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CONVERSION FACTORS
Unit Equivalent To
1 kt 10^12 calories
4.19x10^12 joules
4.19x10^19 ergs
2.62x10^31 eV
2.62x10^25 MeV
fission of 0.241 moles of material (1.45x10^23 nuclei)
fission of approx. 57 g of material
1.16x10^6 kilowatt-hrs
3.97x10^9 BTU
1 eV 1.602177 x 10^-12 erg
11606 degree K
1 Bar 10^5 pascals (nt/m^2)
10^6 dyne/cm^2
0.98687 atmospheres
14.5038 PSI
1 calorie 4.1868 J
Convenient Energy Content Approximations
Fission of U-233: 17.8 kt/kg
Fission of U-235: 17.6 kt/kg
Fission of Pu-239: 17.3 kt/kg
Fusion of pure deuterium: 82.2 kt/kg
Fusion of tritium and deuterium (50/50): 80.4 kt/kg
Fusion of lithium-6 deuteride: 64.0 kt/kg
Fusion of lithium-7 deuteride
Total conversion of matter to energy: 21.47 Mt/kg
Fission of 1.11 g U-235: 1 megawatt-day (thermal)
IMPORTANT UNITS OF MEASUREMENT
Quantity Measured Unit Symbol Formula
Microscopic Cross Section Barn b 10^-24 cm^2
Radioactivity Becquerel Bq 1 decay/sec
Curie Ci 3.7x10^10 decay/sec
Absorbed Radiation Dose Gray Gy 1 J/Kg
Rad None 100 erg/g (.01 J/Kg)
Biological Equivalent Dose Sievert Sv Grays*Q
Rem None Rads*RBE
Absorbed Gamma/X-Ray Dose Roentgen R 94 erg/g
Immediate Explosive Energy Kiloton kt 10^12 calories
Radiation Biological Effect None RBE
Radiation Quality Factor None Q
Pressure Bar None 10^5 pascals (nt/m^2)
PHYSICAL CONSTANTS
[All constants are exact to the precision given]
Quantity Symbol Value Unit
Speed of Light in Vacuum c 2.99792458 x 10^10 cm/sec
Planck Constant h 6.62608 x 10^-27 erg-sec
Avogadro Constant N_A 6.02214 x 10^23 atom/mole
Molar Gas Constant R 8.3145 x 10^7 erg/(mole K)
Boltzmann Constant k 1.3806 x 10^-16 erg/K
Stefan-Boltzmann Constant sigma 5.670 x 10^-5 erg/cm^2 K^4 sec
Perfect Gas Standard Volume V_0 2.2414 x 10^5 cm^3
Atomic Mass Constant m_0 1.66054 x 10^-24 g
m_0 9.31494 x 10^8 eV
This is subsection lists most isotopes of interest for direct, indirect, or theoretical nuclear weapon applications. Basic isotopes characteristics, and summary tables of significant neutron reaction cross sections are included.
The Maxwellian average cross sections are for a peak neutron energy distribution at 0.0253 eV (a room temperature thermal distribution).
Molar volume is the minimum volume per mole for the densest phase at standard pressure and temperature (STP)
SF = spontaneous fission
Critical mass estimates for the fissile isotopes are given for bare spheres at the densest STP phase. Where available these estimates are from other sources and are based either on actual experimental measurement, or reasonably sophisticated numerical computations. All fissile isotopes also include for comparison critical mass estimates made by me, using an exact criticality solution with a one-group representation of neutronic properties. The one-group parameters are fission spectrum averages calculated from the ENDF-VI evaluated nuclear data base.
As can be seen where outside critical mass estimates are also available, this one-group calculation method consistently underestimates the true critical mass - primarily because it does not take into account the effects of inelastic scattering in softening the neutron spectrum. The one-group calculated critical mass estimates are thus lower bounds on the true value. Comparison between the one-group calculations and the actual values for the highly fissile isotopes for which good experimental data is available (U-233, U-235, Pu-239, and Pu-241) shows a consistent underestimate of 70-75% of the true value. For less fissile isotopes, where critical mass estimates have been offered by others (these are mostly calculated estimates also, but with more sophisticated models), the underestimates are more severe (at worst 22-29% of the 'true' value for Pu-242). This too is to be expected because the effects of inelastic scattering is relatively greater in less fissile materials. On the other hand, the estimates for extremely fissile transuranics like the californium isotopes should be quite good.
