WHAT VALUES ARE BEST RECOMMENDED FOR ALPHA- AND GAMMA- ENERGIES IN DECAYS OF

ACTINIDES?

Valery Chechev

V.G. Khlopin Radium Institute, 194021 Saint Petersburg, Russia

Third Workshop for Radioactive Decay Data Evaluators: (DDEP-2010)

9 – 11 June 2010, CIEMAT, Madrid

The DDEP tabulated data files involve consideration of two types of alpha-energies: the nuclear transition energy and the energy of particles emitted in this transition.

   

In spite of the comparative simplicity of these characteristics, to get properly their consistent recommended values and uncertainties, we should consider different sources of information.

GENERAL REMARK

0,0 4984.5(10) 0,0 4902.3(10)

0,1 4939.6(10) 0,1 4858.2(10)

0,2 4836.1(10) 0,2 4756.2(10)

0,3 4677.3(10) 0,3 4600.1(10)

Q (242Pu): 4984,5 (10) keV

2.1. Alpha Transitions 4. Alpha Emissions

These are results of the alpha-particle energy measurements obtained by using magnetic and semiconductor spectrometry. The most important ones are absolute determinations of energies with the BIPM magnetic spectrometer with a semi-circle focusing of alpha-particles. These measurements were done for most intense alpha-transitions in the 70's - 80's last century:

   

for 228Th, 224,226Ra, 220,222,219Rn, 216,212,218,214,215Po, 212Bi, 227Th, 223Ra, 211Bi, 253Es, 242,244Cm, 241Am, 238Pu – B. Grennberg, A. Rytz, Metrologia 7, 65 (1971)for 232U, 240Pu – D.J. Gorman, A. Rytz, H.V. Michel, C. R. Acad. Sci., Ser. B 275, 291 (1972) for 210Po - D.J. Gorman, A. Rytz, C. R. Acad. Sci., Ser. B 277, 29 (1973)for 239Pu - A. Rytz, Proc. Intern. Conf. Atomic Masses and Fundamental Constants, 6th, East Lansing (1979)

1. AVAILABLE EXPERIMENTAL DATA

Two parameters - the radius of curvature and the mean magnetic induction B.

E() = a (B)2 + b (B)4 + d (B)6

The factors a, b, d are derived from the latest adjustment of fundamental constants (me, e and NA).

The components of systematic uncertainty are due to length measurements (4.6105 E()), measurement of mean magnetic induction (1.3105 E()) and combined effect of uncertainties of fundamental constants (0.3105 E()), i.e. the total systematic uncertainty is 5105 E() or 0.3 keV (239Pu).

for 236Pu - A. Rytz, R.A.P. Wiltshire, Nucl. Instrum. Methods 223, 325 (1984)for 252Cf, 227Ac - A. Rytz, R.A.P. Wiltshire, M. King, Nucl. Instrum. Methods Phys. Res. A253, 47 (1986).

Magnetic 2 -spectrometers with high luminosity

In the second half of the last century many measurements of spectra (including weak alpha-transitions) in decays of actinides were performed with high-aperture 2 magnetic spectrometers. In 1960’s three such big magnetic spectrometers were built in the Soviet Union – in Moscow (Baranov et al.), St. Petersburg (Dzhelepov et al.) and Dubna (Golovkov et al.).

B.S. Dzhelepov, R.B. Ivanov, V.G. Nedovesov, V.P. Chechev. Alpha Decay of Curium Isotopes, Zh. Eksperim. i Teor. Fiz. 45, 1360 (1963); Soviet Phys. JETP 18, 937 (1964)

In respect of alpha-particle energies the measurements with 2 magnetic spectrometers are relative with using above-mentioned alpha-energy “standards”.

This is a great special subject. Here I note only that these measurements for alpha-particle energies are also relative. Their results depend substantially on the spectral asymmetric peak-shape analysis. Measurements of the complex alpha-spectra (for example, 239Pu + 240Pu) are proved to be effective for obtaining good alpha-peak fitting parameters by spectral deconvolution. For example, in 1999Sa15 (A.M. Sanchez, P.R. Montero, Nucl. Instrum. Methods Phys. Res. A420, 481 (1999)) authors used for mixture 239Pu + 240Pu branching ratios as constraints for simplifying fitting.

