On the decay of148Pm

In the frame of a soluble coupled channels model we compare the exact lifetimeτ of a resonant state with two approximate estimates for thisτ. The exactτ value is related to the exact total widthΓ byτ=?Γ ^?1. The first approximate method has been derived by Fermi. It consists in a first order perturbation calculation ofΓ. The second one is Smith's time-delay method which leads to a direct relation betweenτ and the behaviour of theS-matrix along the real energy axis. We show that the Smith's method is the most useful one.     

On the theory of auto-ionization in electron-capture decay

Existing theories of auto-ionization in electron-capture decay are reviewed. It is proved that the theoretical model recently developed by Law and Campbell is identical with an earlier theory due to the author. Disagreement between the final results obtained from these two theories is traced to additional approximations introduced by Law and Campbell in the course of their calculations. These approximations are critically examined and found to be invalid thus explaining the reported disagreement. The results of various theoretical calculations previously reported by the author are evaluated for several nuclei of interest.     

Structure of even-even138Nd from the decay of138Pm

The structure of¹³⁸Nd is investigated through theβ ⁺-decay of¹³⁸Pm, whose decay half-life is measured to be 3.24±0.05 min. A level structure comprising 27 excited states and 52 transitions is constructed. With the help of deducedft values and internal conversion coefficients, spin-parity assignments are made to many states in¹³⁸Nd and to the ground states of¹³⁸Pm. From the positron end-point energy measurement, the total decay energy is determined to be 5.4±0.2 MeV, which is compared with the predictions of several mass formulae and with the decay energy systematics of theN=77 isotones. The structure of¹³⁸Nd is discussed in the light of nuclear systematics of theN=78 isotones.     

Search for rare decay modes of Californium

The results ofmeasurements on the search for the cluster decay of ²⁵²Cfnucleus with the emission ofthe bound state of eight neutrons are presented. The value of an upper limit ofthe partial probabilities for this process is obtained, which contradicts to the results ofthe recently published work, in which the possible existence of octaneutron was declared. Based on the results of our measurements, the estimations for the upper limits ofpartial probabilities for the emission of ²⁰C, ²⁴O, ²⁸Ne, 32Mg, ³⁶Si, ⁴⁰S, ⁴⁰P, and ⁴⁰Si clusters are given. The estimation for the upper limit of the partial probability of ²⁵⁰Cf decay with the emission of the bound state of six neutrons is also obtained.     

Search for cluster decay of114Ba

A search for the¹²C decay of¹¹⁴Ba produced in the⁵⁸Ni(⁵⁸Ni,2n) reaction was performed by using polycarbonate track detectors. Assuming the total half-life of¹¹⁴Ba to be 0.1 s, the lower limit T _c ≥10³ s for the partial¹²C-decay half-life was established.     

Search for time dependence of the Cs decay constant

Starting from June 2011, the activity of a ¹³⁷Cs source has been measured by means of a HPGe detector installed deep underground in the Gran Sasso Laboratory. Over 5100 hourly recorded energy spectra have been collected in 217 days. These data allowed the search for time variations of the decay constant with periods from a few hours to 1 year. No signal with amplitude larger than 9.6⋅10⁻⁵$9.6\cdot {10}^{-5}$ at 95% C.L. has been detected. These limits are more than one order of magnitude lower than the values on the oscillation amplitude reported in literature. In particular, for 1 year period an oscillation amplitude larger than 8.5⋅10⁻⁵$8.5\cdot {10}^{-5}$ has been excluded at 95% C.L., independently of the phase. The same data give a value of 29.96±0.08$29.96\pm 0.08$ years for the ¹³⁷Cs half-life, in good agreement with the world mean value of 30.05±0.08$30.05\pm 0.08$ years.     

