特 別 講 演

特別講演 1

D.C.Hoffman

特別講演 2

広瀬立成

特別講演 3

A.G.Maddock

特別講演 4R.H.Herber

FRONT工ERS 工N NUCLEAR AND CHEM工CAL STUD工ES OF THE UPPERMOSTELEMENTS 工N THE PER工ODIC TABLE
Darleane C. Hoffman
Chemistry Department，Un工versity of Ca1ifornia andNuc1ear Science D工vis工on，MS‑70A/3307
Lawrence Berkeley Laboratory，Berkeley，CA 94720
The s七udy of 七he nuc1ear and chemica1 propeど七 ies of 七heelemen七s a七 七 he uppermost end of 七he periodic 七able ispar七icu1ar1y cha11enging. 工n 七his paper 1 wi11 restrict mydiscussion to the e1ements beyond mende1evium (Z=101) becausesuch s七udies involve unique challenges and oppor七uni七1es.
Isotopes of these e1ements are shor七‑1工ved and， ヒ herefore， mus七
be s七udied near ヒhe site of production; ヒhey mus七 be produced
wiヒh charged particle beams at accelera七ors ra七her 七han via
neutron cap七ure; the use of radioactive heavy acヒinide 七argets
is often required and the number of atoms produced is so small七ha
七 any chemis七
工Y 七o be perfo
工medmusヒ be done on an "aヒom‑at‑a‑
七ime" basis. Given all these requiremen
七s， consヒraints， andcha11enges，why 工S l七 worthwhi1e ヒo 七ry ヒo perform nuclear andchemical studies of 七hese elements? 工n addition 七o thescientific excitemen七 inheren七 in studies a七 七 he "edge ofs七abili七y"， can we 1earn anything of fundamenta1 scientificimportance 七haヒ we couldn'ヒ studymore easily in 0ヒher regions of
the periodic ヒable?
From the standpoint of the nuclear properties of 七heseelemen七s， 七he ques七工 on is rela七工 vely easy to answer. Spon七aneousfission (SF) is an increasingly more probable mode of decay as， since SF does not occur
one goes 七o higher Z elemen七s. 工n fac七in e1emen七s ligh七e工 七 han tho工ium (Z=90)，ヒ his p工ocess can only be
S七udied in the heavy elemenヒs. 工nsights into 七he mechanisms offission， fission barriers， nuc1ear structure， and the 1imits 七o
nuc1ear s七abi1i七y can be gained by sヒudies of SF， a process inwhich no external energy is in七roduced in七O 七he nucleus and whichis exquisi七ely sensitive to nuc1ear she11 effects and re1ative1ysma11 changes in nuc1ear s七ructure. The compe七i七ion be七ween SF，a1pha emission，and 0七her decay modes can on1y be investigated in
the heavy e1ements region. Such information is essen七ia1 in thedevelopmenヒ of nuclear models which can predic七 七 he decay
properties of s七i11 heavier e1emen七s and 七he u1七ima七e limiヒ toヒhe ex
ヒension of the periodic ヒab1e.
S七udies of ヒhe chemica1 proper七ies are equally inヒeresヒing
and it has a1ready been shown [1‑3] that 七hese canno七 simply be
ex七rapo1ated fどom the known properヒies of 1ighヒer homologs in the， in the case of the heavies七 ac七inides
periodic 七ab1e. 工n fac七and the transactinides， 工
七 was of great ユ
mportance to demonstraヒe
experimenヒally that 七he fi11ing of the 5f she11 is comple七ed at
1awrencium (Z=工03)， 七 hus ending the actinide series， and thatrutherfordium (104) and hahnium (105) have properties simi1ar ヒO
七he group 4 and 5 e1ements. 工t is postu1a
七ed 七ha
七 七 hey are 七hebeginning of ヒhe new 6d ヒransi七ion series. Even a comparison of
the most rudimentary chemica1 behavior of these elements with七ha七 of 七heir 1ighter homo1ogs is important in assessing thevalidity of predic七工 ons based on extrapola七ion of 七he ヒrends

