Calculation of half-life for 79Se decay

Available online at www.sciencedirect.com SCIENCE

NUCLEAR SCIENCE AND TECHNIQUES

DIRECT.

Nuclear Science and Techniques, Vo1.17, No.1 (2006) 21-23

Calculation of half-life for 79Sedecay ZHOU Chun-Mei

WU Ben-Dong

(china Nuclear Data Cenrer; Deparhnenf of Nuclear Physics, China Institute of Aromic Energy, Beijing 102413, China)

Abstract The half-life for 79Se decay is calculated by using the LogfIut systematics method. Based on the data analysis and comparison with experimental data the 79Sehalf-life is recommended. The scheme for 79Sedecay is also shown and the radiation data are calculated in the text.

Key words 79Se,Nuclear decay, Systematics, Data calculation

CLC number 0571.3

1

Introduction

The 79Seis one of the fission products with long half-life. It is an important nuclide of radioisotope applications and radioactive waste-treatments, and is also used as the fission monitor. The measurement of its half-life is very difficult, because the differences of half-lives in different experiments are very large. Therefore, it is highly important and interesting to calculate its half-life with Logf"? systematics. The calculated half-life has also been compared with reliable experimental data. 2

Calculation codes and flow chart

The calculation codes and their functions are listed in Table 1. They are all ENSDF (Evaluated Nuclear Structure Data File) physics analysis codes"] for the International Network of Nuclear Structure and Decay Data Evaluation, which can be obtained from the National Nuclear Data Center (NNDC) at Brookhaven National Laboratory, USA. In Table 1, a simple description about the codes that was used is given. As seen in Fig. 1, the main steps of 79Sehalf-life calculation are as follows: (1) Prepare the ENSDF format data file for 79Sehalf-life calculation. ENSDF format of input data is adopted by the calculation code. The ENSDF format check must be done before the Received date: 2005-07-24

calculation, so that 79Se half-life calculation will be reliable. (2) Run LOGFT code to calculate the L.ogf'"t values. The Logf"'t values for different half-lives will Table 1 Calculation codes"] and their functions of half-life and radiation data for 79Sedecay Code name Main function FMTCHK ENSDF formatted data check LOGm Calculation of electron capture probabilities and LogfUt RADLST Energy and intensity calculation for Auger electron and X-ray ENSDAT Calculation data output shown in tables and drawings

I ENSDF format check

H

Start

I

4 Input data file

I Report file

. I I

I

Experimental data

Comparision -S recommendation

I

I

I

I OutDut of tables and drawincls I Fig. 1 Calculation flow chart of half-life and radiation data

for 79Sedecay.

22

be calculated when the electron capture branching ratio to the jth-level of daughter nuclide is known and the calculation results will be put into the ENSDF format decay data file that is prepared. (3) Based on the Logfl"t systematics, the correct Logfl"t value of 79 Se decay can be selected and then the half-life of 79 Se can be calculated. (4)Compare the half-life calculated with experimental half-lives and recommend the new half-life of 79Sedecay. ( 5 ) Run W L S T code to calculate the radiation data. (6) Run ENSDAT code to output the calculation data in tables and to draw the decay scheme.

3

vo1.17

NUCLEAR SCIENCE AND TECHNIQUES

LO~J"'~systematics calculation

The spin and parity of the ground-state (GS) are J"=7/2+ for 79Se and J"=3/2- for 7%r, and the change of spin and parity is A J"= 2- in 79Sep- decay. Obviously, this is a first-forbidden unique p- decay and its Logf'"t should be marked as Logf'"t. The ground-state of 79Sedoes not decay to the ground-state of 79As through (E+P+) decay directly and the experimentally determined p- branching ratio from ground-state of 79Seto ground-state of 7$r is Zp- = 100 %,

In "Kr E decay, the spin and parity is J" = 7/2+ for Kr and is J"=3/2- for 81Brand the change of spin and parity is AJ"=2-. Obviously, this is also a 81

first-forbidden unique E decay.

