Application of the sum-peak and coincidence spectrometer to the determination of the absolute efficiency

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Application of the sum-peak and coincidence

spectrometer to the determination of the absolute

efficiency

G. Mallet

To cite this version:

G. Mallet.

Application of the sum-peak and coincidence spectrometer to the determination of

the absolute efficiency.

Journal de Physique Lettres, Edp sciences, 1983, 44 (4), pp.147-150.

�10.1051/jphyslet:01983004404014700�. �jpa-00232156�

Application

of the

_sum-peak

and coincidence

_spectrometer

to

the

determination

of the

absolute

_efficiency

_(*)

G. Mallet

U.E.R. _I.P.M., Université de _Nice, Parc Valrose, 06034 Nice Cedex, France

(Re~u le 13 avril 1982, revise le _{2 juillet, accepte} le 20 decembre 1982)

Résumé. 2014 Nous montrons comment l’utilisation de deux détecteurs de _Ge(Li)

_identiques,

permet

de tirer

_parti

des

_pics

d’addition _{pour déterminer l’efficacité absolue de détection des}

_photocopies.

Abstract - We

point

out that the use of two identical _Ge(Li) detectors allows us to take _advantage of the

_parasitic

_summing effect to _{determinate the full energy}

_peak

_efficiency.

Classification

Physics

Abstracts 29.70

Normally,

in _{y spectra,} we observe distributions due to the addition in the detector of

_pulses

coming

from _gammas emitted in coincidence

_by

the

_sample

studied.

_Generally,

this addition effect not

_only

_complicates

the

_stripping

of the

_spectra,

but also

_impedes

an accurate estimate of the transition intensities

_[1-2].

However,

some authors did

_try

to take

_advantage

of this addition effect

_[3-5].

In

_{previous publications [6-9],}

we have demonstrated that

_great

_improvements

in the

deter-mination _{of the energy levels}

_{of radioisotopes by}

the

_{sum-peak technique}

of coincidence

_counting

have been achieved

by

the use of two identical

Ge(Li)

detectors.

_They

are located on either side of

the

_sample,

and are associated with a coincidence unit. The aim of this work is to show that the

determination of the absolute full energy

peak efficiency (F.E.P.E.)

is also

possible using

this

technique.

Let us consider a nucleus

_having

at least three excited

_levels,

the deexcitation of which is sketched in

_figure

1. It is _easy to show

_[1,

_7-9]

that the

_experimental

intensities

_Sij

and

_Sijk

of the

sum-peaks corresponding respectively

to the simultaneous

_absorption

of the

_{gamma i}

_{and j}

and

_{i, j}

and k are

_{given by}

the

_following

relations :

(*) La version francaise de cet article a ete _proposee aux _Comptes Rendus de 1’Academie des Sciences.

L-148 JOURNAL DE PHYSIQUE - LETTRES

Fig. 1. -

Example

of a deexcitation mode

_allowing

the determination of the F.E.P.E.

where :

_{li,1 J}

and

_Ik

are the intensities

_{of y~, y~}

and _yk

_{respectively;}

_{ei, ej}

_{and Ek}

are the F.E.P.E.

at the

_energies

_{Ei, Ej}

and

_{Ek ;}

_IN2

and

_IN3

the intensities of the

_population

of the levels

_N2

and

_N3

(Fig. 1) ;

N is the

_activity

of the source; T the duration of the

_experiment

and W a

coefficient

of

angular

distribution.

The ratio

_{of (2)}

to

_{(1) gives}

the F.E.P.E. at _energy

_{Ek :}

As an

_application

of the method we have

_measured,

_during

the excitation

of 11 °Cd

_{[10] (Fig. 2)}

the F.E.P.E. at 937.5 keV of two identical

_{44.4 (~}

x 47.5

mm2

_single-ended

_Ge(Li)

detectors grown from the same Ge

_ingot.

The detectors had an active volume of 70.5

cm3

and an _energy

resolution of 2.2 keV at 1.33 MeV. The distance between the detector cases and the source was

10.0 cm. Relation

₍₃₎

allows us to write :

Measurements of

_peak

areas of 2479.9

(937.5

+ 884.7 + 657.7

_keV)

and 1542.4 keV

(657.7

+ 884.7

_keV)

were

_{performed sixty}

six times

_(during

800

_hours)

with a 8192 channel

analyser (Hewlett-Packard 5401/B) during

our

_study

of the

_sum-peak

and coincidence _spectrum of

_{110 Agm+g}

_[8],

while

_{IN(l 542.4kev)}

and

_1Y~93~,s

_keY) are the

_intensities,

due to the results of

_Meyer’s

work

_{[11, 12].}

The

_extensive

use of semi-conductor detectors in

_{y-spectrometry}

has

led

many authors to

propose

original experimental

or theoretical methods for the absolute

_efficiency

determination.