qrushown in a given group in the periodic 七able. Such informa七ion
can also help in investigating the possible influence of relativ‑
isヒic effec七s on 七he chemical behavior of these heavy elemen七s.
For example， relaヒivis七ic effec七s may alヒer 七he relative s七abili‑
七y of the 7s， 6d， 7p valence elec
七rons so that other oxidation
staヒes may be stab工lized and 七he ionic radii may even be affect‑
ed. Early calculat工ons indica七ed 七ha七 七 he gro~nd~state configu‑
ra七ion of elemen七 104 m.igh七 be [Rn]5fl主7s27p2 rather 七han
46d2
[Rn]5f1
7s2， as expec七ed by analogy 七o iヒs lighter homolog，hafnium. However， more recenヒ calcula七ions indica七e a ground
7p while that forsヒa七e configura七ionwhich is_p~edominan七 ly 6d7s2
Ha (105) is predominantly 6d3
7s2.
工七 should be emphasized 七ha七 inves七iga七ions of chemicalproperties depend on a knowledge of the nuclear properties inorder 七o positively iden七ify 七he species being investiga七ed.
Conversely，a knowledge of 七he chemical properties can be used tosepaど a七e new isoヒopes and positively identify 七heir Z. Thus
studies of nuclear and chemical properヒies are syneど gisヒic andshou工d ideally be carried out hand‑in‑hand.
To da七e， boヒh gas and aqueous phase properties of elements
as heavy as 104 and 105 have been invesヒigaヒed，even though theirlonges七‑lived known iso七opes are only 65 second and 35 seconds，respec七ively. (See references 1‑3 for recenヒ reviews of theエ es of elements 103， 104， and 105.) Studies of theproperヒ
chemical proper七ies of 0.8‑second 263106 can probably beconduc七ed using the microS工SAK ヒechnique， if meヒhods for
detecting the alpha and/or SF activity can be devised which avoid
七he 七ime‑consuming s七ep of evapora
七ing 七he resul七ing solu
七ions.
Knowledge of 七he chemical pど operヒies of elemenヒ 105 hasrecenヒly p~rmitted isolation and identification of the new26
3
isotope， "~OjHa ，which has a half‑life of abou七 27 seconds，unexpecヒedly long. The S~_half-li~~~ of abou七 40 minutes andgrea七er 七han 36‑h.
ours for 2
61Lr and 2
62Lど ， respectively indicaヒelarge hindrance fac七ors rela七ive 七o 七heir even proton‑even neu‑
ヒron neighbors. These measuremen七s suppor七 previous observations
七ha七 an odd proton or odd neutron can grea
七ly hinder decay by SF[4] and make i七 appear promising 七hat iso七opes of elemen七s 107
and 109 which are long enough 七o permi七 chemical， as well as
nuclear studies，may exist if methods for ヒheir producヒion can bedeveloped.
References:
1. Hoffman， D. C.， "Recent S七udies of 七he Nuclear and Chemical
Properties of Elements 103， 104， and 105"， Proc. of Symp. on 50th
Anniversary of Discovery of Transuranium Elemen七s， 200七h ACS， 1990， ACS Symposium
Na七ional Mee七ing， Washington， D.C.， Augus七Series (in press).
2. Hoffman， D. C.， "Chemis七ry of the Transacヒinide Elements"，
Proc. of the Roberヒ A. Welch Foundation Conference on Chemical
Research XXX工V F工FTY YEARS WITH TRANSURAN工UM ELEMENTS， Houston，Texas，Dctober，1990.
ヒ‑A‑Time Chemis七工y"， Radiochim. Acヒa，
3. Hoffman， D. C.， "Aヒom‑A
to be published.
4. Hoffman， D. C.， "Spontaneous Fission Properties and Lifeヒime
I
三♀
2.
， 21c (工989).
Sys七ematics"， Nucl. Phys. I

