α decay of the πh11/2 isomer in Ir164

This is an elec onic ep in o he o iginal a icle. This ep in may di e om he o iginal in pagina ion and ypog aphic de ail. Au ho (s): Ti le: Yea : Ve sion: Please ci e he o iginal e sion: All ma e ial supplied ia JYX is p o ec ed by copy igh and o he in ellec ual p ope y igh s, and duplica ion o sale o all o pa o any o he eposi o y collec ions is no pe mi ed, excep ha ma e ial may be duplica ed by you o you esea ch use o educa ional pu poses in elec onic o p in o m. You mus ob ain pe mission o any o he use. Elec onic o p in copies may no be o e ed, whe he o sale o o he wise o anyone who is no an au ho ised use . α decay o he πh11/2 isome in I 164 D ummond, M. C.; O'Donnell, D.; Page, R. D.; Joss, D. T.; Capponi, L.; Cox, D. M.; Da by, Iain; Donosa, L.; Filme , F.; G ahn, Tuomas; G eenlees, Paul; Hauschild, Ka l; He zan, And ej; Jakobsson, Ul ika; Jones, Pe e ; Julin, Rauno; Juu inen, Saka i; Ke elhu , S e en; Leino, Ma i; Lopez-Ma ens, A aceli; Mis y, A. K.; Nieminen, Päi i; Peu a, Pauli; Rahkila, Panu; Rin a-An ila, Sami; Ruo salainen, Panu; Sandzelius, Mikael; Sa én, Jan; Saygi, B.; Scholey, Ca he ine; Simpson, J.; So i, Juha; Tho n hwai e, A.; Uusi alo, Juha D ummond, M. C., O'Donnell, D., Page, R. D., Joss, D. T., Capponi, L., Cox, D. M., Da by, I., Donosa, L., Filme , F., G ahn, T., G eenlees, P., Hauschild, K., He zan, A., Jakobsson, U., Jones, P., Julin, R., Juu inen, S., Ke elhu , S., Leino, M., . . . Uusi alo, J. (2014). α decay o he πh11/2 isome in I 164. Physical Re iew C, 89(6), A icle 064309. h ps://doi.o g/10.1103/PhysRe C.89.064309 2014 PHYSICAL REVIEW C 89, 064309 (2014) αdecay o he πh11/2isome in 164I M. C. D ummond,1D. O’Donnell,1,*R. D. Page,1,†D. T. Joss,1L. Capponi,2D. M. Cox,1I. G. Da by,3,‡L. Donosa,1 F. Filme ,1T. G ahn,3P. T. G eenlees,3K. Hauschild,3,4A. He zan,3U. Jakobsson,3P. M. Jones,3,§R. Julin,3S. Juu inen,3 S. Ke elhu ,3,M. Leino,3A. Lopez-Ma ens,3,4A. K. Mis y,1P. Nieminen,3P. Peu a,3P. Rahkila,3S. Rin a-An ila,3 P. Ruo salainen,3M. Sandzelius,3J. Sa ´ en,3B. Say˘ gı,1C. Scholey,3J. Simpson,5J. So i,3A. Tho n hwai e,1and J. Uusi alo3 1Depa men o Physics, Oli e Lodge Labo a o y, Uni e si y o Li e pool, Li e pool L69 7ZE, Uni ed Kingdom 2School o Enginee ing, Uni e si y o he Wes o Sco land, Paisley PA1 2BE, Uni ed Kingdom 3Depa men o Physics, Uni e si y o Jy ¨ askyl¨ a, PO Box 35, FI-40014 Jy ¨ askyl¨ a, Finland 4CSNSM, CNRS/IN2P3 and Uni e si ´ e Pa is Sud, F-91405 O say, F ance 5STFC Da esbu y Labo a o y, Da esbu y, Wa ing on WA4 4AD, Uni ed Kingdom (Recei ed 15 Ap il 2014; published 16 June 2014) The α-decay b anch o he πh11/2isome in 164I has been iden i ied using he GREAT spec ome e . The 164I nuclei we e p oduced using he 92Mo(78K ,p5n)164I eac ion and sepa a ed in ligh using he ecoil ion anspo uni (RITU) gas- illed sepa a o . The measu ed α-decay ene gy o 6880 ±10 keV allowed he exci a ion o he πh11/2s a e in 160Re o be deduced as 166 ±14 keV. The hal -li e o 164I was measu ed wi h imp o ed p ecision o be 70 ±10 μsandanα-decay b anching a io o 4 ±2% was de e mined. Imp o ed hal -li e and b anching a io measu emen s we e also ob ained o 165I , bu no e idence was ound o he g ound-s a e decays o ei he 164I o 165I . DOI: 10.1103/PhysRe C.89.064309 PACS numbe (s): 23.60.