MÖSSBAUER STUDIES OF 155Tb SOURCES PRODUCED BY RECOIL IMPLANTATION IN IRON AND NICKEL

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MÖSSBAUER STUDIES OF 155Tb SOURCES

PRODUCED BY RECOIL IMPLANTATION IN IRON AND NICKEL

G. Mennenga, L. Niesen

To cite this version:

G. Mennenga, L. Niesen. MÖSSBAUER STUDIES OF 155Tb SOURCES PRODUCED BY RECOIL

IMPLANTATION IN IRON AND NICKEL. Journal de Physique Colloques, 1980, 41 (C1), pp.C1-

439-C1-442. �10.1051/jphyscol:19801171�. �jpa-00219659�

JOURNAL DE PHYSIQUE Colloque CT, suppl6ment au n

1 , Tome 41, janvier 1980, page Cl-439

~ & ~ ~ A U E R STUDIES OF 1 5 5 ~ b SOURCES PRQWCED BY RECOIL IMPLANTATION I N IRON AND NICKEL

G . Mennenga and L. Niesen

Laboratoriwn voor AZgemene Natuurkunde and MateriaZs, Science Center, University of Groningen, the NetherZands.

Introduction. - As part of a program ,to study the "stopper" foils. The recoil energies were in the -fine interaction of rare earth impurities in range 0-2 MeV. The 58Gd foils were by f~anagnetic metals /1,2/ we have produced reducing 100 mg of 58Gd203 (purity 99.9%) and 1 5 5 ~ b sources (T+ = 5.6d) to stw.3~ the 5/; + 3/; rolling the pallet thus abtained. The Fe and Ni 86.5 keV Mijssbauer transition in 5~d. Unlike in foils were rolled fran 99.998% pure material with the other rare e m , the Gd hyperfine field has a thickness of 25 Fun. Irradiations of typi~ally no orbital contribution, thus enabling the study ²⁰ llAh (beam cu~rent

3 @ )

of the contact contribution into sane detail. _{I I}

Moreover, this study was set up as a first ex-

ploration of the merits of the recoil implantation

996

technique for the production of 16ssbauer sources

z *

of (rather) short lived isotopes. -

- E x p r i f u e n t a L - , , 30 158Gd foils and the same _S

number of Fe (Ni) foils, each 1-2 pm thick, were

5 clanped between Al ringssand alternately stacked ⁼ into a cilindrical housing that was "onnected to

a beam line of the Gronirqen cyclotron. Using a

90 MeV a-beam, the 55Dy nuclei in the back side

-8

-

VELOCITY l c r n l s l

0.2 un thick layer of the 158Gd taxgets, pro-

Fig. 1 : Massbauer W t r a of s~ in Fe and Ni, duced via the reaction 158Gd(a,7n) 1 5 5 ~ , were

right after recoil hplantation in a He atroosphere.

directly implanted into the neightouring Fe (Ni) .

Table 1 .- Parameters of Massbauer s-pectra of recoil unplanted 559%.& ad 5 5 ~ 2 ^sources. Isaner shifts with respect to a source of 1 5 5 ~ u in SmPd3.

Cmpnent 2

fraction 1,s. Ig,lln&fi l e 2 4

( 8 ) (lIIn/s) (mn/s) mn/s

-

75-20 +10 -0.04+0.04 0.23.2 4.8t0.4

45220 -0.13f0.04 0.2fl.2 4.0i0.5 Host

Fe Ni

Cmpnent 1

fraction 1.S. 1 ^gnunBhf 1

( W s ) (mn/s)

+20 -0.30+0.04 0.27+0.04 25-10

55220 -0.09+0.01 0.17+0.03

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19801171

c1-4.40 JOURNAL DE PHYSIQUE

yielded, after a few half lives of 5 5 ~

( 3 ⁼ 9.5h), sources of 1 5 5 ~ b in Fe (Ni) with a strength of * ^0.2 MEq (50pCi) , sufficient to produce %ssbauer spectra with quite reasonable statistics.

To prevent beam heating effects the final recoil hplantati~ were carried out in a Heamsphere (50 kPa) . The temperature rise of the foils under these conditions was indepedently masurd, using .the resistivity of the foils, to be 10 K. This can be ampared to the taperatme rise in vacuum, AT = loOK, under the same con- ditions. In order to study possible radiation damage effects of the 90 bbV a-particles

($4 x 1017/,2) a 155TWe source was made with the Groningen Isotope Separator- In this case the

s5Tb was made by the reaction 5 9 ~ b (pr 51-11

1 5 5 ~ ~ a ^{155~b. 157 ,g of '59~b metal was}

irradiated for 30pAh w i t h 50 MeV protons. Within a few hours after the irradiation a radiochemical separation was carried out to rarrxre the unacti- vated 15%. S u b s v t l y the activity was im- planted in Fe (implantation energy 100 KeV, dose

3 1014/~2).

&ssbauer spectra were masurea at 4.2 K using an enriched single line absorber (39 mg/an2 lS5C&

in NaCs2 GdCls) . ^When corrected for thickness effects this absorber yields practically natmal

linewiath. Its isaner shift S = 0.47 mn/s with respect to W 3 .