As example of recent accurate determination of alpha-energies (in decay of 237Np) with semiconductor detectors, the reference 2002Wo03 (M.J. Woods et al., Appl. Radiat. Isot. 56, 415 (2002)) could be pointed out.

Measurements with semiconductor detectors

2. RECOMMENDED DATA BY A. RYTZ A. Rytz, At. Data Nucl. Data Tables 47, 205 (1991)

The DDEP adopted methodology provides guidelines of several important compilations. Among them for alpha-decay this is the third revised version of a collection of selected -particle energies and intensities. It includes 516 energy values from 286 -particle emitters.

However, as DDEP evaluation rules differ from used by Rytz, not all energy values can be taken from his review. Moreover ONLY the results of absolute measurements for the most intense alpha-transitions can be directly accepted, because other alpha-energies could be evaluated from more accurate ray energies. When absolute energy measurements are not available, the results of relative measurements for the most intense alpha-transitions (relatively to “standard” energies) also can be adopted from the compilation by A. Rytz.

The atomic masses evaluated by Audi, Wapstra, and Thibault are determined not only by E() but also by nuclear reaction data. On pages 405-419 the influences on given mass (in %) of three most important contributing data are given.

3. 2003 ATOMIC MASS EVALUATION A.H. Wapstra, G. Audi, and C. Thibault. The AME2003

atomic mass evaluation (I). Evaluation of input data, adjustment procedures, Nucl. Phys. A729, 129 (2003),G. Audi, A.H. Wapstra, and C. Thibault. The AME2003 atomic mass evaluation (II). Tables, graphs, and references, Nucl. Phys. A729, 337 (2003). In the 1st part information is given on the procedures used in deriving the tables in the 2nd part. For our task we take an interest first in alpha-decay energies Q() and also the masses of the parent and daughter nuclei which are important for calculating the recoil energy.

For example, mass of 239Pu is determined by data of 239Pu()235U (44.3% influence), 239Pu(n)240Pu (41.3%) and 238Pu(n)239Pu (14%). For mass of 235U such contributions are 234U(n)235U (31.7%), 239Pu()235U (24.1%), 235U(n)236U (22.3%).

Thus, the evaluated Q()(239Pu)/c2 = M(239Pu) M(235U) M(4He), where M indicates an atomic mass, is deduced from bringing together of different data.

HOW TO FIND THE BEST WAY TO GIVE

RECOMMENDED ALPHA-PARTICLE ENERGY VALUES

TAKING INTO ACCOUNT THE TOTAL INFORMATION 1.,

2. AND 3. ?

As is known, the particle energy is less than the transition energy by the daughter nucleus recoil energy. In the nonrelativistic approximation for the kinetic energy of alpha- particle E( transition) = E( particle) A / (A4) where A – mass number of the alpha-decaying nuclide. Correspondingly, in SAISINUC input of E( particle) gives automatically E( transition) by this formula. And, in particular, for the alpha-transition to the ground state Q() = E(0,0) A / (A4).

BUT we have already adopted Q() from Audi et al. (2003)!!! So to give recommended alpha-particle energy values we need in deducing alpha-transition energies from the adopted Q() using the nuclear-level energies of the daughter nucleus and then we could calculate particle energies taking into account the recoil energy. In Comments these calculated E( particle) can be compared to experimental values. Examples can be found in the DDEP evaluations for decaying isotopes of Pu and Cm.

Here all recommended -particle energies have been deduced from Q value and level energies taking into account the recoil energies except for E(0,0) accepted from absolute measurement. [E(0,0) from Q value = 5168.06(15) keV].

