Transcript оценка и стандартизация радионуклидных данных

ASTROPHYSICAL DECAY DATA
Valery Chechev
V.G. Khlopin Radium Institute,
194021 Saint Petersburg, Russia
Fourth Workshop for Radioactive
Decay Data Evaluators: DDEP-2012
8 – 10 October 2012, LNE / LNHB, Paris
Safeguards
Waste management
Environmental monitoring
DDEP
Detector Efficiency Calibration
Medical Applications
Nuclear fuel cycle
Fission products
Other Applications
WHAT ABOUT nuclear astrophysics ?
Nucleosynthesis from supernova
Picture from the MacMaster University Report at ASTRO_TF_2011
Picture from the ORNL Report at ASTRO_TF_2011
DDEP provides detailed and updated values of decay characteristics. Can
these data be in demand for astrophysics, given that the
astrophysical parameters in the theory of nucleosynthesis have poor
accuracy? It turns out – can!
For example, in recent years it became clear (Begemann F, Ludwig K.R.,
Lugmair G.W. et al. Call for an improved set of decay constants for
geochronical use. 2001BE81 Geochim. Cosmochim. Act. 65, 111 (2001))
that the accuracy of radiometric ages of minerals and rocks is limited by
the accuracy of the constants of radioactive decay. This is due to the fact
that in geochronology the RELATIVE concentration of isotopes is
commonly used. Nuclear cosmochronology unlike geochronology,
determines ages of THEMSELVES RADIONUCLIDES occurring in the
various processes of the galactic nucleosynthesis, but in this case, it also
analyzes the RELATIVE abundances of different pairs of long-lived
radioactive nuclides (238U/232Th, 235U/238U, 244Pu/238U etc.).
I could point to three directions of the demand of decay characteristics in
nuclear astrophysics for radionuclides near the valley of nuclear
stability, which are usually considered by our cooperation. Perhaps the
uncertainty in astrophysics often ls not critical, but in all these cases it is
important to deal with high-quality evaluated decay data.
FIRST DIRECTION
Half-lives of long-lived radionuclides more than 108 years such as of
176Lu, 187Re, 232Th, 235U, and 238U are used in nuclear astrophysics for
dating different cosmic events and also half-lives of 40K and 87Rb are used in
nuclear geochronology for determination of the ages of minerals.
Moreover, recently nuclear cosmochronology increased interest also in
relatively short-lived cosmochronometers with half-lives less than 108
years, now extinct, decay of which provides information about the details of
nucleosynthesis in the early history of the solar system, in particular, about
the time interval during which the solidification of the planetary and
meteoritic material occurs.
Decay data, especially, half-lives, of the
following radionuclides are required for
study of meteorite anomalies in yields
of their stable daughters: 53Mn, 60Fe,
93Zr, 98Tc, 107Pd, 129I, 135Cs, 146Sm, 182Hf,
205Pb, 244Pu, and 247Cm.
2011Ch65 V.P. Chechev, Phys. Atomic Nuclei 74, 1713 (2011)
Evaluated half-lives of the 20 radionuclides used in nuclear
cosmochronology
Radio- Number of experimental Time interval of
nuclide values included in the
publications
evaluation
26Al
4
1972-1984
40K
36
1947-2004
53Mn
4
1971-1974
60Fe
1
1964
87Rb
5
1964-2003
93Zr
1
1972
98Tc
1
1973
107Pd
1
1969
129I
4
1951-1973
135Cs
3
1949-1955
146Sm
4
1963-1987
Evaluated
half-life,
years
7.17(24) .105
1.250(3).109
3.7(2).106
1.5(3).106
4.84(12).1010
1.53(10).106
4.2(3).106
6.5(3).106
1.61(7).107
2.3(3).106
1.00(5).108
176Lu
182Hf
187Re
205Pb
232Th
235U
238U
244Pu
247Cm
8
3
7
1
5
11
10
5
2
1965-2006
1961, 2004
1962-2001
1958
1956-1963
1939-1993
1935-1971
1956-2006
1963, 1971
3.76(8).1010
8.87(9).106
4.33(7).1010
1.73(7).107
1.402(6).1010
7.04(1).108
4.468(5).109
8.00(12).107
1.56(5).107
As the table shows, for the twenty radionuclides considered,
there is a few of evaluated half-life values, based on presentday experimental data. For a number of radionuclides there is
only one (very early) measurement. Additional measurements
are needed primarily for half-lives of the 6 nuclides: 60Fe, 93Zr,
98Tc, 107Pd, 135Cs, and 205Pb.
New half-life of 60Fe is 2.62(4)×106 yr.
SECOND DIRECTION
Decay data including  ray characteristics for radionuclides
decay of which generates gamma rays observed (or can be
observed) by orbital detectors.
Radioactive isotopes are co-produced with stable isotopes in
stellar interiors, supernovae, novae, and interstellar space.
Stellar interiors are opaque, but expanding explosive sites of
nucleosynthesis such as novae and supernovae are gammaray transparent typically a few days to weeks after the
explosion, thus allowing a direct gamma-ray view at the
nucleosynthesis site. Only a small number of isotopes has
lifetimes sufficiently long to not have decayed already before
transparency of the site - these are relevant for gamma-ray
measurements of nucleosynthesis.