Hydrogen
Atomic number: 1
Molar volume: 13.1 cm^3/mole (solid, 13 K)
Density: 0.0763 (solid, 13 K, natural hydrogen)
Melting point: 13.96 K (natural hydrogen)
Boiling point: 20.39 K
1-H-1
Atomic Mass: 1.007825032 +- 0.000000000 (amu)
Excess Mass: 7288.969 +- 0.001 keV
Binding Energy: 0.000 +- 0.000 keV
Stable Isotope
Atomic Percent Abundance: 99.985%
>Magnetic Moment: 2.7928 nuclear magnetons
Spin: 1/2+
Lightest possible atom, and consequently the most efficient neutron moderator. Widely used in nuclear weapon structural materials (i.e. plastics). Due to moderating ability and light weight, used to harden weapons against outside neutron fluxes (especially in combination with Li-6).
Best nuclear reactor moderator due to high moderating efficiency and extremely low abosrption cross section. A principal fusion fuel in thermonuclear weapons, can also be used for fusion boosting, and in neutron generators. Melting point 20.4 K, boiling point 23.67 K.
Half Life: 12.33 years
Specific Activity: 9613 curie/g
Radioisotopic Power: 1.059 W/g
Primary Mode of Decay: Beta to He-3
Decay Energy: B- 18.591 +- 0.001 keV
Magnetic Moment: 2.9789 nuclear magnetons
Spin: 1/2+
A principal thermonuclear fuel, best used in conjunction with deuterium (the D+T reaction is the easiest by far to ignite, as well as one of the most energetic). It is produced in place by tritium breeding reactions in thermonuclear weapons. It can also manufactured and loaded into weapons (with deuterium) for use in fusion boosting of fission weapons, as the neutron source in neutron bombs and neutron generators for commercial or weapons use. Tritium is a pure beta emitter. Due to weak radiation emissions, it is used in safe luminescent displays. This nuclide is useful for thickness gauge of thin plastics.
Helium
Atomic number: 2
Molar volume: 32.05 cm^3/mole (liquid, 4.125 K)
Density: 0.1249 (liquid, 4.125 K, natural helium)
Boiling point: 4.125 K
2-He-3
Atomic Mass: 3.016029310 +- 0.000000001 (amu)
Excess Mass: 14931.204 +- 0.001 keV
Binding Energy: 7718.058 +- 0.002 keV
Stable Isotope
Atomic Percent Abundance: 0.000137%
Magnetic Moment: -2.1276 nuclear magnetons
Spin: 1/2+
This isotope is produced by the decay of tritium and so accumulates in fusion boosting reservoirs as an undesirable contaminant due to its high neutron absorption. It can be recycled to produce tritium by neutron bombardment. It is a valuable fusion fuel produced (and consumed) in the course of deuterium-deuterium fusion. Very rare in nature.
Most common natural isotope of helium. Widely used in industry as an inert gas. Produced as an end product of fusion reactions. This isotope has a zero cross section for all neutron reactions except scattering for neutron energies below 20 MeV.
Natural lithium isotope used as a thermonuclear weapon fusion fuel, in the form of lithium deuteride, due to its production of tritium through the (n,t) reaction. The very high cross section of this reaction for thermalized neutrons, combined with the light weight of the Li-6 atom, make it useful in the form of lithium hydride for hardening of nuclear weapons against external neutron fluxes.
Predominant isotope of natural lithium. Due to the large cross section for the (n,t) reaction at high neutron energies this isotope can breed substantial quantities of tritium in a fusion-driven chain reaction and thus serve as a fusion fuel. Although less efficient that Li-6 for this purpose, and not used in modern thermonuclear weapons it served this function in some early high yield weapons.
