Fifty Years of Nuclear Quadrupole Moments*

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Proceedings of the VIIIth International Symposium on NQR Spectroscopy

D arm sta d t, July 2 2 - 2 6 , 1985 • Z. N atu rfo rsc h . 41 a, 1 -4 6 2 (1986)

International Committee

R. Ambrosetti

T. J. Ba st o w

R. J. C. Br o w n

G . Ju g ie

E. A. C. Lu c k e n

M. MaCk o w ia k

R. A . Ma r in o

J. Mu r g ic h

D. Na k a m u r a

P. T. Na r a sim h a n

I. G. Sh a p o sh n ik o v

J. A . S. Smith

Al. Weiss

M. A. Wh it eh ea d

W. Win d sc h

(Italy) (A ustralia) (C an a d a)

(F ran ce), C h a irm a n (S w itzerland), C o -ch a irm an (P oland)

(USA ) (V enezuela) (Japan) (India) (U S S R )

(U n ited K ingdom ), D e p u ty C h a irm an (W est G e rm a n y ), C o -ch a irm an (C an a d a)

(G D R )

Local Organizing Committee National Advisory Committee

E. A. C. Lucken

Al. Weiss

N . Weiden

B. Elsch ner

K. v o n Kessel

K. H. No th n a g el

P. C. Schm idt

K. G. Weil

(U niversite G en ev e), C o -ch a irm an (T H D ), C o -ch a irm an

(T H D ), Secretary (T H D )

(M erck) (R o h m G m b H ) (T H D )

(T H D )

H. Haas

J. Pelzl

W. Pies

H. Sc h m id b a u r

J. Vo it l ä n d e r

(B erlin) (B ochum ) (L udw igshafen) (M ünchen) (M ünchen)

Fifty Years of Nuclear Quadrupole Moments*

P eter Brix

M ax-Planck-Institut für Kernphysik, Heidelberg

Z. N aturforsch. 41 a, 3 - 1 4 (1986); received Septem ber 14, 1985

On March 2, 1935 Hermann Schiller and Theodor Schmidt reported the first experim ental evidence o f non-spherical nuclei. From careful hyperfine structure studies o f several Eu I-lines, they had shown th at the hyperfine components o f 151Eu and 153Eu did not follow the Lande interval rule exactly. Since the deviations were larger for 153Eu with the smaller magnetic moment, level perturbations were ruled out. This led to the conclusion o f nuclear quadrupole moments. The theory was published June 1, 1935 by H endrik B. G. Casim ir. N uclear deform a

tions are playing a decisive role in modern nuclear structure physics. F or solid state physics, spectroscopic quadrupole moments are very useful, since they probe the electric field gradient at the nuclei.

This review presents the discovery of 1935 in historical context: 1. Early measurem ents of nuclear radii. 2. Discovery o f nuclear quadrupole moments. 3. Spectroscopic quadrupole moments (absolute m easurem ents; relative hyperfine data, europium revisited). 4. Intrinsic quadrupole m om ents (discovery from isotope shifts; present status, sam arium revisited).

5. Charge distribution of deformed nuclei.

1. Early Measurements o f Nuclear Radii

75 years ago, on D ecem b er 14, 1910, Ernest R u th e rfo rd w rote to a friend “ I th in k I can devise an ato m . . . [which] w ill account for th e reflected i particles observed by G e ig e r” [1], O ne o f the m ost im p o rta n t exp erim en ts o f this century had been know n since M ay 1909, and was n o t u nderstood at all. But th a t found little atten tio n o u tsid e M an

chester. T here, in R u th e rfo rd ’s la b o ra to ry , H ans G e ig e r and Ernest M arsden had discovered and convincingly co n firm e d th a t a rays w ere back- scattered from very th in m etal foils [2], N early two years afte r this su rp riz in g discovery, on M arch 7, 1911, R u th erfo rd p rese n ted his n u clea r atom to the M an ch ester L ite ra ry a n d P hilosophical Society [3]

and G eig e r stated at th e sam e m eetin g [4] how he h ad exp erim en tally v erifie d the 1/s in 4 (

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) d ep e n  dence o f large angle scattering calculated by R uther

ford.

G e ig e r and M a rsd e n then sta rted w ith a new series o f careful m easurem ents which proved R uther

fo rd ’s scattering law to be valid w ith respect to all p ara m ete rs. T h e ir results, published in July 1912 [5],

* Presented at the V lllth International Symposium on N uclear Q uadrupole Resonance Spectroscopy, Darmstadt, West G erm any, July 2 2 -2 6 , 1985.

R eprint requests to Prof. Dr. P. Brix, Max-Planck-Institut für Kernphysik, Postfach 10 3980, 6900 Heidelberg.

gave the first ex p e rim en tal n u m b e r for the ex

trem ely sm all rad iu s o f th e nucleus: less th a n 30 fm in the case o f gold.

N iels Bohr, w hose 100th b irth d a y th e scientific w orld is ce le b ra tin g this year, h ad m oved to M an chester early in 1912. T he first o f his th ree fam ous papers “ O n th e C o n stitu tio n o f A tom s an d M ole

cules” is d ated A pril 5, 1913. W ith th e n u clea r atom a new era for physics, chem istry, an d all natural sciences h ad begun.

A lready betw een 1915 an d 1919, a t least 12 geo

m etric nu clear m odels — o f course pu rely specu

lative - w ere p ro p o sed [6], all o f th e m assum ing electrons as constitu en ts o f th e nucleus. R u th e r

fo rd ’s d esin te g ra tio n o f th e nitro g en nucleus by a rays in 1919 gave th e first evidence o f nuclear structure [7], In the sam e y ea r he o b serv ed “ an o m alous results” for a -p -sca tte rin g a n d concluded th a t the a p article was a disc w ith a b o u t 3 fm rad iu s [8]. In 1924 Bieler [9] m e asu red th e d ev iatio n from p oint-nucleus scattering as a fu nction o f angle in ring geom etry for a lu m in iu m and o b ta in e d 3.44 fm for its n u clea r radius. But d iffe re n t analyses yielded substantially d iffe re n t values [10]. T h e sizes o f the heaviest nuclei w ere e v a lu a ted in 1928 by G am ow and H o u term an s [11]. T h ey ap p lie d th e th eo ry o f i decay to th e G e ig e r-N u tta ll-re la tio n o f 1911 [12],

In 1930, th e well know n A

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rule w as w ritten dow n (for light n uclei) by R u th e rfo rd , C hadw ick, and Ellis [13]: “ F o r a rough a p p ro x im a tio n we m ay 0340-4811 / 86 / 0100-0003 $ 01.30/0. - Please order a reprint rather than making your own copy.

Fifty Years of Nuclear Quadrupole Moments*

Proceedings of the VIIIth International Symposium on NQR Spectroscopy

International Committee

Local Organizing Committee National Advisory Committee

Sponsors

Fifty Years of Nuclear Quadrupole Moments*

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