Table 3 shows that the general decay characters of the 79Se p- decay and the "Kr E decay arc basically the same. Therefore, the Logf '"t systematics method for 81Kr E decay is also suitable for calculating the half-life of 79Se. The Logf'"t systematics value of 81 Kr E decay can also be adopted to calculate the half-life of 79Sedecay. From Table 2, we can see that the Logf't values are increased with its half-life T1/2 when Zp- = 100 % is fixed. The Logfl"t systematics results were published by Singh, et al.'*' in 1998. From the results the Logf '"t = 11.01 for the ground-state of 81 Kr to the ground-state of 8'Br through E decay is known when its 1,=99.7 % is fixed. The half-life of 79Se, TI/*= 5.60x105a, can be obtained from this Logf'"r systematics calculation when its 1,- = 100 % is fixed. Table 2 Logfur values of p- decay from GS of 79Seto GS of 79Br calculated by LOGFT code

LQgfU t

TI, /a 1.00x10' 1.00x102 1.ooxlo3 1.00~10~ 1.00x105 2 . 9 5 10' ~' 5.60 x105 1.00x lo6 1.OOX lo7 l.OOxlos

6.26 7.26 8.26 9.26 10.26 10.73. 11.01 11.26 12.26 13.26

I*-/ % 100 100 100 100 100 100' 100 100 100 100

* Recommended values of this work.

Table 3 Decay character comparison between "Kr to "Br and 79Seto 7?3r Parent nuclides

Daughter nuclides

LogfIut

TI, /a

Ip- , I , / %

Nuclide

Level / keV

Jn

79~e

0.0

70'

p-

7%r

0.0

312-

11.01

5.60~10'

100

slKr

0.0

712

E

"Br

0.0

312 -

11.01

2.29~10'

99.7

4

Decay mode

+

Nuclide

Comparison with experimental data

calculated data Table 4, the of the half-life of 79Sedecay are listed. The differences of half-lives among different experimenters are very large

and

only

the latest measured value, T1,,=(2.95f0.38)x 105a[71,obtained by using mass

spectrometry method with projectile X-ray detection, is near the calculated one. Here, TI/*=

Jn

Level / keV

(2.95 k 0.38) x lo5a is recommended as the half-life of 79Sedecay.

Table 4 Measured and calculated half-life of 79Sedecay Tln I a T1nla (measured) (calculated) ~ 6 . 5 104 (4.8 k 0 . 4 ) ~ 10' ( l . l + ~ . 2 ) 1x0 6 < 6.5 x 1 0 (295k0.38)x10' 5.60~10'

'

Published year 1978 1995 1996 1997 2001 2004

Reference

131 [41

PI [61 [71 This work

ZHOU Chun-Mei er al.: Calculation of half-life for 79Sedecay

No. 1

23

~

Decay scheme and radiation data

5

6

On the basis of the half-life of 79Se decay recommended above, the scheme of 79Se p- decay is shown in Fig.2, where the decay characters are also given. In Table 5, the radiation data of 79Se p- decay are listed, which are calculated by using the RADLST code.

-,

7/2+ 0.0

2.95~10~ a

Burrows TW. ENSDF Physics Analysis Codes. Private

Q-= 151.0~7

151.0

100

Log f t

10.73'"

It is a test for us to calculate the half-life of 79Se decay by using the Logfur systematics method. The result is very interesting. This method can be adopted for the experimenters to measure the half-life of some nuclides. The method is also used for data evaluators to select the correct data from different and dispersive data of the half-life.

References

%p- = 100

-$-

Discussion

\

Communications (2000) Singh B, Rodriguez JL, Wong SSM, et al. Nuclear Data 0.0

312-

stable

;: Fig. 2 Decay scheme of 79Se

Sheets, 1998,84: 487 Lederer CM, Shirley RS, Browne E, et al. Table of iso-

Br.4

topes (7" Edition). New York: John Wiley & Sons, Inc,

decay.

1978. YU Run-Lan, GUO Jing-Ru, CUI An-Zhi, et al. J. Nucl.

Table 5 Radiation data of 79SeP- decay Radiation type Energy I keV

P-

15 1.O+ 1.7 (Max)

52.92 f0.62 (Avg)

Radiochem. 1995, 17(1): 33 (in Chinese)

Absolute intensity I %

JIANG Song-Sheng, HE Ming, DIAO Li-Jun, et al. Nucl. Instrum. Methods, 1996, B172: 403

100

Audi C,Bersillon 0, Blachot J, et al. Nucl. Phys. 1997,

A624 1 JIANG Song-Sheng, HE Ming, DIAO Li-Jun, et al. Chin.

Phys. Letter, 2001,18(6): 746