Beryllium is both an excellent neutron reflector and moderator, and is in addition very light. It has one of the highest neutron scattering cross sections per unit volume, and has very low neutron absorption. Beryllium is commonly used as a neutron reflector to make compact light-weight fission weapons. Beryllium also undergoes (n,2n) neutron multiplication reactions, which are not important for fission-spectrum neutons, but may have a significant role in fusion boosted systems. Beryllium can slo generate neutrons through Be-9(gamma,n)Be-8 and Be-9(a,n)C-12 reactions. When combined with an isotope that is a strong alpha-emitter but a weak gamma-emitter (usually Po-210), Be has been used in modulated neutron initiators for fission weapons. Pu-239/Be sources have been used as convenient laboratory neutron sources; Ra-226/Be and Am-241/Be neutron sources are useful for moisture gauges.
This natural isotope is the best absorber of fast neutrons, and an excellent absorber of slow neutrons. As a component of natural boron, it is commonly used as a neutron absorber (control rod or burnable poison) in nuclear reactors. The separated isotpe has been used to harden nuclear weapons against external neutron fluxes, and to reduce the neutron preheating of fusion stages by fission triggers in thermonuclear weapons. Use of B-10 has been proposed to create "clean" (low fallout and low neutron emission) thermonuclear weapons.
Although the concept of the enhanced fallout "cobalt bomb", in which radioactive Co-60 is produced by fusion neutrons, is well known this isotope is not known to have been seriously considered for weapons applications. The 5.26 year half-life of Co-60 is too long to be of real military interest, which favors more intense shorter term effects.
Comprising nearly all of natural tantalum, this isotope was studied for possible use in enhanced fallout radiation weapons by the U.S. in the 1950s. Compared with Co-60 the shorter half-life of Ta-182 (115 days vs 2.56 years) and the higher cross section for epithermal neutrons made Ta-181 a more desirable candidate for this use.
Average neutron induced Nu_p (prompt neutrons/fission)
Incident neutron 1E+00 eV Nu_p = 3.126
Incident neutron 1E+05 eV Nu_p = 3.136
Incident neutron 1E+06 eV Nu_p = 3.233
Incident neutron 4E+06 eV Nu_p = 3.554
Incident neutron 1.5E+07 eV Nu_p = 4.732
Incident neutron fission spectrum average Nu_p = 3.296
92-U-233
Atomic Mass: 233.039628196 +- 0.000003010 (amu)
Excess Mass: 36913.421 +- 2.804 keV
Binding Energy: 1771728.280 +- 2.821 keV
Beta Decay Energy: B- -1028.513 +- 51.640 keV
Half Life: 159200 Y
Specific Activity: 0.009636 curie/g
Radioisotopic Power: 0.0002804 W/g
Primary Mode of Decay: Alpha to Th-229
Decay Energy: 4.909 MeV
Spin: 5/2+
Critical mass: 16 kg (LA-10860-MS "Critical Dimensions of Systems Containing 235-U, 239-Pu, and 233-U; 1986 Rev."; De Volpi, A. in "Proliferation, Plutonium, and Policy", 1979, pg. 86), 11.63 kg (one-group calculation)
