Beta-ray Spectra Research Articles

Characteristics of a New Type of Vinten Dosemeter for Skin-Extremity Monitoring

Abstract A type test has been carried out on a new type of thin TL dosemeter manufactured by Vinten Analytical Systems Ltd of UK. The dosemeter has been tested for its suitability for skin/extremity monitoring in terms of the new ICRU quantity, individual dose equivalent, superficial, Hs (0.07). The new extremity TL dosemeter has a thin cover of 3 mg.cm-2 areal density of an aluminised bilaminar plastic in place of the previous thicker black polyethylene of areal density of ~6 mg.cm-2. The dosemeter is found to be suitable for the measurement of beta ray spectra of mean energies down to 70 keV and for all angles of incidence, but the once-only annealing of these dosemeters may limit the long term field use owing to fading, and sensitivity variations.

Determinations of silicon and phosphorus in rice planted in a district of high incidence of amyotrophic lateral sclerosis by neutron activation and X-ray fluorescence analyses

Silicon and phosphorus contents in polished and unpolished rice planted in a district of high incidence of amyotrophic lateral sclerosis (ALS) have been determined by neutron activation and X-ray fluorescence methods, and compared with those from control areas. In the neutron activation analysis, beta-ray spectra of 32P produced by the 31P(n, gamma)32P reaction on polished and unpolished rice were measured with a low background beta-ray spectrometer. In the X-ray fluorescence analysis, characteristic X-rays were analyzed with a wavelength dispersive X-ray fluorescence spectrometer. Silicon contents in polished and unpolished rice from the ALS area are 42 micrograms.g-1 and 370 micrograms.g-1, respectively, and the corresponding phosphorus contents are 1,210 micrograms.g-1, and 3,370 micrograms.g-1, respectively. The data for ALS area are equal to those for the control area within standard deviation.

An electron-gamma coincidence system for the NPL beta-ray spectrometer

An electron-gamma coincidence system has been developed for the NPL double-focussing, iron-free beta-ray spectrometer. The beta-ray spectrum from the decay of 47Ca has been measured, and a value of (1991.2±1.8) keV obtained for the 47Ca − 47Sc atomic-mass difference.

A New Solid State Beta Dosemeter

The use of a metal oxide silicon field effect transistor (MOSFET) as a gamma and X ray dosemeter has been previously reported. This paper reports measurements on the performance of MOSFETS for beta dosimetry. The sensitive area of the sensor is less than 7 mg.cm-2 below the surface of the MOSFET and hence, with the appropriate window thickness, the MOSFET should be energy independent for beta rays. The sensitivity of MOSFETS to beta rays of different energies has been measured for various thicknesses in order to establish the optimum thickness for energy independence. Using a polycarbonate cover, the optimum thickness was about 5.4 mg.cm-2. With this cover the energy dependence was less than ±10% for beta ray spectra with end point energies from 0.23 to 2.2 MeV. The dependence upon direction was less than 20% for angles of incidence up to 45o. The results of these experiments and other dosimetric parameters are presented. The application of MOSFETS to beta dosimetry is discussed in terms of the values of the dosimetric parameters obtained.

Search for heavy neutrinos in the beta decay of 35S. Evidence against the 17 keV heavy neutrino

A precise measurement of the beta-ray spectrum of 35S has been carried out using a Si(Li) spectrometer system to look for the signiture of heavy neutrino emission. The results are consistent with no heavy neutrino admixture, and the resulting upper limits for the mixing | U eH| 2 ≲0.3% were determined in the mass range 10–50 keV.

