A precise method of Qβ determination with small HPGe detector in an energy range of 1–9 MeV
Introduction
In decay studies on unstable nuclei, a β-decay energy is one of the most fundamental properties because it contains basic information on nuclear binding. Experimental Qβ-values have greatly contributed to the knowledge on nuclear shell structure and deformation. In addition, Qβ-values for short-lived nuclei, which are expected to be about [1], are necessary for refinement and development of mass formulas [2], [3], [4]. Because mass models are used to study fundamental and practical problems, for example nuclear physics, astrophysics and nuclear engineering, improvement in their accuracy is important.
A Qβ-value is directly obtained by measuring the β-ray maximum energy and the decay scheme information. In the measurement of β-ray endpoint energies of short-lived nuclei, a plastic scintillation detector [5], [6], [7], a Si(Li) detector [8] and an HPGe detector [9], [10], [11], [12], [13] have been used. Among these spectrometers, small HPGe detector is well suited. The main advantage of using an HPGe detector is its excellent energy resolution. This can lead to improvement in the accuracy of Qβ-values by a factor of more than 10, compared with the values measured with plastic scintillators. Additional advantages, in comparison with Si(Li) detectors, are an ability to utilize γ-rays to provide an accurate energy calibration and an adequate thickness to stop β-rays as high as 8–10 MeV. On the other hand, a disadvantage is that a β-ray spectrum observed with an HPGe detector is seriously distorted owing to incomplete absorption of the incident β-particle energy. Owing to this experimental complexity, the reliability of results obtained with HPGe detectors is often considered to be lower than one by means of direct mass measurement [14], [15]. To overcome this disadvantage, it is required to know the practical response functions for monoenergetic electrons/positrons, which are used to unfold the β-ray spectrum.
Over the past 10 years, we have accumulated experience in Qβ measurement with HPGe detectors, and reported Qβ-values of neutron-rich and -deficient nuclei in [16], [17], [18], [19], [20], [21]. The present paper is a revision and expansion of our previous work. Experimental response functions in an energy range of 1–9 MeV are presented for four HPGe detectors. The unfolding procedure of β±-ray spectra using the response functions is described in detail. The systematic error of Qβ determination is estimated by a comparison between the well-evaluated Qβ-values [1] with ones obtained in the present method. In this paper, we demonstrate that accurate and reliable Qβ-values can be obtained using a small HPGe detector when the experiment and analysis are performed carefully.
Section snippets
HPGe detectors
Response functions for monoenergetic electrons/positrons in an energy range of 1–9 MeV were measured for a short coaxial and for three different sizes of planar-type HPGe detectors. The energy resolution was 6–8 keV at 8 MeV. Specifications of the detectors are summarized in Table 1.
Energy calibration of the detector was performed up to 8.6 MeV with standard γ-ray sources of 152Eu and 56Co, and prompt γ-rays from the thermal neutron capture of 35Cl; the fast neutrons from a 252Cf source of
A β−-ray spectrum
A β−-ray spectrum was unfolded with the response function before applying a Fermi–Kurie plot method. The unfolding method is based on the following fact: the count recorded in the highest channel of the experimental β−-ray spectrum includes only full energy absorption events. To exemplify the analysis procedure, the Qβ determination for 90Y is described here. The β−-ray spectrum was measured with the 16-mm-diameter HPGe detector.
(1) In order to reduce the statistical fluctuation of counts, the
Qβ measurement of 146La
The method described above was applied to the Qβ measurement of the low-spin 2− isomer of 146La. The Qβ-values were reported to be 6380(30) and by Brenner et al. [35] and Graefenstedt et al. [36], respectively, which deviate outside their experimental uncertainties.
Radioactive sources of 146La were prepared by an on-line mass-separation at the KUR-ISOL, following the thermal neutron fission of 235U [33]. The mass-separated beams were implanted into an aluminum-coated Mylar tape in a
Conclusions and future development
We have shown that measurement with small HPGe detector provides accurate Qβ-values up to . The β±-ray maximum energy was determined using the Fermi–Kurie plot of the unfolded spectrum. In order to unfold the β-ray spectrum observed, the response functions were experimentally determined in an energy range of 1–. The detector response was also calculated by a Monte Carlo simulation code of the EGS4. The two results showed discrepancies. From the linearity check in the Fermi–Kurie plots,
Acknowledgements
We would like to thank Dr. T. Ishii, Mr. H. Ukon, Dr. A. Osa and Dr. T. Ikuta for their great contribution at the early stage of the study. The staff of the KURRI-LINAC and the KUR are acknowledged for operation. This work was partly supported by the Research Collaboration Programme of Research Reactor Institute, Kyoto University. A part of the data analysis was performed with the FUJITSU VP2600/10 computer system at Computer Center, Kyushu University.
References (37)
- et al.
Nucl. Phys.
(1995) At. Data Nucl. Data Tables
(1988)- et al.
At. Data Nucl. Data Tables
(1995) - et al.
At. Data Nucl. Data Tables
(1995) - et al.
Nucl. Instr. and Meth.
(1979) - et al.
Nucl. Instr. and Meth.
(1992) - et al.
Nucl. Instr. and Meth.
(1982) - et al.
Phys. Lett.
(1982) - et al.
Nucl. Instr. and Meth.
(1985) - et al.
Nucl. Instr. and Meth.
(1993)
J. Szerypo and the ISOLDE Collaboration, Nucl. Phys.
Nucl. Instr. and Meth.
Nucl. Instr. and Meth.
Nucl. Instr. and Meth.
Nucl. Instr. and Meth.
Nucl. Instr. and Meth.
At. Data
Nucl. Phys.
Cited by (23)
Nuclear Data Sheets for A=140
2018, Nuclear Data SheetsNuclear Data Sheets for A=217
2018, Nuclear Data SheetsNuclear Data Sheets for A = 42
2016, Nuclear Data SheetsMeasurement of β-decay end point energy with planar HPGe detector
2014, Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated EquipmentCitation Excerpt :However, their use is not suitable in case of very high energy β particles which become more abundant as one moves away from the line of stability. Instead, the planar HPGe detectors, having low Z window materials, have been demonstrated to be quite efficient in this purpose [6,7]. Moreover, these detectors can be calibrated for β detection over a wide energy range using appropriate γ ray sources.
Nuclear data sheets for A = 91
2013, Nuclear Data SheetsNuclear Data Sheets for A = 92
2012, Nuclear Data Sheets