Average neutron induced Nu_p (prompt neutrons/fission)
Incident neutron 1E+00 eV Nu_p = 2.339
Incident neutron 1E+05 eV Nu_p = 2.353
Incident neutron 1E+06 eV Nu_p = 2.474
Incident neutron 4E+06 eV Nu_p = 2.879
Incident neutron 1.5E+07 eV Nu_p = 4.369
Incident neutron fission spectrum average Nu_p = 2.578
92-U-235
Atomic Mass: 235.043923062 +- 0.000002115 (amu)
Excess Mass: 40914.062 +- 1.970 keV
Binding Energy: 1783870.285 +- 1.996 keV
Beta Decay Energy: B- -123.716 +- 0.869 keV
Atomic Percent Abundance: 0.720%
Spin: 7/2- 7
Half Life: 7.038E8 Y
Specific Activity: 2.161E-6 curie/g
Radioisotopic Power: 5.994E-8 W/g
Primary Mode of Decay: Alpha to Th-231
Decay Energy: 4.679 MeV
Primary Mode of Decay: Spontaneous fission
Branch ratio: 7.0E-9%
SF rate (fissions/sec/g) = 5.6E-6
Neutron emission rate (N/sec/g) = 1.1E-5
Meta state at 0.000 Mev
Half Life: ~25 M
Primary Mode of Decay: IT to U-235
Spin: 1/2+
Critical mass: 48 kg (LA-10860-MS "Critical Dimensions of Systems Containing 235-U, 239-Pu, and 233-U; 1986 Rev."; De Volpi, A. in "Proliferation, Plutonium, and Policy", 1979, pg. 86"), 33.4 kg (one-group calculation)
Average neutron induced Nu_p (prompt neutrons/fission)
Incident neutron 1E-05 eV Nu_p = 2.891
Incident neutron 1E+05 eV Nu_p = 2.906
Incident neutron 1E+06 eV Nu_p = 3.039
Incident neutron 4E+06 eV Nu_p = 3.483
Incident neutron 1.4E+07 eV Nu_p = 4.964
Incident neutron fission spectrum average Nu_p = 3.148
94-Pu-239
Atomic Mass: 239.0521565 +- 0.0000021 amu
Excess Mass: 48583.478 +- 1.971 keV
Binding Energy: 1806921.454 +- 1.998 keV
Beta Decay Energy: B- -802.912 +- 2.011 keV
Half Life: 24110 Y
Specific Activity: 0.06203 curie/g
Radioisotopic Power: 0.001929 W/g
Primary Mode of Decay: Alpha to U-235
Decay Energy: 5.245 MeV
Secondary Mode of Decay: Spontaneous fission
Branch ratio: 3E-10 %
Average neutron yield (Nu)
Nu_prompt =
SF rate (fissions/sec/g) = 7.E-3
Neutron emission rate (N/sec/g) = 2.E-2
Spin: 1/2+
Critical mass: 10.5 kg (LA-10860-MS "Critical Dimensions of Systems Containing 235-U, 239-Pu, and 233-U; 1986 Rev."; Glasstone, S. and Redman, L.M. in WASH-1037 Rev. "An Introduction to Nuclear Weapons", 1972, pg. 12), 7.421 kg (one-group calculation)
Average neutron induced Nu_p (prompt neutrons/fission)
Incident neutron 2.53E-02 eV Nu_p = 2.8725
Incident neutron 1E+05 eV Nu_p = 2.8976
Incident neutron 1E+06 eV Nu_p = 3.0107
Incident neutron 4E+06 eV Nu_p = 3.4456
Incident neutron 1.4E+07 eV Nu_p = 4.9397
Incident neutron fission spectrum average Nu_p = 3.1231
94-Pu-240
Atomic Mass: 240.0538075 +- 0.0000021 amu
Excess Mass: 50121.319 +- 1.947 keV
Binding Energy: 1813454.935 +- 1.974 keV
Beta Decay Energy: B- -1378.952 +- 13.790 keV
Half Life: 6564 Y
Specific Activity: 0.227 curie/g
Radioisotopic Power: 0.00707 W/g
Primary Mode of Decay: Alpha to U-236
Decay Energy: 5.256 MeV
Secondary Mode of Decay: Spontaneous fission
Branch ratio: 5.7E-6 %
Average neutron yield (Nu)
Nu_prompt = 2.189 +- 0.026
SF rate (fissions/sec/g) = 478.
Neutron emission rate (N/sec/g) = 1047.