Weak nucleon currents in beta decay and muon capture

We made extensive investigations on the weak charged nucleon currents and structure of complex nuclei in weak nuclear processes. Using our new formalism, which has almost no approximation as far as the lepton part is concerned, we have studied the beta-ray spectra and beta-ray angular distributions in the12B and12N beta decays. The weak magnetism predicted by CVC is in excellent agreement with the experimental data on beta-ray spectra given by the Columbia and Heidelberg groups. It is noticed here that the differenceα−−α+ of the coefficients in the beta-ray angular distributions in aligned12B and12N is free from ambiguity of the nuclear model. We found practically no second-class induced tensor current with the data given by the Osaka, Louvain and Zurich groups. On the other hand, the sumα−+α+ of the coefficients represents the time component of the main axial vector current, and it is free from weak form factors. With this sum we studied the exchange-current and core-polarization effects. These two effects are large, and they are almost cancelled out by each other in this case. We also found the strength of the induced pseudoscalar form factor which is generally consistent with PCAC, from nuclear polarizations of12B in muon capture of12C performed by the Zurich and Tokyo groups. These nuclear polarizations are insensitive to the nuclear model, if the exchange-current and corepolarization effects are properly taken into account.

An Energy Dependent Model for a Gas Effluent Sampler

The sensitivity of a solid, disk-shaped, beta ray detector facing a gas-filled sampling volume has been determined using numerical integration. The calculation uses empirical expressions for electron straggling and the Fermi function. Models have been constructed for asymmetric, cylindrically symmetric and spherically symmetric sampling cavities. A typical sample cavity has been evaluated for beta ray spectra having end points ranging from .01 to 3.0 MeV. The calculation is found to be in good agreement with experimental data for 85Kr and 133Xe.

A short atlas of beta-ray spectra

Graphs are presented of beta-ray spectra for about 100 nuclides of importance for radiation protection and biomedical applications. They are intended to provide a quick and convenient reference for spectral shapes and to give an indication of the wide variation in these shapes.

Measurement of the beta-ray spectra of 90Sr- 90Y

The β-ray spectra of 90Sr and 90Y have been remeasured with the CBNM magnetic β-ray spectrometer. From the measurements the endpoint energies (W 0 [m oc 2] and E 0 [keV]), the spectrum shapes (coefficient, a, of the shape-correction factor, l+aW), and the ratio of the numbers of β particles emitted in the decays of respectively 90Y and 90Sr, ( I β 1 I β 2 ), have been determined. The results are for 90Y, β 1 transition : W 0 1 = 5.4608 ± 0.0058E 0 1 = (2279.5 ± 2.9) keVa 1 = −(0.0078 ± 0.0024), 90Sr, β 2 transition: W 0 2 = 2.0685 ± 0.0032E 0 2 = (546.0 ± 1.6) keVa 2 = −(0.032 ± 0.007). The ratio of the numbers of emitted β particles is I β 1 I β 2 = 1.00 ± 0.01 . Corrections to the measured data and the estimates of uncertainties are discussed.

Calculated beta-ray spectra from decay of fission products produced by thermal-neutron fission of 235U

Beta-ray spectra from decay of fission products created by thermal-neutron fission of 235U have been calculated using summation techniques and using an independently created beta-ray data file. The calculated beta-ray spectra are in very good agreement for E β ≅ 1 to 8 MeV with recently measured specta of beta rays for two very different exposure and counting time conditions: (a) an “instantaneous” spectrum following a 1.5 day exposure, and (b) an 8 s counting-time spectrum obtained 1.7 s following a 1 s exposure of 235U by thermal neutrons.

Beta Transitions from 103Ru to 103Rh Levels

Beta-ray spectrum in 103 Ru decay has been measured placing main emphasis on determination of the highest β-ray component. From comparison with the Q β systematics, we concluded that the highest β-ray component feeds to the ground state of 103 Rh directly, and not to the 39.7-keV isomeric state of 103 Rh as has been widely accepted. The decay scheme was modified and the spin and parity of the ground state of 103 Ru was confirmed to be 3/2 + as proposed in recent studies on 103 Ru.

Electron backscattering.

