N.V. Magradze

A study of the radiation environment on board the Space Shuttle flight STS-57

A joint NASA-Russian study of the radiation environment inside a SPACEHAB 2 locker on Space Shuttle flight STS-57 was conducted. The Shuttle flew in a nearly circular orbit of 28.5 degrees inclination and 462 km altitude. The locker carried a charged particle spectrometer, a tissue equivalent proportional counter (TEPC), and two area passive detectors consisting of combined NASA plastic nuclear track detectors (PNTDs) and thermoluminescent detectors (TLDs), and Russian nuclear emulsions, PNTDs and TLDs. All the detector systems were shielded by the same Shuttle mass distribution. This makes possible a direct comparison of the various dose measurement techniques. In addition, measurements of the neutron energy spectrum were made using the proton recoil technique. The results show good agreement between the integral LET spectrum of the combined galactic and trapped particles using the tissue equivalent proportional counter and track detectors between about 15 keV/micrometers and 200 keV/micrometers. The LET spectrum determined from nuclear emulsions was systematically lower by about 50%, possibly due to emulsion fading. The results show that the TEPC measured an absorbed dose 20% higher than the TLDs, due primarily to an increased TEPC response to neutrons and a low sensitivity of TLDs to high LET particles under normal processing techniques. There is a significant flux of high energy neutrons that is currently not taken into consideration in dose equivalent calculations. The results of the analysis of the spectrometer data will be reported separately.

Studying radiation environment on board STS-55 and STS-57 by the method of passive detectors

Abstract Radiation environment onboard STS-55 and 57 is estimated using experimental and calculated data.

Linear energy transfer (LET) spectra of cosmic radiation in low earth orbit

Integral linear energy transfer (LET) spectra of cosmic radiation (CR) particles were measured on five Cosmos series spacecraft in low Earth orbit (LEO). Particular emphasis is placed on results of the Cosmos 1887 biosatellite which carried a set of joint U.S.S.R.-U.S.A. radiation experiments involving passive detectors that included thermoluminescent detectors (TLDs), plastic nuclear track detectors (PNTDs), fission foils, nuclear photo-emulsions, etc. which were located both inside and outside the spacecraft. Measured LET spectra are compared with those theoretically calculated. Results show that there is some dependence of LET spectra on orbital parameters. The results are used to estimate the CR quality factor (QF) for the Cosmos 1887 mission.

Development of an autoradiographic method of investigation of hot particles from the Chernobyl nuclear power plant

Abstract A method of autoradiographic investigation of hot particles that have risen into the atmosphere and precipitated on the soil and leaves after the Chernobyl accident of April 1986 has been developed. Particular objects of investigation are the α-active radionuclides with their dimensions and activity varying from 0.2 to 200 μm and from 10−6 to 10−1 Bq, respectively. BYa-2 nuclear emulsions were used as detectors. The activity distribution function of particles of different dimension, A = f(d), and the leaf contamination density distribution in the vertical profile are obtained.

Autoradiographic investigation of radionuclide alpha-activity in soil and plant samples from Chernobyl zone

Abstract Alpha-active “hot particles” in soil and plant samples collected in Chernobyl zone have been investigated by the radiographic method. The size and activity of “hot particles” were measured allowing to calculate their contribution into the radiation dose. Correlation between the measured particle parameters was established. The method of the particle size measuring with the help of low sensitive BYa-2 type photoemulsion is described. The measured mean diameter of hot particles varies from 10 to 200 μm and their activity is 10 −1 −10 −5 Bq. The most active particles (10 −1 − 10 −2 Bq) were found only in soil. The leaf samples after the same exposure contained particles with activity not higher than 10 −3 Bq.

Experimental and calculated LET distributions in the Cosmos-2044 biosatellite orbit

During the flight of the Cosmos-2044 biosatellite, joint U.S.S.R.-U.S.A. investigations of different characteristics of cosmic radiation (CR) in the near-Earth environment were carried out. The U.S. dielectric track detectors CR-39 and Soviet BYa- and BR-type nuclear photo-emulsions were used as detectors. The present work shows some results of experimental measurements of linear energy transfer (LET) spectra of CR particles obtained with the use of these detectors, which were placed both inside and outside the satellite. The LET spectra measurement with plastic detectors is composed of two parts: the measurement of galactic cosmic rays (GCR) particles, and of short-range particles. The contributions of these components to the total LET distribution at various thicknesses of the shielding were analyzed and the results of these studies are presented. Calculated LET spectra in the Cosmos-2044 orbit were compared with experimental data. On the basis of experimental and calculated values of the LET spectra, absorbed and equivalent CR doses were calculated. In the shielding range of 1-1.5 g cm-2, outside the spacecraft, the photo-emulsions yielded 10.3 mrad d-1 and 27.5 mrem d-1 (LET > or = 2 MeV cm-1) while the CR-39 yielded averages of 1.43 mrad d-1 and 13.4 mrem d-1 (LET > or = 40 MeV cm-1). Inside the spacecraft (> or = 10 g cm-2) the photo-emulsions yielded 8.9 mrad d-1 and 14.5 mrem d-1.

Assessment of radiation environment on board COSMOS-2044 biosatellite by the nuclear emulsion method

Abstract The results of experimental studying the integral spectra of linear energy transfer (LET) of cosmic ray (CR) particles and the neutron energy spectra obtained using a single type of detectors, namely, nuclear emulsion (NE) on board COSMOS-2044 are presented. Special attention is paid to measuring the total CR particle flux recorded in the NE layers inside and outside the biosatellite. The measurements are necessary for the total absorbed and equivalent doses from the charged and neutral CR components to be determined.

On the possibility of charge identification of particles with Z ⩾ 2 by the grain calculation regime in nuclear emulsions

Abstract It is shown that when using a unique method of selective development with the controlled detection threshold in a wide range of specific ionization loss dE dR = 10 1 − 10 4 MeV/cm , the nuclear emulsion turns into a controllable track detector successfully applied to measure the most important cosmic radiation characteristics. An analytical expression is found for the empirical dependence of grain density-ionization loss which allowed to identify the charge of low energy nuclei with Z ⩾ 2 by the grain counting technique.

Identification of cosmic ray heavy nuclei in an assembly of nuclear photoemulsions and solid state nuclear track detectors, using internal calibration

Abstract Nuclear tracks of cosmic ray heavy nuclei (22 ⩽ Z ⩽ 28) were identified in a multilayer assembly consisting of interlaid solid state nuclear track detectors (SSNTDs) and nuclear photoemulsions (NPEs). The assembly was exposed, as part of the scientific apparatus “Quartz”, aboard the Kosmos-1672 satellite. The nuclear tracks were identified in SSNTDs using the calibrating dependence of the etch rate ratio as a function of restricted energy loss. Those tracks which continued into emulsions were used to make internal calibrations in NPEs treated by the selective development method, enabling control of the registration threshold of nuclear emulsions. In the case of a detected particle with Z = 70 ± 5, the effectiveness of combining two types of detectors in the search for very heavy cosmic ray nuclei is demonstrated.