The decay rate of orthopositronium

We review recent measurements of the orthopositronium decay rate, λT, and present results of a new 230‐ppm measurement using the vacuum technique. It corroborates, at the 6.2 sigma level, the discrepancy between theory and a recent 200‐ppm measurement of λT in gases.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87568/2/481_1.pd

A viable superluminal hypothesis: Tachyon emission from orthopositronium

Tachyons are hypothetical particles that travel faster than the vacuum speed of light. Previous experiments have searched for, but have not found evidence of tachyons. Long-standing, anomalous measurements of the orthopositronium (o-Ps) decay rate are interpreted as evidence for two tachyons being occasionally emitted when o-Ps decays. Restricting the coupling of tachyon pairs to a single photon (no tachyon coupling to matter) yields a new theory where tachyons are only observed in o-Ps decay and not in the previous tachyon experiments. Combining the single photon coupling theory with all previous experiments predicts that these tachyons must deposit energy while traversing scintillator detectors. A new tachyon search experiment will use this energy loss prediction to attempt to find tachyons passing through the apparatus or set limits disproving the original o-Ps to tachyon hypothesis. Viewing an intense o-Ps source, a time-of-flight spectrometer uses the superluminal property of tachyons for identification. Several months of continuous data acquisition will be necessary to completely eliminate the o-Ps to tachyon hypothesis. © 2000 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87640/2/1119_1.pd

Revealing hidden pore structure in nanoporous thin films using positronium annihilation lifetime spectroscopy

The highly inhomogeneous pore morphology of a plasma-enhanced-chemical-vapor-deposited ultralow-kk dielectric film (k = 2.2)(k=2.2) has been revealed using depth-profiled positronium annihilation lifetime spectroscopy (PALS) combined with progressive etch back of the film surface. The film is found to have a dense surface layer, an intermediate layer of 1.8 nm1.8nm diameter mesopores, and a deep region of ∼ 3 nm∼3nm diameter mesopores. After successively etching of the sealing layer and the isolated 1.8 nm1.8nm pore region, PALS reveals that the underlying large pores are highly interconnected. This inhomogeneous pore structure is proposed to account for observed difficulties in film integration.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87843/2/121904_1.pd

Survival Outcomes of Patients with Mycosis Fungoides Involving the External Ear and Ear Canal

OBJECTIVES/HYPOTHESIS: Mycosis Fungoides (MF) is the most common subtype of cutaneous T-cell lymphoma. Disease involvement of specific locations may be more significant than simply the symptoms associated with that site; it is possible that involvement of certain sites could be associated with poor prognosis. We aimed to evaluate the outcomes of patients with MF with documented involvement of the EAC and external ear. STUDY DESIGN: Retrospective analysis. METHODS: We retrospectively reviewed 40 patients with MF that were treated by otologists between 2012 and 2021. RESULTS: We report the largest series of patients with MF involving the external ear and EAC. Of the 40 patients included in this study, 17 presented with Mycosis Fungoides in the otologic region (MFO). Of these 17 MFO patients, 2/17 had involvement of the external ear only, 3/17 of the EAC only, 11/17 of both the external ear and EAC, and 1/17 of the periauricular skin. Of note, 11/14 (79%) patients presenting with EAC disease died compared to11/26 (42%) of patients without involvement. In addition, eight of the 13 (62%) patients with external ear involvement died compared to 14/27 (52%) of patients without involvement. Ear canal involvement was associated with a statistically significant shorter overall survival duration in patients with MF (p = 0.03). Furthermore, disease in the EAC was found to have a hazard ratio value of 2.565 (CI 1.102-5.970). CONCLUSIONS: Involvement of the EAC by MF portends a poor prognosis. This finding highlights the need for a more in-depth otologic evaluation of patients with MF. LEVEL OF EVIDENCE: 4 Laryngoscope, 133:1486-1491, 2023

Characteristics of starch-based films with different amylose contents plasticised by 1-ethyl-3-methylimidazolium acetate

Starch-based films plasticised by an ionic liquid, 1-ethyl-3-methylimidazolium acetate ([Emim][OAc]), were prepared by a simple compression moulding process, facilitated by the strong plasticisation effect of [Emim][OAc]. The effects of amylose content of starch (regular vs. high-amylose maize) and relative humidity (RH) during ageing of the samples on a range of structural and material characteristics were investigated. Surprisingly, plasticisation by [Emim][OAc] made the effect of amylose content insignificant, contrary to most previous studies when other plasticisers were used. In other words, [Emim][OAc] changed the underlying mechanism responsible for mechanical properties from the entanglement of starch macromolecules (mainly amylose), which has been reported as a main responsible factor previously. The crystallinity of the plasticised starch samples was low and thus was unlikely to have a major contribution to the material characteristics, although the amylose content impacted on the crystalline structure and the mobility of amorphous parts in the samples to some extent. Therefore, RH conditioning and thus the sample water content was the major factor influencing the mechanical properties, glass transition temperature, and electrical conductivity of the starch films. This suggests the potential application of ionic liquid-plasticised starch materials in areas where the control of properties by environmental RH is desired

Low early ototoxicity rates for pediatric medulloblastoma patients treated with proton radiotherapy