&sults ard discussian.- Kksbauer s-pctra m u r e d right after implantation are given i n fig. 1. For both hosts the spectra could only be fitted in a satisfactory way by assuming the presence of at least two canpnents. The first capnent, exhibit- ing only mgnetic hyperfine interaction, can be attributed to lS5~d nuclei at substitutional lattice sites. For the other ampnent the magnetic

hyperfine field is strongly reduced a d an appre- ciable quadzupole interaction is found, typicdl for nuclei at sites where the cubic -try is destroyed, for instance by the presence of vacan- cies. The hyperfine parameters of both c m p n e n t s are given in table 1. The isaner shift of 1 5 5 ~ d at substitutional lattice sites, S = -0 -30 2 0.04mn/S;

comeponds to the highest electron density at the nucleus measured thus far. A h m i n e field on

'55Gd nuclei at substitutional sites in iron,

1E&J = 14.2 f 2.3T, is deduced. !Chis value agrees reasonably well with DPAD/~/ and IPAC /4/ measure- ments at ram tertl_nerature, but not w i t h an un-

published Mijssbauer measurauent quoted in the literawe /5/. For the systgn 55'i'bNN we find for the hyprfine field at the substitutional site

lehfl = 8.7 + 1.8T1 sawdmt smller than the result of a man tapratme DPAD m m t /3/- 1Ve note that none of the older experiments have been analyzed a s w m i q the presence of m e than one site for the hplanted ion. This may explain m s t of the discrepancies.

Bernas /6/ has analyzed the contact con- tributions tc the hyperfine field of rare earth impurities in iron. Unfortunately he uses the wrong sign for the 4f core polarization mtri-.

bution.

Corrected for this, his estimate for is -12T, in excellent agr-t w i t h our measurement.

The situation in the nickel host is less well understood. The hyprfine fields of Lu in Fe and Ni /7/ shaw that the host contribution is much smaller for Ni, as witnessed also by the much smaller exchange fields on the rare earth ions /1/.

Therefore one m l d expect a daninant 4f core

polarization contribution and consequently a

_msitive hypxfine field. The IPAC results /8/,

hmever, imply a negative sign.

W e also performed recoil inplantations i n vacuuan ( l 5 5 T b ~ ) , during w h i c h the Fe f o i l s reakhd a tenperatwe of about 120'~. In this

case the s p e c t n ~ ~ ~ shm one canpnent, exhibiting only a quadrupole interaction, le2@I = 7 mn/s and an isaner s h i f t S = +0.30 (4). mn/s. 3 m l l syste- matic variations of the M i parameters are ob- served between various sources, indicating a partial annealing during &plantation, that is sensitively dependent on, irradiation conditions.

To investigate this annealing kehaviour further, sThFZ Iv6ssbauer spectra were measured after annealing the source for half an hour in a H2 flaw a t 300°c, 500'~ and 600'~ successively.

As can be seen fran Fig. 2, the important annealing step takes place between 500'~ and 600°c, after Wch both cmpnents of the original spec-

have disappeared. This is i n agreement with results on other rare earths i n iron /1,2,9/. After the 600'~ anneal the spectrum can be f i t t e d with m e quadrupole s p l i t c a p n e n t with 1 e2@ I = 8.0 (l)mn/s or eq = 1.3 x 1022 v/m2 and an isaner s h i f t

S = +0.30(4) 4 s . The same s-was found after annedlblg i h 2 h@anted in McuUm

or with the isatope separator.

When canparing these results with the im plantations in vacuum one observes a striking effect: an increase,~of the irrplantatim -ature is much more efficient in creating a non-substi- tutional envi,mment for the rare earth impurities than annealing afterwards. This effect has also been &served by ReintseM /lo/ ^{and by} Than5 e t al. /11/. Huivever, their interpretations differ considerably, Lack of space prevents us f r a n dis- Cussing t h i s point fwther.

The spectnnn obtained £ran the saurce pro- duced with the Isotape Separator -ed to be

identical with that of the recoil inplanted source

(fig. land 2, top). This strongly suggests that the final enviroment of the 155Tb atcms deperds only on the l a s t stage of the evolution of its awn damage cascade. Neither the interaction between individual cascades (present t o sane extent i n the sanple inplanted with the Isotope Separator) , nor the large particle flux on the recoil hplanted simples appears to be an important factor.

AFTER IMPLANTATION

,

,

-

VELOCITY I crn 1 s )

Fig. 2: Annealing behaviour of 5 5 ~ e sources produced by recoil inplantation. Spectra were maswed a t 4.2 K after a 30 min anneal a t t a p e r a t m e TA .

References

Niesen, L., Ylperfine Interactions 2 (1976) 15.

Niesen, L. and Ofer, S., w i n e Interactions 4 (1978) 347 .

Klepper, O., Spehl, H., andwertz, N., 2. Phys. 217 (1968) 425..

Kugel, H.W., -1, L., Hubler, G. a d M c k , D.E., Phys. Rev. B13 (1976) 3697.

Fussell, P. , private ccmn. quoted i n Table of Hyperfine fields, Koster, T.A. and Shirley, P .A*, in W f ine Structure and Nuclear Rhliations, ed. Matthias, E. and Shirley, D.A.

(North-Holland, 1968) p. 1244 .

Bernas, H., Phys. Rev. (1977) 596 Keus, H. and Huiskmp, W.J., Physica

(1977) 137 and references therein.

Brenn, R., Lehatm, L. and SpeN, B., 2. Phys.

C 1-442 JOURNAL DE PHYSIQUE

209 (1968) 197.

-

/9/ Cohen, R.L., Beyer, G. and Deutch, B.I., Phys. Rev. letters 2 (1974) 518.

/lo/ Reintsm, S.R., Drentje, S.A., Schurer, P., arad de Waard, H., Radiation Effects 24 (1975) 145.

/11/ T h d , L., Bernas, H. and r.Ieunier, R . , to be

published.