Ferromagnetic effect and spin assignment for the 390 keV state in 62Cu

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Ferromagnetic effect and spin assignment for the 390

keV state in 62Cu

Ung Chan Tsan, M. Agard, J.F. Bruandet, A. Giorni, F. Glaser, J.P.

Longequeue, C. Morand

To cite this version:

L-237

LE JOURNAL DE PHYSIQUE - LETTRES _TOME

37, OCTOBRE _1976, PAGI

Classification

Physics Abstracts

4.220

FERROMAGNETIC EFFECT

AND SPIN ASSIGNMENT

FOR

THE 390

keV

STATE IN 62Cu

TSAN UNG

_CHAN,

M.

_AGARD,

J. F.

BRUANDET,

A.

_GIORNI,

F.

_GLASER,

J. P.

_LONGEQUEUE

and C. MORAND Institut des Sciences

_Nucléaires,

BP

_257,

38044 Grenoble

Cedex,

France

(Re.Cu

le

_{24 juin}

_1976,

_accepte

le

_{15 juillet}

₁₉₇₆₎

Résumé. 2014 Nous _avons attribué à l’état

isomérique à 390 keV du 62Cu les _{caractéristiques} J03C0 = 4+.

L’interaction _hyperfine est observée dans la réaction

_60Ni(03B1,

_pny) 62Cu. La _période de Larmor déduite est _compatible avec les valeurs connues du _{facteur g} et du _champ

_hyperfin

du cuivre dans le nickel.

Abstract. 2014 The 390 keV isomeric state of 62Cu is

assigned as J03C0 = 4+. The

magnetic hyperfine

interaction has been observed in the

_60Ni(03B1,

_pn03B3) 62Cu reaction and the deduced Larmor _period is consistent with known values _{of g} and the

_hyperfine

field of Cu in Ni.

1. Introduction. - The

magnetic

hyperfine

inter-action is often used to measure the

_{g-factor through}

application

of an external field. However this effect can be observed in the

_ordinary

_experimental

_set-up when the studied nucleus recoils in a

_{ferromagnetic}

lattice. This interaction can

_{severely perturb}

the

y-angular

distribution and cause difficulties in the

deduction of the

_{multipolarity}

of the transition under

study.

A

_striking

illustration for the 349 keV _y-ray

decaying

from the isomeric 390 keV state

(T1/2 =

11 ns)

has been observed in the

_6°Ni(a,

_pny)

62Cu

reaction.

2.

_Angular

distribution and

_{magnetic hyperfine}

inter-action. - The

angular

distribution of the 349 keV

y-ray has been measured in the

6°Ni(a,

pny)

reaction

at

_Erx

= 32 MeV. It is almost

isotropic

_as observed

by

Sunyar et

al.

_[1]

in the same reaction at

Ea

= 39 MeV .

This is due to the fact that the time

_{integrated angular}

distribution of this _y-ray is

_severely

_{perturbed by}

the Larmor

_precession

of the

_magnetic

moment of the recoil nuclei around the

_magnetic

field

_randomly

oriented in the

_plane

of a thin _target

_{( ~ 2}

_mg/cm2).

This interaction tends to

_destroy

the

_alignment

produced by

the reaction. If this

_explanation

is correct,

we must observe an

_anisotropy

when we _suppress

this interaction

_{by heating}

the target above the Curie

point

(358 oQ using

the Joule effect

_(-

2.5 A

_through

the

_target).

The

_angular

distribution obtained under these conditions is shown in

_figure

1. It is now

ani-FIG. 1. _{- Angular} distribution of the 349 keV y-ray of 62Cu.

sotropic

as in the case of the

_angular

distribution

observed in the

_63Cu(p,

_pny)

reaction at

_Ep

= 26 MeV where the

_{ferromagnetism}

does not exist.

3. Observation of the Larmor

_frequency

and

life-time measurement - We

can also observe the Larmor

precession

in the

_6°Ni(a,

_pny)

reaction

_by

a time

differential measurement. The _target is in the

_plane

perpendicular

to the beam axis and there is no external

magnetic

field. We observe oscillations when the

target is at room _temperature and these oscillations

disappear

when the _target is heated above the Curie

point.

The

_magnetic

field is

_randomly

oriented in

L-238 JOURNAL DE _{PHYSIQUE -} LETTRES

the _target

_plane,

so we can calculate the time

distri-bution

_{W(O, t) by}

considerations

_analogous

to those

of ref.