3‑

素粒子物理学のフロンティア(東京都立大学・理)広瀬立成

今、素粒子物理学は大きな曲り角にさしかかっている。実験、理論の両面で。
ここ数年の問に、 TRISTAN (高エネルギー物理学研究所)、 TEVATRON(ブエルミ研究所)、 LEP (欧州連合原子核研究機構)、 H ER A (ドイツ電子シンクロトロン研究所)が稼働を始め、多くのデータを提供している。一方、理論面では、ゲージ理論の枠組のなかで、電磁力と弱い力が電弱力として統合され、さらに強い力をも含む一本{とされた力の研究が進んでいる。実験屋(おそらく理論屋も)は、未知のエネルギー領域において現在の標準理論を超えた新しい現象が観測されることを期待した。ところが・・・・・・・である。つぎつぎに発表されるデータは、標準理論によってみごとに説明されてしまうのだ。
では標準理論は完撃に正しいのだろうか。実はこの理論では、 Glashow‑Weinberg‑Salamによって考え出された f
電弱相互作用の対称性の自発的破れ j が仮定されている。
これは、弱い相互作用を伝播するウィークボソンの質量(陽子の約 100倍)を生成するためのメカニズムで、標準理論のもっとも重要な部分である。ところが、この対称性の自発的破れの起源が、まだまったく解明されていないのである。
標準理論では、 6個づつのクオークとレプトン、 4つの基本的な力を伝播する 4種類のゲージ粒子、さらにヒッグスとよぶスピン 0の 2個の粒子が仮定されている。これらの粒子がもっ基本的な物理量、たとえば質量は、はじめから理論のなかにパラメーターとして与えられている。さらに標準理論は、相互作用の強さやヒッグスポテンシャルを記述するパラメーターなど多くのパラメーターを含んでおり、現象論の域を出てはいないのである。
今日の高エネルギー物理学における最大の課題は、対称性の自発的破れの起訴、を実験的に明らかにし、さらに f
標準理論j を超えた新しい現象を発見することである。このような目的に沿って、いくつかの新しいプロジェクトも計画されている。本講演では、高エネルギー物理学の現状と将来の展望を実験面を中心にしてのべてみたい。
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EXPONENTIAL GROWTH AND DECAY IN RADIOCHEMICAL EDUCATION

R. H. Herber
Department of Chemistry，Rutgers University. A.
New Brunswick，New Jersey 08903，U. S

The Twentieth Century ‑which might well be called the "Nuclear Century"‑ opened with the discovery of X‑rays by Roentgen and the nuclear atomby
Rutherford，and may close with the definitive answer to the question of the"missing solar neutrinos" and the mechanism of energy production in the sun.
Between these two epoch‑defining events are sandwiched a multitute ofextraordinary discoveries in nuclear science: artificial radioactivity，
fission and fusion，the characterization of 43Tc， 61Pm and the trans・Uranium
4C dating，the Mossbauer effect，and hot‑atom chemistry，to nameelements，1
only a few. These discoveries have brought about the conception，adolescence，and maturing of nuclear science and have been marked by the awarding of morethan 20 Nobel prizes in Chemistry and Physics，and the accompanying
recognition of the centrality of this field to our understanding of thefundamental description of nature at the Angstrom and sub‑Angstrom level.
The educational aspects of this field ‑ at least in the United States ・
has been strongly influenced by several key events : the inception of "bigscience" in the late 30's，typified by the work of La
wrence andhis group atBerkeley; the discovery and exploitation of fission in relation 亡o national
policy by Fermi，Oppenheimer，Bethe，Teller et al. and the Manhattan Projectoperations; the formation of the Atomic Energy Commission and its vesting ofpolicy‑making decisions in civi1ian hands; the creation of the U.S. National
Science Foundation in 1950 a10ng the 1ines origina11y conceived by Bush; andfina11y，the deve1opment，exp1oitation，contro1，and regulation of theproduction of nuclear power for civi1ian uses in the post‑WWI years and theestab1ishment of the International Atornic Energy Agency as suggested byEisenhower. These events provide the matrix withinwhich nuclear science ・ andspecifically， the fie1d of Nuclear‑ and Radiochemistry ‑has deve10ped as an
academic sub‑discipline in U. S. Universities. Were it not for the inescapabletime frame imposed by the radioactive decay lifetimes of the fission productdebris of nuclear power generation andweapons production (and theirdestruction in the post "cold war" era)，the gradual fading‑out of nuclear
science from the educational enterprise in U.S. Universities would be a benign‑6‑matter， simply ascribed to the natural history of science and its dynamics.
However，these nuclear lifetime "facts of life" impose on us and on coming
generations，a special task，as it relates to the training of future
generations of students who are competent to address the pressing problems
existing in this field. The prospects for successfully addressing this task
will be examined in some detail.

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