+e,23.50.+z,27.70.+q I. INTRODUCTION Alpha adioac i i y is he p incipal decay mode o neu on- de icien iso opes o elemen s om 82Pb o 94Pu. Below Z= 82, α adioac i i y is s ill dominan o e en-Zelemen s down o 76Os, al hough p o on emission domina es o he ligh es known iso opes o he odd-Zelemen s. One ea u e o p o on emi e s wi h N⩾84 is ha mos o he p o on-emi ing s a es also ha e a compe ing α-decay b anch [1]. A ypical example is 170 79 Au, in which p o on and α-pa icle emission ha e been obse ed om bo h he g ound s a e and a low-lying isome ic s a e [2,3]. Measu emen s o he p o on-decay ene gies, hal - li es, and b anching a ios indica e ha he p o ons a e emi ed om πd3/2and πh11/2o bi als, espec i ely. As in o he odd- odd nuclei in his egion, in bo h s a es he odd p o on is assumed o be coupled o a neu on in a ν 7/2o bi al [3]. The unhinde ed αdecays om hese s a es popula e co esponding le els in 166 77 I , which also unde go bo h p o on and α-pa icle emission [4]. In con as , in he p e ious s udies o 164I , he ligh es known i idium iso ope, only p o on emission om a πh11/2 s a e was obse ed [2,5]. The αdecay o his s a e would be expec ed o popula e he πh11/2s a e in 160Re, which is unique in his egion because, ins ead o decaying by *P esen add ess: School o Physics and As onomy, Uni e si y o Glasgow, Glasgow G12 8QQ, Uni ed Kingdom. †Co esponding au ho : [email p o ec ed] .ac.uk ‡P esen add ess: Depa men o Nuclea Sciences and Applica ions, In e na ional A omic Ene gy Agency, A-1400 Vienna, Aus ia. §P esen add ess: Depa men o Nuclea Physics, iThemba Labo a o y o Accele a o Based Sciences, PO Box 722, Some se Wes 7129, Sou h A ica. P esen add ess: TRIUMF, 4004 Wesb ook Mall, Vancou e , B i ish Columbia, V6T 2A3 Canada. p o on o α-pa icle emission, i is obse ed o γdecay wi h a hal -li e o 2.8 μs o heπd3/2g ound s a e [6–8]. The γ- ay cascade iden i ied om he decay o his πh11/2isome comp ises a 96 keV E2 ansi ion ollowed by a 38 keV E1 ansi ion. Howe e , o he unobse ed ansi ions migh be expec ed o o m pa o his cascade since he exci a ion ene gy o he isome has been es ima ed om sys ema ics o be 185 ±21 keV [9]. By using his es ima e, pa ial hal -li es o p o on and α-pa icle emission can be p edic ed, and hese alues a e signi ican ly longe han ha obse ed om he γ decay o he s a e. Howe e , hal -li es o hese decay modes a y apidly wi h Q alue, so i is desi able o de e mine he exci a ion ene gy o his s a e expe imen ally. One me hod o es ablish he exci a ion ene gy o he πh11/2 s a e in 160Re would be h ough a measu emen o he Q alue o he αdecay o he πh11/2s a e 164I (see Fig. 1). The Q alue o his αdecay has been es ima ed om sys ema ics [9], om which a b anching a io o ∼8% could be expec ed. Such a low α-decay b anch would ha e been below he sensi i i y limi s o he p e ious s udies o 164I , in which p o on-decay yields o only ∼ i e e en s [2] and ∼eigh e en s [5]we e ob ained. The Q alues o decays om he πd3/2g ound s a e o 164I can also be es ima ed om sys ema ics. These sugges ha i will p edominan ly decay by p o on emission wi h a hal -li e o ∼1μs. Hal -li es his sho can be p oblema ic o con en ional eadou sys ems based on analog elec onics, such as hose used in he p e ious s udies, bu should be wi hin he capabili ies o digi al eadou