<p>Abstract</p> <p>Background</p> <p>Hearing loss is common following chemoradiotherapy for children with medulloblastoma. Compared to photons, proton radiotherapy reduces radiation dose to the cochlea for these patients. Here we examine whether this dosimetric advantage leads to a clinical benefit in audiometric outcomes.</p> <p>Methods</p> <p>From 2006-2009, 23 children treated with proton radiotherapy for medulloblastoma were enrolled on a prospective observational study, through which they underwent pre- and 1 year post-radiotherapy pure-tone audiometric testing. Ears with moderate to severe hearing loss prior to therapy were censored, leaving 35 ears in 19 patients available for analysis.</p> <p>Results</p> <p>The predicted mean cochlear radiation dose was 30 ⁶⁰Co-Gy Equivalents (range 19-43), and the mean cumulative cisplatin dose was 303 mg/m²(range 298-330). Hearing sensitivity significantly declined following radiotherapy across all frequencies analyzed (<it>P </it>< 0.05). There was partial sparing of mean post-radiation hearing thresholds at low-to-midrange frequencies and, consequently, the rate of high-grade (grade 3 or 4) ototoxicity at 1 year was favorable (5%). Ototoxicity did not correlate with predicted dose to the auditory apparatus for proton-treated patients, potentially reflecting a lower-limit threshold for radiation effect on the cochlea.</p> <p>Conclusions</p> <p>Rates of high-grade early post-radiation ototoxicity following proton radiotherapy for pediatric medulloblastoma are low. Preservation of hearing in the audible speech range, as observed here, may improve both quality of life and cognitive functioning for these patients.</p

Thermalization of Positronium in Gases

The thermalization of positronium ( Ps) formed at a few eV in gases is investigated using timeresolved, Doppler broadening measurements of the annihilation photons. Magnetic quenching permits energy measurements about 40 ns after Ps is formed in H 2 , N 2 , He, Ne, Ar, isobutane, and neopentane. The thermalization rate is measured by changing the gas density, and a classical elastic scattering cross section and a Ps formation energy are determined. The impact of Ps thermalization on decay rate experiments using gases is also discussed. [S0031-9007(98) PACS numbers: 36.10. Dr, 34.50.Bw, 78.70.Bj Collisions between normal gas atoms and the exotic atom positronium (Ps, positron-electron bound state) are interesting and unique because Ps is so light relative to its target. Hence Ps, formed at typically a few eV in most gases, will thermalize very slowly if elastic scattering is the only available energy loss mechanism. In the elastic case, the fractional energy loss per collision is only of order m͞M ϳ 10 24 (m is the Ps mass, M is the atomic/molecular mass.) The low energy Ps-atom collision is also inherently quantum mechanical in nature since the de Broglie wavelength of Ps below 1 eV is greater than 9 Å, larger than the classical geometric atomic size. Moreover, it was recognized early [1] that cross section calculations must include the polarization/Van der Waals interaction and electron exchange. These features apparently complicate the calculations of cross sections, done presently including the exchange interaction for only oneand two-electron systems scattering Ps (H: [2]; H 2 : [3]; He: Positronium as a scattering probe offers a unique experimental advantage since its annihilation into two photons provides a mechanism for determining its velocity and hence the rate of thermalization and the momentum transfer cross section ͑s m ͒ for gas targets. Previous measurements of Ps thermalization in gases In this Letter, we report the measurement of Ps thermalization rates, formation energies, and momentum transfer cross sections in purely gaseous target using time-resolved Doppler Broadening Spectroscopy (DBS). In this complementary technique to ACAR, the Doppler broadening of the back-to-back annihilation photons observed in a single high-resolution Ge detector is a measure of the longitudinal momentum of the annihilating Ps. Timing information as well as DBS is derived from the Ge detector signal, enabling the direct correlation between age and energy of the Ps to be determined. The rate of thermalization and the average formation energy of Ps can then be determined. The gases used in this investigation include He, H 2 , and Ar for comparison to the theoretical calculations The thermalization rate of Ps in a noble gas was calculated 30 years ago by Sauder [14], under the assumption of classical elastic scattering, i.e., an energy-independent cross section for energy loss (momentum transfer) s m which was interpreted as the classical geometrical atomic cross section. If Ps is formed at only a few eV, below the 5.1 eV threshold for excitation of the Ps or the noble gas ͑.10 eV͒ and slow enough to avoid collisional dissociation, Sauder&apos;s elastic model may be appropriate. The Ps kinetic energy E͑t͒, as it asymptotically approaches thermal energy, E th , is given by where b is related to the average initial energy E 0 of Ps that can eventually thermalize: coth 2 b E 0 ͞E th . G is 0031-9007͞98͞80(17)͞3727(4)$15.0

Characterization of fatigue-induced free volume changes in bulk metallic glass using positron annihilation spectroscopy

Depth-profiled Doppler broadening spectroscopy of positron annihilation on the cyclic fatigue-induced fracture surfaces of three amorphous Zr₄₄Ti₁₁Ni₁₀Cu₁₀Be₂₅ metallic glass specimens reveals the presence of a 30–50 nm layer of increased free volume that is generated by the propagating fatigue crack tip. The presence and character of this fatigue transformation zone is independent of the initial amount of bulk free volume, which was varied by structural relaxation via annealing, and the voids generated in the zone by intense cyclic deformation are distinct from those typical of the bulk.Keywords: fatigue cracks, copper alloys, Doppler broadening, deformation, beryllium alloys, voids (solid), annealing, zirconium alloys, titanium alloys, nickel alloys, metallic glasses, positron annihilatio

Spin-polarized low-energy positron beams and their applications

The production and use of low-energy (100 eV to 5 keV) high-intensity, spin-polarized positron beams is reviewed. Methods for obtaining beams with high polarization are discussed. Applications include studies of the moderation process, surface and bulk magnetism, optically active molecules, and the production of polarized anti-protons.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/47033/1/339_2004_Article_BF00635183.pd