_{[2] (where}

the

_magnetic

field is

_randomly

oriented

_throughout

the

_target

_volume).

We find when the

_A4

term is

_{neglected :}

W(O,

t =1

e-t~t 1

+A 2 P2(COS 0) P2(cos

(0t))

(1)

where r is the lifetime of the level.

However,

a convolution is _necessary due to the width of the

_{cyclotron pulse}

and the electronic

_timing

resolution

b(t’)

(FWHM

= 5

ns),

that leads _{to :}

By

fitting

the

_experimental

curve, we can deduce

the values of the Larmor

_period

_TL

and

_{A 2.}

We find

TL

= 37 ± 8 _ns and

A2

= 0.20 ± 0.08. These results

are consistent with the values of

_{A2 (0.22)}

deduced from

_angular

distributions from a heated

_target

and of

_TL

_{(45 ns)}

deduced from known values of

g = 0.667

[3]

and the

magnetic hyperfine

field of Cu in Ni

_(-

45

_{kG) [4].}

The

_{quasi-isotropy}

of time

_{integrated angular}

distribution at room _temperature can be understood

by

integrating

the formula

_(1).

_Performing

this

inte-gration,

we find

_A2

_int./A2

diff. = 0.275.

We

_emphasize

that this result is obtained without

any external

magnetic

field. If

unknown,

either g

or the

_hyperfine

field could be deduced from such

measurements as is

done

in the case of an external

field but now with _very

simple experimental

_set-up.

The lifetime of the 349 keV _y-ray has been measured in the

_63Cu(p,

_pny)

and

_6°Ni(Ct,

_pny)

reactions. The result is

_Tl/2

= 11 _± 1 _ns consistent with those of

Bleck et al.

[4]

and

_{Sunyar et}

al.

_[1].

Several

measure-ments under different conditions

_(reactions,

_energy of incident

_particle,

different detectors at different

angles...)

were each done with relative error of 3

_%.

FIG. 2. - Time

decay of 349 keV y-ray of 62CU observed in the 6°Ni(ex, pny) reaction. Observation of Larmor oscillations with

the cold _target.

However

_owing

to the

_difficulty

of

_giving

absolute time calibrations better than 5

_%

in this time _range,

we

_give

an absolute error of 1 ns. It should be noted

that the lifetime measurement _may be

_perturbed

when the Larmor

_period

is _greater than the time

measurement _range.

_(In

our case less than 70 _ns,

the time between two

_cyclotron

beam

_bursts.)

The deduced _{value may,} in this case, contain a

_systematic

error.

4.

_{Spin assignment}

of the 390 keV state in

62Cu.

-Verheul in a recent

_{compilation [5]}

has

_adopted

a 4+

_assignment

for the 390 keV state of 62Cu

_although

3+ has been

_{assigned by Sunyar et}

al.

_[1]

and Bleck

et al.

_[3].

_(We

_point

out that the

_y-cascade

observed

in the

_6°Ni(a,

_pny)

reaction

_[1]

is

_41,

_{349, 981, 925,}

597 keV and not

_{41, 597, 925,}

981 keV as

reported

in ref.

_[5].)

We

_assign

4+ to this state for the

_following

reasons :

TABLE I

Angular

distribution

_{analysis of}

the 349 keV y-ray in

62CU

(°) W(O) == _{1 + A2 P2(cos 0) + A4 P4(cos 0).}

(b) Fit parameters (alignment ex2, mixing ratio c5) using a Gaussian distribution of magnetic substate population as defined by Yamazaki[5].

’

0 Constant value of _X2 in this range of 5.

L-239

No 10 FERROMAGNETIC EFFECT AND SPIN ASSIGNMENT FOR THE 390 keV STATE IN 62CU

5.

_Angular

distributions. - Table I shows the values of

_A2,

_{A4, b}

and the

_alignment

_parameters of the

349 keV _y-ray deduced from the

_angular

distribution

analysis

using

the formalism of Yamasaki

_[5].

These values _agree well with the JX = 4+

assignment

to

the 390 keV state. The

_hypothesis

of J" = 3+ _cannot be ruled out but we must admit a

_large

value of the

mixing

parameter

(8

=

0.8)

and the obtained

x2

value is three times _greater than the one obtained

in the case of JX = 4+ in the

angular

distribution

analysis.

