ABSTRACT
The neutron energy spectrum of the JRC 241Am-Li(alpha,n) radionuclide source has been measured at the PTB in Germany using various spectrometry systems, such as Bonner spheres, proton recoil counters and NE213 liquid scintillators. The source photon spectrum has been measured and the neutron contamination due to traces of beryllium through the 9Be(alpha,n)12C reaction has been determined. The effects associated with source encapsulation and the materials it contains have been investigated previously, using Monte Carlo simulations, the various structures seen in the spectra have been explained and the anisotropy of fluence distributions in 4pi have been calculated and compared to measurements. These extensive high resolution spectrometry measurements have been coupled to Monte Carlo calculations to provide a realistic spectrum and new spectrum-averaged fluence-to-dose equivalent conversion coefficients for the actual 241Am-Li source.
Subject(s)
Americium/analysis , Lithium/analysis , Neutrons , Radiation Protection/methods , Radiation Protection/standards , Radiometry/methods , Radiometry/standards , Body Burden , Calibration/standards , Computer Simulation , Computer-Aided Design , Equipment Failure Analysis/instrumentation , Equipment Failure Analysis/methods , Equipment Failure Analysis/standards , Germany , Internationality , Models, Statistical , Monte Carlo Method , Nuclear Reactors , Occupational Exposure/analysis , Photons , Radiation Dosage , Radiation Protection/instrumentation , Radioisotopes/analysis , Radiometry/instrumentation , Reference Standards , Relative Biological Effectiveness , Reproducibility of Results , Scattering, Radiation , Sensitivity and SpecificityABSTRACT
Bone mass is reduced in patients with GH deficiency (GHD) leading to an increased vertebral fracture rate and clinically significant osteoporosis. Patients with GHD of juvenile onset have reduced skeletal mineralization. When substituting GH in patients with GHD, bone turnover is increased and bone mineral density initially decreases during the first year due to the increase in remodelling space. From the experience in patients with acromegaly, cortical bone mass is increased and trabecular bone mass is normal in eugonadal or decreased in the hypogonadal patients. However, bone mineral content and bone area are increased leading to a higher biomechanical competence of bone as shown in rats. In patients with GHD of juvenile onset, mineralization and bone maturation are achieved during treatment with GH in adult life after having reached final body height leading to an increase in bone mass. The GH/ IGF-I system is dysregulated in patients with post-menopausal osteoporosis. This is shown by reduced systemic IGF and IGFBP-3-levels in osteoporosis suggesting a decrease of endogenous GH-secretion or a dysregulation of the GH receptor system which is beyond the normal ageing process of the GH/IGF system, the "somatopause". A premature somatopause may be responsible for the dysregulation in some patients with osteoporosis. However, 24-h GH profiles do not differ between patients suffering from osteoporosis or osteoarthritis. Treatment of osteoporosis with GH might be beneficial due to the increased bone metabolism and improved bone geometry which occurs with GH. The substantial increase of bone remodelling achieved with GH may be helpful during late post-menopause with decreased bone turnover and impaired osteoblastic function. Using GH to prevent physiological bone loss that occurs with age seems possible, but has to be discussed on an ethical and economic basis.
