K-SHELL X-RAY INTENSITY RATIOS AND VACANCY TRANSFER PROBABILITIES OF Pt, Au, AND Pb BY A SIMPLE METHOD
L. F. M. Ananda, S. B. Gudennavara* S. G. Bubblya, B. R. Kerurh
" Department of Physics, Christ University Bangalore-560029, Karnataka, India
b Department of Physics. Gulbarga University Gulbarga-585106, Karnataka. India
Received January 8, 2014
The A'-shell X-ray intensity ratios, radiative and total vacancy transfer probablities of platinum, gold, and lead are measured by employing the 27r-geometrical configuration and a weak gamma source, a simple method proposed previously by our group. The targets of Pt, Au, and Pb were excited using 7-rays of weighted energy 123.6 keV from a weak "Co source and the emitted A'-shell X-rays were detected using an HPGo X-ray detector spectrometer coupled to a 16k multichannel analyzer. The measured values of these parameters are compared with the theoretical values and experimental data of other researchers, finding a good agreement. Thus 27r-geometrical configuration method with a weak gamma source can be alternative simple method to measure various atomic parameters in the field of X-ray spectroscopy.
DOI: 10.7868/S0044451014090041 2. THEORY
1. INTRODUCTION
The accurate values of A'-shell X-ray intensity ratios, radiative and total vacancy transfer probablities of elements are essential in the fields of atomic, molecular, and unclear physics, and material science fl 5]. These X-ray fluorescence parameters are also important in studies of the electron capture process, internal conversion electron process, photoelectric effect, and radiative and nonradiative probabilities [6 10]. Over the years, several researchers have measured A'-shell X-ray-intensity ratios and vacancy transfer probabilities using various methods and detectors fll 14]. However, these methods involve complicated single and double reflection geometries, which require strong gamma sources of the order of 10B Bq or more. In this paper, we measure these parameters for platinum, gold, and lead using a simple method proposed previously by our group [15 19], which adopts a 27r-geometrical configuration and weak gamma sources.
E-mail: shivappa.b.gudennavar'&diristuniversity.in
The total vacancy transfer probability from the A' shell to L.j shells of an atom is the sum of radiative vacancy transfer probability j/a"L;(-R) and the nonradiative vacancy transfer probability i/kl^A):
VKL = Vh'Li(R) + VKLi(A).
(1)
The A' L.j radiative vacancy transfer probability is given by
I(KLi)
VKLi (R) = UK
IK(R)
(2)
where J(A'Aj) is the A' L, X-ray intensity, Ik(R) is the total intensity of A'-shell X-rays, and uik is the A'-shell X-ray fluorescence yield. Because the A'-to-Ai radiative transition is forbidden, we have only A' L-2 and A' L?, transitions and the corresponding radiative vacancy transfer probabilities fl] are given by
VKL2(R) =
I(KC
1+
I(R\
I(KC
I(KC
1+
I(Kß)
I (Ka)
= UK
I(R\
IK(R)
(3)
Outlet.
D
T
Inlet.
Dewar-30 liter LN2
Fig. 1. Experimental arrangement: S — source; T target; D — HPGe detector
Vkls (Щ = UK
I(I<C
I(KC
= uK
I(I<a
ЦК a i
IK(R)
(4)
The probability for the radiative transfer of a vacancy from the A' to M shell of an atom is given by
Vkm(R) = uK
i+
I(R\
I(KC
I(KC
1+
/ (A • >
I(KC
= uK
J(A>;) IK(R)
(5)
where J(A>;) = / (l\ r, ) + l(l\r,,).
The total vacancy transfer probability from the A' shell to the L shell can be expressed in terms of the A'-shell X-ray fluorescence yield uik and the A'-shell X-ray intensity ratio I (K j) /1 (K a) [20] as
Vkl =
■ UK
1 + /(A>)//(AC
(6)
The intensity ratio of characteristic X-rays of type i to type j is given by
(7)
where I'(i) and I'(j) are the measured intensities of A'-shell X-rays of types i and j; i = Ka2, Кр, Kp, j =
— Aai. Aai, Kf
гand £j are efficiencies of the detec-
tor for A'-shell X-rays of types i and j: /Jj and Bj are the self-attermation correction factors for A'-shell X-rays of types i and j in the target material and are calculated using Eq. (8); exp(—(iXiwtw) and exp(—(ixjwtw) al'° the detector window attenuation correction factors for A'-shell X-rays of types t and j; here fi.riw and (ixjw al'° the mass attenuation coefficients fcm2/'gm] of A'-shell
X-rays of types i and j in the detector window of thickness tw fg/'em2].
Taking the isotropic emission of A'-shell X-rays into account and recalling that we measure the intensity of all A'-shell X-rays emerging from the target in all forward directions, that is, emitting into a solid angle of nearly 2тг sr, we use the correction factor 3 without involving the scattering angles:
1 — exp (//.j + flc)t]
(8)
(/', + I', )t
where t is the target thickness fg/'em2], and fit and the respective mass attenuation coefficients [cm2/gm] of incident and emitted A'-shell X-rays in the target. These coefficients have been computed using WinXcom software [21]. Following the target thickness criterion in Ref. [2], we have found that the targets of the thickness with 3 values in the range 0.75 < 3 < 0.95 are suitable for accurate determination of A'-shell X-ray fluorescence parameters (for details, see Refs. [15 19]).
