Методика измерения сечений многофотонного поглощения лазерных импульсов в газах с помощью спектрофона

A technique to measure cross section of multiphoton absorption of laser pulses in gases using photoacoustic detector with time resolution of signals (a spectrophone) has been developed. The efficiency of the technique was tested on the example of single-photon and three-photon absorption of nanosecond pulses of quasimonochomatic radiation with a wavelength of 266 nm by molecular oxygen.

STUDY OF THE PROCESS e+e-→π+π-π0 IN THE ENERGY RANGE 1.04-1.38 GEV WITH CMD-2 DETECTOR

The data sample of 6 pb -1 collected by Cryogenic Magnetic Detector (CMD-2) at VEPP-2M collider in the c.m. energy range 1.04-1.38 GeV have been used to measure cross section of the process e+e-→π+π-π0 and to study its dynamics. It is shown that for description of the invariant mass spectra of π+π- pairs one should take into account the ωπ0 contribution arising due to ρ-ω - interference.

Size of Human Lower Thoracic and Lumbosacral Nerve Roots

Background Nerve root size may determine degree of blockade after epidural or spinal anesthesia, but good measures of this fundamental anatomic parameter have not been published. Models of subarachnoid anesthetic distribution have lacked valid cauda equina dimensions. In this study, the author sought to measure cross-section areas of anterior and posterior roots at different levels for basic anthropomorphic analysis. Methods Samples from 12 adult autopsy subjects were obtained from roots at levels T6 through S5. Cross-section area was determined by dividing the root sample weight by length and correcting for tissue density. Results Roots were variably composed of as many as five easily separable independent strands. Areas of anterior roots are approximately half the area of posterior roots. On average, the largest anterior and posterior root is at S1, but this may occur at L3 through S2. There is a large degree of interindividual variability (e.g., range of posterior L5 root is 2.33-7.71 mm2). Conclusions The large size of low lumbar and high sacral roots may cause resistance to anesthetic effects, whereas the smaller dimensions of the thoracic roots may facilitate neural blockade. The small size of the low sacral roots may, in part, explain selective neurotoxic damage of these fibers after subarachnoid injections. Interindividual variability in root sizes may contribute to lack of predictability in anesthetic response.

Excitation Curves for the Reactions of Fast Neutrons with Zinc

The activation method was used to measure cross section values from threshold energies up to 20 MeV for the reactions 64Zn(n,p)64Cu, 68Zn(n,α)65Ni, and 70Zn(n,2n)69Znm. The neutron flux at energies below 5.3 MeV was determined with a calibrated neutron long counter while at higher energies measurements were made relative to the known cross section for the 32S(n,p)32P reaction. Effective cross sections for a fission-neutron spectrum calculated from measured excitation curves are 42.3 ± 2.1 mb for the (n,p) reaction, 0.035 ± 0.003 mb for the (n,α) reaction, and 0.45 ± 0.04 mb for the (n,2n) reaction. Factors influencing precise measurements of fast-neutron cross sections are discussed in detail.