Although electron backscatter has been a subject of investigation for many years, both theory and experimental data are sparse. This article examines the available data and shows that a large percentage of both the theoretical and experimental values fit an empirical relationship for a large range of electron energies. This relationship appears to be valid both for beta-ray spectra and monoenergic electrons. This relationship appears to be valid both for beta-ray spectra and monoenergetic electrons. The empirical relation describing the intensity of electron backscatter is also valid over the entire range of atomic elements. The relationship proposed is that the backscatter of electrons is proportional to the log (Z + 1). Effective atomic numbers of compound and mixtures arrived at using this relationship can be used to predict backscatter coefficients for these.

Beta-ray spectra of 12B and 12N and conserved vector current

Abstract In order to investigate spectral shape factors of 12 B and 12 N, we make a new formalism of β-decay theory, where the radial wave functions of leptons are treated with no approximation and, therefore, the nuclear matrix elements are electron-energy dependent. With this formalism we can show strong support for the conserved vector current hypothesis in analyzing the experimental data which were given by Wu, Lee and Mo in 1963 and revised by them in 1977 using the latest experimental results on the end-point energies and branching ratios of the inner β-groups, in addition to the correct Fermi functions for the positron. In fact, the average slopes of the spectral shape factors for 12 B and 12 N are in excellent agreement with those in our theory. Recent experimental data given by the Heidelberg group are also in good agreement with the theory if we analyze the difference of the average slopes for 12 B and 12 N. There are, however, small discrepancies with the theory in their individual values. The relation of the present formalism with traditional theories of β-decay is discussed.

Evaluation of the reproducibility in radioactivity measurements with liquid scintillation counters--effect of anomalous count rate-dependent photomultiplier gain variations (author's transl)

Time variations in count rate were measured for prolonged period of time using a set of 3H samples and a few other specially prepared samples of 14C, 32P, and 137Cs. Besides, beta-ray spectra of a particular 3H sample were measured as a function of time with a multichannel pulse height analyzer. These measurements lead to the following conclusions: (1) Anomalous count rate variations are attributed to strong dependence of photomultiplier gain on count rate. (2) Different steady state count rates can be observed for 3H samples having activities of approximately 10(5) dps when they are measured immediately after the measurements of background and 3H samples of higher activities. (3) The count rate-dependent effect on photomultiplier gain can be described properly by the current flowing through the tube rather than the count rate. (4) The measurement of the external standard channel ratio using the built-in 137Cs source can affect seriously the successive measurements on 3H samples, while the channels ratio itself exhibits strong time dependence.

Target thickness uniformity gauge

A method to accurately and quickly measure target thickness and uniformity for large area targets is described. The technique takes advantage of the fact that typical transmission curves for continuous beta-ray spectra are exponential up to very small transmission (⪡1%) under suitable conditions. Depending upon the particular beta source used, the technique can be optimized for any region of target thickness between 0–800 mg/cm 2. A system to measure target thicknesses between 1–30 mg/cm 2 using a 147Pm beta source was constructed and its performance is evaluated.

Negatron Decay of122Sb

A unique set of numerical values for six nuclear matrixelements, fa·r, fr5, fr, Ja, Jax rand JBij, were found by means of the chi-square fit' to the experimental data on the beta-ray spectrum and beta-gamma directional correlation in the cascade. transition, 2-(1.4 MeV {3-)2+(0.56 MeV y)O+ of l22Sb, measured by Yamada and Hayashi. These matrix elements are also consistent with .all other available data on this transition.

