Jaenecke, J.

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e::; '?'- :-- .....t\~.~. Cl r~..FK 315GUILLlCMA" 'UI IIlN'OIlCMUNG M.'.IAILlIUMIZeltschnft fur Physik 183.499- 503J.196S)uesellschafr fU r Ker" ~• .d LI SClillf''' (I l:J 'Z l!:j .1 •• 1'1.Aus dem Institut fur Expenmentelle Kernphysik fe~twJejj~li~ochschuleund des Kernforschungszentrums. KarlsruheSearch for a Super-Allowed P- -Decay of H 4ByJ. JANECK£WIth I FIgure In the Te,t(RCCCll cd Dcccmhcr 18, 1964)If a fJ-decaying H4 cxists a supcr-allcw,ed transition to the excIted analogue state ofHe4 is possible. Such a decay mode was not considered in pre'lous expenments. Thereaction Li6(;.. 2p) H4 ",as uscd to produce H4. No super-alkmed IF -decay of H4could be observed and upper IJmits for the productIOn cross sectIon are given.1. IntroductionSeveral experiments have been performed 1 -- 4 to find out vv hetherthe ground state of H 4 is unstable vv Ith regard to the spontaneousdisintegration into l-e +11 or undergoes a fr -decay to He4 • All experi-ments so far have indicated that nuclear disintegration takes place. butthey do not prove it conclusively. In view of this situation it v\ as stillthought worth\\ hile to consider another fJ-decay mode of H 4 \\ hich hasnot been studied and searched for before.2. General ConsiderationsThe ground state of H 4 has an isobaric spin of T = I (isobaric spinT=2 is extremely unlikely). Consequently, the mass of H 4 is closely relatedto the energetic position of the lowest excited state with T = 1 in He4 . Ifone arbitrarily assumes an excitation energy for this state of 22.5 Me\'(dotted line) it becomes clear from Fig. I that H 4 is highly unstable \\ ithregard to the spontaneous emission of a neutron. Ho\\ever, the groundstate of H4 can be stable \\ ith regard to disintegration into H 3 + 11 If theknown 0+ state in He4 at 19.94±O.02 MeV* e\"citation energy5-8 has* ThiS value IS given In rer. 8c v\hIle a value of 19.99±O.02 MeV I' given 111 rer. RbI SPICER. B. M.: Phys. Letters 6. 88 (] 9(3).2 NEFKE"S. B. M. K . and G. Mmc"TI. Phy,. Rcv. 133. B 17 (] %4)3 POPIC, R. V., B. Z. STEPA:'\CIC, and N. R. ALH:slc: Phys. Lettcrs 10, 79 (1964J4 I MHOFf. W. LoO F J. VAUGH1'--. L. F. CH "SE. and H. A. GRr"cH: Nuclear Phy s. 59.81 (1964).5 LElFVRf, H. W., R. R.BoRcHLRs, and C. H. POPPE: Phy s. Rev. 128, 1328 (1962). -POPPE, C. HoO C. H. HOLBROVV', and R. R. BORCHERs: Phys. Rev. 129. 733 (1963).6 hRMI[, NoO M. G. SILBER1, 0 B. S'lITII, and J. L. Loos' Phys. Rev .130, 1987 (I 963l.7 YOUNG. P. G., and G. G. OIILSl:,\: Phys. Letters 8, J24 ( 1903).~ 1\10LU1'--AU£R, J. foO P. F. OO!'.O\ ~'. and J. V. KA'I: Bull Am. Phy;,. Soc. 9.389 (1964). - DOVJVA!\.P.F.. J.\'.K·\"L J.F.MOILF!'."UER, and P.O.p·\RKER:Internal. Conference on Nuclear I'hY;'lc;,. Pam 1964, Vo!. 11, p. 236. - OONOV'AN, P. F.'Conferencc on C0rrc!atlons of Particle, Elllltted In Nuclear ReactIOns. Gatllnhurg 1964500 .I . .IA1';FCKE:isobaric spin T = I as originally suggested by WERNTZ and BRENNAN 9.H+ must then ft-decay to He4 and aT-forbidden 0+ -.0+ -transition tothe ground state of He4 with Ep ::::20 MeV should take place 9. Thenegative results 1 -4 111 the search for such a transition strongly indicateth;t the state at 19.94 MeV in He4 has T=O and not T= I. However,there is a chance 1 0 that the negative results might instead be due to asuppression of the T-forbidden 0+ -.0-'- transition to the ground state of;7-()-III (-~ ,I~ , ..' : '.I II....III:/-;... ": /(1: .7······1,dei,fig I 1 c\cl ..md dcc.l~ ...,(".hem~ for He4 hee ret 8) and H4 If the ,>tate d1 19.94 0.02 Me\' e:\CltdtU)Oenerg~ III He" h.I"- hoh.tr1e "pIll / -- 1. the nucleus H4 can .o~dcc..l) to Hc..l \\Jth IH/J component" If the]0\\C<;t .... t ..lte \\lth J -- I h,," ,I higher eXCIt<ltlOl1 energy (dotted lme. dra\\11 Jrburard)). the nucleus H 4 1Sun"t ..lble \\ Ith reg.lrd to the "'pontaneou,> em's<.,lon of a neutronHe+ in favour of the 5uperallo\\ed 0+ -.0-'- transition to the analogousT = I state In He4 . The latter transition must take place (if the state at19.94 MeV in He+ has T= I and if a ji-decaYll1g H 4 