements are shaded.

View of the equipment used in the 103 experiment

-. -- -.--- ___..7_,7 -

•,,? 2' . 5r I >m I I

1 9

- 172

(Ion. These were carbon (C), suifLir (S), iron (Fe), copper (Cu), silver (Ag), tin (Sn), gold (Au), mercury (Hg), and lead (Pb). The beginning work of these men was with crude equipment, such as the retort and mor- tar and pestle. But however limited, ihrough their interest in theory and experimentation, they were able to pin for the purpose of producing heavy ions and are used by scientists to broaden NEUTRON IRRADIATION FmT their knowledge of the nature of atoms 25,4 and atomic nuclei, The Berkeley accel- E erator (HILAC), used in the element- UO 2I 252 73 103 experiment, can bombard targets Cf2 with particles as heavy as neon ions or 249 250 even heavier ones. The transuranium elements up to 2 4 2 243 244 745 746 247 246 249 Cm fermium (Fm) can be most easily pre-

241 242 243 244 pared by neutron irradiation of plu- tonium (Pu) for several years in a high 239 240 211 42 743 flux reactor (see Figure 2). Einsteinium Pu -----4 (E) has been produced by neutron irradiation in barely weighable amounts. Above fermium the heavy isotopes de- FIGURE 2. Production of heavy elements via slow neutron irradiation. cay just about as fast as they are made. Therefore, this method holds little down some important elements known to reshape natural materials, the pres- promise currently for the production of today. By the middle of the seventeenth ent-day scientist relies on complicated elements as heavy as 103. Lawrencium century, thirteen elements were known, machinery and equipment to perform decays with a half life of 8 + 2 but none of the discoveries have been the necessary chemistry of our day. In seconds and emits an alpha particle recorded in history. isolating tiny quantities of materials, with an energy of 8.6 niev. Today, man has considerable equip- it is necessary to use "hot" cave labo- About ten years after the discovery inent and methods with which to learn ratories, cyclotrons, reactors, accelera- of rhenium (Re) in 1925, it was theo- of the environment of the universe. tors, and other complicated equipment. rized that any subsequent "new ele- Unlike early man who used simple tools Accelerators are designed specifically ments" should be radioactive and would

FIGURE 3. Schematic diagram of the equipment used in the 103 experiment.

DEGRADER FOILS MULTIPLEDETECTOR COLLiMATOR SYSTEM FARADAY CUP TARGET FOR SHORT-LIVED -400 VOLTS ALPHA EMITTERS BEAM ENERGY MEASURING HEY _AM__ SILICON DETECTOR DEGRADER FOILS SILICON- GOLD ALPHA VAC U U M DETECTORS

-150 VOLTS- - PULLER HELIUM / BRAKE NO.2 ATMOSPHERIC / PRESSURE 1)

