Study of nuclear quadrupole interactions indi�erent environments of decaying atoms of 75Se by sum

peak method

Kulwant Singha,*, Kawaldeep b, H.S. Sahotab

aDepartment of Physics, Guru Nanak Dev University, Nuclear Spectroscopy Laboratory, Amritsar 143 005, IndiabDepartment of Physics, Punjabi University, Patiala 147002, India

Received 16 June 1999; received in revised form 9 November 1999; accepted 10 December 1999

Abstract

The sum peak intensity I400 (279 + 121 keV) relative to its singles peak intensity I279 or I121 has been determined

in various environments of 75Se by gamma±gamma summing technique in a single HPGe detector. The change inintensity has been used to determine nuclear quadrupole interaction frequencies and electric ®eld gradientcomponents in di�erent environments, e.g. Se-glycerol, Se-hydrochloric acid (HCl), Se-perchloric acid (HClO4), Se-blood samples with and without anti-coagulant, Se-alanine and Se-cysteine at di�erent pH values. The electric ®eld

gradient is found to vary with chemical complex formation. 7 2001 Elsevier Science Ltd. All rights reserved.

Keywords: Sum peak method; Electric ®eld gradient; Nuclear quadrupole interaction; Asymmetry parameter

1. Introduction

The chemical environments di�erentially a�ect theprobabilities and, consequently, the observed intensities

of radioactive nuclides for the gamma rays accompa-

nying electron capture. The after e�ects (AE) of elec-

tron capture decay of 75Se and the e�ect of the longhalf life of the 279 keV level (280 ps), on the direc-

tional correlation parameter of the cascade involving

this level are still controversial. Baverstam et al. (1972)studied 121±279 keV g correlation in 75Se with Al2O3

and Al metal backings to search for after e�ects and

obtained positive results in Al2O3. Later on, Puri

(1978) measured the 121±279 keV correlation in ®vedi�erent chemical environments to detect the in¯uenceof AE due to the electron capture process in 75Se, but

no such e�ects were found. Mittal (1980) observed thevariation of attenuation coe�cient �A22� in the 121±279 keV cascade in di�erent concentrations of EDTAand attributed the changes to the change in viscosity

of the solution.A sum peak is observed as a result of simultaneous

detection of two cascading gamma rays as one event.

The emission angle between the two gamma's has adistribution pattern which may be altered by the en-vironmental conditions. The intensity ratio of the sum

peak to the singles peak can be used to observechanges caused by the environment (Yoshihara et al.,1983; Yoshihara, 1983). Kudo et al. (1987) applied the

same method to study human platelet cells andmeasured the angular correlation parameters using

Applied Radiation and Isotopes 54 (2001) 261±267

0969-8043/01/$ - see front matter 7 2001 Elsevier Science Ltd. All rights reserved.

PII: S0969-8043(00 )00100-7

www.elsevier.com/locate/apradiso

* Corresponding author. Tel.: +91-183-258840; fax: +91-

183-258819.

E-mail address: kulwant.singh@excite.com (K. Singh).

111In as the PAC nuclide. Mullins and Kaplan (1983)and Butz (1989) applied the perturbed angular corre-

lation technique respectively and reported that 181Hfand 199Hg can act as suitable probes to reveal intermo-lecular motion.

As a sequel to our previous measurements, Dhillonand Singh (1990) and Dhillon et al. (1991) with 133Baand 160Tb as perturbed angular correlation probes, the

present measurements were made for di�erent environ-ments of decaying atoms of 75Se.

2. Measurements

2.1. Sample preparation

The radioactive isotope 75Se was obtained fromBhabha Atomic Research Centre (BARC), Trombay,

Mumbai in the form of sodium selenite in NaOH sol-ution. Di�erent compounds of 75Se viz. Se-Ethylenediamine tetraacetic acid (EDTA), Se-hydrochloric acid

(HCl), Se-perchloric acid (HClO4), Se-Leucine, Se-Blood (A+), Se-Blood serum separated from the bloodsample containing anti coagulant, Se-alanine, Se-

cysteine etc. were prepared by the chemical processingof Se. Blood serum was separated from a whole bloodsample (A+) by the method given by Alexander andGri�th (1983). The pH of the proteins alanine and

cysteine was lowered by adding glacial acetic acid andthe pH was again adjusted to the original value forcysteine by adding NaOH solution. The samples were

kept in perspex cylindrical vials having dimensions of4 � 8 mm. In all the samples, the amount of 75Seadded was enough to give a count rate of the order of

1000 cps.

