francis et al. nsnmrn ooty 2012

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Measurement of K-shell Jump Ratios and Jump Factorsfor Platinum and Lead by using 2-Geometrical

Configuration and a Weak Gamma Source

By

L. Francis Maria Anand, S. B. Gudennavar

and S. G. BubblyDepartment of Physics,

Christ University,

Bangalore-560 029.

National Seminar on New materials research and Nanotechnology,

held during 12-14 September, 2012, at Govt. Arts College, Ooty.


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X-ray Fluorescence has gained importance as a tool for

elemental analysis in the fields of atomic, nuclearmaterial science, medical physics, and forensic science.

This requires the accurate values of the parameterssuch as

Shell and sub-shell X-ray intensity ratios,

K shell jump ratios and jump factors,

K to L vacancy transfer probabilities etc.

K x-ray intensity ratios, the K-shell absorption jumpfactors and jump ratios are of great significance in thefield of interaction of gamma-rays and x-rays withmatter.

Introduction


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When or X-rays interact with an atom, vacancies are created

by photoelectric effect. The creation of a vacancy in anatomic shell initiates a series of rearrangement processesof electrons resulting in the emission of characteristic X-rays or Auger electrons (Fig. 1).

The transitions to K-shell, constitute K-series, and to L-shellsconstitute L series etc.. (Fig. 2) These transitions aresubject to the transition rules

l= 1, m= 0, 1,

Where, l and m are the orbital angular momentum quantumnumber and magnetic quantum number respectively.

X-ray fluorescence and Auger process


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Transitions which lead to various emission lines.

Fig. 2


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A brief theory

The K-shell absorption jump factor is defined as theprobability that an electron is ejected from the K-

shell of the target element other than any shells

where

K is K x-ray production cross section, that is probabilityof number of characteristic x-rays produced per incidentradiation per atom per second, and is calculated using therelation,

K is the K-shell fluorescence yield of the target atom (theratio of number of K x-rays produced to the number K-shell vacancies created in an atom). The K values aretaken from Hubbell (1989) and K values at 123.6 keV are

taken from Scofield tables (1973).


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fK is the fractional emission rate and is given as,

fK = (1+IK/IK)-1

IK/IK is the intensity ratio of the K and K x-rays at

photon energy E. The K x-ray intensity ratios are theratios of the intensities of K to K. The ratio of theintensity of the characteristic x-ray of type i to type j isgiven by

where i = K2, K1, K and j = K1, K1, K, and , and are the

measured intensities of type i and type j K x-rays respectively,

i and j are the efficiencies of the detector for fluorescence

K x-ray of type i and j respectively, i and j are the self-

absorption correction factors for the K x-ray of type i and


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type j respectively in the target material and are calculated

using eqn. ,

exp(-xiwtw) and exp(-xjwtw) are the window attenuation

correction factors for fluorescence x-rays of type i and jrespectively; here xiw and xjw are the mass attenuationcoefficients for fluorescence K x-rays of type i and j in thedetectors window of thickness tw.

t is the total atomic attenuation cross section, ts is the(coherent + incoherent) atomic scattering cross sectioncalculated using WinXcom software (Gerward 2002),

)t(

))texp(-(-1

ei

ei


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Several researchers have adopted various methods to measure

these parameters, namely; the gamma ray attenuation method

(Mallikarjuna et al. 2002), the Compton peak attenuation method[Ayala et al. 1996, Polat et al. 2004, Budak et al. 2004) the energy

dispersive x-ray fluorescence method (Ertugrul et al. 2002, Budak

et al. 2003, Polat et al. 2005) and the bremsstrahlung transmission

method (Nayak and Badiger 2006). These methods have their ownadvantages and disadvantages. For example, the gamma ray

attenuation method requires many monoenergetic gamma sources

and thin foils of given element, while the EDXRF method requires

strong radioactive sources of the order 100mCi or more. In thepresent work, we measure these parameters for platinum and lead

using a simple method proposed by Gudennavar et al. (2003) to

measure K x-ray fluorescence parameters, which employs a weak

gamma source (~2 Ci) and a 2-geometrical configuration.

Review of Literature


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Experimental: 2-Geometry Method


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Procedure The incident source spectrum (source plus background

spectrum) was acquired for 2400s by placing just the weak 57Co

source on the window of the detector. The intensity of 122 and136 keV was carefully estimated from the background correctedsource spectrum

By sandwiching the respective target between the source andthe detectors window, the transmitted spectrum (transmitted

spectrum plus background) is obtained for the same interval oftime.


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By subtracting the source spectrum plus backgroundfrom the transmitted spectrum plus background, weget a clean fluorescence K x-ray spectrum thatcorresponds to the target element underinvestigation.

The area under each peak gives , the measuredintensity of K x-ray of type i(where i = KandK);which is corrected for self-attenuation in the target

( factor), attenuation in the window and efficiencyof the detector.


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Results and Conclusion

The measuredvalues of K x-rayintensity ratios, Kshell jump ratiosand jump factorsdetermined for

platinum and leadare presented inthe table


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The measured values of K x-ray intensity ratiosfor platinum and lead agree well withtheoretical and others values. While themeasured values of K jump ratios and jump

factors are systematically lower than thetheoretical and others values.


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Thank [email protected]

francis et al. nsnmrn ooty 2012

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