WHAT VALUES ARE BEST RECOMMENDED FOR ALPHA- AND GAMMA- ENERGIES IN DECAYS OF ACTINIDES? Valery Chechev V.G. Khlopin Radium Institute, 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 Q  ( 242 Pu): 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 228 Th, 224,226 Ra, 220,222,219 Rn, 216,212,218,214,215 Po, 212 Bi, 227 Th, 223 Ra, 211 Bi, 253 Es, 242,244 Cm, 241 Am, 238 Pu – B. Grennberg, A. Rytz, Metrologia 7, 65 (1971)  for 232 U, 240 Pu – D.J. Gorman, A. Rytz, H.V. Michel, C. R. Acad. Sci., Ser. B 275, 291 (1972)  for 210 Po - D.J. Gorman, A. Rytz, C. R. Acad. Sci., Ser. B 277, 29 (1973)  for 239 Pu - 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 (m e, e and N A ). The components of systematic uncertainty are due to length measurements (4.6  10  5 E(  )), measurement of mean magnetic induction (1.3  10  5 E(  )) and combined effect of uncertainties of fundamental constants (0.3  10  5 E(  )), i.e. the total systematic uncertainty is  5  10  5 E(  ) or  0.3 keV ( 239 Pu ).  for 236 Pu - A. Rytz, R.A.P. Wiltshire, Nucl. Instrum. Methods 223, 325 (1984)  for 252 Cf, 227 Ac - 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, 239 Pu Pu) 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 239 Pu Pu branching ratios as constraints for simplifying fitting. As example of recent accurate determination of alpha-energies (in decay of 237 Np) 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 the influences on given mass (in %) of three most important contributing data are given 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 1 st part information is given on the procedures used in deriving the tables in the 2 nd 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 239 Pu is determined by data of 239 Pu(  ) 235 U (44.3% influence), 239 Pu(n  ) 240 Pu (41.3%) and 238 Pu(n  ) 239 Pu (14%). For mass of 235 U such contributions are 234 U(n  ) 235 U (31.7%), 239 Pu(  ) 235 U (24.1%), 235 U(n  ) 236 U (22.3%). Thus, the evaluated Q(  )( 239 Pu)/c 2 = M( 239 Pu)  M( 235 U)  M( 4 He), 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 / (A  4) 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 / (A  4). 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 = (15) keV]. Measured E(  ) in decay of 240 Pu (Q  = (15) keV) Recommen ded 1956 Ko Go As As Le Go Ba69  0, (4) (7) (15) abs (15) abs (15) abs  0, (5) (7) (23) (25) (2)  0, (2) (5) (2)  0, (5) (5) (2)

A comparison of the adopted Q(  ) with deduced Q  = f(E  0,0 ) 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 / (A  4) Use of more accurate relativistic formula 239 Pu (21) (14) (14) 240 Pu (15) (15) (15) 238 Pu (19) (20) (20) 242 Pu (10) (14) (14) 242 Cm (8) (8) (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 Q i  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 239 Pu the relation Q(  ) – E i level = E i   {M( 239 Pu)/[M( 239 Pu)–m  ] + (79.0 eV)/E i  } =  E i  gives E i  = (21) keV for the most intense  transition to the 235 U level of 76.5 eV while the approximate formula Q i   235/239 leads to E i  = (21) keV in comparison with the absolute measurement E i  = (14) keV. More accurate relativistic formula: Q  = M – m  – {  [(M–m  ) 2 –2E i  M)]} keV +E i level  E i   [M/(M–m  ) + (0.079 keV)/E i  ] + E i level, where M – mass of decaying (parent) atom, m  – mass of  - particle, E i  - kinetic energy of  -particle, keV – total ionization energy for 4 He, E i 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(  )  Q i  = [Q(  ) – E i level ] -  -transition energy  E i  using the recoil energy. CONCLUSION

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

ENSDF Balraj Singh, Jagdish K. Tuli, NDS 105, 109 (2005) Level 233 Pa level energy, keV, from the  decay of 237 Np Level energy, keV, adopted for 233 Pa from all data (25)6.671 (13) (14) (13) (25) (25) (9) (9) (16) (15) (20) (19) (5) (5) (10)133.2 (2) (10) (10) (20) (10) (19) (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 238 Pu (NDS-2007), 239 Pu (NDS- 2003), 240 Pu (NDS-2006), 241 Am (NDS-2006). THAT’S ALL. THANK YOU FOR YOUR ATTENTION.