2.2. Experimental set up

The source detector arrangement for sum peakmeasurements is shown in Fig. 1. The gamma ray sumpeak intensity measurements were carried out by using

a high resolution HPGe detector (active area 200 mm2

and sensitive depth 7 mm) coupled to an EG & G

ORTEC plug in card (4096 channel analyser) with PC/AT computer. Each sample was placed at 5 mm fromthe detector surface on its axial line. We consider that

the ®rst gamma ray (say 121 keV) of the 121±279 keVcascade enters the detector along the central axis andthe second gamma ray (279 keV) enters the same

detector at an angle y: The upper limit of y is y0, halfthe angle of the cone which is formed by the detectorsurface and the point source. Yoshihara et al. (1983)

have shown that in the sum peak method, the sumpeak intensity ratio varies with the detector distance.Therefore, special attention was paid to keep thesource detector geometry ®xed so that y would remain

®xed for all the samples of 75Se. A typical sum spec-trum of 75Se is shown in Fig. 2.

2.3. Sum peak intensity ratio measurement

When two cascade gamma rays emitted from oneradioactive nucleus enter the detector within the resol-ving time 2tg of the detector, besides the singles corre-sponding to the two gamma rays a sum peak appears

at an energy corresponding to the sum of two gammaray energies. Since the observed sum peak intensitycontains contributions from the chance coincidences of

two di�erent nuclei emitting cascade gamma rays,therefore, the observed sum peak ratios were correctedfor the chance coincidences (Kudo et al., 1987) based

on the following, where I OBS is the observed sum peakintensity for the (121 + 279 = 400) keV sum peak:

ISUM

I121� IOBS

SUM

I121ÿ 2tg �1a�

ISUM

I279� IOBS

SUM

I279ÿ 2tg �1b�

I121 and I279 correspond to the intensities of 121 and279 keV gamma ray transitions respectively. The photopeak at 400 keV has contributions from 136 to 264

keV gamma summing besides the 400 keV gammasingles. The counts corresponding to 121±279 keVsumming in the detector were extracted by subtracting400 keV singles from knowledge of the intensity and

e�ciency for 400 keV relative to the strong 264 keVgamma ray. The 136±264 keV sum counts leading to400 keV singles under the 400 keV photo peak were

calculated from 136 to 66 keV sum counts after weigh-ing them for I66 and I264 (I66 and I264 are the intensitiesof 66 and 264 keV gamma rays). These were also sub-

tracted from the observed photo peak at 400 keV. Thetotal error in the 121±279 keV sum counts increased to5% due to these subtractions.

Fig. 1. Geometrical set-up for the source and detector for the

projection of cascade gamma rays.

K. Singh et al. / Applied Radiation and Isotopes 54 (2001) 261±267262

2.4. Determination of perturbed angular correlation

parameters

The time integral attenuation coe�cients G22�1� ofall samples were determined using the following re-

lations given by Kudo et al. (1987):

I400I121� r279e279

�1� A22G22�1�Fgeo

� �2a�

I400I279� r121E121

�1� A22G22�1�Fgeo

� �2b�

where r279 and r121 are the emission probabilities and

were taken from the latest Nuclear Data Sheets (Far-han and Saheen, 1990) e279 and e121 are detection e�-ciencies of 279 and 121 keV gamma rays, respectively,

and were determined in the pre sent work and Fgeo is a

geometrical factor and was calculated by performingsum peak measurements on the specimens Se-EDTAand Se-glycerol whose G22�1� values were known(Singh et al., 1983) for the 121±279 keV cascade and

are listed in Table 1. The measured A22G22�1� valuesfor di�erent environments are shown in Table 2. Sub-stituting the value of the geometrical factor (present

Fig. 2. (a) Partial decay scheme of 75Se. (b) The sum spectrum of 75Se taken with intrinsic Ge detector.

Table 1

Determined geometrical parameters for 75Se

Detection e�ciencies Sum peak used Fgeo

E121 � 1:572220:0492 ISUM=I279 0.667720.0582

E279 � 0:229120:0005 ISUM=I121 0.636520.0624

K. Singh et al. / Applied Radiation and Isotopes 54 (2001) 261±267 263

work), emission probabilities, geometrical e�ciencies,

and �A22 � 0:40420:004� taken from the Nuclear data

sheets (Farhan and Saheen, 1990), G22�1� were deter-

mined which in turn were used to calculate the quadru-

pole frequencies and electric ®eld gradients in di�erent

complexes.