Search for the invisible decay of neutrons with KamLAND

The Kamioka Liquid scintillator Anti-Neutrino Detector is used in a search for single neutron or two-neutron intranuclear disappearance that would produce holes in the -shell energy level of (12)C nuclei. Such holes could be created as a result of nucleon decay into invisible modes (inv), e.g., n--> 3v or nn--> 2v. The deexcitation of the corresponding daughter nucleus results in a sequence of space and time-correlated events observable in the liquid scintillator detector. We report on new limits for one- and two-neutron disappearance: tau(n--> inv) > 5.8 x 10(29) years and tau (nn--> inv) > 1.4 x 10(30) years at 90% C.L. These results represent an improvement of factors of approximately 3 and >10(4) and over previous experiments.     

Allowed electron-capture branches in the decay of 34mCl

The decay of ^34mCl has been studied with 36 and 100 cm³ Ge(Li) detectors and with a high-resolution large volume Ge(Li)-NaI(Tl) Compton-suppression spectrometer. The ^34mCl activity was produced with the reaction ²⁴Mg(¹²C, pn)³⁴Cl at $\text{E(}{}^{12}\text{C}\text{) = 35}\text{MeV}$ by bombarding thick natural Mg targets. The half-life was measured to be $\text{τ}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{= 32.06 ± 0.08}\text{min}$. Nine γ-ray transitions were observed including four γ-rays not seen previously. The measured γ-ray intensities determine new electron-capture branches of (0.030 ± 0.006) % and (0.032 ± 0.003) % to ³⁴S levels at 4.69 and 4.88 MeV with log ft values of 5.48 ± 0.08 and 5.26 ±0.04, respectively. These log ft values imply allowed transitions and are consistent with the known J_π values of J_π = 4⁺ and 3⁺ of the 4.69 and 4.88 MeV levels, respectively. A lower limit of log ft ? 6.9 is obtained for the allowed electron-capture branch to the J^π = 2⁺, 4.89 MeV level. Other previously observed decay branches have been confirmed. Since the decay of ^34mCl proceeds (46.9 ± 1.0)% to the ³⁴Cl ground state, the latter decay was studied concurrently; ³⁴Cl(0)with J^π = 0⁺, T = 1 decays exclusively to its analog ³⁴S(0) and the sum of the intensities of four other allowed branches is less than 1.2 × 10^?4 of the intensity of the ground-state branch. The experimental results are compared with recent shell-model calculations performed in a large configuration space.     

Energy levels of136Pm and136Nd via beta decay of136Sm and136Pm

¹³⁶Pm and¹³⁶Nd were studied using theβ decay of¹³⁶Sm and¹³⁶Pm. The radioactive nuclei were produced by the⁹²Mo (⁴⁸Ti,xpyn) and¹¹²Sn (²⁸Si,xpyn) reactions. The UNISOR isotope separator enabled mass identification. The previously unknown level scheme of¹³⁶Pm was constructed and the half-life of¹³⁶Sm was determined to be 47±2 s. Six new levels and thirteen newγ-ray transitions have been added to the level scheme of¹³⁶Nd.     

On the probability of double beta decay

Double beta decay is discussed in relation to parity non-conservation. Two possible ways of neutrino-less double beta decay (allowed and forbidden) are investigated and the half-life of decay is calculated. For allowed transitions we obtain for Ca⁴⁸ an estimatedT1/2=2×10¹⁹ years. The negative results of the experiments by Lukjanov et al., who give the valueT1/2=0.7×10¹⁹ years for the lower limit of the half-life of double beta decay of Ca⁴⁸, cannot therefore be regarded as a definitive solution of the question, whether the neutrino is a Dirac or Majorana particle. Further study of double beta decay, aimed at finding higher values of the lower limit of half-life, are of considerable importance for theory.

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- . - ( ) . ⁴⁸ T1/2210¹⁹ . - . [1] ( - ⁴⁸ T1/2 0,710¹⁹ ), , . - .

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In conclusion the author thanks Prof. I. S. apiro for suggesting this work and help in elaborating it.     

