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Curium (96 Cm) is an artificial element with an atomic number of 96. Because it is an artificial element, a standard atomic weight cannot be given, and it has no stable isotopes. The first isotope synthesized was 242 Cm in 1944, which has 146 neutrons. There are 19 known radioisotopes ranging from 233 Cm to 251 Cm. There are also ten known ...
With a metal reflector (30 cm of steel), the critical masses of the odd isotopes are about 3–4 kg. When using water (thickness ~20–30 cm) as the reflector, the critical mass can be as small as 59 grams for 245 Cm, 155 grams for 243 Cm and 1550 grams for 247 Cm. There is significant uncertainty in these critical mass values.
In all of these cases, the use of a neutron reflector like beryllium can substantially drop this amount, however: with a 5 centimetres (2.0 in) reflector, the critical mass of 19.75%-enriched uranium drops to 403 kilograms (888 lb), and with a 15 centimetres (5.9 in) reflector it drops to 144 kilograms (317 lb), for example.
The fission cross section value was more problematic. For this, Frisch turned to a 1939 Nature article by L. A. Goldstein, A. Rogozinski and R. J. Walen at the Radium Institute in Paris, who gave a value of (11.2 ± 1.5) × 10 −24 cm 2. [46] This was too large by an order of magnitude; a modern value is about 1.24 × 10 −24 cm 2. [45]
All odd mass numbers have only one beta decay stable nuclide. Among even mass number, five (124, 130, 136, 150, 154) have three beta-stable nuclides. None have more than three; all others have either one or two. From 2 to 34, all have only one. From 36 to 72, only eight (36, 40, 46, 50, 54, 58, 64, 70) have two, and the remaining 11 have one.
The tamper had a radius of 17.5 centimetres (6.9 in) and a thickness of 11.3 centimetres (4.4 in), for a mass of 317 kilograms (699 lb). This was about 3.5 times the mass of the fissile material used. Tungsten carbide has a high density and a low neutron absorbency cross section.
[b] The α form exists below 600–800 °C with a density of 15.10 g/cm 3 and the β form exists above 600–800 °C with a density of 8.74 g/cm 3. [17] At 48 GPa of pressure the β form changes into an orthorhombic crystal system due to delocalization of the atom's 5f electrons , which frees them to bond.
The bulk density of the samples varied between 7.45 and 9.4 g/cm 3 (the densities of UO 2 and ZrO 2 are 10.4 and 5.6 g/cm 3). The porosity of samples varied between 5.7% and 32%, averaging at 18±11%. Striated interconnected porosity was found in some samples, suggesting the corium was liquid for a sufficient time for formation of bubbles of ...