Isotope
Mean
Lifetime
Decay Chain
-Ray Energy (keV)
7Be
77 d
7Be7Li*
478
22Na
3.76 y
22Na22Ne*+
e+
1275
26Al
1.034×106 y
26Al26Mg*+
e+
1809
44Ti
86.6 y
44Ti44Sc*44Ca*+
56Ni
111 d
56Ni56Co56Fe*
57Co
392 d
60Fe
3.78×106 y
e+
+ e+
57Co57Fe*
60Fe60Co*60Ni
78, 68, 1157
158, 812, 847, 1238
122
*
59, 1173, 1332
The third field of decay data of “astrophysical” nuclides relates to
THEORETICAL nuclear astrophysics unlike the first two
EXPERIMENTAL ones, to s- and p- processes of nucleosynthesis.
Generally, there are three basic processes
of stellar nucleosynthesis in which the
chemical elements are produced: sprocess (slow neutron capture alternating
with beta decays occurring along the
valley of nuclear stability), r-process (rapid
multiple (repeated) neutron capture) and
p-process (proton capture occurring in the
limited field of mass numbers).The
contributions of these three processes
have clearly manifested in the curve of
observed abundances of the natural
(stable) nuclides.
Nucleosynthesis s- and r- process tracks
THIRD DIRECTION
Level Schemes and Decay Data of so called “key” nuclides
in the s-process. Such nuclides have relatively long-lived lowlying excited states including isomeric, which are populated
thermally in stellar conditions. Accordingly, the track of sprocess depends from the -decay properties of these
states and the temperature of stellar interior where s-process
occurs. Therefore, based on the known relative abundances of
the stable natural nuclides considered in the end of the sprocess chain, we can estimate the temperature of s-process.
Measurement in laboratory of isomeric  - branching is very important for
stellar synthesis of the two s-process stable isotopes 80Kr and 82Kr as
thermal excitation of isomer 79Sem in the interior of a star will lead to an
enhanced  - decay rate. In stellar conditions s-process branches
occurring also through beta-decay of isomeric state 79mSe. Using the
observed Kr abundances and the measured neutron capture cross
sections in the mass region 78 A 82 it is possible to determine the sprocess temperature.
In total are 30 branching points in the s-process: 63Ni, 64Cu, 79Se, 80Br,
81Kr, 85Kr, 93Zr, 99Tc, 107Pd, 113Cd, 129I, 134Cs, 135Cs, 147Pm, 151Sm, 152Eu,
153Gd,154Eu,155Eu, 160Tb, 163Dy, 163Ho, 170Tm, 171Tm, 176Lu, 182Ta, 192Ir, 193Pt,
204Tl, 205Pb. Among them 14 low-lying isomers are known:
79mSe, 80mBr, 81mKr, 85Kr, 99mTc, 107mPd, 113mCd, 134mCs, 135mCs, 163mHo,
176mLu, 182mTa, 192mIr, 193mPt.
The p-process also produces in significant quantity several interesting
radionuclides with relatively long half-lives, including 92Nb (T1/2 = 3.6 107
yr), 97Tc (T1/2 = 2.6 106 yr), 98Tc (T1/2 = 4.2106 yr), and 146Sm (T1/2 = 1.08
108 yr). In principle, if the production rates of these radioactive nuclides
are known, the measurements of their extinct radioactivity in meteorites
can have them serve as chronometers for the astrophysical p-process and
for supernovae nucleosynthesis. Of these p-process chronometers, 146Sm
is the most interesting, since evidence for its decay has been observed in
meteorites. (W.M. Howard, LLNL, Livermore CA 94550, USA).
At last, there is also one important radionuclide of interest to solar
neutrino physics – 37Ar (T1/2 = 35.01(2) d). 37Ar was proposed as a
calibration source for solar neutrino detectors. Measuring with calorimeter
non-neutrino radiation from such source it is possible to determine and
standardize the neutrino flux from 37Ar.
In conclusion the full list of radionuclides of astrophysical
interest near the line of nuclear stability is given with marked
ones, decay data of which have been already evaluated by
DDEP (by red type).
7Be, 18F, 22Na, 26Al, 40K, 44Sc, 44Ti, 53Mn, 56Ni, 56Co, 57Co,
60Fe, 79Se, 79mSe,80Br, 80mBr, 81Kr, 81mKr, 85Kr, 85mKr, 87Rb,
92Nb, 93Zr, 97Tc, 98Tc, 99Tc, 99mTc, 107Pd, 107mPd, 113Cd,
113mCd, 129I, 134Cs, 134mCs,135Cs, 135mCs, 146Sm, 163Ho,
163mHo, 176Lu, 176mLu,182Hf, 182Ta, 182mTa, 187Re, 192Ir, 192mIr,
193Pt , 193mPt ,205Pb, 232Th, 235U, 238U, 244Pu, 247Cm.
In total – 55 nuclides, of them for 20 nuclides decay data
have been already evaluated by DDEP.
Thank you for your attention!