sys ems which ha e p o ed capable o analyzing signals in double-sided silicon s ip de ec o s (DSSDs) sepa a ed in ime by as li le as 200 ns [10]. Howe e , he usion-e apo a ion eac ions used o p oduce p o on emi e s in his egion gene ally a o he popula ion o πh11/2s a es, so he πd3/2g ound s a e o 164I may be oo weakly popula ed o be obse ed. 0556-2813/2014/89(6)/064309(5) 064309-1 ©2014 Ame ican Physical Socie y M. C. DRUMMOND e al. PHYSICAL REVIEW C 89, 064309 (2014) FIG. 1. Schema ic diag am showing he expec ed p o on and αdecays o s a es in 164I . The odd neu ons in 156Ta, 160Re, and 164I a e p oposed o occupy ν 7/2o bi als [4,5]. The disco e y o he αdecay o he πh11/2isome in 164I shownby hedo edlineis p esen ed in his wo k, bu no e idence could be ound o he p o on decay o he πd3/2g ound s a e indica ed by he dashed line. In he p esen wo k, he α-decay b anch o he πh11/2s a e in 164I has been iden i ied and i s p o on-decay p ope ies ha e been de e mined wi h imp o ed p ecision. A sea ch has been pe o med o he p o on decay o he πd3/2g ound s a e o 164I . Imp o ed hal -li e and b anching- a io measu emen s we e also ob ained o he πh11/2s a e in 165I . II. EXPERIMENTAL DETAILS The expe imen was pe o med a he Accele a o Labo a- o y o he Uni e si y o Jy ¨ askyl¨ a. The 164I nuclei we e p o- duced in he usion-e apo a ion eac ion 92Mo(78K ,p5n)164I . The 78K beam p o ided by he K130 cyclo on bomba ded he iso opically en iched, sel -suppo ing 92Mo a ge oil o hickness 500 μm/cm2. Beam ene gies a he on o he a ge o 428, 435, and 450 MeV we e used o pe iods o 21, 18, and 270 hou s, espec i ely. The a e age beam in ensi y was 10 pa icle nA. The 164I ions ecoiled ou o he a ge and we e anspo ed using he gas- illed sepa a o ecoil ion anspo uni (RITU) [11,12] o he GREAT spec ome e [13] si ua ed a i s ocal plane. The ligh ime was es ima ed o be ∼0.3μs. The ions passed h ough a mul iwi e p opo ional coun e (MWPC) and we e implan ed in o one o wo adjacen ly moun ed DSSDs. The ene gy-loss signal in he MWPC and he ime o ligh be ween he MWPC and he DSSDs allowed e apo a ion esidues o be dis inguished om beam-like pa icles. Bo h o he DSSDs had an ac i e a ea o 60 mm ×40 mm and we e 300 μm hick. The s ips on hei on and back su aces we e o hogonal and he s ip pi ch o 1 mm on bo h aces p o ided 4800 independen pixels. The 120 s ips on he on ace o he DSSDs we e ins umen ed wi h he s anda d analog elec onics, wi h he shaping imes on he ampli ie s educed o hei minimum alue o 0.5 μs. E en so, he dead ime o ex ac ing ene gy in o ma ion om successi e signals in a gi en s ip was 7 μs, which would ha e been oo long o allow o a meaning ul sea ch o he decay o he g ound s a e o 164I o be a emp ed. The e o e, he 80 s ips on he ea ace o he DSSDs we e ins umen ed wi h 16-channel, 14-bi Ly ech VHS-ADC16 digi al elec onics modules, which had a sampling equency o 100 MHz. T aces o leng h 10 μs ep esen ing he elec onic esponse o signals in hese s ips we e eco ded, allowing ene gy and iming in o ma ion o sho -li ed decays o be ex ac ed. These da a we e co ela ed wi h in o ma ion on pileup eco ded simul aneously om he s ips on he on ace, in o de o iden i y aces which may ha e included a as decay and o assign hese aces o a speci ic DSSD pixel. An a ay o 28 silicon PIN diodes