The time integral attenuation coe�cient G22�1� for

the polycrystalline materials is given by:

G22�1� �Xn

S2n

�1� no0t� 2�3�

Fig. 3. Theoretical variation of G22�1� with o0t:

Table 2

A22G22�1� values for di�erent Se compounds

Sample A22G22�1� values Weight average

ISUM=I121 ISUM=I279

Se 0.390620.0391 0.393120.0443 0.391920.0293

Se + EDTA 0.300420.0376 0.298320.0443 0.299520.0286

Se + Glycerol 0.226620.0520 0.224020.0150 0.225320.0144

Se + HCl 0.348620.0227 0.352420.0438 0.349320.0201

Se + HClO4 0.375020.0026 0.369020.0439 0.373420.0225

Se + Blood serum with anticoagulant 0.319320.0379 0.364420.0441 0.338520.0287

Se + Blood without anticoagulant 0.346220.0383 0.350920.0439 0.326420.0256

Se + Leucine 0.379220.0255 0.378220.0441 0.378920.0220

Se + Alanine (pH = 7.40) 0.340020.0384 0.336820.0440 0.337220.0289

Se + Alanine (pH = 5.00) 0.326820.0387 0.311820.0432 0.320120.0288

Se + Cysteine (pH = 7.28 original sol.) 0.384520.0390 0.385320.0442 0.384920.0292

Se + Cysteine (pH = 7.28) regained) 0.384120.0390 0.383020.0442 0.383620.0292

Se + Cysteine (pH = 5.00) 0.357020.0385 0.365020.0044 0.360720.0290

Se + Cysteine (pH = 3.36) 0.354520.0385 0.359420.0420 0.356820.0283

Se + Cysteine (pH = 2.80) 0.342520.0384 0.342320.0441 0.342420.0290

Se + Cysteine (pH = 1.95) 0.333220.0381 0.324320.0437 0.329120.0287

Fig. 4. (a) Variation of precession frequencies o1, o2 and o3

with asymmetry parameter Z: (b) Splitting of intermediate

level of spin 5/2.

K. Singh et al. / Applied Radiation and Isotopes 54 (2001) 261±267264

where the summation index n is �m 2 ÿm 0 2� for theintegral spin I and 2(m 2 ÿm 0 2� for the half integral

spin of the intermediate level, m and m ' are the mag-netic quantum numbers, t is the mean life time of theintermediate state. The numerical values of S2n coe�-

cients are tabulated by Alder et al. (1953). The angularfrequency `o0' is related to the quadrupole interactionfrequency `oQ' by the following expression:

o0 � 6 oQ for half integral spin I �4a�

o0 � 3 oQ for integral spin I �4b�

From the plot of G22�1� versus o0 (Fig. 3), o0 valueswere noted for di�erent environments of 75Se corre-

sponding to the experimental G22�1� values. Thequadrupole interaction frequency oQ is related to theelectric ®eld gradients by the following relation:

Vzz � wQ4I�2Iÿ 1�heQ

�5�

Table 3

The angular frequency o0 and the precession frequencies o1 and o2 with asymmetry parameter Z:

Sample Asymmetry parameter �Z) o0 (M rad/s) o1 (M rad/s) o2 (M rad/s)