The electron capture decay of125I and145Pm

The productP _K ω _K of theK-capture probability and theK-fluorescence yieldω _K was measured in the EC decay of 17.7 y¹⁴⁵Pm and 60.14d¹²⁵I by means ofK x-ray-γ-ray coincidences with semiconductor detectors. Accepting a best value ofω _K =0.920 forZ=60 from the literature, values ofP _K =0.606±0.025 and 0.554±0.025 for decay of¹⁴⁵Pm to the 67.2 and 72.4 keV levels in¹⁴⁵Nd, respectively, were determined, from which the application of EC theory givesQ _EC=153±4 keV to the ground state. TheP _K ω _K ratio to the 67.2 and 72.4 keV levels also was determined independently to be 1.11±0.01, which serves as a good check on theγ-ray-gatedP _K values. Theγ-ray energies were determined more accurately to be 72.4±0.1 and 67.2±0.1 keV, together with a ratio of their relative intensities,I _72.4/I _67.2=3.35±0.09. In the decay of¹²⁵I, a value ofP _K ω _K =0.699±0.030 was measured, and by using an independent determination ofQ _EC=178±2 keV to the ground-state from the literature, a value ofP _K=0.801 is calculated from allowed EC theory, from whichω _K =0.873±0.017 atZ=52 is obtained. This value is in good agreement with theoretical values and with a value of 0.875±0.028 predicted by the best fit curve of Bambyneket al.     

Structure of140Pm from beta decay of140Sm

The structure of¹⁴⁰Pm is investigated through the beta decay of¹⁴⁰Sm, whose half-life is measured to be (14.7 ± 0.2) m. A level structure comprising 41 transitions among 17 excited states is constructed. Using the deduced ft values and measured internal conversion coefficients, spin-parity assignments to several states in¹⁴⁰Pm were made. From beta end-point measurement, the total decay energy is deduced to beQ _EC =3.4±0.3 MeV, which is compared with the predictions of several mass formulae. The systematics of the odd-Z, N=79 isotones are discussed.     

Search for right-handed currents in muon decay

We report new limits on right-handed currents, based on precise measurements of the endpoint of the e⁺ spectrum from ⁺ decay. Highly polarized ⁺ from the TRIUMF surface beam were stopped in pure metal foils within either an 1.1-T spin-holding logitudinal field, or a 70-gauss spin-precessing transverse field. Decay e⁺ emitted within 200 mrad of the beam direction were momentum-analyzed to ±0.2%. For the spin-held data, decay via (V-A) currents requires the e⁺ rate to approach zero in the beam direction at the endpoint. Measurement of this rate sets the 90%-confidence limits P />0.9959 and M(W_R)>380 GeV, where W_R is the possible right-handed gauge boson. For the spin-precessed data we independently determine a 90% confidence limit P />0.9918.We are indebted to the entire TRIUMF management and staff for their splendid support of this experiment. In its early stages we benefited from discussion with J. Brewer, R. Cahn, K. Crowe, and W. Wenzel. Rapid commissioning of the polarimeter was made possible by the superb efforts of the LBL support staff. This research was supported in part by the U.S. Department of Energy, Division of Basic Energy Sciences, Office of Energy Research under contracts W-7405-ENG-48 and AC02-ER02289.     

States inN=80140Nd populated in the decay of140Pm

The level structure of theN=80,¹⁴⁰Nd has been investigated through the beta decay of^140m Pm and^140g Pm, whose decay half-lives were measured to be 5.95±0.05 min and 9.1±0.5 sec, respectively. Decay schemes for the two isomers have been constructed fromγ-ray measurements. With the help of the beta decayft values and internal conversion electron measurements, spins and parities were deduced for levels in¹⁴⁰Nd. Among the levels a 7^? state at 2222.0 keV and a 5^? state at 2273.3 keV are identified as two-neutron quasiparticle states. The (ie233-01) for^140m Pm and^140g Pm have been deduced as 7^? and 1⁺, respectively. From beta end-point measurements, the decay energies of the two isomers have been determined asQ _EC=6.48±0.07 MeV^140m (Pm) andQ _EC=6.08±0.10 MeV (^140gPm). The results are discussed in the light of nuclear systematics of theN=79 and 80 isotones.