was moun ed a ound he pe ime e o he DSSDs in a box-like a angemen . Each PIN diode had an ac i e a ea o 28 ×28 mm2and a hickness o 500 μm. The PIN diodes we e used o measu e he ene gies o αpa icles emi ed in he ups eam di ec ion ha escaped om he DSSDs wi hou deposi ing hei ull ene gy. These escaping αpa icles o m a backg ound in he egion o he DSSD ene gy spec um whe e p o on-decay peaks a e expec ed. By e oing ene gy signals in he DSSDs ha a e coinciden wi h signals in he PIN diodes, his backg ound can be supp essed. A plana double-sided ge manium s ip de ec o was moun ed a ew mm behind he DSSDs inside he same acuum enclosu e o measu e he ene gies o x ays and low-ene gy γ ays emi ed du ing decay p ocesses in he DSSDs. The ene gies o highe -ene gy γ ays we e measu ed using a clo e ge manium de ec o moun ed ou side he acuum chambe abo e he DSSDs. All de ec o signals we e passed o he igge less da a acquisi ion sys em [14], whe e hey we e ime s amped wi h a p ecision o 10 ns. The da a we e analyzed using he GRAIN [15] so wa e package, which was also used o iden i y aces a ibu ed o p o on decays o 164I h ough co ela ions wi h subsequen 163Os αdecays. III. RESULTS The da a we e analyzed o ob ain imp o ed measu emen s o he p o on decay o he πh11/2s a e o 164I and o sea ch o i s α-decay b anch. Figu e 2(a) shows he ene gy spec um o adioac i e decays obse ed in he DSSDs wi hin 0.5 ms o he implan a ion o an e apo a ion esidue in he same pixel. The known p o on-decay peaks om 160,161Re and 164,165I a e isi- ble in his spec um abo e he backg ound om αpa icles ha escape om he DSSDs wi hou deposi ing hei ull ene gy. In o de o isola e he 164I p o on decays, co ela ions wi h he αdecay o i s daugh e 163Os we e pe o med. Figu e 2(b) shows e en s ha occu ed wi hin 350 μs o an ion implan a- ion and we e ollowed in he same DSSD pixel wi hin 28 ms by a 163Os αdecay (Eα=6502 ±5keV, 1/2=5.9±0.6ms [3,16–18]). The 164I p o on-decay peak can clea ly be seen a an ene gy o 1814 ±6 keV, which is in good ag eemen wi h he p e ious measu emen s o 1817 ±8keV[5] and 1807 ±14 keV [2]. The ene gy calib a ion o p o on-decay lines was based on he p o on decays o 160,161Re [7,16,19] and 165I [4]. The yield o app oxima ely 100 164I p o on-decay e en s ob ained in he p esen wo k allowed he hal -li e o be de e mined wi h imp o ed p ecision. A hal -li e o 70 ±10 μs was ob ained by using he me hod o maximum likelihood [20]. 064309-2 αDECAY OF THE πh11/2ISOMER IN 164I PHYSICAL REVIEW C 89, 064309 (2014) 100 101 102 103 104 0 10 20 30 40 Coun s pe 20 keV 123456789 Ene gy (MeV) 0 1 2 3 4 163Os 155Lu 156H 164Os 160W,163Re 161W (a) 164I 161Re 165I 164I 158W (c) (b) 164I 160Re FIG. 2. (a) Ene gy spec um o decay e en s occu ing wi hin 0.5 ms o an ion being implan ed in o he same DSSD pixel. (b) Ene gy spec um o hese e en s ha a e ollowed wi hin 28 ms by an αdecay o 163Os. (c) Ene gy spec um o decay e en s ha occu wi hin 0.35 ms o an ion implan a ion and a e ollowed wi hin 3 ms by a daugh e ene gy cha ac e is ic o 160Re g ound-s a e p o on decays. Escaping αpa icles de ec ed in he a ay o PIN diodes a e no included in hese spec a. Figu e 2(c) shows he ene gy spec um o decay e en s ha occu wi hin 350 μs o an ion implan a ion and a e ollowed wi hin 3 ms by a g ound-s a e p o on decay o 