The

_angular

distribution of the 147 keV

y-ray

decaying

from the same 390 keV state to the 2 +

state at 243 keV has a similar behaviour. If we had

done our

_analysis

with data obtained with cold target, the 4+

_assignment

would

_give

a value of

mixing

of E2 and M3 of 6

= - 2,

a value difficult

to _accept.

6. Lifetime. - As mentionned

by

Bleck et al.

_[3],

the

_Weisskopf

estimate for the transition

_probability

of the 349 keV _{y-ray agrees} with the observed value for E2

_{(0.3 W.U.).}

Under the 3+

_assumption

for the

390 keV state with the obtained value of

_mixing

(5 ~

0.8)

we find for the Ml transition about

3 x

10-5 W.U.,

whereas

10-3

W.U. is the usual

experimental

lower limit for a Ml transition with

large mixing

of E2

_[7].

This favours 4+ .

7.

_Magnetic

moments. -

Magnetic

moments of odd nuclei

_(Mass

number A

_spin

_J)

can be

_interpreted

in terms of moments _{/~p, Jln} of both odd

_particles

coupled

to an even core nucleus of mass number A-2

and

_spin

zero. The total

_magnetic

_{moment ~} can than

be calculated from the

_angular

momenta

_jp

_jn

and

the g

factor _gp

_{and gn}

of

_{single particles [8]}

The 390 keV state is excited in the

_{(d, t)}

reaction

by In

= 3

[9]

_so that the most

probable configuration

of this state is 7r

_{2P312 V}

_1f5~2.

_{Taking the}

_gp

_{and gn}

from the known values of moments of

_neighbouring

odd mass nuclei

(J-l 61CU3/2 - = 2.13 ; ~ ~Ni,/,- =

0.479)

[10],

we find for the 4+ state at 390 keV in

62Cu

the value

g = 0.65 that

agrees well with the

experimental

value g

= 0.667 ± 0.04 measured

by

Bleck

[3].

The

deduced g

factor value in the case of Jx = 3+ is

g = 0.55

(n

2P3/2 v

Ifs/2

configuration) and g

= 0.46

(7T

_2P3/2

v

_2p3/2

configuration).

We remark

_finally

that the

_knowledge

of the exact

r of the 390 keV state in 62Cu is

_important

for the determination of the JX of

_{high spin}

levels deduced from the

_6°Ni(a,

_pny)

and

_63CU(p,

_pny)

reactions,

the main _y-rays observed in these reactions

_being

in coincidence with the 349 keV _y-ray. A detailed level scheme of

62Cu

will be

_published

later.

8. Conclusion. -

Angular

distribution and lifetime

measurement _may be

_{perturbed by}

the

_magnetic

hyperfine

interaction when the

_target

is

_{ferromagnetic}

even without _any external field.

Thus,

analysis

of,

and conclusions

_concerning

these measurements must

be made

_carefully

when the _target is

_{ferromagnetic.}

References

[1] SUNYAR, A. _{W., GELLETLY, W., MARISCOTTI,} M. A. J. and

THIEBERGER, P., Bull. Am. _Phys. Soc. 14 (1969) 1203;

Annual _{report (1970)} Brookhaven.

[2] MATTHIAS, E., ROSENBLUM, S. S. and SHIRLEY, D. A., Phys.

Rev. Lett. 14 (1965) 46.

[3] BLECK, J., BUTT, R., LINDENBERGER, K. _H., RIBBE, W. and

ZEITZ, W., Z. Phys. 263 (1973) 169.

[4] RAO, G. N., At. Data Nucl. Data Tables 15 ₍₁₉₇₅₎ 553.

[5] VERHEUL, H., Nucl. Data Sheets 13 ₍₁₉₇₄₎ 443.

[6] YAMAZAKI, T., Nucl. Data A 3 (1967) 1.

[7] WAPSTRA, A. _{H., NIJGH,} G. J. and VAN LIESHOUT, R., Nucl.

Spectrosc. Tables (North-Holland Publishing Company,

Amsterdam).

[8] DE SHALIT, A. and TALMI, I., Nuclear Shell Theory (Academic Press) 1963.

[9] DAEHNICK, W. W., PARK, Y. S. and DITTMER, D. L., Phys.

Rev. C 8 (1973) 1394.

[10] SHIRLEY, V. S., Hyperfine Interactions in Excited Nuclei

(Gordon and Breach Science Publishers) 1971, p. 1255 ;