Guo Jingru

Determination of the half-life of 79Se with the accelerator mass spectrometry technique

Abstract In the recent charts of the nuclides an accepted half-life of 79 Se is only an upper limit, 4 a. In this paper, we report a measurement of the half-life of 79 Se. The number of 79 Se atoms was determined from measured 79 Se Se ratios with the accelerator mass spectrometry technique and the decay rate of 79 Se was determined by counting the emitted β-rays with a liquid scintillation spectrometer. The half-life of 79 Se was measured to be (1.1 ± 0.2) × 10 6 a. We have also re-examined the 79 Se half-life value in the recent charts, which has been reported in Ref. [1], and have found that from the data related to the calculation of the half-life the upper limit of the half-life was re-calculated to be 6.5 × 10 5 a, other than 6.5 × 10 4 a as reported in the original paper in which a mistake could be made in the calculation.

Remeasurement of the Half-Life of 79Se with the Projectile X-Ray Detection Method

Remeasurement of the half-life of 79Se has been carried out with projectile x-ray detection (PXD) in accelerator mass spectrometry. We made two major improvements over our earlier 79Se half-life determination [Nucl. Instrum. Methods B 123 (1997) 403]. Firstly, the PXD technique has been used for separation of 79Se and 75Se from 79Br and 75As isobars respectively. Secondly, the half-life of 79Se has been measured relative to the known precise half-life of 75Se(119.79±0.04 d). A more reliable half-life of 79Se measured with the PXD technique is (2.95±0.38)×105 y, about a factor of one third lower than the previous value, 1.1 × 106 y. The problems in the previous measurement are discussed.

Measurement of the half-life of79Se using a radiochemical method

The half-life of79Se, a long-lived fission product nuclide, has never been measured accurately. The value quoted in the literature is an upper limit, ≤6.5·104 y, measured in 1949. In the present work we measured accurately the half-life of79Se to be (4.8±0.4)·105 y using a radiochemical method.

A procedure for the separation of79Se from fission products and application to the determination of the79Se half-life

This paper presents a radiochemical separation procedure of79Se from high level liquid radioactive waste, with nitrobenzene extraction and with sulfur dioxide precipitation. The procedure gives a chemical yield of selenium greater than 60%, and satisfactory decontamination is observed for all the relevant radioactive nuclides. Liquid scintillation counting were used for the measurement of79Se radioactivity. The79Se samples obtained from the procedure were used successfully in79Se half-life detemination.

A New Half-Life Value of 79Se

In the recent charts of the nuclides an accepted half-life of 79Se is only an upper limit, < 6.5 × 104 a. In this letter, A new half-life of 79Se has been measured to be (1.13 ± 0.17) × 106 a. The number of 79Se atoms was determined from measured 79Se/Se ratios with the accelerator mass spectrometry technique and the decay rate of 79Se was determined by counting the emitted β rays with a liquid scintillation spectrometer.

Nuclear charge distribution in the spontaneous fission of252Cf: Determination of fractional cumulative yields of133mTe and133gTe

The fractional cumulative yields (FCY) of133mTe and133gTe in the spontaneous fission of252Cf were measured for the first time by a radiochemical method. The values ofFCY are 0.533±0.014 and 0.291±0.042 for133mTe and133gTe, respectively. The isomeric state to ground state fractional independent yield (FIY) ratio of133Te,R, was found to be 3.5. The root-mean-square angular momentum of the primary fragment corresponding to the fission product133Te, Jr.m.s.=8.8h, was estimated according to a simple one-parameter statistical model. The fractional cumulative yields from this work together with other literature data in the mass region A=131–141 are compared with the “normal” yields given by the empiricalZp model by Whhl. It suggests that both theN=82 neutrons shell and nucleus pairing effects are not apparent for the spontaneous fission of252Cf.

The chemical states of tellurium produced by spontaneous fission of252Cf

The distribution of the chemical states of tellurium isotopes produced by252Cf spontaneous fission, collected separately in the matrixes of NaCl, Kl, NaF, CH3COONa·3H2O, Na2SO4 and NaNO3 crystals have been investigated. Two chemical states of tellurium isotopes maintained in these matrixes are Te(IV) and Te(VI). The relationships between the distribution of the chemical states of tellurium isotopes and the produced mode of tellurium, the chemical properties of collection matrixes, the time for collecting fission fragments are studied and the possible mechanism of the interactions of the fission products and the matrixes is discussed. The results show that the distribution of chemical states of tellurium isotopes depends on the chemical properties of the collection matrixes mainly.

Independent yield of88Y from thermal neutron induced fission of235U

The independent yield of88Y from thermal neutron-induced fission of235U was determined relatively to the well-known yield of91Y. An upper limit obtained was ≤1.53×10−8%.