160Re [7]. A peak comp ising ou coun s can be seen a an ene gy o 6880 ±10 keV. Two o hese ecoil-alpha-p o on decay chains we e ollowed by 159Wαdecays whe e he ull ene gy was deposi ed in he DSSD, con i ming he assignmen o his new α adioac i i y as a decay b anch om 164I . The hal -li e de e mined o he ou e en s using he me hod o maximum likelihood was 69 +41 –29 μs. This is an o de o magni ude sho e han would be expec ed o a s a e decaying by α-pa icle emission alone bu is consis en wi h he alue measu ed o p o on emission om he πh11/2s a e in 164I . This ac i i y is he e o e assigned as he α-decay b anch o he πh11/2s a e in 164I . This αdecay o 164I is expec ed o popula e he πh11/2 s a e in 160Re, which unde goes elec omagne ic decay o he πd3/2g ound s a e wi h a hal -li e o 2.8 μs[6–8]. Elec on con e sion o he ansi ions could lead o summing wi h he α-pa icle ene gy signals wi hin he analog ampli ie shaping ime. The e ec o his summing was in es iga ed h ough Mon e Ca lo simula ions o he esponse o he DSSDs and elec onics, using in e nal con e sion coe icien s om Re . [21]. The simula ions indica ed ha ∼25% o he α-decay in ensi y would be shi ed o highe ene gies. Gi en he low s a is ics, he obse a ion o ou e en s close in ene gy, wi h none shi ed o highe ene gies as a esul o summing, is consis en wi h his expec a ion. The obse ed 164I α-decay yield co esponds o a b anch- ing a io o 4 ±2%, a e co ec ing o he ac ion o p o ons and αpa icles ha escaped om he DSSDs wi hou deposi ing hei ull ene gy. A c oss sec ion o ∼4nbwas es ima ed o he popula ion o he πh11/2s a e in 164I om he combined yield o bo h i s decay b anches. This c oss sec ion es ima e assumes ha 30% o all 164I nuclei p oduced we e implan ed in o he DSSDs [22]. A sea ch o p o on decays o he πd3/2g ound s a e o 164I was pe o med by analyzing aces co ela ed wi h e en s cha ac e is ic o 163Os αdecays. Howe e , no e idence o he p o on decay o his s a e was ound. Possible explana ions o his nonobse a ion could be ha he hal -li e may ha e been oo sho (<0.5μs), he yield oo low (<50 pb), o a combina ion o hese e ec s. The p esen da a we e also analyzed o ob ain imp o ed measu emen s o he decays o he πh11/2s a e in 165I , which was p e iously epo ed o ha e a hal -li e o 300 ±60 μs and o decay by bo h p o on and α-pa icle emission [4]. The uppe panels o Fig. 3show sec ions o a decay co ela ion ma ix in which he decay ene gy o implan ed nuclei is plo ed agains he decay ene gy o he daugh e nuclei, while he lowe panels show he p ojec ions o hese ma ix sec ions, in which bo h he p o on- and α-decay b anches o 165I can be seen. In o al, 270 165I p o on decays we e co ela ed wi h 164Os αdecays and 35 αdecays we e co ela ed wi h αdecays o he πh11/2 s a e in 161Re. Howe e , no co ela ions we e obse ed o 165I 6.0 6.1 6.2 6.3 6.4 Daugh e Ene gy (MeV) 1.0 1.2 1.4 1.6 1.8 2.0 0 100 200 300 Coun s pe 20 keV 6.0 6.2 6.4 6.6 6.8 161Re 164Os 165I 165I 159W159W 157Ta 158Ta 161Re 163Os 162Re 160Re Pa en Ene gy (MeV) (a) (b) (c) (d) FIG. 3. (a) A sec ion o a pa en -daugh e decay co ela ion ma ix showing he co ela ions be ween p o on decays o 160Re and 165I wi h he αdecays o hei espec i e daugh e s, 159Wand164Os. The maximum ime in e als be ween he implan a ion and pa en decay and be ween he pa en and daugh e decays we e 1 ms and 63 ms, espec i ely. (b) A sec ion o he same decay co ela ion ma ix ea u ing he αdecays o 165I co ela ed wi h hose o i s daugh e 161Re. Co ela ions o 163Os-159W, 161Re-157Ta, and 162Re-158Ta a e also isible. Panels (c) and (d) a e p ojec ions o panels (a) and (b) showing he ene gies o he pa en decays. 