Positron annihilation in methane gas

1970 ◽  
Vol 48 (24) ◽  
pp. 2984-2990 ◽  
Author(s):  
P. M. Smith ◽  
D. A. L. Paul
Keyword(s):  
Positron Annihilation ◽  
Standard Error ◽  
Room Temperature ◽  
Annihilation Rate ◽  
Effective Number ◽  
Gas Density ◽  
Methane Gas ◽  
Free Positron

The annihilation of positrons in methane gas at room temperature has been measured at pressures below 2 atm. The annihilation rate for the free positron component is proportional to the gas density and corresponds to an effective number of electrons per molecule taking part in annihilation, Zeff = 139.6 ± 1.0 (standard error). The quenching of orthopositronium corresponds to 1Zeff = 0.57 ± 0.07. Resonance annihilation is discussed in a general way.

Complex dependence of the positron annihilation rate on methane gas density and temperature

1975 ◽  
Vol 62 (5) ◽  
pp. 1777-1789 ◽  
Author(s):  
J. D. McNutt ◽  
V. B. Summerour ◽  
A. D. Ray ◽  
P. H. Huang ◽  
D. A. Johnson
Keyword(s):  
Positron Annihilation ◽  
Annihilation Rate ◽  
Gas Density ◽  
Methane Gas ◽  
Complex Dependence

Positron annihilation in methane

1977 ◽  
Vol 55 (3) ◽  
pp. 235-239 ◽  
Author(s):  
A. C. Mao ◽  
D. A. L. Paul
Keyword(s):  
Electric Field ◽  
Positron Annihilation ◽  
Applied Electric Field ◽  
Room Temperature ◽  
Positive Energy ◽  
Annihilation Rate ◽  
Linear Region ◽  
Gas Density ◽  
Single Level ◽  
Made In

Measurements of positron annihilation rates at room temperature under the influence of an applied electric field have been made in methane at different pressures. The experiments were all carried out in the linear region in which the annihilation rate is accurately proportional to gas density. We find Zeff = 142.7 ± 2.0 at 21 °C and zero electric field. At 1000 Torr Zeff decreases linearly with the electric field, the gradient being about 2.5 × 10−2 per (V cm−1 atm−1) at that temperature. The results repudiate the idea of a positive energy single level Breit–Wigner resonance as being responsible for the high value of Zeff, and in this sense are in agreement with the findings of McNutt, Summerour, Ray, and Huang.

Encapsulated protamine-hyaluronic acid particles for targeting carboplatin directed by radiation

2017 ◽  
Vol 27 (01n02) ◽  
pp. 37-42
Author(s):  
T. Segawa ◽  
S. Harada ◽  
S. Ehara ◽  
K. Ishii ◽  
T. Sato ◽  
...  
Keyword(s):  
Hyaluronic Acid ◽  
Radiation Dose ◽  
Cancer Treatment ◽  
Standard Error ◽  
Room Temperature ◽  
Pixe Analysis ◽  
X Ray ◽  
Clinical Cancer

Encapsulated protamine-hyaluronic acid particles containing carboplatin were prepared and their ability to release carboplatin was tested in vivo. Protamine–hyaluronic acid particles containing carboplatin were prepared by mixing protamine (1.6 mg) and hyaluronic acid (1.28 mg) into a 5 mg/mL carboplatin solution for 30 min at room temperature. A 1 mL solution of protamine–hyaluronic acid particles was poured into an ampule of COATSOME[Formula: see text] EL-010 (Nichiyu, Tokyo, Japan), shaken three times by hand, and allowed to incubate at room temperature for 15 min. Following that, 10 or 20 Gy of 100 kiloelectronvolt (KeV) soft X-ray was applied. The release of carboplatin was imaged using a microparticle-induced X-ray emission (PIXE) camera. The amount of carboplatin released was expressed as the amount of platinum released and measured via quantitative micro-PIXE analysis. The diameter of the generated encapsulated particles measured [Formula: see text] nm (mean ± standard error). The release of carboplatin from the encapsulated protamine–hyaluronic acid particles was observed under a micro-PIXE camera. The amount of carboplatin released was [Formula: see text] under 10 Gy of radiation, and [Formula: see text] under 20 Gy of radiation, which was a sufficient dose for cancer treatment. However, 10 or 20 Gy of radiation is much greater than the dose used for clinical cancer treatment (2 Gy). Further research to reduce the radiation dose to 2 Gy in order to release sufficient carboplatin for cancer treatment is required.

The Evolution Behavior of Defects in the Nanofilms of W/Cu and W Probed by Doppler Broadening Positron Annihilation Spectroscopy

2017 ◽  
Vol 373 ◽  
pp. 104-107
Author(s):  
Ling Wang ◽  
Ai Hong Deng ◽  
Kang Wang ◽  
Yong Wang ◽  
Xiao Bo Lu ◽  
...  
Keyword(s):  
Magnetron Sputtering ◽  
Positron Annihilation ◽  
Room Temperature ◽  
Storage Time ◽  
Positron Annihilation Spectroscopy ◽  
Doppler Broadening ◽  
Radio Frequency Magnetron Sputtering ◽  
Helium Ions ◽  
Near Surface ◽  
Evolution Behavior

W/Cu multilayer nanofilms and pure W nanofilms were prepared in pure Ar and He/Ar mixing atmosphere by radio frequency magnetron sputtering method. The defect evolution of the samples was characterized by Doppler broadening positron annihilation spectroscopy (DB-PAS).The results show that plenty of defects can be produced by introducing helium (He) into W/Cu multilayer nanofilms. With the natural storage time increasing, the helium located in the near surface of W/Cu multilayer nanofilm would be released gradually and induce the coalescence of the helium related defects due to the diffusion of the helium and defects. In addition, the pure W nanofilms were irradiated by 30 keV helium ions and 40 keV hydrogen (H) ions in sequence at room temperature. From the DB-PAS analysis, it can be shown that a large number of vacancy-type defects are produced due to the He and/or H irradiation. H ions would be trapped by He related defects and produced He-H-V complexes.

Study of Defects in Croconic Acid Single Crystals Using Positron Annihilation Lifetime Spectroscopy

2017 ◽  
Vol 373 ◽  
pp. 179-182 ◽  
Author(s):  
Francisco Guzman ◽  
Judy Tran ◽  
Kimberley Cousins ◽  
Paul K. Dixon ◽  
Douglas Smith ◽  
...  
Keyword(s):  
Thermal Treatment ◽  
Positron Annihilation ◽  
Room Temperature ◽  
Ferroelectric Material ◽  
Positron Annihilation Lifetime Spectroscopy ◽  
Positron Annihilation Lifetime ◽  
Void Defect ◽  
Void Defects ◽  
Ferroelectric Hysteresis ◽  
Very High

Croconic acid is the first single molecular organic ferroelectric material exhibiting very high spontaneous polarization (~ 20 μC/cm2) at room temperature. Maximizing polarization depends on minimizing void defects in croconic acid crystals. In this experiment, the change in void defects upon the thermal treatment is characterized using positron annihilation lifetime spectroscopy. Both defect void size and intensity are measured, and their dependence upon the thermal treatment duration is studied. In addition, the relation between the void defect and ferroelectric hysteresis of croconic acid is established.

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