- / SUPPLY REEL--- COPPER TAPE L. SUCTION I" WIDE x0.5 MIL THICK

- TAKE-UP REEL SUCTION ------BRAKE NO. I The interior of o new type of atom.smasher or accelerator (the i-lILAC) consiructed for an Atomic Energy Commission research program at the University of California Radiation Laboratory, Berkeley. Heavy fragments of matter are hurled through the doughnut-shaped "drift tubes" that extend the length of the atom "gun's" barrel, Man standing at the end of the big barrel (the post-stripper), gives idea of the size of the tonk-90 feet long and 10 feet in diameter. probably therefore have to be syn- atoms. For this purpose, the heavy-ion is formed which has a very excited thesized. Actually, some of the lighter linear accelerator—H ILAC—was built state. This new nucleus then does one synthetic c]cments do exist in nature in several years ago at the Lawrence Ra- of two things to lose some of its extra uranium orcs—elements 43 and 61 as diation Laboratory. The HILAC ac- energy. Most likely it breaks up or fis- radioactive fission fragments, elements celerates particles up to 10 mev per sions, but a few of the new nuclei lose 85 and 87 as members of a rare decay nucleon, that is, for instance 11 0-mev their extra energy by emitting neutrons, chain, and at least two of the "trans- B''. With this energy, it is possible to or neutrons and protons in some com- uranium elements" from neutron cap- push two atoms together and create bination. This dc-excitement or loss of ture. All the transuranium elements, a new one. energy takes place immediately (less and perhaps some yet undiscovered In the 103 experiment, californium than 10-12 see) after the compound e]cments, may have existed some four (Cf) was bombarded by boron ions. nucleus is formed. billion years ago when the earth was The californium had previously been The few atoms during a bombard- formed. But in the long time interval produced by neutron irradiation. Three ment that de-excited themselves by that has elapsed since the formation, it micrograms of californium, one-half losing particles recoiled from the target is expected that all have decayed away. the world's supply, was electroplated in and stopped in a helium atmosphere. Charged-particle bombardment is an area 0.10 inch in diameter on a very The new atoms were then carried with the only path left open for the produc- thin nickel foil. The heavy-ion beam the helium gas out through a 0.050- tion of the very heaviest elements. To was collimated so as to pass only inch orifice and electrically collected on produce a new heavy nucleus out of through the target material. a copper conveyor tape (see Figure 3). two lighter nuclei, one must overcome When a boron atom hits a califor- This tape was periodically pulled along the coulombic repulsion of the two nium atom, a new conipound nucleus a short distance in order to place the successive groups of collected atoms in Au-Si solid-state detectors are a very Before the experiments started, it front of Au-Si (gold-silicon) solid- recent development. Each one, with its was predicted that 103 would have state detectors. Each time the tape was volume of about a cubic inch, can re- a half life somewhere between 0.3 pulled, a new group of collected atoms place a Frisch grid chamber with a and 30 seconds and have an alpha- was brought in front of the first of the volume of about one cubic foot. The decay energy in the range of 8.0 mev five detcctors, while the group that had detectors are solid-state ionization to 8.8 mev. With everything working been there moved to the second col- chambers. They are in many respects correctly, up to five counts an hour lector, and so on. The tape was pulled just half a transistor—a diode. When a might be detected during the operation. automatically every ten seconds, and charged particle—an alpha particle, for In the experiments, counts from de- about once in every hundred pulls or instance—passes into the detector, ion caying 103 atoms were not, unfortu- experiments the detectors would record pairs are produced. These ion pairs are nately, the only counts expected. Tracer the decay of an atom of 103. When the collected in the depletion region of the amounts of lead and bismuth also pro- tape was pulled once every ten seconds, detector and an electrical pulse de- duce, when bombarded with boron an activity with a 10-second half life velops which is proportional to the atoms, alpha activity of 8.1 and 8.8 produced twice as many counts in the energy of the charged particle. The mev. Early experiments showed that first detector as in the second, the sec- pulse is thcn amplilied and analyzed this activity could completely niask any ond twice as many as in the third, etc. in a 100-channel pulse-height analyzer. activity produced from the californium, unless the aniounts of lead and bismuth were reduced to a very low level. The After colikrnium (Ct) is bombarded by neutron irratiation, it is placed in the target holder illustrated. target material was finally purified by heating californium in a vacuum and boiling out the lead and bismuth. It was impossible to separate out the im- purities chemically, as even the best reagents available contain too much lead and bismuth. After the "pure" target had been bombarded for many hours, the 8.6-mev activity began to stand out. Many more hours of bombardment were needed to determine that its half life was about 8 seconds. When these two feats had been accom- plished, many different targets such as curium (Cm), americium (Am), lead (Pb), and bismuth (Bi) were bombarded under exactly the same condi- tions to show that they would not produce the activity. During a two-month period, about 100 countable atoms of lawrencium were produced. Although lawrencium has not been chemically isolated, the experiments conclusively showed that it is a new clement. Chemically, it will exhibit the properties of an actinide element. The last 5/ electron is filled in lawrencium, thus making it the last of the actinide series. In the future, when increased amounts of lawrencium are produced, its chemical and physical properties can be further studied.

Bibliography Samuel Glasstone. Source Book on Atomic Energy. Second Edition. D. Van Nostrand Company, Inc., New York. 1958. Glenn T. Scaborg. "The Synthetic Chemi- cal Elenients." The Science Teacher, 26:314. September 1959. Glenn T. Seaborg and Evans G. Valens. Elentents 0/the Universe. a P. Dutton and Company, Inc., New York. 1958.