064309-3 M. C. DRUMMOND e al. PHYSICAL REVIEW C 89, 064309 (2014) αdecays wi h p o on decays o 161Re, o which he b anching a io is only a ew pe cen [19,23]. Co ec ing o he daugh e b anching a ios [19,23,24], he α-decay b anching a io o 165I was measu ed o be 12 ±2%. A hal -li e o 340 ±40 μs was measu ed using he me hod o maximum likelihood, which ag ees wi h he p e iously measu ed alue [4]. No e idence was ound o he decay o he g ound s a e o 165I . IV. DISCUSSION The measu ed α-decay ene gy o 164I co esponds o a Q alue o 7052 ±10 keV. This alue is shown in Fig. 4, in which he α-decay Q alues o πh11/2s a es o odd-Z elemen s a e plo ed as a unc ion o neu on numbe , oge he wi h hose o he g ound s a es o e en-Zelemen s. The alue o 164I con inues he nea ly linea end obse ed o ligh e I iso opes, which is simila o ha exhibi ed by he chain o P iso opes, whe eas he ligh Os iso opes show a sligh odd-e en s agge ing in hei Q alues. The Q alues measu ed o he p o on- and α-decay b anches o 164I in he p esen wo k can be combined wi h known Q alues o calcula e he exci a ion ene gy and he p o on- and α-decay Q alues o he πh11/2s a e in 160Re (see Fig. 1). An exci a ion ene gy o 166 ±14 keV was de e mined o he πh11/2isome in 160Re, while he Q alues deduced o p o on and α-pa icle emission we e 1438 ±12 keV and 6761 ±16 keV, espec i ely. Bo h o hese Q alues a e consis en wi h hose es ima ed in Re . [9], whe e pa ial hal -li es o ∼10 ms and ∼1 ms we e p edic ed o p o on emission and α-pa icle emission, espec i ely. Nei he o hese decay modes is he e o e able o compe e e ec i ely wi h he obse ed γ-decay b anch om his 2.8 μsisome . Fu he mo e, he deduced exci a ion ene gy means ha any emaining ansi ions om he cascade ha we e no obse ed FIG. 4. (Colo online) Q alues o αdecays o πh11/2s a es in odd-Znuclei and he g ound s a es o e en-Znuclei. The measu ed alue o 164I ob ained in he p esen wo k and he Q alue o 160Re deduced om i a e indica ed by he la ge ed symbols. Da a a e aken om Re s. [3,4,16–19,25–40]. The alue plo ed o 164Re89 co esponds o he α-pa icle ene gy o 5486 keV discussed in Re . [39]. by Da by e al. [6,7] o by Sapple e al. [8]wouldbeo low ene gy and would p obably ha e a la ge in e nal con e sion coe icien . The α-decay Q alue is plo ed in Fig. 4, om which i can be seen ha 160Re exhibi s a la ge inc ease in Q alue han migh be expec ed om he Q alues o i s hea ie iso opes. A simila inc ease in Q alue is also ound o i s Ta, W, and Os iso ones ha a e plo ed and o he g ound s a es o Ta and Re iso opes a N=85. The measu ed hal -li e and α-decay b anching a io o 164I gi e a pa ial α-decay hal -li e o 1.8±0.9ms.Using he me hod o Rasmussen [41] yields a educed α-decay wid h o 33 ±17 keV, which is consis en wi h an unhinde ed l =0 decay and is compa able o he alue o 43 ±3 keV de e mined o 166I [4]. The pa ial hal -li es o p o on emission om 164,165I deduced om he measu emen s in he p esen wo k a e 73 ±10 μs and 370 ±40 μs, espec i