NEUTRON FIELD CHARACTERISTICS AT RADIATION METROLOGY LABORATORY OF STUK.

Radiation metrology laboratory at Radiation and Nuclear Safety Authority (STUK) is Finnish national laboratory for ionizing radiation. In order to establish personal dose equivalent available for neutron calibration service, a project was started to evaluate the neutron reference fields in the present facility. The irradiation room conditions were characterized in order to establish reference conditions for personal dose equivalent. To verify the validity of the calculations, ambient dose equivalent rates and room return were measured and calculated for 241AmBe and 252Cf sources. First results of Monte Carlo calculations and measurements are presented in this article.

Occupational exposure to 131I-a case study.

In a laboratory in a company manufacturing radiopharmaceuticals, a laboratory technician was contaminated with I. The employee was preparing I capsules for thyroid carcinoma treatment. The employee was wearing two pairs of protective gloves and, when changing gloves, noticed a rupture in the right inner glove but no visible rupture in the outer glove. Only 3-4 h later, routine monitoring revealed heavy contamination of the back of the right hand. Immediate actions to decontaminate the hand were taken on-site. Stable iodine was not administered. On the next day, besides persisting heavy contamination of the hand, I was also detected in the thyroid gland. Based on original measurements on-site and later follow-up at STUK, including surface contamination measurements and whole body counting, the original I activity on the hand was estimated at 12 MBq and the superficial skin dose at 33 Gy, affecting a skin area of about 10 cm. The thyroid dose was estimated at 430 mGy. Eleven days after the incident, the skin was dry and slightly desquamated. After 15 d, the skin was intact with no desquamation left. No further signs of skin damage have occurred. Cytogenetic analysis of circulating lymphocytes indicated a slight elevation of chromosomal aberrations.

Revised rates for the stellar triple-alpha process from measurement of 12C nuclear resonances.

In the centres of stars where the temperature is high enough, three alpha-particles (helium nuclei) are able to combine to form 12C because of a resonant reaction leading to a nuclear excited state. (Stars with masses greater than approximately 0.5 times that of the Sun will at some point in their lives have a central temperature high enough for this reaction to proceed.) Although the reaction rate is of critical significance for determining elemental abundances in the Universe, and for determining the size of the iron core of a star just before it goes supernova, it has hitherto been insufficiently determined. Here we report a measurement of the inverse process, where a 12C nucleus decays to three alpha-particles. We find a dominant resonance at an energy of approximately 11 MeV, but do not confirm the presence of a resonance at 9.1 MeV (ref. 3). We show that interference between two resonances has important effects on our measured spectrum. Using these data, we calculate the triple-alpha rate for temperatures from 10(7) K to 10(10) K and find significant deviations from the standard rates. Our rate below approximately 5 x 10(7) K is higher than the previous standard, implying that the critical amounts of carbon that catalysed hydrogen burning in the first stars are produced twice as fast as previously believed. At temperatures above 10(9) K, our rate is much less, which modifies predicted nucleosynthesis in supernovae.