Waibel et ale

_[13]

have classified the

_experimental

methods in four

_{categories :}

1)

the

_simplest

method _{needs calibrated y-ray} sources. The

_{experimental photopeak efficiency}

Fig. 2. - Partial level scheme of 11 °Cd.

where : N is the number of detected

_pulses

in the

_photopeak

area, A is the

_{disintegration}

rate of the _y-ray source,

t is the

_counting

time,

and

I is the absolute

intensity

of the relevant

y-emission ;

2)

for

_high

_y-ray

_energies,

well defined y-ray sources

_{produced by}

nuclear reactions are used.

In this case, it is

absolutely

necessary to know the cross sections and the emission

_{probabilities;}

3)

the coincidence method allows us to determine

simultaneously

the

_efficiency

of the detector and the source

_strength;

4)

above 1.022

_MeV,

relative

_efficiency

determination is

_possible

with a

pair

_{spectrometer,}

but

the absolute

_efficiency

determination

requires

a calibrated source.

The accuracy of

Ge(Li) efficiency

curves over _{the range 0.1-3.0 MeV obtained with these}

methods is

_generally

contained between 0.5 and 5

_%

_[15-18].

Several authors have

_{proposed semi-empirical}

formulae and

_analytical

functions to _represent

the F.E.P.E. curves of the

Ge(Li)

detectors

[19-21].

The

validity

of these relations has been tested

successfully

for a

_great

_range of

_detectors,

the accuracy

_being

related to a

_precise

_knowledge

of the

detector dimensions.

In addition to the fact that the

_suggested

_technique

i.e.

_using

the

_{parasitic summing}

effect

positively

is _easy to use when it is

enlarged

to the F.E.P.E. determination of one detector used

in the

_single

_mode,

we remark that in the chosen

example

the

uncertainty

is lower than 3

_%

and

consequently

comparable

to the

_previous

methods.

References

[1] WAPSTRA, A. _H., in

_{03B1, 03B2}

and 03B3-ray spectroscopy, ed. K.

_{Siegbahn (North-Holland, Amsterdam)}

1965,

539.

[2] GIRGIS, R. K. and VAN LIESHOUT, R., Nucl. _{Phys. 12 (1959)} 672.

150 JOURNAL DE _{PHYSIQUE -} LETTRES

[4] KANTELE, J. and SUOMINEN, P., Nucl.

Instrum.

Meth. 86 (1970) 65.

[5] HUTCHINSON, J. M. R., MANN, W. B. and MULLEN, P. _A., Nucl. Instrum. Meth. 112 (1973) 187. [6] MALLET, G. and _{YTHIER, C.,} C. R. Hebd. Séan. Acad. Sci. B. 286 ₍₁₉₇₈₎ 183.

[7] MALLET, G. and YTHIER, C., C. R. Hebd. Séan. Acad. Sci. B. 286 ₍₁₉₇₈₎ 211. [8] MALLET, G., Thèse, Nice, 1978.

[9] MALLET, G. and _PRAVIKOFF, M. S., Nucl. Instrum. Meth. 184 ₍₁₉₈₁₎ 469.

[10] MALLET, G., DALMASSO, J., MARIA, H. and ARDISSON, G., J.

_Phys.

G. 7 _{(1981) 1259.} [11] MEYER, R. _{A., private} communication to Nucl. Data Sheets 22

_{(1977) 135.}

[12] MALLET, G., J. _Phys. Soc. _Japan. 50 ₍₁₉₈₁₎ 384.

[13]

WAIBEL, E. and GROSSWENDT, B., Nucl. Instrum. Meth.131 (1975) 133.

[14]

CEJNAR, F. and KOVA0158, I., Int. J.

_Appl.

Radiat. _Isotopes 31 (1980) 79.

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L.,

Nucl. Instrum. Meth. 91 ₍₁₉₇₁₎ 349.

[16]

MC NELLES, L. A. and CAMPBELL, J. L., Nucl. Instrum. Meth. _{109 (1973)} 241.

[17]

ABREU, M. _{C., MAIO,} A. A. and TEMES D’OLIVEIRA, M. _J., Nucl. Instrum. Meth. 123 ₍₁₉₇₅₎ 295.

[18]

HELMER, R. _G., Nucl. Instrum. Meth. 193 ₍₁₉₈₂₎ 87.

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