Magnetic Moment and Beta Decay of RaE

A.-symmetry of the beta-ray angular distribution in polarized RaE is evaluated with the numerical values of nuclear matrix elements, if r, fa and J q X r, which are , derived by the method of the least chi-square fit to the experimental data on the spectral shap'e, longitudinal polarization and jt value. . The magnetic moment of RaE is known to have a negative sign from this calculation, the measured asymmetry in Tokyo and the knowledge about the internal magnetic field at decaying nucleus. A consistent explanation of i J r, f q X r and the magnetic moment of RaE is obtained in a shell model, where the tensor forces in the residual interaction and the core po­ amples which have been studied repeatedly in con~ection with nature of weak interactions as well as nuclear structure of relevant nuclei. In this decay, the spectral shape of emitted beta rays is considerably different from the simple statistical spectrul? predicted by the Fermi theory, and it is strongly energy dependent. As is well known, this is due to the cancellation among con­ tributions of several nuclear matrix elements of the first forbidden transition; This property has been applied to examine different kinds of theoretical assumptions. Leaving a review of these problems elsewhere)!> we study here a possible way of finding the sign of the magnetic moment for RaE. For this purpose, we have to measure the beta,ray angular distribution in polarized RaE and to find nuclear matrix elements of beta decays from complete ex­ periments. In connection with these quantities, nuclear structure of RaE and RaF is investigated in a shell mo<;lel. We first describe qualitatively how we can find the sign of the magnetic · . moment by measuring the angular distribution of beta rays in polarized nuclei, and- an experimental evidence is introduced in § 2. Exact values of the asymmetry of beta-ray angular distribution are predicted by using the nuclear matrix elements, .. which are derived from the least chi-square fit to the experi­ mental data on the beta-ray spectrum, longitudinal polarization and ft value,

Radiative Corrections to Nuclear Beta Decay

Recent investigations on the ra~iative corrections to the lifetime of beta decay, beta-ray spectrum and beta-ray angular di,tribution are briefly reviewed. Explicit formulas of the radiative corrections are given for the asymmetry of the beta-ray angular distribution in polarized nuclei. The asymmetry factor is scarcely affected by these corrections, which i;; independent of the cutoff for the Gamow-Teller transition. Numerical values of the radiative corrections are t~bulated for the beta decays of

A swept-current magnetic lens plus Si(Li) electron spectrometer with simultaneous momentum and energy selection

A combined swept-current magnetic lens plus Si(Li) electron spectrometer with simultaneous momentum and energy selection is presented. The spectrometer is intended for in-beam measurements of conversion electron lines up to several MeV in energy and for nanosecond lifetime determinations, as well as for off-beam studies of continuous beta-ray spectra and conversion lines from short-lived activities. The sweeping of the lens current is automatized and the energy selection, synchronously with the momentum, is performed using a simple digital window arrangement. The performance of the spectrometer is demonstrated in conversion electron and continuous spectrum measurements. Different versions of the system are considered, including fixed-current and high-efficiency modes of operation. The spectrometer features great versatility, good energy resolution, improved line shape, moderate transmission and low background. Easy methods of energy and efficiency calibration, and of tuning the spectrometer, are described.

Measurements of Equilibrium and Time-Dependent Energy Spectra of Beta Rays from Californium-252 Fission Fragments

Absolute measurements were made for the equilibrium and time-dependent beta-ray energy spectra from flssion fragments produced bv spontaneous fission of /sup 252/Cf. The beta rays were detected by a plastic scintillator, and the fission rate was monitored by a semiconductor detector. The equilibrium spectrum was measured from a /sup 252/Cf source permanently encapsulated between two Mylar foils thick enough to stop the fragments. The time-dependent measurements used a /sup 252/Cf source supported on a thin nickel foil and covered with a thin collodion foil. Virtually all fragments from this second source escaped the foils. By use of a special transport system, the time dependence of the /sup 252/ Cf beta-ray energy spectrum was measured for two cases: buildup of the spectrum following initiation of fragment collection on clean catcher foils, and decay of the spectrum following a period of fragment collection. The measured spectra were corrected for energy resolution effects by unfolding them with the use of a measured system response function. The measured data were used to generate empirical expressions for the equilibrium and time-dependent beta-ray spectra from /sup 252/Cf fission fragments. The total number of beta rays from one fission was estimated to be 6.7 plus or minusmore » 0.3, while the total beta-ray energy was estimated to be 6.1 plus or minus 0.5 MeV. The results of the measurements were compared with the analogous measurements for thermal-neutron fission of /sup 235/U. High-energy transitions (5 to 10 MeV) found for /sup 235/ U fission were not found for /sup 252/Cf fission. (11 figures) (auth)« less