Precise measurement of K-shell fluorescence yield in iridium: An improved test of internal-conversion theory

Journals published by the American Physical Society can be found at http://publish.aps.org/We have measured the total intensity of K x rays relative to 129.4-keV gamma rays from decay of the second excited state in Ir-191. This (M1+E2) transition was observed following the beta decay of 15.4-d Os-191. Our measured ratio yields the result alpha(K)omega(K)=2.044(11). When combined with a recent measurement of the same ratio for the 80.2-keV M4 transition from Ir-193(m), this result strongly confirms the need for the K-shell hole to be included in calculations of internal-conversion coefficients alpha(K). Since the alpha(K) value calculated for the Ir-191 transition is virtually independent of the hole treatment, our result also yields a model-independent value for the iridium fluorescence yield, omega(K)=0.954(9)

Precise measurement of alpha(K) for the M4 transition from Ir-193(m): A test of internal-conversion theory

Journals published by the American Physical Society can be found at http://publish.aps.org/The 10.5-day isomer in Ir-193 decays by a single 80.2-keV M4 transition directly to the ground state of that nucleus. We have measured the total intensity of K x rays relative to 80.2-keV gamma rays for this transition to be 98.7(6). With the K-shell fluorescent yield for iridium taken to be 0.958(4), this result yields alpha(K) = 103.0(8) for the K-shell internal conversion coefficient (ICC). The calculated alpha(K) for this transition is particularly sensitive to the treatment of the hole that is created by conversion in the atomic K shell. Recent ICC tables, which ignore the hole, yield alpha(K) = 92.0. We demonstrate that calculations incorporating the hole produce values between 99.6 and 103.3 depending on the approximation used. Our result strongly supports the need to include the hole

Element a hybnost rozlišená elektronická struktura zředěného magnetického polovodiče: manganem dopovaného gallium arsenidu

Zředěné magnetické polovodiče slibují v aplikacích založených na spinových elektronických zařízeních na jejich potenciál pro feromagnetický pořádek při pokojové teplotě a různé unikátní přepínání a spin-závislé vodivosti. Nicméně přesný mechanismus, kterým dopování z přechodného kovu způsobuje, že ferromagnetismus je kontroverzní. Tady máme studoval zředěný magnetický polovodič (5% manganem dopovaný gallium arsenid) s Braggův reflexní stojatý vlnový paprsek s pevným rentgenovým paprskem se spektrální rozlišovací schopností a vyřešila svou elektronickou strukturu na součásti, které byly vyřešeny prvkem a momentem. The měřené intenzity valenčního pásma byly promítány do prvků vyřešených prvkem pomocí analogových energetických skenů Ga 3d, Mn 2p a As 3D úrovní jádra, s vynikajícími výsledky dohodu s elementy-projektované Bloch spektrální funkce a objasnění elektronické struktury tohoto prototypového materiálu. Tato technika by měla být široce použitelná pro jiné vícevrstvých materiálů.The dilute magnetic semiconductors have promise in spin-based electronics applications due to their potential for ferromagnetic order at room temperature, and various unique switching and spin-dependent conductivity properties. However, the precise mechanism by which the transition-metal doping produces ferromagnetism has been controversial. Here we have studied a dilute magnetic semiconductor (5% manganese-doped gallium arsenide) with Bragg-reflection standing-wave hard X-ray angle-resolved photoemission spectroscopy, and resolved its electronic structure into element- and momentum- resolved components. The measured valence band intensities have been projected into element-resolved components using analogous energy scans of Ga 3d, Mn 2 p, and As 3d core levels, with results in excellent agreement with element-projected Bloch spectral functions and clarification of the electronic structure of this prototypical material. This technique should be broadly applicable to other multi-element materials

Momentum-transfer model of valence-band photoelectron diffraction

Recent instrumental progress of valence-band photoemission in the X-ray range allows uncovering bulk- and surface-related electronic properties. Four-dimensional recording of energy and momentum-vector gives access to the complete spectral-density function. Systematic measurements for a number of transition metals between 15 eV-6 keV reveal unexpected strong intensity modulations due to photoelectron diffraction. Here, we present a graphical model that illustrates the role of momentum-conservation in Fermi’s Golden-Rule in an intuitive way. Intensity enhancement or reduction by factors >5 are confined to small energy- and momentum-intervals (widths 0.03 Å−1 and 200 meV). Laue-type diffraction involves the photon momentum and is intrinsic in the photoemission process, in accordance with Pendry’s final-state-model. At higher energies, Kikuchi-diffraction imprints additional modulations on valence-band-patterns and quasi-elastic background. The absence of photon-momentum transfer uncovers the extrinsic nature of Kikuchi-diffraction. For Re at 30 K and 3.4 keV the relative weight of the Kikuchi-branch is comparable to the Laue-branch, whereas at 6 keV the Kikuchi-branch prevails