Se 0.5998 143.2 1145.31 619.16

Se + EDTA 0.5715 956.0 7646.08 10802.50

Se + Glycerol 0.6234 1768.6 14140.46 19989.71

Se + HCl 0.3895 532.9 3711.65 6202.28

Se + HClO4 0.4992 334.6 2676.13 3588.32

Se + Blood(A+) 0.5492 286.8 2293.82 3242.84

Se + Blood serum with anticoagulant 0.5925 621.4 5337.82 6909.78

Se + Blood without anticoagulant 0.7215 717.0 6617.91 7855.45

Se + Leucine 0.3916 310.7 2162.47 3618.32

Se + Alanine (pH = 7.40) 0.8082 597.5 5514.92 6532.46

Se + Alanine (pH = 5.00) 0.4235 764.8 5326.83 8909.65

Se + Cysteine (pH = 7.28) original sol.) 0.8991 239.9 2363.71 2569.96

Se + Cysteine (pH = 7.28) regained) 0.6991 274.8 2360.53 3055.77

Se + Cysteine (pH = 5.00) 0.7018 454.1 3903.62 5049.59

Se + Cysteine (pH = 3.36) 0.4009 478.0 3329.27 5568.70

Se + Cysteine (pH = 2.80) 0.8524 573.6 5577.13 6068.03

Se + Cysteine (pH = 1.95) 0.7997 669.2 6176.90 7316.58

Table 4

The components of electric ®eld gradient for di�erent compounds of Se

Sample VZZ � 1025 (esu/cm2) VYY � 1025 (esu/cm2) VXX � 1025 (esu/cm2)

Se 0.629 0.503 0.126

Se + EDTA 4.190 3.305 0.885

Se + Glycerol 7.764 6.302 1.462

Se + HCl 2.370 1.646 0.723

Se + HClO4 1.469 1.101 0.735

Se + Blood (A+) 1.259 0.975 0.284

Se + Blood serum with anticoagulant 2.728 2.172 0.556

Se + Blood without anticoagulant 3.148 2.709 0.438

Se + Leucine 1.364 0.949 0.415

Se + Alanine (pH = 7.40) 2.624 2.372 0.252

Se + Alanine (pH = 5.00) 3.362 2.393 0.969

Se + Cysteine (pH = 7.28 original sol. 1.049 0.996 0.053

Se + Cysteine (pH = 7.28 regained 1.206 1.205 0.182

Se + Cysteine (pH = 5.00) 1.994 1.696 0.297

Se + Cysteine (pH = 3.36) 2.099 1.470 0.629

Se + Cysteine (pH = 2.80) 2.519 2.333 0.186

Se + Cysteine (pH = 1.95) 2.938 2.645 0.294

K. Singh et al. / Applied Radiation and Isotopes 54 (2001) 261±267 265

where e is the unit charge and Q is the nuclear quadru-pole moment for the 5/2 state.

When the nucleus is under the in¯uence of externalforces during the time between the emissions of thetwo g-rays, the correlation is perturbed. The inter-

action of the electric ®eld gradient with the nuclearquadrupole moment causes an energy splitting of theintermediate level (I = 5/2) of the nucleus. The inter-

mediate level with I = 5/2 splits into three energylevels (Fig. 4(a)) which in turn gives rise to three fre-quencies o1, o2 and o3 and are given by Butz (1989):

o1 � �E2 ÿ E1 �oQ �6a�

o2 � �E1 ÿ E2 �oQ �6b�

o3 � �E1 ÿ E3 �oQ �6c�

The ratio R�Z� � o2=o1 determines the asymmetry par-ameter Z for di�erent complexes of 75Se.

Z �������������������������������20ÿ 21y� y3

20� 7y

s

where

y � su1=3

cos�f=3� , f � arccos�u�

with

u ����� 21s

20� s3

����3=2

s ������ 20�Rÿ 1� 2�R� 2��2R� 1�

�����The variation of precession frequencies o1, o2 and o3

with asymmetry parameter Z is shown in Fig. 4(b) andthe values of the asymmetry parameter Z calculatedfrom o1 and o2 for di�erent compounds of Se are

shown in Table 3. These values of Z were used to cal-culate the components of electric ®eld gradients ofdi�erent complexes by the following relations and are

listed in Table 4.

jVYYj � jVZZj�1� Z�=2 �7a�

jVXXj � jVZZj�1ÿ Z�=2 �7b�

Z � VXX ÿ VYY

VZZ

�8�

where VZZ, VYY and VXX are the components of the

electric ®eld gradient tensor in the co-ordinate systemwhere the tensor is diagonal and jVZZjrjVYYjrjVXX

3. Discussion

It is clear from Table 2 that the intensity ratio of thesum peak to the singles peak changes with chemicalcomplex formation and the change in pH of the sol-

ution and consequently the angular frequency is in¯u-enced. It is important to mention here that cysteinesolution with re-attained pH attains the G22�1� valueof the original solution. Large variation in the valuesof angular frequency (Table 3) indicates that variousenvironments in¯uence the magnitude of EFG at the

Se site di�erently. It is clearly demonstrated that thestudy of sum peak formation provides information onvarious chemical environments surrounding the decay-ing atoms of 75Se. Thus 75Se can be used as a useful

probe to study biological specimens and proteins.

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