exists: both relatedassumption~ \\ ill be maintained in the follo\\lng paragraphs until statedotherVl Ise) and its ft-value can be predicted very accurately from theother known 0+ --->0- transitions (0 14 , A1 26m , CI34 etc.).The ft-value of the T-forbidden O~ -.0+ transition on the otherhand depends very sensitively on the isobaric spin impurities Y. of theground state of He+ according to( I)') \\rR'iT7. C. and.l. G. BRE:"""": Phy'i. LetIer'i 6,1 U (ll)63).]0 .I"'i~CKI, .I.: Kernfor,chungszentrum Karl'iruhe report KFK-lS5 (1%3), p. 33.Search for a Super-Allowed /1- -Decay of H4or for our special case with T = Ier 1)0'4() t h.forblddcn = --;2~ .501(2)The situation for this T-forbidden transition is very similar to the kno\\ nfi-decays of Ge66 and Ga66 as discussed by ALFORD and FRE"<CIJ 11 •WERNTZ and BRENNAN 9 estimated the T = I admixtures to the groundstate of He4 and obtained from the j I-value with El! ~20 MeV a partIalhalf-life of T, ~ 1 h.The II-v~lue of the superallO\\ed O~ --+0+ fl~ -transition IS (1=3100 sec. From an estllnate of the Coulomb energy difference Y 12 andthe Thomas shift 9, 13 one obtains for the maximum fi-energy Ep-;::;:0.45 MeV. The maXIlnum permissible value is Ep- =0.65 MeV. Other-\\ ise. H 4 can disintegrate into H 3 + Jl despite the assumptions made(sce Fig. 1). For E p- in the range 0.65 MeV -0.45 MeV -0.25 l'vleV thepartial half-life becomes l" I h-4h-1.5d.Thus. onc ha~ a branching bet\\een the ground state transitIon andthe transItion to the e\clted state 111 He4 of > 0.5. Consequently. theconclusions of NITI-;EC"S and MOSCATI 2 (a jJ-decaying H" seems not toeXist) hold. e.\cept that the upper limIt for the production cross sectionof the Li6(". 2p) H 4 reaction must be slightly JIlcreased. The situationremains essentially unchanged If the Isobaric spin Impurities )'. of theground state of He" are bigger than estimated by \VER" TZ and BRE"-~A~ 9. IL hO\\e\er, the isobaric spin lmpuritI~s of the ground state ofHe4 are much smaller than estimated. th~ ground state transition issuppressed accordlllgl) and H 4 decays through the super-allovledchannel. It \Iould then hale escaped all II-ex.periments undertahcn so far\1 hich discriminatcd agalllst hIgh cnerg) IJ-rays (and ~'-ra) s). Tlm ISbecause the super-allolled O~ -.O~ Ir -transition has a lOll ma\lmumII-energy and i.., follovlcd by the dclayed emi,sll1n of prowns. I.e. by aspontaneous brcakup into t+ p. Subsequent emission of ·,'-r:.1y' IS notpossible. and the emission of internal electron pairs is suprcs,;cd b) man)orders of magnitudc 6.3. Experimental ProcedureAs in Nher iJ1\estigatIons l . 2 the Li6(~,. 2p) H 4 reaction lIas used toproduce H. 4 . Li-Ioaded sCll1tillation gla"es (Thorn Elcctr0nlcs. typcKG I and KG 2) \\crc bombardcd \\ith ~'-radlation. TII() gLb,CS (dia-metcr 38 mm. thlckne5' 6.3 mm. LI content, 8.8 ",,) \\ere u'cd. one \1 nhII '\L1mw.\\ P.. and.l B FRI"oCH. PI1\S Re\. Letter,6.119(19611.12 .I.\~LCKL • .I.: Z. Phy,lk 160. 171 (1961)]J L""l. -\ r-..I.. and R G TIIO\I-\,' Rc\. \lod. Phys. 30. ~2<) (I<).'i~).14 D?rI Hm, B. S . ,md L. ~. Z, R) ' ....m·\· Influence of Alomlc I::lectnc hclds onBcta Deca> [111 Ru"lan] 1\1c)';cva: Izd. Akad Nauk SSSR 19.'i0502 J. JANECKl:Li of natural isotopic abundance, the other with Li enriched in Li6 by96°0. Both glasses were irradiated several times with 31 MeV maximumenergy bremsstrahlung from the Karlsruhe betatron and with 51 MeVmaximum energy bremsstrahlung from the Darmstadt electron linearaccelerator. If a fl-decaying H4 exists, the l'-threshold must be ;;;;23.5 MeV.Carbon disks were activated simultaneously and the well knownC12 (y.l1) C ll reaction l5 was used for reference. The glasses were irradi-ated for periods of up to three hours and then mounted on a RCA 6810 Aphotomultip1ier. The pulse height spectrum from the induced activitieswas recorded repeatedly in 16 successive time intervals \dth 300 sec to10,000 sec each. An Intertechnique 4096-channel analyzer was used inthe 16 x 256 channel mode. The decay of the activities wa~ observed forperiods of up to 14 days. The gain of