Spin: 0+
Critical mass: 40 kg (Lovins, A.B. Nature. 283, p. 818, 1980; De Volpi, A. in "Proliferation, Plutonium, and Policy", 1979, pg. 86), 15.2 kg (one-group calculation)
Average neutron induced Nu_p (prompt neutrons/fission)
Incident neutron 1E-05 eV Nu_p = 2.794
Incident neutron 4E+06 eV Nu_p = 3.402
Incident neutron 1.4E+07 eV Nu_p = 4.922
Incident neutron fission spectrum average Nu_p = 3.061
94-Pu-241
Atomic Mass: 241.0568453 +- 0.0000021 amu
Excess Mass: 52951.039 +- 1.948 keV
Binding Energy: 1818696.538 +- 1.975 keV
Beta Decay Energy: B- 20.815 +- 0.199 keV
Spin: 5/2+
Half Life: 14.35 Y
Specific Activity: 103.3 curie/g
Radioisotopic Power: 0.1294 W/g
Primary Mode of Decay: Beta to Am-241
Decay Energy: 0.021 MeV
Secondary Mode of Decay: Alpha to U-237
Branch ratio: 0.0025 %
Decay Energy: 5.140 MeV
Tertiary Mode of Decay: Spontaneous fission
Branch ratio: <2.E-14 %
SF rate (fissions/sec/g) = <8.E-4
Spin: 5/2+
Critical mass: 12 kg (Lovins, A.B. Nature. 283, p. 818, 1980; De Volpi, A. in "Proliferation, Plutonium, and Policy", 1979, pg. 86"), 9.03 kg (one-group calculation)
Average neutron induced Nu_p (prompt neutrons/fission)
Incident neutron 1E-05 eV Nu_p = 2.930
Incident neutron 1E+05 eV Nu_p = 2.930
Incident neutron 1E+06 eV Nu_p = 3.013
Incident neutron 4E+06 eV Nu_p = 3.490
Incident neutron 2E+07 eV Nu_p = 5.963
Incident neutron fission spectrum average Nu_p = 3.142
94-Pu-242
Atomic Mass: 242.0587368 +- 0.0000021 amu
Excess Mass: 54713.012 +- 1.966 keV
Binding Energy: 1825005.887 +- 1.993 keV
Beta Decay Energy: B- -750.963 +- 0.718 keV
Half Life: 3.733E5 Y
Specific Activity: 0.003956 curie/g
Radioisotopic Power: 0.0001169 W/g
Primary Mode of Decay: Alpha to U-238
Decay Energy: 4.984 MeV
Secondary Mode of Decay: Spontaneous fission
Branch ratio: 0.00055 %
Average neutron yield (Nu)
Nu_prompt = 2.28 +- 0.13
SF rate (fissions/sec/g) = 805.
Neutron emission rate (N/sec/g) = 1840
Spin: 0+
Critical mass: 95 kg, range 75-100 kg (Lovins, A.B. Nature. 283, p. 818, 1980; De Volpi, A. in "Proliferation, Plutonium, and Policy", 1979, pg. 86"); 22.1 kg (one-group calculation)
Average neutron induced Nu_p (prompt neutrons/fission)
Incident neutron 1E-05 eV Nu_p = 3.235
Incident neutron 2E+05 eV Nu_p = 3.262
Incident neutron 1E+06 eV Nu_p = 3.369
Incident neutron 4E+06 eV Nu_p = 3.769
Incident neutron 1.4E+07 eV Nu_p = 5.057
Incident neutron fission spectrum average Nu_p = 3.457
95-Am-243
Atomic Mass: 243.0613727 +- 0.0000023 amu
Excess Mass: 57168.280 +- 2.178 keV
Binding Energy: 1829839.589 +- 2.203 keV
Beta Decay Energy: B- -8.908 +- 1.434 keV
Half Life: 7370 Y
Specific Activity: 0.1996 curie/g
Radioisotopic Power: 0.006433 W/g
Primary Mode of Decay: Alpha to Np-239
Decay Energy: 5.438 MeV
Secondary Mode of Decay: Spontaneous fission
Branch ratio: 3.7E-9 %
SF rate (fissions/sec/g) = 0.27
Neutron emission rate (N/sec/g) = 0.76
Spin: 5/2-
Critical mass: no published estimate, 38.1 kg (one-group calculation, assuming the same ratio between one-group and multi-group values as Am-241 a 'true' value of 140 kg can be estimated)