Measured E() in decay of 240Pu (Q = 5255.75(15) keV)

Recommended

1956Ko67

1956Go43

1952As281957As83

1962Le11

1972Go33

1977Ba69

0

,0

5166 5165 5168(4)

5167.7(7)

5168.13(15) abs

5168.13(15) abs

5168.13(15) abs

0

,1

5122 5121 5123(5)

5123.3(7)

5123.26(23)

5123.45(25)

5123.6(2)

0

,2

5021(2)

5020 5019 5021.3(5)

5021.1(2)

0

,3

4858(5)

4856 4863.4(5)

4863.5(2)

A comparison of the adopted Q() with deduced Q = f(E0,0) from E(0,0) abs using the recoil energies by two formulas (nonrelativistic and more accurate relativistic) is given in table: Q()

Audi et al. (2003)E(0,0) abs

A / (A4)

Use of more accurate relativistic

formula239Pu 5244.51 (21) 5244.44 (14) 5244.53 (14)240Pu 5255.75 (15) 5255.73 (15) 5255.82 (15)238Pu 5593.20 (19) 5593.03 (20) 5593.13 (20)242Pu 4984.5 (10) 4984.7 (14) 4984.8 (14)

242Cm 6215.56 (8) 6215.45 (8) 6215.55 (8)

This table indicates: (1) Q() from Audi et al. (2003) is based not only on alpha-decay data and (2) difference of two formulas for recoil energies is 0.1 keV.

When the uncertainty of the alpha-transition energy Qi is

small (0.1 – 0.2 keV) for taking into account of the recoil energy it is better to use more accurate relativistic formula. For example, for 239Pu the relation Q() – Ei

level = Ei

{M(239Pu)/[M(239Pu)–m] + (79.0 eV)/Ei} = 1.0170393Ei

gives Ei

= 5156.57 (21) keV for the most intense transition to the 235U level of 76.5 eV while the approximate formula Qi

235/239 leads to Ei

= 5156.66 (21) keV in comparison with the absolute measurement Ei

= 5156.59 (14) keV.

More accurate relativistic formula:

Q = M – m – {[(M–m)2–2EiM)]} + 0.079 keV +Ei

level Ei

[M/(M–m) + (0.079 keV)/Ei] + Ei

level,

where M – mass of decaying (parent) atom, m – mass of -particle, Ei

- kinetic energy of -particle, 0.079 keV – total ionization energy for 4He, Ei

level – energy of i-level in a daughter nucleus. (All values – in keV).

Thus, as we adopt Q() from Audi et al. (2003)

we should accept the following scheme of

deducing alpha-energies:

Q() Qi = [Q() – Ei

level ] - -transition energy

Ei using the recoil energy.

CONCLUSION

LEVEL ENERGIES AND GAMMA-RAY ENERGIES

For example, for decaying 237Np we have from ENSDF two sets of nuclear-level energies and gamma-rays for the daughter nucleus 233Pa – (1) directly from the decay of 237Np and (2) adopted for 233Pa from all available data associated with production and de-exciting of 233Pa levels.

In this respect I would like to do only one note connected with need in these energies for evaluating alpha-energies: If there are not available new experimental data, the level energies and gamma-ray energies for DDEP tables can be taken from ENSDF evaluations.

However the ENSDF provides usually two types of such information while the recommended energies of gamma-rays and level energies in the DDEP tables must be single-valued.

ENSDFBalraj Singh, Jagdish K. Tuli, NDS 105, 109 (2005)

Level 233Pa level energy, keV, from the decay of 237Np

Level energy, keV, adopted for 233Pa from all data

0 0.0 0.0

1 6.654 (25) 6.671 (13)

2 57.101 (14) 57.100 (13)

3 70.510 (25) 70.544 (25)

4 86.469 (9) 86.468 (9)

5 94.645 (16) 94.646 (15)

6 103.636 (20) 103.635 (19)

7 109.04 (5) 109.07 (5)

8 133.2 (10) 133.2 (2)

9 163.34 (10) 163.51 (10)

10 169.152 (20) 169.166 (10)

12 201.594 (19) 201.634 (23)

I think for DDEP we should unify our approach and in all cases use the second set, namely, “Adopted Levels and Gammas” from ENSDF (NDS). Examples of such use can be found for decaying actinides 238Pu (NDS-2007), 239Pu (NDS-2003), 240Pu (NDS-2006), 241Am (NDS-2006).

THAT’S ALL. THANK YOU FOR YOUR ATTENTION.