the photomultiplier and electronicsystem including the multi-channel analyzer was stabilized.As the activated nuclei are dispersed in the detector there is noabsorption for the emitted fl-rays. Also, the discrimination threshold forthe hypothetical H4 spectrum can be set for an energy of practically zero.A constant energy of about 100 keY is added to every single fl-ray pulsebecame the fl-rays from H 4 and the proton and tritium from the sub-sequent breakup are detected simultaneously. The detection efficiency is100')0. At first sight it appears as a disadvantage that interfering acti-vities can be produced from the other chemical compounds. above allfrom oxygen and silicon. However, there are only very few reactions(with 10\\ cross sections) resulting in activities with half-lives in the regionof interest.4. Results and ConclusionsDetailed half-life analyses were carried out for various parts of themeasured decay spectra. It turned out that C ll \v Ith T+ = 20.5 min(shorter half-hves were not considered) from the 0 16 (,'. ::I.,;) C II reac-tion l " with uprod::::::5llb at 31 MeV and uprod::::::45llb at 51 MeV was thestrongest component. The C ll counting rates were med as additionalconvenient reference values for the calculatIOn of absolute cross sections.In addition, three weak components vvere observed with h:.llf-IIves upto 10-20 d. The activities are probably due to Si J o(". 2p) Mg2S andphoto-reactions on Ce 142 . No effort wa~ made for deflllitc assignmentsbecause the production cross sections for the reactions on the glasseswith natural Li and with LI" were equal and are therefore not due to areaction on Lib. r"rom the 51 MeV bombardment of the natural Li glassan additional component with T,::::::: 35 min was obtall1ed vv hich did not15 BARBER. W. C, W. D. GWR(Jc, and D. D. R[Alu\J',: Phys. Re\. 98. n (1955)16 HOLTZMO\N. R. B, and N SUGARMAN: Phys. Rev 87,633 (1952). - SCmlnUKfR.J , P. ERnos, P. JORDAN et P. STOLL: J. phys. radium 16, 169 (1955). - BISHOP. G. R..B. GROSS[f[ll et J. C. Rlssrr: J phys. radium 23,31 (1962).Search for a Super-Alhmed f3 -Deca) of }_j4sho\\ Up in the 51 MeY bombardment of the LI 6 glass. SlI1ce this actiYit\cannot be due to Li 7 it is concluded that impurities. possibly Cl. \\crecontaincd in thc natural Li glass.From thc half-hfc analysis and from the companson of the dcca~curvcs for thc two i'-actiYatcd Li-loaded scintillation glasses it must beconcluded that no super-allo\\cd (r-·dccay of H 4 could be obscrvcd \\lthhalf-Iivcs bctwcen 0.8 hand 5 d. If H 4 \\ ith such a dccay modc cxists.thc upper limit for the production cross section at 51 \l1c\' of thcLIO(I'. 2/1) H 4 rcaction is urrod ~2.4 flb (for half-lives from 0.8 h to 5 d)and uprod ~ 1.2 flb (for half-hYcs from 2 h to 1.5 d). respectl\cly.The rcsult of this \\ ark IS 111 agrccment \\ Ith all prc\ la us 1I1\ Cstlg:l-tions l - 4 . 17 . They already strongl~ indicated that a (f-decaying H 4 doesnot exist but did not completely rule out the possibJlIt) of a super-allO\\ed 0-" ---+O~ [5- -transition to the state at 19.94 r.lcV c\citatIoncncrgy in He4 . Direct proof of an unbound H 4 must come from reactl,)Jlstudlcs likc 10\\ energy 11 + t elastic scattenng \\ ith a phasc shift analysl"or from a st udy of fmal statc interaction in the rcaction cl+ t ---+ P+ 11 + t.Thc author IS ll1debted to Professor BR]\, and hI' co\\orlers for ma]."mg a\aIlablethe Darmstadt electron Imear accelera'Or. Than].,,;, are due to Profe"m SCHOPPER 101hi' mterest In this wor]." and to Or L LLRIC H for h" a,s"lance m runnmg the betatronTh!'; \\ork was supported b) the Bunde,mmlstcrlum fur \\ Issen,chafthche For-;chllngand the Dcutsche Forschungsgcmelllschafti7 ROGfRS. P. C. and R. H SIOUS' Ph), Letters 8. ~20 (19M) - C-'-RLSO'. R R.E. NORIJlCK. and \. H'\Hl: Bull. Am, Ph)s Soc 9.419119(4).})rw h dt'1 1 1l1\{'J .. ltat ...dnl\ ht>rf'! 11 ..... tllrtz AG .. "~llrlhurr:

Search for a super-allowed β⁻-decay of H⁴

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Search for a super-allowed β⁻-decay of H⁴

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