INSTRUMENTATION
Q1. Which factor can lead to peak broadening in an X ray emission spectrum?
a. Use of a monochromator
b. Low detector noise
c. Multiple ionisation states of an element
d. High purity of the sample
ANSWER:
c. multiple ionization states of an element
EXPLANATION:
An element present in different oxidation or chemical states can cause chemical shifts in X-ray energies. For example, Fe²⁺ and Fe³⁺ will have slightly different binding energies, leading to slight shifts or broadening in the X-ray emission lines.
This is particularly observed in:
• XPS (X-ray Photoelectron Spectroscopy)
• XANES (X-ray Absorption Near Edge Spectroscopy)
Other factors like instrument resolution, detector response, and sample charging can also affect line shape, but multiple ionization states is a major chemical cause.
Q2. The intensity of characteristic X-rays in a sample is influenced by which of the following?
a. Bragg angle
b. Sample atomic number and concentration
c. Detector resolution only
d. Phase of the material only
ANSWER:
b. sample atomic number and concentration
EXPLANATION:
The intensity of X-rays depends on:
• Atomic number (Z): Higher Z means more electrons and higher probability of inner-shell ionization.
• Concentration: More of the element means more emissions.
• Excitation conditions: Higher beam current/voltage leads to more ionization.
• Matrix effects: The surrounding elements can enhance or suppress the signal (due to secondary fluorescence or absorption).
This relationship forms the basis of quantitative X-ray analysis.
Q3. Given below are two statements
Statement I: In X-ray diffraction, Bragg's law is used to calculate the energy of X-ray photons.
Statement II: Bragg’s law relates the wavelength of X-rays to the diffraction angle and interplanar spacing.
In the light of the above statements, choose the most appropriate answer from the options given below
a. both statement I and II are correct
b. both statement I and II are incorrect
c. Statement I is correct but statement II is incorrect
d. Statement I is incorrect but statement II is correct
ANSWER:
c. Statement I is correct but statement II is incorrect
EXPLANATION:
Bragg’s law:
nλ = 2dsinθ
relates wavelength (λ) of incident X-rays to angle of diffraction (θ) and interatomic spacing (d) — not directly to energy. To get energy, you’d need:
E= hc/λ
So, while Bragg’s law determines wavelength, it does not directly calculate energy.
Q4. What is the main reason for using a vacuum environment in X-ray spectroscopy intstruments?
a. Prevent oxidation of the sample
b. Enhance photon speed
c. Minimize absorption of the low energy X-rays by air
d. Improve cooling of the detector
ANSWER:
c. Minimize absorption of low energy X-rays by air
EXPLANATION:
Air (especially oxygen and nitrogen) strongly absorbs low-energy X-rays (<2 keV). To detect these accurately (especially for light elements like B, C, N, O), a vacuum environment is used in X-ray spectroscopy chambers. Alternatives include using helium atmosphere, which has low absorption.
This improves signal-to-noise ratio and sensitivity, particularly for low-Z elements.
Q5. Which detector is commonly used in EDX systems for X-ray detection?
a. Geiger-Muller tube
b. Photomultiplier tube
c. Silicon drift detector
d. Liquid scintillator
ANSWER:
c. Silicon drift detector
EXPLANATION:
Silicon Drift Detectors (SDDs) are widely used in EDS because of:
• High energy resolution (~125 eV)
• Fast signal processing
• Compact size
• No need for liquid nitrogen (unlike older Si(Li) detectors)
They work by creating electron-hole pairs when an X-ray hits the silicon, and the number of pairs is proportional to the X-ray energy. This signal is then amplified and converted into an energy spectrum.
Q6. Why are X-ray photons suitable for probing atomic scale structures in materials?
a. They have very low energy
b. Their wavelengths are comparable to atomic spacings
c. They are easily absorbed by all elements
d. They have zero interaction with electrons
ANSWER:
b. Their wavelengths are comparable to atomic spacings
EXPLANATION:
X-rays have wavelengths typically in the range of 0.01–10 nm, which matches the interatomic distances in solids (0.1–0.3 nm). This makes them ideal for:
• X-ray diffraction (XRD) — to probe crystal structure.
• X-ray absorption — to examine electronic states.
• X-ray spectroscopy — to determine elemental composition.
They interact with electron clouds around atoms, making them sensitive to both structure and composition.
Q7. Given below are two statements
Statement I: The presence of multiple oxidation states of an element in a sample can cause broadening or splitting of X-ray spectral lines.
Statement II: Different oxidation states lead to variations in binding energies of core electrons.
In the light of the above statements, choose the most appropriate answer from the options given below
a. both statement I and II are correct
b. both statement I and II are incorrect
c. Statement I is correct but statement II is incorrect
d. Statement I is incorrect but statement II is correct
ANSWER:
a. Both statement I and II are correct
EXPLANATION:
When an element exists in multiple chemical states, the core-level binding energies shift slightly due to changes in electron density and screening effects. This causes chemical shifts in X-ray peaks, leading to peak broadening or multiple peaks in high-resolution spectra.
Q8. Given below are two statements
Statement I: Wavelength Dispersive Spectroscopy (WDS) provides better resolution than Energy Dispersive Spectroscopy (EDS).
Statement II: WDS uses a crystal and Bragg’s law to disperse X-rays based on their wavelengths.
In the light of the above statements, choose the most appropriate answer from the options given below
a. both statement I and II are correct
b. both statement I and II are incorrect
c. Statement I is correct but statement II is incorrect
d. Statement I is incorrect but statement II is correct
ANSWER:
a. Both statement I and II are correct
EXPLANATION:
WDS achieves higher spectral resolution (~5–10 eV) because it uses a crystal monochromator to separate X-rays based on Bragg diffraction. EDS, in contrast, relies on solid-state detectors and suffers from peak overlap.
Q9. Given below are two statements
Statement I: The absorption edge in X-ray absorption spectroscopy (XAS) corresponds to ionization of a core-level electron.
Statement II: An absorption edge occurs when the photon energy matches the binding energy of a core electron.
In the light of the above statements, choose the most appropriate answer from the options given below
a. both statement I and II are correct
b. both statement I and II are incorrect
c. Statement I is correct but statement II is incorrect
d. Statement I is incorrect but statement II is correct
ANSWER:
a. Both statement I and II are correct
EXPLANATION:
In XAS (including XANES (X-ray Absorption Near Edge Structure) and EXAFS (Extended X-ray Absorption Fine Structure), the absorption edge is observed when the X-ray energy is sufficient to eject a core electron (e.g., from the K-shell). This corresponds exactly to the binding energy, and a sharp rise in absorption is detected.
Q10. Which of the following leads to X-ray emission from an atom?
a. Photoelectric absorption
b. Auger electron emission
c. Electron transitions in inner shells
d. Compton scattering
ANSWER:
c. Electron transitions in inner shells
EXPLANATION:
X-rays are generated when:
1. An inner-shell electron (e.g., K or L shell) is ejected.
2. An electron from a higher shell drops into the vacancy.
3. The energy difference between the two levels is emitted as an X-ray photon.
This is called characteristic X-ray emission because the energies depend on the atomic structure of the element.
Content Writer:- Bhawana Sharma
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