3. EXPERIMENTAL
The schematic diagram of the experimental arrangement is shown in Fig. 1. In the present investigation, we used an X-ray detector spectrometer consisting of a HPGe detector (active area 500 mm2, 10 111111 thick high-purity n-type germanium crystal, Be window 0.C mm in thickness) coupled to a 16k multichannel analyzer (DSA-1000). The energy resolution of the HPGe detector (Model: GL0510P, procured from Canberra USA) is 200 eV at 5.9 keV. The dead layer of the detector is 0.7 mm. The distance from the cryostat window (Be) to the detector material is 5 mm. The HPGe detector is operational in the energy range 3 to 500 keV. This detector is cooled to 77 Iv using a liquid-nitrogen cryostat. The coolant liquid nitrogen is filled in the cryostat through the inlet and the air escapes from the outlet (Fig. 1). The spectrometer is calibrated and standardized using various gamma and X-ray sources.
A 5' Co radioactive source with a strength of the order of 104 Bq is used as the excitation source. We used the photon energy 123.6 keV, i. e., the weighted average of 122 and 136 keV, in the calculation of mass attenuation coefficients //..;, which are required in the calculation of the self-attenuation correction factor 3- The target materials were pure elements (99.99%). Platinum was procured in the form of thin foil of the required thickness from Alfa Aesar A Johnson Matthey Company UK, whereas high-purity gold and lead targets were purchased from a local company.
3 ЖЭТФ, выи. 3(9)
449
Table 1. The measured values of A'-shell X-ray intensity ratios for Pt, Au, and Pb along with the theoretical and
others' experimental values
Element Parameter Present Theoretical values [23] Others' experimental References
Platinum (Z = 78) /(A'a2) I(Kai) 0.597 ± 0.010 0.585 0.584 0.574 ± 0.026 0.583 0.563 fill [24] fl] [28]
HKvO I(Kai) 0.340 ± 0.010 0.328 0.322 0.328 ± 0.026 fill [24]
/ (/v.,) I(Kai) 0.108 ± 0.011 0.089 0.0896 fill
/(A>) I(Ka) 0.084 [24]
0.260 ± 0.006 0.263 0.259 0.2682 ± 0.005 0.275 fill [29] fl]
Gold (Z = 79) I(Ka2) I(Kai) 0.583 ± 0.011 0.588 0.618 0.591 ±0.032 0.585 ± 0.004 0.584 ± 0.012 0.57 ± 0.03 [12] [24] [25] [30] [31]
HKvO I(Kai) 0.336 ± 0.011 0.329 0.585 0.357 0.333 ± 0.021 0.329 ± 0.003 0.333 ± 0.011 [28] [12] [24] [25] [30]
I(Kai) 0.210 ± 0.02 [31]
0.089 ± 0.015 0.091 0.091 ±0.004 0.098 ± 0.005 [24] [30]
/(A>) I(Ka) 0.11 ± 0.01 [31]
0.264 ± 0.010 0.265 0.280 0.2680 ± 0.005 0.262 ± 0.003 0.210 ± 0.012 0.210 ± 0.03 [12] [29] [25] [30] [31]
The intensities of A'-shell X-rays were measured as follows. The "source with background spectrum" was acquired first, by placing the source on the face of the detector for the live time of 2000 s to minimize the uncertainties in the results due to counting statistics.
The "transmitted spectrum with background" was then acquired by sandwiching the target between the source and the detector window. By subtracting the former from the latter, we obtain a clean fluorescence A'-shell X-ray spectrum that corresponds to the target element
Table 1
Element Parameter Present Theoretical values [23] Others' experimental References
Lead (Z = 82) /(A'a2) I(Kai) 0.596 ± 0.010 0.595 0.606 ± 0.042 0.594 ± 0.003 0.593 ± 0.019 0.592 0.589 ± 0.012 0.590 ±0.03 0.596 [24] [25] [26] fl] [30] [31] [28]
HKßO I(Kai) 0.330 ± 0.008 0.334 0.296 ± 0.019 0.332 ± 0.002 0.343 ± 0.026 0.333 ± 0.011 [24] [25] [26] [30]
I(Kß,) I(Kai) 0.085 ±0.01 0.096 0.087 ± 0.004 0.098 ± 0.005 [24] [30]
I(Kß) I(Ka) 0.11 ±0.01 [31]
0.262 ± 0.006 0.270 0.279 0.268 ± 0.003 0.275 ± 0.019 0.2822 ±0.007 0.271 ±0.011 0.207 ± 0.018 fl] [25] [26] [29] [30] [31]
under investigation (Fig. 2). Each A'-shell X-ray peak is fitted to a Gaussian distribution function using the ORIGIN software for estimating the area under the peak. The area under each peak gives the intensity of the A'-shell X-ray of a given type, which is then corrected for self-attenuation in the target, attenuation in the window of the detector, efficiently of the detector, and the dead layer attenuation to obtain the total number of A'-shell X-rays emitted into the forward hemisphere. The A'-shell X-ray intensity ratios and the radiative and the total vacancy transfer probabilities were calculated using Eqs. (7) and (3) (C). The vacancy transfer probabilities of the elements were calculated using the A'-shell X-ray fluorescence yield (uik) values from Hubbell tables [3], Ivrause [22], and Bam-bynek et al. [2]. The experiment was repeated four times for each element and the weighted average of the four trials has been presented.
Counts/2000 s
Fig. 2. A'-shell X-ray fluorescence spectrum of platinum
451
3*
Table 2. The present experimental values of radiative and total vacancy transfer probabilities for Pt, Au, and Pb
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