ely. Compa ison wi h Wen zel–K ame s–B illouin (WKB) calcula ions using he global op ical model o Becche i and G eenlees [42] assuming p o on emission om a πh11/2o bi al yields educed p o on- decay wid hs o 0.29 ±0.04 and 0.30 ±0.05, espec i ely. As can be seen in Fig. 5(a), bo h o hese alues a e consis en wi h he alue o 1/3 ha would be expec ed om he low-senio i y shell-model calcula ion p oposed by Da ids e al. [4] bu a e lowe han spec oscopic ac o s calcula ed in he BCS heo y using he p o on pai ing s eng h om Re . [43] and p o on single-pa icle ene gies om Re . [44]. Figu e 5(b) shows he p o on-decay hal -li es calcula ed o he πh11/2s a es o Ta, 156 158 160 162 164 166 168 170 0.0 0.2 0.4 0.6 0.8 1.0 (a) Au I Re Ta Reduced p o on–decay wid h 156 158 160 162 164 166 168 170 Mass numbe A 0.0 0.5 1.0 1.5 2.0 2.5 (b) AuI ReTa FIG. 5. Reduced p o on-decay wid hs o πh11/2s a es o Ta, Re, I , and Au nuclei. (a) Values calcula ed using he WKB app oxima ion compa ed wi h spec oscopic ac o s om low-senio i y shell-model calcula ions (dashed lines) and BCS heo y (do ed lines). (b) Values calcula ed using he simple o mula om Re . [45]. Expe imen al da a a e aken om Re s. [2–5,16,19,23,38,46], and he p esen wo k. 064309-4 αDECAY OF THE πh11/2ISOMER IN 164I PHYSICAL REVIEW C 89, 064309 (2014) Re, I , and Au nuclei using he simple o mula in Re . [45] di ided by he co esponding measu ed pa ial hal -li e. The expe imen al alues o 164,165I a e app oxima ely a ac o o wo sho e han p edic ed, bu he e does seem o be a endency o he o mula o p edic longe hal -li es han a e measu ed o he s a es ha a e plo ed. V. SUMMARY The decay p ope ies o he ligh es -known i idium iso ope 164I ha e been in es iga ed, esul ing in imp o ed measu e- men s o i s p o on-decay b anch. The α-decay b anch o he πh11/2isome ic s a e in 164I has been iden i ied, es ablishing he exci a ion ene gy o he co esponding s a e in he daugh e nuclide, 160Re. The esul s ag ee well wi h alues es ima ed om local ex apola ions o he sys ema ics o p o on-decay Q alues [9]. Co esponding es ima es o he e en-ligh e iso opes 162,163I sugges ha hal -li es o 90 ns and 410 ns, espec i ely, could be expec ed [9], which may be oo sho o s udy using ecoil sepa a o de ices such as ha used in he p esen wo k. Ex apola ing he nea ly linea a ia ion o α-decay Q alues wi h neu on numbe o I iso opes sugges s ha a pa ial hal -li e o ∼300 μs could be expec ed o he πh11/2s a e in 163I . This would imply an α-decay b anching a io o only ∼0.1%. A simila b anching a io could be expec ed o 162I , assuming ha i s Q alue has an inc ease simila o ha seen in i s N=85 iso ones. Wi h such low b anching a ios, sho hal -li es, and expec ed low p oduc ion c oss sec ions, 164I could be he ligh es I iso ope in which an α-decay b anch can be iden i ied. ACKNOWLEDGMENTS Financial suppo o his wo k has been p o ided by he UK Science and Technology Facili ies Council (STFC); he EU 7 h F amewo k P og amme “In eg a ing Ac i i ies-T ansna ional Access,” P ojec No. 262010 (ENSAR); and by he Academy o Finland unde he Finnish Cen e o Excellence P og amme 2012–2017 (Nuclea - and Accele a o -Based Physics P o- g amme a JYFL). T.G. acknowledges he suppo o he Academy o Finland, con ac No. 131665. 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